Concrete slab | EPFL Graph Search

A concrete slab is a common structural element of modern buildings, consisting of a flat, horizontal surface made of cast concrete. Steel-reinforced slabs, typically between 100 and 500 mm thick, are most often used to construct floors and ceilings, while thinner mud slabs may be used for exterior paving . In many domestic and industrial buildings, a thick concrete slab supported on foundations or directly on the subsoil, is used to construct the ground floor. These slabs are generally classified as ground-bearing or suspended. A slab is ground-bearing if it rests directly on the foundation, otherwise the slab is suspended.
For multi-story buildings, there are several common slab designs :

Beam and block, also referred to as rib and block, is mostly used in residential and industrial applications. This slab type is made up of pre-stressed beams and hollow blocks and are temporarily propped until set, typically after 21 days.
A hollow core slab which is precast and instal

Post-punching behavior of reinforced concrete slabs

Yaser Mirzaei

Reinforced concrete flat slabs are extensively used in buildings and parking garages. Their design is governed by deflection at the serviceability limit state and punching shear at the ultimate limit state. When no punching shear reinforcement is provided, failure develops in a brittle manner. Punching shear failure occurs with almost no warning signs, because deflections are small and cracks at the top side of the slab are usually not visible. Over the past decades, several structural collapses occurred due to punching shear failure resulting in human casualties and large damages. These collapses revealed some shortcomings in codes of practice and the necessity of reconsidering punching provisions. The investigations of these collapses showed that the collapse initiated from a local punching failure and propagated throughout the structure, in a progressive collapse. The term progressive collapse refers to the spreading of an initial local failure triggered by the loss of one or more load carrying members and leading to partial or total collapse of the structure in a manner analogous to the chain reaction. As a local punching failure can trigger progressive collapse, the study of the post-punching behavior can help adopting constructive solutions to avoid progressive collapse. The post-punching behavior of flat slabs supported by columns has not yet been thoroughly investigated. Therefore, an extensive experimental campaign was performed in the framework of this dissertation to investigate the post-punching behavior of 24 slabs with various reinforcement layouts. The effects of bending reinforcement, integrity reinforcement, bent-up bars, steel type, and anchorage conditions on the post-punching behavior of slab-column connections were investigated. The performance and robustness of the various solutions was investigated to obtain physical explanations of the load-carrying mechanisms. Test results showed that the post-punching strength provided by the top reinforcement is small because the concrete cover is thin and spalling of the concrete cover occurs leaving the reinforcement ineffective. In addition, it was observed that integrity reinforcing bars passing through the column significantly improve the post-punching behavior in terms of strength and deformation capacity. The integrity bars behave as a tensile membrane inclined to the plane of the slab and are able to sustain damaged portions from the column. Thus, one possibility to enhance the robustness of the structure against progressive collapse is to provide well-anchored bottom reinforcing bars passing through the column. A mechanical model capable of predicting the post-punching behavior of slab-column connections without shear reinforcement was developed. The model predicts the contribution of the tensile reinforcement and of the integrity reinforcement to the post-punching strength. The model accounts for possible failure modes including the fracture of the bars and the destruction of the concrete over the integrity bars. The progressive destruction of the concrete within and outside the punching cone is treated by considering the pullout behavior of reinforcement embedded in the concrete. Finally, a parametric study was performed to evaluate the influence of various parameters and their relative importance in order to develop practical proposals for the estimation of the post-punching strength. It showed that the post-punching strength is not only a function of the cross sectional area and yield strength of the integrity reinforcement as it appears in provisions and codes of practices but also of the diameter of the bars, the effective depth, the ductility, and the type of reinforcement.

EPFL2010

Post punching behaviour of reinforced concrete slab-column connections

Yaser Mirzaei

Reinforced concrete flat slabs are extensively used in buildings and parking garages. At the ultimate limit state, their design is usually governed by punching shear. In the case where no punching shear reinforcement is provided, failure develops in a brittle manner. Furthermore, punching shear failure of one column may propagate to adjacent columns, eventually leading to the total collapse of the structure. Punching shear failure occurs with almost no warning signs, because deflections are small and cracks at top side of the slab are usually not visible. Over the past decades, several collapses due to punching shear failures have occurred, resulting in human casualties and large damages. Some solutions can be adopted to enhance the post punching behavior of flat slabs and to avoid progressive collapse. This paper presents some results of an extensive experimental campaign performed at the Ecole Polytechnique Fédérale de Lausanne. The post punching behavior of 24 tested slabs, with various flexural reinforcement layouts are introduced and compared. The performance and robustness of the various solutions is investigated to obtain physical explanations of the load-carrying mechanisms.

7th International fib Symposium in Civil Engineering2008

The mechanics of shear failures in RC slabs based on refined measurements

Raffaele Cantone

Reinforced concrete planar members, as slabs and shells, are structural elements commonly used in the construction technique, which are typically designed without the arrangement of shear reinforcement. Despite the fact that this solution allows for fast and economic construction, the absence of shear reinforcement can give rise to the potential localization of strains within a critical shear crack and eventually to the shear failure of the member. In the case of redundant systems, most research on the mechanics of shear failures has been devoted to the strength of the member, neglecting in many cases the development of shear deformations due to inclined cracking as well as the redistributions of internal forces, which are instrumental for the analysis of the response of these members. The contribution to the state-of-the-art includes a series of theoretical works explaining the observed responses for a series of experimental programmes. These experimental campaigns comprise tests in tension, shear tests in one- and two-way slabs as well as punching tests. For their instrumentation, in addition to classical measurement devices, Fibre-Optic Measurements and Digital Image Correlation were intensively used.This thesis starts by revisiting the basis of the interaction between reinforcement and concrete. A series of bond tests show the stress concentrations occurring near the ribs and its complex transfer of forces with the surrounding concrete. In addition, tests on beams failing in shear show a complex interaction between bond stresses and kinking on the reinforcement due to the development of dowel action. These phenomena are normally neglected for concrete design due to the ductile nature of reinforcement, but may be relevant for fatigue and negative tension-stiffening effects.An important step in the knowledge is performed on the understanding of the shear response with respect to the characterization of the deformations in concrete members. Based on a series of test results, a complete description of the deformation field (including shear strains) is presented. On that basis, a rational model is proposed, consistent with the mechanical model of the Critical Shear Crack Theory. This model allows for a precise description of the response and also to describe the through-thickness distribution of the shear deformation.A general frame for modelling of reinforced concrete slabs is thus presented accounting for the redistribution of internal forces during propagation of the shear crack. This approach is used to investigate a testing programme performed on three wide slabs, analysing in a scientific manner the influence of the width of the member on the shear resistance. The detailed experimental data allow to capture the crack propagation and internal forces redistributions. Clear conclusions and answers are obtained, showing the influence of the shape of the failure surface and of its propagation on the load-carrying capacity.The research ends with a final investigation on the dowelling action of compression reinforcement, with an application to slabs failing in punching. Based on a large testing programme including eleven axisymmetric punching tests, an analytical approach is developed to estimate the contribution of the dowel action on the load-carrying capacity. This approach is formulated within the frame of the Critical Shear Crack Theory, and is incorporated in a consistent and efficient manner for design purposes.

EPFL2021

Post-punching behavior of reinforced concrete slabs

Yaser Mirzaei

EPFL2010

The mechanics of shear failures in RC slabs based on refined measurements

Raffaele Cantone

EPFL2021