Title:
Long-Term Deflections of Reinforced Concrete Beams: Reconsideration of Their Validity
Author(s):
Bernard Espion and PierreE Halleux
Publication:
Structural Journal
Volume:
87
Issue:
2
Appears on pages(s):
232-236
Keywords:
beams (supports); building codes; confidence limits; humidity; cracking (fracturing); creep properties; deflection; loads (forces); reinforced concrete; shrinkage; standard deviation; statistical analysis; structural design; variability; Structural Resear
DOI:
10.14359/2744
Date:
3/1/1990
Abstract:
It has generally been assumed that the variability of the ACI method for predicting long-term deflections is ñ 30 percent around the mean value; this assumption was supported by a 1972 variability study by ACI Committee 435 on a relatively small number of long-term experiments carried out in the United States. This paper shows that this confidence interval is only valid for beams undergoing sustained loading under rather dry environmental conditions. When the ACI method is applied to a larger set of long-term experimental results, including other kinds of environmental conditions, a much wider variability ( ñ 62 percent) is found. For the same set of results, lower variability ( ñ 35 percent) is achieved with the new CEB method, which is much more complete than the ACI method, but which explicitly accounts for more conditions.