Ting-Hua Yi

Methodology Developments in Sensor Placement for Health Monitoring of Civil Infrastructures

Optimal sensor placement (OSP) technique plays a key role in the structural health monitoring (SHM) of large-scale civil infrastructures. This paper outlines an overview of current research and development in the field of OSP problems in a perspective of both researchers and engineers. The paper begins with a definition of the model of sensor placement and provides the basic issues covering relevant methodologies. The primary evaluation criteria and main sensor placement methods are then discussed in details. Following that, the linkage between several influential sensor placement methods is described. Finally, existing problems and promising research efforts in the OSP problem of civil SHM are discussed.

Sensor placement on Canton Tower for health monitoring using asynchronous-climb monkey algorithm

Heuristic optimization algorithms have become a popular choice for solving complex and intricate sensor placement problems which are difficult to solve by traditional methods. This paper proposes a novel and interesting methodology called the asynchronous-climb monkey algorithm (AMA) for the optimum design of sensor arrays for a structural health monitoring system. Different from the existing algorithms, the dual-structure coding method is designed and adopted for the representation of the design variables. The asynchronous-climb process is incorporated in the proposed AMA that can adjust the trajectory of each individual dynamically in the search space according to its own experience and other monkeys. The concept of ?monkey king? is introduced in the AMA, which reflects the Darwinian principle of natural selection and can create an interaction network to correctly guide the movement of other monkeys. Numerical experiments are carried out using two different objective functions by considering the Canton Tower in China with or without the antenna mast to evaluate the performance of the proposed algorithm. Investigations have indicated that the proposed AMA exhibits faster convergence characteristics and can generate sensor configurations superior in all instances when compared to the conventional monkey algorithm. For structures with stiffness mutation such as the Canton Tower, the sensor placement needs to be considered for each part separately.

Noise Smoothing for Structural Vibration Test Signals Using an Improved Wavelet Thresholding Technique

In structural vibration tests, one of the main factors which disturb the reliability and accuracy of the results are the noise signals encountered. To overcome this deficiency, this paper presents a discrete wavelet transform (DWT) approach to denoise the measured signals. The denoising performance of DWT is discussed by several processing parameters, including the type of wavelet, decomposition level, thresholding method, and threshold selection rules. To overcome the disadvantages of the traditional hard- and soft-thresholding methods, an improved thresholding technique called the sigmoid function-based thresholding scheme is presented. The procedure is validated by using four benchmarks signals with three degrees of degradation as well as a real measured signal obtained from a three-story reinforced concrete scale model shaking table experiment. The performance of the proposed method is evaluated by computing the signal-to-noise ratio (SNR) and the root-mean-square error (RMSE) after denoising. Results reveal that the proposed method offers superior performance than the traditional methods no matter whether the signals have heavy or light noises embedded.

A modified monkey algorithm for optimal sensor placement in structural health monitoring

Proper placement of sensors plays a key role in construction and implementation of an effective structural health monitoring (SHM) system. This paper outlines a novel methodology called the modified monkey algorithm (MA) for the optimum design of SHM system sensor arrays, which is very different from the conventional method and is simple to implement. The integer coding method instead of the binary coding method is proposed to code the solution. The Euclidean distance operator and the stochastic perturbation mechanism of the harmony search algorithm are employed to improve the local and global search capability. A computational case of a high-rise building has been implemented to demonstrate the effectiveness of the modified method. The obtained sensor placements using the modified MA are compared with those gained by the existing MA using the integer coding method and the famous forward sequential sensor placement algorithm. Results showed that the innovations in the MA proposed in this paper could improve the convergence of the algorithm and the method is effective in solving combinatorial optimization problems such as optimal sensor placement.

Optimal Sensor Placement for Health Monitoring of High-Rise Structure Based on Genetic Algorithm

Optimal sensor placement (OSP) technique plays a key role in the structural health monitoring (SHM) of large-scale structures. Based on the criterion of the OSP for the modal test, an improved genetic algorithm, called “generalized genetic algorithm (GGA)”, is adopted to find the optimal placement of sensors. The dual-structure coding method instead of binary coding method is proposed to code the solution. Accordingly, the dual-structure coding-based selection scheme, crossover strategy and mutation mechanism are given in detail. The tallest building in the north of China is implemented to demonstrate the feasibility and effectiveness of the GGA. The sensor placements obtained by the GGA are compared with those by exiting genetic algorithm, which shows that the GGA can improve the convergence of the algorithm and get the better placement scheme.

Characterization and extraction of global positioning system multipath signals using an improved particle-filtering algorithm

Driving down multipath errors is probably the single most important objective of the current research into the use of the global positioning system (GPS) for high-accuracy applications. This paper focuses on the characterization of multipath signals and techniques for their removal by improved particle filtering. By the characteristic analysis of the GPS multipath signal in carrier phase observations, a specific set of generating and monitoring systems for multipath signals is established and a series of controlled experiments are carried out to assess the efficiency of the improved particle filtering. Experimental results show that the method has the advantage of being able to adapt to the close reflector situation, while remaining quite efficient when the reflector gets further away. The extracted multipath signals may be used to improve positioning accuracies.

Measurement and Analysis of Wind-Induced Response of Tall Building Based on GPS Technology

The Global Positioning System (GPS) has been used in the health monitoring of large structures in recent years since it is weather independent, capable of autonomous operation, and does not require a line-of-sight between target points. In this paper, a structural health monitoring system based on the GPS is devised for a high-rise building. The field data, such as wind speed, wind direction and displacement responses were simultaneously and continuously measured under strong wind conditions. The relation between velocity components of the atmospheric wind and pressure fluctuations on the roof of the building are analyzed using the wavelet scalogram and wavelet coherence method, and a statistical significance level estimation method based on Monte Carlo simulation is presented to isolate the meaningful coherence from the spurious noise map. Finally, the responses of the high-rise building are investigated using the Periodogram method to conclude that the identified results agree well with the results computed by the Finite Element Method (FEM).

Thermal Load in Large-Scale Bridges: A State-of-the-Art Review:

Thermal load is an important factor that must be taken into account during the procedure of bridge design and structural condition evaluation especially for those statically indeterminate bridges and cable-supported bridges. This paper presents an overview of current research and development activities in the field of thermal load in bridge, in which emphasis is placed on the thermal load models established by numerical analysis and field measurement. The theoretical formulations and boundary conditions of heat transfer in bridge are firstly outlined. And then, the states of the art of numerical solutions for temperature distribution in bridge including finite difference method and finite element method are reviewed in detail. Following that, the progress on thermal load in three types of representative bridges that are concrete bridge, steel-concrete composite bridge, and steel bridge based on field measurement data is discussed extensively. Finally, some existing problems and promising research efforts about thermal load in bridge are remarked.

Freeze-Thaw Durability of Air-Entrained Concrete

One of the most damaging actions affecting concrete is the abrupt temperature change (freeze-thaw cycles). The types of deterioration of concrete structures by cyclic freeze-thaw can be largely classified into surface scaling (characterized by the weight loss) and internal crack growth (characterized by the loss of dynamic modulus of elasticity). The present study explored the durability of concrete made with air-entraining agent subjected to 0, 100, 200, 300, and 400 cycles of freeze-thaw. The experimental study of C20, C25, C30, C40, and C50 air-entrained concrete specimens was completed according to “the test method of long-term and durability on ordinary concrete” GB/T 50082-2009. The dynamic modulus of elasticity and weight loss of specimens were measured after different cycles of freeze-thaw. The influence of freeze-thaw cycles on the relative dynamic modulus of elasticity and weight loss was analyzed. The findings showed that the dynamic modulus of elasticity and weight decreased as the freeze-thaw cycles were repeated. They revealed that the C30, C40, and C50 air-entrained concrete was still durable after 300 cycles of freeze-thaw according to the experimental results.

Sensor Placement Optimization in Structural Health Monitoring Using Niching Monkey Algorithm

Optimal sensor placement (OSP) method plays a key role in setting up a health monitoring system for large-scale structures. This paper describes the implementation of monkey algorithm (MA) as a strategy for the optimal placement of a predefined number of sensors. To effectively maintain the population diversity while enhancing the exploitation capacities during the optimization process, a novel niching monkey algorithm (NMA) by combining the MA with the niching techniques is developed in this paper. In the NMA, the dual-structure coding method is adopted to code the design variables and a chaos-based approach instead of a pure random initialization is employed to initialize the monkey population. Meanwhile, the niche generation operation and fitness sharing mechanism are modified and incorporated to alleviate the premature convergence problem while enhancing the exploration of new search domain. In addition, to promote interactions and share the available resources, the replacement scheme is proposed and adopted among the niches. Finally, numerical experiments are conducted on a high-rise structure to evaluate the performance of the proposed NMA. It is found that the innovations in the proposed NMA can effectively improve the convergence of algorithm and generate superior sensor configurations when compared to the original MA.