CMU non-conforming lintel beam / how serious an issue?? 1

[boffintech]

Have a CMU 8" block wall going up.

You can see from the picture that the 15' wide opening has 1 precast lintel beam 8" deep. The plan calls for a 48" deep lintel beam with 3 sets of 2#5 horizontal rebars placed bot/mid/top of the beam.

48" of lintel beam was grouted and with all of rebar; however, the middle and top rebar and grout is discontinuous at the control joints (see picture).

Is this condition an issue?

 

[ishvaaag]

At least is going out of what specified. It may work in some strut and tie scheme. In fact most of the old edge members were designed for such function even more than bridging gaps. It may be demolished and rebuilt; or reinforced, making perforations from below and forming some kind of simple span beam of more depth through, of course, grouting from behind or above etc.

 

[ishvaaag]

And look for the shear at supports. Subject what you have to analysis.

 

[ash060]

You should not have a huge problem other than bearing and shear. The moment capacity should not be effected as the maximum moment is in the middle of the span and there is not a problem there.

 

[JAE]

I think you will have a big shear issue to check at the ends. The overall wall will arch across the opening and focus all the load at the ends, where you just have an 8" lintel taking 100% of the end shear (due to the vertical CJ's).

 

[jeff91]

These comments are based on the assumption that the original plans called for a "pure" 48" deep CMU lintel and that the contractor substituted the concrete lintel in order to avoid placing shoring in the opening while the grout cured in the wall.

A couple of things to take into consideration:

1. Did the original analysis for the lintel take into consideration the control joints and evaluate the member for a uniform load or were the control joints not taken into consideration and a triangular load used in the analysis? With the control joints a uniform load should be used.

2. In order to take credit for the bars in the concrete lintel beam as the bottom bars in an overall 48" deep member the masonry and the concrete lintel have to work together. This means that there has to be a horizontal shear transfer across the interface between the concrete lintel and the first CMU course. Is this really occuring? It looks as if a mortar joint occurs on top of the concrete lintel so I suspect some transfer is occuring.

3. Check the dead load deflection of the concrete lintel under the weight of the total height of CMU + concrete lintel selfweight. Conservatively ignore any contribution of the CMU just to get a "feel" for the vertical displacement of the concrete lintel.

4. The entire shear is being taken by the concrete lintel. This has to be checked. Do you have certified drawings of the concrete lintel showing where the bars are located and the concrete strengths for the shear evaluation.

5. Check the bearing for both the concrete lintel and the CMU pier supporting the lintel.

 

[JLNJ]

I agree with JAE.

You can play with the flexure through arch action, but shear tends to control in a lintel. Add in the fact you have control joints right at the ends and the shear is probably 4 times the allowable. Maybe more.

 

[RacingAZ]

It is an issue as others have already stated. The 8" concrete lintel is pretty much picking up the rest of the wall. If the plan calls out 48" deep lintel, I can guarantee you that 8" CL would not be enough.

Did you specify the control joints? Bad CJ locations. A rake joint would have been better. On all the projects that I have done, I have never located any CJ's at that location, not even once. If the Architect shows them at that location, I would always insist on moving them to the mid-span of the lintel.

It seems that the wall blocks would get some sort of an exterior finish then if this is my job, I would suggest breaking them out to extend the horizontal rebars into the piers and put in the rake joints instead of the real CJ's, at least at the lintel depth.

 

[JAE]

Jeff91 brings up a good point regarding the possible lack of shear transfer between the top of the 8" deep precast beam and the masonry above.

 

[BAretired]

It is not clear how a 48" deep lintel beam could have worked with the control joints positioned as they are. It appears that the control joint on the right hand side of the photo is about 2" inside the opening so the lintel would not be bearing on the pier.

As constructed, remedial measures, if not mandatory, would seem prudent.

BA

 

[msquared48]

I would also ask, what, if anything, is functioning as the chord steel for the diaphragm?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[boffintech]

I'm the inspector not the EOR. I'm interested in how/why these things work out.

jeff91 (Structural) asked
1. No. The CJs shown on the arch were for the brick, not the CMU.

2. A very good point to put in the data back for future reference.
Is this really occurring? It appears so.

3. EOR question.
4. Certified drawings of the concrete lintel from manufacturer but an EOR question.

 

[Ron]

EOR apparently intended the 48" section to work compositely with the precast lintel. As JAE pointed out, little or no shear capacity and certainly not what was likely intended.

EOR needs to review and address this issue in writing. This could be a tear-out, depending on design capacity needed.

 

[boffintech]

I have seen a number of instance where masons have simply substituted a piece precast for the bottom course of a multiple course lintel beam. This appears to such a case.

RacingAZ was correct however, the horizontal rebar in the mid and top course should have been carried through the CJ and a raked mortar joint applied.

Two other 10-foot wide openings had, or were supposed to have had, 24-inch deep lintel beams; however, these were bisected dead in the middle by a CJ above a similar precast lintel beam.

Nor sure what if anything was done to correct the condition. I'll see if anything was ever put in the file.......

 

[dik]

If those are true joints... I don't know what's holding it up right now... in addition to shear, there could be a real serious problem with rebar bond...

Dik

 

[Lion06]

I'd just like to point out one other small (in comparison) thing. Our General Notes typically call for 1" of bearing per foot of opening. I don't know what other firms do. The opening to the left apears to have a full block of bearing, which makes sense with the 15' opening. The other end, however, appears to have 8"-9" of bearing. Doing a design check might make it not a problem.