Structural Analysis Program Issues

[wbrice]

Hello,

I work for a precaster in AZ and we are making the switch from Salmon's BEAM program and our in-house program to Bentley's Presto. I have been testing Presto and comparing it to our other programs and the PCI/ACI codes. Unfortunately, for final losses Presto outputs roughly 13% higher tension in the bottom under full DL and LL.
Something else that Presto outputs that we surprised by is when it cracks under tension it displays -0 (negative zero). I thought ACI had equations for a reduced ultimate strength and for calculated the stresses in cracked sections of concrete.
We have a help ticket with Bentley, but I'm under a little pressure to figure this out sooner than later.

Thanks for your help in advance (This is my first post!),

Wyatt

 

[ishvaaag]

Hmm apart of remembering something like that of both ACI and PCI, maybe PTI as well, I am clear on something: when you analyze a section in flexure and part becomes cracked but restrained by reinforcement, between the neutral fiber and the strain of rupture in tension ther is some height of beam the tensile stresses of which can be accounted if so wanted for the equilibrium of deformations of the section. I know it well because I did many worksheets to study compatibility of deformations in sections, both to study actual status and strength, and I left the option in many of them. Usually the tensile stress present is just some proplongation through the neutral axis point till the strain of flexural rupture in tension is met. Below that you shouldn't account on the tensile strength of concrete, for at cracks such is the situation. Other thing is where you study the separation of cracks for which some other considerations are made, and some estimate of the situation between cracks is needed to get some equations.

So, most of what you are asking you can solve with a spreadsheet or worksheet able to study your section in compatibility of deformations; they are not so difficult to build, and also there are out there a number of them, myself's at Mathcad Collaboratory that unfortunately I don't think are available to the public as it was the case before PTC's Mathsoft purchase.