# The Behaviour of Half-Slabs and Hollow-Core Slab in Four-Edge Supported Conditions
## 1 Introduction  
Composite slabs with precast panels are being increasingly used in the construction sector as an alternative to monolithic slabs or beam and block systems [1]. Half-slabs consist of (flat or ribbed) reinforced concrete or prestressed slab serving as stay-in-place formwork and monolithic concrete topping. Compared to beam and block floor systems or monolithic slabs, use of this type of structure is characterised by allowing a rapid erection time requiring lower work input in addition to having elements of relatively low cost [2; 3; 4]. Prestressed slabs are more crack-resistant and lighter at the same length, allowing considerably greater spans. Being able to reduce the number of erection supports to a minimum is a crucial advantage of panel slabs, as they usually tend to be self-supporting. Due to the extrusion method used during their production, the cross-section of panels can be easily shaped. Different types of filling inserts can reduce the weight of panels and improve their insulation properties [5; 6; 7]. Many tests have been performed in recent years, and new types of composite slabs have been designed. They include but are not limited to a slab bonded to vertical tongues serving as shear keys that join two layers of the slab [8], multi-span slabs of slimfloor type with prestressed steel beams bonded to hollow-core (HC) slabs [9], and one- or two-way slabs on thin prestressed boards (narrow slabs) [10]. Basalt rebars are pretensioned using various methods [11], and steel reinforcements have been used astrusses to increase the load capacity of the joint system at the interface between ribbed pre-cast units and concrete topping, also referred to as a joint advanced slab system (JAS) [12]. In an optimised-section precast slab (OPS), precast units with the cross-section shape at the support and the span varying over the length are also used [13]. The main area of tests carried out on composite slabs principally includes the concrete-concrete interface and the distribution of shear stresses under short- and long-term loading. A series of slant-shear and direct-shear tests were conducted [14; 15; 16] on test specimens. Digital image correlation (DIC) and ultrasonic techniques were used to evaluate the behaviour of the interface area [17; 18; 19; 20]. The relationships between surface roughness and interface resistance [21; 22] were also defined in the fibre-reinforced concrete used in the concrete topping slab [23]. The following issues were the subject of a separate examination: the strength of concrete components, the age of individual erected layers, and strength development of the composite structure over time [24]. It was demonstrated that a difference in concrete strength did not have a proportional effect on the composite structure strength increase. However, it affected the strength interface between the precast unit and the concrete topping. The tests also confirmed that the curing method of the concrete topping slab substantially increased the joint strength. Stresses at the beam supports and slab were studied in full-scale models [25; 26; 27; 28; 29; 30]. The behaviour of prestressed hollow-core (HC) slabs and beam and block systems have been thoroughly investigated. These studies have demonstrated the full shear connection between the concrete topping and the precast unit with a rough interface [31; 32; 33; 34; 35; 36]. The tests and theoretical and numerical analyses described in the papers [37; 38; 39] revealed that the ultimate limit state of cracking could not be separated from the ultimate limit state of shearing for slabs with reinforcement serving as the main shear connector. An interesting observation also found in the paper [40] demonstrates that the proper connection between layers or effective anchorage of tension reinforcement at the support can lead to the full load capacity of composite members. Single tests refer to cyclic or dynamic loading in predicting and measuring the displacement amplitude at delamination [41].