09/09/2026
๐๐ก๐ ๐๐ญ๐ซ๐ฎ๐๐ญ๐ฎ๐ซ๐๐ฅ ๐๐๐ฉ - ๐๐๐๐ - ๐๐๐ข๐ฌ๐ฆ๐ข๐ ๐๐จ๐๐๐ฌ
๐๐๐ข๐ฌ๐ฆ๐ข๐ ๐๐จ๐๐ ๐๐๐ฌ๐ ๐๐๐ญ๐ฎ๐ฉ: ๐๐จ๐๐ ๐๐จ๐ฆ๐ฉ๐ฅ๐ข๐๐ง๐๐ ๐ฏ๐ฌ. ๐๐ญ๐ซ๐ฎ๐๐ญ๐ฎ๐ซ๐๐ฅ ๐๐๐๐ฅ๐ข๐ญ๐ฒ
When defining seismic load cases in Analysis Software both code requirements and actual structural behavior should be considered.
๐๐๐๐ข๐๐๐ง๐ญ๐๐ฅ ๐๐จ๐ซ๐ฌ๐ข๐จ๐ง ๐ข๐ง ๐๐ฒ๐ฆ๐ฆ๐๐ญ๐ซ๐ข๐๐๐ฅ ๐๐ญ๐ซ๐ฎ๐๐ญ๐ฎ๐ซ๐๐ฌ
ASCE 7 and NSCP 2015 recognize that even a symmetrical structure can have unintended variations in mass and stiffness. Therefore, the code prescribes consideration of ยฑ5% accidental eccentricity of the seismic mass, subject to the applicable provisions and exceptions.
However, CM = CR does not eliminate accidental torsion. It only indicates that there is little or no calculated inherent eccentricity. The code-prescribed accidental eccentricity may still produce torsional redistribution.
For a well-balanced and torsionally regular structure, this effect may be relatively small. Nevertheless, it should be verified through analysis rather than assumed from geometric symmetry alone.
For preliminary iterations, engineers may initially analyze the principal seismic directions to understand periods, drift, base shear, and force distribution. Before final design, however, the applicable accidental torsion, torsional irregularity, orthogonal effects, and required load combinations should be checked in accordance with the governing code.
๐๐จ๐ญ๐ญ๐จ๐ฆ ๐ฅ๐ข๐ง๐:
Symmetry reduces inherent torsion, but it does not automatically eliminate code-required accidental torsion. Model efficiently during preliminary design, but let the governing code control the final analysis and design.
