Unbonded, Post-tensioned Shop Drawing 1

[dik]

The query I received in a recent eMail was as follows:

Can you please provide me the easy way to draw shop drawing for Post Tesnion Drawing? Is there any software ? I am doing it from AutoCAD and getting some errors on elongation and CGS. Is there any precise way? Please help.

Can anyone provide me with a copy of a typical unbonded, post-tensioned flat slab shop drawing that shows the essential information. My work does not generally include this information. The query came from Nepal.

Thanks in advance, Dik

 

[Ingenuity]

dik:

Attached are your 'typical' USA-standard UNbonded PT shop drawings for a 2-way slab consisting of layout, banded tendons and uniform/distributed drawings. Project data has been removed.

We typically do the shop drawings with AutoCAD and not custom software, however, we do use a lot of 'blocks', and occasionally LISP routines.

I personally do NOT like stating the tendon elongations on shop drawings, but when we have to we usually use a XLS spreadsheet and insert it using dynamic OLE.

 

[dik]

Thanks very much... I'll take a look at them, and if anything inappropriate will remove it. Don't know how the fellow got my name, but, I knew the project architect on the international airport in Kathmandu and I did a 747 hanger in Nepalgunj. That was a long way back...

Dik

 

[dik]

Ingenuity:

I've sent the drawings on as *.dwg files and have checked for 'remnants'... my pdf2dwg converter sometimes finds 'erased' information that was not intended to be included. Nothing found. Thanks so much for the information.

Dik

 

[dik]

Ingenuity:

I've sent him information on calculating the elongation of strand. Is there an easy manner of calculating chair heights, other than drawing out the profile?

[Added] High point: thickness less concrete cover and strand dia,
PI at 2'-0 from support centre line for spans to 20' and 2'-6 for others,
Height of strand at PI, 1" less than height of strand at support centre line,
Low point: concrete cover.
End span low point at 0.6 of span.

anything more? Do you provide height of strand at other locations?


Dik

 

[Ingenuity]

dik:

I use RAPT software to both design and detail the PT: Link

Typical output for elongations and tendon drapes to underside of tendon/s:

Alternatively, a spreadsheet using compound parabolas (to account for the reverse tendon curvatures and flat profiles over supports), and accounting for the transition lengths at tendon stressing ends, work okay. However, it is a bit of a pain to take into account non-typical cases.

 

[dik]

Thanks very much.

Dik

 

[Ingenuity]

[Added] High point: thickness less concrete cover and strand dia,
PI at 2'-0 from support centre line for spans to 20' and 2'-6 for others,
Height of strand at PI, 1" less than height of strand at support centre line,
Low point: concrete cover.
End span low point at 0.6 of span.

anything more? Do you provide height of strand at other locations?

PT drapes are referenced from the top of forms (bottom of concrete), except in circumstances where there is ambiguity, and that is usually tagged next to the profile dimension to avoid confusion, usually using a "*" or some other symbol.

Typically tendon profiles are given at 3 ft (1m) spacings, and rounded, based upon equal spacing of profiles, for the given drape/span. For short spans, minimum of 5 profiles (top each end, midspan, and one each between btm and top).

 

[dik]

Thanks again... looking at solving a parabola through 3 points using a the solution of a quadratic and determining the coefficients using a 3x3 matrix solution. Looks like they typically use a 2'offset to PI and keep it at the same elevation as the support centre line Using SMath Studio. Have another problem to do first.

Dik

 

[dik]

Something like the attached... needs a little work. Done in SMath Studio... free MathCAD work alike... I can post the SMath sheet if anyone wants...

Dik

 

[Ingenuity]

dik: It is a starting point for single span conditions.

However, you need to consider the straight 'tangent' length that is applicable at the stressing-end of tendons, and that is something that is somewhat system dependent (less so for UNbonded monostrand system), and PT shop drawings are the appropriate place to address it.

Also, for multi span conditions, and/or spans with cantilevers, you are going to have to address: reverse profiles (over supports) with realistic tendon curvatures; flat portions over supports with transition profiles to go from 'span profile' to 'support profile'...etc,

 

[dik]

It allows the calculation of the support heights between points of inflection within the span and if the equivalent points are determined for end span, and 'wierd' conditions, it will not give an exact solution, but somewhat close. Also at supports, if the strand is not horizontal between points of inflection, an approximate parabola can be developed for this condition.

There will be a cusp at the points of inflection due to the parabolas not having the same slope...I think due to the stiffness of the strand, this would give an approximate solution.

First kick at the cat... from grade 11 or 12 math of 50 years ago... not too shabby.

Dik