Partial hinge detailing to improve catenary action of reinforced concrete frames

• Main Authors: Yu, Jun, Tan, Kang Hai
• Other Authors: School of Civil and Environmental Engineering
• Format: Conference or Workshop Item
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Civil engineering::Structures and design
• Online Access: https://hdl.handle.net/10356/95664; http://hdl.handle.net/10220/9814; http://daps2012.org/
• Institution: Nanyang Technological University

Progressive collapse resistance of buildings can be evaluated by introducing a middle column removal scenario to mobilize alternate load paths (ALP). Catenary action, one of ALPs, uses tensile force throughout beams to balance external loads applied onto structures. To this end, large deflections and rotations of beams must be achieved. Due to the tensile mechanism, the continuity of longitudinal steel reinforcement becomes critical. In this paper, the development of catenary action of two reinforced concrete (RC) frames is presented in detail. Both specimens consisted of two one-bay beams, one middle joint, two side columns and two beam extensions. One frame was designed with conventional non-seismic detailing in accordance with ACI 318-05. To avoid any possible failure at the joint panels and to increase the rotation capacities of beams, detailing of the second frame was improved by designing partial hinges in the beams at one beam depth away from the joint interfaces. The hinges were constructed by bending down one top bar and then leveling it at the bottom bar layer, and bending up one bottom bar and then leveling it to the top bar layer. Test results on the specimen with conventional detailing show that catenary action could be mobilized successfully but failed to significantly increase structural resistance due to excessively premature fracture of top bars at the side joint interfaces. In contrast, the presence of partial hinges in the second frame enabled catenary action to significantly enhance structural resistance, with more than twice the capacity of compressive arch action. This is because that the in-built hinges helped the beams rotate easily without causing premature bar fracture at the initial rotation stage.