Fiber Beam-Column Element Considering Flange Contribution for Steel Links under Cyclic Loads

摘要

Steel links are widely used as key energy dissipation components in steel eccentrically braced frames and hybrid coupled walls. This paper proposes a new displacement-based fiber beam-column element for simulating the seismic behavior of links with high efficiency, satisfactory accuracy, and sufficient convenience. All the three well-known important factors that affect the link overstrength are carefully and suitably considered in the model, including the complex hardening behavior of steel, the flange contribution, and the influence of axial restraint. Firstly, two-dimensional strain and stress fields and a Chaboche elasto-plastic material model incorporating both nonlinear kinematic and isotropic hardening are implemented for each fiber. Therefore, the model is based on the material response exhibiting improved convenience and applicability in contrast to existing concentrated plasticity models that require complex parameter calibration. Then, to account for the flange contribution to the link overstrength, simplified shear strain distributions of both webs and flanges are proposed on the basis of a detailed parametric study with solid finite-element models and data fitting procedures. In addition, the influence of axial restraint is properly reproduced, thus the model is able to predict the link overstrength accurately. To adequately verify the proposed model, a number of shell models with a wide range of parameters and test results from different research groups are both compared to the proposed fiber model. The quantitative effects of flange and axial restraint are also intensively studied. It is found that the flange and axial restraint effects can increase the capacity of shear links as much as 20 and 35% when the sectional flange-to-web area ratio of the link is larger than 3.0, respectively. The proposed model is proved to be a reliable and powerful tool for the seismic simulation of structures with steel links.