Load Bearing Behaviour of Plastic Anchors in Cracked Concrete

Plastic anchors consist of a plastic sleeve and a steel expansion element. The expansion element is screwed or hammered into the plastic sleeve. This impresses a radial strain on the plastic.

The visco-elastic deformation behaviour of the plastic strongly influences the load bearing behaviour of plastic anchors in cracked and uncracked concrete. In uncracked concrete, the expansion forces of plastic anchors in concrete decrease with time due to relaxation of the plastic. A crack running through the centre of the drilled hole of a plastic anchor further reduces the expansion force of the anchor. However, if the crack width stays constant, the expansion force increases with time after cracking. The coefficient of friction between plastic sleeve and concrete increases in cracked and uncracked concrete with time. Hence the pullout failure loads of plastic anchors also increase in cracked and uncracked concrete with time.