A prestressing anchorage method is designed and licensed for a wide variety of 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 approximately 55 strands
YM Series products are made up of tensioning anchor head, wedges, Anchorage Barrel And Wedge plate and spiral reinforcement. Wedge: also called grips or jaws, is produced by high-class alloy steel 20CrMnTi. The two main kinds, the first is called working grips which is with 2 chips; the main one is known as tool grips which can be with 3 chips.
Anchor head, also called anchor rings or anchor block, is the key part of bearing the prestressing tension. The two main forms of anchor head: the initial one is round anchor head which can be created by 45# high-quality carbon construction steel, and also the other is flat anchorage which is produced by 40Cr steel. And also the prestressing Anchor head should be worked with wedges.
Bearing plate is vital component, which transfer the load from anchor head over to concrete under anchor. The technique of transfer and distribution of stress impact the anti-cracking and load capacity of concrete. Spiral reinforcement, also called hoop reinforcement, is used for distributing the concrete and strengthening tendons.
A typical 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 to not be the case. Post-formed holes in PT slabs will be different in proportions starting from the tiniest penetrations, which may be necessary to incorporate suspended services, to much bigger openings to enable adding lifts or similar installations. In most post-tensioned slabs, the most frequent tendon layouts make use of a banded design which offers large, regular spaces between tendons that can easily accommodate smaller openings.
In such instances, alterations is often more straightforward than in other kinds of construction, as the creation of holes within these areas may 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 very first of these relates to the littlest holes, not more than 20mm in diameter, involving no tendon cutting and that provides minimal risk towards the structural integrity from the slab. The second group is classed as a low risk to structural integrity and includes somewhat larger openings, as much as 200mm in diameter in beams or near columns, but larger in areas that are less stressed.
The voids continue to be located between tendons to prevent the requirement to cut these. In the third and fourth categories of penetrations, where it will become necessary to sever the tendons, the effect on the integrity in the structure will probably be more significant and demands strengthening and temporary propping in the slab. As the amount of cut traditional reinforcement is significantly less, so is the necessity for corrosion protection to exposed cut steel.
The most frequent form of post-tensioning in the UK market is bonded PT (Figure 4). Ducts carrying high-tensile steel strands are filled with grout following the tendons have been stressed and locked off through split wedges in the anchors, thereby bonding the tendons for the concrete. If larger openings are needed in slab steel anchor, they can often be treated in the same way as traditional reinforced concrete slabs as the effects of cutting through 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 actually essential to cut multiple tendons, mechanical or epoxy anchorages can be put on the ends in the severed tendons to supply even greater security. CCL recently undertook an application that required the development of voids within bonded slabs, in order to house a number of hoists plus an escalator inside an existing building. After non-destructively choosing the tendons that spanned from the proposed void in the slab, by means of the ‘as built’ drawings from the operations and maintenance manual, the posttensioning duct was opened (Figure 5) and epoxy grout anchors were then installed round the exposed strand prior to cutting, thereby giving enhanced surety of anchoring.