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 composed of tensioning anchor head, wedges, Post Tension Anchor plate and spiral reinforcement. Wedge: also called grips or jaws, is made by high-class alloy steel 20CrMnTi. There are 2 kinds, the first is called working grips which is with 2 chips; the main one is referred to as tool grips which is with 3 chips.
Anchor head, also referred to as anchor rings or anchor block, is vital element of bearing the prestressing tension. The two main kinds of anchor head: the initial one is round anchor head that is produced by 45# high-quality carbon construction steel, as well as the other is flat anchorage which can be created by 40Cr steel. And the prestressing Anchor head should be dealt with wedges.
Bearing plate is the key component, which transfer the load from anchor visit concrete under anchor. The technique of transfer and distribution of stress change the anti-cracking and load capacity of concrete. Spiral reinforcement, also referred to as hoop reinforcement, can be used for distributing the concrete and strengthening tendons.
A common misconception exists, which leads some to imagine that the creation of openings in existing PT slabs is either extremely complex or impossible. Consideration of the correct procedures demonstrates this not to become the case. Post-formed holes in PT slabs will vary in proportions ranging from the tiniest penetrations, which can be required to incorporate suspended services, to much larger openings to permit adding lifts or similar installations. In all post-tensioned slabs, the most frequent tendon layouts utilize a banded design which supplies large, regular spaces between tendons which will easily accommodate smaller openings.
Such instances, alterations can be more straightforward than in other kinds of construction, as the roll-out of holes within these areas can be achieved without affecting structural performance. The post tension anchorage, in their Guidance Note, identifies four kinds of post-formed penetration that are categorised based on the effect the operation will have on structural integrity. The first of those pertains to the smallest holes, not more than 20mm in diameter, involving no tendon cutting and that offers minimal risk to the structural integrity from the slab. The second group is classed being 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 need to cut these. In the third and fourth types of penetrations, where it might be required to sever the tendons, the result on the integrity in the structure is likely to be more significant and demands strengthening and temporary propping in the slab. As the quantity of cut traditional reinforcement is quite a bit less, so is the requirement for corrosion protection to exposed cut steel.
The most typical type of post-tensioning in the united kingdom marketplace is bonded PT (Figure 4). Ducts carrying high-tensile steel strands are filled with grout right after the tendons have already been stressed and locked off through split wedges in the anchors, thereby bonding the tendons for the concrete. If larger openings are required in barrel and wedge anchor, they can often be treated in the same manner as traditional reinforced concrete slabs as the results of cutting through 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 necessary to cut multiple tendons, mechanical or epoxy anchorages can be put on the ends in the severed tendons to supply even greater security. CCL recently undertook an application that required the roll-out of voids within bonded slabs, in order to house several hoists plus an escalator within an existing building. After non-destructively choosing the tendons that spanned through the proposed void in the slab, by means of the ‘as built’ drawings from the operations and maintenance manual, the posttensioning duct was opened (Figure 5) and epoxy grout anchors were then installed across the exposed strand just before cutting, thereby giving enhanced surety of anchoring.