Dowel action and shear strength contribution of high strength rebar embedded in ultra-high performance fiber reinforced concrete

The influence of dowel action is usually ignored during normal reinforced concrete beam designs since vertical shear reinforcing bars always offer significant shear resistance. However, for ultra-high performance concrete (UHPC) beams without shear reinforcement, the dowel action contribution to the shear strength becomes considerable and is important in assuring a non-brittle type of shear failure. The embedded longitudinal rebar transfers the shear force by concrete core bearing and UHPC support in tension on alternate sides of the shear crack. A series of notched UHPC dowel specimens were tested to verify the contribution from dowel action. The interfacial bond between UHPC and rebar was eliminated by covering plastic tubes on the embedded rebar. Important dowel action contribution parameters were obtained and the load versus displacement curves were used to calibrate beam on elastic foundation (BEF) and beam on nonlinear foundation (BNF) theoretical models. The experimental and analytical estimates of the peak dowel force are compared with existing equations calibrated for normal strength concrete.