Traditional light duty steel wall frames of the kind used in the walls of single storey houses, sheds and other relatively small buildings are generally made from structural members that are roll formed from light gauge sheet metal and comprise a plurality of spaced apart vertical studs, a horizontal top plate affixed to the upper end of the studs, a horizontal bottom plate affixed to the lower end of the studs and bracing straps or noggings affixed to and traversing the studs.
It has been proposed to secure together the base and well frame by a simple angle shaped steel metal bracket, having a horizontal flange fastened to the top face of the base anchored by bolts and a vertical flange fastened to the side of the end portion of the wall stud of the metal frame. Wall frames are designed to bear the weight of the roof truss and the roof covering on the basis that loads will be transferred to the load support members at or near the ends of the wall studs. Customarily, when conventional angle brackets are used to secure the wall studs to the base, undesirable reaction loads and torsional stresses are imposed on the end portions of the wall studs and/or the base anchor bolts at the position of the bracket. When extraneous forces are applied to the structure by means of for example, earthquake, the loads and stresses at these joints are even more pronounced.
In areas subject to earthquake and other extraneous load imposing natural phenomena, high capacity bracing panels have been proposed to resist such loads. These generally comprise a metal wall frame of the above kind clad with sheeting formed of, for example, metal such as for example steel, or wood such as for example plywood.
These bracing panels are generally anchored to concrete footings, floor slabs or other building components by affixture of the bottom plate thereto.
However under earthquake loads, it has been found that anchoring of this kind generally offers insufficient rigidity and strength to prevent damage to the wall and building structure.
A basic requirement of a bracing system to resist earthquake loads is for ultimate strength and resistance to deflection (stiffness). Steel wall frames can fairly easily be designed for strength but it has be proven difficult to design adequate stiffness into light gauge steel wall frames. This is because light gauge steel wall frame members readily exhibit small deflections around fasteners and across the members.
Earthquake forces generally come from horizontal shaking of the roof structure and enter the bracing panel horizontally through the top plate.
These horizontal forces at the top of the panel are resisted by vertical forces holding the bracing panel to the concrete slab or other parts of the structure.
Generally a bracing panel is held down by providing a fixing through the bottom plate, sometimes reinforcing the stud to plate connection with a strap, but all these systems ail the deflection criteria because of local bending between elements.