Spread of Plasticity: An Adaptive Gradual Plastic-hinge Approach for Steel Frames

Abstract

IntroductionConsiderable studies have been undertaken on the inelastic analysis of steel frames in recent years (Chen and Toma 1994, Xu et al. 2005). The inelastic analysis methods are generally classified into two types: the distributed plasticity method and the plastic-hinge method. The distributed plasticity method discretizes frame members both along their length and through their cross section into many elements. The spread of plasticity is traced by the sequential yielding of the elements. This method is usually adopted to create benchmark solutions, as it is too computationally intensive and not suitable for practical design purposes. On the contrary, the plastic-hinge method usually involves using single or multiple elements to model a frame member, thus making it more efficient and the preferred method in engineering practice. The plastic-hinge method assumes that inelastic deformations are concentrated at plastic hinges at the end of elastic elements. The early studies used an elastic-plastichinge model, where the relationship between moment and curvature is linear up to the full plasticmoment of a section, after which the section becomes a perfect hinge. Though this approach is easy to implement, it often overestimates the ultimate strength of structural systems. More recently, refinedand quasi-plastic-hinge approaches (Liew et al. 1993, Attalla et al. 1994) with two-surface yielding criteria were proposed to account for the gradual plastification within steel members. Often, a model was constructed to simulate the gradual softening of plastic-hinges whose force point falls within the two yielding surfaces (Chen and Chan 1995, Hasan et al. 2002.This study proposes a new gradual plastic-hinge model for the inelastic analysis of planar steel frames. The analysis approach belongs to the domain of matrix displacement method. The plastichinge model is capable of mimicking the spread of plasticity both through the depth of a section and along the length of an element. The moment gradient of a frame member is directly taken into account in the plastic-hinge model. The model is unique and applicable to a general steel beam-column.In this study, it is assumed that the cross sections are doubly symmetric and the stress-strain relation for steel material is elastic-perfectly-plastic. Only moment yielding is considered, while shear and axial yielding are ignored. Local plate, torsional, and lateral-torsional buckling are not considered. Inelastic Beam-Column ModelA hybrid element (see Fig.1) is employed to model planar inelastic beam-columns. The element consists of two potential plastic-hinges at the ends of an elastic beam-column. Each plastic-hinge is modeled by a nonlinear zero-length rotational spring (which is called a hinge-spring or spring hereafter). For the elastic beam-column, E, I, and A correspond to Young's modulus, moment of Department of Civil Engineering, Lakehead University, Thunder Bay, Ontario, Abstract This paper presents a new plastic-hinge method for inelastic analysis of steel frames. The p...

Plieninio Rėmo PlastinėS Deformacijos: Statika Ir Dinamika

“…Plastines deformacijas kolonoje galima apytikriai aprašyti taikant plastinio lanksto modelį. Tokią aproksimaciją aprašo Gong (2006) ir pateikia apytikres empirines lenkimo momento priklausomybes nuo plastinio lanksto posūkio. Attalla ir kiti (1994) taip pat teikia pusiau empirinius plastinio lanksto modelius.…”