Bidirectional Cyclic Loading Experiment on a 3D Beam-Column Joint Designed for Damage Avoidance
A near full-scale 3D jointed precast prestressed concrete beam to column connection designed and constructed in accordance with an emerging Damage Avoidance Design (DAD) philosophy is tested under displacement controlled quasi-static reverse cyclic loading. The performance of the subassembly is assessed under unidirectional loading along both orthogonal directions as well as under concurrent bi-directional loading. The specimen is shown to perform well up to 4% column drift with only some minor flexural cracking in the precast beams, while the precast column remains uncracked and damage-free. This superior performance is attributed to steel armoring of the beam-ends to mitigate the potential for concrete crushing. Under bi-directional loading a tapered shear-key layout is used to effectively protect the beams against adverse torsional movements. A three-phase force-displacement relationship is proposed which gives due consideration to: the prerocking flexural deformation of the beam; the rigid body kinematics during the rocking phase; and the yielding of the external dissipaters and post-tensioning tendons. Good agreement between the proposed theoretical model and experimental observation is demonstrated. An equivalent viscous damping model is also proposed to represent both change in the prestress force in the subassembly and yielding of the supplemental energy dissipaters in the rocking connection.