I am a Professional Engineer and a firefighter in N.Y. City. I have n 2

[pruho]

I am a Professional Engineer and a firefighter in N.Y. City. I have no direct experience in post-tensioned construction, and would like to obtain the following information:<br>
1. In a non-bonded post-tensioned slab or beam, is it possible to cut through a tendon without life safety issues to the cutter or anyone else nearby?<br>
2. How often is this technique used in modern construction (part. in the northeast), and how often has it been used in the past?<br>
3. Are there any external indicators in an existing structure as to whether it contains post-tensioned construction members?<br>
Thank you for your consideration in this matter.<br>
Yours truly, John P. Flynn, P.E., Pruho@aol.com<br>
<br>

 

[merbas]

first you place the post tension wires which covered plastic sheet.

 

[jales]

John,<br>
<br>
1. In general, it is possible to cut through an unbonded tendon without life safety issues. Cutting through tendons and tendon breakage occur commonly during construction. Typically, concrete spalling will occur or the anchorage will pop out of the side of the slab or beam a few inches. However, explosive concrete ruptures can occur which may injure anyone close by. Slabs that are renovated, such as those that have openings added for elevators, require tendons to be cut and reanchored. Refer to the Post-tensioning Institute's publication, "Controlled Demolition of an Unbonded Post-Tensioned Concrete Slab" for more info. Their number is 602-870-7540.<br>
2. Post-tensioning has been in use since 1957.<br>
3. The easiest way to tell whether a slab or beam is post-tensioned is to look at the slab edge or beam edge for the grouted anchorage pockets. <br>
4. In flat slabs and flat plates, the tendons are layed out in what are termed the banded and uniform directions. In the banded the direction, which is typically the long dimension of the structure, the tendons are grouped along the column lines. In the direction perpendicular to this, the tendons are located uniformly in the slab at a 2' to 3' spacing. This should at least give you an idea where the tendons will be located.

 

[Jimerna]

John:The informatin from "jales" is correct. I would add emphasis to the danger of cutting through an unbonded tendon. It is very dangerous as the tendon could have up to 30,000 lbs of tension and an instaneous release of a tendon from a slab could send the freed end a dangerously lond distance until it hit something solid. Tendon released from a residential slab could travel several hundred feet and still injure or kill a person. The PTI's publication covers the subject quite well. Please be careful.<br>
<br>
Jim Seaman P.E.

 

[merbas]

I am incharge of the construction of new airport complex in Istanbul/Turkey.We make the autopark building using post-tension system, because of we need large area and less coloums.Post-tensioned tendons carry ALOTS of strenght and very long as stated above.<br>
<br>
I advice never touch them . WHY?<br>
<br>
Because, when slab system prepered the scarfolding system is under the slabs and they carry the floor. When executive engineer tested the concrete and say it is ready to carry itself, post-tension engineers start to pull tendons untill the concrete leave from scarfolding and carry itself.After this operation you can remove the bottom molds. JUST think the power in the tendons and never touch it pls.<br>

 

[Jimerna]

Another good idea to follow is never drill into a post-tensioned or pre-tensioned slab to install anchors, etc. If you damage a tendon failure could result and damage or injury can follow.

 

[ramezkamel]

Hi, could someone give me more details on what happens when cutting a pre-tensionned tendon (bonded) ?

Will the anchorage region (the new one)'explode' because of the dynamic effect of re-anchoring ?

Is there any detailed documentation on this ? on the web, PCI, etc ...

Thank you !

Ramez.

[sig][/sig]

 

what are the safety issues in regards to all post-tensing works done and not including demolition.

 

[ishvaaag]

I suggest you to read the

Post-tensioning manual 5th ed
by PTI,
the Post Tensioning Institute,

where the more important aspects of the practice are given, construction advice included.

 

[Clare]

Can a post-tension concret slab (for a tennis court) be installed within the confines of a walled space that allows only one foot of clearance between the wall and the finished dimensions of the court? Minimum clearance requirement?

 

[Ingenuity]

Clare,

Short answer is &quot;yes&quot;. 1 foot is a little short for perimeter stressing, but you can do internal stressing - little more difficult and a few more $ but it can be done.

On multistory building, at the contractor's request, we often detail stressing such that NONE is at the perimeter to avoid personnel and equipment on exterior scaffolding.

You could also consider, alterantive dead and live ends, and the live ends could be recessed from the slab perimeter by 3 feet, and the last 3 feet gets conventionally reinforced. The dead ends can go as close to the slab perimeter as end concrete cover permits.

HTH

 

For post tension tennis, how far should cables be placed apart? at what direction?