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# 2305.3 Design of Wood Shear Walls

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For SI:

Where

Wood shear walls are permitted to resist horizontal forces in vertical distributing or resisting elements, provided the deflection in the plane of the shear wall, as determined by calculations, tests or analogies drawn therefrom, does not exceed the more restrictive of the permissible deflection of attached distributing or resisting elements or the drift limits of Section 1617.3.

Permissible deflection shall be that deflection up to which the shear wall and any attached distributing or resisting element will maintain its structural integrity under design load conditions, i.e., continue to support design loads without danger to occupants of the structure.

The deflection (Δ) of a blocked wood structural panel shear wall uniformly fastened throughout is permitted to be calculated by the use of the following formula:

**(Equation 23-2)**

For SI:

Where: | ||
---|---|---|

A |
= | Area of boundary element cross section in square inches (mm2) (vertical member at shear wall boundary). |

b |
= | Wall width, in feet (mm). |

d_{a} |
= | Deflection due to anchorage details (rotation and slip at tie-down bolts) in inches (mm). |

E |
= | Elastic modulus of boundary element (vertical member at shear wall boundary), in pounds per square inch (N/mm^{2}). |

e_{n} |
= | Deformation of mechanically fastened connections, in inches (mm). |

G |
= | Modulus of rigidity of wood structural panel, in pounds per square inch (N/mm^{2}). |

h |
= | Wall height, in feet (mm). |

t |
= | Effective thickness of wood structural panel for shear, in inches (mm). |

ν |
= | Maximum shear due to design loads at the top of the wall, in pounds per linear foot (N/mm |

Δ |
= | The calculated deflection, in inches (mm). |

Size and shape of shear walls and shear wall segments within shear walls containing openings shall be limited as set forth in Table 2305.3.3.

TYPE |
MAXIMUM HEIGHT- WIDTH RATIO |
---|---|

Wood structural panels or particleboard, nailed edges | For other than seismic: 3^{1}/_{2}:1For seismic: 2:1 ^{a} |

Diagonal sheathing, single | 2:1 |

Gypsum board, gypsum lath, cement plaster | 1^{1}/_{2}:1^{b} |

- For design to resist seismic forces, shear wall height-width ratios greater than 2:1, but not exceeding 3
^{1}/_{2}:1, are permitted provided the allowable shear values in Table 2306.4.1 are multiplied by 2*w/h*. - Ratio shown is for unblocked construction. Aspect ratio is permitted to be 2:1 where the wall is installed as blocked construction in accordance with Section 2306.4.5.1.2.

The height of a shear wall shall be defined as:

1. The maximum clear height from top of foundation to bottom of diaphragm framing above; or

The width of a shear wall shall be defined as the sheathed dimension of the shear wall in the direction of application of force [see Figure 2305.3.4(a)].

The width of full-height sheathing adjacent to unrestrained openings in a shear wall.

Where the dead load stabilizing moment in accordance with Chapter 16 allowable stress design load combinations is not sufficient to prevent uplift due to overturning moments on the wall, an anchoring device shall be provided. Anchoring devices shall maintain a continuous load path to the foundation.

The provisions of this section shall apply to the design of shear walls with openings. Where framing and connections around the openings are designed for force transfer around the openings, the provisions of Section 2305.3.7.1 shall apply. Where framing and connections around the openings are not designed for force transfer around the openings, the provisions of Section 2305.3.7.2 shall apply.

Where shear walls with openings are designed for force transfer around the openings, the limitations of Table 2305.3.3 shall apply to the overall shear wall including openings and to each wall pier at the side of an opening. The height of a wall pier shall be defined as the clear height of the pier at the side of an opening. The width of a wall pier shall be defined as the sheathed width of the pier at the side of an opening. Design for force transfer shall be based on a rational analysis. Detailing of boundary elements around the opening shall be provided in accordance with the provisions of this section [see Figure 2305.3.4(b)].

The provisions of Section 2305.3.7.2 shall be permitted to be used for the design of perforated shear walls.

The following limitations shall apply to the use of Section 2305.3.7.2:

1. A perforated shear wall segment shall be located at each end of a perforated shear wall. Openings shall be permitted to occur beyond the ends of the perforated shear wall; however, the width of such openings shall not be included in the width of the perforated shear wall.

2. The allowable shear set forth in Table 2306.4.1 shall not exceed 490 plf (7150 N/m).

3. Where out-of-plane offsets occur, portions of the wall on each side of the offset shall be considered as separate perforated shear walls.

4. Collectors for shear transfer shall be provided through the full length of the perforated shear wall.

5. A perforated shear wall shall have uniform top of wall and bottom of wall elevations. Perforated shear walls not having uniform elevations shall be designed by other methods.

6. Perforated shear wall height,

*h*, shall not exceed 20 feet (6096 mm). The resistance of a perforated shear wall shall be calculated in accordance with the following:

1. The percent of full-height sheathing shall be calculated as the sum of the widths of perforated shear wall segments divided by the total width of the perforated shear wall including openings.

2. The maximum opening height shall be taken as the maximum opening clear height. Where areas above and below an opening remain unsheathed, the height of opening shall be defined as the height of the wall.

3. The adjusted shear resistance shall be calculated by multiplying the unadjusted shear resistance by the shear resistance adjustment factors of Table 2305.3.7.2. For intermediate percentages of full-height sheathing, the values in Table 2305.3.7.2 are permitted to be interpolated.

4. The perforated shear wall resistance shall be equal to the adjusted shear resistance times the sum of the widths of the perforated shear wall segments.

Design of perforated shear wall anchorage and load path shall conform to the requirements of Sections 2305.3.7.2.4 through 2305.3.7.2.8, or shall be calculated using principles of mechanics. Except as modified by these sections, wall framing, sheathing, sheathing attachment and fastener schedules shall conform to the requirements of Section 2305.2.4 and Table 2306.4.1.

Anchorage for uplift forces due to overturning shall be provided at each end of the perforated shear wall. The uplift anchorage shall conform to the requirements of Section 2305.3.6 except that for each story the minimum tension chord uplift force, T, shall be calculated in accordance with the following:

**(Equation 23-3)**

T |
= | Tension chord uplift force, pounds (N). |

V |
= | Shear force in perforated shear wall, pounds (N). |

h |
= | Shear wall height, feet (mm). |

C_{o} |
= | Shear resistance adjustment factor from Table 2305.3.7.2. |

ΣL_{i} |
= |
Sum of widths of perforated shear wall segments, feet (mm). |

The unit shear force,

*v*, transmitted into the top of a perforated shear wall, out of the base of the perforated shear wall at full-height sheathing and into collectors (drag struts) connecting shear wall segments, shall be calculated in accordance with the following:**(Equation 23-3)**

Where | ||
---|---|---|

ν |
= | Unit shear force, pounds per lineal feet (N/m). |

V |
= | Shear force in perforated shear wall, pounds(N). |

C_{o} |
= | Shear resistance adjustment factor from Table 2305.3.7.2. |

ΣL_{i} |
= | Sum of widths of perforated shear wall segments, feet (mm). |

In addition to the requirements of Section 2305.3.7.2.4, perforated shear wall bottom plates at full-height sheathing shall be anchored for a uniform uplift force,

*t*, equal to the unit shear force,*v*, determined in Section 2305.3.7.2.5.Each end of each perforated shear wall segment shall be designed for a compression chord force,

*C*, equal to the tension chord uplift force,*T*, calculated in Section 2305.3.7.2.4.A load path to the foundation shall be provided for each uplift force,

*T*and*t*, for each shear force,*V*and*v*, and for each compression chord force,*C*. Elements resisting shear wall forces contributed by multiple stories shall be designed for the sum of forces contributed by each story.The controlling deflection of a blocked shear wall with openings uniformly nailed throughout shall be taken as the maximum individual deflection of the shear wall segments calculated in accordance with Section 2305.3.2, divided by the appropriate shear resistance adjustment factors of Table 2305.3.7.2.

The shear values for shear panels of different capacities applied to the same side of the wall are not cumulative except as allowed in Table 2306.4.1.

The shear values for material of the same type and capacity applied to both faces of the same wall are cumulative. Where the material capacities are not equal, the allowable shear shall be either two times the smaller shear capacity or the capacity of the stronger side, whichever is greater. Summing shear capacities of dissimilar materials applied to opposite faces or to the same wall line is not allowed.

**Exception:**For wind design, the allowable shear capacity of shear wall segments sheathed with a combination of wood structural panels and gypsum wallboard on opposite faces, fiberboard structural sheathing and gypsum wall board on opposite faces or hardboard panel siding and gypsum wallboard on opposite faces shall equal the sum of the sheathing capacities of each face separately.

Adhesive attachment of shear wall sheathing is not permitted as a substitute for mechanical fasteners, and shall not be used in shear wall strength calculations alone, or in combination with mechanical fasteners in Seismic Design Category D.

Two-inch (51 mm) nominal wood sill plates for shear walls shall include steel plate washers, a minimum of

^{3}/_{1}_{6}inch by 2 inches by 2 inches (4.76 mm by 51 mm by 51 mm) in size, between the sill plate and nut. Sill plates resisting a design load greater than 490 plf (LRFD) (7154 N/m) or 350 plf (ASD) (5110 N/m) shall not be less than a 3-inch (76 mm) nominal member. Where a single 3-inch (76 mm) nominal sill plate is used, 2-20d box end nails shall be substituted for 2-16d common end nails found in Line 8 of Table 2304.9.1.**Exception:**In shear walls where the design load is less than 840 plf (LRFD) (12 264 N/m) or 600 plf (ASD) (8760 N/m), the sill plate is permitted to be a 2-inch (51mm) nominal member if the sill plate is anchored by two times the number of bolts required by design and

^{3}/

_{1}

_{6}inch by 2 inch by 2 inch (4.76 mm by 51 mm by 51 mm) plate washers are used.

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