A prestressing anchorage method is designed and certified 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 up of tensioning anchor head, wedges, Anchorhead plate and spiral reinforcement. Wedge: also called grips or jaws, is made by high-class alloy steel 20CrMnTi. The two main kinds, the initial one is called working grips that is with 2 chips; the one is called tool grips which is with 3 chips.
Anchor head, also referred to as anchor rings or anchor block, is vital a part of bearing the prestressing tension. The two main forms of anchor head: one is round anchor head which can be created by 45# high-quality carbon construction steel, as well as the other is flat anchorage which can be made by 40Cr steel. And the prestressing Anchor head has to be worked with wedges.
Bearing plate is vital component, which transfer the burden from anchor head over to concrete under anchor. The method of transfer and distribution of stress change 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 imagine that the roll-out of openings in existing PT slabs is either extremely complex or impossible. Consideration in the correct procedures demonstrates this to not become the case. Post-formed holes in PT slabs will vary in proportions starting from the tiniest penetrations, which might be needed to incorporate suspended services, to much bigger openings to permit adding lifts or similar installations. In all post-tensioned slabs, the most typical tendon layouts use a banded design which offers large, regular spaces between tendons that will easily accommodate smaller openings.
In such instances, alterations can be more straightforward when compared to other sorts of construction, as the roll-out of holes within these areas can be achieved without affecting structural performance. The anchorage grip, in the Guidance Note, identifies four varieties of post-formed penetration which can be categorised in accordance with the effect the operation will have on structural integrity. The very first of such relates to the tiniest holes, no more than 20mm in diameter, involving no tendon cutting and that offers minimal risk towards the structural integrity of the slab. The 2nd group is classed as a low risk to structural integrity and includes somewhat larger openings, approximately 200mm in diameter in beams or near to columns, but larger in areas which can be less stressed.
The voids continue to be located between tendons in order to avoid the requirement to cut these. Inside the third and fourth categories of penetrations, where it will become required to sever the tendons, the effect on the integrity from the structure will probably 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 typical form of post-tensioning in the UK market is bonded PT (Figure 4). Ducts carrying high-tensile steel strands are loaded with grout after the tendons have already 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 post stressed accessories, they can be treated in the same way as traditional reinforced concrete slabs since the effects of cutting through a bonded tendon remain localised and the rwkhni redevelops its bond both sides in 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 more security. CCL recently undertook an application that required the creation of voids within bonded slabs, in order to house a number of hoists as well as an escalator in a existing building. After non-destructively choosing the tendons that spanned from the proposed void within 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.