Control of Deflection in Concrete Slabs and Effects of Construction Loads

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Title: Control of Deflection in Concrete Slabs and Effects of Construction Loads

Author(s): Pericles C. Stivaros

Publication: Special Publication

Volume: 284

Issue:

Appears on pages(s): 1-22

Keywords: Concrete slabs, construction failures, cracking, deflection control, long term deflection, serviceability, shoring/reshoring, two-way slabs.

Date: 3/1/2012

Abstract:
This paper is concerned with the effects of high construction loads on long term deflections, and evaluates the ACI 318 deflection control requirements. Practical applications involving two building construction cases are presented. In these cases, the concrete slabs developed extensive cracking and excessive deflections soon after the slab construction and formwork removal. Additional deflections were developed following the installation of interior partitions. The paper also investigates the effects of the shoring/reshoring operations and the construction load history, as well as the effects of improper deflection control design procedures on the slab deflections. The ACI 318 slab deflection control requirements, along with other published proposed methods on deflection control are applied and compared. The conclusions of this study indicate that the ACI’s minimum slab thickness requirements for deflection control are not sufficient since they do not account for the creep and shrinkage effects, as well as the effects of early-age high construction loads, and the resulting initial cracking of the concrete members.