This paper describes tests on specimens in which prestress into the transverse reinforcement of a reinforced concrete column was introduced. Tests on specimens in which prestress was not introduced were performed for comparison of shear strength. In reinforced concrete structures, the columns which are subjected to axial force develop a three-dimensional compressive stress condition, if it is possible to confine the core concrete laterally by introducing prestress transverse reinforcement, and it is considered that the compressive strength is improved by this method. Hence, it is also possible to laterally introduce prestress into existing columns. Therefore, the idea is considered as a new and effective method for strengthening a column. From the shearing test of reinforced concrete short columns in which prestress is added to the transverse reinforcement, the following facts are indicated. (1) The prestress introduced into the transverse reinforcement is a very effective method for improving the shear strength. (2) It is possible to improve the shear strength by increase of the transverse reinforcement quantity, when prestress was introduced into the transverse reinforcement. (3) It is found theoretically that the formula of evaluation, known as the New RC Formula, for shear strength derived for concrete and reinforcement with high strength is agreed well with the experimental results of shear tests.
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