Optimum Depth of a Lower Concrete Grade at the Tension Zone in a Two-Layer Reinforced Concrete Beam
Keywords:
Optimum depth, Two-layer RC beam, Load carrying Capacity, Stiffness, Bending capacityAbstract
This paper presents the results of an investigation into the optimum depth of the lower concrete grade (LCG) at the tension region in a two-layer reinforced concrete beam. A total of nine (9) simply supported two-layer RC beams (1100 x100 x150 mm) were studied. Two 8 mm and two 6 mm diameter rods were used as reinforcement at the bottom and top of each two-layer beam, respectively. The beam samples were grouped into two: the first group comprises two-layer RC beams produced with 1:2:4 as the higher grade and 1:3:6 as the lower grade; the
second group comprises two-layer RC beams cast with 1:2:4 as the higher grade and 1:4:8 as the lower grade. The depth of LCG adopted for each group is 25 mm to 100 mm at a step of 25 mm out of the total beam depth of 150 mm. The beams were subjected to two-point static loading to evaluate the load resistance and deflection. The results show that the greater the depth of the layer under compression, the stiffer the beam. The two-layer RC beam has an
equal loading carrying capacity as the beam made entirely of higher grade. The depth of the layer of RC beam under tension in two-layer beams should be kept between 40 and 50% of the overall beam depth, which would be desirable structurally.
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