REDUNDANCY IN STEEL MOMENT FRAME SYSTEMS UNDER SEISMIC EXCITATIONS

REDUNDANCY IN STEEL MOMENT FRAME SYSTEMS UNDER SEISMIC EXCITATIONS - Printable Version

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REDUNDANCY IN STEEL MOMENT FRAME SYSTEMS UNDER SEISMIC EXCITATIONS - TAFATNEB - 09-10-2013

Although the importance and the positive effects of structural redundancy have
been long recognized, structural redundancy became the focus of research only after the
1994 Northridge and 1995 Kobe earthquakes. Several researchers have investigated the
benefit of redundancy to structural system. However, the definition and interpretation of
structural redundancy vary significantly and it remains a controversial subject.
A reliability/redundancy factor, p, 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 (e.g. Searer G. R. and Freeman S. A.,
2002, Wen and Song, 2003). A new reliability/redundancy factor, primary a function of
plan configuration of the structures such as the number of moment frames in the direction
of earthquake excitations, 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 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 poorly designed structure. In view of the complicated nonlinear structural behaviors and
the effects of uncertainty in demand and capacity, redundancies of structures under
seismic loads can be measured meaningfully only in terms of reliability of a given system.
Therefore, a systematic and probabilistic study of redundancy in structural system is
needed and a uniform-risk redundancy factor is used for reliability assessment of
structural redundancy.

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