RECOMMENDATIONS FOR DESIGN OF ANCHORING DEVICES FOR BOTTOM RAILS IN PARTIALLY ANCHORED TIMBER FRAME SHEAR WALLS

摘要

The authors have developed a new plastic design method for light-frame timber shear walls. The method is capable of analyzing the load-bearing capacity of partially anchored shear walls. For proper application of the plastic method it is necessary to ensure ductile behaviour of the sheathing-to-framing joints and to avoid brittle failure of the bottom rail in particular. In a partially anchored shear wall the leading stud is not fully anchored against uplift and corresponding tying down forces are developed in the sheathing-to-framing joints along the bottom rail in the sheathing segments close to the leading stud. These tying down forces in the joints may introduce a number of possible brittle failure modes or serviceability problems for the bottom rail that need to be eliminated or restricted in order for the plastic method to be applicable. This paper describes experimental results for proper design of washers or bearing plates for the anchor bolts in order to avoid splitting failure of and excessive washer indentation into the bottom rail. Specimens with both double and single sided sheathing and different locations of anchor bolts are studied. With respect to splitting of the bottom rail, the tests indicate that the failure load depends on the distance from the edge of the washer to the loaded edge of the bottom rail. With respect to large deformations due to bearing stresses of the washers of the anchoring bolts, the size of the washer is the most important parameter. The test results indicate that the bearing strength for large washers is lower than that proposed by Eurocode 5. In this paper, it is therefore proposed to make the bearing strength inverse proportional to the diameter or side length of the washer. Then, good agreement with the test results was found. The results show that failure due to splitting is the determining design mode.