Journal of the Japan Society of Erosion Control Engineering, Vol.56,No.4,p.21-31,2003

Durability, degree of deterioration, and methods for evaluating the bending strength of members of wooden structures based on various tests

Yoshiharu ISHIKAWA,Youji NAITOU,Hirotaka OCHIAI,Isamu KAMIHARA Abstract
The durability, methods for in‐situ measurement of the degree of deterioration, and methods for evaluating the bending strength of wooden members, which are important factors for the planning, design, and maintenance of wooden erosion control structures, were studied. Wooden members were collected as test specimens from a wooden groundsill and a revetment which were constructed in Nigori Creek which runs on the southern flank of Mt. Ontake, Nagano Prefecture, in 1985. Four types of test were conducted on the wooden members to assess the degree of deterioration: the ultrasonic pulse test, stress wave impact test, pin penetration test and drilling resistance test, and bending test. The correlations between the bending strength and values measured by the four tests and oven‐dry density indicate that the bending strength of wooden members is most closely correlated with the values derived from the drilling resistance test. The test results also indicate that the bending strength of the deteriorated part is almost zero and the bending strength of the non‐deteriorated part is the same as that of sound wood. Methods for evaluating the bending strength and bending capacity of deteriorated wood were obtained by using the ratio of the thickness of the deteriorated part measured by the drilling resistance test. The investigation revealed that the difference of circumstances of wooden members, even those for the same structures, greatly influences the degree of deterioration. The wooden members which were wetted with water or soaked in water at all times have been slightly deteriorated in 17years, while the wooden members which are not usually wetted with water had deteriorated significantly. Except for the wooden member at the highest portion of the revetment, the members of the17‐year‐old wooden groundsill and revetment have maintained sufficient bending strength to assure the safety of the structure.

Key words:wooden structure, test for degree of deterioration, durability, bending strength, bending capacity