Prestressed, pretensioned and post-tensioned are methods used for reinforcing concrete. Experts define prestressed concrete as the process used to overcome concrete's natural weakness in tension by introducing internal stresses to counteract the tensile stresses encountered in service. “The stress is usually imposed by tendons of individual hard-drawn wires, cables of hard-drawn wires, or bars of high strength alloy steel.” Prestressed concrete is commonly used to produce beams, floors or bridges that require a longer span than would be safe with ordinary reinforced concrete, and may be pretensioned or post-tensioned.
Pretension concrete describes the process of tensioning the steel between anchorages or in a frame and then casting concrete around it. Once the concrete has sufficient strength the “tension is slowly released from the frame or anchorage to transfer the stress to the concrete to which the tendons have become bonded.”
In the case of post-tensioned concrete, the concrete has preset ducts or sleeves that are designed to allow tendons to be threaded through them. The tendons are positioned before the concrete is placed. Once the concrete has sufficient strength the tendons are tensioned by portable jacks and anchored against the outer edges of the concrete.
One high-profile problem that was solved by a complex post-tensioning fix was the San Francisco area’s Bay Bridge. The problem started when the anchor rods that secured the earthquake shock absorbers, known as shear keys, to the deck of the bridge failed. Since the failed rods were embedded in concrete and inaccessible, replacement was impossible. A team of experts, including Conco, designed and installed a complex series of steel saddles and post-tensioned jacket walls to provide the required clamping force required to secure the bridge deck framing to the E2 crossbeam.
The Conco Companies have a reputation for expertly fabricating precision-engineered rebar and post-tension cable in our two state-of-the-art facilities. To meet the most exacting specification and demand, our plants are outfitted with modern shear lines, benders and post-tension cable manufacturing equipment.
At The Conco Companies, we are one of the leading concrete contractors in the Western U.S. and offer a wide range of quality services and products. Our experience includes providing services for commercial, educational, parking and other construction development as well as public works projects. We serve California, Washington State, Oregon, Colorado and Nevada.