A story shear-based adaptive pushover procedure for estimating seismic demands of buildings

In recent years some adaptive pushover methods have been proposed to include the effects of the higher modes and the changes in the vibration characteristics during the inelastic response. However, because of using the quadratic combination rules to combine the modal forces, the changes in the sign of the story components in the higher modes are removed. Consequently, the magnitudes of the applied loads in all story levels are positive and these adaptive methods are not superior to their non-adaptive counterparts. Here, an innovative adaptive pushover method. called "SSAP", is proposed based on the story shears which takes into account the reversal of sign in the higher modes. in each step, the applied load pattern is derived from the instantaneous combined modal story shear profile. The sign of the applied loads in consecutive steps are changed and the structure is simultaneously pushed and pulled in different story levels. Another aspect of the proposed method is that at each step an assumed fundamental mode shape is derived from the load profile. Based on this adaptive fundamental mode shape and the energy concept, the multi degree of freedom system is converted into a single degree of freedom system. The proposed method is applied to two steel moment-frame buildings. The results show an admirable accuracy in prediction of peak inelastic drift response, especially where the effects of the higher modes are important. A combination of this method with the conventional pushover approach, called "SS-MI", results in more accurate estimation of peak inelastic drift in all story levels compared to the other pushover approaches. (C) 2009 Elsevier Ltd. All rights reserved.