| Deflection | |||
| There are two primary reasons for limiting shear wall deflection (also known as story drift). The first reason is for serviceability in order to limit cracking in wall coverings such as plaster, gypsum, and paint. The second reason has to do with limiting the maximum inelastic response of the shear wall, which is important in the seismic design of wood buildings. Furthermore, the story drift is also used to determine the relative flexibility or rigidity of diaphragms and shear walls. | |||
| The
method for calculating shear wall deflection can be found in IBC 2305.3 and UBC Standard
23-2. It accounts for bending, shear, nail deformation and
anchorage slip. - Bending: the shear wall performs like a cantilevered beam with the chords acting as the flanges of an I-beam. - Shear: the wall sheathing carries the shear like the web of a deep I-beam. - Nail Slip: slip in the nail connections between the sheathing and the framing allows relative movement of the sheathing panels. - Anchorage: Slip may occur between the chords and the hold-down connector, or between the hold-down connector and the foundation. |
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Total shear wall deflection (story drift) is the sum of the deflections from each of these components. |
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b = length of shear wall A = cross-sectional area of chord E = modulus of elasticity of chord h = shear wall height v = unit shear t = effective thickness of structural sheathing panel G = modulus of rigidity of structural sheathing panel en = nail deformation under load da = hold-down deflection |
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