Vibrating wire

Abstract: The available literature indicates that pile side shear increases almost linearly with the logarithm of time elapsed after driving, sometimes described using a dimensionless setup factor. A test pile program conducted by the University of Florida measured side shear setup (SSS) for up to 4.7 years on five, 457-mm (18-in), square, prestressed, concrete piles driven into coastal plain soils at different sites. Dynamic tests performed during initial driving and two restrikes measured short-term SSS. Osterberg cells, the first installed in driven concrete piles, measured long-term SSS starting within 24 h of driving and continuing with two to five additional, staged tests. Extensive instrumentation, including vibrating wire strain gauges, Marchetti total stress cells, and vibrating wire piezometers, divided the five piles into 28 segments by soil type with horizontal effective stress measurements for 18 of the segments. This paper describes the University of Florida test pile program and its results. A companion paper analyzes the test results and recommends procedures for implementing SSS in design.

Abstract: A new vibrating-wire instrument for the meaasurement of the density of fluids at high pressures was described in a previous paper. The technique makes use of the buoyancy force on a solid sinker and detect, this force with a vibrating wire placed inside the measuring cell. Owing to the simple geometry of the oscillating element there exists a complete theoretical description of its resonance characteristics. enabling the calculation of the density of the fluid from their measurement. In the present paper a new method for the determination of the cell constants is outlined which permits the operation of the densimeter essentially as an absolute instrument. Furthermore. it is shown that the viscosity ol the fluid can be measured Simultaneously with the density. New results for three fluids are presented: for cyclohexane at temperatures from 298 to 348 K and pressures up to 40 MPa. for 2,2,4-trimethylpentane between 197 and 348 K at 0.1 MPa, and for 1,1,1,2-tetrafluoroethane from 197 to 298 K close to saturation. The sets of measurements where chosen with the intention of testing the performance of the apparatus. complementing previous work at higher pressures. The densities and viscosities measured exhibit the same accuracy for all of the three fluids over the entire temperature and pressure ranges and were obtained using the same set of cell parameters The precision of the densities is ±0.03% and their estimated accuracy is ±0.05%. File viscosities have a precision of ±0.6%, and an estimated accuracy of ±2%.

Abstract: Autogenous shrinkage, which is a consequence of the absolute volume contraction resulting from cement hydration, occurs in any concrete but its effect is particularly amplified in high performance concrete in which it can be as large as drying shrinkage. Autogenous shrinkage can be directly measured in concrete samples under isothermal conditions but from a practical standpoint the experimental procedure is not always possible. On the other hand, it can be evaluated after having taken into account volumetric variations due to the release in heat during cement hydration. To separate the thermal effect from autogenous shrinkage, it is necessary to know at any moment the evolution of the coefficient of thermal expansion of the concrete from initial setting. A simple method to determine the coefficient of thermal expansion at early ages is proposed in this paper. It consists in submitting concrete samples instrumented with vibrating wire extensometers to thermal shocks. The response of the concrete sample to this shock results in a nearly instantaneous deformation, which is measured by the sensor. These deformations, as well as the temperature signal, are used to calculate the coefficient of thermal expansion. By repeating this experiment at various ages, it is possible to follow the variation in the coefficient of thermal expansion of the concrete over time.