A steel-framed house is constructed using walls and floors made of plywood board panels and light-gauge cold-formed steel frames fastened with drill screws. The seismic performance of steel-framed houses prlmarily depends on the force-deformation relation of shear walls. Most conventional plywood shear walls show poor ductility because they tend to suddenly lose strength owing to the breaking of screws or punching out of the board when the deflection angle becomes around 1/30[rad]. Therefore, the energy absorbing ability of these walls is very low because of their pinching property in load-deflection relationships. The objective of this research is to improve the structural performance of shear walls in steel-framed houses by employing built-in friction dampers.
First, basic performance tests were conducted on a friction damper. The friction force was found to be sufficiently stable when the lubricated coating steel sheets were tightened with high-strength bolts. Furthermore, the insertion of disk springs and square washers on the bolt shank was found to be effective in reducing the fluctuation and decrease of the bolt tension during the friction damper sliding. Since the friction force of the damper has a linear relationship with the bolt tension, it can be arbitrarily adjusted by changing the bolt tension.
Next, a tension control method for the bolts used in the damper was studied. A method to control the bolt tension by adjusting the diameter of the pintail fracture groove of the torque-shear-type high-strength bolt was proposed. This method enables the accurate and reliable provision of an arbitrary bolt tension to the friction damper.
Furthermore, static loading tests were conducted on full-scale built-in friction shear walls with varying bolt tension. It was found that the walls have a high and stable energy absorption capability as compared with general plywood shear walls. It is also possible to design With reduced wall quantity while suppressing stress by employing dominant design characteristic values.
Finally, a numerical analysis model of the built-in friction shear wall was constructed using the loading test results. By using this analysis model, it is possible to analyze the restoring force characteristics corresponding to the change in the bolt tension of the walls.
