Abstract
This paper reports experimental data on the behavior and strength of high-strength concrete deep beams reinforced with shear reinforcement. Tests were conducted on eight reinforced concrete deep beams with stirrups in different type and positions using high-strength concrete (compressive strength of about 85.0 MPa). The beams measured 1400 mm long, 100 mm wide and 300 mm deep, and were tested under two point loads. The test variables were type and position of web reinforcements [Shear stress of vertical stirrups (vfy), Shear stress of horizontal stirrups (hfy) and Shear stress of inclined stirrups (αfy)] within shear span, within middle span(between two point loads) and along the beam. Conventional steel bars were used as longitudinal reinforcement in this investigation. The test results indicated that beams with vertical and inclined shear reinforcement within the shear span (B4) resisting the ultimate load of about 417.90kN. While beams with horizontal shear reinforcement (B3), shear reinforcement between two point loads (B7), and the beam without shear reinforcement (B8) resisting, 255.77, 260.18 and 250.55kN respectively. All the beams failed in shear and the optimum position of stirrups is the shear span for high strength concrete deep beams and with combination of vertical and inclined stirrups. Keywords: Concrete; Deep beams; High strength; Position; Shear; Stirrups.
Highlights
Deep beams are defined as members loaded on one face and supported on the opposite face, so that compression struts can develop between the loads and the supports
The results showed that the horizontal stirrups has little influence on the magnitude of failure load and the researcher proposed imperical equations for estimatingthe shear strength of deep beams and compared with several codes and works of investigators, the result of comparison of 244 high and normal strength concret deep beams with stirrups showed lowest standar deviation, COV and conservatives predictions for the proposed equations
All the beams were failed in shear – compression or shear tension according to the following sequence: 1- Vertical shear-flexural cracks formed at the shear span. 2- The crack propagation continued towards the point load, approaching the compression zone
Summary
Deep beams are defined as members loaded on one face and supported on the opposite face, so that compression struts can develop between the loads and the supports. The results of the investigation show that the design methods given ACI 318 generally conservative for deep beams fabricated with high-strength concrete. Beams and compared with several codes and works of investigators, the result of comparison of 244 high and normal strength concret deep beams with stirrups showed lowest standar deviation, COV and conservatives predictions for the proposed equations. Eleven girders were cast and tested to predict the first diagonal crack and ultimate shear load of reinforced girder made of ultra-high performance fiber reinforced concrete (UHPFRC) in which eight girders failed in shear. These higher dowel forces, together with the highly concentrated bond stresses in HSC beams, result in higher bond-splitting stresses where the shear cracks cross the longitudinal tension bars These combined effects can lead to brittle shear failures for beams without shear reinforcement within shear span [8, 9]. The minimum shear reinforcement is required to provide somewhat ductile behavior prior to failure [1, 10]
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