Rectangular Stress Block
Rectangular Stress Block
(OP)
Hello everyone,
I have seen in the SAFE 14 manual that they use an equation for the depth of the compression block in concrete according to AS 8.1.2.2, I could not find the equation in the code, and I tried to get at it without much luck. The equation is a = d - sqrt(d^2-(2M*/0.85f'c*phi*b))
I would love if you could point me in the right direction.
Thank you!
I have seen in the SAFE 14 manual that they use an equation for the depth of the compression block in concrete according to AS 8.1.2.2, I could not find the equation in the code, and I tried to get at it without much luck. The equation is a = d - sqrt(d^2-(2M*/0.85f'c*phi*b))
I would love if you could point me in the right direction.
Thank you!






RE: Rectangular Stress Block
M*=0.85*f'c*phi*b*a*(d-a/2)
Got to solve for a.
RE: Rectangular Stress Block
RE: Rectangular Stress Block
Mike McCann, PE, SE (WA)
RE: Rectangular Stress Block
I think you meant ULTIMATE STRENGTH DESIGN, not WORKING STRESS DESIGN?
RE: Rectangular Stress Block
Working Stress Design would be to compute the area of steel required directly from the moment applied, and then check your concrete stress to see if you needed to add compressive steel to carry the full load.
Tensile Reinforcement: As = M/(fs*j*d) where j = 1-k/3 and k = [SQRT(2*n*p + (n*p)^2) - n*p] or, more commonly, k = 1/(1+fs/(n*fc))
Then the moment of compressive concrete stresses about the tensile reinforcement:
Mr = 1/2 fc*k*j*(bd^2)
if this exceeds your allowable (working) tensile stress, increase some parameters or add steel and try again.
And despite the "simplicity" [note: This should be seem as very sarcastic - I find the working stress, or any stress based formulation for concrete, very complex and onerous], this was nearly never done - Everyone used the tables of "canned" beams for flexural strengths... It was common to specifically design stirrups, however, much as we do today.
RE: Rectangular Stress Block
RE: Rectangular Stress Block
Later refinements corrected those gross assumptkons...