Improvement and Application of Immune Genetic Algorithm in Structural Damage Identification

In order to solve structural multi-damage identification problem, a two-stage method based on Bayesian theory and immune genetic algorithm (IGA) is presented. Firstly, structural modal strain energy and frequency are considered as two kinds of information sources, and Bayesian theory is utilized to integrate the two information sources and preliminarily detect structural damage locations. Then, immune genetic algorithm is used to identify structural damage extents. Considering the convergence rate of basic IGA is still not very good, some improved strategies, such as culture vaccine, two termination conditions, are presented. It is shown that the two-stage method can precisely identify structural damage locations and extent, and the calculated results of the proposed improved IGA are obviously better than those of both the basic IGA and simple genetic algorithm.     

模式识别的斜拉桥损伤诊断动力指纹与识别算法

为有效并准确诊断出斜拉桥损伤,对基于模式识别的斜拉桥损伤诊断方法进行了研究。选取易于测试出的低阶模态频率和部分关键点竖向振型数据为动力指纹,无需模态扩展或模型缩聚。研究并采用全因子设计进行动力指纹库的创建,可精确评估设定的损伤因子及其交互作用对损伤识别结果的影响。设计并增加了带随机误差的动力指纹库样本集。编制了基于Matlab的模式识别的多种算法,重点研究了精确度高的多层感知器识别算法及其提高该算法预测准确率的装袋集成算法。最后给出一座单塔双跨双索面斜拉桥的多种识别算法的损伤诊断过程和结果,得到一种可包容测试随机误差的高精确度斜拉桥损伤诊断评估模型。     

Application of Improved Multi-population Genetic Algorithm to Damage Identification of Soil-wall System

The method of damage identification in soil-wall system was studied; a new approach based on improved multi-population genetic algorithm (IMGA) was developed. First, the simplified dynamic-detection model of soil-wall system was established, meanwhile, the theoretical analysis of characteristic equations in soil-wall system was conducted when soil in damage status. The objective function based on characteristic equations was established. Then, the improvements of multi-population genetic algorithm, including the adoption of real-valued representation, adaptive cross operator and adaptive mutation operator, were conducted. Finally, the localization and quantification of the soil-wall system damage were performed by IMGA with and without the consideration of noise, respectively. The results indicate that damage location and damage extent can be detected efficiently, and anti-noise performance is better.     

Application Study on Optimal Sensor Placement Technique of Cable-stayed Bridge

Based on the modal assurance criterion, using simulated annealing algorithm, the dynamic characteristic data of cable-stayed bridge are extracted, optimal acceleration sensor layout scheme of main beam is obtained. According to this optimization scheme, we carry out a dynamic characteristics test on one cable-stayed bridge. The results between test data and finite element modal calculation are very closely. Theory technique research and field modal test demonstrated that the simulated annealing algorithm based on modal assurance criterion is effective and viable for optimal acceleration sensors placement of cable-stayed bridge.     

Step-by-step Method of Structural Damage Diagnosis

Base on the existing step-by-step structural damage diagnosis method, a three-step structural damage diagnosis method is developed. According to the analysis of the characteristic of genetic algorithm, a new idea of excluding the undamaged element by means of step-by-step evaluation is developed to deal with the damage diagnosis problem. In this method, sensitivity genetic algorithm is used to exclude the undamaged element step by step and residual force method is used to fix the damage district. According to the simulation research of a 2D framed structure, it is shown that the step-by-step structural damage diagnosis method can gain the ideal results when it's difficult for a single damage diagnosis method to get the good results. It is also indicated that sensitivity genetic algorithm is a good way to exclude the undamaged element step by step.     

Improved Genetic Algorithm of Float Encoding and Its Application

As an optimal method, Genetic Algorithm has obvious advantages, which is based on the nature selection and genetic transmission mechanisms such as high collateral,stochastic,self-reliance. but when in practical application, it usually has problems of premature convergence and result swing near optimum value.To solve the problem of premature convergence, the method called Monte-Carlo is adopted to prevent the algorithm from local optimal, and to the problem of result swing, the method changing the hunting zone dynamically is proposed to improve the accuracy of the optimal result. Further more, it devises programs to optimize the test functions of two famous optimal methods. The test results indicate that the improved Genetic Algorithm is valid, which can not only avoid local optimal but also improve the accuracy of the optimal result.     

Numerical simulation for the residual stress of U-rib welding onto the flat steel box girder

The flat steel box girder is commonly used for long-span cable-stayed bridges. the structural complexity, construction details and manufactures cause damage to the bridge and the damages seriously grow overtime. The main reason for these damages is that welding technology of flat steel box girder with thin plates and rib elements produces residual stress and strain fields during the welding process, and further more welding cracks commonly appear. In this study, thermal-structural couple methods was adopted to numerically simulate the welding high temperature fields and the stress fields at the joint of U rid and decks of a flat steel box. The welding residual stress distribution was studied as well for further analyzing on the structural damage and strengthening design strategies.     

Fuzzy Assessment Method for Seismic Damage of CFST Arch Bridges

In order to investigate the conditions of damage and failure of concrete-filled steel tube(CFST) arch bridges, considering the structural and mechanical characteristics of CFST arch bridges, the dual damage criteria assessment models of the various components based on deformation or strength and energy were developed. The nonlinear seismic response of CFST arch bridges was analyzed by finite element method and the fuzzy evaluation method of seismic damage based on fuzzy theory and analytic hierarchy process was studied. Finally, taking a long-span CFST arch bridge as example, the damage index of the bridge was 0.150, 0.152, 0.172 and 0.318 respectively when the seismic peak acceleration was respectively 0.1g, 0.2g, 0.4g and 0.8g. The results show that the CFST arch bridge is slightly damaged under the earthquake when the seismic peak acceleration is 0.4g, and the bridge is damaged moderately when the peak acceleration is 0.8g.     

Time Domain Analysis on Buffeting of Jinma Bridge

Jinma bridge is a long span cooperative-system cable-stayed bridge with one tower cooperated with T frames on both sides.Owing to artistic form and lying in typhoonprone area,it is essential to process the buffeting analysis.In this paper,the turbulent wind velocity was first simulated with cosine wave superposition method as multi-correlated random processes;then,the time domain expressions for the buffeting and self-excited forces were given.On this basis,the buffeting analysis of Jinma Bridge was made.The results show that the anti-wind capacity of the cooperative-system cable-stayed bridge is ensured although the torsional resistibility of the main girders of this bridge is not good.     

An edge detection method based on a good point set genetic algorithm

In order to improve the convergence rate of genetic algorithms based on edge detection, a novel edge detection method based on a good point set genetic algorithm (GGA) was proposed. The proposed method designed the crossover operation with the theory of good point set in which the progeny inherits the common genes of the parents which represent its family so as to improve the convergence rate of the genetic algorithm. Furthermore, before the algorithm was used for edge detection, the feature space of the image grey level was transformed into the feature space of the fuzzy entropy. Dissimilarity enhancement processing next was applied to the image by using a fuzzy entropy theory to filter the non edge pixels so as to reduce the scale of the solution domain. This approach offered another efficient way to improve the convergence rate. Experimental results show the proposed algorithm performs very well in terms of convergence rate. The detected edge image is well localized, thin, and robustly resistant to noise.     

Research of Sensitivity Genetic Algorithm for Inverse Computation of Structure

The sensitivity genetic algorithm is developed in order to carry out effectively the inversion analysis of the diagnosis of the structure damage. The genetic algorithm with the technique of sensitivity can not only reduce the operation time of the program     

Damage Detection for Beam and Bridge under Dead Load

We address damage detection based on dead loads in monitoring the health of beams and bridges. We discuss the damage characteristics of statically indeterminate beams under dead loads and analyze monitoring parameters and sensor placement in monitoring. We used an amended genetic algorithm to solve the optimization problem under constrained parameters. Damage in a beam was detected successfully based on dead loads with limited sensor allocations. We present a way to detect damage based on dead loads in bridge health monitoring.     

Static Load Test and Calculation on Multi-tower Cable-Stayed Bridge with Tie-down Cables

The static load test and the finite element analysis of the multi-tower cable-stayed bridge with tie-down cables are carried out. The test and analysis model of the bridge is created by referencing to the actual structure of a Changjiang River bridge. The static mechanical behaviors of such bridge with tie-down cables and the normal multi-tower cable-stayed bridge are comparatively analyzed by the static load test and the finite element analysis. It is shown that the structural system of the cable-stayed bridge with tie-down cables can effectively improve the structural rigidity and reduce the bending moment of the main beams, pylons and piers. According to the results, the best scheme about the location and number of tie-down cables is proposed.     

Turbulent Wind Velocity Spectrum Analysis Approach Based on Proper Orthogonal Decomposition

The emergence of large-span bridge and extreme weather attract much more attention of researchers on the bridge buffeting problem. One of the most important factors that affect bridge buffeting response is wind velocity spectrum. In the precious investigations, wind velocity of various frequency has impact on the bridge buffeting response. While Proper Orthogonal Decomposition(POD)method is proposed to decompose the wind velocity to solve the above problem and a cable-stayed bridge was used to investigate the contribution of effective model to bridge buffeting response. The result showed that not all frequency ranges of wind velocity spectrum contributed to the response which had relationship with both structural self-vibration mode and turbulence effective mode coefficient.     

Construction Stage Analysis on Replacement of Closure Segment in Prestressed Concrete Cable-stayed Bridges

To deal with failure of wet joint between a closure segment and its neighboring segments of main girder in an existing prestressed concrete cable-stayed bridge, the technology on replacement of closure segment was presented. In order to analyze structural characteristics of this technology, its technical approaches and construction key points were introduced. Then a FEM model for a typical prestressed concrete cable-stayed bridge was established, and a construction stage analysis method was given in detail, including establishing a structural basement calculation model for replacement of closure segment and simulating its construction procedures. Based upon calculation results, variations of some structural state parameters with construction stages, such as deck deflection of main girder, longitudinal horizontal displacement at the top of pylons, cable forces, were analyzed. The results showed, this method could reflect actual change process of structural state and existing inspected results of cable-stayed bridge, and FEM results could well meet with construction monitoring results during replacement of closure segment. Thus variations of structural characteristics with construction stages could actually be revealed. This method could provide references for design and construction control of replacement of closure segment in existing prestressed concrete cable-stayed bridges.     

A Genetic Algorithm Based on Repeating Crossover and Optimum Maintaining Strategy

A novel genetic algorithm,simply written as REGA, is proposed with the idea to limit the number of repeating crossover and replacing the worst individuals of the current generation by the best ones of the former generation. The algorithm overcomes the premature phenomenon of the simple genetic algorithm. According to Markov's limitation theorem, we prove its global convergence,explore the properties of the genetic algorithm written as RSGA only based on repeating crossover,and provide a method to calculate the mathematic expectation on the absorption time for the two algorithms. Finally,the simulation shows that the algorithm REGA can solve the optimization problem containing more than one global optimal solutions,on one hand,while eliminating the drawback of local optimum and rapidly enhancing the average fitness. On the other hand, REGA is valuable for function optimization.     

Hybrid Genetic Algorithms for Multimodal Optimization

Hybrid genetic algorithms, which are based on steepest descent algorithm and genetic algorithm, are investigated for the purpose of multimodal optimization. The performances of the hybrid genetic algorithms are evaluated with criteria such as convergence probability, average convergence time and average convergence value of the function in the case of solving global optimization for Schaffer function. It is shown that the performances of the hybrid genetic algorithms are better than steepest decent algorithm or genetic algorithm, and the hybrid genetic algorithm, in which the individuals used for local optimization by steepest decent method are chosen by chance in each generation population, is more efficient than that in which the individuals used for local optimization by steepest descent method are selected from excellent individuals.     

高烈度区斜拉桥横向约束方案优化分析

为了确定强震作用下斜拉桥合理的横向抗震约束体系,以可克达拉大桥为工程背景,采用非线性时程分析法,分析了4种横向约束体系即横向滑动体系、全限位体系、位移相关型减震体系和速度相关型减震体系对强震区大跨度桥梁地震响应的影响,重点对钢阻尼器的屈服荷载和黏滞阻尼器的位置及相关参数进行优化分析,并与其他体系的地震响应进行了对比。结果表明：在强震作用下,对于大跨度桥梁横向滑动体系和全限位体系均不是理想的抗震体系;而在墩梁、塔梁之间设置减隔震装置可以有效减少横桥向的墩梁、塔梁的相对位移及地震剪力和弯矩;然而,从桥梁正常使用的角度来看,塔梁之间布设横向钢阻尼器装置优于黏滞阻尼器装置。     

QTL混合遗传模型扩展至2对主基因＋多基因时的多世代联合分析

本文将Gai and Wang(1998)的P1、 F1、 P2、 B1、 B2和F2 6个世代 联合分离分析方 法从A、 B、 C、 D 4类共17种遗传模型扩展至E(2对主基因＋多基因)共5类24种遗传模型 。 成分分布参数估计的方法由EM算法改进为迭代条件EM算法(IECM), 其收敛性和所获结果 优于EM算法。 水稻株高例中2对主基因+多基因的遗传模型(E-2)优于原所     

Three-dimensional Random Damage Prediction Model of Concrete Caused by Freeze-thaw

In order to effectively assess the damage of concrete in freeze-thaw condition, prediction model for concrete frost damage is presented based on damage mechanical theory and the experimental test. The degeneration of tension strength of air-entraining concrete is tested after freezing and thawing. Provided with the fact that the degeneration of concrete is an interior damage evolving process, freezing and thawing damage accumulation of concrete is analyzed based on the discrete grid with probability of stochastic method. And Three-dimensional multi-parameters Weibull distribution model about concrete damage evolutions is presented. Parameters are estimated based on gradient method, and the mathematical model is verified according to the tested data. Corresponding algorithm is designed and programming is completed by C + + programming language to establish concrete durability prediction model under freeze-thaw conditions. It is indicated that the damage of concrete develops in nonlinear way as the freezing and thawing increases.