Robert J. Ross

Nondestructive evaluation of incipient decay in hardwood logs

Decay can cause significant damage to high-value hardwood timber. New nondestructive evaluation (NDE) technologies are urgently needed to effectively detect incipient decay in hardwood timber at the earliest possible stage. Currently, the primary means of inspecting timber relies on visual assessment criteria. When visual inspections are used exclusively, they provide no indication of the extent of internal deterioration that may exist in timber. In this study, time-of-flight, stress-wave tomography, and micro-drilling resistance methods were investigated for locating incipient decay in sugar maple logs. We found that the capability of the single-path time-of-flight method for decay detection is very limited, and the method can be used only to identify logs and trees with moderate and severe decay. Resistance-based detection of decay (including early stages) is effective if the resistance drilling device is oriented so that its path goes through the decay zone; however, orienting the drill through the decay is difficult to guarantee. A multi- sensor stress-wave device can overcome the path-dependent detection issue. Results from laboratory testing indicate that the eight-sensor two dimensional stress-wave device has good potential for assisting in the detection of incipient decay in roundwood, such as logs and standing timber. However, to more effectively locate early-stage decay within a hardwood timber, more sensors should be added to the measurement system to obtain a higher resolution two-dimensional tomography image of a cross section. Field studies on standing hardwood timber should further investigate the effectiveness of these NDE methods with improved systems and procedures. This research could benefit field foresters and managers in using NDE technologies to assess the health condition of hardwood timber in the forest and could potentially lead to significant economic savings.

Nondestructive Assessment of Timber Bridges Using a Vibration-Based Method

This paper describes an effort to develop a global dynamic testing technique for evaluating the overall stiffness of timber bridge superstructures. A forced vibration method was used to measure the natural frequency of single-span timber bridges in the laboratory and field. An analytical model based on simple beam theory was proposed to represent the relationship between the first bending mode frequency and bridge stiffness (characterized as EI product). The results indicated that the forced vibration method has potential for quickly assessing superstructure stiffness of timber bridges, but improvements must be made in measurement system to correctly identify the first bending mode frequency in bridges in the field. The beam theory model was found to fit the physics of the superstructure of single-span timber bridges and could be used to correlate first bending frequency to global stiffness if appropriate system parameters are identified.

Detecting Decay in Wood Components

This paper reviewed current inspection techniques for decay detection and it provides guidelines on the use of various non-destructive (NDE) methods in locating and defining areas of decay within wood structural members. Visual inspection and probing techniques are commonly used for locating exterior deterioration of wood members. When suspect decay areas are located by these methods, further investigation by coring or drilling is suggested to confirm and define the extent of the damage. Internal decay of wood structural members can be detected by a variety of means. Among the most effective and cost-efficient techniques for field applications are coring, resistance drilling, and the stress wave propagation method. But the sensitivity of these methods to detect and quantify an early stage of decay is limited. New technologies are yet to be developed for more efficiently identifying deteriorated wood structures and detecting incipient decay in individual structural members before significant strength loss occurs.

Floor Vibration: A Possible Assessment Method for Historic Buildings

stiffness of timber floors. The United States Department of Agriculture Forest Service, Forest Products Laboratory, has been developing nondestructive evaluation techniques to identify the degradation of wood in structures and the performance characteristics that remain in the structure. The work at the Forest Products Laboratory has focused on dynamic testing techniques, particularly stress-wave and ultrasonic-transmission nondestructive evaluation techniques for both laboratory and field investigations. Our initial efforts were aimed at using stress-wave techniques. In a previous publication, we reported on an inexpensive experimental technique that was developed to observe longitudinal stress-wave behavior in small wood specimens. The technique utilized a mechanical impactor to induce a wave in the specimens. Wave propagation in the specimens was observed by placing a piezo film sensor on the woods surface. Output of the sensor was recorded and

Nondestructive evaluation of timber bridges

A study was recently conducted to assess the technical feasibility of using stress wave nondestructive evaluation methods to locate decayed members in timber bridges. Stress wave nondestructive evaluation techniques were used to locate decayed components in several timber bridges in eastern Oregon. Various stress wave techniques were used to conduct an in-situ evaluation of stringers, decking, and compression members. Components suspected as having decay were identified and evaluated in a laboratory after dismantling. Both visual evaluation of the members and subsequent laboratory testing indicated that the stress wave techniques were able to locate decayed components with a high degree of accuracy.

Low Frequency Vibration Approach to Assess the Performance of Wood Structural Systems

The primary means of inspecting buildings and other structures is to evaluate each structure member individually. This is a time consuming process that is expensive, particularly if sheathing or other covering materials must be removed to access the structural members. This paper presents an effort to use a low frequency vibration method for assessing the structural performance of wood floor systems.

Nondestructive Evaluation of Biologically Degraded Wood

Wood is a complex material that can be attacked and degraded by a wide range of biological organisms. The USDA Forest Service, Forest Products Laboratory (FPL), has been investigating the use of nondestructive evaluation (NDE) techniques to identify when degradation of wood occurs in the structure and the performance characteristics that remain in the structure. In particular, FPL’s work has focused on using longitudinal stress wave NDE techniques for laboratory and field applications.

Structural Performance of the Second Oldest Glued-Laminated Structure in the United States

The second glued-laminated structure built in the United States was constructed at the USDA Forest Products Laboratory (FPL) in 1934 to demonstrate the performance of wooden arch buildings. After 75 years of use the structure was decommissioned in 2010. Shortly after construction, researchers structurally evaluated the gluedlaminated arch structure for uniform loading on the center arch. This structural system evaluation was added to the existing laboratory work on glued-laminated arches to develop the foundation on which the current glued-laminated arch design criteria is based. After 75 years of service and decommisioning, recovered arches were tested in the laboratory to evaluate the loss of structural performance. Loss of structural performance was evaluated by comparing original and current deformation. Based on a preliminary visual and structural assessment, the degradation of structural performance was minimal in the arches, except for two arch that were affected by the building fire.

Field assessment of wood stake decomposition in forest soil

Abstract A pulse-echo acoustic method was investigated for evaluating wood stake decomposition in the field. A total of 58 wood stakes (29 loblolly pine, Pinus taeda, and 29 aspen, Populus tremuloides) that were vertically installed (full length) in forest soils were non-destructively tested by means of a laboratory-type acoustic measurement system. The same acoustic measurements were also conducted on the wood stakes after they were removed from the soil. Compression (parallel to grain) tests were then performed on the stakes in the laboratory to obtain residual elastic and strength properties. The results indicate that the pulse-echo acoustic method is a good approach to characterize wood stakes that are fully inserted into mineral soils. Statistical analysis showed good relationships between acoustic parameters (number of pulse echoes and in-ground acoustic velocity) and percentage weight loss, modulus of elasticity in compression, and residual compressive strength. The pulse-echo acoustic method could be used as a monitoring tool to assess progressive levels of wood stake decomposition in forest soil.