Källsner and Girhammar have presented a new plastic design method for wood-framed shear walls at ultimate limit state. This method allows the designer to calculate the load-carrying capacity of shear walls partially anchored, where the leading stud is not fully anchored against uplift. The anchorage system of shear walls is provided from anchor bolts and hold downs. Anchor bolts provide horizontal shear continuity between the bottom rail and the foundation. Hold downs are directly connected from the vertical end stud to the foundation. When hold downs are not provided, the bottom row of nails transmits the vertical forces in the sheathing to the bottom rail (instead of the vertical stud) where the anchor bolts will further transmit the forces into the foundation. Because of the eccentric load transfer, due to forces acting in the same vertical plane, transverse bending is created in the bottom rail and splitting often occurs. It is important to evaluate this cross-wise bending and to ensure that no brittle failure occur in the bottom rail.
The bottom rail is experimentally studied with respect to two primary failure modes, splitting along the bottom of the bottom rail due to cross-wise bending and splitting along the edge side of the bottom rail due forces perpendicular to the grain from the sheathing-to-framing connections. The parameters varied are the size of the washer and the orientation of the pith. The bottom rail was subjected to loading perpendicular to grain through two-sided sheathing. In this report the different set of series are presented. Five sets were conducted depending on the size of the washer and in each set the pith was placed upwards and downwards.
The tests showed three different failure modes. In addition to the failure modes that the testing program was aimed at, splitting along the bottom or side of the bottom rail, the final failure was also due to plastic bending and withdrawal of the sheathing-to-framing nails. The results show that the size of the washer has a significant influence on the maximum load and the failure modes. The results show also that the orientation of the pith have a significant influence on the maximum load.