Prescon Technology

Prescon Philippines, Inc. introduced a lot of technologies that helped the construction industry in the country. Back in 1967, our founder pioneered a new method of pre-stressed concrete construction-the post-tensioning system.

Over the years we have made it our mission to continue developing and improving these systems and we are proud to offer the most efficient and economical ways of constructing a building.

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"A method of reinforcing or strengthening concrete or other materials with high-strength steel strands or bars typically referred to as tendons."
- Post-Tensioning Institute

To better understand post-tensioning, one must know the difference between reinforced and pre-stressed concrete. Concrete is very strong in compression but relatively weak in tension. These two utilize the structural capabilities of steel and concrete.

The ordinary reinforced concrete beam supports a load by developing compressive stresses at the top, but since the concrete cannot resist the tension at the bottom, it cracks there. Reinforcing steel bars are placed within this tension zone to resist the tension and control the cracking.

Pre-stressed concrete, however, involves the application of force or forces tending to bend and compress a concrete structure or structural element in order to counteract the bending which results from loading. The force applied is the tensioning or stretching of the steel component which is usually in the form of high-tensile strands, wires or bars.

In a reinforced concrete beam, less than half the concrete is in compression, and cracks will appear in the bottom of the beam under full load.

When a concrete beam is pre-stressed, all the concrete acts in compression. The off-center location of the pre-stressing steel causes a camber in the beam.

Under loading, the pre-stressed beam becomes flatter, but all the concrete still acts in compression, and no cracks appear.

TWO TYPES OF PRE-STRESSED CONCRETE

1) Pre-tension pre-stressed concrete

The beams or elements are constructed on a stressing bed and stranded cable is placed between two buttresses anchored to a stressing bed which holds the force in the stretched cables. After stretching the steel with hydraulic jacks, concrete is placed in forms around the cables and allowed to harden. When the concrete reaches sufficient strength, the pre-stress force is transferred to the concrete by bond when the steel strand at the ends of the beam is cut loose from buttresses. It is usually fabricated away from the job site in a pre-stressing plant.

2) Post-tension pre-stressed concrete

The concrete member (beam, slab, or girder) is first cast and allowed to harden, with ducts/sleeves or tendon pathways already placed inside the formwork. After the concrete reaches the required strength, steel tendons/cables are inserted (or already positioned) and then stressed using hydraulic jacks from one or both ends. The stressed tendons are then anchored using mechanical anchorages at the ends of the member to lock in the force. In most cases, the ducts are grouted after stressing to protect the tendons from corrosion and to improve bonding. Post-tensioning is commonly done on-site (in-situ) or in precast yards, especially for long spans and heavily loaded structures.

Multi-Bulb Type

Multi-Loop Type

Prescon Type

Double-Lock Type

ADVANTAGES OF POST-TENSIONING

SERVICEABILITY

More suitable for structures of long span and those carrying heavy loads because of the higher strengths of materials employed.
Members are slender and adaptable to artistic treatment. They yield more clearance and don't crack under working loads. Whatever cracks may be developed under overloads will be closed as soon as the load is removed.
Where limited height is required, more floors can be constructed because of shallower beams and slabs.
Cranes and other heavy equipment are unnecessary.
Waterproofing is not required for a two-way post-tensioned slab.

SAFETY

For many structures during post-tensioning, both steel and concrete are subjected to the highest stresses that will exist in them during their service period. Hence, if materials can stand post-tensioning, they are likely to possess sufficient strength for service loads.
The ability to resist shock and impact loads and repeated working loads is as good in post-tensioned as in reinforced concrete. The resistance to corrosion is better than that of reinforced concrete for the same amount of cover, owing to the non-existence of cracks.
Cast-in-place solid monolithic construction is completely safe and resistant to earthquakes.

ECONOMICS

Smaller quantities of materials, both steel and concrete, are required to carry the same loads since the materials are of higher strength.
The reduced weight of members will help in economizing the cost of structures; the smaller dead load and section of the member will result in saving materials and labor such as the foundation, columns, shear walls, etc.
No joints can be seen as it is a monolithic structure. Concrete topping is not required.
Construction can be stopped at any floor which is automatically waterproofed when tendons are placed in both directions. Thus, there is no additional expense for the next phase of construction.

SPEED

Camber and deflection are reduced in a post-tensioned member at the service load. Construction is much faster than another system of construction because formwork can be removed after stressing usually after seven days.