Studies on identifying critical joints in RC framed building subjected to seismic loading

Abstract

A beam-column joint is very critical element in reinforced concrete (RC) framed structure where the elements intersect in all three orthogonal directions. In normal design practice for gravity loads, the design check for joints is not usually critical in reinforced concrete (RC) frames and hence not warranted in general. However, failures of RC frames during recent earthquakes have revealed heavy distress in the joints and resulted in the collapse of several structures due to joint shear failure. Despite the critical role of joints in sustaining large deformations and forces during earthquakes, specific guidelines are not explicitly included in currentIndian codes of practice IS 1893:[1], IS 13920:[2] and IS 456:[3]. On account of this, it is tacitly assumed in practice that adequate lapping of the main reinforcement and provision of transverse ties satisfies the integrity and strength of joints. However, the kind of reinforcement detailing given in the design codes is not consistent with the Indian practice of construction in terms of implementation. This paper aims to study the behaviour of beam-column joints in multi-storeyed RC framed structure with an objective to identify the location of deficient joints and developing alternative design scheme suitable for Indian construction industry. A family of multi-storeyed building of 2 bay × 2 bay (at 5 m) frames from 3 storey (10.5 m height) to 10 storey (35 m height) is studied. Shear force demand in the joint is estimated from the concept of capacity design. The shear capacity is calculated for the interior joints at different height (i.e., at different floor level) of the buildings as per selected international building codes and other methods available in literature. This result shows that the maximum joint demand occurs not in the lowest storey level of the building but somewhere in the second, third or fourth storey level. The maximum joint shear demand found to be more than the corresponding capacity for all building above 5 storeys (i.e., 17.5 m height) studied here. An effort has been made for correlating the joint shear demand in any interior joint with the height of the joint. This will be helpful for identifying the critical joint location in a building.