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.
Predicting shrinkage induced curvature in plain and reinforced concrete
Abstract Shrinkage induced curvatures in reinforced concrete elements are thought to be affected only by section geometry and distribution/ratio of reinforcement. The variation in the level of internal restraint caused by the non-uniform distribution of concrete constituents within the section, however, can also lead to additional shrinkage induced deformations, and potentially to larger than expected deformations in critical structural elements, even under service conditions. This study examines experimentally the development of non-uniform shrinkage strains in unreinforced as well as symmetrically and asymmetrically reinforced concrete elements. Results confirm that shrinkage is non-uniform due to the variations in internal restrains (coarse aggregates and reinforcement). The addition of steel fibres mitigates this effect and reduces overall shrinkage curvature. A prediction model for shrinkage induced curvature of plain and reinforced concrete is proposed, taking into account the non-uniform distribution of concrete constituents. The proposed model yields results in good agreement with experimentally observed values of shrinkage curvature and can be used to improve the predictions of design guidelines.
Teaching self-care to delinquent adolescents.
Adolescent delinquency is an ever-increasing societal concern. Certain health problems are concentrated in the delinquent population. Families of delinquent youths often fail to reinforce self-care. Therefore health care providers need to focus on ways to teach delinquent adolescents to care for themselves. This article reviews delinquency and characteristics of juvenile delinquents and their families. A model is presented to guide health care providers to assess delinquent adolescents' abilities to care for themselves and to teach them strategies for self-care.