Although pre-stressed concrete was patented by a San Francisco engineer in 1886, it did not emerge as an accepted building material until a half-century later. The shortage of steel in Europe after World War II coupled with technological advancements in high-strength concrete and steel made pre-stressed concrete the building material of choice during European post-war reconstruction. North America's first pre-stressed concrete structure, the Walnut Lane Memorial Bridge in Philadelphia, Pennsylvania, however, was not completed until 1951.
In conventional reinforced concrete, the high tensile strength of steel is combined with concrete's great compressive strength to form a structural material that is strong in both compression and tension. The principle behind pre-stressed concrete is that compressive stresses induced by high-strength steel tendons in a concrete member before loads are applied will balance the tensile stresses imposed in the member during service.
So we could say that Pre-stressed concrete is an architectural and structural material possessing great strength. This strength accomplished by combining the best properties of tow quality materials: high strength concrete for compressing and high tensile steel strand for tension.
Actually, pre-stressing is quite simple. High tensile strands are stretched between abutments at each end of long casting beds. Concrete is then poured into casting machine encasing the strands. As the concrete sets, it bonds to the tensioned steel. When the concrete reaches as a specific strength, the strands are released from abutments this compresses the concrete, arches the member, and creates a built in resistance to service leads.
Pre stressed Hollow core
A hollow core slab is a precast slab of pre-stressed concrete typically used in the construction of floors in multi-story apartment buildings. The slab has been especially popular in countries where the emphasis of home construction has been on precast concrete, including Northern Europe and former socialist countries of Eastern Europe. Precast concrete popularity is linked with low-seismic zones and more economical constructions because of fast building assembly lower self weight (less material), etc.
The precast concrete slab has tubular voids extending the full length of the slab, typically with a diameter equal to the 65% to 75% of the slab. This makes the slab much lighter than a massive solid concrete floor slab of equal thickness or strength. The reduced weight is important because it lowers the costs of transportation as well as material (concrete) costs. The slabs are typically 120 cm wide with standard thicknesses between 15 cm and 50 cm. Reinforcing steel wire rope provides resistance to bending moment from loads.
Regular width of hollow core pre-stressed slab units is 1100mm, including joints.
The standard profiles have a fire resistance of 60 to 120 minutes.
Our standard thicknesses: 200, 265, 320mm which can reach 20m spans for outside cladding