Wood Shear Wall (ASD, NDS 2018)

How it calculates

Lateral system and wall classification

The calculator classifies the wall as either a segmented shear wall or a perforated shear wall per AWC SDPWS 2021. In the segmented method, only full-height segments without openings contribute to lateral resistance and each segment requires a holdown at each end. In the perforated method, the entire wall length - including segments with openings - participates, with capacity reduced by the percentage of full-height sheathing per SDPWS 2021 Table 4.3.4.2.

Unit shear demand

For a given story, the applied shear force V (wind or seismic) is divided by the shear-resisting length to obtain the unit shear demand v:

• Segmented method: v = V / (sum of segment lengths)
• Perforated method: v = V / (C_o × L_total), where C_o is a function of the ratio of full-height sheathed area to total wall area per SDPWS 2021 Table 4.3.4.2

The unit shear demand is compared against the tabulated allowable unit shear capacity v_s from SDPWS 2021 Tables 4.3A or 4.3B for the specified sheathing type, fastener schedule, and framing species.

Chord force derivation

The overturning moment at the base of each wall segment generates axial forces in the boundary chord members - compression at the loaded end and tension at the far end. For a wall of height h and segment length L_s with unit shear v:

T = C = (v × h × L_s - N_gravity × L_s / 2) / L_s

Gravity loads from the floor or roof above reduce the net chord tension. For multi-story walls, cumulative chord forces from upper stories are added to the overturning demand at each story, increasing holdown requirements at lower levels.

Chord member design

The calculated chord tension and compression forces are checked against the ASD capacity of the boundary stud or post per NDS 2018. Tension capacity uses the net cross-sectional area and the reference tensile design value F't adjusted for C_D, C_M, C_t, and C_F. Compression capacity uses the column stability factor C_P derived from the stud effective length between floor plates.

Holdown selection

The required holdown uplift capacity equals the net chord tension force after gravity load offset. The calculator searches the Simpson Strong-Tie holdown catalogue - including HDU, HDUE, and PHD series products - and returns the lightest product meeting the required capacity, together with its allowable load at the governing load duration factor C_D. The minimum post size and fastener schedule are reported to support detailing.

Shear wall deflection

Total shear wall deflection is computed per SDPWS 2021 Section 4.3.2 as the sum of four components: bending deflection of the chord members, shear deformation of the sheathing panel, nail deformation at the sheathing-to-framing interface, and holdown elongation. The calculated deflection is compared against the inter-story drift limit from ASCE 7 Table 12.12-1.