Due to the increasing usage of concrete-filled steel tube (CFST) members in structural engineering, there will be more chances of fire hazards on these structures in the near future. Externally bonding carbon fiber reinforced polymer (CFRP) composites has emerged as a popular method for repairing damaged steel-reinforced concrete members. However, limited research is available to evaluate the behavior of CFRP strengthened CFST members. This paper presents the results of an experimental investigation on the compressive behavior of the post-heated circular CFST short columns externally strengthened with CFRP sheets. A total of twenty-one specimens are tested to investigate the influence of temperature and the number of CFRP layers on the mechanical behavior of repaired specimens. The ultimate strength is obtained from monotone static tests. The extensometer technique based on gauge strain is used to measure strains of electric gauges glued to the external surface of specimens. The results indicate that the increase in the number of CFRP layers leads to a significant change in the mechanical properties of post-heated CFST columns. Furthermore, it is shown that increases in the number of CFRP layers remarkably enhance the ultimate strength and initial stiffness of specimens subjected to the same heat treatments, while deteriorate the ductility. Based on extensive experimental analysis, simplified formulae are proposed to estimate the compressive ultimate strength of all specimens tested, providing reasonably good correlation with the experimental results. Besides, the proposed formulae are compared with some existing empirical models, and validity of the proposed formulae is evaluated.
Vibration is a very important signal for the health monitoring of bridge. Wireless sensor network powered by batteries are widely used in the monitoring system. How to prolong the network life cycle becomes an important problem due to the limitation of battery energy. This paper presents a new method of optimal acceleration sensor placement for monitoring the vibration of bridges, the method considers network life cycle as the second target on the basis of traditional modal assurance criterion (MAC). And multiple-objective optimization is performed by using a genetic algorithm. The simulation result shows that when the sensors number is less than 30, the networks life cycle can be greatly extended with the addition of only the little cost of MAC indicators.
To optimize node energy consumption and improve its security, this paper uses the DEEC algorithm to layer WSN and reduce the probability of channel information collision and uses the weighted probability of cluster head election to optimize node energy expenditure, so that WSN can obtain a longer lifecycle. Improved Particle Swarm Optimization-based Support Vector Machine (IPSO-SVM) algorithm is used for intrusion detection and experimental testing in WSN. The results showed that the IPSO-SVM algorithm exhibited good convergence, with a convergence step size of 5 steps, which converged earlier than the Support Vector Machine Algorithm based on Particle Swarm Optimization (PSO-SVM), which had a convergence step size of 10 steps. The IPSO-SVM algorithm performed best in WSN intrusion detection, with the highest detection rate of 96.20% in Probe attack data detection, which was 0.80% higher than the Support Vector Machine Algorithm based on Genetic Algorithm (GA-SVM). The PSO-SVM algorithm had the lowest detection rate of 95.20%. The IPSO-SVM algorithm had a minimum false positive rate of 1.54% in Dos attack data detection. In terms of average training time, the IPSO-SVM algorithm had a minimum average training time of 323.45 seconds. Compared to the Low Energy Adaptive Clustering Hierarchy (LEACH) algorithm, the Distributed Energy Efficient Clustering (DEEC) algorithm performs better, has less energy consumption, and retains more nodes. The method adopted in this study can make WSN have a longer life cycle and ensure its security.
The multilayer relaxation of Cu(100),(110),(111)and(311) surfaces are calculated- using the modified embedded atom method,from which the results obtained are in good agreement with the experiments. The self-diffusion mechanisms on the Cu(100) surface are investigated,and the result is colse to the available experimental data and that obtained by local density approximation method.In addition,the diffusion barrier heights on Cu(110) and (111) surface are predicted.
Based on the energy method, this article presents a theoretical study on the elastic local buckling of steel plates in rectangular concrete-filled steel tubular columns with binding bars subjected to eccentric compression. The formulas for elastic local buckling strength of the steel plates in eccentrically loaded rectangular concrete-filled steel tubular columns with binding bars are derived, assuming that the loaded edges are clamped and the unloaded edges of the steel plate are elastically restrained against rotation. Then, the experimental results are compared with these formulas, which exhibits good agreement. Subsequently, the formulas are used to study the elastic local buckling behavior of steel plates in rectangular concrete-filled steel tubular columns with binding bars under eccentric compression. It is found that the local buckling stress of steel plates in eccentrically loaded rectangular concrete-filled steel tubular columns with binding bars is significantly influenced by the stress gradient coefficient, width-to-thickness ratio, and the longitudinal spacing of binding bars. With the decrease of width–thickness ratios or the longitudinal spacing of binding bars or with the increase of the stress gradient coefficient, the local buckling stress increases. Furthermore, the influence of the longitudinal spacing of binding bar is more significant than the stress gradient coefficients. Finally, appropriate limitation for depth-to-thickness ratios ( D/ t), width-to-thickness ratios ( B/ t), and binding bar longitudinal spacing at various stress gradient coefficients ( α 0 ) corresponding to different cross-sectional aspect ratios ( D/ B) are suggested for the design of rectangular concrete-filled steel tubular columns with binding bars under eccentric compression.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)