Kbi

Solution

The wall defined in the problem description meets the application criteria outlined for the perforated shear wall design method. Hold-downs provide overturning restraint at perforated shear wall ends and anchor bolts provide shear and uplift resistance between perforated shear wall ends. Perforated shear wall height, factored shear resistances for the wood structural panel shear wall, and aspect ratio of full-height sheathing at perforated shear wall ends meet requirements of the perforated shear wall method.

The process of determining the shear resistance adjustment factor involves determining percent full-height sheathing and maximum opening height ratio. Once these are known, a shear resistance adjustment factor can be determined from Table 2305.3.7.2 of the 2003 IBC (International Code Council 2003a). From the problem description and Figure 10.12

Percent full-height sheathing = sum of perforated shear wall segment widths, ^^ L

, r r , , „ 4 ft + 4 ft + 4 ft Length of perforated shear wall =-^ -x 100 = 50%

Maximum opening height ratio = maximum opening height

For a maximum opening height ratio of | (or maximum opening height of 6.67 ft when wall height h = 8 ft) and percent full-height sheathing equal to 50%, a shear resistance adjustment factor C0 = 0.57 is obtained from Table 2305.3.7.2 of the 2003 IBC (International Code Council 2003a). Note that if wood structural panel sheathing were not provided above and below the window or above the door, the maximum opening height would equal the wall height h.

EXAMPLE 10.2: Perforated Shear Wall Problem Description

Figure 10.13 illustrates one face of a two-story building with the first- and second-floor walls designed as perforated shear walls. Window heights are 4 ft and door height is 6.67 ft. A trial design is performed in this example based on applied loads V. For simplification, dead load contribution to overturning and uplift restraint is ignored and the effective width for shear in each perforated shear wall segment is assumed to be the sheathed width. Framing is Douglas fir. After basic perforated shear wall resistance and force requirements are calculated, detailing options to provide for adequate shear, v, and uplift, t, transfer between perforated shear wall ends are covered. Method A considers the condition

Second-floor perforated shear wall

Second-floor perforated shear wall

FIGURE 10.13 Perforated shear wall (Example 10.2), two-story building.

where a continuous rim joist is present at the second floor. Method B considers the case where a continuous rim joist is not provided, as when floor framing runs perpendicular to the perforated shear wall with blocking between floor framing joists.

Solution, second-floor wall

Determine the wood structural panel sheathing thickness and fastener schedule needed to resist applied load V = 2.250 kip, from the roof diaphragm, such that the shear resistance of the perforated shear wall is greater than the applied force. Also, determine anchorage and load path requirements for uplift force at ends, in plane shear, uplift between wall ends, and compression.

16 ft

Shear resistance adjustment factor C0 = 0.80.

Try 15/32 rated sheathing with 8d common nails (0.131 by 2.5 in.) at 6-in. perimeter spacing. Unadjusted shear resistance (Table 5.4 LRFD Structural-Use Panels Supplement) = 0.36 klf (American Forest and Paper Association 1996). Adjusted shear resistance = (unadjusted shear resistance)(C0) = (0.36 klf )(0.80) = 0.288 klf. Perforated shear wall resistance = (adjusted shear resistance)^ L,) = (0.288 klf)(4ft + 4ft) = 2.304 kip

2.304 kip > 2.250 kip. Required resistance due to story shear forces V. Overturning at shear wall ends

In-plane shear

V 2.25 kip

Compression chord force C, at each end of each perforated shear wall segment = T = 2.813 kip.

Solution, first-floor wall

Determine the wood structural panel sheathing thickness and fastener schedule needed to resist applied load V = 2.600 kip, at the second-floor diaphragm, such that the shear resistance of the perforated shear wall is greater than the applied force. Also, determine anchorage and load path requirements for uplift force at ends, in plane shear, uplift between wall ends, and compression.

Percent full-height sheathing = [(4 ft + 4 ft)/12 ft]x 100 = 67%. Shear resistance adjustment factor, C0 = 0.67.

Unadjusted shear resistance (Table 5.4 LRFD Structural-Use Panels Supplement) = 0.49 klf (American

Forest and Paper Association 1996). Adjusted shear resistance = (unadjusted shear resistance)(C0) = (0.49 klf)(0.67) = 0.328 klf.

Perforated shear wall resistance = (adjusted shear resistance) (ELi) = (0.328 klf)(4ft + 4 ft) = 2.626 kip, 2.626 kip > 2.600 kip.

Required resistance due to story shear forces = V.

Overturning at shear wall ends

When maintaining load path from story above, T = T from second floor + T from first floor =

Uplift t, can be cumulative with 0.352 klf from story above to maintain load path. Whether this occurs depends on detailing for transfer of uplift forces between end walls.

Compression chord force C at each end of each perforated shear wall segment = T = 3.880 kip.

When maintaining load path from story above, C = 3.880 kip + 2.813 kip = 6.693 kip.

Hold-downs and posts and the ends of perforated shear wall are sized using calculated force T. The compressive force, C, is used to size compression chords as columns and ensure adequate bearing.

Method A: continuous rim joist

See Figure 10.14.

Second floor: Determine fastener schedule for shear and uplift attachment between perforated shear wall ends. Recall that v = t = 0.352 klf.

Wall bottom plate (1.5-in. thickness) to rim joist: Use 20d box nail (0.148 by 4 in.). Lateral resistance flZ = 0.254 kip per nail and withdrawal resistance flW' = 0.155 kip per nail.

Nails for shear transfer = (shear force, v)/f!Z' = 0.352 klf/0.254 kip per nail = 1.39 nails per foot.

Nails for uplift transfer = (uplift force, t)/f1W' = 0.352 klf/0.155 kip per nail = 2.27 nails per foot.

Net spacing for shear and uplift = 3.3 in. on center.

Rim joist to wall top plate: Use 8d box nails (0.113 by 2.5 in.) toe-nailed to provide shear transfer. Lateral resistance flZ = 0.129 kip per nail.

Nails for shear transfer = (shear force, v)/f!Z' = 0.352 klf/0.129 kip per nail = 2.73 nails per foot.

Net spacing for shear = 4.4 in. on center.

See detail in Figure 10.14 for alternate means for shear transfer (e.g., metal angle or plate connector).

Transfer of uplift, t, from the second floor in this example is accomplished through attachment of second-floor wall to the continuous rim joist, which has been designed to provide sufficient strength to resist the induced moments and shears. Continuity of load path is provided by hold-downs at the ends of the perforated shear wall.

First floor: Determine the anchorage for shear and uplift attachment between perforated shear wall ends. Recall that v = t = 0.485 klf. Wall bottom plate (1.5-in. thickness) to concrete. Use 0.5-in. anchor bolt with lateral resistance flZ = 1.34 kip.

Bolts for shear transfer = (shear force, v)/f1Z' = 0.485 klf/1.34 kip per bolt = 0.36 bolts per foot.

Net spacing for shear = 33 in. on center.

Bolts for uplift transfer: Check axial capacity of bolts for t = v = 0.485 klf and size plate washers accordingly. No interaction between axial and lateral load on anchor bolt is assumed (e.g., presence of axial tension does not affect lateral strength).

Method B: blocking between joists

See Figure 10.14.

Second floor: Determine fasteners schedule for shear and uplift attachment between perforated shear wall ends. Recall that v = t = 0.352 klf.

Wall bottom plate (1.5-in. thickness) to rim joist: Use 20d box nail (0.148 by 4 in.). Lateral resistance flZ = 0.254 kip per nail.

Nails for shear transfer = (shear force, v)/f!Z' = 0.352 klf/0.254 kip per nail = 1.39 nails per foot.

Net spacing for shear = 8.63 in. on center.

Rim joist to wall top plate: Use 8d box nails (0.113 by 2.5 in.) toe-nailed to provide shear transfer. Lateral resistance flZ = 0.129 kip per nail.

Nails for shear transfer = (shear force, v)/f!Z' = 0.352 klf/0.129 kip per nail = 2.73 nails per foot.

Net spacing for shear = 4.4 in. on center.

See detail in Figure 10.14 for alternative means for shear transfer (e.g., metal angle or plate connector).

Method A

20d box at 8.6" o.c. for shear and 20d box at 5.3" o.c. for uplift (3.3" net spacing, stagger nails)

Continuous rim joist

Wood structural panel sheathing

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