Title:
Effects of Variation of Axial Load on Seismic Performance of Shear Deficient RC Exterior BCJs
Author(s):
Mohammed Ali Al-Osta / Umais Khan / Mohammed Hussain Baluch / Muhammad Kalimur Rahman
Publication:
IJCSM
Volume:
12
Issue:
Appears on pages(s):
Keywords:
shear failure, beam-column joints, axial load, monotonic, reverse cyclic tests, finite element model, mechanistic model
DOI:
Date:
7/26/2018
Abstract:
The focus of this paper is to investigate the effect of column axial load levels on the performance of shear deficient
reinforced concrete beam column joints (BCJs) under monotonic and cyclic loading. The problem of interaction
between shear stress in BCJ and axial load on column has been addressed in this work by initially postulating a mechanistic
model and substantiated by an experimental test program. This was achieved by conducting appropriate tests
on seven BCJ sub-assemblies subjected to monotonic and reversed cyclic loading, with varying levels of the column
axial load. Experimental results were further validated using a finite element model in an ABAQUS environment. The
effect of variation of compressive strength of concrete was considered in a subsequent parametric study, in order to
obtain sufficient data, and utilized to develop a new shear strength model for BCJs which includes influences of all the
important parameters required to predict the shear strength of BCJs. The results showed that column axial load affects
the seismic performance of BCJs significantly. Experimental results demonstrated that at initial stages of loading,
increase in axial load enhances the shear capacity of the joint and reduces its ductility. However, when the column
axial load/axial strength ratio increases to about 0.6–0.7, shear strength starts to decrease rapidly, leading to pure axial
failure of the joint. The magnitude of axial load/axial capacity ratio also dictates the failure mode and development of
crack patterns in BCJs. Results of reverse cyclic tests on BCJs showed that high value of axial load/axial capacity ratio
increases the initial stiffness of BCJ but rate of stiffness degradation is accelerated after peak strength attenuation.