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Post tension cable experts

Miyagi Construction ltd – Our team has a total of 15 years’ experience replacing Post-Tension Cable. Cable Replacement Cable Drying Cable Re-Greasing Cable Testing New Recess Installation Call us (778) 513-7471

Post Tension Cable

Post-Tension overview

Post-Tension Materials provide advantages over convention designs (rebar & concrete) and pre-cast structures for several reasons. Concrete is very weak in tension but extremely strong in compression. Post-tensioning acts on the concrete structure or elements by compressing the cast-in-place concrete to high pressures. Some advantages of post-tensioned concrete include crack control and lower construction costs.

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Post-tension materials (PT) can provide thinner slabs and is especially important in high rise buildings in which floor thickness savings can translate into additional floors for the same (or lower) cost. PT can optimize constructability by having fewer joints since the distance that can be spanned by post-tensioned slabs exceeds that of reinforced construction with the same thickness. Architects like having a PT option since increased span lengths also increases the usable floor space in buildings and provides more parking spaces in garages. Post-tensioning has advantages over pre-cast since it has lower maintenance costs over the life-cycle of the structure. Architectural shapes other than rectangles give post-tensioning an advantage over pre-cast, as well, since strands in cast-in-place construction can be curved or swept into place.

Post-tension systems use high strength steel strands that are comprised of seven individual wires spiraled together tightly. The most common diameter of the strands are 0.5” and 0.6”. These strands are stressed under high forces and an anchoring device, along with wedges, clamp down on the strand to retain the force applied while stressing. These anchorages help to distribute these forces into the concrete resulting in the desirable concrete compression.

There are basically two types of post-tension system categories – “Bonded Multi-strand” and “Un-bonded Mono-strand”. Both types have a wide range of uses and applications. Another post-tensioning material is the PT Threaded Bar. It is a piece of steel rod that has threads that are cold-rolled into the rod. These bars can be stressed and anchored similar to the strands.

Utilizing post-tension materials in designs and construction is a very economical choice. PT designs lend themselves to speedier construction and easier installations.


Post-Tension Repair

Corrosion of unbounded tendons is common for post-tension structures exposed to aggressive environments. Insufficient cover over the tendons and lack of corrosion protection at anchorages combined with exposure to chlorides through deicing materials and coastal air lead to the corrosion of post-tension systems. Barrier cables used in parking garages are similar to post-tension cables in concrete slabs and are subject to similar deterioration mechanisms. In some cases the failures occur quicker since the cables are directly exposed to the elements and do not have the added protection provided by concrete cover. Replacing barrier cables and anchors requires the same expertise as repairing post-tension tendons.

Repairs to post-tension systems fall into two categories:

Structural Repairs:

These repairs address system failures. Signs of structural post-tension system distress disclosed in the inspection can include the following and will require immediate repairs to restore strength and integrity to the structure:

  • Broken strands which can be seen coming out of the structure
  • End anchorage which has lifted out of the concrete
  • Cracking concrete which is running parallel to the strands
  • Excessive deflections
  • Punching shear cracks in slabs
  • Diagonal shear / flexure cracks in beams and joists

Preventative Maintenance:

Regular inspection of strand systems for signs of distress is one of the best ways for a building owner to prevent costly repairs. Items to be considered in the inspection of post-tension structures:

  • Appropriate concrete cover over strands exposed to aggressive environments
  • Condition of protective grease and sheathing
  • Cracking near strands (P-T systems are designed to reduce or eliminate cracking, so any excess cracking may indicate a problem)
  • Condition of concrete at anchorage pockets
  • Rust staining on the concrete near strands
  • Grease staining on slab soffits

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