FRICTION CHARACTERISTICS BETWEEN WOOD AND STEEL IN CONSIDERATION WITH SURFACE CONDITION VARIED PRESSURE OF CONTACTED SURFACE

Study on friction of wood surface

Abstract

 The use of timber for public buildings is being promoted in Japan. Various efforts were made to realize medium and large scale wooden buildings from these background. However, in timber structure, the analytical environment has not been established yet compared to other structural material. This paper focuses on the friction characteristics between wood and steel, which is used to boundary condition of joints where stress is not uniform. According to the theory of adhesion, friction between wood and steel can be deal with sum of adhesion force, which is shear force in proportion to contact area between steel and wood, and the effect digging up the wood surface by steel. In this study, friction tests and measurement of wood surface were carried out, and investigating these correspondence based on theory of adhesion. The friction tests were conducted in the wide range of 0.5 to 11 MPa for previous research. Wood surface were measured three stages after compressive load and after friction tests. The main findings are as follows.

 

 ・When the pressure of contacted surface was higher than 1 MPa, the deformation of wood was confirmed. The influence was observed that two peaks were shown in time history of friction coefficient. In this study, the coefficient of static friction was evaluated from the second peak time by the reason why the time shows only sliding movement.

 ・The coefficient of static friction of the wood surface is about 0.3 to 0.4 on average, but the variation due to the test piece is large, and it is about 0.07 for sliding T direction and 0.1 for sliding R direction against the average.

 ・Without the lowest pressure of contacted surface of 0.55 MPa, the coefficient of static friction increased with repeated friction, which can be explained from the waviness component of wood surface.

 ・When the pressure of contacted surface is 2.2 MPa, the highest coefficient of static friction is obtained by conducted tests. The area where the pressure of contacted surface is lower than this can be explained only by the adhesion force. On the other hands, the factor that the coefficient of static friction decreases when the pressure of contacted surface is higher than 2.2 MPa is estimated by the effect of digging up. Since the deformation within the range of 1 mm from contact surface is allowed in this research, we plan to continue investigation in order to verify the inference in future.