Prestressed Masonry
“Masonry is great in compression, but not so great in tension.”
That masonry engineering basic helps explain how prestressed masonry systems work. In prestressed masonry, tendons in the form of wires, strands or bars are used to produce controlled precompression, which reduces or eliminates the tensile forces in the masonry and makes the assembly more efficient structurally. Prestressed masonry does not replace conventional reinforced and grouted masonry, but simply provides another alternative.
The two general types of prestressing are pre-tensioned (stressed against an external base before the masonry is placed) and post-tensioned (stressed against the masonry after it has been placed). Post-tensioned is easier to construct.Openings with prestressing tendons may use a special prestressing grout, which can save money by reducing the amount of grouting.
Typical components are a bottom anchor, tendon and top anchor. Bottom anchors are cast into the foundation or built into the wall. Tendons are installed with the wall or later. The top anchor is then set. Once the specified strength is reached (3 to 7 days), tendons are tightened to clamp the wall into compression.
IMI Tech Brief
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IMI Post Tensioning Case Studies of Two Buildings in Southeastern Michigan
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