Flexural Behavior for External Beam–Column SFRC Joints: Experimental Investigation and Design Suggestions

Experimental research was carried out on the flexural behavior of full-scale external beam–column concrete joints cast with plain and steel fibrous reinforced concrete (SFRC) with hooked steel fibers, subjected to cyclic reversal loading. Four beam–column sub-assemblages were cast. Two of them, denoted as control specimens, were made of plain concrete (RC) and were reinforced with longitudinal bars and transverse stirrups, and two were made of hooked steel fiber-reinforced concrete (SFRC) with same longitudinal steel reinforcements of control specimens but with higher spacing of stirrups in the beam. The experimental results show that it is possible to avoid brittle failure of external beam to column joint assigning, as it is well-known, high percentage of transverse steel in joint region or utilizing less stirrups in all critical regions and replacing plain concrete with SFRC. In this case, it is possible also a more efficient control in the opening of the cracks. From the analytical point of view, experimental results were reproduced numerically by using a non-linear finite-element program (ABAQUS). With ABAQUS constitutive laws in compression and in tension able to include post-cracking resistance of material were adopted. In addition, utilizing a simplified closed-form softened strut-and-tie macro-model, it was possible reproduce the load-deflection curves of beam to column sub-assemblages. Analytical results were in a good agreement with monotonic response observed experimentally. Finally, design guides for ductile behavior of SFRC beam to column joints are given