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Re: Nonlinear Static Analysis of RC buildings

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On May 13, 2006, at 12:51 AM, Carlos Avila wrote:

Is there any structural analysis software performing Nonlinear Static Analysis of RC buildings?
Depends on what you're looking to do. ABAQUS and ANSYS do excellent non-linear analysis for both material and large displacement non-linearities, but they don't incorporate the kinds of practical assumptions that go into design code analysis. For example, LRFD assumes elastic/perfectly plastic material behavior for steel, but if you try to mimic a zero tangent modulus with ANSYS, the problem is numerically unstable and it'll crash. Sometimes you'll see new engineers, most of whom have never seen welds being made, modeling welds explicitly without accounting for the real world behavior and appearance of actual welds.

I don't do concrete, but I think you'll run into the same kinds of material response problems with concrete. If you're looking at mimicking lab tests with FEA, you need a realistic material model that may incorporate local fracture and internal friction rather than the simplified model used for structural design.

One of the worst abuses of FEA is trying to justify lower design margins because FEA is 'more accurate.' FEA is just as much an idealization as ordinary structural design, but the idealizations are incorporated in different ways. When you do a FEA model of an actual structure, the analysis doesn't incorporate the effects of real-world construction and material behavior. Practical design, based in part on test results, uses test results and incorporate margins to account for scatter in material properties, and the possibilities that construction practices can be less than ideal.
Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania 1864)

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