Experimental Investigation on a Beam-Column Joint with Slab and Transverse Beam under Cyclic Loading

The presence of in-situ cast slabs and transverse beams in reinforced-concrete (RC) beamcolumn joints is usually neglected in RC design practice concerning frames subjected to seismic actions for at least two reasons: (i) the need of simplification in the design process and (ii) the limited experimental studies which are mainly focused on two-dimensional subassemblies. As a part of a research project addressing innovative retrofit solutions based on post-installed fasteners, an external beam-column joint subassembly including a two-way floor slab and a transverse beam is tested (prior to be retrofitted) under a quasi-static cyclic load yielding a 6% drift. The specimen was designed for gravity loads, with limited transverse reinforcement and poor detailing in the joint zone. As expected, the slab and the transverse beam increase the stiffness and the load-carrying capacity of the sub-assembly when the beam flange acts in tension until the joint fails in shear. The effective width of the slab bars, evaluated using strain gauges measurement, is compared with codes’ provisions, showing a good agreement. Compared with preliminary analytical predictions mostly based on two-dimensional models, the load-bearing capacity in shear of the 3D joint assembly is higher. The crack pattern suggests that the increased loadbearing capacity may be primarily attributed to the transverse beam, which increases the joint width and exerts a passive confinement on the joint.