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Cracked Masonry Beam Repair
2

Cracked Masonry Beam Repair

Cracked Masonry Beam Repair

(OP)
Hey everyone,

I'm looking for a second opinion on a repair detail for a cracked masonry beam I observed last week. In the pictures attached you can see an overall view of the beam and crack as well as some closer shots taken from a lift on the opposite side of the beam.

The structure is:
- precast roof spanning 25'
- the roof sits on what appear to be masonry beam spanning between columns (the cracked beam shown). The beam is 16" deep (nominal) x 12" wide (nominal) and ea course is 8".
- 12" dia concrete columns spaces at ≈19'-0" oc.
- crack is approximately 3' long and runs horizontal for about 2'-6" then curves up to vertical at a joint in the CMU.

From what I can find the structure is 1940s era but I don't know what has been done to is since then other than reroof. Upon inspecting it we were hoping to find a steel beam encased in the masonry as fireproofing. However I can't find any reasonable evidence there is a beam in there. I was able to pull a large chunk of the beam out with my hands and expose about 1/2 the thickness (no steel beam appeared to be grout filled).

That being said we got some shoring out there ASAP just in case and now I'm looking to place a new steel beam under the cracked masonry beam to hold up the roof. She ain't pretty but I'm not sure what other options I have. I could potenial use a C15 on either side but the connection at the column makes me a little nervous because of the proximity to the top of the member (edge distance) and the fact the column is slightly wider than the beam.

In my detail I'm providing a steel collar to help provide confienment. Then through bolts to get loads into the column. Like I said - she ain't pretty but I thnk it'll do. Just wondering if anyone else here sees a potential issue with my scheme or has an easier way to do this.

Excuse some of the sloppiness on the drawing as well - still havent cleaned these up.

Thanks!

RE: Cracked Masonry Beam Repair

- I'd be inclined not to jack unless the sag is producing some manner of undesirable serviceability issue. I worry that it does more harm than good in many cases. Some boats are best left un-rocked.

- I'd leave a gap between the steel beam and the masonry and fill that with grout intermittently or something along those lines.

- 12" round is not a big column. I worry that there'll be nothing left inside the collar but well confined dust when all is said and done. Could you hanger up as shown schematically below and make the column connection nominal?

- I like your C15 idea, especially if you can combine it with the hanger up concept. Perhaps you could install the top of the C15 flush with the top of the beam and bolt some hanger plates to the bottom intermittently that can be dialed in for a snug fit.



I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Cracked Masonry Beam Repair

(OP)
Thanks for the response KootK. There was some ponding on the roof but I'm not sure if that's a functions of the cracked beam or imporperly installed tapered insulation. That's why I was hoping to jack things back to normal. I could install the beam with a slight gap then have them wedge shims into the gap to "pre-load" my steel and relive the CMU beam.

As far as the hanger goes - I'll need to think on it more. I'd be hanging off of the precast planks that my steel beam are suppsoed to support. I sort of end up with a cirular load path. I was also hopping to avoid having to go through the roof to keep them from having to do any roof work until they reroof again. YOu could be on to something here - I'll just need to think through how I could make it happen.

Could you clarify what you mean by "hanger plates" in regard to the channels? I like the channels from an aesthetic stanpoint but I'm not sure how to make the connections work. Run the channels past the column and through bolt? I'll end up with a small gap between the steel and the CMU away from the column - but I'm not sure that would matter.

RE: Cracked Masonry Beam Repair

Quote (T_Bat)

I'd be hanging off of the precast planks that my steel beam are suppsoed to support.

I was reading the clouded bit below as diaphragm that could be penetrated to do my nasty hanger business. Is that so? Tell me fast as I'm working up some sketches based on that. I see the actual "hanging" being from the cmu beam.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Cracked Masonry Beam Repair

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Cracked Masonry Beam Repair

All good ideas.

I wonder....what was the cause of this? If this beam system is repetitive throughout the building is there a possibility that it may happen elsewhere?
Is there a type of flaw, or weakness in the originally designed system?

Shear cracking like that is a huge warning sign so kudos to you in getting it shored immediately.
I would think that once you get this particular beam "fixed" that you would need to recommend to the owner/client that further investigation is warranted to ensure that this doesn't happen again at another beam...

And the reason I say this is that many times shear cracks, and beam shear failures in general, are sudden things. The fact that this time you had a crack warn you is fortunate.

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RE: Cracked Masonry Beam Repair

(OP)
Sorry for the delay guys - girls night so my wife kicked me out. Thanks for the sketch KootK, I’m liking this scheme. Less “intrusion” into the open space below. To avoid field welding I’m thinking of using sandwiched angles back to back with space for a rod inbetween. Just to confirm though, the hanger on the right takes the reaction from the beam to the right then transfer to the channels. Then the W8 takes the reaction from the channels and transfers it through bearing on the cmu down into the column? I’ve attached a markup for clarity (excuse the messiness again - working of my phone).

JAE - I did a visual check of the other beam and I couldn’t see any signs of distress. I did this from the ground though.

I’m wondering if there is any merit to shoring from below simliar to my orginal design in case a similar failure forms on the opposite end. The sandwhiched channels would make visual observation impossible. Alternatively we could weld some stitch plates across the bottom of the channels to “catch” anything in the future. Wouldn’t necessarily be designed but could provide some suspenders for the belt we are installing.

RE: Cracked Masonry Beam Repair

T_Bat:
This might be a place for the application of fiber-reinforced polymer (FRP) reinforcement systems. It could be wrapped around the sides and bottom of the beam, and them all the way around btwn. the stems of the roof planks/channel shapes. There doesn’t appear to be any bearing/crushing btwn. the column and the beam. Does this have anything to do with a heavy roof loading of some sort in this area? Is it related to poor grouting in that area or bad rebar placement, etc?

That looks like a school bldg., any chance that you can find some bldg. plans and specs. on this bldg. down in the boiler room, maintenance office, or the school district offices? I would be surprised if “the structure is 1940s era” structure. I don’t know that you would have seen those kinds and spans (25'?) of those 3' wide roof plank/channel shapes, a 19-20' long reinforced CMU beam, made up of 16" deep lintel blks. or columns formed that way. You might also reinforce that CMU beam with some harped tendons or tie rods on both sides of the beam; and running from saddles above the beam over the columns and 12-16" below the beam at mid span. This would take load and shear off the beam and through the rods to the columns.

RE: Cracked Masonry Beam Repair

(OP)
dhengr - Unfortunately there are no drawings. I'm always asking for those before I even look at a building. From the property history I can find the first record of it is 1947. It did seem odd to me considering the span and size on the masonry beam but I'm no expert on historical construction practice. I'm not sure the clients would go with FRP - the steel beams would fit more with the aesthetic that's currently there. Do you have an idea of how expensive something like that would be compared to conventional steel?

I like the harred tendon idea and have always wanted to use that scheme but I'm looking for something that is completly (or almost) independant of the existing beam for redundancy since I don't really know anything about the beam's reinforcing or material strengths. And I would still need something the restablish continuity across the crack.

RE: Cracked Masonry Beam Repair

What about laying a long vertical channel against the column (legs in) and bolt it? This would give you a nice attachment point for the dropped I-beam and lots of area for bolts without taking up alot of real estate.

RE: Cracked Masonry Beam Repair

(OP)
XR250 - you mean run a channel vertically and make it as long as I need to fit enough bolt? if that's correct, I guess my main concern is the small amount of material we have to work with. The rolled plate clamp was to provide some amount of confinemnt.

RE: Cracked Masonry Beam Repair

Correct. I figure you could run it the entire length of the column.

RE: Cracked Masonry Beam Repair

Just don't discount the possibility of this occurring elsewhere, without a pre-crack warning.

Your obligation is to public welfare and safety (noticed in your photos that there were people standing below this structure).
Shear can have warning cracks in some cases (your case here) and no warning cracks elsewhere. You need to be a detective and understand fully WHY this happened...not just fix the crack and go away.

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RE: Cracked Masonry Beam Repair

(OP)
Definitely JAE - I am leaning towards an overload at some point. The fact is the building is around 70 years old and does not show similar signs of distress. I say that with the understanding that past performance does not always guarantee future results. It just seems that is this were a deficient system there would be other signs at this point. From getting on the roof there was a fair amount of ponded water on the roof (2.25" deep) located right over this area. Obviously there may be some chick or egg going on here (did the ponding cause the crack or settlement from the crack cause the ponding?) The owner has been made aware of the ponding issues.

My question is when does our obligation to the public end? Speaking hypothetically now - if a client doesn't want us to do something or won't pay when are we obligated to work for free. In clear cases of unethical behavior or clear signs of structural deficiency there is no question we have to do what is best for the public health, safety & welfare - as well as our insurance ;)

Now for something similar to the structure in question - is this something that the owner needs to know could happen again or do I need to actually go through and do testing, analysis, and investigation of the entire structure for any future issues (even if I'm not getting paid)?

Hopefully that doesn't read as adversarial - As a young engineer I'm genuinely interested in navigating the ethical implications of our work.

RE: Cracked Masonry Beam Repair

T Bat - I think you are on the right track in terms of a possible ponding issue if that is the reason.

I think it would be wrong for an engineer to just "fix" the cracked beam and not take any time to understand the "why" of the matter.
I think that doing some engineering investigation (asking questions, reviewing the original plans if any, running some numbers, etc.) to find out why this occurred is essential...even if you aren't directly paid for it.

When you get into engineering ethics, the issue of whether you are paid to perform your duty to the public is almost never an issue.

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RE: Cracked Masonry Beam Repair

(OP)
Good points JAE - and duly noted. I appreciate your advice. I made notes of the other conditions through the building but I will run some quick and dirty numbers for the typical conditions.

I've decided on going with scheme similar to what KootK showed. I've used back to back angles with a space for rods to make my hangers. Let me know if you guys see any major issues (attached).

RE: Cracked Masonry Beam Repair

Is this the time to re-visit the masonry thru bolt discussion? :>

RE: Cracked Masonry Beam Repair

(OP)
Depends on what you mean haha... Are you saying go back to the original dropped beam design? The through bolts I show on the channels are really just to help hold the pieces of the masonry beam up and give a little bit of redundancy. The channels are designed to span from column to column without any consideration of the masonry...

I feel better about this than my original design.

RE: Cracked Masonry Beam Repair


Got it. There has been debates in the past about the capacity of thru bolts. Seems you are fine in this case.

RE: Cracked Masonry Beam Repair

1) Are you fairly convinced that the crack extends through the full thickness of the member as opposed so just the face shell of the block? I ask because, given the construction and the rotation at the ends of the roof planks, I could totally see this being an application where the face shells are loaded directly. Imperfect bond between CMU and grout, a maybe a little prying action, and I could see things developing as they have.

2) I worry a bit about the connection shown below which will have to transfer the entire beam reaction. Are steel bearing or pull through issues at all? Are masonry bearing stresses going to be high with the force concentrated under the vertical legs of the angles? I freely admit that my paranoia probably stems from the fact that I don't actually know how to evaluate such a connection myself. Perhaps you can educate me a bit in that regard. I will grant that the connection is clever and preferable from a constructability perspective.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Cracked Masonry Beam Repair

At least at this one connection. Maybe a plate washer on top of the angles would be nice.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Cracked Masonry Beam Repair

(OP)
KootK,

I'm not 100% sure what you mean in point #1. The crack does not extend all the way through in the areas I could observe. A large chunk near the end of the crack at the top of the beam came off with some light prodding and it appears the grout was "intact" (i.e. smooth surface that appeared to match the profile of the block).

As far as #2 goes - For steel bearing on the bolts head - I'll be honest I didn't run the calc. I would look at the F dimensions (flat width) of the bolt head divided by 2 for the max bearing width. Then for each bearing length you would use the flat width again since it would be the minimum length in contact with the bolts. The product of those would give the bearing area per leg for one bolt. Then use EQN J7-1? If I do that, I'm definitely good but that still doesn't seem quite right to me. It may be a good idea to add a plate washer up there to mitigate pull through issues.

RE: Cracked Masonry Beam Repair

(OP)
Ha! You beat me to it. Plate washer feels like a good idea.

RE: Cracked Masonry Beam Repair

Quote (T_bat)

I'm not 100% sure what you mean in point #1.

I'm trying to ascertain if your crack is a shear crack:

1) Through the CMU AND the grout or;

2) Through the CMU but NOT the grout.

In my mind those are quite different problems.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Cracked Masonry Beam Repair

Yeah, that looks like the real deal. Does it telegraph to the other side?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Cracked Masonry Beam Repair

I can't see a cap plate on the steel column. Does anyone know how the column terminates?

I like the idea of the double C15. The hanger detail assumes that the bearing of the existing beam on the column is reliable. Who knows whether it is or isn't? My preference would be to weld a gusset or other suitable attachment each side of the column directly below the channels.

BA

RE: Cracked Masonry Beam Repair

(OP)
Kootk,

The crack occurs on both sides but I can't see if either is cracked all the way through. The cracks aren't exact mirror images but pretty much follow the same path. The side I have attached a picture of showed the worse side. I wasn't able to get the lift to the other side due to some cubicles and workers doing their thing.

BAretired,

The column is 12" dia concrete. From what I could see it looked like the columns extended up to the b/roof planks and the masonry framed into the side. Hard to tell to be honest but the first block on either side of the column appeared to be cut around the column.

RE: Cracked Masonry Beam Repair

I didn't read your sketch carefully enough. For some reason, I thought the column was a steel HSS or Pipe. Please disregard my previous remark.

BA

RE: Cracked Masonry Beam Repair

(OP)
No worries. Thanks for the help thinking through this everyone!

RE: Cracked Masonry Beam Repair

One thing you may want to consider about the thru bolts is the constructability issues. How are they going to get a hole drilled perfectly straight to align with the hole in the opposite plate?
Are you going to field drill one of the plates from the backside with a long bit? Chemical anchors may be better for that reason.

RE: Cracked Masonry Beam Repair

(OP)
Quick update - the steel repair beam has been installed. I added plate washers to all the hanger (thanks for pointing that out KootK). Just wanted to send my gratitude to everyone who helped on this!

RE: Cracked Masonry Beam Repair

a) Most welcome.

b) Absolutely love seeing our ideas take form in real life. Thanks for reporting back on this.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

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