SHEAR STRENGTH OF CONCRETE EMBEDDED BEAMS AND HOLLOW BLOCK SLABS

In Egypt, it is a common practice to utilize floor systems consisting of hollow block
slabs resting on embedded beams having the same depth. For the embedded
beams and the hollow block slabs, the current Egyptian Code requires that the shear
resistance to be solely provided by concrete with no dependence on any form of
shear reinforcement. Four international code requirements were reviewed and no
similar provisions were found. In this paper, the shear strength of embedded beams
and hollow block slabs with intermediate length (shear span-to-depth ratio of
approximately 5) is evaluated. Nine medium-scale simply-supported conventionally
reinforced concrete embedded beams and five full-scale hollow block one way slabs
with normal concrete strength subjected to three-point monotonic loading were
experimentally loaded to failure. The specimens were typically proportioned so that
shear failure would preclude flexural failure. The study examines the shear strength
of the tested specimens with special emphasize on the effect of shear reinforcement
in the form of vertical stirrups with varying shapes, configuration, and amount.
During testing, deflections, strains in main reinforcement, concrete, and stirrups were
monitored. Recorded capacities of specimens with shear reinforcement reached as
high as 300% of those without shear reinforcement. Laboratory recorded shear
strengths at failure are compared with theoretical strengths calculated according to
the current Egyptian Code procedures and the reviewed international codes.
Further, the shear capacity of tested specimens was assessed in the light of the
modified compression field theory. Test results clearly demonstrated that the shear
reinforcement significantly improved the shear capacity and enhanced the ductility of
the tested specimens. As such, the study concludes that the vertical stirrups are
effective as shear reinforcement in embedded beams and in one-way hollow block
slabs. A simplified empirical formula for predicting the shear strength of such
elements is also proposed based on the Egyptian Code provisions.