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In order to provide a comprehensive assessment of the structural components, behavior of structures should be traced and predicted far into inelastic region. For this purpose, analytical hysteresis models are needed which are capable of representing all modes of deterioration. In order to utilize these models,a database is required to calibrate models. In this paper relationships are proposed to predict modified Ibarra-Krawinkler model parameters for welded flange plate steel connections. To provide the database, a number of welded flange plate connections are designed based on Iran Steel Code. The designed connections have been modeled and analyzed numerically in a finite element software. Prior to proceed the investigation, finite element numerical model of the connection was created in the ABAQUS computer program in order to predict the micro-mechanical behavior of the welded flange plate steel connection. Using the nonlinear method of analysis, the cyclic behavior of such moment resisting connection was obtained. The numerical results were verified by comparing the results obtained experimentally and specifically for the steel welded flange plate moment connection. Simulation of several numerical models and in comparison with the laboratory results indicate the accuracy of the finite element model. Once the finite element micro behavior was verified, then fifty three different welded flange plate moment connections were designed for different number of steel moment frame with various heights and floor numbers. All the connections are modeled in the ABAQUS computer program and the cyclic behavior of such connections such as the hysteresis behavior are obtained. The hysteresis behavior of the connections were included in the moment frame connections by utilizing the rotation behavior in the connection. The steel frames are modeled in a customized version of OPENSEES computer program. The numerical model consists of nonlinear beam column elements with the rotational spring element at the end in which the rotational behavior of the spring were the hysteresis behavior of the connection obtained from ABAQUS computer program. These springs simulate the hysteretic response a steel component (beam or olumn) subjected to cyclic loading including strength and stiffness deterioration based on the modified Ibarra-Krawinkler deterioration model. Panel zones are modeled in such away that the shear distortions were explicitly included with the possibility of nonlinear behavior during an earthquake. The numerical results show that most numerical specimens predict the plastic hing location to be right after the top flange plate. Using numerical results as a database, the model parameters are calibrated and effective geometrical properties of connections are determined. The most effective parameters are beam depth, beam span to beam depth ratio, beam web depth to web thickness ratio, top plate length to top plate thickness ratio, bottom plate length to bottom thickness ratio, and beam flange width to beam flange thickness ratio. Finally, using nonlinear regression equations, relationships for predicting the model and deterioration parameters are proposed. Also different rotational capacity such as maximum plastic rotation, plastic rotation spectrum and cumulative plastic rotation are predicted. From the regression analysis the pertinent parameters effecting the detioration of the connection are identified.

Keywords: Stiffness, Strength deterioration, Steel connections, Moment Frames, Nonlinear behavior, Cyclic loading

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