oa Civil Engineer in South Africa - The strength of large concrete blocks subjected to concentrated loads



Concrete blocks, 800 mm x 600 mm x 600 mm in size, reinforced with grids or coils, as well as unreinforced blocks, were loaded through a bearing plate either 100 mm x 200 mm or 200 mm square in area. The ultimate bearing stress of unreinforced blocks was less than has been found in previous investigations using small specimens.

Coil reinforcement required the smallest proportion of steel to give the highest ultimate bearing stress. Some of the grid arrangements, however, gave better resistance to cracking. Grid reinforcement appeared to be less sensitive than coil reinforcement to eccentricity of load.
Those codes of practice in which the permissible bearing stress is related to the ratio of loaded to effective area may be unsafe for unreinforced concrete at levels of this ratio of about 0,1 or less.


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