Q.: Are slipformed structures ever prestressed? If so, how is the prestressing done?

A.: Continental Slipform Builders constructed a 200-foot-high cement storage silo at Nazareth, Pennsylvania that is post-tensioned. In the 14-inch-thick walls, horizontal 3 1/4-inch-diameter post-tensioned ducts were installed at intervals as the slipform rose. Post-tensioning steel strands were later threaded through the ducts and tensioned.