PT Cables Horizontal Sweep 1

[slickdeals]

Folks,
I am trying to get a feel for the limits that you folks set for horizontal sweeps in unbonded cables on post-tensioned buildings.

Are there any published limits for how much the radius of a sweep can be for cables? I realize that more severe the sweep, greater are the losses. In addition, it leads to problems of occasional blowouts.

Architects love to offset columns as much as 8-10 feet over 30 foot spans etc, causing exaggerated sweeps. Do you guys have any limits on them?

Thanks

 

[civilperson]

The minimum radii of curvature is given in "TESIT Post-Tensioning Systems" for various diameters of sheaths. The friction coefficients increase with decreasing radius of curvature. Empty ducts for supplementary tendons should be provided in case the friction losses are greater than expected.

 

[slickdeals]

Thanks, but a quick google on TESIT does not give me any results. Any help?

 

[AUCE98]

A typical radius of curvature should be limited to 15-feet for 1/2" dia unbonded monostrand tendons. Reason being two fold, increased chance of blowouts as you had stated and secondly forcing a strand into a sharp curvature induces flexural stresses in the strand wires that may become significant if the curvature is extremely tight. This limitation is typically 20 times the strand diameter. The second stipulation controls the stresses in the strand while the first stipulation controls the stresses in the concrete. I have worked for 2 post-tension suppliers in the past and have typically maintained a 15-foot radius. Sharper curvature is possible; however you should place hairpins within the curve to minimize the horizontal pressure on the concrete. The PTI manual would be a good resource.

Regards,

AUCE98