In conventional reinforced concrete design, end anchorage between reinforcing steel elements and concrete is achieved by means of hooked ends to the reinforcement. In critical structures, or in situations where the level of reinforcement is high, it may not be possible to incorporate hooked ends, and in such situations, headed anchors are often used. These transfer anchorage loads into the concrete by means of a steel plate, which is fixed mechanically to the end of the reinforcing steel.
Headed anchors come in many proprietary systems, which vary in the way in which the head is attached to the reinforcing steel. This may for example be by a threaded connection, a friction weld, a hot forged head or a swaged connection. R-Tech has experience of testing all of these systems.
Although they have been in use for many years, particularly in the USA, their use in the UK is starting to increase, driven in particular by their use in the new nuclear construction programme. The requirements for headed anchors have been incorporated into the Sellafield Engineering Standard ES_0_3110_2, within which headed anchors are subject to the full range of tests normally applied to mechanical couplers. R-Tech is able to conduct the full range of tests on headed anchors specified by the Sellafield standard, which also forms the basis for the CARES approval scheme for headed anchors.
The international standard ISO 15698 Part 1 (requirements) and Part 2 (test methods) were published in 2012. Although not adopted as British Standards, these form the basis for the general specification and testing of headed anchors in the UK. Routine tests involve a standard tensile test, and a wedge tensile test. In the standard tensile test, the head of the anchor has to be supported by a plate with a hole of defined dimensions through which the bar passes. R-Tech has designed and built a purpose-made rig for testing of headed anchors, which can test all sizes up to 40mm diameter. In the wedge tensile test, a wedge is used to apply the load along the bar with an intentional misalignment to the plane of the anchor head. Again, R-Tech has a purpose-designed system for conducting these wedge tensile tests.