A prestressing anchorage system is designed and licensed for numerous applications: use of 13 mm (.5″) and 15 mm (.6″) strands of all grades (1,770 or 1,860 MPa) including galvanised strands or greased sheathed strands. Prestressing units holding as much as 55 strands
YM Series items are composed of tensioning anchor head, wedges, stressing anchorage plate and spiral reinforcement. Wedge: also referred to as grips or jaws, is produced by high-class alloy steel 20CrMnTi. There are 2 kinds, the initial one is called working grips that is with 2 chips; the one is called tool grips that is with 3 chips.
Anchor head, also known as anchor rings or anchor block, is key part of bearing the prestressing tension. There are two kinds of anchor head: the initial one is round anchor head which can be created by 45# high-quality carbon construction steel, and the other is flat anchorage which is made by 40Cr steel. And the prestressing Anchor head has to be worked with wedges.
Bearing plate is vital component, which transfer the load from anchor head to concrete under anchor. The technique of transfer and distribution of stress affect the anti-cracking and load capacity of concrete. Spiral reinforcement, also called hoop reinforcement, can be used for distributing the concrete and strengthening tendons.
A standard misconception exists, which leads some to think that the roll-out of openings in existing PT slabs is either extremely complex or impossible. Consideration from the correct procedures demonstrates this not to become the case. Post-formed holes in PT slabs will vary in dimensions starting from the tiniest penetrations, which might be required to incorporate suspended services, to much bigger openings to allow adding lifts or similar installations. In most post-tensioned slabs, the most frequent tendon layouts make use of a banded design which supplies large, regular spaces between tendons that will easily accommodate smaller openings.
In these instances, alterations can often be more straightforward than in other kinds of construction, as the roll-out of holes within these areas may be accomplished without affecting structural performance. The dead-end anchorage, in their Guidance Note, identifies four kinds of post-formed penetration which are categorised according to the effect the operation may have on structural integrity. The first of those pertains to the littlest holes, a maximum of 20mm in diameter, involving no tendon cutting and that offers minimal risk for the structural integrity in the slab. The 2nd group is classed as a low risk to structural integrity and includes somewhat larger openings, approximately 200mm in diameter in beams or close to columns, but larger in areas that are less stressed.
The voids remain located between tendons to prevent the requirement to cut these. Inside the third and fourth types of penetrations, where it will become necessary to sever the tendons, the result on the integrity in the structure is likely to be more significant and calls for strengthening and temporary propping in the slab. As the amount of cut traditional reinforcement is quite a bit less, so is the requirement for corrosion protection to exposed cut steel.
The most common kind of post-tensioning throughout the uk marketplace is bonded PT (Figure 4). Ducts carrying high-tensile steel strands are full of grout after the tendons have been stressed and locked off through split wedges within the anchors, thereby bonding the tendons to the concrete. If larger openings are essential in barrel and wedge anchor, they can be treated in the same manner as traditional reinforced concrete slabs because the effects of cutting by way of a bonded tendon remain localised as well as the rwkhni redevelops its bond each side of the cut, typically within 1m.
In instances where it is essential to cut multiple tendons, mechanical or epoxy anchorages may be placed on the ends of the severed tendons to supply even more security. CCL recently undertook an application that required the roll-out of voids within bonded slabs, in order to house a number of hoists plus an escalator inside an existing building. After non-destructively locating the tendons that spanned with the proposed void inside the slab, by way of the ‘as built’ drawings through the operations and maintenance manual, the posttensioning duct was opened (Figure 5) and epoxy grout anchors were then installed across the exposed strand just before cutting, thereby giving enhanced surety of anchoring.