A Novel Incremental Iterative Force Recovery Method for Second-Order Beam-Column Elements in Plastic Hinge Analysis of Steel Frames

This paper is concerned with an incremental iterative force recovery method in the second-order plastic hinge analysis of steel frames mainly modelled by a single element per member. Second-order beam-column elements are preferred in the direct analysis of steel frames due to their high accuracy and efficiency. However, formulations of these elements are complicated, and therefore they may have a problem of getting element force recovery in inelastic analysis. To overcome this difficulty, a novel incremental iterative force recovery method for second-order beam-column elements is proposed to perform plastic hinge analysis. The proposed method is derived more strictly and has good performance. Also, the section assemblage approach and the refined plastic hinge method are adopted in this study to consider the gradual degradation of section stiffness in the plastic hinge analysis. To verify the accuracy, efficiency and robustness of the proposed method, several benchmark examples are analyzed by the proposed method and compared with solutions reported by early researchers.

Nonlinear Inelastic Earthquake Analysis of 2D Steel Frames

In this work, a new method for nonlinear time-history earthquake analysis of 2D steel frames by a fiber plastic hinge method is presented. The beam-column element based on the displacement-based finite element method is established and formulated in detail using a fiber plastic hinge approach and stability functions. Geometric nonlinearities are taken into accounting by stability functions and the geometric stiffness matrix. A nonlinear dynamic algorithm is established based on the combination of the Newmark integration method and the Newton-Raphson iterative algorithm for solving dynamic equations. The proposed program predicts the nonlinear inelastic responses of 2D steel frames subjected to earthquakes as efficiently and accurately as commercial software. This study also shows that the initial residual stresses of steel should be considered in nonlinear inelastic time-history earthquake analysis of 2D steel frames while SAP2000 does not consider the effects of residual stresses.

Nonlinear Inelastic Analysis of 2D Steel Frames

In this study, a new method for nonlinear analysis of 2D steel frames, by improving the conventional plastic hinge method, is presented. The beam-column element is established and formulated in detail using a fiber plastic hinge approach. Residual stresses of I-shape sections are declared at the two ends through fibers. Gradual yielding by residual stresses along the member length due to axial force is accounted for by the tangent elastic modulus concept. The P-δ effect is captured by stability functions, whereas the P-Δ effect is estimated by the geometric stiffness matrix. A nonlinear algorithm is established for solving nonlinear problems. The present study predicts the strength and behavior of 2D steel frames as efficiently and accurately as the plastic zone method did.

Research on Skeleton Curves of Steel-Concrete Composite Beams

In order to model the elasto-plastic behavior of steel-concrete beams in high-rise buildings correctly and conveniently, plastic hinge method is used. Based on experimental and theoretical research on composite beams, the trilinear moment-curvature skeleton curve of steel-concrete composite beams is amended by numerical simulation and theoretical analysis. And the 4 poly-line moment-curvature skeleton curve model is suggested for elasto-plastic analysis of steel-concrete composite beams. The elastic-plastic model is then used for real composite beams under monotonic load experimental analysis to verify its precision. The suggested model can lay a foundation for the dynamic analysis under strong earthquake for the globe steel-concrete composite structures.