Why the tensile strength of concrete is called modulus of ru

Why the tensile strength of concrete is called “modulus of rupture”? What is the empirical formula that the ACI 318 code provides to estimate the modulus of rupture based on fc’? How small is the tensile strength of a NW fc’=4000 psi concrete in comparison with its compressive strength (percentage)?

Solution

Concrete is weak in tension, so deciding factor of concrete being failed is its tensile strength so it is being called modulus of rupture.(strength after which cracks will develop in concrete due to loads).

Modulus of rupture as per ACI 318,

fr = 7.5??fc\'

for fc\'=4000

taking ?=1

fr = 7.5?4000 = 474.34 psi.

percentage of compressive strength =(474.34/4000)*100 = 11.85%

It is only 11.85 % of compressive strength.