Question

$\text{Assertion (A):}$ The stress block used in the limit state design method is obtained by testing of concrete cylinder under uniform rate of strain.
$\text{Reason (R)}:$ If a uniform rate of strain is not adopted it is not possible to obtain the descending portion of stress and strain curve beyond maximum stress.

• A. both A and R are true and R is the correct explanation of A
• B. both A and R are true but R is not a correct explanation of A
• C. A is true but R is false
• D. A is false but R is true

Answer 1

The correct option is D A is false but R is true

The stress-strain curve of concrete is obtained by testing of cubes under uniform rate of strain. Although it can also be conducted on cylindrical specimen.
The stress-strain curve for concrete (tested by cubes) is very complicated. The IS code has idealized it for design purposes. This is referred to as short term static design stress-strain curve of concrete.
In order to account for difference in strength indicated by a cube test and strength of concrete in structure is taken 0.67 times the characteristic strength. The partial safety factor of 1.5 is applied in addition to this.