City Research Online

Abstract

Reinforced concrete beams supporting plain or reinforced brickwork walls act compositely with them to exhibit a structural action similar to that of a tied arch. The stress distribution is very different to that of conventional beams, the shear and direct stresses over the supports being greater while the bending stress in the central regions of the beam is reduced. The supporting beam, sometimes referred to as the base of the overall composite beam, acts as a tie in extreme cases and is under tension.

Two theoretical methods of analysis and design which take account of composite action are presented. The first method, based on elastic material properties, identifies a distribution of shear and direct stresses at the interface of the wall and the base. Expressions for direct and shear stresses as well as bending stress are provided for the wall and the base. The distribution of all these stresses depends on a number of parameters including the flexural and axial stiffnesses of the wall and the supporting base, the overall span to depth ratio and the tensile/shear reinforcement. The second method assumes shear failure to be critical. A collapse mechanism is assumed and the structure is designed to ensure that the stresses remain within the bounds suggested by relevant building standards.

Seven full scale composite beams were prepared in the laboratory. These were uniformly loaded at the top and the resultant deflections and strains were recorded. The strain intensity and pattern of cracking was plotted at each stage using GINO-GRAF package on a mainframe computer. The test results were used to validate the stress distribution and the effect of different parameters identified in the theory. A comparison of the test results with the theory confirms the applicability of the theory to composite beams. The results highlight the positive effect of composite structural action on load bearing capacity of these beams and the role of shear mesh in ensuring such action. The need for further research to determine more accurately some of the parameters involved is also stressed.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Departments:	School of Science & Technology > Engineering > Civil Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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