Jikai Zhou

Compressive Strength of Concrete Cores under High Strain Rates

AbstractA pulse-shaped split Hopkinson pressure (SHPB) was employed to determine the dynamic compressive mechanical responses of concrete cores. The loading pulses in SHPB experiments were precisely controlled to ensure that the core specimen deforms at a nearly constant strain rate under dynamically equilibrated stress during compression. A modified two-parameter Weibull distribution was used to analyze the test data. The Kolmogorov-Smirnov goodness-of-fit test was used to decide whether test data come from a population with this distribution. On the basis of the test data, Kolmogorov-Smirnov goodness-of-fit test, and probability plot, it is found that the modified Weibull model can be applied to compressive strength for concrete cores. In addition, the strain rate effect on the compressive strength of cores can be accurately predicted from the modified Weibull model.

Variability of Compressive Strength of Concrete Cores

AbstractA comprehensive test program was conducted on the compressive strength of concrete cores. The tests involved eight mixes of concrete. Because over 200 tests were conducted, it was possible to undertake an analysis of the concrete cores using the probabilistic treatment of strength. The present work reports a comparative study of alternative probabilistic models to describe the compressive strength of concrete cores. A large class of probability models including two-parameter Weibull, three-parameter Weibull, normal, lognormal, and gamma distributions were validated using test data. This information is useful in the theoretical description of concrete failure. Furthermore, the results were compared in terms of modified Kolmogorov-Smirnov, log-likelihood, and minimum chi-square criterion. The results suggested that none of the described probability methods are adequate for determining the variability of the compressive strength of concrete cores.

Early-Age Temperature and Strain in Basement Concrete Walls: Field Monitoring and Numerical Modeling

AbstractEarly-age cracking of base restrained concrete walls is a common problem. To provide the owner with an early warning of in-place quality problems resulting primarily as a result of thermal and shrinkage effects, it is helpful to apply monitoring and analytical techniques to examine the early-age behavior of basement concrete walls. In this paper, the temperature and strain monitoring on a basement concrete wall is conducted. Major factors that contribute to the early-age behavior of concrete walls constructed in cold weather are evaluated using analytical models along with measured field data and finite-element modeling. The results show that the monitoring process eliminated much of the guesswork frequently associated with basement concrete walls constructed in cold weather. Temperature varies laterally within the wall. The strain remains unchanged after six days with formwork removal. And the numerical predictions for strains and temperature are in agreement with the measured results, during bot...