Variation of Shrinkage Strain within the Depth of Concrete Beams
The variation of shrinkage strain within beam depth was examined through four series of time-dependent laboratory experiments on unreinforced concrete beam specimens. Two types of beam specimens, horizontally cast and vertically cast, were tested; shrinkage variation was observed in the horizontally cast specimens. This indicated that the shrinkage variation within the beam depth was due to water bleeding and tamping during the placement of the fresh concrete. Shrinkage strains were measured within the beam depth by two types of strain gages, surface-attached and embedded. The shrinkage strain distribution within the beam depth showed a consistent tendency for the two types of gages. The test beams were cut into four sections after completion of the test, and the cutting planes were divided into four equal sub-areas to measure the aggregate concentration for each sub-area of the cutting plane. The aggregate concentration increased towards the bottom of the beam. The shrinkage strain distribution was estimated by Hobbs’ equation, which accounts for the change of aggregate volume concentration.
Impact of shrinkage on crack width and deflections of reinforced concrete beams with and without steel fibres
Abstract Current recommendations by fib Model Code 2010 only consider the effect of shrinkage strains on long-term crack width calculations of reinforced concrete (RC) elements. However, shrinkage strains develop fairly early and can influence mean strains as well as short-term crack width and deflection calculations. This paper examines the effect of shrinkage strains on short-term deformations using experiments on eight RC beams, with and without steel fibres, at the age of 4–5 months. The results show that due to shrinkage, measured strains, deflections and crack widths are higher than expected for fully cracked sections. The MC-2010 predictive equation for crack widths is amended to account for shrinkage strains and induced curvatures. This work will lead to better design equations and less serviceability problems in RC structures.
SR topography of plastically deformed Fe-Si bicrystals - observation in situ and post mortem
SR reflection topography was applied to study the interaction of slip dislocations with the grain boundaries in Fe-4at%Si bicrystals deformed by compression. Three experimental settings with either a white or monochromatic beam were used and the corresponding orientation contrast analysed. Dislocation transmission through the grain boundary was observed in bicrystals with favourable geometry of the slip systems.