Keywords: steel structure, tapered steel slit damper, optimized stiffness, performance criteria, endurance time method, time history analysis.

Based on special properties of metal dampers such as high energy dissipation, stable hysteric cycles, simple application, low cost, insensitivity to changes of temperature and the ability to substitute after the occurrence of earthquakes, they are being used for structural control. One of these metal dampers which has been of special interest is the tapered steel slit damper (TSS). When shear forces are applied, this damper yields and enters the plastic zone. The TSS damper is made of pieces of standard wide flanges where slits have been extracted from their web. These dampers are connected to the top of the chevron braces and under the middle of the beams. In the endurance time (ET) method gradually intensifying acceleration functions are created in a manner that the linear and nonlinear response spectra of them, while being proportional to average of real earthquake spectra, intensifies in a uniform manner with time. These functions are used as input functions for nonlinear time history analysis of structures and the performance of structures is based on the maximum time duration that they can meet the specified performance objectives.

In this paper, application of the ET method in nonlinear seismic analysis of structures has been investigated. The high speed of the nonlinear dynamic analysis and the ability to being matched with the primary concepts of the performance base design codes are the most important features of the method. A set of three acceleration functions have been applied to one steel frame and the results of the analyses are compared to the results of the IDA analyses. The ET results of different frames proved that this method can be a good technique to estimate IDA results with reasonably good accuracy using a few numbers of time history analyses. It is shown that this method can be used in nonlinear analysis of structures as a powerful tool. In order to design the building and dampers, the newest performance base design has been used. Based on good performance of the Opensees to control inputs and outputs such as geometry model and loading, and the ability to adapt with another programs for instance MATLAB, it has been used for frequent analysis.

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