Moment® Multi Strand Round System
Moment® Multi Strand Round System is a method of reinforcing and pre-stressing concrete, masonry and other structural elements. Today, it is used for a wide range of applications including office buildings, condominiums, hotels, parking structures, slab-on-ground foundations, ground anchors, storage tanks, stadiums, silos, and bridges.
The systems are normally adopted for bonded tendons. The tendons consist of a bundle of strands with a nominal diameter of 0.5″ (12.7 mm.) or 0.6″ (15.2 mm.). The number of strands per tendon can be from 4 strands up to 42 strands of diameter 0.5″ or 31 strands of diameter 0.6″. The strands in the tendons are contained in one round duct which is made of corrugated galvanized metal.
The strands are individually gripped in one anchor head unit and transmit their pre-stressing force by means of an anchor plate casting unit. For each anchor size, special spiral reinforcement is provided at the anchor plate casting to give adequate splitting reinforcement for bustling stresses developed at the anchorage zone. The strands in tendon are stressed simultaneously by means of a multi strand stressing jack from capacity 1,100 KN up to 5,000 KN. The strands can also be stressed individually by means of mono jack.
The Strands are formed with seven steel wires: one central wire around which the other six are wrapped. They are generally supplied already stabilized (low relaxation) and certified according to the regulations by an independent laboratory, in coils weighing kg 2500-3000.
Usually greased or waxed strands, incased in a HDPE sheath, commonly called unbounded, are used to manufacture the external tendons. Such Strands can be hot-dip galvanized too.
|Appearance||Nominal Dia (mm)||Tensile Strength (Mpa)||Relaxation (1000h)||Standards|
left or right lay
Strands are formed with seven steel wires
The Stressing Jack is placed over the strand and when tensioning starts they are automatically and simultaneously engaged in the pulling head of the jack. Once the required elongation and load are reached the lock-off device of the jack can be activated to house the wedges in the anchor head uniformly. The tensioning can be accomplished in more steps basing the elongation of the cable. A tensioned cable can be released using proper releasing device.
Mono Strand Stressing Jack
Stressing Jack will be removed after stressing and anchoring. In post-tensioning the prestressing force is applied directly to the concrete. In the case of pre-tensioning the anchor holds the strands until after the concrete has gained sufficient strength; the strands are then released, transferring the prestressing force to the concrete.
Cables are normally grouted after sealing their anchorages with the concrete or; if required, using the proper grouting caps. Before grouting the tendons, they should be flushed to ensure that no obstruction would impede the flow of the injected grout.
The sandless grout, injected using MPT grouting pump, is keep under pressure during its curing. The water-to-cement ratio is kept as low as possible. Usually the proportion of ingredients are: 36-38 liters of water, 100kg of cement and additive according to the instruction of the manufacturer. The mix produces 72-74 liters of grout.
MPT Grouting Pump
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