Post-tensioning of elevated slabs is a construction process that requires experience, coordination, knowledge, and preparation. Choosing an experienced post-tensioning (P/T) material supplier and installer will help ensure a smooth construction process, but there is much more that contractors should know about the post-tensioning process.
Before beginning the elevated P/T portion of the work, the contractor, engineer, installation subcontractor, third-party inspection agency, and P/T material supplier should hold a pre-construction meeting to discuss the logistics and specific requirements of the project. Understanding the order of installation by reviewing the installation drawings can help when it comes to planning for deliveries and storage, installation, and stressing.
Storage and handling
A suitable storage area for the P/T materials must be dry and large enough to accommodate the material necessary for the project. It also should be located to minimize handling, which reduces the chance of jobsite damage to the P/T material. For example, when unloading the P/T materials for more than one level or pour, stage it such that the next level or pour can be accessed without moving other materials that are not required.
The P/T material supplier should deliver the material in bundles marked by level or pour and should deliver paperwork indicating the position of each bundle on the truck. This paperwork should be used when unloading and storing the material to ensure that it is in the order in which it will be used. P/T material deliveries should be overlapped so that the site always has one level or pour of material beyond what is required to meet the project schedule. If this is not possible because of limited storage area, several extra tendons of the longest length required for the project can be supplied in case a tendon is damaged.
Once the P/T materials are delivered to the job, the buyer or installer becomes responsible to ensure their
safekeeping. The installer should check the delivered materials against the shipping list at the time of unloading and notify the P/T material supplier of any discrepancies immediately. P/T tendons are typically delivered in bundles identified by job, level, pour, and so forth. These tendons are individually tied and then secured into master bundles with metal strapping.
To move master bundles with a crane, rig the bundles using nylon slings by cradling, not choking. Metal cables and chains should never be used, as they will damage the tendon's plastic sheathing. Alternately, if you use a forklift to move the tendon bundles, they should be on a pallet, or fork protectors should be used so the edges of the forks do not damage the tendon's plastic sheathing.
When moving the tendons to the location where they are to be placed, consider the order in which they are moved. For example, in a two-way flat-plate slab with banded tendons, the uniform tendons crossing over columns are placed first, then the banded tendons, followed by the balance of the uniform tendons; it may be advantageous to have the P/T supplier bundle uniform column line tendons along with the banded tendons. Using this procedure will limit the number of material movements needed to get the required material to where work is being done.
Care should be taken whenever handling a coiled tendon. Coiled tendons will uncoil like a spring when the restraining ties are cut. Awareness and the proper use of personal protective equipment can help prevent injury when uncoiling tendons.
Wedges and anchors should be kept clean and dry. They are shipped to the site and identified by the specific portion of the project for which they are intended. For traceability of materials, the wedges and anchors should be used only in the portion of the project as identified by the shipping documents.
The three types of anchorages are the stressing-end anchorage, the fixed-end anchorage, and in certain applications intermediate anchorages. All tendons will have at least one stressing anchorage. Tendons longer than approximately 130 feet will typically be stressed from both ends. The fixed-end anchorage assembly is already installed when the tendon arrives at the jobsite. The installation drawings will show where the fixed ends and stressing ends are located.