Validation of a numerical model for use in non-linear time history analysis of CBFs

During medium and large earthquakes, concentrically braced steel frames (CBFs) are usually expected to dissipate energy through nonlinear behaviour of brace members, which yield in tension and buckle in compression, while all other elements such as columns, beams and connections are expected to behave elastically. In this paper, the performances of single storey concentrically braced frames (CBFs) are assessed with non-linear time-history analysis (NLTHA), where a robust analytical model that simulates the behaviour of shake table tests is developed. The numerical model of the brace element used in the analysis was calibrated using data measured in physical tests on brace members subjected to cyclic loading. The model is then validated by comparing predictions from NLTHA to measured performance of brace members in full scale shake table tests. Furthermore, the sensitivity of the performance of the CBF to different earthquake ground motions is investigated by subjecting the CBF to eight ground motions that have been scaled to have similar displacement response spectra. A good comparison is found between the performance of the analytical and physical models in terms of maximum displacement and base shear force. The energy dissipated and, more particular, the equivalent viscous damping are important parameters required when developing an accurate displacement based design methodology for CBFs subjected to earthquake loading. In this study, a relatively good prediction of the equivalent viscous damping is obtained from the numerical model when compared to that obtained from measured data obtained from the shake table tests. However, it was found that already established equations to determine the equivalent viscous damping of CBFs may give closer values to those obtained from the physical tests.