Synopsis The paper reports punching tests on 28 reinforced concrete slabs. The tests were divided into five series primarily concerned with the effects of the arrangement of flexural reinforcement, absolute size or depth, concrete strength and ratio of reinforcement, boundary restraint and the size of the loaded area. The results are compared with the predictions of four Codes of Practice-BS 8110, CP 110, ACI 318-83 and the CEB-FIP Model Code. In regard to BS 8110 it is demonstrated that the Code generally gives a small scatter of the ratio of calculated and experimental strengths, although its method of defining the ratio of flexural reinforcement is inferior to that of CP 110. It is also shown that BS 8110 does not achieve the level of safety intended in the definition of characteristic strength. If the ddefinition of the ratio of reinforcement were improved, the intended level of safety could be attained by a 10% reduction in either the basic shear stress or the size factor ξS.
Fifteen tests on high strength concrete slabs with rectangular supports and three different load patterns are reported. The results show that current code preovisions can overestimate punching resistance in some cases. An investigation, made using the finite element method, shows the influences of the shape of a support and the pattern of loading on the distribution of shear. Factors are proposed to allow for these effects while using the control perimeter and basic shear resistance of the CEB Model Code 90, and it is demonstrated that this approach provides strength estimates better than those of MC 90, BS 8110 and ACI 318. There remains a problem of the punching capacity of slabs almost failing in flexure and this is discussed.
The paper reports tests designed to study the improvement in the post-punching resistance of slab–column connections by the provision of bottom bars passing through the columns and anchored in the slab. A series of model tests on slabs was used to developan expression for the strength limit governed by the slab concrete, while large-scale tests on abbreviated specimens were used to formulate the criterion dependent on the failure of the reinforcement. It is demonstrated that bottom reinforcement can be of significant benefit and that the resistance given by it can be assessed with reasonable accuracy.
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