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Re: Tension Stress Graphs

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<<<frp 2000 wrote:

I received "flexural" demands for some prestressed beams.

What I received were : Tension Stress Graphs (length on x-axis, psi on
y-axis)

Are these equivalent to the moment curve divided by the Section Modulus ??

i.e. stress = M/S = Mc/I ,    where c = distance to furthest tension fiber>>>


Any response you get from the list will be an educated guess.  You should ask the person who sent you the submittal for clarification.  That said, here's my guess.

ACI code limits tensile and compressive concrete stresses in prestressed members at service loads (at transfer of prestress and after losses).  The intent of the graphs may be to show compliance with these stress limits.  The concrete stresses are computed by:

f = P/A + M/S

where

P = axial compression due to prestress force
M = bending moment due to profile of prestressing, self-weight and applied loads

The prestressing steel stresses are also limited by code, but should not vary drastically along the length of most members.  Some variation will occur due to friction, but it should be obvious by looking at the graphs whether they show tendon stresses.

Jason Emoto