Damage Pattern of RC Beam Column Connections Subjected to Cyclic Loading

Introduction

Designing beam–column joints is considered to be a complex and challenging task for structural engineers, and careful design of joints in RC frame structures is crucial to the safety of the structure. Although the size of the joint is controlled by the size of the frame members, joints are subjected to a different set of loads from those used in designing beams and columns.

Figure 1: (a) joint shear failure and (b) end anchorage failure [1]

As a result, it is necessary to pay special attention to the detailing of reinforcement within a joint region. It has been identified that the deficiencies of joints are mainly caused due to inadequate design to resist shear forces (horizontal and vertical) and consequently by inadequate transverse and vertical shear reinforcement and of course due to insufficient anchorage capacity in the joint. Therefore, inadequate transverse reinforcement and insufficient anchorage in the joint are two major problems of the joints designed as per non-seismic guidelines [2]. These problems have been highlighted, in recent past, by the damage observed in devastating earthquakes in different countries. The two major failure modes for the failure at joints are (a) joint shear failure and (b) end anchorage failure (Figure 1). A typical example of a beam–column joint failure during the 1999 Turkey earthquake is shown in Figure 2 [2].

In this study, a conventional four-storey RC school building (Fig. 3) is considered for analysis, design and detailing of exterior joints. Different failure modes are expected in beam-column joints depending on the type of joint (exterior or interior) and the adopted structural details. Due to sudden discontinuity of the geometry, exterior joints are found to be more vulnerable to seismic loading than the interior one because it demands to explore additional parameters such as bond-slip of reinforcement [Pampanin et al. (2003)]. Hence, in the present study, exterior beam-column joint has been chosen for investigating the performance under seismic type loading.