Civil Engineering Association

Design of Anchor Reinforcement for Seismic Shear Loads

Existing design codes recommend hairpins and surface reinforcement
consisting of hooked bars encasing an edge reinforcement
to improve the behavior of anchor connections in shear. Concrete
breakout is assumed to occur before anchor reinforcement takes
effect in the current design methods. This paper presents an alternative
design method for anchor shear reinforcement. The proposed
anchor shear reinforcement consists of a group of closed stirrups
proportioned to resist the code-specified anchor steel capacity in
shear and placed within a distance from the anchor bolt equal to
the front-edge distance. Steel fracture was achieved in the tests of
twenty 25 mm (1 in.) reinforced anchors with a front-edge distance
of 152 mm (6 in.). Meanwhile, the observed anchor capacities
were smaller than the code-specified anchor steel capacity in
shear because concrete cover spalling caused combined bending
and shear action in the anchor bolts. Reinforcing bars are needed
along all concrete surfaces to minimize concrete damage in front
of reinforced anchors for consistent seismic behavior in shear.