Hello,
My RAM concept model is showing a service design gross top stress failure and I am having trouble figuring out how RAM is calculating this value. I am trying to find the maximum negative moment overstress in order to design FRP reinforcing around the columns. I've uploaded my concept model and the ACI design guide I reference below.
Is there a report I can print to view RAM's calculations for this value at column 23C-3, Section 1 (worst case)? Additionally, (i) what is the column strip length RAM uses? (ii) what is the tendon drape value RAM uses? and (iii) what is the column strip trib width RAM uses?
I followed the two-way slab example 3 of the uploaded design guide (pg 118) and am calculating a top gross stress (pg 122) of 487 psi while RAM is showing 553.4 psi. I'm using the maximum negative moment RAM shows of -299.8 k*ft. My calculations assume a column strip length of 27'-4" (face of column to face of column) and tendon drape a = 7" giving me a PT tendon force of 15 kips/ft. I am assuming a full column strip trib width of 29'-4" giving me a maximum negative moment of 10.2 kip*ft/ft.
Thanks
The audit report should help you. It gives you the critical input (Ps, Mr, Ac etc.) to hand calculate this stress which is just a (P/A + M/S) calculation. Here's my hand calc for Envelope 2.
Auditing 23C-3, section 1.html
As for span length, it's determined by the span segment length. There are cases where we use the full span length, and other places where the clear span length is used. It's not directly used in the stress determination however.
I suspect that the nature of this model with tendons running between two rigid shear wall cores is hurting you (i.e. second order effects that reduce the PT effectiveness). There is also the matter of the gap in the tendons which are terminating a little below the slab centroid. See also: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/30231/modeling-a-pour-strip