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

Simplified Load Distribution Factors for Fiber Reinforced Polymer Composite Bridge Decks

In recent years, researchers have investigated the load distribution factors due to vehicle wheel loads. Several load distribution factors for fiber reinforced polymer deck-steel stringer bridge systems have been proposed. Unfortunately, these load distribution factors are only used for each particular fiber reinforced polymer bridge deck system. Therefore, the objective of the research effort is to present the load distribution results of a parametric study using finite element analysis. The simplified load distribution factors were developed herein. The bridge parameters for this study were stringer spacing, bridge span, width of bridge models, types of fiber reinforced polymer bridge decks and numbers of traffic lanes. The bridge responses under various wheel loading conditions were investigated. The simplified distribution factors based on “S-over-factor” formula were proposed and compared with the load distribution factors obtained from specifications, analytical and field data. The load distribution results for this present study were correlated to the previous research data. The upper and lower bound limit of the load distribution factors were presented to purpose of preliminary guidelines

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

Non-baseline detection of small damages from changes in strain energy mode shapes

Several methods for damage detection based on identifying changes in strain energy mode shapes have been recently described in the literature. Most of these methods require knowing strain energy distribution for the undamaged structure (baseline strain energy mode shapes). This is especially true for detection of small damages, where changes in the strain energy mode shapes cannot be observed otherwise. Usually, the mode shapes from the structure under test should be compared to the baseline mode shapes to provide sufficient data for damage detection. However, these methods do not cover damage detection on structures where baseline mode shapes cannot be readily obtained, for example, structures with preexisting damage. Conventional methods, like building a finite element model of a structure to be used as a baseline might be an expensive and time-consuming task that can be impossible for complex structures. This paper suggests a method for extraction of localized changes (damage peaks) from strain energy mode shapes based on Fourier analysis of the strain energy distribution. A detailed analytical proof is given for the case of a pinned-pinned beam and a numerical proof for the free-free beam. The analytical predictions have been confirmed both by the finite element model and impact testing experiments on a free-free aluminum beam, including single and multiple damage scenarios