This study evaluates the size effect of shear strength in reinforced concrete (RC) beams with various replacement ratios of recycled coarse aggregate. A total of 15 simply supported specimens with recycled aggregates were cast and tested in shear. The test variables were designed to be the width and effective depth of the beam and the replacement ratio of recycled coarse aggregate. The width of the specimens was varied from 200 mm to 400 mm, and the effective depth was changed from 300 mm to 600 mm. To estimate the size effect of shear strength in recycled aggregate concrete beams, the specimens had no shear reinforcement. The experimental results showed that the shear strength of the specimens made of recycled aggregate decreased with a higher effective depth irrespective of the replacement ratio, whereas the beam width exhibited no size effect. Furthermore, the strength reduction and crack patterns of the specimens with recycled aggregates were similar to those of the specimens with natural aggregates.
It is well known that shear stress at peak of reinforced concrete beams decreases with increasing effective depth. Thus, several existing design codes and models have included various forms of formulas considering the size effect on shear strength of reinforced concrete beams; however, past experimental researches show that tension reinforcement ratio is also associated with the shear strength of reinforced concrete beams. To examine the effect of tension reinforcement ratio and effective depth on shear strength of reinforced concrete beams, this study has conducted experiments in which the effective depth (150, 300, 500, and 780 mm) and tension reinforcement ratio (1%, 2%, and 3%) are employed as variables. Besides, a formula for the shear strength considering both variables is proposed based on data samples collected from the present experiment and previous research. The proposed formula gives predictions comparable to the results of existing shear tests. Furthermore, rational predictions are made for effective depth of beams, compressive strength of concrete, shear span-to-depth ratio, and even tension reinforcement ratio exceeding 3%.
The shear strength of concrete beams without shear reinforcement is determined by the shear strength of the concrete compressive zone, the shear force due to dowel action, and the shear force due to aggregate interlock. The existing models and formulas to predict shear strength of concrete beams based on geometric theories related to beam action and arch action that only consider shear resistance in relation to arch action while neglecting dowel action and aggregate interlock have been unable to accurately explain the shear resistance mechanism. This study proposes a more rational shear strength prediction formula that reflects the contribution of each component by linking the bond characteristics of longitudinal reinforcements based on the size effect and stress changes in longitudinal reinforcement to dowel action. The precision of the proposed formula was assessed by carrying out experiments with the shear-span-to-depth ratio (a/d = 2.0, 2.5, 3.0, and 4.0) as a variable. A ratio of shear bond failure distance to effective depth and the shear strength of concrete beams without shear reinforcement were compared to those obtained from the proposed prediction formula. As a result, it was confirmed that the proposed formula gives rational predictions for each shear contribution and exhibits a high accuracy compared to previous experimental results.
This study evaluates the flexural performance of precast concrete beams using ground granulated blastfurnace slag. A total of four specimens with various replacement ratios of ground granulated blast-furnace slag are cast and tested in flexure. The specimens under four-point loading had a shear span-to-depth ratio of 4 and a rectangular section with a width of 200 mm and an effective depth of 300 mm. It can be shown from experimental results that the specimens with ground granulated blast-furnace slag had a similar flexural performance to the specimen with natural aggregates, regardless of the replacement ratios of ground granulated blast-furnace slag.
This study evaluates the shear performance of precast beams with ground granulated blast furnace slag. A total of four specimens according to replacement ratio of ground granulated blast furnace slag. The specimens under three loading points had a shear span-to-depth ratio of 2.5, and a rectangular section with a width of 200mm and a effect depth of 300 mm. In this study, existing equations were used for predicting the shear strength of the specimens. The shear strength by existing equations was compared with those of 89 reinforced concrete beams without shear reinforcement. It can be shown from experimental results that all specimens with ground granulated blast furnace slag showed a similar shear strength as compared with the specimen with portland cements alone.
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