Cracking behavior and crack width predictions of FRP strengthened RC members under tension

This paper presents and discusses the experimental results of uniaxial tensile tests of fiber reinforced polymer externally strengthened reinforced concrete (FRP strengthened RC) prisms in terms of crack width and crack spacing. As a non-contact and material independent system for in-time measurement of displacement and strain, the digital image correlation (DIC) technique has been used in this study for investigating the evolution of strains and formation of cracks during uniaxial tensile tests. As a result, the cracks were measured precisely at any load stage. The experimental results of tests performed by authors and other researchers on FRP strengthened RC members in tension are compared to prediction models from code provisions and guidelines (Eurocode 2 and fib 14), and their suitability are analyzed and discussed. The results show the dependence of the behavior and crack characteristics of FRP strengthened RC members to parameters such as wrapping scheme and FRP reinforcement ratios which are not included in design provisions for crack analysis. A new formulation for predicting crack width and spacing in FRP strengthened RC members, calibrated using the experimental results, has been proposed which considers all the main affecting parameters

Mechanical behavior of concrete prisms reinforced with steel and GFRP bar systems

Being immune to corrosion, and having a tensile strength up to three times higher than structural steel, glass fiber reinforced polymer (GFRP) bars are suitable for reinforcing concrete structures exposed to aggressive environmental conditions. However, a relatively low elasticity modulus of GFRP bars (in respect to the steel) favors the occurrence of relatively large deformability of cracked reinforced concrete. Lack of ductility and degradation of properties under high temperature can be also identified as debilities of GFRP bars over steel ones. Combining GFRP and steel bars can be a suitable solution to overcoming these concerns. Nevertheless, the application of such hybrid reinforcement systems requires reliable material models. The influence of the relative area of GFRP and steel bars on the tensile capacity of cracked concrete (generally known as tension-stiffening effect), was never investigated from the experimental point of view, mainly crossing results from different tools on the assessment of the cracking process. This paper experimentally investigates deformations and cracking behavior of concrete prisms reinforced with steel bars and GFRP bars in different combinations. The test results of 11 elements are reported. A tensile stress-strain diagram is conceptually proposed for modelling the tension-stiffening effect in elements with such hybrid combination of the reinforcement. The cracking process in terms of crack width and crack spacing is analyzed considering the hybrid reinforcement particularities and a preliminary approach is proposed for the prediction of the crack width for this type of reinforced concrete elementsResearch Council of Lithuania (Research Project S-MIP-17-62). The second author also 590 wish to acknowledge the support provided by FCT through the PTDC/ECM591 EST/1882/2014 projec

Bond in Concrete - from research to standards - Proceedings Budapest, Hungary

Multi-level marketing schemes (MLMs) is one of the fastest growing types of business in the world. Especially in China, with the development of e-commerce and social network application, increasingly people start doing business for MLM companies in social network platform. However, there are few academic articles have been written about the ethicality of MLMs on social media application in China. What surprising is, even in China, the ethical issue of MLMs on Wechat is controversial. Among the ordinary person, MLMs sometimes have been accused of being pyramid schemes, which is illegal in China. Besides, many people complain that some of their friends sell products on Wechat, which make them uncomfortable and sometimes be pressured to buy it. This research explores the nature of MLMs and the ethical issues of it. It argues that MLMs on Wechat in China posed some unique ethical issues and attempts to search for the solutions for them

How Investigators Can Assess Concrete Strength with On-site Non-destructive Tests and Lessons to Draw from a Benchmark

A benchmark is carried out in order to compare how 13 experts define and can carry out an NDT investigation program and derive strength values from NDT measurements. The benchmark is based on simulations, which reproduces a synthetic data set corresponding to a grid of twenty 3m-high columns defining the structure of a building made up of beams and columns. The experts must assess the mean and the standard deviation of compressive strength. Three levels of assessment are considered corresponding to different quantities of test results (destructive or non destructive) available for the experts. The comparison of the various strategies used by the experts and the analysis of results enables the identification of the most influential parameters that define an investigation approach and influence its efficiency and accuracy. A special emphasis is placed on the magnitude of the measurement error. A model of the investigation strategy is also proposed