| A reliability/redundancy factor, rho, was introduced in NEHRP 97, UBC 1997, and IBC 2000. It is used as a multiplier of the lateral design earthquake load and takes into account only the floor area and maximum element-story shear ratio. It lacks an adequate rationale and can lead to poor structural designs. A new reliability/redundancy factor has been adopted in NEHRP 2003 and also proposed in ASCE-7. This new factor attempts a more reasonable and mechanism-based approach, and it is likely to be implemented in other codes in the near future. However, the uniform multiplied factor (1.3) of lateral design force for non-redundancy structures fails to account for different structural configurations and could lead to serious damage in a poorly designed structure.; To accurately describe the inelastic connection behaviors, the Bouc-Wen model is used and incorporated into the ABAQUS computer program. A 3-D finite element model is developed, which allows one to examine the effects of 3-D motions including torsion oscillation and biaxial bending interaction. The capacity uncertainties of connections that were documented in the FEMA/SAC projects are included in the Bouc-Wen model and used in the reliability analysis.; Finally, a framework is proposed for evaluation of structural redundancy against incipient collapse limit state. In this framework: (1) the maximum column drift ratio (MCDR) or biaxial spectral acceleration (BSA) is used to measure both demand and capacity of a given building; (2) the demand and capacity analyses of a building are performed, from which the probabilistic demand curves and the distribution of capacity are constructed; (3) both aleatory and epistemic uncertainties in demand and capacity are taken into account; (4) based on the results of (2), a uniform-risk redundancy factor, RR, for design to achieve a uniform reliability level for buildings of different redundancies is obtained. This method is also used to evaluate the redundancy of a given structural system. The rho factors in NEHRP 97 and in NEHRP 2003 and the proposed RR factor are compared and the inadequacies of rho factors are pointed out. |
