A prestressing anchorage product is designed and certified for a wide variety of applications: utilization 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 products are made from 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; usually the one is called tool grips that is with 3 chips.
Anchor head, also called anchor rings or anchor block, is key a part of bearing the prestressing tension. There are two kinds of anchor head: the first is round anchor head which is made by 45# high-quality carbon construction steel, and the other is flat anchorage which can be produced by 40Cr steel. And the prestressing Anchor head should be dealt with wedges.
Bearing plate is key component, which transfer the stress from anchor head over to concrete under anchor. The process of transfer and distribution of stress change 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 believe that the creation of openings in existing PT slabs is either extremely complex or impossible. Consideration in the correct procedures demonstrates this to not be the case. Post-formed holes in PT slabs can vary in dimensions which range from the smallest penetrations, which can be necessary to incorporate suspended services, to 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 provides large, regular spaces between tendons which will easily accommodate smaller openings.
Such instances, alterations can often be more straightforward than in other sorts of construction, as the roll-out of holes within these areas can be accomplished without affecting structural performance. The anchorage grip, in the Guidance Note, identifies four kinds of post-formed penetration which can be categorised in accordance with the effect the operation could have on structural integrity. The initial of these relates to the littlest holes, a maximum of 20mm in diameter, involving no tendon cutting and which offers minimal risk towards the structural integrity of the slab. The 2nd group is classed being a low risk to structural integrity and includes somewhat larger openings, as much as 200mm in diameter in beams or near to columns, but larger in areas that are less stressed.
The voids are still located between tendons in order to avoid the need to cut these. Within the third and fourth categories of penetrations, where it becomes required to sever the tendons, the effect on the integrity from the structure may very well 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 of corrosion protection to exposed cut steel.
The most frequent kind of post-tensioning in the united kingdom industry is bonded PT (Figure 4). Ducts carrying high-tensile steel strands are loaded with grout following the tendons happen to be stressed and locked off by way of split wedges in the anchors, thereby bonding the tendons to the concrete. If larger openings are essential in post stressed accessories, they is often treated in a similar manner as traditional reinforced concrete slabs as the effects of cutting through a bonded tendon remain localised and the rwkhni redevelops its bond both sides of the cut, typically within 1m.
In instances where it is actually required to cut multiple tendons, mechanical or epoxy anchorages can be put on the ends in 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 numerous hoists plus an escalator within an existing building. After non-destructively seeking the tendons that spanned from 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 around the exposed strand prior to cutting, thereby giving enhanced surety of anchoring.