The Slab STRESS Research Program

A research program at Politecnico di Milano (D. Coronelli), EPFL Lausanne (A. Muttoni), UNOVA Lisbon (A. Ramos) and UTCB Bucharest (R. Pascu) is being developed within the SERA-TA program - H2020. The aim is studying flat slab response for seismic actions and developing the design with European codes. There is an urgent need to extend the Seismic European Code for reinforced concrete buildings to cover flat slabs ( Fardis, 2009; Pinto et al., 2007). These have been and are intensively used because of the cutting of construction costs and time, the simplicity of the geometry and increased available architectural space. Flat slabs cannot be considered to contribute to the primary seismic resistant system and can be designed as secondary systems supporting gravity loads at the design deformations, due to their compatibility with the primary system ( Fardis, 2009; Coronelli and Martinelli, 2017). Particular care is needed for the punching shear capacity of slab-column connections (Coronelli and Corti, 2014, Drakatos et al. 2017, Pinho Ramos et al., 2008, Pinho Ramos et al., 2011). Results aim at providing basis for code and design practice improvement (Pascu et al., 2015; Muttoni, 2018).

Using the JRC ELSA Reaction wall facility, a flat slab structural system will be tested. The structure is made of two flat slab floors supported on R/C columns. Each floor has 3 bays in the longitudinal direction and two bays in the transverse direction, and the spans are 5m and 4.5m (Fig. 1 and 2). Each floor is made of a reinforced concretemslab, with thickness 20 cm. The 1st floor does not contain punching shear reinforcement, while the 2nd floor has stud shear reinforcement. Previous research considered isolated slab-column connections (Almeida et al., 2016; Drakatos et al, 2016).The size is that of a real scale building, designed using the Eurocodes with primary ductile walls and flat slabs as a secondary system. In a first seismic hybrid pseudo-dynamic test (Pinto et al., 2004) the response to the design earthquake will be studied at service and ultimate states, and ductile walls will be modelled virtually (Test A). A second quasi-static cyclic test will investigate the response up to failure (Test B).

The mass for each slab floor is 63 tons without added gravity loads and 108 tons with added loads. The design was based on uniform distributed load of 3KN/m2for non-structural gravity loads and 2KN/m2 for the live loads. The materials are normal strength concrete C30/37and steel S450 Class C.

Loading phases and structural scheme

The loading program comprises two types of loading, and related to this different constraints at the base of the building. The first test A is for seismic loading and the base of the columns is a fixed constraint; the flat slab system is connected to the primary walls, modeled numerically, limiting the drift to a design value. The second phase B is cyclic loading of the flat slab frame to failure. The floors will be tested for gravity and lateral cyclic loading of increasing amplitude to failure. (A) Seismic loading Seismic loading will be simulated using the pseudo-dynamic technique with nonlinear substructuring (Pinto et al., 2004) for two levels of seismic motion (service Test A.1 and ultimate state Test A.2). Gravity loading will be self-weight and supplementary weight supported on the slabs. (B) Cyclic loading The floors will be then tested for gravity and lateral cyclic loading of increasing amplitude to near-failure conditions. Lateral actions will be imposed by displacement controlled jacks connected to reinforcement bars anchored within the slab, along the centerline between lateral and interior frames.