ABSTRACT
In all types of reinforced-concrete members there are situations where the ends of steel reinforcing acting in tension must be bent into hooks or cogs to provide additional anchorage over a short distance. The values of minimum bending radius and straight extension length beyond the bend of hooks and cogs are specified in the Concrete Structures Standard AS 3600 and vary depending on the application and the type of reinforcement. For example, hooks on stirrups in beams must have a longer straight extension than on column ligatures of the same diameter, while fitments made from wire may be bent around smaller diameter pins than bars. In AS 3600, reference is also made to a standard hook which confusingly can be a hook or a cog that cannot be used in all applications. Furthermore, the capacity of shear reinforcement (fitments) is reduced by 20 percent when anchored in the tensile region of the cross-section.
A detailed review into the requirements for hooks and cogs in reinforced-concrete members has been carried out at the University of Western Sydney in order to arrive at standard details suitable for all applications. The program has included several series of pull-out tests which have been performed to examine the influence that important variables have on the anchorage strength of bars and wires with different hook and cog details in different applications. The main variables investigated have been bar type, bar diameter, radius of bend, straight extension length, trimmer bar diameter, concrete cover and concrete compressive strength. In this paper the experimental investigation of hooks and cogs in tensile zones are presented, with a particular emphasis on the effects of the tensile region on the anchorage of the reinforcement.
