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Re: seaint Digest for 14 May 2000
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- Subject: Re: seaint Digest for 14 May 2000
- From: "Ron O. Hamburger" <ROH(--nospam--at)eqe.com>
- Date: Mon, 15 May 2000 08:21:39 -0700
Respnose to the questions from: Jake Watson on Sunday 5/14. >Has anyone gone through the concrete shearwall provisions in detail? My question is this. If you follow the code, you are allowed to assume yield curvature as Ec/(Length of wall). This amounts to assumed maximum concrete strain (0.003) divided by wall length. Two questions come from this: >1) Is the point to find the concrete or steel yield point? >2a) If it is steel, shouldn't the curvature be (Es+Ec)/(Length of Wall) >2b) If it is concrete, shouldn't the curvature be Ec/C`u? "Flexural yielding" of concrete shear walls is generally controlled by yielding of the steel, not crushing of the concrete. Unless a wall has been designed or carries large axial loads, it generally will yield as a result of the reinforcing steel yielding. This is why the code provsion limits the amount of axial load that may be carried by the wall and requires confinement steel for walls that carry large axial loads. The real yield curvature should indeed be (Es+Ec)/Length of wall. If you want to, the code permits you to calculate what this curavture is. It takes a somewhat tedious trial and error process, in which you must iterate to a nuetral axis location. Because many bars along the length of a wall will typically yield, Es in the above equation is going to be somewhat higher than Ey = yield strength/ Young's modulus. For Grade 60 rebar Ey = 0.002. The 0.003/Lw formulation is intended to be a lower bound approximation of what you would get from a real analysis. The curvature indicated in 2b) above is the "failure" curvature, not the yield curavture. Also, Ec is only 0.003 for unconfined concrete. For confined concrete, it gets much larger.
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