Variable Shear Force (Not a variable section)
Variable Shear Force (Not a variable section)
(OP)
I have had to model a wall panel in FE software, and I'm looking at the shear stress maps. At the lintel over an opening, the FE shear force map gives a reasonable looking output, but the shear force in the cut through the lintel is not constant --- it varies by about 20% from bottom to top (29kN/m to 36 kN/m). So I am wondering if I need to / how I would properly calculate the shear stress in that section. The lintel is 500mm deep, so I've gone ahead and calculated the shear force in the cut as 36*0.5, but I suspect that's conservative; and I wonder if taking an average is a bad idea because part of the lintel could be over stressed.






RE: Variable Shear Force (Not a variable section)
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: Variable Shear Force (Not a variable section)
The material is CLT -- which I appreciate is a challenge for modeling in FEA software like Robot.
RE: Variable Shear Force (Not a variable section)
Why don't you just model the lintel with stick (2-node) members and use that?
Using the average shear stress might ignore a critical hot spot where the material might "unzip" and progressively fail.
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RE: Variable Shear Force (Not a variable section)
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: Variable Shear Force (Not a variable section)
The model is a bit more complex than this, including a full panel with cutouts, and lifting points for a crane, hence the Fea model rather than stick and node.
RE: Variable Shear Force (Not a variable section)
RE: Variable Shear Force (Not a variable section)
Actually no. 0.66Fy reflects the expected shear yield stress of the material (Von Mises / Tresca formulation). We do, in fact assume that shear stress is uniform on the webs of steel wide flange beams.
That said, I had the same question regarding the 1.5, peak stress factor here. Here's what I know:
1) You use the 1.5 factor when designing for out of plane bending.
2) You don't use the 1.5 factor when designing diaphragms for in-plane bending.
I can't say that I've actually seen an example where a CLT header has been designed for in plane shear. Even the CLT handbook seems to be silent on that particular issue.
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: Variable Shear Force (Not a variable section)
RE: Variable Shear Force (Not a variable section)
I've decided to cast my vote for applying the 1.5 factor to the lintel shear stress. With no "chords" and flexural resistance distributed throughout the height, that makes sense to me. I figured looking at shear wall panels would yield the answer as they typically don't have discrete chords either. Couldn't find a damn thing. My Googling must be getting weak.
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: Variable Shear Force (Not a variable section)
RE: Variable Shear Force (Not a variable section)
If you are using FE, I would use the maximum stress from the analysis to design it but then I would check it with basic line elements with the 1.5 factor to see how far off the stress from the FE analysis was.
RE: Variable Shear Force (Not a variable section)
Interesting enough, when I had FE meshing set to 0.20m, and used the maximum shear value to calc the shear force over the interface, I got the same result as the integral value when I reduced the mesh size to 0.10m, even though reducing the FE mesh size results in larger peak shear values! This is slightly reassuring...