Quality Assurance for Caltrans Bridge Shear Retrofit Projects

A quality assurance (QA) process is proposed to prevent the possibility of legal issues for a multibridge retrofit project recently conducted by the California Department of Transportation (Caltrans) to increase the horizontal shear resistance of decks. Providing a solution requires determining an appropriate number of samples with the corresponding sampling scheme to ensure 95% compliance with the specification requirements. The determination of the appropriate sample size must recognize the practical considerations of cost, time, statistical simulation results, and the binomial distribution theory. It is not uncommon for many agencies to base quality assurance on just three samples. Using a binomial distribution, a discussion is also presented why it is not appropriate to take this limited number of samples for quality assurance. With the selection of sample size for each bridge, a representative sampling scheme that is random and unbiased was developed using the concept of uniform design as sampling strategy. The recommended acceptance criteria are specified based on the hypothesis testing results with the normal approximation of a binomial distribution

ON THE RESAMPLING METHOD IN SAMPLE MEDIAN ESTIMATION

Bootstrap is one of the resampling statistical methods. This method was proposed by B. Efron. The main idea of bootstrap is to treat the original sample of values as a stand-in for the population and to resample with replacement from it repeatedly. Bootstrap allows estimation of the sampling distribution of almost any statistics using only very simple methods. This paper presents a modification of a resampling procedure based on bootstrap sampling. The proposal leads to sampling from population with density function f(x), where f(x) is estimated based on the kernel estimation. The properties of the method were analyzed in the median estimation in Monte Carlo study.The proposal could be useful for the parameters estimation in the case of a small sample. This method could be used in quality control procedures such as control charts or in the acceptance sampling