An Investigation into tensile membrane action as a means of emergency load redistribution

Abstract

This thesis presents a review of structural robustness in conventional (non-hardened, nongovernmental and non-military) buildings subjected to malicious actions and has also investigated the capability of tensile membrane (catenary) action as a means of emergency load redistribution in reinforced concrete (RC) framed buildings, designed in accordance with BS 8110 and Eurocode 2.

Case studies and forensic data relating to the response of conventional blast damaged buildings have been investigated. Based on the conclusions drawn from this investigation a simple ranking system has been presented that identifies the level of confidence offered by various forms of direct and indirect robust design.

Catenary action has been shown to be a fundamental mechanism of emergency load redistribution for which research has been relatively limited, particularly in relation to RC frame constructions. An experimental investigation has been carried out; this involved the testing to failure of a series of half scale RC strip specimens, detailed to conventional detailing practices, to investigate the large displacement behaviour and ultimate collapse resistance of laterally restrained RC floor components following the loss of intermediate column support. The results showed characteristic compressive and tensile membrane responses. However, tensile membrane action was found to provide the largest reserve of strength and to offer the highest potential as a means of emergency load redistribution. By testing specimens to outright collapse the investigation identified factors influencing catenary performance and demonstrated that the total energy absorption by work done in catenary action was influenced by the tensile properties and detailing of the specimens.

The current ultimate limit criteria and theoretical approach to ultimate load prediction in catenary response have been critically reviewed using results obtained in testing. The findings have been implemented in an analytical study of collapse resistance by ultimate catenary response. A series of exemplar floor systems, of different size and detailing arrangements have been examined. The conclusions presented indicate that safe load redistribution by catenary action is dependent on the area of the unsupported structural bays and the area of the bottom reinforcement specified at or across structural connections, for which design parameters such as moment redistribution, detailing rules and tie force requirements are governing factors.

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