Shear resistance at normal and high temperatures of reinforced concrete members with links and central bars
This report, in its earlier part, reviews some important aspects of research and development in the design of reinforced concrete members against shear. This review includes a study of the background of design method for shear resistance given in the British Standard code of practice and a comparison of this method with the methods recommended by the Eurocode and the American code of practice for concrete structures. Based on this study, the contributions to shear resistance of a member afforded by concrete, the tension steel and the links are identified. The influence of these constituents on the modes of transfer of shear has been investigated, in order to examine the method for estimating the overall shear resistance of the member. A test programme is reported, concerning horizontal steel at the centre of the cross-section as an alternative form of shear reinforcement. Tests on some fifty beam specimens were carried out, allowing for variation in the main parameters; for example, the span of beams, the strength of concrete and the amount of tension steel. Also, some beams did not have any shear reinforcement and some were provided with central bars, some with links and some with the combination of central bar and links. A design method has been derived on the basis of these tests, for estimating the contribution of central steel to the shear resistance of beams. This method has been verified with the help of measurement of stresses in the web steel, using strain gauges fixed on the reinforcement of two of the test beams. A similar design method is proposed for using central steel to enhance the punching shear resistance of slabs, based on the results of tests on fifteen slab specimens, allowing for variations in thickness of slabs, the strength of concrete and the amount of central steel. The design methods for beams and slabs have been examined with the help of a finite element computer program capable of using the non-linear properties of structural materials. Finally, the normal temperature design rules for beams have been modified and a method is proposed for design of beams exposed to high temperatures. This method has been verified on the basis of fire exposure tests on ten beam specimens provided with differing amount and type of web steel and with gauges for measurement of temperatures inside, the beams.