Incorporating joint flexibility in collapse risk assessment

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September, 2016
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Several two-dimensional analytical beam column joint models with varying complexities have been proposed in quantifying joint flexibility during seismic vulnerability assessment of non-ductile reinforced concrete (RC) frames. Notable models are the single component rotational spring element and the super element joint model that can effectively capture the governing inelastic mechanisms under severe ground motions. Even though both models have been extensively calibrated and verified using quasi-static test of joint sub-assemblages, a comparative study of the inelastic seismic responses under nonlinear time history analysis (NTHA) of RC frames has not been thoroughly evaluated. This study employs three hypothetical case study RC frames subjected to increasing ground motion intensities to study their inherent variations. Secondly, the issue of super-element joint models, causing numerical divergence in non-linear time history analysis of reinforced concrete frames, is investigated. The rigid joint assumption and a single rotational spring model are implemented for comparison. Reinforced concrete joint sub-assemblages and a one-third scaled frame have been employed for model validation. Results indicate that the super element joint model overestimates the transient drift ratio at the first storey and becomes highly unconservative by under-predicting the drift ratios at the roof level when compared to the single-component model and the conventional rigid joint assumption. In addition, between these storey levels, a decline in the drift ratios is observed as the storey level increased. However, from this limited study, there is no consistent evidence to suggest that care should be taken in selecting either a single or multi component joint model for seismic risk assessment of buildings when a global demand measure, such as maximum inter-storey drift, is employed in the seismic assessment framework. Probabilistic seismic demand analysis also indicates that super-element joint model may be less vulnerable relative to the single-component joint model. Furthermore, the shift in fragility function may lie in between the rigid joint and single-component joint modelling schemes, implying non-divergence
A thesis submitted to the Department of Civil Engineering, College of Engineering in partial fulfillment of the requirement for the degree of Master of Philosophy,