Modelling of tension stiffening in reinforced concrete slabs

A realistic prediction of deflection in slabs is only possible if the effects of early age striking, and construction loads on tension stiffening are included. Non-linear finite element analyses have been made to gain a better understanding ofthe 'mechanisms of tension stiffening in tension members and slabs. Laboratory tests have been carried out to gather information on the cracking moment, the mean moment resisted by cracked concrete (derived from strain measurements and back analysis of deflecti~n data) and influence ofpeak construction loading on deflection. Nine tests on slabs have provided data on the cracking moment of slab compared with companion beams. Mean surface strains were measured' in the constant moment region of the slabs with a Demec gauge. These strains were used to determine the position of neutral axis and the curvature which was also determined from a back analysis of deflection data measured by transducers. The mean strain in the reinforcement over the constant moment region is obtained by assuming it equals the mean surface strain at the level of reinforcement. An improved method is developed for taking account of construction loading in deflection calculations with EC2. Crack spacing and crack width were two phenomena which were measured and taken into account for non-linear fInite element analysis made in parallel with experiment. Numerical investigation into mechanisms Jor tension stiffening has been carried out with non linear fInite element analys'is 'of tension spec'imens and beams with discrete cracks and bond slip. The output from the one-dimensional analys~s includes crack spacings, distribution of bond stress, slip, tensile stress in concrete, tensile stress in reinforcement and load-displacement. In the two-dimensional model mechanism of tension stiffening in beams has been investigated. Comparison has been made between predicted deflections and deflection given by EC2 as well as tension tie model. Vollum's previous assumption, which was derived from a back analysis of Cardington data, has been validated. The results of the analysis have been used to develop a simplifIed tension stiffening model for use in NLFEA in which the stiffness of the reinforcement is modifIed to model tension stiffening in reinforced concrete slabs.EThOS - Electronic Theses Online ServiceGBUnited Kingdo