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DYWIDAG Monostrand Tendons for Santa Monica Civic Center, CA

Monostrand Post-Tensioning System

System Description


The strength, serviceability and design flexibility of concrete are greatly enhanced by the DYWIDAG Monostrand Post-Tensioning System. DYWIDAG Monostrands are made up of cold-drawn, low-relaxation, seven wire strands of 0.5" (12.7 mm) or 0.6" (15.2 mm) diameter, conforming to ASTM A 416. DYWIDAG's small tendon diameters and small anchor plate dimensions meet the edge dimension requirements of slabs as thin as 4-½" (114.3 mm).
All components illustrated are for unbonded construction. Contact your local DSI representative for details for bonded tendon construction or other specialized construction materials.

The DYWIDAG Wedge-Anchor System exceeds ACI Code requirements for guaranteed ultimate capacity of the tendon, and seating losses are reduced to a minimum by the two-piece wedge design. The system meets PTI Guide specifications. Intermediate anchors can be installed at points along the tendon to suit construction joints, and the stressing can be applied at these points. DYWIDAG provides plastic pocket formers as part of standard anchor hardware.Attached to the formwork for quick positioning of anchors, the pocket formers create small, clean stressing voids that are easily patched. DYWIDAG Monostrand Tendons are assembled at the job site from strand, which is coated and protected by an extruded plastic sheathing. Intermediate and fixed end anchors or anchorages are installed in the plant and stressing anchorages in the field. Wedges for fixed anchorages are hydraulically seated in the plant for positive grip.

Corrosion Protection

Durability over the lifetime of the structure has become a principal quality objective. Many factors play a determining role in assessing the adequate level of corrosion protection. Corrosion is an electrochemical process that degenerates the prestressing steel.

The primary and secondary barrier against corrosion is the grease and tendon sheathing. The main objective of corrosion protection is to keep water away from the prestressing steel, especially when the water is contaminated with corrosive elements such as chlorides.
There are four main considerations in order to select the appropriate corrosion protection system. First the environment needs to be considered:
geographical latitude, coastal areas versus central regions, salt spray zone, altitude, precipitation, salt contamination. Second, the exposure should be considered. Is the structure directly exposed to the elements (parking garages, balconies) or is it enclosed in a protective shell (apartment building)?
Third consideration is design service life of the structure and fourth is safety.

DSI offers a variety of systems in order to allow an unbiased assessment of corrosion protection requirements. Consider all tradeoffs with respect to life-cycle cost in order to achieve consistent durability results on every project.
When the tendon is delivered to the site with the fixed end anchorage in place, a clear soft plastic sleeve is attached and a cap filled with grease is seated into the anchor to ensure a tight seal. After stressing the tendon and burning off the strand extension, a plastic grease filled cap is pushed into the anchor, providing a tight seal.The grease, extruded sheathing, strand, and anchorages all meet or exceed the PTI Guide Specifications as noted in the Fifth Edition of the Post-Tensioning Manual. With the introduction of this new Corrosion Protection System, DYWIDAG is proud to offer a system believed to be the best available on the market today at competitive prices.

Assistance

DYWIDAG field technicians are available to assist the general contractor in placing and stressing DYWIDAG supplied tendons where required. Strict compliance with the project's specifications with regard to placing and stressing of the DYWIDAG Tendons must be maintained.Tendons need to be placed to the specific required ordinates of the tendons in order to achieve the structural capacity and the required concrete cover to assure proper corrosion protection for the DYWIDAG tendons.
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