Generalized Plastic Hinge Method for Failure Analysis of Steel Framed Structures

Abstract

For steel framed structures with small geometric nonlinearity, the conventional first-order plastic hinge method (FPHM) estimates rapidly the failure mode and ultimate strength of frames according to the proportionality property. However, it ignores the combined action of multiple internal forces on the development of plastic hinge, leading to mistakes in estimating the failure mode and ultimate strength of frames. Though the second-order plastic hinge method (SPHM) and the refined plastic hinge method (RPHM) overcome this problem, they lose the FPHM’s proportionality property and the high efficiency of computation as well. In this paper, the generalized plastic hinge method (GPHM) featuring proportionality property is proposed for steel framed structures to overcome the drawbacks of the conventional FPHM, the SPHM and the RPHM. Firstly, a linearly elastic analysis is performed on the steel framed structure between the formation of any two plastic hinges; then the strength reduction factor is developed by means of the generalized yield criterion (GYC) for modification of the sectional strength of frame component under multiple internal forces during loading process. Secondly, the element bearing ratio (EBR) is defined on the basis of the homogeneous generalized yield function and is in proportion to the loading, so that the position of generalized plastic hinge and the corresponding load increment are determined for each loading step according to this proportional property. Furthermore, the balance vector is developed by means of the GYC and the slope-deflection relation to modify the result of the calculated load increment. Finally, several examples are presented to validate the much higher computational efficiency and accuracy of the proposed method by comparing it with the plastic zone analysis (PZA), the SPHM and the conventional FPHM.