Spalling reinforcement for pre stressing works in anchor blocks

Reinforcement of anchor blocks in prestressing works usuallycomprises equilibrium reinforcement, bursting reinforcement and spalling reinforcement. Bursting reinforcement is used where tensile stresses are induced throughout pre-stressingoperation and maximum bursting stress takes place where stress trajectories are concave towardsthe line of action of the load. Reinforcement is required to resist these lateral tensile forces. For equilibrium reinforcement, it is needed where there are many anchorages in that pre-stressing loads are applied sequentially.

During pre-stressing, spalling stresses are produced in the region behind loaded faces of anchor blocks. At the zone between two anchorages, there is a volume of concrete surrounded by compressive stress trajectories. Forces are induced in opposite direction to applied forces and it forces the concrete out of the anchor block. Instead spalling stresses are set up because of the strain compatibility relating to the effect of Poisson's ratio.