A prestressing anchorage product is designed and certified for a wide variety of 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. The two main kinds, the first is called working grips which can be with 2 chips; the main one is called tool grips which is with 3 chips.
Anchor head, also known as anchor rings or anchor block, is vital part of bearing the prestressing tension. There are 2 kinds of anchor head: one is round anchor head that is produced by 45# high-quality carbon construction steel, and the other is flat anchorage which is created by 40Cr steel. As well as the prestressing Anchor head has to be dealt with wedges.
Bearing plate is vital component, which transfer the stress from anchor visit 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 utilized for distributing the concrete and strengthening tendons.
A common misconception exists, which leads some to imagine that the development of openings in existing PT slabs is either extremely complex or impossible. Consideration of the correct procedures demonstrates this to not be the case. Post-formed holes in PT slabs will vary in size ranging from the smallest penetrations, which might be required to incorporate suspended services, to larger openings to allow the addition of lifts or similar installations. In every post-tensioned slabs, the most typical tendon layouts make use of a banded design which supplies large, regular spaces between tendons which will easily accommodate smaller openings.
In these instances, alterations can often be more straightforward compared to other types of construction, as the creation of holes within these areas may be accomplished without affecting structural performance. The wedge anchor, in their Guidance Note, identifies four types of post-formed penetration which are categorised based on the effect the operation may have on structural integrity. The very first of those relates to the tiniest holes, not more than 20mm in diameter, involving no tendon cutting and which offers minimal risk for the structural integrity of the slab. The second group is classed as 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 that are less stressed.
The voids remain located between tendons to prevent the requirement to cut these. Within the third and fourth categories of penetrations, where it will become necessary to sever the tendons, the result on the integrity in the structure may very well 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 of corrosion protection to exposed cut steel.
The most frequent form of post-tensioning in the united kingdom market is bonded PT (Figure 4). Ducts carrying high-tensile steel strands are full of grout right after the tendons happen to be stressed and locked off by way of split wedges within the anchors, thereby bonding the tendons towards the concrete. If larger openings are needed in slab steel anchor, they is often treated in the same manner as traditional reinforced concrete slabs as the outcomes of cutting via a bonded tendon remain localised and the rwkhni redevelops its bond either side from the cut, typically within 1m.
In instances where it is actually essential to cut multiple tendons, mechanical or epoxy anchorages may be placed on the ends of the severed tendons to supply even more security. CCL recently undertook an application that required the development of voids within bonded slabs, to be able to house a number of hoists and an escalator inside an existing building. After non-destructively locating the tendons that spanned with 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 prior to cutting, thereby giving enhanced surety of anchoring.