As title states. Do you put diagonal bars at concrete wall opening corners? Why or why not? Standard practice? Code? Forces? Does it make a difference if shear loads are considerable vs. a wall sized for convenience/other reasons? Some people tend to put these bars at every corner, but I can't figure out why, especially if I have a header and wall pier with ties crossing the corner, and the wall isn't seeing much load.
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Do you use diagonal bars at window corners in concrete walls?
- Thread starter AaronMcD
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I get that that's the idea, but why can't the other 4 bars control cracks? Especially when forces are low. Is there a study or code reference you can cite, or is it just one of those "that's how we've always does it" things?
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Remember stress concentration at member geometric changes? Corner of opening represent one. And, remember concrete failure plan is 45° from the principle plans? The crack on the corner is usually extended approximately 45° (from horiz. or vertical) out, the diagonal bars minimize the crack width and length by taking control of the tensile stress developed on each side of the crack. Make sense?
Member self weight, temperature effect, deflections, quality of the concrete, and different rate of shrinkage, all are contributors to the complex stresses around corners. The influence of member forces is minimal if the wall/slab is properly reinforced. The diagonal bars are sometimes joked as "feel good bars", but a good insurance for sure, especially for large openings.
If you still have doubt, walk around a residential area and look around, see where you can spot most cracks, and the pattern of the cracks. Pay attention to houses with brick, stucco, and concrete facade. Have fun.
Member self weight, temperature effect, deflections, quality of the concrete, and different rate of shrinkage, all are contributors to the complex stresses around corners. The influence of member forces is minimal if the wall/slab is properly reinforced. The diagonal bars are sometimes joked as "feel good bars", but a good insurance for sure, especially for large openings.
If you still have doubt, walk around a residential area and look around, see where you can spot most cracks, and the pattern of the cracks. Pay attention to houses with brick, stucco, and concrete facade. Have fun.
JoelTXCive
Civil/Environmental
I know the diagonal bars are shown in Chapter 7 of CRSI's design guide for enconomical RC Structures, but they do not provide much additional detail other than "The main purpose of the diagonal bars at the corners of openings is to arrest cracks that can form at these reentrant corners."
msquared48
Structural
Always have and always will - do need to verify bar clearances though as previously mentioned.
Diagonal bars are just more effective than the vertical and horizontal bars in resisting the diagonal tension loads.
Mike McCann, PE, SE (WA, HI)
Diagonal bars are just more effective than the vertical and horizontal bars in resisting the diagonal tension loads.
Mike McCann, PE, SE (WA, HI)
msquared48
Structural
Dik:
I see your point, but I just prefer a direct tie. Plus I have never had a problem with congestion related Deterioration.
Cheers.
Mike McCann, PE, SE (WA, HI)
I see your point, but I just prefer a direct tie. Plus I have never had a problem with congestion related Deterioration.
Cheers.
Mike McCann, PE, SE (WA, HI)
I usually design and specify a minimum clear cover of 1.5", on the cross section views, to the outer/top & bottom most reinforcement. The diagonals are mostly 2 - #3 or #4 bars placed locally, thus congestion wouldn't be a problem. But if the member thickness is too thin to maintain required covers to the main reinforcement, then it is better not to have the diagonal bars, which tend to introduce more problems than gain benefits.
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