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Post Tensioned Shop Drawings

Post Tensioned Shop Drawings

Post Tensioned Shop Drawings

(OP)
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?

RE: Post Tensioned Shop Drawings

Look for whether or not the shop drawings correspond with the engineering drawings.

BA

RE: Post Tensioned Shop Drawings

I am not structural so my question is wouldn't the engineering drawings be the shop drawings?

RE: Post Tensioned Shop Drawings

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.

BA

RE: Post Tensioned Shop Drawings

We don’t post tension our shop drawing, so I can’t be of much help.

RE: Post Tensioned Shop Drawings

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.

RE: Post Tensioned Shop Drawings

@dhengr - still laughing!

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.

RE: Post Tensioned Shop Drawings

(OP)
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.

RE: Post Tensioned Shop Drawings

I'd suggest you get some professional outside hell!!

RE: Post Tensioned Shop Drawings

Prestressing a beam doesn't change the moments due to external loading.

RE: Post Tensioned Shop Drawings

Mike - most of us professionals are definitely outside hell. Those of us who are inside hell drink profusely and would be no help at all.

RE: Post Tensioned Shop Drawings

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.

VoD

RE: Post Tensioned Shop Drawings

Moments from prestressing and secondary moments should not be used to reduce the design moment if they are benificial.

RE: Post Tensioned Shop Drawings

Hi asixth,

Which Code makes that requirement?

VoD

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