Estimates of Average Inelastic Deformation Demands for Regular Steel Frames by the Endurance Time Method


Department of Civil Engineering,Sharif University of Technology


Abstract. 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 ETA20f 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 sti ness equal to 3% of the initial elastic sti ness have been
considered. For frames with an elastic-perfectly-plastic material model, which are P ????  sensitive cases,
the ET analysis for the maximum interstory drift ratio somewhat underestimates the nonlinear response
history analysis results. The di erence between the results of the ET analysis and the nonlinear response
history analysis for the material model with 3% post-yield sti ness 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.