Theoretical and Experimental investigation on conventional and Innovative reinforced concrete beam-to-column joints with and without floor deck

Abstract

Results of experimental tests carried out on Reinforced Concrete (RC) frames and connections equipped with integrated slab pointed out that the presence of the slab increases the flexural capacity of the connection, by acting as a flange for the beam. Consequently, the lateral resistance and stiffness of the structure are enhanced, and the capacity design weak beam-strong column failure can be altered. This thesis work focused on the effect of the floor deck on the flexural capacity of RC beam-to-column connections designed in compliance with the seismic European code, Eurocode 8 (EC8). Specifically, the effect of the floor deck made up of RC joists and upper slab, with interlaid hollow tile blocks, is investigated. Concerning this floor-system, indeed, few in-depth studies are available and EC8 does not specify how to account for the floor joists contribution in the resistance of RC connections. The goals of this thesis were two. Firstly, the over-resistance due to the deck presence in conventional beam-to-column connection was experimentally evaluated and compared to the “equivalent beam” theoretical model prediction, to verify the model accuracy. The “equivalent beam” model provides a proper formula to evaluate the number of joists enhancing the beam resistance. Secondly, an innovative constructional detail for RC beams was proposed, aiming at reducing the joint resistance, by computing the existence of the deck contribution. According to the basic concept of the Reduced Beam Section (RBS) design, typical of the steel connections, the flexural capacity of the beam was reduced to create a localized plastic zone far from the column, able to avoid undesired partial collapse mechanisms. The work is divided into three parts, the theoretical study, the experimental study, and the numerical modelling. The theoretical study consisted in modifying the formula of the “equivalent beam” model with reference to the test layout boundary conditions. The experimental campaign was conducted at the STRENGTH laboratory of the University of Salerno. In total, 12 full-scale specimens were tested in quasi-static loading, 6 of them are conventional beam-to-column joints with and without the floor deck, while the other 6 are innovative beam-to-column joints with and without the floor deck. The 3D Finite Element Model (FEM) of the RC joints, developed in the Abaqus software, reproduced the actual geometry of the experiments, as well as the same boundary conditions and loading as in the experimental program. The results of the experimental tests confirm that the floor deck enhances the resistance of the connection, greatly in hogging rather than in sagging bending. Moreover, the accuracy of the “equivalent beam” theoretical model is proved. The resistance of specimens equipped with the deck is predicted fairly in positive loading direction, while it is slightly overrated in the negative one. The cracking evolution confirms the actual interaction between the elements assumed in the theoretical model. The innovative detail effectively reduces the flexural strength of the connection. In particular, the resistance of innovative specimens with the floor deck is in perfect agreement with the resistance of simple conventional specimens, especially in the positive loading direction. The plastic hinge develops in the RBS and smaller damage on the beam supporting the joists is observed. The FE-Models of the tested specimens show good agreements with the experimental results. However, further analyses have to be carried out. [edited by Author]