A prestressing anchorage product is designed and certified for numerous 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 up to 55 strands
YM Series products are made from tensioning anchor head, wedges, Anchorage Barrel And Wedge plate and spiral reinforcement. Wedge: also called grips or jaws, is made by high-class alloy steel 20CrMnTi. The two main kinds, the initial one is called working grips which can be with 2 chips; the one is known as tool grips which can be with 3 chips.
Anchor head, also known as anchor rings or anchor block, is key element of bearing the prestressing tension. There are two types of anchor head: the initial one is round anchor head that is created by 45# high-quality carbon construction steel, as well as the other is flat anchorage that is produced by 40Cr steel. And the prestressing Anchor head has to be dealt with wedges.
Bearing plate is vital component, which transfer the load from anchor head over to concrete under anchor. The method of transfer and distribution of stress change the anti-cracking and load capacity of concrete. Spiral reinforcement, also known as hoop reinforcement, is utilized for distributing the concrete and strengthening tendons.
A common misconception exists, which leads some to think that the development 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 be different in dimensions starting from the littlest penetrations, which may be needed to incorporate suspended services, to larger openings to allow incorporating lifts or similar installations. In every 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.
In these instances, alterations can often be more straightforward compared to other types of construction, as the roll-out of holes within these areas may be accomplished without affecting structural performance. The anchorage grip, in their Guidance Note, identifies four varieties of post-formed penetration which are categorised based on the effect the operation will have on structural integrity. The very first of such concerns the littlest holes, no more than 20mm in diameter, involving no tendon cutting and which offers minimal risk towards 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 columns, but larger in areas which can be less stressed.
The voids remain located between tendons to prevent the necessity to cut these. Inside the third and fourth kinds of penetrations, where it becomes necessary to sever the tendons, the impact on the integrity of the structure will probably be more significant and calls for strengthening and temporary propping in the slab. As the amount of cut traditional reinforcement is significantly less, so is the requirement of corrosion protection to exposed cut steel.
The most common type of post-tensioning in the UK industry is bonded PT (Figure 4). Ducts carrying high-tensile steel strands are full of grout right after the tendons have already been stressed and locked off by way of split wedges within the anchors, thereby bonding the tendons to the concrete. If larger openings are required in slab steel anchor, they is often treated in the same manner as traditional reinforced concrete slabs since the effects of cutting by way of a bonded tendon remain localised and also the rwkhni redevelops its bond each side in the cut, typically within 1m.
In instances where it is actually necessary to cut multiple tendons, mechanical or epoxy anchorages can be placed 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 a number of hoists plus an escalator within an existing building. After non-destructively seeking the tendons that spanned with the proposed void within 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 around the exposed strand just before cutting, thereby giving enhanced surety of anchoring.