Comparison of slab failure loads by the yield line method

Abstract

The Yield Line Method was used to investigate the ultimate load capacity of restrained, uniformly-loaded, two-way spanning, rectangular, reinforced concrete slabs, supported on four sides. The basics of the method, which can be implemented using either equations of equilibrium or virtual work equations, were briefly reviewed and used to derive the bending moment and shear coefficients for each case investigated. Said coefficients were compared to those presented in the British Standard. At failure, the basic yield line pattern for the said slabs was expressed in two modes. The exact yield line pattern of each mode was found to depend on the slab boundary conditions; the aspect ratio of the slab and the coefficient of orthotropy. The Yield Line Method was used to design new slabs, by the Minimum-Weight Method, as well as to verify the ultimate load capacity and load distribution on rigid supports, of existing slabs, with areas of reinforcement different from those suggested in the design codes. The latter was also correlated to laterally-loaded wall panels. Even though serviceability checks need to be carried out separately, the derived results by the Yield Line Method were compared and found to be similar to those achieved by: slab testing results (quoted from Johansen's Dissertation); Finite Element Analysis; Elastic Method; slab design according to SS 8110-1-1997 and wall design according to EC6. The graphical representation of results can assist the designer in obtaining an economical reinforcement distribution in design and in determining the failure loads of existing slabs or wall panels. Results encourage further analysis to be carried out for other slab configurations and load arrangements.