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Big Dig Boston ceiling collapse

Big Dig Boston ceiling collapse

Big Dig Boston ceiling collapse

Killed one person.  Not sure if this is a structural issue but with "large concrete ceiling panels" it sounds like one.

Collapse link

RE: Big Dig Boston ceiling collapse

...and they are going after whoever screwed up.

uh oh

RE: Big Dig Boston ceiling collapse

"negligent homicide"

RE: Big Dig Boston ceiling collapse

Massachusetts State Troopers and another worker (wearing hard hat) inspect hardware removed Tuesday, July 11, 2006, from a Big Dig tunnel where cement slabs fell late Monday night in Boston. The falling slabs crushed a passing car killing a woman and injuring her husband.

Damn press and "cement vs concrete"!

From the photo of steel tie back (turnbuckle with clevise and pin arrangement), seems that two (2) epoxied anchors secured a fabricated T-plate to the concrete panel, and the pullout failure looks like possibly that the drilled holes were not cleaned correctly resulting in premature failure. Speculation on my behalf, but I was expecting to see a cast-in insert to the panel and a pullout cone.

RE: Big Dig Boston ceiling collapse

With all due respect to those with the hard job of investigating this tragedy....why is a state trooper inspecting anything?!  Structural Engineers should be dispatched to the site to assist any transportation official with the appropriate actions such as closing roads etc.


Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

RE: Big Dig Boston ceiling collapse

He probably just happened to be handy for a photo op.

RE: Big Dig Boston ceiling collapse

I got the inpression it was the attachment to the concrete tunnel that failed, not the panel.

RE: Big Dig Boston ceiling collapse

State trooper because they are treating it as a crime scene.

RE: Big Dig Boston ceiling collapse

I was reading the following in the Standard times which the main newspaper for the southcost of Mass.

"John Christian, a geotechnical engineer hired to conduct an investigation on behalf of the Turnpike Authority, said the attachment bolt design was fairly standard. He said holes were drilled in the tunnel's concrete ceiling and then bolts were inserted along with a pressure-injected epoxy packing."

Now why Hire a Geotechnical engineer to study a structural failure?

RE: Big Dig Boston ceiling collapse

All those politicians demanding accountability are probably the same ones that look down their nose at structural engineers and sniff, "You guys are so conservative."

RE: Big Dig Boston ceiling collapse

mbullism (Structural) Jul 13, 2006
I'm still a bit puzzled by the overhead use of epoxy anchors in the tensile zone of the concrete tunnel ceiling above... I know they have caps and seals to keep the epoxy in the hole while it sets, but I always thought these type of anchors were a no-no in "cracked concrete".  Admittedly, I've yet to hear how thick the base material is or how deep the anchors were.  Several outlets have reported that the bolts and epoxy came out of the holes cleanly...

Is it possible that the anchors were meant to be set deep enough so as to "ignore" the tensile region and be actually secured in the top/compression zone?

RE: Big Dig Boston ceiling collapse

I suspect the geotechnical because it's a tunnel, though I definitely agree it's a structural concern.

Also, does it trouble anyone but me that vertical epoxy inserts were used such that zero redundancy exists in failure mode.  I would have less troubled to see a studded plate cast in the slab than what was done.

Comments are welcome.


Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

RE: Big Dig Boston ceiling collapse

It was likely a Geotech, because we are also the ones that tend to do a lot of the material testing and inspections work.  We do tend to know more than just soil.

I do agree however, that a structural should be leading this, and working closely with someone that is quite familiar with the materials and construction aspects of this work.

RE: Big Dig Boston ceiling collapse


I believe one article said that the threaded insert pulled out, leaving the epoxy in place.  That would indicate that the bond between the anchor and the epoxy failed.  I didn't see a report that the epoxy came out of the concrete.


One official (forget now, which one) said that the system was designed so that , if one bolt gave, the others could hold the panel.  Though looking at the graphic, it's not clear how that would work.  It would seem that if one corner gave way, the bolts on the other diagonal would see double the load.

RE: Big Dig Boston ceiling collapse

Tension anchors such as this are required to have a factor of safety (by code) of at least 4.  Considering that, it appears that the assembly had been holding for a while and gave way.  That points moreso toward an installation anomaly, likely exacerbated by vibration or other repetitive loading, or potentially a material failure (excessive creep under load, embrittlement, corrosion, etc.), or as usual, some combination of those.

Such a forensic venture should involve a team to include a structural, a geotechnical, and a materials engineer.

RE: Big Dig Boston ceiling collapse

Insert stupid question here.

What is the "tunnel ceiling"? What were the anchors anchored to? Rock? Concrete? It seems the assumption that the epoxy would bond to the "tunnel ceiling" with little redundancy is questionable. I could definitely see the entire epoxy/bolt assembly pulling out but not the epoxy away from the bolt... seems unlikely.

RE: Big Dig Boston ceiling collapse

Also... grouting upside definitely fights gravity and makes you wonder if the problems lies there...

RE: Big Dig Boston ceiling collapse

For hanging loads - a form of redundancy can be provided by these three methods:

1.  Use a much higher safety factor on the anchors you use.
        I remember after the Hyatt Regency collapse that a walkway system in Des Moines, Iowa as built with a SF of 10.

2.  Use more anchors than needed (per comments above) such that a portion of the anchors can do the full support.
         I used this on a stay cable structure where four separate cables were used - 2 of 4 could support the dead load and 3 of 4 could support the dead + live + wind.

3.   Provide a supplemental support system that would allow full release by the primary support, and may allow large, damaging deflections, but would not allow collapse.  Sort of like a seismic bend-like-crazy-but-don't-fall-down system.

There may be others here but these would be what I would look at.

I also seem to recall someone in another forum discussing the fact that adhesive anchors are very very susceptible to the in-field quality.  In fact, I think this is one of the selling points for the new Simpson Titan anchors...as they are not as susceptible to installation QC.

RE: Big Dig Boston ceiling collapse

Here's a link to an article that discusses the reason for having such heavy panels in the first place:  When the large vent fans kicked in to evacuate smoke in the case of a fire, explosion, etc., the plenum above the ceiling would have enormous air velocity and the ceiling needed to remain static and not flutter with such winds.

Ceiling Panel link

RE: Big Dig Boston ceiling collapse


This is not my field but what IS a tunnel ceiling?
Why are "decorative" concrete panels suspended over
a roadway, mounted by anchors/rods/grout all of which are
loaded in tension?  Why go to the effort of putting
large concrete elements in a tunnel with no load bearing
responsibility?  That seems like a waste of mat'l.
Hanging a concrete block over a roadway can have two
possible outcomes...and one is bad.  Is this normal or
traditional construction?


The more you know, the more you
know you don't know....

RE: Big Dig Boston ceiling collapse

Read the links.  They were using the space between tunnel roof and celing panel for a mechanical plenum for venting purposes.

RE: Big Dig Boston ceiling collapse

As the article says, the panels are part of the ventilation system.  It is similar use as the drop ceiling in many buildings serving to form the air return.  In this case:  "Michael P. Lewis, the state's Big Dig project manager, said during a press conference yesterday that the panels in the I-90 connector needed to be heavy for stability in the face of 'hurricane force winds' generated by fans near the roof of the tunnel."  So, basically they were made with sufficient dead load to counteract vibrations caused by the 75+ MPH winds they expected.

Now for the sad part: "Now that the concrete panels are all being removed from the connector tunnel as part of the safety review, Turnpike Authority chairman Matthew J. Amorello has said he will consider reopening the tunnel without any drop ceiling at all. Some industry observers have said all along that the drop ceiling was mainly cosmetic, concealing the fans from the drivers below."  They likely served no real purpose, but it was obviously a dangerous setting.

"Big Dig officials were not interested in using a lighter material, because doing so would have required many more supports to prevent the ceiling from vibrating." <= A good lesson for redundancy.

RE: Big Dig Boston ceiling collapse

snippets from an article on thebostonchannel.com:

"Reilly described one of the bolts that failed as a "clean break" and said there wasn't any concrete attached to it."

"Avi Mor, of Dr. Mor & Associates, a California-based consulting firm specializing in analysis of construction defects, said if concrete failure was to blame for the collapse of the panel, investigators would likely find pieces of concrete still epoxied to the tie rods. Reilly said there was no concrete attached to the rod that failed Monday night."

Admittedly, I haven't heard if the epoxy pulled out of the hole as a plug, sheared through leaving some on the bolt and some in the whole, or failed at the bolt which may have pulled out clean (though I'm not sure how as they are generally threaded), but it appears the concrete did not fail around the anchor epoxy and that the anchor rod itself did not fail in tension...

My question remains the same regarding epoxy anchors in the concrete tenisile zone...  it seems to me that if you epoxy these in (threaded inserts or not), and then apply by all accounts what amounts to tons of static loading, that the concrete tunnel ceiling structure (not the hung panel system but the actual top of the tunnel) that the tunnel ceiling will deflect under load.  While the reinforcing in the tensile zone takes up the tensile loading it will stretch, the concrete in that zone subject to "cracking", even if minute.  The whole system is then additionally subject to creep over time...  none of the Hilti or Simpson literature we have in the office list an epoxy anchor suitable for overhead application in the tensile zone (with the exception of the "new Hilti "TZ" spiraled anchor which I'm pretty sure was not around as early as 1999...

RE: Big Dig Boston ceiling collapse

I would not want to have post-installed epoxy anchors holding those loads in tension over moving (many times heavy) traffic for many year and with mechanical wind...over that many miles.  Come on, that can't be the way they wanted it?  That just seems crazy, you're expecting too much of the contractor relative to the liability.  Seems like these elements were ok'd by someone and never inspected and probably never intended to be.

Set it and forget it didn't work this time and it looks like they have a BIG problem.


RE: Big Dig Boston ceiling collapse


Thanks for the links...It does smell like a political


The more you know, the more you
know you don't know....

RE: Big Dig Boston ceiling collapse

Note: I do not necessarily agree with the opinions stated in the above link.

RE: Big Dig Boston ceiling collapse

mbullism, in answer to your earlier question, the typcial "roof" section of the cut-and-cover tunnel sections, as opposed to the immersed tube sections, is about 6-8 feet.  I could stand on the travelling form and the top of the pour was above my head...

tw, the anchors were installed as designed and I have no doubt they were inspected.  There was never a shortage of inspectors on the project.

What probably should have been used are the Richmond inserts that are embedded in the concrete.  

I'm afraid the issue will become a political witchhunt. It already has...unfortunately, much of the same political energy and pressure on display now is what drove many decisions during the project.  I hope we get a good forensic analysis out of this that we can all learn from because the careers of many honest, ethical, and honorable engineers are about to get ruined as political fodder.  Maybe something good can come of the mess.

RE: Big Dig Boston ceiling collapse

wermmm in the first place, how could it have hapened??!?!?!

RE: Big Dig Boston ceiling collapse


A few preliminary thoughts. I would expect that pullout tests were performed during conctruction on at least a portion of the anchors.  Believe it is widely undertood that adhesive anchors are sensitive to poor installation.  Poor bond due to debris in the hole or oil in the compressed air used to clean the holes are two examples.  SInce failuire occurred years after installation perhaps not just initial installation may have played a role.
Personally I probably would not use adhesive anchors in an overhead application, but that doesnt mean it cant be done. Does anyone recognize the red cap on the anchor in the photos and graphics? What adhesive system was used? A cast-in-place anchor may not have been feasible depending on how the tunnel wall concrete was placed.  Generally also it may have been simpler to lay out these anchors precisely after the concrete was done. That means using either a mechanical or adhesive based anchor. Many types of post-installed mechanical anchors are susceptible to load reverals, so they may not have been the best choice.

Wonder what the real loads these anchors resisted were.  No data out on that yet.

Hope that full data on what happened is made available to public.  

Very sorry for the loss of life.

RE: Big Dig Boston ceiling collapse

Been discussing this with some non-structural engineers.  They all have the same question:  how can you guys hold tons of concrete over the public with glue? Worse, epoxy, that everyone knows requires precise preparation, mixing, and curing, or else it doesn't work.

I tell them about lunch seminars I've dutifully attended for the last 25 years.  Where salesmen tell me of the latest products and research and so on.  My wife, who's a nurse practitioner, tells of the drug representatives who do the same in her field.

RE: Big Dig Boston ceiling collapse

It seems like common sense to avoid overhead epoxy installations but I am wondering if there is mention in any of the chemical anchor manufacturer's literature regarding not installing in overhead applications?

RE: Big Dig Boston ceiling collapse

Most of the manufacturers specifically allow overhead installations -  e.g. section 4.10 of the following Simpson product: http://www.simpsonanchors.com/pdf/codes/er5791.pdf  provided certain considerations such as elevated installation temperature are adresses.  As someone mentioned previously these products typically have a safety factor of 4.0 on them, and I for one would not have a problem specifying them in the same type situation as long as I felt I was following the manufacturer's recommendations and that proper inspections and testing were taking place.  

RE: Big Dig Boston ceiling collapse

I don't think I would have even if this had not happened, just by the quality I usually see in the simple applications. I specified metal stud trusses to be anchored with 3/4" dia epoxy bolts into cmu recently, I got to the site and they had put in 3/8" expansion bolts at every location and none of them were even straight and half not tightened down all the way. But maybe the work is generally better in other areas.

RE: Big Dig Boston ceiling collapse

I agree with Haynewp and having noted this earlier in the thread am completely at a loss to explain why such an application was used to hang concrete panels of such mass.  

Over traffic such as it is, no matter if the number of anchors is twice necessary there is always the one per panel that may fail and induce not only more axial load on the remaining anchors but possible torsion on the system as well.


Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

RE: Big Dig Boston ceiling collapse

There seem to be two camps here, overhead epoxy okay, overhead epoxy not okay.  I'm wondering if those camps separate along heavy structural/general building designers?  In California Caltrans specifically allows the use of epoxy anchors in overhead applications on their bridges.  Their use requires heavy inspection which is much more prevalent in heavy structural public works projects.

I think it is important to keep in mind that the tunnel sections were not designed by one person or even one company.  The entire project was broken up into a large number of design segments, and further broken down into construction contracts.  Many structural engineers from different firms were involved in the decision to allow the epoxy anchors.  I don't know, however, if different manufactured systems were used in different segments of the tunnels.  Were they all supplied by one manufacturer?  Seems unlikely given that the first panels were installed in 1995 and the last ones in 2004.

RE: Big Dig Boston ceiling collapse

Ingy, it sounds like from your earlier response that you were actually involved with the construction of this part of the project?

Unless someone was there monitoring every hole installation, I don't see the inspection as being completely effective. It is not like inspecting a weld after it has been placed.

RE: Big Dig Boston ceiling collapse

I've used epoxy anchors often and if properly installed, they can have a greater capacity than mechanical anchors.  I still have confidence in them but now with heightened concerns.  There are a couple of caveats... epoxy anchors are very susceptable to the condition of the material that they are bonding to as noted in earlier posts, and they are very temperature sensitive.  I don't recall ever using them for a similar situation.  For life safety issues, I would have specified a regimen of testing to ensure that a large number were tested... realizing that thousands of anchors may be installed, the number tested could easily be in the hundreds with additional testing if proof loads failed.  Some engineers may have been lulled into a false sense of security because of the large safety factor without, perhaps, fully appreciating the problems of installation.  

I've been aware of safety issues, and spec that the installer be experienced and that the anchors be installed strictly in accord with the manufacturer's printed specs, but my greatest concerns until now have been temperature related.

From the links, it appears that the cause of the problem goes far beyond the engineering aspects of it... a matter of time, cost over-runs and political interference... but, the responsibility for the tragedy rests with the engineering.  We are the tekkies that are responsible to make things work... but, the lawyers will have a 'field day' with this.  Based on my own past experience, it could be a bit dicey... the engineer of record may have advised others verbally or in writing of concerns or may have been frightened or insecure for real reasons such as loss of employment... Also, in some large firms, contract management may be handled by others completely separate from the design group...

Hopefully, we'll see the issues unfold as time progresses...


RE: Big Dig Boston ceiling collapse

Ingy -

I'm in the heavy infrastructure market which includes everything from bridges to ports and harbors.  That said I've never designed a building for occupancy by the general public.


Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

RE: Big Dig Boston ceiling collapse

folks, following is a message i posted to the seaint list server two days ago.  i just heard of this website, so thought i'd share my post.  

some of this has been discussed on this thread already, but rather than edit, thought i'd just send as is.  next i will send a follow-up i just sent earlier today.  

I lived in California for 13 years, including 3 years in the construction industry and 10 years practicing structural engineering.  According to my recollection, I never met, worked for, or worked with ONE SINGLE engineer who would specify anchors grouted with epoxy to be used in an overhead application supporting gravity loads.  And yet, that is what was apparently used in some areas of the big dig to anchor the concrete hung ceiling to the tunnel's concrete roof.  Frankly, I am shocked that epoxy anchors were used.  Perhaps I am wrong about this.  I would appreciate comments on this.  

If that system IS acceptable, I will state categorically that the Boston area is not the place to do it.  This is due to the culture of the Boston area.  After my 13 years in California, I have spent the last six years in construction management (of buildings, not highways!) in Massachusetts.  My experience over the last six years points to a PROFOUND difference in culture and mentality with respect to attention to plan review, professional collaboration, compliance with building codes, inspection quality, use of new technologies, and commitment to excellence.  

In my work here, I attempt to hold all of us to the highest standards of design and construction, and yet on a daily basis I am met with incredulity by my colleagues, and by the architects, engineers, and contractors involved in construction of buildings here.  

During the last six years in Massachusetts I have never seen an evaluation report for a manufactured item, such as an epoxy anchor.  It simply isn't done here, in my experience.  The typical process is this: the engineer will be vague in the specs, indicating say epoxy OR mechanical anchors.  Then there may be a submittal, maybe not.  If there is, there is no follow-up.  The contractor is free to install them as he sees it.  There is no inspection required by the authorities having jurisdiction.  The inspection firms sometimes may be asked to inspect, but in general the particular individuals are not qualified to inspect such a thing.  

For instance, yesterday when I read in the paper that the epoxy had "pulled out cleanly", I told some colleagues that it seemed to me the only way that could happen was if the threaded rod was NOT galvanized.  Plain steel comes from the supplier with a coating of oil.  Incompatible with epoxy grout.  Now it looks like that's what happened.  Only in Boston could this happen with the culture we have here.  

As another example, in six years I have never seen a list of plan check comments.  It simply isn't done.  If I ever question some aspect of the design during the construction phase, no one will look into my comments, but instead the reaction will be "we have a building permit, so your question doesn't matter".  Or I am met with a stone wall of puzzled looks.  "Who are you to question the engineer?"  "Well, the engineer has his stamp on it, so it's OK."  "That's the way we've always done it."  But NEVER an answer to the question.  

This mentality in Massachusetts covers ALL aspects of construction, not just structural, but also HVAC, fire protection, civil design, egress requirements, accessible design, etc etc etc.  

My experience in California was completely different.  Plans are checked, comments are made, professionals revise the drawings, building inspectors require inspections, building inspectors require inspections by the professionals, etc etc etc.  Questions raised are viewed as an OPPORTUNITY.  

Any thoughts?  

Mark Swingle  

RE: Big Dig Boston ceiling collapse

folks, perhaps i overstepped on the galvanized vs not-galvanized, but i still think it makes no sense to use plain steel (due to the coating of oil and/or rust).  it may be allowed, but i never would.  following is what i sent earlier today to the seaint website.  these were my thoughts after seeing the photos.  

all for discussion. . . .  

Now that I've seen the picture, I have a few more points for discussion.

1. Based on the relative capacities of the four anchor rods (if installed correctly) and the cable, it appears there was no consideration of ultimate strength design.  the basic design of this should have considered that the only ductile failure would be the cable yielding in tension, so it should be the weakest link by a reliable factor.  Just based upon experience it is clear that those four anchor rods would fail in tension (if installed correctly) well before the cable yields.  Result is a brittle and sudden failure with no warning.  If the connection system had been designed such that the cable yielded first, there would likely have been warning (sagging ceiling) and possible redistribution of the gravity loads to other members.  Less likely to kill someone.

2. The anchor rods in each group should have been drilled at an angle, so that they are not parallel to each other, and are not parallel to the primary tension force.  Failure would then require combined shear and tension, or combined bending of the anchor and fracture of concrete.  Drilling far enough into the concrete such that the rebar cage is engaged would help prevent the brittle fracture mode.  I realize this is more expensive to install, but engineers are supposed to enforce public safety.

3. Note one of the photos in the link provided below shows some of the rods are bent.  Apparently some anchor rods failed before others and the T section rotated before the remaining rods failed.  Of course the investigators will have to verify this.

4. I still maintain that using non-galvanized threaded rod is a problem.  I agree that it appear the epoxy engaged the threads somewhat, so it would never be a truly "clean" break.  However, the non-galvanized rods have a coating of oil and rust which is likely not compatible with the epoxy.  It would get mixed in with the epoxy, and probably reduce the bond strength.  Time will tell on that one, but I would like to hear your opinions.

5. Clearly mechanical, rather than chemical, anchors should have been considered.  [of course i am assuming cast-in-place anchors were somehow out of the question.]  Expansion anchors and undercut anchors require less inspection effort and are more difficult to install INCORRECTLY.  As long as the hole is the proper length and diameter, it is fairly hard to mis-install these.  And at least in an overhead application, you don't have a pile of dust sitting at the BOTTOM  of the hole!

6. I predict the epoxy manufacturer will be held second-most liable (after the engineer of record).  This amount of epoxy clearly was not bought off the shelf at Home Depot or Lowe's.  The supplier would have provided free technical advice and their engineer would have been involved in reviewing the application (if not the actual design) and in reviewing the installation & testing.

My points above are some pretty basic engineering principles that have been taught in engineering school, studied, researched, and practiced for decades.  I still maintain that the culture in Boston (see my email from Friday 14 July 2006) contributed to the lack of care for proper engineering, proper construction practices, and proper inspection practices.

I do want to make it clear there are glaring examples TO THE CONTRARY in the Boston area.  There are many firms and individuals who practice state-of-the-art engineering and demand excellence and accountability.  Sadly, however, I believe they are in the minority.

Mark Swingle

RE: Big Dig Boston ceiling collapse

"As long as the hole is the proper length and diameter"

But you simply cannot know that.

Amongst many other "interesting" fixes, I've seen the boys fix mechanical anchor slop by wrapping them in cardboard, so I for one am not getting on this "mech anchors would have saved the day" bandwagon.

Bottom line is that all anchors are succeptible to poor installation. You have to assume it in the design.

RE: Big Dig Boston ceiling collapse

Anyone have an idea of what epoxy system was spec'd?  It would be nice to be able to review design loads as well as recommended installation or any caveats about use...

Just some idle speculation....

There's a likelihood that the anchors were properly designed ,based on information provided by the anchorage supplier... whether or not he was was ever consulted.  For liability reasons, the engineer is not likely going to recant his choice of anchorage although he may have initially recommended a more costly mechanical anchorage (contrition is not necessarily good for the soul).  If he's used any specifications it likely contains the provisions that installation should occur in accordance with the suppliers recommendations, and,as well, testing procedures may have been specified.  For something this critical, the engineer might take a hit for not following through with testing; it may, however, be the contractual responsibility of the installer to arrange for testing.  The engineering company is rather large and savvy...

In addition, the anchorage supplier likely has data coming out his kazoo regarding the adequacy of his system.  In addition suppliers usually have recommended installation procedures that address temperature, preparation of the hole and any deleterious material on the object to be anchored.  I suspect the anchorage supplier is carefully reviewing his installation procedures to see if there are any 'holes' or contraindications to the use...

That only leaves the installer... and based on information so far available, it appears that the anchorages were not properly installed as per the design as well as the recommendations of the supplier.

The issue of it being HDG might come into play if corrosion were the issue or cause.  If the threaded rod had a coating to reduce corrosion this should be reviewed in light of the supplier's recommendations.

As far as installation of hangers on an angle, I've used this for bonding a surface so that any movement pulls the sufrace closer to the backing.  With respect to hangers, the added moment from the inclined installation may cause stress risers (for fatigue) as well as additional tensile stresses from bending... not necessarily good things for either method of anchorage.

RE: Big Dig Boston ceiling collapse


Yes, I was on the big dig for four years.  I agree that unless every hole is inspected, you just don't know.  As the old saying goes, you don't know what you don't know.

Having worked in Boston for several years on heavy civil projects and now in California for the past 8 years on more heavy civil projects as a general contractor with a PE, I feel I can speak with some authority of how things are done in both locations.  I did not work on commercial building in Boston but have in San Francisco.  I agree that the general attitude and certainly the production rates of the craft workers are different. I can also say that regardless of what the press and politicians like to say, there was a huge amount of oversight and inspection on the all aspects of the CA/T project.

The one point I really want to get across is that it is highly unlikely that one engineer was involved and if there is an error it was systematic.  The ceiling panels are similar throughout the project which, as we all know, was built over 15 years.  Lots of engineers and reviewers and differing design firms were involved.

That being said, I would be very curious to know what time of year the failed anchor assemblies were installed.  The project was always under extreme schedule pressure and a lot of work was done in the winter.  Epoxy does not cure very well cold conditions.  Like I said before, I hope we get some very good forensic analyis out of this.

RE: Big Dig Boston ceiling collapse

Yes, that looks like those red things in the photos.

RE: Big Dig Boston ceiling collapse

I agree with Tomfh about expansion anchors versus epoxy anchors.  I've never head anyone suggest mechanical anchors were more reliable than epoxy anchors.  It looks like it should have been cast-in-place as others have said previously, or outrageously over designed.

Hopefully this will prompt a change in what mark3333 views as standard procedure in MA.  I've never been or worked there myself but I understand the mentality having run into it before.

RE: Big Dig Boston ceiling collapse

This brings back memories of the Kansas city hotel walkway debacle! (although it was a different failure) Why not just cast in weld plates with studs or slotted channels into the ceiling and weld or bolt the hanger brackets to them in the first place?

RE: Big Dig Boston ceiling collapse

"The anchors were made by Hilti."


From you reference at www.telegram.com it implies that the NEW reduntant anchors to be installed will be HILTI, not the existing anchors are HILTI.

RE: Big Dig Boston ceiling collapse


I was in error in making that statement. Hilti is making the replacement anchors.

RE: Big Dig Boston ceiling collapse

Does anyone know if the tunnel concrete is shotcrete or gunite?  Or is it cast in place from above?

RE: Big Dig Boston ceiling collapse

The holes were reportedly cored rather than percussion drilled because of the quantity of reinforcement.  Coring leaves a much smoother surface.  If the problem is failure of the epoxy/concrete interface, this would be a likely reason.  Don't know if that is the case or not.

Loading on the bolts would not be just dead load.  Overpressure due to the ventilation system could contribute significantly.

RE: Big Dig Boston ceiling collapse

what sort of annual inspection proceedures would normally be called for before and now after the failure?

proper design and installation is only part of the equation

RE: Big Dig Boston ceiling collapse

hokie66 - the reports were that the bolts pulled out clean.  That would indicate that the failure was in the bolt-epoxy interface and not in the epoxy-concrete interface.

RE: Big Dig Boston ceiling collapse

Apparantly there is a more straightforward explanation for the clean bolts - There was never any epoxy in the first place:


This wouldn't surprise me. On some of our jobs I've seen the amount of epoxy per hole drop off to near nothing when someone is trying to stretch out their remaining cartridges/sausages.

RE: Big Dig Boston ceiling collapse

So let me pose a question here.

Bolts with no epoxy, bolts with some epoxy, holes not adequately cleaned before installation, etc.  These are all workmanship issues are they not?  In light of the "criminal" investigation, how does the blame get distributed among the parties involved?

I don't know all the contractual relationships in this large project, but I assume there would be the state, city, or whoever would be considered the "Owner".  Then there is the general contractor, the sub-contractors, etc.
Also - there could be a construction project manager (Parsons?).  Also the bolt manufacturer who supplied the bolts and epoxy.  Then you'd have the design engineers.

For the 100's of bolts, was there a full time inspector there watching the drilling, installation?  How could the design engineer get blamed if the overhead bolt design "worked" on paper - which assumed "good" workmanship practices?

I'm just reflecting on the "criminal" aspect of this.  Are we engineers subject to criminal penalties if we design something that gets put in poorly and falls down?

RE: Big Dig Boston ceiling collapse


From past experience, I can tell you that the attorneys don't care who was at fault, they will name everyone even remotely connected to the project and then let the chips fall where they may.  It will be guilty until proven innocent and you will have to defend yourself regardless of your level of involvement or guilt.  The more parties involved, the bigger the purse.  

RE: Big Dig Boston ceiling collapse

I don't see how the engineer could be criminally charged if he was not onsight during the installation of these particular bolts. I would expect civil wrongful death suits being distributed around the hiring companies and the engineer may get dragged in on that.

I would think the actual "criminal" (the guys that end up in jail) charges would be against the field installers individually (and possibly the full time inspectors). The actual workers that installed the bolts are probably headed back for the border right now.

RE: Big Dig Boston ceiling collapse

The issue of concrete/epoxy bond seems to be the focus point of the failure. It also appears that the fact that the anchors were core drilled instead of hammer drilled weakened more the problematic adhesion bond. The water used in the core drilling process may also contribute to the weakened bond.

Another issue, likely underestimated initially, is the huge incompatibility in between thermal expansion coefficients in between epoxy and concrete/steel.

Same years ago my very educated friend demonstrated to me the simple test of the bond in between epoxy coating and steel rod. We moved the epoxy coated rebar several times from liquid nitrogen into warm water. The epoxy coating cleanly delaminated from the rebar.

The infamous anchors likely behave in the same manner. Heavy steel anchors act as a heat conducting bridges, introducing rapid temperature changes to the anchors and surrounding material. In the process, the adhesion bond in between epoxy and concrete releases, and anchor could cleanly pull out. Should the holes be percussion drilled, the jagged surface is less prone to this type of failure.

As conclusion, the new (or additional) anchors shall be or percussion drilled, or core drilled, but the hole should be roughened and cleaned before installation.     

RE: Big Dig Boston ceiling collapse

Does anyone know who supplied the original epoxy anchors?  

RE: Big Dig Boston ceiling collapse

That hasn't been revealed yet as far as I know.  They think it might be a stand-alone epoxy (2 component) with some threaded rod/nut combinations.  

RE: Big Dig Boston ceiling collapse

If the epoxy was left out or minimally installed I don't think it really even matters. It is construction negligence.

RE: Big Dig Boston ceiling collapse

As usual, the variety of opinion on this has addressed almost every question that popped into my pinhead.

One of  them I'm still curious about.  Could damaging sympathetic vibrations have been induced into the panels because of the (probably) constantly changing exhaust volume requirements?  If indeed those fans are load-managed instead of operating at a constant level 24/7.

I'd prefer leaving the equipment bare and beautiful -- that's MY type of sculpture.  Leave the cosmetics to lady shoppers.  But, politicians like certain types of cosmetics too.

RE: Big Dig Boston ceiling collapse

If you read the links up above, they weren't even sure if the bolts they found without epoxy were pulled out, or if those were loose ones that had been left on top of the slabs.

RE: Big Dig Boston ceiling collapse

Count me as one who has never used an adhesive anchor in an overhead application, and never in critical tension.  Whatever the manufacturers say (and they don't say much about overhead installation), there are more things that can go wrong with adhesive anchors than mechanical anchors.

I believe the new anchors will be undercut anchors.  These will probably have to be longer than the original bolts to get past the reinforcing, as I don't think undercutting reinforcing is a done thing.

Wonder who is leading the forensic investigation?  Hope as well as looking at the bolts, they are considering the whole system, e.g. fluctuating loading, stability.

RE: Big Dig Boston ceiling collapse

One article said that the replacement bolts would be Hilti.  That's a good indication that the failing bolts were not Hilti.  Has anyone heard the brand?

I use epoxy bolts in horizontal and vertical-down applications.  Horizontal applications are principally shear, but reasonable tension as well.  Vertical down applications are uplift tension and some shear.  So far so good under fairly high wind loads.

I've also tested quite a few epoxy bolts in pullout resistance.  Failure mode is almost always concrete-epoxy interface.  

RE: Big Dig Boston ceiling collapse

I spoke with a Hilti rep and he confirmed that they may be the supplier of the replacement bolts.  hokie66 says the same thing this guy said - undercut anchors will be used.

RE: Big Dig Boston ceiling collapse

regarding the use of the epoxy or adhesive anchors in tension:  do any of you allow the anchors to be used for baseplates where uplift occurs and the contractor misplaces or damages the cast-in-place anchor bolts?  I do not, but wondering what others allow.

as far as Hilti's replacement anchor:  what will that be?  will they use the epoxy anchor again, but with greater QC?  or the HUS-H threaded bolt which is similar to the Simpson Titan HD or Powers Wedge bolt?  

RE: Big Dig Boston ceiling collapse

archeng59 - not epoxy - they'll use an undercut anchor.

I believe its this one:

Undercut Anchor Link

RE: Big Dig Boston ceiling collapse

I understand why they need to do it _now_, but I'm puzzled about why there was a need to drill blind fasteners into the tunnel ceiling in the first place, given that it's a cut and cover tunnel.

Mike Halloran
Pembroke Pines, FL, USA

RE: Big Dig Boston ceiling collapse

thanks, JAE.  did Hilti say that's the one they would use?

RE: Big Dig Boston ceiling collapse

Mike--It was a poor design decision, or possibly a poor decision forced on the designer.  We may never know, unless someone involved is prepared to enlighten us.

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archeng59 - that's what the Hilti rep told me.  

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archeng59...yes, I allow the use of epoxy anchors for uplift, but it's limited based on the size and configuration of the connection.

As for fixing contractor screw-ups in anchor bolt placement, I typically take a harder line on repair, though if a practicable epoxy solution is proposed, I'll consider it.  However, if the contractor screwed up the location, he won't suddenly get smart and do all the right things that make epoxy anchors work.  Epoxy anchors to replace misplaced bolts are difficult for clearance, bonding, cleaning, size, and embedment issues.

RE: Big Dig Boston ceiling collapse

I have nearly 20 years of experience performing both placement and post-placement inspections of rebar, post-tensioning systems, concrete, masonry, etc.  I’ve said it once and I’ll say it again:  If structural engineers who specify epoxy for dowels and the like believe that the work is being done correctly then they live in a world unfamiliar to me.  The key instructions to correctly epoxy in a dowel are either unknown to or widely ignored by contractors. You would be astonished at the number of so-caled epoxied dowels that I can pull out with one bare hand.

The following is of particular importance to a correctly epoxied dowel: The hole is cleaned with oil-free compressed air, brushed with a nylon brush, and cleaned again with oil-free compressed air.  Generally speaking on a job site oil-free compressed air can only be obtained from a wet-dry vac or an air-compressor with the correct filters installed.  Explaining to a contractor that the on-site air compressor can not be used for hole cleaning because the air contains oil that will act as a bond breaker between epoxy and concrete is like banging your head against a concrete wall and we haven’t even gotten to the brush part.  A brush for cleaning the drilled holes is as elusive as a non-working rebar foreman; they rarely, if ever, exist on a job site.

I arrived at one particular job site last week to find the contractor in the process of placing #4 rebar dowels in 1.25” diameter drilled.  The holes were drilled for 1” diameter SMOOTH dowels (the interface of an interior slab and an exterior slab where large trucks enter a service area).  The contractor had no oil-free compressed air and no brush to clean the holes.  On another job a pile cap had 18 #11 column dowels misplaced so all were cut off with a plan to drill and epoxy new dowels in the correct location.  The contractor had no oil-free compressed air and no brush to clean the holes.

Over the years I’ve caught numerous contractors using the following procedure for placing epoxied dowels.  1) drill hole 2) hammer rebar into hole 3) squeeze epoxy onto the little mound of dust around the top of the hole.  Seriously!  I’ve also seen numerous dowels in place that have two different colors of epoxy on either side of the dowel/hole which means that the epoxy was squeezed into the hole without the mixing tube attached to the dispenser!  I’ve seen numerous contractors attempt to mix the two parts of the epoxy mix on a board and then try to cram the “mix” into the hole with a little stick..

A couple of months ago I looked at a fix on a 300’ long retaining wall with #7 dowels at 6” and #5 dowels at 6”.  When the foundation was placed (in three separate 100’ concrete placements) the dowels were placed in opposite faces of the wall and the EOR wanted new dowels #7 dowels epoxied in the correct face.  I was able to dislodge 3 of the first 10 “epoxied” dowels I tested with two bare hands.  I knew to test them because upon arrival to the site I bypassed the superintendent and went straight to the labor and asked how they installed all those dowels.  This is a favorite tactic of mine, “How’d you do it?”  I discovered that there was no on-site oil-free compressed air, no hole cleaning brush, and no correct size drill bit.  OK, so I didn’t make it on that contractor’s Christmas card list.

RE: Big Dig Boston ceiling collapse

I have a question about accountability in these such matters...

(although I think I know the answer) What degrees of responsibility should fall on the engineers/designers/planners versus on the construction companies/crews when the construction is not done according to design/specification?

Or, how much should the engineering side of it be held responsible for things, under the presumption that they should 'know' that the labor won't do what is specified (whether it's due to ignorance or complacency, etc.)?
In other words, if and when the engineering should have 'known better'?

RE: Big Dig Boston ceiling collapse

Boffintech...Let me know if you're ever looking for a job in NE or Central Florida!

You're right.  Most of the time they don't install epoxy dowels or anchor bolts correctly.  For repair work, I specify independent inspection.

Luftweg...we can't just rotely assume incompetence.  There are those conscientious contractors and labor who strive to do the right thing.  Further, it isn't always a commission error...often it is just ignorance.  

Our obligation is to specify clearly and set the parameters.  Their obligation is to do it right within those parameters. To quote one of my favorite Presidents (Ronald Reagan)....Trust, but verify!

RE: Big Dig Boston ceiling collapse

I think all the engineers with substantial field experience who have commented here agree that epoxy anchors are fraught with danger, and that their use in this situation was a poor choice.  Back to my answer to MikeHalloran's question, I imagine the use of drilled in anchors was schedule driven.  Cast in anchors would have been right on the critical path in the way of the rebar, and the drilled in anchors could be done later.  For a cut and cover tunnel, that would allow earlier completion of the work above the tunnel.  But the choice of sequence does not explain or excuse the use of epoxy rather than mechanical anchors.

RE: Big Dig Boston ceiling collapse

There are a few epoxys that work in overhead applications. Most are too viscous. Most anchors require careful cleaning to develop proper capacities. Proper mixing and distribution of the epoxy in the hole is also critical. Cored holes need to be scored. In many applications the full capacity of the ancor is not needed, so sloppy instalation woreks. Here instalation was obviously critical, as well as proper product selection and preoof testing. I would not use epoxy overhead unless i had to. Here there seemed to be many othe options. One thing that bothers me are the turn bukles. The rods provied a highly redundent support path for the pannels.The loads in the hanger anchors could varry considerably from what may have been assumed for design based on how the rods were designed. This may have a significant contribution to the failure.
My sympathies go to the woman's family. It is also a shame engineering has suffered yet another black eye from this project.

RE: Big Dig Boston ceiling collapse

That last link screams criminal negligence.  Low factor of saftey on the testing, known issue of bolt pull out, and not enough done to correct / verify the situation. At this point, I think the odds are pretty good we will see some loss of license / jail time.

RE: Big Dig Boston ceiling collapse

Finally had to add my $.02. As more and more info is released to the press and we get to see what was going on the more this looks like a total screw-up. Sorry this is so long but just had to get this out.

Gov Romney called the adhesive bonded bolt failures a systemic failure meaning many if not all of the bolts were of questionable strength. What he should have said was the entire project was a systemic failure.

A 1998 Inpspector general report on bolts used in the Ted Williams tunnel raised serious doubts about the use of this type of fastener. While this report probably started as a look at cost overruns, the technical gaffs are blatant. No overhead hangers were included in the tunnel section design so all were later added as drilled and bonded bolts. WHY! These tunnels were built very early as prefab sections, I believe at a shipyard in Baltimore, and are steel shell with an inner rebar strengthened concrete liner. Rebar placement is very dense and difficult to drill into.

IG report found that plan was to locate rebar via x-ray etc. and then drill. This proved impossible, blame was placed on density of rebar grid or use of epoxy coated bar. Don't understand why epoxy would mask location of bar. Report indicates some 26,000 fasteners would be needed in tunnel alone. Sure looks like better plan would have been to have embedded rails or cast in anchors etc. Drilling was difficult since they kept hitting bar. Plan was if you hit bar, move drill about 2 inch and drill again, grout in first hole.

This also proved difficult (read $ and Time) so brought in contractor to core drill holes right through rebar. Drilling through bar was questioned but approved by someone higher up. Of course CORE drilling is usually not recommended for adhesive anchors, depends on manufacturer and adhesive system, due to smoother hole.

Pull tests on sample of bolts were poor with failure rates at proof loads of 10-30+% of bolts tested. Nothing indicates that this poor performance was ever adequately resolved. Report indicates that suppliers and independant expert advise was that proper installations should have < 1% failure rates and anything higher should be cause for concern.

These are overhead, CRITICAL applications. Failure means someone will likely be injured or killed. You wouldne't use unrated and uninspected cranes, hoists and shackles for overhead lifting. If these were welded steel joints they would have been done by certified welders and inspected by certified inspectors. Not suggesting the work crews installing the bolts did shoddy work but rather they were never trained how to do job right. If you were doing this on an assembly line and had those kinds of failure rates, you would stop and retrain or retool etc until failure rate was reduced. Ideally installers should have done dozens of test bolts with pulls to failure to demonstrate ability to do consistant installations. I seem to recall testing like this is part of a welders certification process.

Lesson from this early use of bonded fasteners was partially learned as most of the rest of the Big Dig system uses embedded rails or cast in anchors. This is not true everywhere, especially on systems near Williams tunnel as these were fairly early in project and also did not have anchor points designed in from start.

But here they used fewer, smaller diameter bonded bolts to support much heavier panels compared to in the Ted Williams tunnel portion. WHY? Contractors and others raised questions about design being too heavily loaded but these concerns were generally swept aside by the engineering and management contractors like Bechtel. Clearly someone still had resevations about use of the bolts as some areas apperently were to be 100% pull tested although proof load may not have been much over working load.

Again problems were found with high failure rates but it doesn't appear anything was done to rectify. This is not to say fault lies with Adhesive anchors. Properly installed, they have strengths comparable to the undercut anchors being put in now. Any anchor system is only as good as the design and installation make it. Screw either one up and you will have problems

This project was a problem from the start when cast in anchor points or rails were not used. Continued when overhead hangers were designed, clearly with inadequate safety magin and redundancy. Compounded by an apparent lack of design rewiew and checking to catch these issues. Add in work by the construction contractor that may have been deficient plus a lack of proper inspection/oversight by the managing contractor. Also a healthy dose of ignoring or explaining away all of the warning signs/reports about problems. Both state and fed overseers of project seemed to have same blindspot.

Of course by late 90's everyone was up in arms about the huge cost overruns of project, so can't imagine anyone (this includes project managers, state and federal elected reps and appointed Department/Agency officials) wanted to hear about something which might cost a few million to fix. Now it will cost many times that and is having a much greater impact on commerce, never mind the likely 10s of millions from a wrongful death suit.

Also sick of hearing about the supposed cost overrun of project. Just a quick look at salaries + OH/Benefits (let's say approx. $100K/person/year) for the 1000s of people who worked on project for 10-20 years, you quickly get 5-10 billion, never mind millions of tons of materials, heavy equipment, etc. Anyone who looked at this project at state or federal level can't seriously expect us to believe they only thought this was going to cost $2 billion.

RE: Big Dig Boston ceiling collapse

The attachment detail is a physical resultant of poor planning and lack of judgment.  My first observations of the detail fall into two categories: schedule and judgment.

First, is related to schedule.  Mechanical attachments are usually for smaller elements. Substantial elements need to be factored in early on in the design phases and embedded anchors, unistrut, or steel is usually placed for anchorage.  Because not even a flexible/adaptable system was put in place it makes one wonder if the nature of the ceiling system and exhaust fans (same mechanical anchorage) were even on the designers’ radar during the early planning stages. This was a design/build project. After investigating this, I found that research done in tunnel fires in West Virginia created the basis for the use of jet fans to exhaust/supply the tunnel.  I'm wondering what the original (at the time when the section was cast) schematic plan was for the ceiling and ventilation system; specifically, what the ceiling was.  


I wonder if these tests influenced the current NFPA 502 (interesting that someone from P.B. was the chair of this proposal)  


Second relates to judgment.  It appears that the whole assembly seems out of balance.  When you look at the size of all the members in the assembly, the little bolts meant to be attached to the concrete seem way out of scale.  If the same set of forces and reactions were used as the basis of design, why would the little bolts be so out of scale with the rest of the members? I wonder if someone improperly adapted the assembly meant for a steel attachment for a concrete one.  

Lastly, after what we now know about this anchorage system in this application, you will still find people that think we should still employ this in future projects. The engineering community needs to determine first, what conditions this approach should be used and second check projects currently online that have employed this system so we can catch any future tragedies.

RE: Big Dig Boston ceiling collapse

In going over some of the articles, it appears that some of the epoxy 'plugs' had worked free from the hole.  Could be that with coring, there was little bond of the epoxy to the concrete.  Possibly thermal conditions or residue from the coring operation.  There doesn't seem to be a bond between the epoxy and the concrete.  Still no news on the type of fastener used?


RE: Big Dig Boston ceiling collapse

In the not so fine print of their installation instructions for epoxy bolts, Hilti specifically disallows use of diamond drills, presumably because of the resulting smooth finish.

If you were faced with drilling through rebar, what else would you use?

Mike Halloran
Pembroke Pines, FL, USA

RE: Big Dig Boston ceiling collapse

As I am not a structural engineer, perhaps I have missed something, but it appears to me that the choice of epoxy bolts was flawed for another more fundamental reason from the start:

The purpose of the concrete slabs was to facilitate ventilation in the event of a fire. However, in the event of a fire, any heat from the fire would have been rapidly transmitted to the steel structure supporting the slabs.

This heat would then be transmitted to the bolts and the epoxy holding them.

Epoxy strength diminishes rapidly with heat.

Therefore, the risk of roof failure in the event of fire would have been dramatically increased, creating a hazard, the opposite of the design intention.

Or have I missed something obvious.

RE: Big Dig Boston ceiling collapse

Steve75002....I'm not sure if that was the purpose of the concrete slabs that failed; however, that is precisely the reason epoxy anchors are not used for hanging sprinkler systems  or for fire suppression systems.

RE: Big Dig Boston ceiling collapse

It is now reported that the epoxy used was supplied by Powers Fasteners, formerly Rawl.  Old name in that business.  Will be interesting to hear how much input Powers had in the selection of fastener, or if they just supplied material as ordered.

RE: Big Dig Boston ceiling collapse

I only have experience with some of their mechanical anchors.  Good products from my experience.  Will be interesting to see the results as the investigation unfolds.

RE: Big Dig Boston ceiling collapse

Ron ... according to many different references in this thread and elsewhere, the heavy concrete slabs were necessary to withstand "the hurricane force winds" that would have passed over them in the event of a fire - anything less would have not have had sufficient rigidity and moved/vibrated/resonated under the pressure.

In consequence, it appears that epoxy bolts are not suited for this application, because of lower heat resistance, as fire has to be a major design consideration in tunnel design.

How is it therefore that they were specified, and their use was permitted, in preference to mechanical fixings that, suitably specified, would have been inherently safer, but probably more expensive to impliment?

RE: Big Dig Boston ceiling collapse

  Steve75002, I think some argued that no system for hiding the overhead ventilation was actually necessary but if a system were used it would have to be concrete slabs to withstand "the hurricane force winds" and not move/vibrate/resonate under the pressure.

RE: Big Dig Boston ceiling collapse

boffintech ... either way, hanging masses of concrete from epoxy bolts significantly increases the danger in the event of fire.

How is it that such risks were permitted, not withstanding the actual consequences?

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Steve...that is a significant question, the answer to which is probably balled up in politics and finger pointing.

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Again, not that the product is necessarily to blame (only the investigation report will tell this) but for those interested in what product was used I found the attached link
[link http://news.bostonherald.com/galleries/?title=behindthescenes07262006&record=3#photo] http://news.bostonherald.com/galleries/?title=behindthescenes07262006&record=3#photo [/link]

RE: Big Dig Boston ceiling collapse

KDengineer's reference shows a photo of adhesive being used which is a product of ITW Ramset Redhead.  Other reports say Powers Fasteners.  Did the contractor just buy from whomever gave him the best deal?  Or maybe that was a different part of the project.  Bet Hilti is glad their name is only being mentioned as suppliers for the rectification anchors.   

RE: Big Dig Boston ceiling collapse

From the photos published in the media, there does not appear to be any insulation on the bottom of the steel T sections. It seems that if one of these failed in major fire event, the entire system would be compromised. The hanger rods and anchors would be exposed, possibly leading to a cascade failure.

RE: Big Dig Boston ceiling collapse

Not an engineer but have worked in the epoxy adhesives industry since 1986.
This link, listed earlier seems to put a lot of the credulity for this scheem on the shoulders of Power Fasteners.

Never in all my years of advising structural engineers on the use of epoxy adhesives have I ever so much as suggested that you could use them for overhead loading conditions.

As to cored, smooth holes vs. impact hammer drilled holes, back in the mid 1990's an evaluation was done. Cleaning of the core drilled holes was the principal drawback, not smoothness of the concrete. The cored holes properly cleaned (no roughening of the hole) yielded the most consistant results. Roughening of the smooth-sided holes proved to be impractical. For a smooth surface example, consider that lap shear (tensile)strengths for acetone wiped, smooth-aluminum coupons. They can easily exceed 1400psi. The smooth hole problem can be manifested when coring through rebar, since the progress slows and slurry is pumped into the pores of the concrete and the surface becomes highly polished/burnished by and/or with fines.
The pull-out strengths for impact hammer drilled holes were somewhat lower, presumabley due to microfracturing but the results had their own level of consistency based on the easier hole cleaning schedule.

Cleaning cored holes should really be in the first instance, the responsibility of the coring contractor and subsequently by the grouting contractor. A dirty hole is not suitable for any grouting material, polymer or cementitious.

My reasoning for why coring contractors should be assigned the first burden of cleaning is based on the premise that water does not wet-out fines that pass the 400 sieve. So if the coring slurry is allowed to dry and left for the grouting contractor to deal with, the hole will not be substancially cleanable without repeated pressure water blasting and brushing after which you can wait for the holes to dry and come back and dry-brush them again before flushing with oil-free compressed air.

I personally don't see Power Fasteners as a adhesive supplier but rather as a fastener supplier that has a few products to compete in adhesive grouted dowel applications. It maybe that their fastener sense got the better of what limited adhesive sense they have on staff. Cold, Wet, and Overhead. Hydrolisis?, Soponification? Apart from gravity, some thing bad happened.

Frankly, I have always felt that the use of cartridge packaged adhesives lowered the competency level of the labor. The cartridges were important to building code organizations, sense they don't approve materials but building systems.
The cartridges introduced a Idiot-proof perception that many manufacturers and contractors have been more than willing to take advantage of. Truth is your best mixing and assurance of proper proportioning(ratio) is with bulk mixing and single component pumping.

RE: Big Dig Boston ceiling collapse

Epoxybot--it is obvious that you know a lot more about the use of adhesives than most if not all of us engineers who have been commenting, and I think you have hit the nail, or bolt in this case, on the head.  You have the same opinion as most of us about the use of adhesive anchors in critical overhead applications.  I doubt that the coring contractor made much of an effort to clean the holes.  So that left the installer with a very difficult cleaning task, which he probably did not fully understand.      

RE: Big Dig Boston ceiling collapse

I always used lots of water whenever core-drilling concrete.  An article with comments about holes dripping water, not sure whether from initial coring or washing as mentioned by epoxybot.
"...J. Keaveney, the on-site safety officer for the Interstate 90 connector, sent a memo in 1999 that directly warned his superiors the tunnel ceiling could collapse because the bolts could not support the heavy concrete panels, and feared for his conscience if someone died as a result...
He also observated water dripping from the holes that construction workers drilled before the epoxy and bolts were inserted. Given the water pressure on the tunnel ceiling [rather, water from coring or washing], he questioned whether the epoxy would hold..."

RE: Big Dig Boston ceiling collapse

Makes one wonder if those "strength tests" were done in dry lab or under a shade tree.

Also, I worked on one job where 10 columns on 2 column lines from levels 1 to 4 had to be increased in size by 4" on all four sides.  This required the drilling of a massive number of holes for epoxied in #3 "J" hooks to hold the additional vertical bars in place.  It only took 4 hours on the first day of work to discover the primary impediment to proper placement of the "J" ties: operator fatigue.

Those guys could only operate that gun for so long before just giving up.  By the end of the first day 2 electric guns were ordered.

We also performed pullout tests on this job.  We hooked up a jack (similar to a PT stressing jack) but with hand pump and tested different installation methods on #4 bars.  For drilled holes nothing held better than a hole that was blown/brushed/blown (oil free air).

RE: Big Dig Boston ceiling collapse

Boffintech--drilling holes overhead would be even more fatigueing than horizontally as in your columns.  Wonder how they supported the core drill.  

RE: Big Dig Boston ceiling collapse

kenvlach... that memo is dynamite! and should be a real concern for the recipient...


RE: Big Dig Boston ceiling collapse

Not an Engineer
I going to step out on a limb here and make some assumptions. So I may wind up making a fool out of myself. On the other hand, you guys might find some information and understanding in what I think worth future polymer anchoring material selection consideration.

One anchoring material supplier’s name has come up in the media, so I ventured to their website and searched for the material that I would select, if I were so cavalier, as to use a polymer anchoring material for overhead grouting in a tensile-shear loading application.
Based on the magnitude of the project, need for longevity, consideration for heat/strength reduction, damp or wet conditions, anticipated underground low-ambient and low-substrate temperature and the benefit of speed of construction/cure schedule; my knee-jerk choice would be the material with the 176 deg. F. HDT (Heat Deflection Temperature).

The product certainly has lots of comfort notations i.e., IIC Research Report #, City of LA-RR#, references to DOT’s blah, blah, blah. It also claims it “meets” with ASTM C881 Type IV (Structural) Grade 3 (Paste) Class A, B, & C.

Reviewing the IIC-RR and the LA-RR, there ARE in fact provisions for the use of this material in overhead grouting, which to some extent, caution the structural engineer, (from here you’re on your own). I was surprised somewhat, to see this.

Fastener companies have been manufacturer-members of ICBO/ICC far, far longer than adhesive manufacturers. Prior to circa 1990 (Loma Prieta, Earthquake) few epoxy adhesive manufacturers were willing to forfeit the money to join regional organizations such as ICBO and submit their products for UBC evaluation. The test criteria were mostly developed for and influenced by the fastener producers and relevant to Polyester and Vinyl Ester capsule anchoring systems. Subsequently, in the wake of Loma Prieta, if you were fortunate enough that your product had, at the very least, a LA-RR and independent test results demonstrating compliance with ASTM C881-87; your product became an engineer’s preferred, specified brand.

The provincial aspects of City of Los Angeles-Research Reports and the esoteric properties of ASTM C881 were not always enough for Code compliance officials, who were now looking hard at a long overlooked area of concern, the pull-out strength of polymer grouted dowels, rebar and threaded rod. And while construction adhesive producers had flirted with cartridge type packaging for years, the cost of this packaging (including labor) was and still is very high, especially when considering the volume of material supplied per package. Necessity proved to be the courage that forced adhesive producers supplying the California construction market, to swallow the bitter pill of applying to ICBO now ICC for a UBC harmonized research report regulated product.  

The problem I find is that the research reports focus so much on the pull-out data that little information is revealed or caveats made about the handling of the materials reported.

According to one Big Dig media blurb, wet - in other words, more than damp (ASTM C882 Bond Strength-saturated surface dry) test conditions were a frequent jobsite condition. WET Conditions existed.

According to the manufacturer -

NOT A PROBLEM – The material is used in “wet environments”. It is “All-Weather” and fast cure, even in low temperatures. Better still it is an optimal material for use in “diamond core drilled holes” It is also non-flammable, something worth noting when working underground.

This is the best product – Yes?
It has charts coming out the yin-yang and thousands of numbers.

So what’s wrong?

There is no % tensile elongation value and no compressive, tensile or flexural modulus values. Any of these might give an engineer cause to think twice. The valves shown are not qualified by test temperature. You have to therefore “assume” standard conditions (23 deg C).

Here is what else I see: The compressive strength is low for so high and HDT “Epoxy”. The C882 bond strengths are low and no explanation is given for the 2 values shown. Wet? Dry? What is this information? The values are low, very low if 23 deg C. is the test temperature. Well… 2 days is not that long, WHAT IS THE FULL CURE CYCLE, DOESN’T SAY ANYWHERE. The Slant shear number looks good, but then slant shear and ASTM C882 are supposed to be the same thing, so just what does ASTM C732 represent?

Oh, Punch Shear, but how thick was the test specimen? Thickness vs. result in this case, is kind of important; they make the same mistake on there other literature, wrong test description.
+ The Shore D hardness is very good. You can barely dent this material with a sharp spring loaded needle.
+ The shrinkage is very low and the absorption is right on target for a high strength epoxy.

I scratch my head when it comes to the flexural strength. For epoxies, the flexural strength ought to be half way between the tensile strength and the compressive strength, or more towards the compressive strength. Modulus numbers would help to explain the low flexural strength. Without the modulus numbers I can’t really tell if there is something weird about the product. One possibility is that the modulus numbers are higher that usual, which follows with the HDT and a very respectable Shore D. This causes me some worry, because the shrinkage is very low, not too low but this material is described as an epoxy-acrylate. Acrylates shrink. And fast reacting materials generate a lot of reaction heat. Could this material have a high internal stress? The product is listed and approved for live loading, so even though it may be high-stressed in its cured state - for highly confined applications such as grouting dowels into holes with minimal bond line thickness and “proportionally”, a low volume of adhesive and a very large surface area for bond; internal stress and the strain it would impart to the bond line does not appear to be problematic.

This material really does have some outstanding properties. The high HDT, the ability to cure in wet conditions AND over a wide range of temperatures (even below freezing). This material is not your everyday epoxy something else is going on.

To begin with, the 176 deg F. HDT is virtually impossible to achieve using the kinds of epoxy materials that engineers are accustom to seeing. At best under standard laboratory (room temp) cure conditions (23 deg. C), the maximum HDT for the best civil engineering epoxy adhesives tops out at about 145 deg. F., with a full cure of 14 days. Elevated temperature post curing for some formulations will yield HDT’s of around 165 deg. F. This elevated (120 deg. F +) temperature cure would not occur in a cold dank tunnel.

These typical epoxy formulas are frequently used for composites but the gel-time, cure to handling time, and subsequent “oven-cure” time are all scheduled. Under these conditions, the same formula can yield HDT’s as high as 250 deg. F.

Epoxy materials also have different stages of cure or “cure envelopes”. The cure stages are A, B, and C.
Stage A – is working life to gel time, Stage – B is a hard material, that is brittle (you can handle it, but you shouldn’t apply dynamic or sustained static loads) it is not impact or creep resistant and Stage – C, Full cure. Sometimes materials get stuck in the B stage; this is usually because temperatures have dipped below the activation energy temperature of the curing agent. If or when temperatures return to the activation energy temperature, the epoxy will continue to cure. The material will not usually gain the full strength that it would have if the cure cycle had been uninterrupted but in many cases a C stage cure is obtained. Think of it this way, for the molecules trying to hook-up (crosslink) it is like getting frozen in water as it plunges over the falls and after thawing out into hip deep muck. It is much much harder to get around. Inertia…

So how does the 176 deg. F, material obtain the high HDT? Looking at the MSDS reveals that this product is not cured using the Amine type curing agents typical of most civil engineering epoxy adhesives. The reactant is Dibenzoyl Peroxide. The “epoxy-acrylate” resin is also a vinyl ester, so some polyester is part of the monomer.

This material reacts via Free Radical/Homo-polymerization. This is why it cures at low temperatures, cures quickly and develops enough energy to gain such a high HDT. And, both the resin and the initiator are immiscible in water, which is why it can cure largely unaffected by immersion in water. It is fast like MMA polymer concrete or Bondo autobody filler. It is low temperature cure like MMA polymer concrete and some HMWM bridge deck sealers.

And like MMA and HMWM it can suffer oxygen inhibition. When Free Radical polymerization gets stuck it stops completely and does not start back up. It dead and you’ve got crap. Wet aggregate can inhibit MMA polymer concrete. HMWM bridge deck sealers can suffer surface inhibition under cold damp “heavy dew” conditions (this happened to Sika and CalTrans years ago on the San Mateo-Hayward bridge). Likewise, moisture/oxygen inhibition can inhibit adhesion/cure properties at the bond line.

This material may be fast and it may have a high HDT, it may cure at low temperatures and it may cure to a very hard solid underwater; it just can’t be all these things at the same time. And the data provided by the manufacturer, WHOOPS! Actually the manufacturer is a company, according to my internet sleuthing is called SOCOM in Cardet, France that private labels. The data does not come anywhere near to demonstrating just how it can do all these things at the same time.

Here are three scenarios, each of which could/probably did happened.

- Low Temperature, Wet, Slow Cure & Difficult placement (bar was pushed in repeatedly while trying to make it fast) = Inhibition & brittle material, degraded overtime by hydrolysis. OH! And damp threaded rod.

- 60 deg. Air temp & 50 deg. Concrete (wet or damp). OH! And damp threaded rod and fast cure = Hard full strength material with some oxygen inhibition at the concrete and threaded rod bond lines. Consequently hydrolytic degradation.

- 60 deg. Air temp & 50 deg. Concrete (dry). Everything is great except it is really difficult to squirt material out of a long nozzle, get it to stick to the end of the hole and somehow tweek the nozzle, without being able to see what is going on, up in there, to get it to stick to the sides of the hole. Building layer upon layer, it would take a lot of time. Otherwise you stick the nozzle in the hole a keep filling until you feel resistance and start withdrawing the nozzle, creating air pockets as you go. = You took to much time; the material has started to gel beyond its ability to wet-out the threaded rod. THIS stuff goes off like polyurea that’s why the bond strengths are so low. I question whether the 2 day, bond strengths increase and would not be surprised it the Wet bond strength was less at 14 days. It is so fast that it is starting to thicken before it exits the static mixer and quickly reaches a gellation phase where it sticks together internally but doesn’t grab the substrate.

There is nothing about this material that suggests it bonds better to wet or damp concrete than other epoxy formulations; it is the immiscible property of the material that lends itself to a high degree of mechanical bond in the confines of a hole than would give it some (maybe temporary) advantage. I think its elcometer tensile pull-off values would be relative to other moisture tolerant epoxies but possibly degrade much faster over time if oxygen inhibition plays a role. Given conditions where immiscibility and mechanical bond are the pull out resistance building properties, internal stress in the adhesive and subsequent strain to the bond line would become a concern. And field testing threaded rod by sounding with a hammer would not be beneficial.

I’m not a Guru when it come to Free-Radical polymerization so the full depth of how much oxygen inhibition and the role water can play in such a circumstance is based on my knowledge of MMA and HMWM.

I think it would be well worth it to ACI, ASTM and Building Code organizations to qualify manufactures (perhaps on a proprietary basis) as genuine formulator or private label/repackager, and restrict their committee participation accordingly. Absent in-house formulating knowledge gross assumptions are frequently made. To make a point, please note that Dibenzoyl Peroxide is a DOT Haz Class, Packing Group II, Oxidative Peroxide material with its very own Yellow Hazard label and label # 5.2, UN3108, PG II, seemingly the epoxy-acrylate from this source has the special ability to transcend DOT restrictions by Air, Sea and Land. Can’t find another MSDS for a material that includes Dibenzoyl Peroxide were this is kind of exemption exists. Wishful thinking or greed?

I started out with a remark about the assumptions I have made here, so enough said.

RE: Big Dig Boston ceiling collapse

epxoybot... that post was worth a couple of stars!

thanks for the excellent work, Dik

RE: Big Dig Boston ceiling collapse

Epoxybot, you are just showing off now.  Most of us don't understand what you are talking about, and I wager neither did the engineer who specified and/or approved this system.  But thank you for showing us how complicated this stuff is.  Materials like concrete, steel, aluminum, timber, etc. are enough to get my mind around without trying to be a chemist.  Whatever else may come out of this disaster, I think the use of adhesives in structures will take a big hit.  

RE: Big Dig Boston ceiling collapse

An Engineer
Epoxybot, thank you for presenting to all of us, that the king is really naked. I really do not think that any epoxy expert was consulted prior to specifying and approving the system. I will even say more - common sense should suffice to determine that the bond in between any epoxy and wet, water saturated concrete could be questionable and some probes or inquires should be done. It was not a string budget project - for $14.6 billion and counting, such services could be expected.

RE: Big Dig Boston ceiling collapse

"Manufacturer" has been determined to be Powers Fasteners from Brewster NY. Powers is a repackager selling "epoxies" from many sources both US and European.  They are the only "manufacturer" to be supeoned to date.

The term EPOXY is used in a very general sense on each post I have read.  Everyone is eager to blame poor specification and poor installation, but not so quick to demonstrate knowledge about the type of anchoring used.  

Epoxies come in many forms and many of the most often used "epoxies" today are actually not epoxies at all but acrylic based.

Wet, damp applications can be overcome with the proper adhesive.

Almost any load strength can be met with the proper adhesive, proper depth, and proper installation.

Overhead applications can be easily handled with the proper adhesive (gel), proper installation, and proper embedment depth.

Epoxies have a chemical resistance to 41F degrees so cold installation is often a deterrent.  This can be overcome by many non-epoxy adhesives manufactured by ITW Red Head, Hilti, and Simpson.

There is plenty of blame to go around.  Sounds to me like the engineer did not properly follow-up on his specification, the installation is questionable, and the "epoxy" used might not have been the right choice.

The most important question to me is - Why, on a project of this magnitude, was there not better oversight of specification, installation inspection, and products used for this application???

Lastly, what were the designers thinking when they designed this 3,000lb drop-ceiling?

RE: Big Dig Boston ceiling collapse

Just saw on the news that the big lawsuit, victims family, has been filed. It names the Mass Turnpike Authority, and 9 other companies.
I dont think it will get to trial as too many skeletons would fall out of the tunnels.

RE: Big Dig Boston ceiling collapse

Interesting development:  The memo (cited above) by John J. Keaveney, former safety official for Modern Continental Construction Co., may be an after-the-fact, CYA effort.  See
Memo writer gets 2d lawyer

"The field notes say Keaveney did not make his ``first weekly safety inspection" of the tunnel until June 3. The engineer's notes say that Keaveney found no safety violations by Modern Continental that day.

The engineer's notes also show that by the date of Keaveney's memo, construction workers had not yet begun drilling holes in the tunnel roof. In his May 17 memo, Keaveney said he could see water dripping from holes in the roof, but the field notes show that drilling did not begin until June 10."

RE: Big Dig Boston ceiling collapse

Some new info divulged here:
Big Dig designers asked to reduce bolts

Original design was 4 anchor bolts per plate, but in a 1998 memo
'Gannett Fleming officials agreed to reduce the number of bolts, calculating that the ceiling would be safe "assuming proper installation and quality of the product materials,"'

So, 2 to 4 anchor bolts per plate, installed in possibly drippping wet holes using epoxy rated for damp conditions, with the epoxy possibly not filling the drilled holes, installed by workmen posssibly tired from overhead work.  And, an inspector in legal trouble for backdating reports in an attempt to cover his you-know-what.  Although we shouldn't speculate (too much), it seems like a clearcut example of the assume rule.

RE: Big Dig Boston ceiling collapse

Assuming proper installation and quality in an engineering calculation is not unreasonable.  What factor of safety should one use when one assumes bad workmanship or poor equipment quality?

On the other hand, taking steps to ASSURE that quality is also not unreasonable.


Eng-Tips policies:  FAQ731-376

RE: Big Dig Boston ceiling collapse

The difference is not quality of workmanship, but rather reasonable constructibility. The first is the responsibility of the constructor the second is the responsibility of the designer.

RE: Big Dig Boston ceiling collapse

After reading all of this I'd venture to guess that everyone looking at it assumed someone else had verified things. This is the way of group projects, nobody takes ownership. The PE probably based his approval on a "baffle them with BS" dog and pony show by Power Fasteners' salesman based on the vauge and misleading data form HIS supplier that epoxybot pointed out.  I too give him a star for that BTW. I'd be willing to bet there is a BIG LEGAL DISCLAIMER in the cut sheet on this material stating that they are not liable for basically anything and you are basically using it at your own risk. I'm sure that bit was not emphasized very much during the dog and pony show. The guys doing the work I'm sure probably had little to no training in the proper procedures and probably none of the tools required to do a proper job. This sounds like a charlie-foxtrot all around.

HgTX, when I'm designing something for field installation, I do my best to make it as idiot resistant as possible because I KNOW that if there is a possible way to screw it up, the guys doing the work will find it. Even if there is NO WAY to screw it up, they will often INVENT a way to do it, idiots are most clever in that manner. Assuming technical competence on the part of others is a recipe for disaster most of the time.

Was there a written procedure or work instruction on how to install these things? were the guys trained in using it? was anyone verifying that it was followed or understood or even possible to follow given the circumstances? or was there merely some vague wording about following manufacturer instructions?

He who does not specify what he wants, deserves what he gets.

RE: Big Dig Boston ceiling collapse

Our product has been tested in compliance, to the conformance that it meets.
Yes, that right, we state what we say because we mean what you want.

I once worked for a very reputable adhesive manufacturer that has since been absorbed by one of the concrete building materials giants; they too are a very reputable company. It was and probably still is, the habit of both of these companies, when required to write manufacturers letters of certification, to use strict guidelines. Sadly, product literature does not always adhere to the same principals.

Manufacturer certified test results are typically written by laboratory testing personnel and product data sheets are written by marketing product managers. A good letter of certification will include a stamp from a notary public and be signed by the senior lab QC testing person or the Manager of R&D. Signing off on Certs. can be, well kind of, sort of iffy, if you in fact are not the actual producer; but you can, as long as you have all your manufacturer’s QC records and are specific as to what you are certifying to.

Sometimes, product managers have a background in construction and some have educations in business marketing and are learning the construction stuff as they go. Some companies require R&D management to give their approval to the information presented in product literature and a lot don’t.

It used to be that compliance testing meant that a manufacturer could present data that demonstrated a particular product had been tested in accordance with a specified test or standard. It used to be that conformance, meant that a particular product conformed to the general intent of the specification with certain, possibly inconsequential exceptions “as noted”. It used to mean, and it should without exception, mean that if a material meets a specification, then that material has point for point, been tested and “meets or exceeds” the minimum requirements set forth in the specification.

Well, my mother was born in the “Show Me” state and I was raised according to the caveat – “Believe only half of what you see and nothing that you hear”. My material manufacturers experience has made me skeptical about the claims that many manufactures make on their data sheets. As I read a competitors data sheet, the features and benefits are less important to me, than whether the ASTM test results are in context and representative of the material, and that the results demonstrate the material actually meets the requirements of a given specification.

“Hypothetically”, let’s take an example:
ASTM C881 - Standard Specification for Epoxy-Resin-Base Bonding Systems for Concrete
Material: Power Fasteners - AC100

I take exception to Power Fasteners published literature, with regard to its “meeting ASTM C881, Types I and IV Grade 3”. It is true that types I & IV are the categories relevant to grouting a fastener into a hole in concrete. They are also the categories relevant to general purpose bonding and the repair of cracked concrete. AC100 could be used for general purpose bonding and if I were a boat owner, who fished in the gulf of Mexico or the sea of Cortez; I would keep a couple cartridges of this stuff in my emergency repair kit, except, I would also need an epoxy primer because this material would not bond very well to fiberglass. This is because it is not an epoxy; it is a vinyl ester. And it would be a lousy concrete crack repair material.

In fairness to Power Fasteners, most the ASTM tests embodied in ASTM C881 are tests that characterize the properties of plastics. The tests have been culled from ASTM testing methods and assembled into a specification with minimum performance values attributable to epoxy resin systems used for concrete. The tests presented in specification C881 are relevant to AC100. AC100 just isn’t an epoxy.

I decided to bone-up on vinyl esters; I already had a good idea why this material was being called an epoxy acrylate instead of the well established nomenclature: vinyl ester. So dust off you Bunsen burner, break out your Erlenmeyer flask, pour yourself some brandy, warm gently (see Bunsen burner) and let’s get small.

A vinyl ester is a polymer, in the middle of which is an epoxy molecule but the functionality of the epoxy molecule is used up. Attached to the functional groups, at the ends of the epoxy molecule are either, methyl-acrylic acid or acrylic acid molecules. What left are half used acrylic molecules, the remains of which are characterized by a constellation of atoms that have been ascribed the term vinyl group. They, in turn, are tipped by a functional ester. Hence vinyl-ester or if you don’t feel that people will have good feelings about vinyl esters you can stretch it a bit and call it an epoxy acrylate.

Most commonly there are Bis A epoxy resins, Bis F and Novalac epoxy resins and by extension vinyl esters are usually built from one of the 3. It’s just that calling a vinyl ester an epoxy acrylate is like calling a paper clip a wire fastener; it lacks for something. School’s Out, no more chemistry.

If you are not new to dowel grouting, then you are probably familiar with capsule anchors. Capsule anchors look really cool. The capsules are glass and shaped like a test tube. The contents are usually a thick liquid in the form of polyester or a vinyl ester and these materials set up very quickly. There are certain problems with capsule anchors and for some engineers the association between vinyl ester and capsules probably has a lot to do with fastener companies, not just Power Fasteners, renaming this material.

To begin with, capsules have a specific volume of material and you can’t break one in two to make up the difference. You can make up the difference with material dispensed from a cartridge but you would probably want to use the cartridge first, and then insert the capsule except you might not know if you were going to need extra material. Depth and diameter of the hole makes capsules a problem because field experience has proven that contractors will use one capsule per hole and not consider the complete filling requirement.

Capsules also require in-place mixing; the glass capsule must be broken and pulverized. The procedure for doing this, involves an attachment inserted in the chuck of a power drill to which a thread rod is mounted. The rod is inserted in the hole breaking the capsule and the drill then pulverizes the glass while mixing the material. Some contractors, finding they lacked the attachment would try and do this by hand; this is a VERY bad idea.

Vinyl ester and capsules are for some engineers a bad memory. “Allakhazam - Epoxy Acrylate”

The ASTM C882 bond strengths of AC100 are, for me, a concern. ASTM C881 provides for a 14 day room temperature cure. Are the AC100 test results for wet or dry specimens? It is possible that the 14 day wet cure bond strengths are LOWER than the 2 day results. Here is why…

http://www.wes.army.mil/REMR/pdf/cs/mg-1-1.pdf    and

I firmly believe that any engineer encountering a bond strength at 14 days that was less than the 2 day value would want a in-depth explanation as to just how this phenomenon occurs.

It should be noted that the REMR testing was done years ago and that Rawl and Power Fasteners are historically the same company. Furthermore, while epoxy resins are water insoluble the typical amine curing agents are not, so they suffer hydrolysis more readily than vinyl esters. It should also be noted that in the testing, vinyl esters did out-perform the epoxies and the polyester but there is definitely a lot to take into consideration and a statement of “Used in wet environments” for a bolt grouting material, is attributing a boiler plate level of performance that is, at best questionable, especially when used overhead. This brings me to the matter of Non-Sag. I don’t believe it.

ASTM C881, Grade 3 materials are non-sag; the requirement is 1/4 inch (approx. 6mm), from time of application to gel. It is a pass or fail test. The adhesive is mixed and troweled into a trough 1/4" deep and about 1 & 1/2" wide. The material must hold its shape supporting its own weight until it is hard.

AC100 does not indicate the non-sag thickness. Likewise, it does not list a viscosity. Viscosity is actually a meaningless number for non-sag materials because a very high viscosity material, lacking internal bonding, will nevertheless sag under its own weight; it is only a matter of time. See the Pitch Drop experiment.

I just do not believe that a material with a gel time of 7 minutes at 68 degrees F. is NOT a high viscosity flowing liquid. A 1/4" inch a non-sag paste in a cartridge would require some effort to dispense using a manual delivery gun and if AC100 were a paste, even with a compressed air gun, the speed at which free-radical polymerization thickens is so fast, a contractor, without machine-like execution; would be throwing away static mix nozzles left and right.

So I am going to ASSUME, having not ever seen this material. I get the feeling that it is goopy, molasses goopy, vinyl ester capsule goopy. If it is, would any engineer seriously consider specifying a flowing material for overhead application? I don’t think so. Mind you, at 68 degrees F, after 7 minutes you are not to disturb the dowel.

If I am right, then it does not meet ASTM C881, Grade 3 and this might be important to know. There is certainly enough about the AC100 bulletin to give ME reason to doubt.
ASTM C881… Show Me an independent test result, point on point.

I don’t know which Power Fasteners material was used on the Big Dig. If not a vinyl ester and wet conditions exited, judging from the REMR testing, I would be even more concerned.

For the record, I am not currently working in the adhesive industry so every house is built of glue and glass.

RE: Big Dig Boston ceiling collapse

Many of epoxybot's comments are irrelevant to the issue at hand. An antiquated capsule system wasn't used; a dual cartridge metering gun mixed the components immediately prior to inectiing into the holes.  The epoxy was ASTM-rated for damp applications and hole temperatures as low as 49 oF. I haven't seen evidence that the epoxy itself failed, as would be the case if improperly mixed or insufficiently cured.
The direct problem was improper application, such as not cleaning the holes, not cleaning the bolts, not filling the holes, etc. Possibly, excessive moisture -- the reported dripping water was from a CYA source.  
The indirect problem was that management &  engineering assumed perfect installation by workers, even to the point that the number of bolts was halved in some areas to cut costs.
Followup lawsuits:

Massachusetts to file civil suit against 15 Big Dig contractors
By Elizabeth Mehren, Los Angeles Times, November 28, 2006
"BOSTON — Charging that sections of the Big Dig tunnel system here were so defective that "it was just a matter of time before a tragedy occurred," the state attorney general said Monday that he would sue 15 companies involved in the project.

Atty. Gen. Thomas F. Reilly said the civil lawsuit to be filed today in no way abrogated a criminal investigation against project manager Bechtel/Parsons Brinckerhoff and other contractors on the $14.6-billion network of highways and tunnels that run under Boston.

Reilly's civil suit stems from the July 10 death of a Boston woman when two-ton ceiling panels fell on the car in which she was a passenger. The family of 38-year-old Milena Del Valle has filed a separate wrongful death lawsuit against nine Big Dig construction companies and the Massachusetts Turnpike Authority.

The attorney general said Monday that the Big Dig contractors named in his lawsuit were negligent in using epoxy anchor bolts to secure the massive ceiling panels.

"If you were going to hang concrete panels that weigh about 2 tons apiece and you expect this system to be secure, you'd better get it right — or don't do it at all," Reilly said at a news conference.

After examining the damage and reviewing reams of documents, Reilly said, "It's clear to me that they didn't get it right. The consequences were great. A woman lost her life."

Andrew Paven, a spokesman for Bechtel/Parsons Brinckerhoff, said Monday that the firm would have no comment.

Reilly said a criminal investigation that could result in manslaughter charges remains ongoing. He said he felt compelled to file the civil suit because of a statute that could set a Nov. 29 deadline for civil action connected with certain parts of the Big Dig.

His suit does not specify monetary damages. But by alleging gross negligence — one of several charges — the attorney general's office could circumvent a $150-million cap on damages negotiated by Bechtel Parsons/Brinckerhoff as part of its construction management contract.

RE: Big Dig Boston ceiling collapse

I don't think we can say for sure what the problem is, so it may or may not be improper instalation. I have found epoxy in a an overhad application is very difficult. Further, it appeared that bolted fitxture supported a continuos tee. this tee was suppoted at 4 or 5 points by turnbucle hangers. It would be impossible with out significant testing to know how mucjh load was in each hanger. By the same token, it would be very easy to overload a connection. There are many questions yet to be answered before we can say what really happened.

RE: Big Dig Boston ceiling collapse


Latest News on Epoxy

Boston Globe
Big Dig job may have used wrong epoxy
Total of bolts affected not clear; probers ask who knew
By Scott Allen and Sean P. Murphy, Globe Staff  |  May 3, 2007

Contractors apparently used the wrong adhesive to install at least some of the bolts in a Big Dig tunnel ceiling that partially collapsed last summer, project records show, prompting criminal investigators to focus on whether the mix-up was a significant factor in the accident that killed a Jamaica Plain woman.

Invoices from the 1999 ceiling construction job show that Modern Continental Construction Co. received and apparently used at least one case of a quick-drying epoxy to secure ceiling bolts to the tunnel roof rather than standard epoxy, which the ceiling designers had specified.

The distinction was crucial to the safety of the ceiling: The "fast-set" epoxy holds 25 percent less weight than standard epoxy and is not recommended for suspending heavy objects overhead.

It is unclear how widespread the use of fast-set epoxy was, since most sales records don't list the epoxy type, but state criminal investigators are looking seriously at the possibility that the weaker epoxy was used in the ceiling section that collapsed when 20 bolts popped out on the night of July 10, 2006, according to representatives of several firms under investigation.

The investigators also want to know why no one raised the possibility that the wrong epoxy had been used when ceiling bolts started coming loose during construction of the Interstate 90 connector tunnel.

"If [workers] used the wrong stuff, which appears to be the case, the issue is who knew about this or were they reckless about letting the project go forward with the wrong stuff?" said a consultant to one of the firms involved in the ceiling project, who asked not to be named so as not to anger prosecutors who are presenting their evidence in secret to a Suffolk County grand jury.

Paul F. Ware, the special prosecutor leading the state's criminal investigation, has sent investigators back into the tunnel over the last few days to collect more ceiling bolts for lab analysis, according to a letter from the Massachusetts Turnpike Authority, which manages the Big Dig tunnel system, to the companies involved in the ceiling project. The tests could help investigators determine the strength and type of epoxy that was used.

Use of fast-set epoxy in the ceiling is one in a series of missteps that may have contributed to the accident and, at the least, point out oversight lapses in the $14.6 billion Big Dig project.

The Globe has previously reported that, to save time, Big Dig managers and designers eliminated half the ceiling bolts called for in the original ceiling design and that construction workers made numerous mistakes during installation of the bolts that could have weakened them. The newspaper has also reported that ceiling bolts in the area of the collapse were safety-tested with a weight now regarded as too low, potentially allowing defective bolts to pass.

If the bolts were held in place by fast-set epoxy, the ceiling would have had little, if any, margin of safety left. Bolts secured with fast-set epoxy could safely carry 4,285 pounds each, rather than the 6,350 pounds the designers had planned on, based on their final report to Big Dig managers on the ceiling. Two independent engineers who have reviewed the ceiling's specifications for the Globe estimated that the ceiling's weight was close to 5,000 pounds per bolt, which is more than bolts secured with fast-set epoxy were designed to bear over the long term.

After the accident, the tunnel ceiling was permanently removed in the area of the accident, and elsewhere in the connector the ceiling was reinforced with additional bolts and brackets.

Construction of the ceiling was supervised by engineers at the joint venture of Bechtel and Parsons Brinckerhoff, but responsibility for using the right epoxy is difficult to pin down. The Braintree office of Gannett Fleming designed the ceiling to be secured with standard epoxy, but that require ment is not highlighted in project documents. Modern Continental built the ceiling, but workers have said they weren't told there was an important difference between the epoxies. Powers Fasteners of New York had a contract to supply the epoxy and bolts, but only through a small distribution company that bought the products wholesale and then delivered them to the job.

As a result, each company has said it bears no responsibility for use of the wrong epoxy. In fact, Powers Fasteners officials have told investigators that they aren't even certain that the epoxy in the accident area was their product, even though, during construction, company officials visited the tunnel and provided technical advice to workers on how to install the ceiling bolts properly. Powers' distributor, Newman, Renner, Colony of Plymouth, declined to comment.

The investigation into what epoxy was used has been hampered by both the imprecise sales records and the difficulty of chemically identifying the epoxy used in the area of the accident. The National Transportation Safety Board reported four months after the crash that it could not identify the epoxy taken from the failed bolts even after comparing it with samples of standard and fast-set epoxy. And the sales records that show what Newman, Renner, Colony delivered to Modern Continental distinguish between standard and fast-set epoxy in only one invoice.

State investigators in recent months have intensified their interest in Powers, sending company officials a fresh subpoena in March asking for documents concerning its role in the ceiling project. In addition, witnesses from other companies called before the grand jury hearing evidence in the case say they are being questioned closely about the type of epoxy used to hold up the ceiling.

"All the discussion outside the jury room is about the question of which epoxy was used and was it fast-set epoxy?" said an official for one of the companies under investigation who asked not to be named.

The focus on epoxy comes as Ware and his boss, Attorney General Martha Coakley, strive to meet a self-imposed deadline of June to decide whether to ask the grand jury to return indictments against anyone for criminal negligence in the accident. Legal analysts say that winning a conviction would require Coakley to prove that people or companies knew they were building a dangerous ceiling or they were so reckless that they missed obvious warning signs.

Before taking office in January, Coakley had raised doubts that the evidence was strong enough to prove criminal negligence, but, since Ware's arrival on March 1, some in her office say they have become more optimistic that there could be enough evidence for criminal indictments.

But fixing responsibility for the epoxy remains challenging, in part because the design documents produced by Gannett Fleming and Bechtel/Parsons Brinckerhoff say only in passing that contractors should use standard epoxy rather than fast-set for ceiling bolts. All of the safety calculations are based on bolts secured by standard epoxy, but the design specifications don't explicitly forbid fast-set, and the fact that fast-set can support less weight than standard epoxy is contained only in a footnote.

Adding to the confusion, although fast-set epoxy cartridges were clearly marked, the workers installing the ceiling may not have known there was a difference between fast-set and standard aside from drying time. Construction workers on the ceiling project have said they used Powers Fasteners epoxy and bolts, but they don't recall whether the label said fast-set.

Finally, the epoxy passed through many hands on its way to the tunnel. Sika Corp. manufactured the epoxy at a plant in Ohio, then shipped it to a warehouse in New Jersey in barrels marked with a prominent "FS" to denote fast-set epoxy, according to Sika officials. Powers then transported Sika's epoxy to its plant in New York where workers repackaged it into small cartridges, placing Powers's label on it. Then, Newman, Renner, Colony brought the cartridges and bolts to Modern Continental at the tunnel site.

Criminal investigators are focusing on a period in October 1999 when five ceiling bolts came loose shortly after the ceiling was hung from them, prompting Modern Continental officials to call in Powers Fasteners officials for advice. Over the next three months, officials from Powers, Modern and Bechtel/Parsons Brinckerhoff discussed ways to install bolts more securely, but there is no evidence anyone asked: Did workers use the right epoxy?

As one lawyer with direct knowledge of the investigation put it, "Was the right advice given by the experts?"

RE: Big Dig Boston ceiling collapse

I love that "As a result, each company has said it bears no responsibility for use of the wrong epoxy." Huh? Who is at fault, the Easter Bunny? No, don't think the Easter Bunny was involved in this project, though with as much money as was spent and wasted, I wouldn't be surprised if Mr. Bunny was on the payroll. Sarcasm aside, who is the project manager for this tunnel?
Possible culprits:
Designer: The designer specified the right epoxy, how can he be at fault if they build it incorrectly? How much oversight does the designer really have? (ask the engineers who lost their licenses after the Hyatt walkway collapsed).

Epoxy maker: how is he supposed to know what load they put on the epoxy? It's only his job to tell them how to use it, not to figure out if it should be used at all.

Workers: the workers put in whatever epoxy was handed them. Nope, they look to be guilt free, unless you have some rogue workers running around to hardware stores, buying up whatever epoxy fit their fancies.

Program manager: The program manager is responsible for building as designed AND fixing any unforseen problems; I say they are completely at fault. That's why you get paid the big bucks, so take your medicine, I say.

RE: Big Dig Boston ceiling collapse

I don't know, it appears to me that the epoxy company, Powers Fasteners may have culpability here.

1. If the standard material was approved and the fast set (the story stated that fast set was not recommended to suspend loads overhead) material was sent to the job to secure ceiling panels overhead.

2. There were problems during installation and the contractor had the epoxy company come to the jobsite to check on the installation.

3. It appears the epoxy firm had the knowledge on the material limitations but failed to tell the contractor.

So the questions are: Why was fast set sent in the first place (wasn't approved)? Why didn't the epoxy company notice this in at the jobsite? Why didn't they act if they knew? How could they know of the problem?

RE: Big Dig Boston ceiling collapse

Maybe I don't understand the relationship the epoxy company has with the actual construction. I would think that the epoxy company is just responsible for sending whatever was ordered, and how it was used was not their place to say. The application looked right, the loads were wrong (that is, too high for that particular epoxy); since the epoxy company wasn't paid to do the stress analysis that determined the load, then how could they be responsible for incorrect use of their epoxy?

RE: Big Dig Boston ceiling collapse

....or it could be that there were multiple uses on that project for overhead, and non-overhead, applications and the fast-set was sent for the non-overhead uses, but got mixed up by personnel in the field and used incorrectly in the overhead applications.  Powers may not have ever known that they were using the fast-set.

This is all speculation of course - the investigation hopefully will find who did what, when, and who knew what and when.

RE: Big Dig Boston ceiling collapse

The epoxie manufacturer (repackager)is possibly at risk here.  Many times on large jobs (and even smaller jobs) manufacturers or repackagers like Powers tend to stretch the numbers to make their adhesive work in any and all situations to "get the business".  I would imagine situations where the salesperson is on-site and says whatever is needed to make the adhesive on-hand "work" for whatever the application.  Once it is in the hole and cured "nobody knows" what is in the hole.  As it is the NTSB cannot figure out what adhesives are in any hole after they are cured.  I find it hard to believe that the distributor on such a high-profile job sent whatever was on the shelf instead of the specified material.  Key takeaway from this is to use manufacturers of adhesive, not repackagers.  Simpson, Hilti, Sika, Red Head are all liable for bad product because they make it.  Powers will pass liability on to Sika without second thought.  KNOW WHAT YOU ARE SPECIFYING, CONTROL THE JOB!!

RE: Big Dig Boston ceiling collapse

Hope this dispute over which epoxy was used doesn't obscure the real question, which is whether or not epoxy bolts should have been used in this application.  I think the clear answer is NO!

RE: Big Dig Boston ceiling collapse

It seems to me also that this misses the point.  If the quick-fix could "safely" carry 4,285 lbs, but failed at 5,000 lbs, either their definition of "safely" is way different than mine or else there was still some serious problem.

With regards to whether the quick-set was supposed to be used in overhead, I would think that would have more to do with insurance, liability, and legalese than actual suitability.  I know a lot of the chains, ropes, and cables sold have a "not for overhead lifting" warning label, sounds a lot like "don't blame us when you kill yourself."

RE: Big Dig Boston ceiling collapse

With proper engineering and installation, epoxy secured anchorages can be used successfully and can be 'proofed' for load capacity.

By safely carrying, 4285 pounds, the anchorages should have a safety factor of 3 to 4, typical for fasteners...  This means that they can actually carry roughly 15000 lbs under ideal conditions, including installation... With proper installation they should be capable of supporting a 5000 lb load...

the kicker to the discussion is the fasteners have an incredible variability in installation, hence a safety factor of 3 to 4.  The installation should have been more closely monitored and tested.  I'm not aware of any testing during the installation.  There are simple pull out devices that can be used to test any or all of them, if necessary.  It is likely that field review was limited due to budgetary restraints and if I were the adhesive supplier, I'd be looking at field review, skilled field personnel (both contractor and consultant) and budgets.  The epoxy material is sound and the failure appears to be one of attachment of the epoxy to the concrete... epoxies are adhesives and should be used as such.

The use of safely using innovative and economical materials is clearly the realm of the engineer and this includes proper checking the installation, in particular for innovative construction (I'm not sure that epoxy anchorage is innovative, though; it's fairly common).  When proper testing and field review is factored into the cost, there may be more economical methods of fastening, but that's another scenario.


RE: Big Dig Boston ceiling collapse

Reading back through the postings, I see that you were always a supporter of epoxy, as I was always a naysayer.  Guess my jobs won't use them and yours will.  Simple as that.  I completely understand your argument and disagree on the grounds of what my experience tells me is achievable in the field.

RE: Big Dig Boston ceiling collapse

FYI...this should be good for the debate.

NTSB Advisory
National Transportation Safety Board
Washington, DC 20594
July 5, 2007



Washington, DC -- The National Transportation Safety Board will hold a public Board meeting on Tuesday, July 10, 2007, at 9:30 a.m., in its Board Room and Conference Center, 429 L'Enfant Plaza, S.W., Washington, DC.

There is one item on the agenda:

On July 10, 2006, a passenger car was traveling eastbound in the Interstate 90 (I-90) connector tunnel in Boston, Massachusetts, en route to Logan International Airport. As the car approached the end of the I-90 connector tunnel, a section of the tunnel's suspended concrete ceiling became detached from the tunnel roof and fell onto the vehicle. Concrete panels from the ceiling crushed the right side of the vehicle roof as the car came to rest against the north wall of the tunnel. The passenger was fatally injured and the driver had minor injuries. A total of about 26 tons of concrete and associated suspension hardware fell onto the vehicle and the roadway.

Directions to the Board Room: Front door located on Lower 10th Street, directly below L'Enfant Plaza. From Metro, exit L'Enfant Plaza station at 9th and D streets escalator, walk through shopping mall, at CVS store take escalator down one level. Board Room will be to your left. A live and archived webcast of the proceedings will be available on the Board's website at www.ntsb.gov. Technical support details are available under "Board Meetings." To report any problems, please call (703) 993-3100 and ask for Webcast Technical Support.

A summary of the final report, which will include findings, probable cause and safety recommendations, will appear on the web site shortly after the conclusion of the meeting. The entire report will appear on the web site several weeks later.


Media Contact: Keith Holloway, (202)-314-6100

RE: Big Dig Boston ceiling collapse

A cople of weeks ago the news carried a story that the repairs had been completed and the tunnel reopened. They were able to fix the problem for just over $50.000.000 of our dollars.

RE: Big Dig Boston ceiling collapse

Stuff is starting to come in on the Big Dig.

I'm sure it will be better reported than the AP wire eventually.  Epoxy creep is taking some heat.  i'm interested to see if the failure analysis looked at just the pulled out ones and the holes or if there was creep all over the place.  link below.


RE: Big Dig Boston ceiling collapse

Most of the reports are out.  It should be noted that this creep issue was specific to this type and brand of adhesive/epoxy.  Not all adhesive/expoy anchors have creep issues.  You will probably want to verify the anchors you are specifying do not have this creep issue.  I work closely with adhesive anchors and had no idea this was an issue with this product.  As I understand, the fast set version is the cheaper of the two and is most commonly sold even though the slow set version data is typically published.





RE: Big Dig Boston ceiling collapse



I work closely with adhesive anchors and had no idea this was an issue with this product.

PackerFan - you and me both!

(btw:  Go Vikings)

RE: Big Dig Boston ceiling collapse

Read 'Engineers of Dreams' by Duke University's CE dept head, Petrosky.

In one of the last chapters he describes the generation gap effect in bridge engineering. In 30 yr cycles, later generations choose to ignore the wisdom and experience of their mentors. This explained successive bridge disasters:
- Tay rail bridge, truss, ~1880;
- Quebec rail bridge, cantilever, ~1910;
- Tacoma hwy bridge, suspension, 1940;
- Various box girder bridges, 1970;
- We are overdue for a stayed bridge disaster.

RE: Big Dig Boston ceiling collapse

More than enough blame to go around.
More legal fees.
More grist for the wheels of justice.

Ultimately, some jury or a federal judge will apportion damages according to who has the deepest pockets.

RE: Big Dig Boston ceiling collapse



Today’s indictment represents one of several phases in reaching a just result for the Commonwealth and the family of Milena Del Valle,” Coakley said.

...one of several....I guess there's more coming?

RE: Big Dig Boston ceiling collapse



The attorney general did express disdain at the maximum penalty a corporation in Massachusetts faces for involuntary manslaughter -- a $1,000 fine.


RE: Big Dig Boston ceiling collapse

$1000.00, that law must be as old as german beer law.

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