Concrete is typically not intended to withstand direct tension. However, concrete members can experience tensile stresses due to factors such as flexure, shrinkage, and changes in temperature. Additionally, multi-axial states of stress can lead to principal tensile stresses. When the tensile strength of concrete surpasses its limit, cracking may occur.
Pure shear in concrete can create tension on diagonal planes, which means that understanding the direct tensile strength of concrete is helpful for approximating the shear strength of beams that lack reinforced webs, among other applications. Additionally, knowledge of the flexural tensile strength of concrete is necessary for determining the moment at first crack in order to calculate deflections and crack widths in flexural members.
Concrete exhibits a low resistance to tension, with its direct tensile strength ranging between 7 to 15 percent of its compressive strength. Testing the direct tensile strength of concrete is challenging, as it necessitates the application of a purely axial tensile force, which is free of any misalignment or secondary stress in the specimen at the grips of the testing machine. Consequently, indirect tension tests are commonly performed to determine the direct tensile strength of concrete, usually by means of the flexure test or the cylinder splitting test.
Stress-Strain Curve of Concrete in Tension
The failure strain of concrete in uniaxial tension is relatively low, typically ranging from 0.0001 to 0.0002. When subjected to tension, the stress-strain curve of concrete is typically approximated as a straight line from the origin to the point of failure. It is worth noting that the modulus of elasticity in tension is generally considered to be the same as that in compression.
Due to the fact that concrete has a very low tensile strength, its tensile stress-strain relation is often disregarded in the design process, making it of little practical value. As a result, other factors such as compressive strength and durability are given more consideration. Nonetheless, understanding the properties of concrete under tension remains important for the overall understanding of its behavior and performance. Despite its shortcomings in tension, concrete is still widely used as a construction material due to its many desirable properties, such as its high compressive strength and ability to resist fire and extreme weather conditions.