ABSTRACT
Figure 1(b) shows an elevation of one half (due to symmetry) of a RC segment situated between a pair of adjacent primary cracks. The bending moment at a cracked section may be resolved into a tension force T in the bare reinforcement and a compressive force C in the form of a triangular stress block acting above the neutral axis. For an average crack spacing of sm, the average strain in the embedded reinforcement is εs,m = es/sm and the average strain at the extreme compressive fibres is εc,m = ec/sm, where es and ec are the elongation and shortening of the segment at those respective locations. Thus, the average curvature κm of the RC segment may be defined as:
κ ε εm s,m c,m−( ) d (2)
1 INTRODUCTION
Serviceability models based on the variation of strains in concrete and reinforcement between pairs of adjacent primary cracks have been used successfully to predict cracking behaviour and stiffness of RC flexural members (EC2 2004, Gilbert & Ranzi 2011, fib 2013, Castel et al. 2014). However, few serviceability models in the literature account for the significant disturbed strain regions in the neighbourhood of cracks. This paper presents an analytical model for estimating instantaneous flexural stiffness of cracked RC members based on recent FE studies of disturbed strain regions near cracks.
