CAPACITY BASED DESIGN OF COLD FORMED STORAGE RACK STRUCTURES UNDER SEISMIC LOAD FOR RIGID AND SEMI RIGID CONNECTIONS

摘要

Rack systems are very similar to the framed steelworks traditionally used for civil and commercial buildings, but great differences in member geometry and in connection systems. In the pallet rack system bracing systems are generally placed only in the cross aisle direction. Therefore design of pallet racks is quite complex. The capacity design based on deterministic allocation of strength and ductility in the structural elements for successful response and collapse prevention during a catastrophic earthquake by rationally choosing the successive regions of energy dissipation so that pre-decided energy dissipation mechanism would hold throughout the seismic action. The most accurate method of seismic demand prediction and performance evaluation of structures is nonlinear time history analysis. However, this technique requires the selection and employment of an appropriate set of ground motions and having a computational tool able to handle the analysis of the data and to produce ready-to-use results within the time constrains of design offices. A simple analysis method that has been gaining ground, as an alternative to time history analysis, is the nonlinear static pushover analysis. The purpose of the push over analysis is to assess the structural performance by estimating the strength and deformation capacities using static, nonlinear analysis and comparing these capacities with the demands at the corresponding performance levels. Model of conventional pallet racking systems were done using the finite element program Sap2000NL and were analyzed using non-linear static pushover analysis. Parameters selected for analysis and design are cross section of uprights, thickness of uprights, and stiffness of the connections (beam to upright and base). Nonlinear push over analysis found to be a useful analysis tool for the conventional pallet racking systems giving good estimates of the overall displacement demands, base shears and plastic hinge formation.