A prestressing anchorage method is designed and certified for a multitude of applications: utilization 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, stressing anchorage plate and spiral reinforcement. Wedge: also known as grips or jaws, is produced by high-class alloy steel 20CrMnTi. There are two kinds, the first is called working grips that 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 vital part of bearing the prestressing tension. There are 2 types of anchor head: the first is round anchor head that is produced by 45# high-quality carbon construction steel, and also the other is flat anchorage which is made by 40Cr steel. And also the prestressing Anchor head has to be dealt with wedges.
Bearing plate is vital component, which transfer the load from anchor head to concrete under anchor. The method of transfer and distribution of stress change the anti-cracking and load capacity of concrete. Spiral reinforcement, also referred to as hoop reinforcement, is used for distributing the concrete and strengthening tendons.
A standard misconception exists, which leads some to believe that the roll-out 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 vary in proportions starting from the smallest penetrations, which might be necessary to incorporate suspended services, to much larger openings to permit the addition of lifts or similar installations. In every post-tensioned slabs, the most frequent tendon layouts utilize a banded design which offers large, regular spaces between tendons that will easily accommodate smaller openings.
Such instances, alterations can often be more straightforward when compared to other kinds of construction, as the creation of holes within these areas can be achieved without affecting structural performance. The dead-end anchorage, in the Guidance Note, identifies four kinds of post-formed penetration which can be categorised based on the effect the operation may have on structural integrity. The initial of those relates to the tiniest holes, not more than 20mm in diameter, involving no tendon cutting and that provides minimal risk towards the structural integrity from the slab. The next group is classed being a low risk to structural integrity and includes somewhat larger openings, as much as 200mm in diameter in beams or close to columns, but larger in areas which are less stressed.
The voids remain located between tendons to avoid the need to cut these. Inside the third and fourth categories of penetrations, where it will become required to sever the tendons, the impact on the integrity in the structure will probably be more significant and requires strengthening and temporary propping in the slab. As the amount of cut traditional reinforcement is quite a bit less, so is the requirement for 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 after the tendons have already been stressed and locked off by way of split wedges inside the anchors, thereby bonding the tendons for the concrete. If larger openings are required in slab steel anchor, they can often be treated in the same way as traditional reinforced concrete slabs since the effects of cutting via a bonded tendon remain localised and also the rwkhni redevelops its bond each side of the cut, typically within 1m.
In instances where it really is essential to cut multiple tendons, mechanical or epoxy anchorages can be put on the ends of the severed tendons to offer even greater security. CCL recently undertook a software that required the roll-out of voids within bonded slabs, in order to house several hoists plus an escalator inside an existing building. After non-destructively choosing the tendons that spanned through the proposed void within 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 around the exposed strand prior to cutting, thereby giving enhanced surety of anchoring.