DIRECT PERFORMANCE-BASED SEISMIC DESIGN OF A STRONG-BACK BRACING SYSTEM BY USING YIELD FREQUENCY SPECTRA METHOD

The prescriptive methods of seismic design of structures that are used in conventional codes, while not having sufficient insurance to achieve performance objectives, are also due to the structural adaptability weakness of designing new combinational systems. In these regulations, the design of the structure is based on force and then, by controlling the amount of displacement and deflections, the structural serviceability is checked and in order to simplify the nonlinear response of some specific structural systems, response modification factors, over-strength factors, and deflection amplification factors are used. However, the use of these methods does not have optimal results for the design of new and hybrid systems, whose seismic behavior is not determined in the regulations. Determining these parameters for designing new and hybrid systems requires a set of nonlinear structural analyzes. In fact, it is necessary to design these systems based on performance and considering the structural vulnerability behavior at different hazard levels. On the other hand, due to the complexity of performance based seismic design techniques and their inverse probabilistic nature, their use has not been much welcomed by engineers. In this research, one of the functional performance-based design methods, called Yield Frequency Spectra (YFS), is used for designing a new hybrid steel bracing system called Strong-Back System (SBS). In this system, by combining a leaning frame into a conventional concentrically steel braced system or Buckling Restrained Brace (BRB) system, a vertical truss in a part of the bracing span is formed and by its elastic behavior, the formation of a soft or weak story is prevented. The performance-based design results show that by using ordinary seismic design methods, the required performance levels are not necessarily met. However, using the YFS method, all the specified performance objectives are provided with proper accuracy

کلیدواژه ها:

Performance-based seismic design ، yield frequency spectra ، strong-back system ، probabilistic performance assessment ، nonlinear analyses