Shear strength and seismic performance of non-seismically designed reinforced concrete beam-column joints.

摘要

Moment resisting frame is a common structural form and widely adopted to provide lateral resistance to earthquake in a seismic region. When a frame is under seismic excitation, the beam-column joints play an important role in transferring moments and internal forces among adjacent beams and columns. This action induces both vertical and horizontal shearing forces, whose magnitudes are typically many times higher than those in the adjacent members, to the connection. Without proper design to the joint shear strength, beam-column joints can be the most vulnerable element. To avoid sudden loss of strength of the frame, it is principally necessary to maintain the integrity of beam-column joints.; Building design codes of practice in regions of nil or low to moderate seismicity, such as in the UK and Hong Kong, etc., do not generally include any provision for consideration of joint design. Apart from longitudinal reinforcing bars from beams and columns, no transverse reinforcement is usually incorporated. This partly resulted from the common misconception that the joints are much more rigid than the adjacent beams and columns. The performance of the existing beam-column joints, which are non-seismically detailed, is unknown. For design, adoption of available code provisions for beam-column joints, which usually require enormous amount of steel, in low to moderate seismic regions would complicate the fabrication process and make the placement of concrete tedious.; In this thesis, a study of shear strength and seismic behaviour of non-seismically designed beam-column joints is presented. It covers both experimental investigation and the development of theoretical modelling for beam-column joints. Experimental studies are first conducted to clarify the performance of non-seismically designed joints under reversed cyclic loading. The main variables studied include beam to column depth ratio, transverse reinforcement ratio, longitudinal reinforcement ratio, axial load ratio and the type of beam reinforcement anchorage. From the experiment, two major failure modes, namely joint shear failure and beam yielding joint shear failure are observed. It is surprising that most of the joints show low ductility and fail before reaching the flexural capacity of beam. However, under certain condition, a high level of ductility factor can be reached, even there is no transverse reinforcement incorporated in the joint region. (Abstract shortened by UMI.)