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EFFECTS OF WOOD CONDITION ON STRESS WAVE AND TORQUE DRILL NDE TECHNIQUES

Michael Aibright, P.Eng.
Wood Science & Technology Centre
University of New Brunswick

Lonie Fardy, FE 5990
Faculty of Forestry and Environmental Management
University of New Brunswick

Lyse Blanchet, P.Eng.
Public Works Canada


INTRODUCTION

Since 1992, the Wood Science and Technology Centre (WSTC) has been utilizing stress wave techniques to evaluate numerous structures for the presence and extent of decay within their members. The majority of these were conducted in conjunction with the Architectural and Engineering services branch of Public Works Canada (PWC) who utilize a decay detecting drill of the resistance or torque type. The combination of the stress wave technique used by WSTC and the Torque Drill method of PWC was found to be an efficient and reliable means of rapidly evaluating historic structures with minimal damage to the structures' fabric.

Much of the operating data known for both techniques was that gained by the operators. Considerable experience was required to make accurate interpretations of device readings. At the conference on the Preservation of Historic Ships in Dundee Scotland, it was noted that data was not available on the effects of wood species, wood temperature and moisture content on the readings generated by the two techniques. To quantify these effects, WSTC and PWC initiated a testing program which would evaluate the performance of the stress wave and torque drill techniques under known conditions. The test program was made part of the Faculty of Forestry and Environmental Management Senior Thesis Program FE5990 and was conducted by Mr. Lome Fardy.

The data presented here are from analysis conducted to date. Further analysis and testing was still underway at time of printing.

TESTING PROGRAM

To evaluate the species effect, samples of Douglas Fir, Red Pine, Southern Yellow Pine, Eastern White Cedar, Spruce and Red Maple were tested utilizing torque drill technique. The latter two species were in the form of glue laminated beams with three voids per specimen machined into the laminates to simulate regions of decay (See figure #1). The stress wave technique was used to evaluate both the solid and the void regions of laminated beams (See figure #2). The torque drill was utilized in the solid sections only since trial tests indicated that damage to the drill might result from traversing void regions. The techniques were applied in both the radial and tangential directions to the laminates at two locations per specimen (See figure #3). The two techniques were evaluated on the laminated specimens under the following exposure conditions:
  1. 20o Celsius and 15% equilibrium moisture content
  2. -10o Celsius and 15% equilibrium moisture content
  3. Pressure treated with water then submersed in 200 Celsius water
  4. Saturated samples frozen at -10o Celsius

PRELIMINARY TEST RESULTS

Data gathered and compiled thus far from the stress wave device for the laminated Spruce specimens for each exposure condition are presented in graph 1 and graph 2 for the Radial and tangential test directions respectively. Graph 3 and graph 4 represent stress wave data collected for the Maple specimens. Average drill resistance in Spruce and Maple for each condition is given in graph 5. Average drill resistance and specific gravity for each species tested is given in graph 6.

Final test results are expected later this summer.

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Version 1.01, June 1997