2ND-ORDER INELASTIC ANALYSIS-METHODS FOR STEEL-FRAME DESIGN

Two simplified methods for second-order inelastic analysis of steel frames, termed the modified plastic-hinge and the beam-column strength approaches, are presented. These analysis models are comparable to elastic-plastic-hinge analysis in efficiency, and yet, they alleviate the problems associated with overprediction of stiffness and strength by the usual elastic-plastic-hinge analysis methods. The modified plastic-hinge method is based on simple modifications to the elastic-plastic-hinge model, which account for the degradation in stiffness as the cross-section strength is approached at critical locations along the member length. The beam-column strength method is similar to the modified plastic-hinge approach, except that in this model, equations for the strength of the overall member are employed rather than expressions for the cross-section strength. The performance of these analysis models is contrasted with results from elastic-plastic-hinge and refined plastic-zone analysis solutions as well as results from experimental tests. Recommendations are provided with regard to the acceptability of simplified analysis models for use in predicting inelastic load-deflection behavior and maximum strength.