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.
Shrinkage and flexural behaviour of free and restrained hybrid steel fibre reinforced concrete
Abstract The effect of restrained shrinkage on the mechanical performance of concrete and steel fibre reinforced concrete (SFRC) requires more investigation, especially when using recycled tyre steel fibre (RTSF). This paper examines the free and restrained shrinkage strains and the mechanical performance of seven SFRC mixes. Results show that both free and restrained average shrinkage strains are very similar in all blends of fibres and they exhibited non-uniform shrinkage through the height of the section. All examined blends meet strength requirements by MC-2010 for fibres to replace part of the conventional reinforcement in RC structures.
RESTRAINT MOMENTS IN BRIDGES WITH FULL-SPAN PRESTRESSED CONCRETE FORM PANELS
An experimental investigation was carried out to evaluate the restraint moments generated at interior piers of bridges constructed with full-span prestressed concrete form panels. These moments result from the restraint of time-dependent deformation after adjacent spans are made continuous through a composite cast-in-place concrete topping. The experimentally determined moments from this investigation were compared with values calculated using current design methods for continuous prestressed concrete girders. It was concluded that these design methods, which ignore cracking of the cast-in-place topping, greatly overestimate the negative restraint moments in composite construction with shallow prestressed members. A new method for calculating restraint moments in bridges with shallow prestressed members, which includes provisions for cracking, is presented. Numerical design examples are included to illustrate the proposed method.