Seismic performance evaluation of glulam structures with either braced frames or knee-braced frames as the main lateral load resisting system

The glulam knee-braced frames and braced frames are both conventional structural systems that are generally adopted in engineering practice. However, it remains a question what are the advantages and challenges of the knee-braced frames compared with the braced frames and how to choose the appropriate lateral-resisting structures for the projects under a given design requirements. This paper provides numerical models of 3- story, 5- story, 6- story and 9- story glulam braced frames and glulam knee-braced frames with the same architectural plan view. Increment dynamic analysis (IDA) is performed to determine the limit state of MaxISDR (maximum inter-story drift ratio) for the glulam braced frames and the glulam knee-braced frames under different seismic hazard levels, i.e., IO (Immediate Occupancy), LS (Life Safety), CP (Collapse Prevention) and CD (Complete Destroy). Fifty earthquake records are adopted for the subsequent probabilistic seismic demand analysis based on the MaxISDR and ResISDR (residual inter-story drift ratio) damage indices. The fragility curves of these two types of structures are highlighted. The results show that, the limit state of MaxISDR for the glulam braced frames under the IO, LS, CP and CD hazard level are recommended to be 0.6%, 1.2%, 2.0% and 3.5% respectively. The limit state of MaxISDR for the glulam knee-braced frames under the IO, LS, CP and CD hazard levels are recommended to be 1.0%, 2.0%, 3.2% and 5.5% respectively. In addition, for the structural height that below 6 stories, the knee-braced frames have lower probability of MaxISDR exceedance than the braced frames under the earthquake with high PGA and lower probability of ResISDR exceedance than the braced frames. However, for the structural height of 9-stories, the recoverability of the knee-braced frames decreases rapidly. Adding some braces to the knee-braced frames can be a good solution to increase the lateral stiffness of the structures. The comparison results may provide technical reference for the structural design of glulam structures.