Estimates of average inelastic deformation demands for regular steel frames by the Endurance Time method

The Endurance Time (ET) method is a new dynamic pushover procedure in which structures are subjected to gradually intensifying acceleration functions and their performance is assessed based on the length of the time interval that they can satisfy required performance objectives. In this paper, the accuracy of the Endurance Time method in estimating average deformation demands of low and medium rise steel frames using ETASOf series of ET acceleration functions has been investigated. The precision of the ET method in predicting the response of steel frames in nonlinear analysis is investigated by considering a simple set of moment-resisting frames. An elastic-perfectly-plastic material model and a bilinear material model with a post-yield stiffness equal to 3% of the initial elastic stiffness have been considered. For frames with an elastic-perfectly- plastic material model, which are P - Δ sensitive cases, the ET analysis for the maximum interstory drift ratio somewhat underestimates the nonlinear response history analysis results. The difference between the results of the ET analysis and the nonlinear response history analysis for the material model with 3% post-yield stiffness is acceptable. The consistency of the base shears obtained by the two methods is also satisfactory. It is shown that, although the results of the ET analysis are not exactly consistent with the results of ground motions analysis, the ET method can clearly identify the structure with a better performance even in the case of structures with a relatively complicated nonlinear behavior. © Sharif University of Technology, October 2009.