Advances in Fracture and Damage Mechanics VI

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Authors: Hong Nan Li, Ying Wu Zhou, Su Yan Wang, Gui Liu
Abstract: Recently, concrete structures deteriorating for various reasons and upgrading by bonding FRP using epoxy resins has attracted significant researches. Experimental studies in literates indicate that the anchorage between concrete and FRP laminates plays an important role in the reinforcing design. However, few and no special study has extended to high strength concrete. This research examines the bond behaviour between FRP laminates and high strength concrete. To obtain the bond strength and regulation of debonding propagation, a simple face shear type bond test is conducted. With the explicit material and geometric descriptions and the fairly general boundary conditions, the interfacial fracture energy release rate, Gf of this test model which is then used to propose the prediction of the bond strength is derived. Comparison of this energy basis model in prediction of bond strength with the model of Chen & Teng which has a high accuracy in this area and results from this experiment demonstrates the derived prediction model as a feasible and effective measure in analyzing the bond behaviour between FRP and high strength concrete.
Authors: Chang Sik Choi, Yun Cheul Choi, Hyun Ki Choi, M.S. Lee
Abstract: A series of three shear wall specimens were tested under constant axial stress and reversed cyclical lateral loading in order to evaluate the seismic retrofit that had been proposed for the shear wall with the opening induced by remodeling. One of these specimens was tested in the as-built condition and the other two were retrofitted prior to testing. The retrofit involved the use of carbon fiber sheets and steel plates (a thickness of 3mm) over the entire face of the wall. The test results showed that the failed specimens had shear fractures and that two different types of retrofitting strategies had different effects on the strengths of each specimen.
Authors: Kab Soo Kyung, Seung Yong Lee, Sung Geun Lee, Kwang Seok Kim
Abstract: In the study herein, the fatigue test was conducted on the fillet welds of the load carrying cruciform joint, which is frequently used in the steel structures such as bridges, ships, etc. In addition, the fatigue stress was analyzed with respect to the different post-weld treatment. The treatment methods used include Toe Grinding, TIG Dressing, and Weld Profiling. The fatigue test was under constant amplitude with repeated load for these test specimens. In the load carrying full penetration fillet welded joints, regardless the conduction of the post-weld treatment or not, they all secured the fatigue strength of category "F", which exceeds the fatigue design specifications of BS Code. In the comparison of the fatigue strength upon the post-weld treatment, the fatigue strength tends to increase according to the order: Toe Grinding, TIG Dressing, and Weld Profiling.
Authors: Cheol Woo Park, Jong Sung Sim
Abstract: Among various types of fiber reinforced polymer (FRP) materials, sheet-formed materials are commonly used for the strengthening of reinforced concrete structures. Basalt fiber sheet has shown a good durability to a harsh environmental condition comparing to other typical fiber sheets, such as glass and carbon fiber sheets [1]. This study investigates the debonding failure characteristics of the basalt fiber sheet for its application in the field. Fundamental mechanical characteristics were evaluated prior to the bond fracture test. Experimental variables include the number of fiber sheet layers, bonding length and bonding width. Debonding failure mode was typical at the bonded interface and the failure strength increased as the number of layer increased. From the results, the effective bond length and effective bond strength were calculated and compared with the literatures. It was also found that the debonding failure strength was a function of the bonding width rather than the bonding length. Based on the test data, an equation to calculate the effective bonding length and strength was suggested.
Authors: Shao Peng Wu, Gang Liu, Jian Ying Yu, Ting Wei Cao
Abstract: In this study, organomodified montmorillonite (OMMT) modified asphalt was used in porous asphalt, and fatigue characteristics of the mixtures with or without OMMT were investigated. Special attention was paid to the beam specimens aged in a forced draft oven at 60°C for 500h. Basic fatigue information, such as stiffness, dissipated energy of the material, was obtained through four-point bending beam testing under different controlled strain. The classical fatigue life definition was used to evaluate fatigue resistance of different mixtures. The research results indicate that the OMMT mixture exhibits better fatigue and ageing resistance than the neat one. It is suggested that OMMT should be an excellent alternative for the durability of porous asphalt.
Authors: Yan Hua Zhao, Shi Lang Xu, Zhi Min Wu, Hong Bo Gao
Abstract: The apparent size effect of the specific fracture energy of concrete according to the RILEM procedure has been confirmed by numerous published works. The paper offers an explanation for this size effect by considering the specimen boundary influence on local fracture energy over the ligament length, which is closely associated with the measured fracture energy of concrete. To address this boundary influence, boundary affected length is introduced, over which local fracture energy is different from that in the bulk far away from the surface of the specimen. Based on previous work, a continuous smooth function is hypothesized to simulate the distribution of local fracture energy. At the same time, the model established was compared to the existing models, i.e. Perturbed Ligament Model (PLM) and Bilinear Model (BLM). Some test results from wedge splitting specimen in the literature were used to verify these three models. The results show that the true fracture energy of concrete, irrespective of the specimen size, could be obtained from the measured values directly from RILEM, and is less sensitive to determination approach. The predicted boundary affected length when the crack reaches the specimen surface is more close to the value of the perturbation length in PLM.
Authors: Jian Zhuang Xiao, Chuan Zeng Zhang
Abstract: In this paper, recycled aggregate concrete subjected to severe fire or high temperature loading condition is investigated. Special attention of the study is devoted to analyze the fire-induced damage and the residual strengths of recycled aggregate concrete. For this purpose, 160 cube specimens are heated under a single thermal cycle of 20oC (ambient temperature), 200oC, 300oC, 400oC, 500oC, 600o, 700oC and 800oC, respectively. Different replacement percentages of the recycled coarse aggregates (RCA) with 0, 30%, 50%, 70% and 100% are considered. Damage and failure patterns of the recycled aggregate concrete specimens are analyzed systematically based on experimental observations. The residual compressive strengths of the recycled aggregate concrete (RAC) at elevated temperatures are studied and evaluated in details. Some differences between the recycled aggregate concretes with different replacement percentages of the recycled coarse aggregates are observed. On the basis of the experimentally measured residual compressive strengths of the recycled concrete, relationships between the residual compressive strengths of the recycled aggregate concrete and the elevated temperature are derived. The results presented in this paper have direct applications in the design and structural analysis of reinforced concrete structures consisting of recycled aggregate concrete.
Authors: Li Juan Cao, Shou Ju Li, Zi Chang Shangguan
Abstract: Freezing and thawing damage is one of the major problems of concrete dams in cold climate. Cracking and splitting are the most common results of freezing and thawing deterioration in concrete dam. The cracking problem owing to freezing and thawing was investigated by making sue of finite element methods. The interpretation of the mechanism of failure was also given. In order to compute the thermal stress fields of concrete dam caused by freezing and thawing, the temperature changes versus seasons is determined according to measured data. The temperature fields of concrete dam versus seasons are simulated by using finite element method. Basing on the computational results of the temperature fields of concrete dam, the thermal stress fields are calculated numerically. The researches show that the first principal stress of concrete dam at downstream surface can exceed the tensile strength of concrete material. The numerical simulation results of fractured regions of concrete dam agreed with practical observed data.
Authors: Peter Dabnichki, Marco La Mantia
Abstract: The study is part of a wider biomimetic investigation focusing on flapping wing in water - penguin wing. The long-term aim is to design a hybrid vehicle capable of flying in fluids with very different densities. The paper analyses the dynamic loads on an oscillating wing used for obtaining the trust generated throughout harmonic motion. The strength requirements for such wing have not been analysed up to now and this study is to be followed shortly by experimental simulation in a wind-tunnel. The acting forces in the current analysis were obtained through a potential flow based panel method computer program.
Authors: Xiao Ling Zheng, Ming Song Zhang, Min You, Hai Zhou Yu, Zhi Li
Abstract: The normal stress distributed in the mid-bondline of the adhesively bonded joint under cleavage loading was investigated using the elastic finite element method (FEM) and the strain gauges method to reveal the real normal stresses distribution in the metal-to-metal joint while the load was increased. The results from the finite element analysis (FEA) showed that there is always a peak stress of the normal stress Sy in the mid-bondline occurred at a point close to the loading pin axis. When the load was increased from 0.5 kN to 3 kN, there was also a point located at about x = 16mm along the length of specimen where there is without any normal stress at all. The result of stress Sy from the FEA is nearly the same as that one obtained from the strain gauges method. It was also found that there was a evidently hardness change in the bonded zone of the adherend made from structural steel or pure copper, which can be used to explain the procedure of the joint and discuss the distribution model of the normal stress Sy in the joint under the cleavage loading.

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