Keywords: performance assessment, artificial intelligence, back propagation neural network, nonlinear analysis.

Earthquake induced forces are a direct function of energy absorption, damping and ultimate damage capacity of structural members, which all depend on deformation. The purpose of performance based design is to design the structure with sufficient and proportioned stiffness and strength in the structural members so as to develop inelastic action in the ductile designed members and to have an appropriate over strength in the brittle members. The structure must be checked so that the demands do not exceed the existing capacities. This is best performed using a set of nonlinear dynamic analyses under earthquake loading with appropriate characteristics. In the last four decades the concept of displacement based design (DBD) has been introduced and developed by different researchers, started by introducing the concept of substitute structures [1]. This idea has been adopted for a direct displacement design of SDOF and MDOF reinforced concrete bridges [2]. In all of this research, seismic demand is specified as either a displacement spectrum or an acceleration-displacement response spectrum.

Performance based seismic design usually requires nonlinear dynamic or static analyses to assess the performance level of the structure under seismic action. To trace the exact performance of a structure these analyses should some time be repeated several times. Analysis iterations mainly depend on the initial design and performance of the structure. So a method that can present an appropriate initial selection with minimum time and effort would be important. Such a method would also be very effective for seismic structural assessment [3]. In this paper an intelligent system has been created for estimation of plastic hinge distribution and lateral ductility distribution and also for the assessment of existing steel structures based on a direct displacement based design procedure. The method has been applied to steel braced frames with concentric and eccentric bracing systems in low, medium and high rise buildings. The designer can use this knowledge based system to obtain the performance level of existing steel structures according to the proposed seismic code levels. Finally the intelligent system has been verified using nonlinear dynamic analysis.

1

Shibata A., Sozen M.A., "Substitute-structure method for seismic design in RCs", Journal of the Structural Division ASCE, Vol. 102, pp 1-18, 1976.

2

H. Krawinkler, "Earthquake design and performance of steel structures", Bulletin of NZ National Society of Earthquake Engineering., Vol. 29, No. 4, pp 229-241, 1996.

3

M.Tehranizadeh, M.Safi, "Displacement Based Seismic Design of Ductile Braced Steel Frames", Journal of European Earthquake Engineering, Issue 3, p. 10-26, 2003.

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