دراسة سلوك القص في العتبات العميقة الهجينة المتكونة من خرسانة المساحيق الفعالة وخرسانة الاعتيادية المقاومة

Shear Behavior of Hybrid Deep Beams with Reactive Powder and Normal Strength Concrete

The main aim of the present research was to study the usefulness of the use of hybridization technique in the deep beam by investigation the shear behavior of reinforced concrete deep beams with hybrid cross-section containing two different types of concrete, reactive powder concrete (RPC) and normal strength concrete (NSC) experimentally and numerically.

    The experimental program included testing of eight simply supported reinforced concrete deep beams under the effect of symmetrical concentrated two-point load. The dimensions of all beams are (150 × 300 × 800) mm. The specimens were divided into four groups: group (A) normal beam, group (B) hybrid beam with RPC (75 mm in tension region), group (C) hybrid beam with RPC (75 mm in compression region), and group (D) hybrid beam with RPC (125mm in tension region), to study the effect of: Shear span / total depth (a / h= 2/3 and 1.25/3), the thickness of the RPC layer (75 and 125) mm, and the location of the RPC layer (tension or compression region) on the first cracking load and ultimate load, load-vertical midspan deflection, and type of failure. The experimental results showed that the use of hybridization technique improved the behavior of the deep beams and increase in the first crack and ultimate loads, the largest increase in first crack and ultimate loads about (17.8 and 54) %, respectively when RPC (125 mm) in tension region with compared with the normal strength concrete deep beam. The ultimate load of the hybrid deep beam with RPC layer in tension region is greater than the hybrid deep beam with RPC in the compression region about (6.7 and 28.7) % when (a/h= 2/3 and 1.25/3) respectively. Also, the first crack and ultimate loads increased with increasing the thickness of RPC layer about (2.4 and 8.6) %, respectively at (a/h=1.25/3). The load-midspan deflection behavior in deep beams was more ductility with increased (a/h), the load-vertical midspan deflection in hybrid deep beams is stiffer than the normal deep beams, the load-vertical midspan deflection in hybrid deep beams was stiffer with increased thickness of RPC layer. The best behavior of the load-vertical midspan deflection curve was in the hybrid deep beam with RPC (125 mm in tension region) and (a / h=1.25/3). The ultimate loads increased with decreasing (a/h) about (21.5, 27.4, 5.6, and 22.6) % in groups (A, B, C, and D) respectively, but the negligible effect of the a/h on first cracking load.

    The numerical part included the use of the Finite Element Method (FEM) to simulate the specimen’s behavior and improving the search by adding more variables. Analysis conducted with (ANSYS-2016- R 17.2) showed an acceptable agreement between the experimental and the numerical results. The experimental ultimate loads to the numerical ultimate loads were between (0.19 – 6.67) %.