A prestressing anchorage system is designed and certified for numerous applications: usage 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 up to 55 strands
YM Series goods are made from tensioning anchor head, wedges, Anchorage Barrel And Wedge plate and spiral reinforcement. Wedge: also called grips or jaws, is made by high-class alloy steel 20CrMnTi. There are 2 kinds, the first is called working grips which is with 2 chips; usually the one is referred to as tool grips which is with 3 chips.
Anchor head, also known as anchor rings or anchor block, is key a part of bearing the prestressing tension. There are two forms of anchor head: the first is round anchor head which can be produced by 45# high-quality carbon construction steel, and also the other is flat anchorage which can be made by 40Cr steel. And the prestressing Anchor head should be dealt with wedges.
Bearing plate is the key component, which transfer the stress from anchor head over to concrete under anchor. The method of transfer and distribution of stress impact the anti-cracking and load capacity of concrete. Spiral reinforcement, also known as hoop reinforcement, is used for distributing the concrete and strengthening tendons.
A common misconception exists, which leads some to think that the development of openings in existing PT slabs is either extremely complex or impossible. Consideration from the correct procedures demonstrates this never to be the case. Post-formed holes in PT slabs will be different in proportions starting from the littlest penetrations, which can be required to incorporate suspended services, to much larger openings to permit the addition of lifts or similar installations. In most post-tensioned slabs, the most typical tendon layouts make use of a banded design which supplies large, regular spaces between tendons which will easily accommodate smaller openings.
Such instances, alterations can be more straightforward when compared to other kinds of construction, as the roll-out of holes within these areas may be accomplished without affecting structural performance. The post tension anchorage, in the Guidance Note, identifies four types of post-formed penetration which can be categorised according to the effect the operation may have on structural integrity. The first of those relates to the littlest holes, a maximum of 20mm in diameter, involving no tendon cutting and which offers minimal risk towards the structural integrity from 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 which are less stressed.
The voids continue to be located between tendons to prevent the need to cut these. Inside the third and fourth categories of penetrations, where it becomes necessary to sever the tendons, the effect on the integrity of the structure is likely to be more significant and demands strengthening and temporary propping of the slab. As the amount of cut traditional reinforcement is significantly less, so is the requirement for corrosion protection to exposed cut steel.
The most typical type of post-tensioning throughout the uk marketplace is bonded PT (Figure 4). Ducts carrying high-tensile steel strands are filled with grout right after the tendons have already been stressed and locked off by way of split wedges within the anchors, thereby bonding the tendons for the concrete. If larger openings are required in barrel and wedge anchor, they can often be treated in the same way as traditional reinforced concrete slabs since the effects of cutting by way of a bonded tendon remain localised as well as the rwkhni redevelops its bond both sides in the cut, typically within 1m.
In instances where it is required to cut multiple tendons, mechanical or epoxy anchorages may be placed on the ends from the severed tendons to provide even greater security. CCL recently undertook a software that required the roll-out of voids within bonded slabs, in order to house a number of hoists and an escalator inside an existing building. After non-destructively seeking the tendons that spanned with the proposed void within the slab, by means 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 around the exposed strand before cutting, thereby giving enhanced surety of anchoring.