Investigation of Computer Vision Concepts and Methods for Structural Health Monitoring and Identification Applications

This study presents a comprehensive investigation of methods and technologies for developing a computer vision-based framework for Structural Health Monitoring (SHM) and Structural Identification (St-Id) for civil infrastructure systems, with particular emphasis on various types of bridges. SHM is implemented on various structures over the last two decades, yet, there are some issues such as considerable cost, field implementation time and excessive labor needs for the instrumentation of sensors, cable wiring work and possible interruptions during implementation. These issues make it only viable when major investments for SHM are warranted for decision making. For other cases, there needs to be a practical and effective solution, which computer-vision based framework can be a viable alternative. Computer vision based SHM has been explored over the last decade. Unlike most of the vision-based structural identification studies and practices, which focus either on structural input (vehicle location) estimation or on structural output (structural displacement and strain responses) estimation, the proposed framework combines the vision-based structural input and the structural output from non-contact sensors to overcome the limitations given above. First, this study develops a series of computer vision-based displacement measurement methods for structural response (structural output) monitoring which can be applied to different infrastructures such as grandstands, stadiums, towers, footbridges, small/medium span concrete bridges, railway bridges, and long span bridges, and under different loading cases such as human crowd, pedestrians, wind, vehicle, etc. Structural behavior, modal properties, load carrying capacities, structural serviceability and performance are investigated using vision-based methods and validated by comparing with conventional SHM approaches. In this study, some of the most famous landmark structures such as long span bridges are utilized as case studies. This study also investigated the serviceability status of structures by using computer vision-based methods. Subsequently, issues and considerations for computer vision-based measurement in field application are discussed and recommendations are provided for better results. This study also proposes a robust vision-based method for displacement measurement using spatio-temporal context learning and Taylor approximation to overcome the difficulties of vision-based monitoring under adverse environmental factors such as fog and illumination change. In addition, it is shown that the external load distribution on structures (structural input) can be estimated by using visual tracking, and afterward load rating of a bridge can be determined by using the load distribution factors extracted from computer vision-based methods. By combining the structural input and output results, the unit influence line (UIL) of structures are extracted during daily traffic just using cameras from which the external loads can be estimated by using just cameras and extracted UIL. Finally, the condition assessment at global structural level can be achieved using the structural input and output, both obtained from computer vision approaches, would give a normalized response irrespective of the type and/or load configurations of the vehicles or human loads

Research on the Psychological Satisfaction Mechanism of Video Platform Users’ Re-creation Behavior

Re-creation behavior is an important way for video website users to generate content. It can help users understand and develop themselves, improve the retention rate of platform users, and promote the emergence of new business models for video websites. Based on the uses and gratifications approach, this study proposes a research model of the psychological satisfaction process of "motivation-emotion-intention" with the re-creation video platform as the research background. Through data verification using SmartPLS, the research results show that four types of motivations, namely mimicking, helping, validation, and self-expression promote the satisfaction of lurkers' emotional needs; two types of emotions, the sense of belonging and the sense of achievement, promote lurkers to generate re-creation intentions

LOW CYCLE FATIGUE LIFE PREDICTIONS OF 15CrMoR PARENT MATERIAL AND WELD METAL

Butt-weld specimen has been made for coke drum material 15 Cr MoR. For both parent and weld materials,uniaxial tensile tests and uniaxial ratcheting tests have been conducted under different temperatures. The OW-II kinematic hardening constitutive model has been used to predict the material ratcheting effect using the experimental data obtained. Test results show that the OW-II model can well predict ratcheting strain rates for the stable period. Based on the obtained uniaxial tensile test data,basic parameters for predicting low cycle fatigue life have been obtained. The MSRS model has been used to predict the fatigue lives of the parent material and weld metal. The predicted results are within the 2 times error band and are uniformly distributed on both sides of 45 ° line accurately. Furthermore,the ratcheting strain rate and the strain amplitude for the stable period are obtained for the parent metal and the weld metal respectively by the OW-II kinematic hardening constitutive model under the same conditions. The MSRS model predicts that the fatigue life of the parent material is significantly lower than that of the weld metal and during the stable period the ratcheting strain rate of parent material is significantly higher than that of the weld metal

THE WEAK STIFFENING STRUCTURE OF EXTERNAL PRESSURIZED THIN WALLED CYLINDRICAL SHELL AND DETERMINATION OF ITS CRITICAL EXTERNAL PRESSURE

Some external pressurized thin walled cylindrical shells could only be stiffened by small stiffening rings due to structural limitations. Such stiffening rings can only partially stiffen the cylinder which is less effective than big stiffening rings.Eigenvalue buckling analysis was done for a series of external pressurized thin walled cylindrical shells with various stiffening rings,which demonstrates two different types of buckling mode according to stiffening ring dimensions. When the stiffening ring is strong enough,buckling occurs only in the cylindrical shell with wave number bigger than 3,and the critical external pressure is irrelevant to the dimension of the stiffening ring,which should be defined as strong stiffening structure,and the ring as strong stiffening ring. However,when the stiffening ring is small,buckling occurs in both the cylindrical shell and the stiffening ring with wave number changing from 3 to 2 as the stiffening ring gets stronger,and the critical external pressure increases with the dimension of the stiffening ring,which should be defined as weak stiffening structure,and the ring as small stiffening ring. By parametric study,the design boundary curve was worked out for the weak and strong stiffening structures. For the weak stiffening structure,the design boundary curves have been also worked out to separate the 2 waves and 3 waves buckling. Empirical formulae were given out for the weak stiffening structures. Compared with the allowable external pressure given by the approximate calculation of HG / T20582-2011,the result by the suggested method is about 100% 450% higher,which is in favor of light weight design of structures

Analysis of Sealing Performance of Metal B-ring Self-Tightening Structure

Process industries often use B-ring self-tightening sealing structures and rely on interference assembly to meet the initial sealing requirements. Therefore, determining reasonable B-ring material, size and interference is crucial to ensure the sealing performance of the structure. In this paper, based on elastic deformation analysis, the deformation co-ordination equation of a B-ring sealing structure was established, and a sealing contact pressure calculation formula was obtained, with discussion of the main factors affecting sealing performance. With the finite element method, transient temperature field analysis was carried out for startup and shutdown load cases, and contact analysis was carried out for interference assembly, startup and shutdown. Based on the evaluation criteria of sealing performance with proposed sealing rate and leakage parameters, the effects of material properties, interference, B-ring size, etc., on sealing performance were investigated, revealing that although a B-ring with high material yield stress can meet the sealing requirements, both the B-ring and the sealing surface of a reactor body will yield plastic deformation. B-rings with a low material yield stress exhibit obvious plastic deformation during startup and leak during shutdown. However, leakage parameters can be minimized by smaller interference and moderate wave radius

Form-Finding Analysis of Mesh Reflector of Large Parabolic Cylindrical Antenna

In this study, a hybrid iteration force density method (HIFDM) was proposed to ensure both tension uniformity and accuracy of an antenna mesh reflector. Based on a genetic algorithm (GA), the boundary cable tension of the antenna reflector net was optimized, which further improved the precision of the antenna mesh reflector. The static model of the large deployable structure was established using the finite element method (FEM), and thus, an iterative strategy for form-finding of the antenna reflector net was proposed, which considered the influence of the elastic deformation of the deployable structure. The results showed that the HIFDM was effective for the form-finding of the antenna mesh reflector, and the shape precision was improved by further optimization using the GA. Finally, it was noted that the elastic deformation of the deployable structure will reduce the uniformity of cable tension and affect the precision of antenna reflectors. Due to the large-scale and soft stiffness, the large deployable structure had a high sensitivity to cable pretension, and it is important to design a reasonable cable pretension to ensure the accurate shape of antenna mesh reflectors

Form-Finding Analysis of Mesh Reflector of Large Parabolic Cylindrical Antenna

In this study, a hybrid iteration force density method (HIFDM) was proposed to ensure both tension uniformity and accuracy of an antenna mesh reflector. Based on a genetic algorithm (GA), the boundary cable tension of the antenna reflector net was optimized, which further improved the precision of the antenna mesh reflector. The static model of the large deployable structure was established using the finite element method (FEM), and thus, an iterative strategy for form-finding of the antenna reflector net was proposed, which considered the influence of the elastic deformation of the deployable structure. The results showed that the HIFDM was effective for the form-finding of the antenna mesh reflector, and the shape precision was improved by further optimization using the GA. Finally, it was noted that the elastic deformation of the deployable structure will reduce the uniformity of cable tension and affect the precision of antenna reflectors. Due to the large-scale and soft stiffness, the large deployable structure had a high sensitivity to cable pretension, and it is important to design a reasonable cable pretension to ensure the accurate shape of antenna mesh reflectors