Abstract
A reliability analysis of an existing structure and a carbon fiber-reinforced plastic (CFRP)-strengthened structure is commonly used to evaluate the effectiveness of strengthening. It also provides the basis for the calibration of the partial factors involved in strengthening design codes. As the fundamental data, the statistical characteristics of the CFRP tensile strength affect the evaluation result. In general, the statistical characteristics of the CFRP strength were obtained from laboratory experiments with small-scale specimens, which resulted in errors caused by the size effect. In this study, a probabilistic series-parallel model is developed to describe the size effect of CFRP. The CFRP fabric is divided into a set of representative volume elements. By numerically simulating the CFRP strength, the relationship between the number of representative volume elements and the mean and coefficient of variation (COV) of the CFRP strength is analyzed. A chi-square test is carried out to determine the distribution type of the CFRP strength. An analytical expression of the mean, COV, and the cumulated density function of the CFRP strength are derived. Finally, an existing bridge, which has operated for 41 years, is selected for the case study; it is strengthened by using CFRP fabric. Reliability indexes of the existing and the strengthened bridges are calculated to analyze the size effect on the reliability of the strengthened structure.
Highlights
Externally-bonded carbon fiber-reinforced plastic (CFRP) is widely used globally for strengthening the existing concrete structures because of its effectiveness and convenience of construction [1,2].In recent years, some design specifications related to structure strengthening by CFRP have been issued
An existing bridge, which has operated for 41 years, is selected for the case study; it is strengthened by using CFRP fabric
A hybrid procedure is used for the estimation of the reliability index, in which descriptive statistics of performance function Z are obtained by using Monte-Carlo (MC) simulation, and the reliability of the existing bridge is assessed using the first-order reliability method (FORM), as shown in Equation (21)
Summary
Externally-bonded carbon fiber-reinforced plastic (CFRP) is widely used globally for strengthening the existing concrete structures because of its effectiveness and convenience of construction [1,2]. Most of the experiments conducted far used small-scale specimens, which have higher strength than the material regularly used in structural strengthening because of the size effect This resulted in certain errors of the evaluated reliability index and the calibrated partial factors. Based on the weakest-link model, Harlow and Phoenix [19,20] proposed a chain-of-bundles probability model to analyze the strength of fibrous materials. They reviewed the results for the chain-of-bundles model of the strength distribution of unidirectional fiber composites. A reliability evaluation of the CFRP-strengthened structures would be more rational when the proposed model was adopted; further, the calibrated partial factor would be more accurate
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