Behavior of FRP-confined normal- and high-strength concrete under cyclic axial compression

An important application of fiber-reinforced polymer (FRP) composites is as a confining material for concrete, both in the seismic retrofit of existing reinforced concrete columns and in the construction of concrete-filled FRP tubes as earthquake-resistant columns in new construction. The reliable design of these structural members against earthquake-induced forces necessitates a clear understanding of the stress-strain behavior of FRP-confined concrete under load cycles. This paper presents the results of an experimental study on the behavior of FRP-confined normal- and high-strength concrete under axial compression. A total of 24 aramid and carbon FRP-confined concrete cylinders with different concrete strengths and FRP jacket thicknesses were tested under monotonic and cyclic loading. Examination of the test results has led to a number of significant conclusions in regards to both the trend and ultimate condition of the axial stress-strain behavior of FRP-confined concrete. These results are presented, and a discussion is provided on the influence of the main test parameters in the observed behaviors. The results are also compared with two existing cyclic axial stress-strain models for FRP-confined concrete. © 2012 American Society of Civil Engineers.Togay Ozbakkaloglu and Emre Aki

Association of paraoxonase activity and atherosclerosis in patients with chronic hepatitis B

Background: The hepatitis B virus is a significant pathogen that causes cirrhosis, and hepatocellular cancer as a result of the damage it causes to liver cells. Its infection affects more than 400 million people globally. Although there is an effective vaccine and treatment methods, almost 1, 000, 000 people die every year. Objective: To investigate paraoxonase and arylesterase activities along with oxidative status parameters and serum lipid levels, and to find out if there is any increased susceptibility to atherogenesis. Methods: Thirty-four subjects with chronic hepatitis B and 39 healthy subjects as control were enrolled in the study. Age, body mass index and gender, Serum Triglycerides (TG), High-density Lipoprotein (HDL) and Low-Density lipoprotein (LDL) levels, serum paraoxonase-1 and arylesterase activities were determined. Oxidative and antioxidative statuses were evaluated by measuring serum-free sulfhydryl groups, lipid hydroperoxide levels, total antioxidant capacity, total oxidant status, and oxidative stress index. Results: Serum TG and LDL levels were higher while serum HDL levels were lower in patients with chronic hepatitis B than in controls but the differences did not reach statistical significance. Serum paraoxonase-1 and arylesterase activities, plasma free sulfhydryl groups, and total antioxidant capacity were significantly lower in patients than in controls (p=0.018, p=0.005, p<0.001, p=0.037 respectively), while lipid hydroperoxide, total oxidant status, and oxidative stress index were significantly higher (for all p<0.001). Conclusion: The diminution in the paraoxonase-1 and arylesterase activities could contribute to the accelerated development of atherosclerosis in patients with chronic hepatitis B

Spherically Propagating Thermal Polymerization Fronts

We demonstrate for the first time spherically propagating frontal polymerization that also exhibits spin modes. We have developed an interesting system using the amine-catalyzed Michael addition of a trithiol to a triacrylate to create a rubbery gel. The gel suppresses convection and bubble formation during front propagation. A peroxide is also present to act as a thermal initiator. The front propagates via free-radical polymerization of the remaining triacrylate after being initiated photochemically in the center of the reactor. It is possible to prepare the rubbery gel in any shape and then initiate thermal frontal polymerization. So-called spin modes have been observed for the first time in spherically propagating fronts in which waves of polymerization propagate on the expanding spherical front. A system using a diacrylate dissolved in dimethyl sulfoxide with added silica gel and with persulfate as the initiator supports spherical fronts but does not exhibit spin modes. (c) 2006 Wiley Periodicals, Inc

Comparison of the expected damage patterns from two- and three-dimensional nonlinear dynamic analyses of a roller compacted concrete dam

The seismic performance of the tallest roller-compacted concrete gravity dam in Turkey is investigated in this study. For this purpose, two- and three-dimensional nonlinear dynamic finite element analyses were conducted to investigate the expected damage under simulated ground motions. Based on the results of finite element simulations, it was found that the three-dimensional behaviour of the dam is substantially different from the idealised two-dimensional monolith behaviour, even for a dam having monoliths separated with transverse joints. In addition, it was determined that in order to limit the cracking at the base of the dam, higher strength grout-enriched concrete must be used on the upstream and downstream faces. This study demonstrates the importance of three-dimensional modelling for gravity dams built in relatively narrow valleys along with the significance of the modelling of the nonlinear response for seismic performance assessment