Seismic behaviour of deficient exterior RC beam-column joints.

Post-earthquake reconnaissance and results of previously conducted experiments show that
stiffness and strength deterioration of beam-column joints can have a detrimental effect on the
integrity and vulnerability of reinforced concrete frame structures, especially in older buildings
in developing countries. As a result, there is a need to develop efficient structural evaluation
techniques that are capable of accurately estimating the strength and deformability of existing
buildings to facilitate the development of safer, simpler, and lower cost retrofit solutions and
thus contributing to risk mitigation.
The current research is part of a general effort that is being carried out at the University of
Sheffield to quantify and develop strategies for the mitigation of seismic risk in developing
countries. The primary aim of this work is to improve the current understanding of the seismic
behaviour of deficient exterior reinforce concrete beam-column joints. Seven full-scale isolated
exterior beam-column joints were tested under quasi-static cyclic loading to investigate and
quantify the effects of using different types of beam reinforcement anchorages and low column
axial loads on the seismic shear performance of exterior beam-column joints with no shear
reinforcement.
Contrary to what is reported in the literature, the test results show that increasing the column
axial load even at very low levels «O.2f'oAg,) can enhance the joint shear strength of deficient
exterior joints (exhibiting pure shear failure) by up to 15%. The test results also show that, for
the same joint panel geometry and column axial load, the type of beam anchorage detail,
whether it is a straight bar, long or short hook, can influence the joint shear strength by up to
34%.
A new analytical model that predicts the shear strength of deficient exterior beam-column joints
in both loading directions and takes into account the column axial load and bond conditions
within the joint is developed. The model predicts with good accuracy the strength of the tested
specimens in addition to other specimens reported by other researchers. Furthermore, a springbased
exterior beam-column joint model for finite element analysis of deficient RC frames is
proposed. The model development includes a joint shear stress-strain constitutive model based
on the developed strength model. The simulated response using the proposed model shows good
agreement with the experimentally observed response.