Accurate Long-Term Deflection Prediction in Flat Slabs Using Linear Elastic Global Analysis White Paper

Synopsis: With long-term deflection being a critical design criterion, accurate deflection prediction is an important aspect of slab design. The many factors that influence long-term deflections and their interdependence as well as variability in material strengths and characteristics make this a challenging problem. Most building codes and standards provide methods and formulae to account for these factors, although the predictions are sometimes crude. In this paper an approach is presented that comprehensively considers the factors commonly considered important in the calculation of long-term deflections – cracking, tension stiffening, creep, and shrinkage. The load history effects on the applicable factors are also considered. After detailed non-linear calculations are performed on the cross sections, an approach is discussed that uses the cross section results in conjunction with a linear elastic global analysis to calculate accurate two-way slab deflections.