Experimental Study On Whole Stress-Strain Curves Of Concrete Under Axial Tension

Concrete is a brittle material with high compressive strength and low tensile strength, With the increase of compressive strength, they are more prominent and the study on the tensile performance of concrete become increasingly important. The stress-strain entire curve of concrete in direct tension can reflect the tensile performance greatly, however, no reasonable test method for direct tension is available to appraise the tensile performance of concrete sciencely yet, and seriously has restricted the research about the tensile performance of concrete and its modification. In view of this question, Comparisons to the merits and defects of different test methods used by researchers, a new test method for obtaining the stress-strain entire curve in direct tension is developed in this paper, mean-while the characteristic parameters for describing stress-strain curve in direct tension and the tensile properties of different types of concrete are studied. The main results from the tests are as follows:(1) The test method used in this paper can arrive both tensile strength and stress -strain entire curve of concrete in direct tension. The test method is simple and reasonable for aniaxial tensile test of concrete.(2)The test method used in this paper can enhance the experimental success ratio. The test method installs four same electronic extensometer on the concrete specimen, takes the reaction control signal by the deformation of entire length of specimen, can guarantee the break position to occur in the gauging scale distance scope.(3)The stress-strain entire curve in direct tension can comprehensively reflect the tensile performance of concrete. Many characteristic points and the characteristic parameter can be determined from the stress-strain entire curve of concrete, including peak strength and peak strain, first crack strength and first crack strain, elasticity modulus, toughness index, fracture energy.(4) The conventional method for determining the first crack point of concrete in direct tension is greatly dependent on the judgment of idvidual.The method"Threshold of Linear Variation"developed in this paper, which can be used to determine the first crack point of concrete specimen by computer automatically, is relatively reasonable and accurate. The results show, this method is effective. Compared the method"Sudden Reduction of Linearly Related Coefficient",when the threshold is 3%,the result is basically consistent.