Health Monitoring and Evaluation of Long-Span Bridges Based on Sensing and Data Analysis: A Survey <s> (4) Safety Evaluation Based on Dynamic Response <s> Abstract This paper proposes a method of locating and quantifying the damage in structural members using the concept of residual forces. To describe the damage in a structure, finite element (FE) models are parameterised by structural stiffness reduction parameters. The damage parameters are determined by minimising a global error derived from dynamic residual vectors, which are obtained by introducing a simulated “experimental” data into the eigenproblem. An eigenvalue prediction algorithm along with normalised residual function is employed to formulate the objective function. Two-point crossover binary coded genetic algorithm (GA) with tournament selection approach is adopted in minimising the objective and optimum set of stiffness reduction parameters are predicted. Current structural defect-identification scheme is verified and assessed using an analytically derived plane truss, a cantilever Euler–Bernoulli beam and a portal truss. Results are presented in the form of tables and graphs. <s> BIB001 </s> Health Monitoring and Evaluation of Long-Span Bridges Based on Sensing and Data Analysis: A Survey <s> (4) Safety Evaluation Based on Dynamic Response <s> Structural health monitoring (SHM) technology has been successfully applied to understand the loads, environment actions, and behaviors of a structure subjected to various actions through solving a reverse problem. The sensing technology is a critical part of SHM. In this article, the development of advanced sensing technology and sensors in mainland China in the past decade, such as optic fiber sensing technology, wave propagation-based piezoelectric ceramic (PZT) sensing technology, smart cement-based sensing technology, and corrosion detection technology, have been critically reviewed. In addition, the article also summarizes the application of SHM technologies in earthquake engineering, wind engineering and life-cycle performance evaluation and corresponding progress achieved in mainland China. The challenges and future trends in the development of sensing technology and SHM are put forward in this paper. <s> BIB002 </s> Health Monitoring and Evaluation of Long-Span Bridges Based on Sensing and Data Analysis: A Survey <s> (4) Safety Evaluation Based on Dynamic Response <s> Abstract In this paper, the performances of two wavelet based damage detection approaches to find the location and the size of a crack in a beam subjected to a moving load are compared. In the first approach, designated as ‘Fixed Sensor Approach’, a sensor is assumed to be located at the mid span of the beam. Thus in this approach, Continuous Wavelet Transform (CWT) coefficient of the time varying deflection attributed to the beam at mid span is used. In the second approach, the sensor is attached to the moving load and CWT coefficient of moving sensor is analyzed. The crack is modeled as a rotational spring which its stiffness is obtained from fracture mechanics, and modal expansion theory is used to find the deflection of cracked beam. The two approaches are compared for several cases of moving load speeds, crack sizes and crack locations, and also several scales of CWT. In the both approaches, wavelet Gaussian 4 is employed. It is shown that, the highest magnitude of CWT coefficient occurs at the exact location of crack and its value depends on damage size. As a result, it can be considered as a damage index. It is found that the moving sensor approach is more effective than the fixed sensor. Thereafter, the effect of beam parameters such as length, width, modulus of elasticity and density and also, crack size and location on the damage index were investigated based on the moving sensor approach. The obtained damage index has two significant features: (a) it has an explicit expression and shows the effects of all parameters clearly, (b) it is not dependent upon the response of the undamaged beam. From the obtained explicit relation for damage index, it is illustrated that the damage index does not depend on material properties of a homogeneous beam. Moreover in a rectangular cross section beam, the damage index is independent of width and has a linear relationship with the height to length ratio. It is shown that using this damage index, small cracks with a depth more than 10% of the beam height can be detected. <s> BIB003 </s> Health Monitoring and Evaluation of Long-Span Bridges Based on Sensing and Data Analysis: A Survey <s> (4) Safety Evaluation Based on Dynamic Response <s> This paper uses time series and chaos theory of phase space reconstruction. First, it monitors information phase space reconstruction parameters from the deflection of the mid-span in Masangxi Bridge. As a result, the delay value is 4, the embedded dimension for 15, the maximum number of predictable of 10. Then, it constructs the multiple-step recursive BP neural network and RBF neural network model and realizes the analysis and prediction of monitoring information based on space reconstruction parameters. As the results show, the BP neural network and RBF neural network are all effective in monitoring information prediction and RBF shares more advantages than the BP in keeping the structural dynamic performance. <s> BIB004
According to the sensing information, the dynamic characteristics parameters BIB004 of the structure can be obtained as well as the judgment, localization, and quantification BIB003 BIB001 of the structural damage. Then the finite element model can be corrected via the reanalysis of the ultimate bearing capacity, implementing the structural safety evaluation. Regarding the fatigue damage evaluation for a steel box girder based on sensing information, the S-N curve (fatigue curve) of the construction details can be adopted to evaluate the fatigue status according to the Miner principle. Under special meteorological conditions (such as the wind, rainfall, etc.) regarding natural factors which will affect the normal service of the bridge, it is necessary to carry out this special evaluation. Based on the sensing information, although bridge safety evaluation has obtained some great achievements which have been successfully applied to some long-span bridges, most of them focus on the overall evaluation of historical data accumulation and accidents. So we are confronted with a technical bottleneck BIB002 for early damage warning and online safety evaluation. According to the limit state principle of bearing capacity based on the plastic theory, the design value of the unfavorable combination of the loading effect must be less than or equal to that of the structural resistance. It can be expressed as Equation (2). where: γ 0 indicates the importance factor of the structure, S indicates the loading effect function, R indicates the resistance effect function, f d indicates the design value of material strength, a dc indicates the geometric parameter of concrete, a ds indicates the geometric parameter of rebar, Z 1 indicates the calculating coefficient of the bearing capacity, ξ e indicates the deterioration coefficient of the bearing capacity, ξ c indicates the cross section reduction coefficient of the reinforced concrete structure, and ξ s indicates the cross section reduction coefficient of rebar  . Therefore, the loading effect diagram of each section reflected by the sensing information can be compared and analyzed with the modified limit resistance effect diagram of the bridge. The purpose is to obtain the structural safety evaluation. According to the sensing information, the dynamic characteristics parameters BIB004 of the structure can be obtained as well as the judgment, localization, and quantification BIB003 BIB001 of the structural damage. Then the finite element model can be corrected via the reanalysis of the ultimate bearing capacity, implementing the structural safety evaluation. Regarding the fatigue damage evaluation for a steel box girder based on sensing information, the S-N curve (fatigue curve) of the construction details can be adopted to evaluate the fatigue status according to the Miner principle. Under special meteorological conditions (such as the wind, rainfall, etc.) regarding natural factors which will affect the normal service of the bridge, it is necessary to carry out this special evaluation. Based on the sensing information, although bridge safety evaluation has obtained some great achievements which have been successfully applied to some long-span bridges, most of them focus on the overall evaluation of historical data accumulation and accidents. So we are confronted with a technical bottleneck BIB002 for early damage warning and online safety evaluation.