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Selected, peer reviewed papers from the 2nd International Conference on Structural Health Assessment of Timber Structures (SHATIS 13), September 4-6, 2013, Trento, Italy
This book covers some of the most recent developments and application potentials in structural health assessment for non-experts in the subject. Among topics addressed are sensor types, platforms and data conditioning for practical applications, wireless collection of sensor data, sensor power needs and on-site energy harvesting, long-term monitoring of structures, uncertainty in collected data, and future directions in structural health assessment.
Wood is one of the most intriguing structural materials and the only one that is truly renewable. Along with stone, wood is the oldest structural material on the planet and has been extensively used throughout human history. Due to its aesthetical value and positive environmental impact, wood has experienced a renaissance in construction. As a biodegradable, hygroscopic, non-isotropic material, wood presents special challenges for a professional and requires through knowledge ranging from biology to continuum mechanics. This state-of-the-art report reflects the current knowledge in the area of in situ assessment of the physical and mechanical properties of wood structures. Nondestructive, semi-destructive and destructive methods are described in a systematic manner where technology, equipment and limitations are discussed. Some of the discussed methods are used in other materials such as masonry and concrete. Most of the methods, however, are specific to wood and special qualifications are required to understand and apply these methods effectively. Existing methods are constantly improved and new methods are being developed. This report includes methods that are used in practice or have shown significant promise and have a body of knowledge that supports statements made in this report. This is a useable tool for professionals, researchers, educators and students
Prepared by the Subcommittee on Evaluation, Maintenance, and Upgrading of Timber Structures of the Committee on Wood of the Structural Division of ASCE. This report presents information on technical aspects of inspection, evaluation, reinforcement, repair, and rehabilitation of timber structures. Any structure, regardless of the material from which it is made, may be subject to a review of its ability to perform a specific function or functions. This report reviews factors that influence the serviceability of wood structures, including loadings, duration of loads, temperature, moisture and weathering. Effects of chemicals and fire, as well as insects, fungi, and other organisms that attack wood are also covered. Designing to avoid problems caused by these factors is discussed. Inspection techniques and equipment are described, along with guidelines on where to look and what to look for. A section of evaluation of wood structures includes criteria such as structural analysis, determination of loads, and estimating load carrying capacity.
Many nondestructive techniques for structural health monitoring are subjective and based on visual observations of degradation. In addition, dynamic properties of structures are already used to obtain quantitative structural health data. However, most current data collection is limited to localized damage on the structure, rather than global response. Recent research involves the use of commercially available digital video cameras, or virtual visual sensors, to observe structural dynamic behavior. This project focuses on the determination of natural vibration frequencies by monitoring the intensity value of a single pixel coordinate over the course of a few seconds of a video of structural vibration, and then applying a fast Fourier transform to extract signal frequencies. Natural frequencies can be used to observe changes in stiffness properties of materials and structural systems that may relate to deterioration. The focus here is primarily on the development and application of the virtual visual sensor technique to wood structures to obtain information relevant to objective structural health monitoring. The experiments focus on verification of the method to extract natural frequencies in various scenarios, using the natural color gradients in wood structures to observe the motion. Additionally, effects of moisture content and simulated damage on natural frequencies are observed on simply-supported beams of dimensional lumber. Applications are also made to an in-place US Forest Service pedestrian bridge. Results show comparable accuracy in determining vibrational frequencies with virtual visual sensors and accelerometer measurements, successful observation of vibrational frequencies in a timber bridge, and good use of naturally occurring color gradients in both laboratory and field tests. Moisture content and simulated damage had measureable effects on natural frequencies using conventional accelerometers and virtual visual sensors. Digital video cameras show potential to be a promising tool for structural health monitoring of timber structures.