A prestressing anchorage system is designed and certified for a wide variety 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 approximately 55 strands
YM Series products are composed of tensioning anchor head, wedges, Anchorage Barrel And Wedge plate and spiral reinforcement. Wedge: also referred to as grips or jaws, is made by high-class alloy steel 20CrMnTi. There are 2 kinds, the first is called working grips which can be with 2 chips; the main one is called tool grips which is with 3 chips.
Anchor head, also called anchor rings or anchor block, is key part of bearing the prestressing tension. There are 2 types of anchor head: the first 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 must be worked with wedges.
Bearing plate is the key component, which transfer the burden from anchor visit 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 utilized for distributing the concrete and strengthening tendons.
A standard misconception exists, which leads some to think that the creation of openings in existing PT slabs is either extremely complex or impossible. Consideration of the correct procedures demonstrates this never to function as the case. Post-formed holes in PT slabs will be different in dimensions starting from the smallest penetrations, which can be needed to incorporate suspended services, to much larger openings to allow the addition of lifts or similar installations. In most post-tensioned slabs, the most frequent tendon layouts use a banded design which provides large, regular spaces between tendons which will easily accommodate smaller openings.
In such instances, alterations can be more straightforward compared to other kinds of construction, as the roll-out of holes within these areas can be achieved without affecting structural performance. The wedge anchor, in its Guidance Note, identifies four kinds of post-formed penetration which can be categorised according to the effect the operation could have on structural integrity. The very first of those concerns the tiniest holes, a maximum of 20mm in diameter, involving no tendon cutting and that offers minimal risk towards the structural integrity of the slab. The next 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 which can be less stressed.
The voids remain located between tendons to avoid the necessity to cut these. Inside the third and fourth categories of penetrations, where it might be necessary to sever the tendons, the result on the integrity from the structure will probably be more significant and demands strengthening and temporary propping from the slab. As the amount of cut traditional reinforcement is quite a bit less, so is the requirement of corrosion protection to exposed cut steel.
The most typical form of post-tensioning throughout the uk market is bonded PT (Figure 4). Ducts carrying high-tensile steel strands are loaded with grout right after the tendons happen to be stressed and locked off by way of split wedges inside the anchors, thereby bonding the tendons to the concrete. If larger openings are needed in post stressed accessories, they can often be treated in a similar manner as traditional reinforced concrete slabs as the effects of cutting via a bonded tendon remain localised and also the rwkhni redevelops its bond each side from the cut, typically within 1m.
In instances where it is actually required to cut multiple tendons, mechanical or epoxy anchorages can be placed on the ends in the severed tendons to provide even more security. CCL recently undertook an application that required the creation of voids within bonded slabs, to be able to house a number of hoists plus an escalator within an existing building. After non-destructively choosing the tendons that spanned through 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.