High strength concrete continuous deep beams - With web reinforcement and shear-span variations

Tests under two-point loads were carried out to destruction on 12 reinforced concrete two-span continuous deep beams. The beams were tested for two shear-span/depth ratios of 0.45 and 0.24 giving clear shear-span/depth ratio of 0.21 and 0.00 respectively. Various arrangements of web reinforcement were used such as minimum and maximum vertical bars, minimum and maximum horizontal bars and minimum and maximum inclined bars. Sagging and hogging tensile steel was used in accordance with the shallow beam bending moment distribution and was kept constant for all the beams. The results of the present tests are compared with those of the moderately deep beams reported in the litterature by Rogowsky et al. and with the two-beam tests of Leonhardth and Walther. The present tests show that the current codes and design manuals covering continuous deep beams could lead to severe cracking and may be unsafe for this type of structural members. The actual bending moment distribution is completely different from that recommended by these documents, with moments at spans higher and those at internal supports lower. The tests also showed that the CIRIA guide may be too tolerant and hence unsafe towards bearing failure which, in the presence of an effective pattern of web reinforcement, is the dominant type of failure of reinforced concrete continuous deep beams.