Yield strength failure to high yield steel rebar

[defg]

What is the cause of yield strength failure in steel reinforcements?If such occation occur in high yield steel bars is it necessary to verify it by carrying out proof test?What is the help of stress-strain curve for defining the proof stress?If tensile test is carriedout concurrent with the yield stregth test,is it possible to obtain no yield results?

 

[Ron]

Your questions are broad and textbooks have been filled with the answers.

To answer your first question....either overstressing or defective rebar.

Rebar is not the highest quality steel and has quite a few variabilities in production. Depending on the manufacturer, and the variables of production, the actual yield strength can vary quite a bit. ASTM and other standards typically give the MINIMUM yield strength the material should meet.

Should you test it? If you suspect wide variability, of course have it tested. It isn't a difficult test and it isn't very expensive. You can do an ultimate tensile test or you can do a yield point/tensile test.

The stress-strain curve is used to determine where you might be in the elastic portion of the curve when computing stresses or when doing a proof test. I would caution that doing a proof test on a reinforced concrete section then trying to match the rebar stress to its stress-strain curve can be a bit difficult.

The most common use of the stress-strain curve is to obtain a representative curve from the rebar manufacturer based on their heat numbers, then do a tensile test with stress-strain plotting as a proof test on a sample of rebar, and see how the curves match.