Development and assessment of a modified ζ-method for deflection control of two-way slabs

Abstract

Deflection control of two-way slabs is a very complex task considering their possible geometries, structural systems, reinforcement layouts and loading histories, as well as the large number of influencing parameters and moment redistribution due to cracking and time-dependent effects of creep and shrinkage. As a consequence, sufficiently simple and accurate methods for deflection control of two-way reinforced concrete slabs have are still missing. In order to fill this gap, a novel method was developed as an adaptation of the ζ-method (as defined by the fib Model Code 2010) of interpolating deflections between the uncracked and fully cracked state. The method is based on deflections obtained using linear-elastic analyses in finite element software, which are then transformed through a series of stiffness normalizations to obtain time-dependent deflections due to load and shrinkage. Furthermore, the moment redistribution capacity of two-way slabs is accounted for through adjustments of the interpolation coefficient ζ. The method is tested against available experimental results from literature and compared with results obtained using existing methods such as the crossing beam method. The results show good precision and accuracy of the proposed method and an improvement compared with existing methods.