Grid model for the non-linear behavior of R/C flat-slab subjected to gravity and lateral loads

Use of flat plate floor systems consisting of conventional reinforced concrete slab-column system is becoming increasingly popular for non-participating systems in medium and high seismic zones, as Italy is. Thus, it is of great interest to develop models able to represent their non-linear behavior under horizontal loads, both for the verification and design of this structural typology. The aim of his dissertation is to apply a grid model, designed for the nonlinear behavior of flat slab-column connections, on a real study case in order to test its performance in representing the experimental observed behavior. The considered experimental study is the one carried out by Hwang and Moehle at the University of California at Berkeley (1993), consisting on a flat slab structure with sixteen slab-column joints, subjected to gravity and biaxial cyclic lateral loading. The geometry of the grid has been designed in order to model in the best way the real geometry of the structure with its asymmetries; plastic hinges properties have been computed accordingly to the aforementioned grid model; loads applied are the same of the real slab. A force controlled non-linear analysis under gravity loads and non-linear static (pushover) analyses under horizontal loading in the two principal directions of the structure, are performed on the model slab. The software used for all the analyses is SAP 2000 v.10. The numerical global structural behavior and the joints behavior have been compared with the experimental ones; the influence of column rectangularity has been also investigated in relation of experimental studies on this topic. Analyses show a good correspondence between the numerical and experimental global structural behavior; interior connections are absolutely well modeled, whereas edge and corner connections show departures from experimental behavior, because the latter are strongly influenced by degradation of mechanical properties due to biaxial cyclic loading. All the results obtained may be interpreted taking into account for this fact. Rectangularity of columns influence both the numerical global and connection response; this is less evident in the experimental case because of slab degradation due to biaxial cyclic loading.