A prestressing anchorage method is designed and licensed for a wide variety 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 from tensioning anchor head, wedges, stressing anchorage plate and spiral reinforcement. Wedge: also referred to as grips or jaws, is produced by high-class alloy steel 20CrMnTi. There are 2 kinds, the initial one is called working grips that is with 2 chips; the one is known as tool grips which can be with 3 chips.
Anchor head, also called anchor rings or anchor block, is key a part of bearing the prestressing tension. There are 2 types of anchor head: one is round anchor head which can be made by 45# high-quality carbon construction steel, and also the other is flat anchorage which is produced by 40Cr steel. As well as the prestressing Anchor head should be dealt with wedges.
Bearing plate is key component, which transfer the stress from anchor head over to concrete under anchor. The method of transfer and distribution of stress affect the anti-cracking and load capacity of concrete. Spiral reinforcement, also called hoop reinforcement, can be used for distributing the concrete and strengthening tendons.
A common misconception exists, which leads some to believe that the development 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 can vary in proportions starting from the smallest penetrations, which might be required to incorporate suspended services, to larger openings to allow incorporating lifts or similar installations. In every post-tensioned slabs, the most common tendon layouts utilize a banded design which provides large, regular spaces between tendons which will easily accommodate smaller openings.
In these instances, alterations can be more straightforward when compared to other types of construction, as the creation of holes within these areas can be accomplished without affecting structural performance. The dead-end anchorage, in its 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 concerns the littlest holes, not more than 20mm in diameter, involving no tendon cutting and which offers minimal risk to the structural integrity from the slab. The 2nd group is classed as 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 can be less stressed.
The voids remain located between tendons in order to avoid the necessity to cut these. Inside the third and fourth types of penetrations, where it might be essential to sever the tendons, the result on the integrity from the structure will probably be more significant and demands strengthening and temporary propping from the slab. As the quantity of cut traditional reinforcement is quite a bit less, so is the requirement of corrosion protection to exposed cut steel.
The most common form of post-tensioning in the UK marketplace is bonded PT (Figure 4). Ducts carrying high-tensile steel strands are full of grout right after the tendons have been stressed and locked off by way of split wedges within the anchors, thereby bonding the tendons towards the concrete. If larger openings are required in slab steel anchor, they can often be treated in a similar manner as traditional reinforced concrete slabs because the effects of cutting by way of a bonded tendon remain localised as well as the rwkhni redevelops its bond either side of the cut, typically within 1m.
In instances where it really is necessary to cut multiple tendons, mechanical or epoxy anchorages may be placed on the ends in the severed tendons to supply even greater security. CCL recently undertook an application that required the development of voids within bonded slabs, so that you can house several hoists and an escalator in a existing building. After non-destructively choosing the tendons that spanned through 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 across the exposed strand before cutting, thereby giving enhanced surety of anchoring.