# Structural Behavior of Floor Systems Made by Floor Plates--Mechanical Model Based on Test Results
## 1 Introduction  
Floor systems made by floor plates consist of reinforced or prestressed precast concrete plates that will be used as permanent formwork for cast-in-situ concrete (topping), which, when hardened, forms a composite slab [1]. Such slabs should behave monolithically after hardening of the topping, and a significant part of mechanical resistance is not taken by the precast element. In the opposite case, other product standards and prescriptions are valid [2, 3], which will not be discussed in this article. Major properties of the precast floor plate are a minimum thickness (\(h_{p}\)) of about 50 mm, an upper surface that should be at least smooth (according to the definition in clause 6.25 from [4]), and the presence of lattice girders. The latter are used for handling in the factory and/or on-site; they determine the distance in between the temporary props in the formwork phase, and as connecting reinforcement in the final stage between floor plate and topping. Sometimes they can also be used as shear or even punching reinforcement; however, this application is also outside the scope of the present article. The direction of the lattice girders mostly shows the main or span direction of the floor plates; it is supporting the most important bending moment. Perpendicular to this direction, indicated by the length \(L\), the width \(b\) is used, which is typically limited to about 2.4 or 3.0 m. Subsequently, due to the limited width of the floor plates, longitudinal joints are presented with details, as shown in Figure 1. Out of ecological aspects and to reduce the weight of the system, sometimes void formers are used; these slabs are so-called hollow composite slabs. The void formers are glued,connected, or partially incorporated in the floor plate. They are available in any shape and can be optimized [5], but should by preference comply with clause 5.3.1 (6) from [4] and annex C of [1]. Floor slabs made with precast floor plates should be analyzed as massive floor slabs. This can be easily derived from the mechanical behavior of a simple beam element with a locally reduced section, i.e., the joint in between the floor plates. Indeed, the deflection is nothing more than the double integration of the curvature diagram, where the curvature is equal to \(M/EI\) with \(M\) the moment, \(E\) the Young modulus, and \(I\) the second moment of area. Even with a strong local reduction of \(I\) (due to the reduction of \(h\) by \(h_{p}\), see Figure 1), the influence will be neglectable as long as the width of the joint is limited. Thus, the assumption of a one-way bearing system is not appropriate when there are no two free edges or outside the central region of a slab with width/span ratio > two [4]. Consequently, outside the one-way bearing regions, joints will transfer bending moments and research about the mechanics and the contribution of the different components in such a joint is rare. Only some preliminary guidance can be found in the literature [6; 7; 8]. In addition, currently, flat slabs are also designed and constructed using a combination of precast floor plates and voiding elements. This makes the design of the joints even more challenging and there is a clear need to understand the behavior and mechanisms that govern the load transfer in such floor systems. Only a few national guidelines exist; for example, in [8] about the transfer of forces through such a joint and insight is missing; in addition, some limitations to the diameter of the overlap bars (\(\leq\)\(\mathcal{O}\) 14 mm) and the amount of reinforcement (\(\leq\)1000 mm\({}^{2}\)/m) exist. For this reason, a large set of experimental results (20 large-scale tests in total) is presented and analyzed in this paper. With this information (i) the misuse of existing rules for verifications where they are not developed can and will be avoided, (ii) understanding of the physical phenomena should be improved, and (iii) design recommendations can be developed.