I am reviewing post-tensioned concrete slab and beam shop drawings and calculations. It is my first time. What advice do you have on things to look for?
No, the engineering drawings are prepared by the Engineer of Record (EOR) who is ordinarily retained by the client (the owner or his representative). Those drawings set out the specific requirements for the job, but in some cases, leave a bit of leeway for fabricator ingenuity to meet specified criteria.
Shop drawings are prepared by the fabricator or supplier and must meet the criteria set out by the EOR.
In the case of post-tensioned slabs and beams, the EOR might have specified a prestressing force per foot of width. Or he might have specified tendon sizes and locations and anchor types. In some cases, he might leave the entire design up to the supplier, subject to checking by the EOR.
What you should look for is anything which affects the capacity of the floor or roof to carry load because, in the end, the responsibility for the final design rests with the EOR.
Ask for engineering certification. Check that the drapes are logical and that the strands provided can provide the required prestress. I like to have 1.4MPa for normal slabs and 3.0MPa for roof slabs. If there are no transfers and the span to depth ratios are sensible than the pt alone should be able to provide the required flexural strength on it's own with the additional of bar reinforcement at the supports for shear.
Bands normally have tendons spaced at 300-600mm and slab spans at 800-1200mm.
I'd check for an engineers stamp on the SDs and calcs. Check the concrete mix design against the volume change calcs for assumed values. Verify conventional reinforcement placement and do a qucik check on a couple of tension strands.
I did a back check of the bending moments and shears for the beams and found that the moments in the PT designer's calcs are much smaller. I used a simple program to find the moment for multi-span beam and my numbers are significantly higher. The PT engineer thought that the pt caused the lower moments, but that doesn't make sense to me. I am missing something?
For example, on a three span beam (46', 31.5' and 48') I get maximum factored positive moment of 1,250 kip feet. His calcs show only 890 kip feet.
To clear this up look into secondary moments created by post-tensioning and see if you agree with the designers assumptions along with the applicable Code.
