Response of reinforced concrete elements and structures following loss of load bearing elements.

摘要

Membrane action of beams and floors are important mechanisms of load redistribution and progressive collapse resistance in the event of failure of load-bearing elements. The behavior of RC beams under compressive and tensile membrane actions is not yet fully understood. This dissertation characterizes the development of compressive and tensile membrane actions in RC beams and their effects on collapse resistance, at the element and structural levels, using experimental and analytical studies.;Experimental studies on a two-span fixed-end RC beam, designed satisfying the ACI structural integrity requirements and subjected to increasing vertical displacement at the middle, demonstrated the development of compressive and tensile membrane actions. Test results showed that an increase in the resisting force through tensile membrane action was triggered by the fracture of the continuous bottom reinforcement and developed through the continuous top reinforcement. The transverse reinforcement allowed the top reinforcement to develop catenary action without tearing up the concrete cover. Experimental and analytical studies also showed that, during the development of catenary action, the strains on the top reinforcement concentrated in the middle regions of each span, where a smaller amount of top reinforcement was provided. Furthermore, the results were used to demonstrate and evaluate the effect of beam growth on the development of compressive axial force and its contribution to increasing the flexural capacity of RC beams as well as its adverse effect on the beam resistance through the second order axial force-deflection interaction.;Analytical studies of an RC frame structure, subjected to the removal of a central ground floor column of an exterior frame, demonstrated the development of compressive and tensile membrane actions in the beam bridging over the removed column as a mechanism of progressive collapse resistance. It is found that the decay of the compressive and flexural actions of the beam corresponds to compressive failure of the beam critical sections under maximum bending moment and axial compressive force. The tensile membrane action of the beam is characterized by the development and increase of the tensile axial force with no increase of the beam flexural resistance.