Incorporating joint flexibility in collapse risk assessment
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Date
September, 2016
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Abstract
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
Description
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,