Effects of Story-by-Story Post-Tensioning on Multi-Story Buildings

The effects of story-by-story horizontal post-tensioning (PT) on multi-story buildings are investigated using staged construction analyses. Analytical column-supported and wall-supported multi-story models are studied to represent different degrees of restraint by supports. Findings include a determination that part of the PT force applied to an upper floor slab is diverted to floors below through flexure and shear of vertical structural elements. The first elevated PT floor and a PT roof may experience significantly reduced slab precompression from PT force diversion. Design recommendations are provided. The design of structural frames incorporating post-tensioned concrete members should consider secondary actions, such as moments and shears, for both horizontal and vertical members due to staged PT construction, in addition to gravity and lateral loads. Concrete PT floor slab serviceability stress checks should use realistic slab effective precompression forces, considering diversion of precompression forces through supports, rather than forces in tendons at that floor.