W. K. Tso

Engineering implication of ground motion A/V ratio

Abstract An earthquake data set consisting of 45 strong motion records was analyzed to investigate the significance of the peak ground acceleration-to-velocity (A/V) ratio as a parameter to indicate the dynamic characteristics of earthquake ground motions. It was found that the A/V ratio of ground motions is a viable indicator of the M (magnitude)-R (epicentral distance) relationships associated with the motions. Due to its tacit correlation with the M-R relationship, the A/V ratio provides useful information regarding the relative frequency content and duration of strong shaking for ground motions resulting from different seismic environments. In light of these observations, the implications of seismic ground motions having different A/V ratios on engineering design were discussed, and an example to incorporate this ratio into the specification of seismic design forces for building structures was illustrated.

Re‐evaluation of seismic torsional provisions

Traditionally, seismic torsional provisions have been evaluated based on the assumption that the strength of the lateral load resisting elements can be adjusted without changing their stiffness. There is an important class of elements that a change of their lateral strength implies a corresponding change of stiffness, as exemplified by reinforced concrete flexural walls. This would imply that when torsional provisions are applied to adjust the strengths of these elements, the stiffness distribution, and also the eccentricity of the system, will change. This paper re-evaluates the consequences of applying the torsional provisions of the Uniform Building Code (UBC, 1997) and also the Eurocode (Eurocode 8, 1994) to single mass eccentric systems supported by elements having such characteristics. In conjunction with the results based on the traditional assumption, the effectiveness of the two provisions to mitigate torsional effects is discussed from a broader perspective. Copyright