Question

What is the relationship between the flexural tensile strength and the compressive strength? Do your results fit this relationship? Show the relationship mathematically. Why are the results discarded if the fracture occurs beyond the middle third of the span by more than 5% of the span length

Answer 1

Different code books give different relationships. So it depends on the code book followed in your country.

ft =0.7(fck)^0.5  as per IS476 where ft= tensile strength and fck= compressive strengh

But the relation may vary as per code followed in your country.

The reason for rejecting samples where fracture occurs beyond middle third of the span by more than 5% of the span length is that the load is applied at 1/3rd of span length from each side and thus the bending moment is maximum and constant in the middle one third portion. The stress caused by bending in maximum in middle third portion of span so the failure location should be in that range only. If not it means that some error had been made and test should be repeated.