Effect of Overstrength on the Seismic Behaviour of Multi-Storey Regularly Asymmetric Buildings

Abstract

In past years, seismic response of asymmetric structures has been frequently analysed by means of single-storey models, because of their simplicity and low computational cost. However, it is widely believed that use of more realistic multi-storey models is needed in order to investigate effects of some system characteristics (such as overstrength, higher modes of vibration, etc.) that make behaviour of multi-storey schemes different from that of single-storey systems. This paper examines effects of the overstrength in element cross-sections on the seismic behaviour of multi-storey asymmetric buildings. It is shown that in actual buildings this characteristic, which is sometimes very variable both in plan and along the height of the building, may lead to distributions of ductility demands different from those expected according to the results from single-storey models. Consequently, torsional provisions, which aim at reducing ductility demands of single-storey asymmetric systems to those of the corresponding torsionally balanced systems, should be re-checked in light of the behaviour of realistic multi-storey buildings.

Static versus modal analysis: influence on inelastic response of multi-storey asymmetric buildings

“…4). The result is consistent with those obtained on single- Stefano et al 2006). More interesting observations may arise from the comparison of the seismic behaviour of buildings designed by static and modal analysis.…”

“…Indeed, the use of this simplified model for the study of the influence of asymmetry on the seismic response of multi-storey systems is rigorously valid only for a restricted category of in-plan irregular buildings, called regularly asymmetric (Hejal and Chopra 1987), and in the case of an elastic structural behaviour. Many researchers (e.g., Duan and Chandler 1992;Moghadam and Tso 1996;Marino 2000;Anagnostopoulos 2003, 2005;De Stefano et al 2006) have remarked that fundamental aspects of design and response of multistorey systems (overstrength, influence of higher modes of vibration, change of dynamic properties of structures due to yielding, etc.) are neglected if buildings are schematized by means of one-storey models.…”

“…Out of the many causes of overstrength, the use of multiple load combinations in the design phase has a significant role. Indeed, this kind of overstrength always exists in actual multi-storey structures and strongly influences their seismic response (Marino 2000;Stathopoulos and Anagnostopoulos 2005;De Stefano et al 2006).…”

A review of research on seismic behaviour of irregular building structures since 2002

“…5b) (Marušic and Fajfar 2005) those expected according to results from single-storey models. In particular, De Stefano et al (2006) also found that, in the upper floors, the larger ductility demands occur at the building flexible side, compared to those at the stiff side. Marušic and Fajfar (2005) investigated the elastic and inelastic response of massasymmetric multi-storey steel frame buildings under bi-directional ground motions.…”

“…Further confirmation of the impossibility of directly extending results from one-storey models to multi-storey structures comes from De Stefano et al (2006), who presented a study of a code-designed 6-storey framed building subjected to uni-directional records. The paper examines the effects of overstrength in element cross-sections.…”