Tensile Strength of Concrete for Design
The tensile strength of concrete is a very important parameter that is considered in the design. It can make a significant impact on other strengths of the structural element in flexure as it is about 10% of concrete compressive strength.
In this article, we are concentrating on the background and methods of evaluating the tensile strength of concrete.
What is the Tensile Strength of Concrete?
Concrete element subjected to pure tension or combined effect of compression and tension. A concrete column used to hag a floor can be considered as an example of pure tension.
A concrete beam subjected to bending action has the tensile and compressive stresses in the same section. However, consideration of the tensile strength of the concrete in flexural design is minimal as the section could crack and lose its stiffness provided by the tensile capacity of the concrete.
However, in prestress designs, tensile strength is considered for the desing. It incorporates the certain value of the tensile capacity of concrete to the design.
Why Tensile Strenth of Concrete is Important?
As discussed above, we consider the tensile strength for the desing to get the best of the concrete. If we can consider it, it is a fairly large value that can contribute to the design.
However, in most cases, we can not consider the tensile strength as when it cracks, it loses the stiffness provided by the tensile strength.
In post-tension and pretension beam design, we consider the tensile strength to improve the structural capacity. According to BS 8110, there are three strength classes for prestress designs.
The following table indicates the allowable tensile stressed considering the cracking of concrete. The allowances are made considering the durability of concrete too.
In addition, tensile strength is the dominant factor in crack control. Tensile strength is one of the important factors that can contribute to avoiding cracks.
How to Find the Tensil Strength of Concrete?
There is the empirical method proposed by different researchers to find the tensile strength and the values to be considered for the design.
In this article, we are concentrating on the values given in the different standards.
- BS 8110 Part 01 1997
Code specifies the tensile strength criteria for post-tension ad pretension members.
- Eurocode 2
Table 3.1 indicates the tensile strength of concrete for each grade of concrete and an equation has been given to calculate it depending on its compressive strength.
Here, fck denotes the cylinder strength, fck denotes the cube strength and fctm denotes the tensile strength of concrete.
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