Authors

Abstract

This study presents experimental and theoretical investigation of the overall shear behavior of reinforced concrete deep beams made from hybrid concrete strength : Normal strength concrete (NSC) in tension zone and high strength concrete (HSC) in compression zone. The experimental work included testing of nine models of hybrid reinforced concrete deep beams under the effect of two point loads. One of the beams was tested as pilot and the other eight beams were divided into two groups namely group (A) and group (B) to study the effects of the following parameters: (HSC) the layer thickness, the effect of presence of web reinforcement and method of casting (i.e. monolithically or at different times), on the ultimate shear strength, the cracking load, the cracking pattern, the deflection, the ductility and failure modes.
The experimental test results obtained from the adopted hybridization technique of (HSC) and (NSC) have shown that for beams made from (HSC) (about 45MPa) with a layer in compression zone of thickness (25 - 50)% of total beam depth, the ultimate shear strength was increased about (11.2 - 19.5)% for beams without web reinforcement and (16.75 - 22.25)% for beams with minimum web reinforcement. It has also shown that, the first cracking load was increased about (32.8 - 48)% and (43.4 - 57.9)% for beams without and with web reinforcement, respectively.
The hybrid concrete beams that cast monolithically, have exhibited an increase in ductility about (13.3- 22.6) % and (17.3 - 26.3) % for specimens without and with web reinforcement, respectively. While, the hybrid concrete beams with construction joint and epoxy resin layer of thickness about (1mm), have exhibited larger increasing in ductility about (28.7%) and (30.2%) for specimens without and with web reinforcement, respectively.
On the other hand, a non-linear three dimensional finite elements simulation using ANSYS computer program was adopted to trace the load-deflection response, cracking pattern and ultimate shear strength of the tested reinforced hybrid concrete beams with or without construction joint. Afterward, a parametric study has been conducted to investigate the effects of many important variables (compression strength for (HSC) layer, thickness of (HSC) layer, shear span to effective depth ratio ( ), thickness of resin bond layer).
Comparison between the analytical and experimental results has shown a reasonable agreement of the load-deflection response, where, the average of the maximum difference in first cracking a