L Further Reduced Tangent Modulus Method Braced Frames

The idea of using the reduced tangent modulus concept is to further reduce the tangent modulus, E, to account for further stiffness degradation due to geometrical imperfections. The degradation of member stiffness due to geometric imperfections may be simulated by an equivalent reduction of member stiffness. This may be achieved by a further reduction of tangent modulus [6,9]:

where E is the reduced E and X is the reduction factor for geometric imperfection.

Herein, a reduction factor of 0.85 is used; the further reduced tangent modulus curves for the CRC E with geometric imperfections are shown in Figure 5.14. The further reduced tangent modulus concept satisfies one of the requirements for advanced analysis recommended by the SSRC task force report [29], that is, ''The geometric imperfections should be accommodated implicitly within the element model.

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