This paper assesses the effects of the vertical component of ground motions on steel structures and evaluates the current seismic design provisions of ASCE 7 on the basis of a structural reliability outlook. Eight special moment-resisting frame (SMRF) and special concentrically braced frame braced frame (SCBF) steel structures were analyzed under two groups of near-fault (i.e., strike slip and reverse fault) ground motions. Detailed methodology for calculating the reliability index (β) of structural components is explained; β is computed for structural component actions including moment and shear in beams, axial load in braces, and axial load and moment in columns. Seismic provisions of ASCE 7 were developed with an intention of achieving target β of 1.75 for earthquake-resistant structural members. Results indicated that the implementation of current seismic load combinations, in which a load factor equal to 20% of design level short-period spectral acceleration on structural dead load is used to account for the effects of the vertical component of ground motions, results in β1.3 for most structural members. Application of structural system drift limits, however, resulted in increased member sizes in SMRFs by which β values larger than 1.75 were achieved. It is concluded that current seismic load combinations in ASCE 7 are inadequate to account for the effects of the vertical component of near-fault ground motions. Nevertheless, performance-based design provisions can provide a reasonable and adequate margin of safety against structural member failure.
|Journal||Journal of Structural Engineering (United States)|
|Publication status||Published - 2 May 2019|
Bibliographical notePublisher Copyright:
© 2019 American Society of Civil Engineers.