Optimum lateral load distribution for seismic design of nonlinear shear-buildings considering soil-structure interaction

Abstract

The lateral load distributions specified by seismic design provisions are primarily based on elastic behaviour of fixed-base structures without considering the effects of soil-structure-interaction (SSI).Consequently, such load patterns may not be suitable for seismic design of non-linear flexible-base structures. In this paper, a practical optimization technique is introduced to obtain optimum seismic design loads for non-linear shear-buildings on soft soils based on the concept of uniform damage distribution. SSI effects are taken into account by using the cone model. Over 30,000 optimum load patterns are obtained for 21 earthquake excitations recorded on soft soils to investigate the effects of fundamental period of the structure, number of stories, ductility demand, earthquake excitation, damping ratio, damping model, structural post yield behaviour, soil flexibility and structural aspect ratio on the optimum load patterns.The results indicate that the proposed optimum load patterns can significantly improve the seismic performance of flexible-base buildings on soft soils.

More adequate seismic design force pattern for yielding structures considering structural and ground motion uncertainties effects

“…[ μ i / μ t ] α where [ V i ] j is the shear strength of the i th floor at j th iteration, μ i is the story ductility ratio of the i th floor, and α is a convergence parameter ranging from 0 to 1 (Step 12). Results of this study and the study carried out by Ganjavi and Hao and Ganjavi et al indicate that this factor is dependent on the design earthquake excitation and dynamic properties of the structure (e.g., fundamental period, damping model, and the level of inelasticity). Based on intensive analyses performed in the present study, it is concluded that for nonlinear systems an acceptable convergence is usually obtained by using α values ranging from 0.02 to 0.08.…”

“…In this investigation, steel building frames are modeled on the basis of the concept of FEMA‐440 for parametric study, which permits researchers to model special complex building structures as shear‐type buildings, representing multistory buildings having so‐called shear beams or those with relatively stiff diaphragms when compared with columns. In spite of some shortcomings, shear‐building models have been frequently utilized to evaluate the seismic behavior of multistory structures due to their simple forms and low computational efforts enabling a various ranges of parametric studies . In the steel shear‐building structures, beam‐column joints are modeled by bilinear elastic–plastic springs with 3% post‐yield strain hardening as representative of the story lateral stiffness.…”

“…Consequently, this study has excluded near‐fault ground motion records in the selected ground motion ensemble and is primarily focused on far‐fault ground motion effects. In order to have reliable results for design objectives, SeismoMatch computer program, which has the ability of adjusting earthquake ground motion to match a given target response spectrum using wavelets algorithm with preserving the high‐frequency characteristics of the input ground motion, has been used for adjusting the 40 earthquake records to the International Building Code (IBC) elastic design response spectrum with soil profile D. These adjusted earthquakes can be representatives of the design response spectrum and, hence, are suitable for general design purposes . Figure demonstrates the good agreement between the response spectra of 40 compatible ground motions with the elastic design response spectrum of IBC…”

“…Following the research performed by Moghaddam and Hahirasouliha, Hajirasouliha and Moghaddam developed an interesting optimization approach to obtain optimum lateral load distribution for seismic design of regular shear‐building structures to obtain uniform story ductility. They asserted that, for a given story ductility ratio, buildings designed with the mean of optimum load distributions for a family of earthquakes with similar characteristics have considerable less structural weight in comparison with those designed conventionally.…”

“…However, as it will be shown in the next sections, their proposed load patterns may not adequately take into account for the influence of higher modes, which are important in mid‐ and high‐rise buildings. The most recent work in this field may be those of Ganjavi and Hao, and Ganjavi et al in which they have investigated the effect of soil‐structure interactions on the effectiveness of different lateral load patterns to achieve the equal ductility demands in all stories for elastic and inelastic soil‐structure systems. On the other hand, Haukaas and Kiureghian and Kwon and Elnashai showed that the nonlinear response of building structures would be more sensitive to changes in dynamic properties of structural models and characteristics of future earthquake ground motions when compared with the elastic response of the corresponding structures.…”