A practical analytical model for special concentrically braced frames

Special concentrically braced frames (SCBFs) are extensively used in high seismicity regions because of structural efficiency and high ductility for energy dissipation. SCBFs exhibit large inelastic deformation through tensile yielding, buckling and post-buckling behaviors of braces. A simple and accurate model for brace with low computational cost is vital to capture the complex structural behavior of SCBFs. The previous researches generally recommended ten elements per brace, which significantly increases both modeling and computer time. In this paper, a new hybrid flexibility-based beam-column element, considering initial geometrical imperfection and residual stress explicitly, distributed plasticity along member length, and semi-rigid behavior of gusset plate connections is proposed for modeling of SCBFs. It is worth to point out that the zero-length springs attached to element ends for simulation of gusset plate connections can consider the influence of axial force, which has not been reported in literature. Furthermore, the influences of initial geometrical imperfection and residual stresses on the performance of SCBFs are firstly evaluated on the basis of direct analysis method (DAM) specified in AISC360 (2016) and Eurocode-3 (2005). As all dominant factors affecting structural behaviors have been considered, the proposed method using one-element-per-member model provides sufficiently accurate results for practical design with enhancement of computational efficiency. Several examples illustrate the accuracy and efficiency of the proposed model for performance-based seismic design of SCBFs.