Nondestructive Evaluation of Wood using Ultrasonic Frequency Domain Analysis

In-situ performance assessment of wooden structural components are very important for maintenance and rehabilitation of timber structures. Nondestructive evaluation (NDE) methods can play an important role in the in-situ assessment of structural performance. The ultrasonic technique has been found to be more accurate than the conventional practice of visual inspection in assessing the defects such as decays, knots, and splits in wood [1]

Nondestructive Evaluation of Wood Using Ultrasonic Dry-Coupled Transducers

The nondestructive evaluation of wood is of considerable importance in several structural applications such as wooden bridge decks, wooden structural components, and wooden railway ties. This problem has attracted the attention of several researchers [1–19]. The specific topics that are being considered include: detection of natural defects like bacterial growth, knots, and splits; grading of wood; estimation of strength and stiffness characteristics; assessment of the effect of chemical treatment on strength; and, in-situ evaluation of degradation in wooden structural components and railway ties. Ultrasonic techniques have achieved a reasonable amount of success in the estimation of structural properties and defects [11, 16, 18]. Detection of natural defects such as knots, splits and decays provides valuable information which can be used for the grading of wood. The wave velocity measurements can also be used for the determination of structural properties (e.g., modulus of elasticity) of wood leading to grading, and to monitor the in-situ degradation of wooden structural members exposed to loads and environmental conditions

Wave growth patterns in a non-linear dispersive system with instability and dissipation

A simple one-dimensional non linear equation including effects of instability, dissipation, and dispersion is examined numerically. Periodic solution of a non linear dispersive equation is presented for different values of α, β, and γ characterizing the constants for instability, dissipation, and dispersion respectively. In this paper, the growth pattern for the wave at different time intervals is discussed. Various equilibrium states with different initial configuration have been observed depending on initial conditions

Parametric Study on Dynamic Response of Fiber Reinforced Polymer Composite Bridges

Because of high strength and stiffness to low self-weight ratio and ease of field installation, fiber reinforced polymer (FRP) composite materials are gaining popularity as the materials of choice to replace deteriorated concrete bridge decks. FRP bridge deck systems with lower damping compared to conventional bridge decks can lead to higher amplitudes of vibration causing dynamically active bridge deck leading serviceability problems. The FRP bridge models with different bridge configurations and loading patterns were simulated using finite element method. The dynamic response results under varying FRP deck system parameters were discussed and compared with standard specifications of bridge deck designs under dynamic loads. In addition, the dynamic load allowance equation as a function of natural frequency, span length, and vehicle speed was proposed in this study. The proposed dynamic load allowance related to the first flexural frequency was presented herein. The upper and lower bounds’ limits were established to provide design guidance in selecting suitable dynamic load allowance for FRP bridge systems

Combined Effects of Sustained Loads and Wet-Dry Cycles on Durability of Glass Fiber Reinforced Polymer Composites

This paper deals with durability of glass fiber reinforced polymer (GFRP) composites under the combined effects of sustained tensile loads and wet-dry (WD) cycles. Two different solutions (distilled water and saltwater) were used to imitate the freshwater and marine environments, respectively. Tensile properties of the unconditioned and conditioned specimens were measured to study the durability of GFRP composites under these 2 effects. The response indicated that both tensile strength and elastic modulus increased initially upon WD cycles, which was attributed to both the postcuring of resin and the sustained tensile stress allowing for fastec cure. Further exposure to WD cycles in distilled water or saltwater led to a steady decrease in tensile strength and modulus. WD cycles of saltwater and distilled water have similar effects on the degradation of the tensile properties for unstressed specimens. However, the elastic modulus and elongation at rupture of stressed specimens under WD cycles of saltwater decreased more than those specimens under WD cycles of distilled water. Moreover, increase of sustained loads led to a decrease in tensile strength. Based on Arrhenius method, a prediction model which accounted for the effects of postcure processes was developed. The predicted results of tensile strength and elastic modulus agree well with those obtained from the experiments

Combined Effects of Sustained Loads and Wet-Dry Cycles on Durability of Glass Fiber Reinforced Polymer Composites

This paper deals with durability of glass fiber reinforced polymer (GFRP) composites under the combined effects of sustained tensile loads and wet-dry (WD) cycles. Two different solutions (distilled water and saltwater) were used to imitate the freshwater and marine environments, respectively. Tensile properties of the unconditioned and conditioned specimens were measured to study the durability of GFRP composites under these 2 effects. The response indicated that both tensile strength and elastic modulus increased initially upon WD cycles, which was attributed to both the postcuring of resin and the sustained tensile stress allowing for fastec cure. Further exposure to WD cycles in distilled water or saltwater led to a steady decrease in tensile strength and modulus. WD cycles of saltwater and distilled water have similar effects on the degradation of the tensile properties for unstressed specimens. However, the elastic modulus and elongation at rupture of stressed specimens under WD cycles of saltwater decreased more than those specimens under WD cycles of distilled water. Moreover, increase of sustained loads led to a decrease in tensile strength. Based on Arrhenius method, a prediction model which accounted for the effects of postcure processes was developed. The predicted results of tensile strength and elastic modulus agree well with those obtained from the experiments

Nondestructive Evaluation of Historic Hakka Rammed Earth Structures

The in-service Hakka rammed earth buildings, in the Fujian Province of China, are unique in design and performance. Their UNESCO’s inscription as World Heritage sites recognizes their artistic, cultural, social and historic significance. Sponsored by the National Science Foundation of the United States, the authors have examined the engineering values of these buildings in terms of comfortable living at low energy consumption, sustainability and durability. The objective of this study was to better understand the thermo-mechanical and aging responses of Hakka earth buildings under thermal and earthquake loads through nondestructive field evaluation, including full-scale roof truss and floor testing, laboratory testing of field samples and finite element modeling. This paper presents our observations and findings from the field nondestructive evaluations with emphasis on the integrity of the rammed earth outer walls and inner wood structures, as well as the thermal comfort of living in these buildings, while a second paper presents the results from the material characterization of field samples and the structural responses of a representative building under earthquake induced loads through finite element analysis

Tolerable Movement Criteria for Highway Bridges

DOT-FH-11-9440This investigation included (a) a state-of-the-art assessment of tolerable bridge movements based on a literature review, an appraisal of existing design specifications and practice, the collection and analysis of field data on foundation movements, structural damage and the tolerance to movements for a large number of bridges (314) in the Unites States and Canada, and an appraisal of the reliability of the methods currently used for settlement prediction; (b) a series of analytical studies to evaluate the effect of different magnitudes and rates of differential movement on the potential level of distress produced in a wide variety of steel and concrete bridge structures of different span lengths and stiffnesses; and (c) the development of methodology for the design of bridges and their foundations that embodies a rational set of criteria for tolerable bridge movements

Nondestructive Evaluation of Wood using Ultrasonic Frequency Domain Analysis

In-situ performance assessment of wooden structural components are very important for maintenance and rehabilitation of timber structures. Nondestructive evaluation (NDE) methods can play an important role in the in-situ assessment of structural performance. The ultrasonic technique has been found to be more accurate than the conventional practice of visual inspection in assessing the defects such as decays, knots, and splits in wood [1].</p