Title:
Effects of High Construction Loads on the Long-Term Deflections of Flat Slabs
Author(s):
N. J. Gardner and H. C. Fu
Publication:
Structural Journal
Volume:
84
Issue:
4
Appears on pages(s):
349-360
Keywords:
concrete construction; creep properties; deflection; flat concrete slabs; formwork (construction); loads (forces); reinforced concrete; shrinkage; structural design; Structural Research
DOI:
10.14359/1641
Date:
7/1/1987
Abstract:
Typical construction procedure for multistory flat-slab structures involves casting the new slab onto forms that are supported by one or more previously cast floors. The loads occurring on the supporting slabs are large relative to the slabs' design capacity. The large construction loads on immature slabs cause large immediate deflections. Furthermore, the high stress/developed strength due to construction loads will cause large creep deflections. This paper describes an experimental investigation into the effect of early age construction loads on the long-term deflections of reinforced concrete flat slabs. The measured long-term deflections were five to eight times the sustained load deflections calculated using the 28-day concrete properties. The high construction loads in shored and shore/reshore construction cannot be ignored when considering long-term deflection. Consequently, to insure adequate deflection behavior, the slab designer must specify the construction schedule, including number of forms and reshores and concrete strength at stripping. A design method that includes a construction load dependent creep term is presented to calculate the long-term deflections of flat-slab structures.