A prestressing anchorage method is designed and licensed for a multitude of 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 as much as 55 strands
YM Series goods are made from tensioning anchor head, wedges, stressing anchorage plate and spiral reinforcement. Wedge: also referred to as grips or jaws, is created by high-class alloy steel 20CrMnTi. There are two kinds, the initial one is called working grips which is with 2 chips; usually the one is known as tool grips which is with 3 chips.
Anchor head, also known as anchor rings or anchor block, is key part of bearing the prestressing tension. There are 2 kinds of anchor head: the initial one is round anchor head which can be created by 45# high-quality carbon construction steel, as well as the other is flat anchorage that is made by 40Cr steel. As well as the prestressing Anchor head should be dealt with wedges.
Bearing plate is vital component, which transfer the stress from anchor head to concrete under anchor. The process of transfer and distribution of stress impact the anti-cracking and load capacity of concrete. Spiral reinforcement, also referred to as hoop reinforcement, is utilized for distributing the concrete and strengthening tendons.
A typical misconception exists, which leads some to imagine that the development of openings in existing PT slabs is either extremely complex or impossible. Consideration of the correct procedures demonstrates this never to become the case. Post-formed holes in PT slabs will vary in proportions starting from the smallest penetrations, which may be needed to incorporate suspended services, to larger openings to permit adding lifts or similar installations. In all post-tensioned slabs, the most typical 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 compared to other kinds of construction, as the creation of holes within these areas may be accomplished without affecting structural performance. The post tension anchorage, in their Guidance Note, identifies four types of post-formed penetration that are categorised based on the effect the operation could have on structural integrity. The very first of these relates to the tiniest holes, no more than 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 being 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 continue to be located between tendons in order to avoid the need to cut these. In the third and fourth categories of penetrations, where it becomes necessary to sever the tendons, the impact on the integrity of the structure will probably be more significant and calls for strengthening and temporary propping from the slab. As the quantity of cut traditional reinforcement is significantly less, so is the necessity for corrosion protection to exposed cut steel.
The most common type of post-tensioning in the UK industry is bonded PT (Figure 4). Ducts carrying high-tensile steel strands are loaded with grout following the tendons have already been stressed and locked off through split wedges within the anchors, thereby bonding the tendons to the concrete. If larger openings are needed in pre-stressing anchor, they can be treated in a similar manner as traditional reinforced concrete slabs because the effects of cutting through a bonded tendon remain localised and also the rwkhni redevelops its bond both sides from the cut, typically within 1m.
In instances where it is actually necessary to cut multiple tendons, mechanical or epoxy anchorages can be put on the ends in the severed tendons to provide even more security. CCL recently undertook a software that required the development of voids within bonded slabs, in order to house numerous hoists as well as an escalator in a existing building. After non-destructively locating the tendons that spanned from the proposed void in the slab, through the ‘as built’ drawings through the operations and maintenance manual, the posttensioning duct was opened (Figure 5) and epoxy grout anchors were then installed round the exposed strand before cutting, thereby giving enhanced surety of anchoring.