The rigid-plastic yield-line analysis of isotropic slabs under uniformly distributed loading is achieved by a linear programming formulation. This technique requires the investigation of a triangulated meshing of the slab, the sides of which are treated as potential yield-lines. The analysis is extended to consider the geometric variation of chosen yield-line patterns by the technique of sequenJia1 linear programming. A strategy is developed whereby critical yield-line patterns may be established by initial consideration of a fine-mesh arrangement, which is not subjected to geometrical optimisation. The critical geometry is subsequently established by consideration of a simplified net which is representative of the critical yield-line pattern determined initially. The procedure represents a systematic approach to the determination of critical collapse modes. Although not formally guaranteed to achieve correct mechanisms, the suggested strategy is unlikely to produce solutions which deviate substantially from the critical. David Johnson
The Hong Kong Housing Authority is responsible for housing alrnost 3M people in over 1500 multistorey reinforced-concrete buildings. It is also responsible for the construction and maintenance of a number of 'flatted factories' that provide employment for public-housing tenants. In the mid-1980s, deficiencies in concrete strength, giving rise to serious concerns over structural adequacy, came to light in a number of domestic and industrial buildings which had been constructed during the late 1960s and early 1970s. This paper describes how these deficiencies were remedied by strengthening techniques developed against a background of social considerations and practical constraints. P.R. Ainsworth, R. Crane, G.G. Payne and R.A.M. Watkins