How to handle uncomfortable technical disagreement/concern over design
How to handle uncomfortable technical disagreement/concern over design
(OP)
I have a situation in my office where I'm involved in a design and disagree with a principle that, in my mind, could have significant safety considerations. I've already aired my opinion, but others disagree, because it's just been done in other applications without problems. I just don't buy into that philosophy, especially when there is no technical literature on the subject.
I genuinely have concerns, but I don't know what else to do given that I've already put my concerns on the table and they've been dismissed.
I genuinely have concerns, but I don't know what else to do given that I've already put my concerns on the table and they've been dismissed.






RE: How to handle uncomfortable technical disagreement/concern over design
I agree that "the old guys" often seem to dismiss "the young guys" as a matter of course, but virtually all of these situations can be resolved by asking the senior, "OK, so what am I missing?"
RE: How to handle uncomfortable technical disagreement/concern over design
You need to let those who don't listen understand that because there has been no repercussion in the past does not mean that the approach is correct. That's considered anecdotal evidence, not supporting corroboration. Anecdotal evidence is often a "one-time"occurrence. It does not establish precedence.
Document your objection in writing to your principals. It only takes one of these issues to completely sink a firm...and it's usually because someone didn't pay attention to reality.
Stick to your guns...you seem to know what you're doing.
RE: How to handle uncomfortable technical disagreement/concern over design
As far as "it's worked all along," is this something that is particular to your company, or is this some industry-wide standard?
RE: How to handle uncomfortable technical disagreement/concern over design
I have to agree with Ron here. You can push your point, but only so far. Without your PE, after you have voiced your opinion, you have to CYA in writing, then move on with your life. It's their decision and their responsibility at that point. You have done your due dilligence.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: How to handle uncomfortable technical disagreement/concern over design
I understand that some things come down to judgment, and I also understand that I'm not signing or sealing anything and I'm just an EIT, but, again, THAT, in and of itself, does nothing to address my concern.
Using it in x application means little to me. There's no telling how "overdesigned" using their principle, or what % of the design load it's ever seen.
Thanks for the vote of confidence, Ron. I'll try to do some more research to demonstrate the lack of literature on the topic and bring it up again.
RE: How to handle uncomfortable technical disagreement/concern over design
I can't say I'm right for sure, there's no literature on the subject, but a previous.post on this forum suggests that I'm certainly not wrong. I admit there is definitely some judgment involved, but the criticality of the condition along with the forces involved and the fact that this is a global stbaility of the structure issue makes me uncomfortable.
RE: How to handle uncomfortable technical disagreement/concern over design
There isn't technical literature on every detail and every situation, so you can't count on that in every case. You might explain the problem here in detail and get some outside ideas or direction. Maybe someone outside your office has run into this issue before. But, you do have a gut feeling that you should get resolved. You seem smart enough to me too, so that I would give you a listen if you came to me with your concerns. And, I would try to explain to your satisfaction, but you better come with evidence, because I know that what we have been doing has worked in the past. We all hate to admit that we were wrong or could do it better, all at the hands of the young guy.
I agree with TXS when he says that the boss is signing the plans and has ultimate responsibility. You usually do have trouble arguing with success, when it has worked before. But, most good bosses will explain their thinking when asked properly, and presented with sound, logical well reasoned concern, given a little time so cooler heads prevail. We want you to succeed, you're the best asset we've got, we secretly want you to keep us on our toes, we're not infallible. Approach each of the 'others' individually to air and explain your concerns. Sometimes you get a better hearing, one-on-one, when the group thinking thing, agree with the boss mentality isn't prevailing.
I agree with Ron, but would say it a bit differently. You must present your best case, explaining your concerns, with whatever corroborating evidence you can find. Explain your gut feeling with the best evidence you can muster, and dissect what they are doing with your best examples and disproofs at every step along the way as to why you think their way is unsafe or wrong. I don't think Ron meant notarized letter, by certified mail.
Good Luck
RE: How to handle uncomfortable technical disagreement/concern over design
RE: How to handle uncomfortable technical disagreement/concern over design
We have some braced frame columns subject to net uplifts on the order of 2000 kips (that's not a typo). It is being suggested to lap anchor rods with rebar in a drilled pier with no consideration of any other failure mechanism from App. D (specifically, pullout). It is suggested that you can lap the threaded rods directly with rebar with no nut on the threaded rods (or an inadequate nut by pullout capacity) and all is good.
I suggested that App. D is written specifically for this type of application and that we can get out of the tension breakout calcs by lapping with rebar, but we still need to comply with the pullout requirements.
I was told that micropiles are done all the time with threaded bars with no nuts on the ends and that the rod just develops in the concrete.
I've done a pretty exhaustive search, but can't find any literature on development lengths of threaded rods. The thing that concerns me most is the magnitude of the loads and the fact that this type of failure could literally cause the building to topple over. I just don't feel comfortable lapping extremely heavy threaded rods (Gr. 105) with rebar as though the transfer mechanism into the concrete is equivalent.
Any thoughts?
RE: How to handle uncomfortable technical disagreement/concern over design
RE: How to handle uncomfortable technical disagreement/concern over design
http://w
RE: How to handle uncomfortable technical disagreement/concern over design
I am not sure how that 2000 kips is getting distributed so you may still have major concerns.
RE: How to handle uncomfortable technical disagreement/concern over design
How bad does it fail if you check pullout?
RE: How to handle uncomfortable technical disagreement/concern over design
RE: How to handle uncomfortable technical disagreement/concern over design
RE: How to handle uncomfortable technical disagreement/concern over design
The threaded rod obviously has capacity, else adhesive anchors don't work. I would look at the ratio of capacity of threaded rods to reinforcing bars using the same adhesive, then apply this ratio to the splice length required in the concrete. Testing of this type splice would help, but I would be comfortable with this logic in the interim.
RE: How to handle uncomfortable technical disagreement/concern over design
Isn't the difference here that you are providing a threaded rod? There will be a superior bond around the rod due to the threads (similar to a deformed bar). Aren't most typical anchor bolts that are smooth most of the length and thus need the nut at the end for pullout capacity?
RE: How to handle uncomfortable technical disagreement/concern over design
Put down Appendix D for the day and play devil's advocate.
See if some of the information provided can develop the capacities you are looking for. Call Williams...tell them you are planning to embed 2" DIA. 150 KSI All Thread Bar in concrete and see what they say. Then call DSI Dwyidag and get the European feel for what you are doing.
It might not be the perfect application or the 100% correct way of doing things in a perfect world...but lets see if it works with some basic analysis techniques. You need to build a case either for or against your argument.
RE: How to handle uncomfortable technical disagreement/concern over design
RE: How to handle uncomfortable technical disagreement/concern over design
RE: How to handle uncomfortable technical disagreement/concern over design
RE: How to handle uncomfortable technical disagreement/concern over design
RE: How to handle uncomfortable technical disagreement/concern over design
One piece of advice I would give you, is approach the PE with a SOLUTION, not just a problem. If you can say, "hey I've done a lot of research, and we may be able to do it better using this detail", you're likely to get a lot further than throwing your hands in the air and saying "it doesn't work, and I don't know how to make it work"
RE: How to handle uncomfortable technical disagreement/concern over design
As others have said, stick to your guns.
But I am questioning if the detail can be slightly modified for it to work. I am assuming that you have nuts at the ends of these threaded rods. The failure mechanism is by pulling shear cone failure.
Per Appendix D, if you are able to provide U bands that are developed past the shear plane, then you are okay to transfer the tension from the anchor rod (by nut bearing) into rebar. If you remember, we had discussion on this very topic not too long ago.
Just lapping anchor rods to rebar does not sound too convincing.
RE: How to handle uncomfortable technical disagreement/concern over design
http:
RE: How to handle uncomfortable technical disagreement/concern over design
Believe me, I am by no means a "chicken little" proclaiming that the sky is falling, but I like to have a good gut reaction to details.
slick- it is proposed to have no nuts or plates at the ends of the rods, just straight up lapping them with rebar.
I'm trying to find out if there are any "threaded" rods that have been tested to comply with A-615. Maybe some have been tested for this purpose, but it didn't jump out in my search on development of threaded rods.
RE: How to handle uncomfortable technical disagreement/concern over design
Dik
RE: How to handle uncomfortable technical disagreement/concern over design
That 2000k is service, the factored uplift is near 3000k.
RE: How to handle uncomfortable technical disagreement/concern over design
you say they've analyzed it but you're worried about a combination loadcase ... maybe their opinion is that the combination is improbable (what we'd call a double failure case ... doesn't happen)
they've used this in the past, so they'd be reluctant to test it now ... a failure now would result in considerable and expensive rework to existing structures.
is there some oversight group you can go to ?
can you Prove it bad, or do you just think it's not good ? to prove it bad, are you assumptions too conservative ?
could you interest a nearby university into studying it as a thesis ??
good luck, and when it's your turn, you can design it properly.
RE: How to handle uncomfortable technical disagreement/concern over design
Per FHWA-RD-96-017, Drilled and Grouted Micropiles: State -of-Practice Review, Page 91, the typical ultimate design bond value for grout and a deformed steel bar is 2.0 to 3.0 MPa. 3.0 MPa = 435 PSI.
www.PeirceEngineering.com
RE: How to handle uncomfortable technical disagreement/concern over design
Is there any way to do a small scale test?
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: How to handle uncomfortable technical disagreement/concern over design
obviously you've brought this to attention and been "shot down" repeatedly. i would document your concerns like Ron said, but by email to multiple people in your company. keep it in house.
i agree that "it's how we've always done it" is the worst answer in the world for your question. it's moronic and uses no engineering ration. but make sure you maintain honor and respect when dealing with your employer. always maintain that respect so no one can ever say you were hot-headed or a finger pointer (i'm not implying that your are, just saying).
plead your case, give your reasons, back it up with calculations, and let them make the ultimate decision. do everthing necessary and in your power so that you can sleep at night knowing you did everything you could do.
what i'm having a hard time understanding is why are they so resistant to putting a nut on the end of the threaded bar? how expensive can nuts be in relation to the cost of a structure that has 2000 kip uplift column forces? IMO, putting nuts on the threaded bars solves the issue.
p.s. i saw an advertisement in recent SEA magazine for 97ksi #20 bar used in new WTC tower. it seems like the ceiling for threaded bar size/strength of has been raised.
RE: How to handle uncomfortable technical disagreement/concern over design
RE: How to handle uncomfortable technical disagreement/concern over design
I have looked at the Williams bars and they say that they meet A-615 for deformations.
That makes me feel a lot better and I think that is the direction that we're heading after a recent conversation I initiated.
RE: How to handle uncomfortable technical disagreement/concern over design
That and "the threads have some ability to develop the bar, so it's contribution isn't nothing" is all I was given.
I agree it isn't nothing, but there's nothing I can find that gives a rational way to quantify it.
RE: How to handle uncomfortable technical disagreement/concern over design
RE: How to handle uncomfortable technical disagreement/concern over design
I'm not saying we can't validate the design because it's no in App. D, but I wasn't being anything to make me feel comfortable about it. The fact that it may have been done a thousand times before does not make me sleep any better at night.
It looks like the Williams bars, however, put the issue to rest.
RE: How to handle uncomfortable technical disagreement/concern over design
How many anchors are we talking about here?
I have not read the thread thoroughly, and I didn't catch the diameter of the rods either.
My concerns with the threaded rods has always been that the load is transferred through the threads to the concrete anywhere there are threads. So, there can be load transferred to the concrete near the surface. To me, this is a poor detail.
I routinely design anchor rods/bolts with an anchor plate and a nut. The lapping of the rods and foundation bars is to ensure that the load is properly transferred to the foundation system. I usually use smooth anchor material and only thread the portion that extends above the pier or foundation. This helps ensure that the load engagement is at the anchor plate depth, not near the surface.
AISC DG1 has a table for the pullout strength of rods with jsut single embedded nuts, but even that scares me because often the bearing area of the nut is small. If you to due a straight bearing check on the area of the nut, the bearing stresses are are very high. A small anchor plate usually is more than enough to completely eliminate this concern.
RE: How to handle uncomfortable technical disagreement/concern over design
BTW-for a braced frame with uplift forces in that range, you must also have some incredibly high shear forces at the column bases...just a thought.
I agree with you that there are concerns ....foundations are a hard thing to fix; if not impossible.
RE: How to handle uncomfortable technical disagreement/concern over design
I've designed micropiles for both tension and compression using threaded bars without any lower nuts and plates.
www.PeirceEngineering.com
RE: How to handle uncomfortable technical disagreement/concern over design
RE: How to handle uncomfortable technical disagreement/concern over design
An expert is a man who has made all the mistakes which can be made in a very narrow field
RE: How to handle uncomfortable technical disagreement/concern over design
The most likely tension-failure plane in the pier concrete is a horizontal cross-section near the end of the anchors, which will be restrained by the rebar crossing the plane, and developed fully above that plane.
The pier reinforcing needs to be developed above the failure plane, extending to a depth of pier sufficient to hold down the structure. Headed or hooked reinforcing can be used to reduce development length.
Use of A615-conforming threadbar (Dywidag, SAS, etc.) as an anchor rod requires more consideration than using A1554 anchor rods. Bars and nuts are different sizes, and special details will be required. Mechanical splices may be preferred to laps with the high loads described, and threadbar can be connected to standard A615/A706 rebar with typical mechanical splices for rebar.
John Turner CSP PE
CRSI Greater Southwestern Regional Manager
RE: How to handle uncomfortable technical disagreement/concern over design
I can't pretend to fully understand what's been said, but to resist a force one needs a static component, right?
Wouldn't welded components in concrete resist better with a perpendicular head/washer/disk than none?
I think there's also the consideration of ethics.
Best of success, StructuralEIT
RE: How to handle uncomfortable technical disagreement/concern over design
In accordance with ACI 318-08 12.6, headed bars can develop the reinforcing bars (or anchor rods) in tension over a short distance (l_dt), which is roughly 15 bar diameters.
A few practical considerations:
-Pier cages are sometimes placed and then cut to length, or otherwise cut to length in the field.
-Congestion may be an issue, resulting in conflict between anchor rods and pier reinforcing, particularly where anchor rods are connected as a unit before placement.
-12.6 requires minimum spacing of headed bars.
Headed anchors are not permitted for development of bars in compression, per ACI 318-08 12.6.3. (Similar to the restriction on hooked bars.)
RE: How to handle uncomfortable technical disagreement/concern over design
An expert is a man who has made all the mistakes which can be made in a very narrow field
RE: How to handle uncomfortable technical disagreement/concern over design
Threadbar which has deformations equal to A615/A706 rebar will develop. Machine thread "all thread" does not develop to any usable extent.
A straight, smooth bar will not develop, even at hooks. Adhesion between portland cement concrete and smooth steel is negligible.
RE: How to handle uncomfortable technical disagreement/concern over design
RE: How to handle uncomfortable technical disagreement/concern over design
may help
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: How to handle uncomfortable technical disagreement/concern over design
Perhaps our concrete comes with extra stickiness.
BS8110 Table 3.27 lists bond/lap lengths for plain bars (ie those with no deformations) which are generally about 80% greater than for deformed bar.
It stands to reason that all-thread bar bond lengths will lie somewhere between that for plain and deformed bars.
RE: How to handle uncomfortable technical disagreement/concern over design
http://w
TXS,
I can see that in high seismic regions that smooth bar should be considered like a deformation anchor. That is to say: the development length should be such that little to no deflection along the bar anchorage should occur before plastic behaviour of the structure. While this requirement may limit the use, it shouldn't negate the use.
An expert is a man who has made all the mistakes which can be made in a very narrow field
RE: How to handle uncomfortable technical disagreement/concern over design
www.PeirceEngineering.com
RE: How to handle uncomfortable technical disagreement/concern over design
Interesting to me that people depend on modern glue for developing threaded rods, but don't like to depend on portland cement glue.
RE: How to handle uncomfortable technical disagreement/concern over design
An expert is a man who has made all the mistakes which can be made in a very narrow field
RE: How to handle uncomfortable technical disagreement/concern over design
Dik
RE: How to handle uncomfortable technical disagreement/concern over design
I am certainly not saying that there is zero surface bond between steel reinforcing and portland cement paste. Deformed bar develops primarily because of mechanical interlocking of the deformations, paste and aggregate, and surface bond with cement plays a significantly lesser role. Surface bond is susceptible to factors which do not adversely affect development of deformed bars or wire to the same extent.
As for ASTM F1554 all-thread, there will be some development, but again, it is not comparable to A615/A706 deformed bar.
RE: How to handle uncomfortable technical disagreement/concern over design
Thanks for clarifying your earlier posts. I think we all agree that deformed bars are the way to go in most cases.
RE: How to handle uncomfortable technical disagreement/concern over design
Thanks to all for the input and discussion.
RE: How to handle uncomfortable technical disagreement/concern over design
www.PeirceEngineering.com
RE: How to handle uncomfortable technical disagreement/concern over design
Also, mechanical interlock ramps up after surface bond slip occurs, so in reality many deformed bars are working via surface bond anyway...
That's not to say you should use use smooth bars!, but just to point out that bond isn't "zero" for smooth bars.
Back in the olden days all bars were smooth....
RE: How to handle uncomfortable technical disagreement/concern over design
It is incorrect to say that all bars were smooth in the old days. What can be said is that there was a wide variety of types of reinforcement, including smooth bars, twisted bars, and a lot of different types of deformed bars. Not until about 1947 did the US standardise on the deformations, and that time period varied in other countries.
RE: How to handle uncomfortable technical disagreement/concern over design