Comparison of Preshore and Reshore Procedures for Flat Slabs


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Title: Comparison of Preshore and Reshore Procedures for Flat Slabs

Author(s): N. J. Gardner and Chi-Seng Chan

Publication: Special Publication

Volume: 90


Appears on pages(s): 157-174

Keywords: concrete construction; deflection; flat concrete slabs; shoring; formwork (construction); loads (forces); multistory buildings; reinforced concrete; structural analysis; General

Date: 4/1/1986

Multistory reinforced concrete structures are generally constructed using one level of shores and multiple levels of reshores. The stripping schedule is to completely strip a bay of shores before reshoring. Reshoring results in high-early-age construction loads being applied to the immature slab structures. Preshoring, or scheduled reshoring, is an attempt to reduce the adverse effects of clear bay reshoring by reducing the area stripped before reshoring. The load-strength ratio in preshored construction is little different to reshored construction but the loads are applied later which will reduce creep deflection effects. Using 2D and 3D models the slab, shore, and reshore loads were calculated for preshored construction. The advantage of preshoring is that the unsupported span lengths are reduced thus reducing slab deflections. The disadvantage of preshoring is that to realize the benefits close control of the construction process is needed.