A prestressing anchorage product is designed and certified for numerous 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 as much as 55 strands
YM Series products are made up of tensioning anchor head, wedges, Anchorhead plate and spiral reinforcement. Wedge: also referred to as grips or jaws, is made by high-class alloy steel 20CrMnTi. There are 2 kinds, one is called working grips which is with 2 chips; the main one is referred to as tool grips that is with 3 chips.
Anchor head, also called anchor rings or anchor block, is vital a part of bearing the prestressing tension. The two main forms of anchor head: the first is round anchor head which is made by 45# high-quality carbon construction steel, as well as the other is flat anchorage which can be produced by 40Cr steel. As well as the prestressing Anchor head has to be worked with wedges.
Bearing plate is vital component, which transfer the load from anchor head to concrete under anchor. The technique of transfer and distribution of stress change the anti-cracking and load capacity of concrete. Spiral reinforcement, also known as hoop reinforcement, can be used for distributing the concrete and strengthening tendons.
A common 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 to not become the case. Post-formed holes in PT slabs can vary in proportions which range from the littlest penetrations, which may be required to incorporate suspended services, to much larger openings to allow the addition of lifts or similar installations. In most post-tensioned slabs, the most common tendon layouts use a banded design which provides large, regular spaces between tendons that will easily accommodate smaller openings.
Such instances, alterations is often more straightforward than in other types of construction, as the development of holes within these areas can be achieved without affecting structural performance. The dead-end anchorage, in its Guidance Note, identifies four types of post-formed penetration that are categorised based on the effect the operation could have on structural integrity. The first of those pertains to the tiniest holes, not more than 20mm in diameter, involving no tendon cutting and that offers minimal risk for the structural integrity in the slab. The second group is classed being a low risk to structural integrity and includes somewhat larger openings, up to 200mm in diameter in beams or near to columns, but larger in areas which can be less stressed.
The voids are still located between tendons to prevent the requirement to cut these. Within the third and fourth kinds of penetrations, where it might be essential to sever the tendons, the effect on the integrity from the structure will probably be more significant and calls for 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 kind of post-tensioning throughout the uk industry is bonded PT (Figure 4). Ducts carrying high-tensile steel strands are full of grout after the tendons have been stressed and locked off by means of split wedges within the anchors, thereby bonding the tendons to the concrete. If larger openings are required in pre-stressing anchor, they is often treated in a similar manner as traditional reinforced concrete slabs as the outcomes of cutting via a bonded tendon remain localised and the rwkhni redevelops its bond either 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 from the severed tendons to supply even more security. CCL recently undertook a software that required the creation of voids within bonded slabs, so that you can house several hoists as well as an escalator in a existing building. After non-destructively locating the tendons that spanned with the proposed void in 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.