Prestressed Concrete: The Future of Construction

Even though a San Francisco engineer developed prestressed concrete in 1886, it took fifty years for it to become a widely used building material. During the Second World War, prestressed concrete was the preferred building material in Europe due to a scarcity of steel and developments in high-strength concrete and steel technology. However, the Walnut Lane Memorial Bridge in Philadelphia, Pennsylvania—the first prestressed concrete construction in North America—was not finished until 1951.

The high tensile strength of steel and the excellent compressive strength of concrete are combined in conventional reinforced concrete to create a structural material that is strong in both compression and tension. Prestressed concrete works on the basis of the idea that tensile stresses placed on a concrete member during service would be balanced by compressive stresses created by high-strength steel tendons in the member prior to loads being applied.

Prestressing enables the construction of walls, floors, roofs, bridges, and other structures with longer unsupported spans by removing certain design restrictions that ordinary concrete imposes on span and load. Because of this, engineers and architects are able to create concrete buildings that are shallower and lighter without compromising strength.

When a row of books is shifted, the prestressing theory is put into practice. By exerting pressure to the books at the end of the row, you may move the books in a horizontal position as an alternative to stacking them vertically and transporting them. The row may be raised and transported horizontally all at once when enough pressure is applied to cause compressive stresses to be created throughout the row.

Increased Compressive Strength

Pretensioning or post-tensioning the steel reinforcement causes compressive stresses in prestressed concrete.

The steel is stretched prior to the concrete being poured in pretensioning. Strains of high-strength steel are stretched to between 70 and 80 percent of their maximal strength and positioned between two abutments. After pouring concrete into molds around the tendons, it is left to cure. The stretching forces are released when the concrete reaches the desired strength. Tensile tensions are converted into compressive stresses in the concrete when the steel reverts to its original length. Pretensioned concrete is commonly used to create wall panels, railroad ties, piles, poles, and roof slabs.

Post-tensioning involves stretching the steel following the hardening of the concrete. Unstretched steel is surrounded by concrete, but not in touch with it. Steel forms with thin walls are frequently used to create ducts inside concrete units. The steel tendons are inserted, stretched against the ends of the unit, and anchored off externally to put the concrete into compression after it has hardened to the necessary strength. For cast-in-place concrete, bridges, big girders, floor slabs, shells, roofs, and pavements, post-tensioned concrete is utilized.

The commercial building industry has witnessed the most rise in the use of prestressed concrete. Prestressed concrete is a great option for structures like retail complexes because it offers the span length required for internal structural modification and flexibility. Prestressed concrete’s acoustical qualities and capacity to create vast, open spaces make it a popular choice for school auditoriums, gyms, and cafeterias. Parking garages are among the most common applications for prestressed concrete.

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