Dirk Gouverneur

Influence of Design Parameters on Tensile Membrane Action in Reinforced Concrete Slabs

Abstract Reinforced concrete slabs are traditionally designed to carry a specified design load for adequate capacity at ultimate limit state (ULS). In case of an accidental event, however, tensile membrane action can be activated to establish an alternative load path, which will delay or prevent the collapse of the structure. As such, this tensile action increases the bearing capacity, safety and, hence, the robustness of structures. However, research on this important strength reserve is scarce and the residual capacity is commonly not taken into account during the design. In previous contributions of the authors, a unique test set-up was developed and described to investigate the tensile behaviour of slabs under large deformations because of the accidental removal of a support. A set of three real-scale reinforced concrete slabs of a total length of 14 m was tested. The experiments provided a unique set of data that was subsequently used to develop and validate a numerical model. In this study, this numerical model was used to perform a parameter study to identify the influence of the most important design parameters: span length, slab thickness and reinforcement (ultimate strain and geometric ratio); the results of the analysis are presented in this article. Further, the boundary conditions were shown to have an important influence on the development of tensile membrane action and this effect was investigated considering different restraint conditions as well as using the finite element model analysis of a frame.

Catenary behaviour in concrete slabs: experimental and numerical investigation of the structural behaviour

A very important property of concrete structures with regard to robustness is the rigid connectivity with neighbouring elements. When a hyperstatic concrete slab is excessively loaded or when a certain support is lost due to an accidental situation, membrane forces can be activated in order to establish a load transfer to the remaining supports. This favourable effect can considerably enhance the slabs load-carrying capacity compared to predictions obtained from small deformation theories. Thus, membrane actions can prevent or delay a progressive collapse and increase the robustness of concrete structures. A novel real-scale test set-up has been developed in order to assess the structural behaviour under catenary action in real-scale concrete slabs and the influence of reinforcement curtailment, since in current design practice the main flexural reinforcement is calculated for the slabs critical sections and consequently the reinforcement is curtailed based on the envelope of the acting internal actions. The investigations include the testing of a reinforced concrete slab strip with continuous flexural reinforcement over the entire length and a second test differing only from the reinforcement arrangement, considering current design codes for reinforcement curtailment. The slab specimens were exposed to an artificial failure of the central support and subsequent vertical loading until collapse. Furthermore, finite element methods allow to simulate the behaviour of concrete slabs under these large deformations. Numerical FEM analysis of the executed real-scale tests will be explained and compared with the experimental results. Finally, the influence of reinforcement curtailment on the overall performance under catenary action will be discussed.

Numerical and experimental analysis of a novel real-scale test set-up for the analysis of tensile membrane actions in concrete slabs

Research with respect to robustness of (concrete) structures gained wide interest due to the partial collapse of some case examples, such as the famous collapse of the apartment building in Ronan Point (UK) in 1968. A very important property of concrete structures with respect to robustness is the rigid connectivity with neighbouring elements. When a hyperstatic concrete slab is excessively loaded or when a certain support is lost due to an accidental event, membrane forces can be activated in order to establish a load transfer to the remaining supports, which can considerably enhance its load-carrying capacity compared to predictions obtained from small deformation theories. Thus, membrane actions can prevent a progressive collapse and increase the robustness of concrete structures. Finite element methods can simulate the behaviour of concrete plates under these large deformations. Currently, however, different questions remain unsolved in order to properly assess the membrane actions, i.e. the influence of the constitutive laws which are implemented, the modelling of connectivity, fracture mechanical aspects under tensile membrane actions and large displacements, etc. As currently only limited research has been focussing on tensile membrane actions, a novel real-scale test set-up has been developed in order to assess these actions in realscale concrete plates. The details of this test set-up will be explained and some experimental test results will be discussed. Finally, the results will be compared with numerical FEM analyses and the influence of different model assumptions will be evaluated.