A prestressing anchorage system 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 approximately 55 strands
YM Series items are made up of tensioning anchor head, wedges, stressing anchorage plate and spiral reinforcement. Wedge: also called grips or jaws, is produced by high-class alloy steel 20CrMnTi. There are two kinds, the initial one is called working grips which can be with 2 chips; the main one is called tool grips which can be with 3 chips.
Anchor head, also referred to as anchor rings or anchor block, is the key element of bearing the prestressing tension. The two main types of anchor head: one is round anchor head which is created by 45# high-quality carbon construction steel, and the other is flat anchorage which can be produced by 40Cr steel. And the prestressing Anchor head should be worked with wedges.
Bearing plate is the key component, which transfer the burden from anchor head to concrete under anchor. The method of transfer and distribution of stress impact the anti-cracking and load capacity of concrete. Spiral reinforcement, also known as hoop reinforcement, is used for distributing the concrete and strengthening tendons.
A standard misconception exists, which leads some to imagine that the development of openings in existing PT slabs is either extremely complex or impossible. Consideration from the correct procedures demonstrates this not to be the case. Post-formed holes in PT slabs can vary in dimensions which range from the smallest penetrations, which can be necessary to incorporate suspended services, to much larger openings to permit the addition of lifts or similar installations. In all post-tensioned slabs, the most frequent tendon layouts utilize a banded design which provides large, regular spaces between tendons which will easily accommodate smaller openings.
In such instances, alterations is often more straightforward than in other types of construction, as the development of holes within these areas may be accomplished without affecting structural performance. The anchorage grip, in the Guidance Note, identifies four varieties of post-formed penetration that are categorised in accordance with the effect the operation will have on structural integrity. The initial of such pertains to the tiniest holes, no more than 20mm in diameter, involving no tendon cutting and that provides minimal risk for the structural integrity in the slab. The second group is classed as a low risk to structural integrity and includes somewhat larger openings, as much as 200mm in diameter in beams or near columns, but larger in areas that are less stressed.
The voids remain located between tendons in order to avoid the necessity to cut these. Within the third and fourth types of penetrations, where it might be required to sever the tendons, the effect on the integrity of the structure may very well 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 of corrosion protection to exposed cut steel.
The most typical kind of post-tensioning throughout the uk marketplace is bonded PT (Figure 4). Ducts carrying high-tensile steel strands are loaded with grout following the tendons have been stressed and locked off by means of split wedges in the anchors, thereby bonding the tendons to the concrete. If larger openings are essential in pre-stressing anchor, they can often be treated in the same way as traditional reinforced concrete slabs as the outcomes of cutting by way of a bonded tendon remain localised and the rwkhni redevelops its bond both sides of the cut, typically within 1m.
In instances where it really is essential to cut multiple tendons, mechanical or epoxy anchorages may be placed on the ends from the severed tendons to supply even greater security. CCL recently undertook an application that required the creation of voids within bonded slabs, so that you can house a number of hoists plus an escalator in a existing building. After non-destructively choosing the tendons that spanned from the proposed void in the slab, by way of the ‘as built’ drawings from your 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.