Compressive membrane action in reinforced concrete beams

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Research studies have demonstrated that membrane action is primarily a compressive load carrying mechanism that can significantly improves the load-bearing capacity of reinforced concrete beams during extreme loading scenarios such as column loss. However, the behaviour of reinforced concrete (RC) beam assemblages under membrane action has not been thoroughly explored and therefore, the development of the compressive (arching) and tensile (catenary) membrane actions in RC beams should be investigated further by experimental and analytical studies. Membrane action is affected by various parameters such as compressive strength of the concrete, reinforcement ratio and transverse reinforcement of the beam. However; previously conducted researches indicate that compressive membrane (arching) action is not considerably influenced by reinforcement ratio which was shown to be the critical parameter in development of the tensile membrane (catenary) action. Also, both translational and rotational stiffness of end supports have significant influence on development of membrane action. Development of membrane action in RC members is typically associated with geometrical as well as material nonlinearities (including concrete cracking and crushing, reinforcing bar yielding and fracture) and due to these strong nonlinearities, most of the existing implicit finite element (FE) models and simplified analytical methods fail to adequately capture the compressive and tensile membrane behaviour of RC elements. The main focus of this research project is to experimentally and numerically investigate development of membrane action in RC beam assemblages. In the experimental program, influence of various parameters including concrete compressive strength, reinforcement bar arrangement and ratio and boundary conditions on the membrane response of RC beam assemblages following a column loss scenario are investigated. Furthermore, two different classes of nonlinear FE models, i.e. a 1D discrete frame and a continuum-based FE models are developed and data obtained from the experimental program are employed to verify and validate the developed FE models. Using a simplified approach, the influence of steel bar rupture is incorporated into the formulation of an existing flexibility-based frame element and it is shown that the proposed strategy has the ability to adequately model the rupture of steel bars and its implications at global level.
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