Chapter 3 QUALITY ASSURANCE
12.3 ENGINEERED WOOD CONSTRUCTION
12.3.1 General: The proportioning, design, and detailing of engineered wood systems, members, and connections shall be in accordance with the reference documents, except as modified by this section.
12.3.2 Framing Requirements: All wood columns and posts shall be framed to provide full end bearing. Alternatively, column and post end connections shall be designed to resist the full compressive loads, neglecting all end bearing capacity. Column and post end connections shall be fastened to resist lateral and net induced uplift forces.
12.3.3 Deformation Compatibility Requirements: Deformation compatibility of connections within and between structural elements shall be considered in design such that the deformation of each
element and connection comprising the seismic-force-resisting system is compatible with the
deformations of the other seismic-force-resisting elements and connections and with the overall system.
See Sec. 5.2.8 for story drift limitations.
12.3.4 Design Limitations:
12.3.4.1 Wood Members Resisting Horizontal Seismic Forces Contributed by Masonry and Concrete: Wood shear walls, diaphragms, horizontal trusses and other members shall not be used to resist horizontal seismic forces contributed by masonry or concrete construction in structures over one story in height.
Exceptions:
1. Wood floor and roof members shall be permitted to be used in horizontal trusses and diaphragms to resist horizontal seismic forces (including those due to masonry veneer, fireplaces, and chimneys) provided such forces do not result in torsional force distribution through the truss or diaphragm.
2. Vertical wood structural-use panel sheathed shear walls shall be permitted to be used to provide resistance to seismic forces in two-story structures of masonry or concrete constr- uction, provided the following requirements are met:
a. Story-to-story wall heights shall not exceed 12 feet (3660 mm).
b. Diaphragms shall not be considered to transmit lateral forces by torsional force distribution or cantilever past the outermost supporting shear wall.
c. Combined deflections of diaphragms and shear walls shall not permit per story drift of supported masonry or concrete walls to exceed the limits of Table 5.2.8.
d. Wood structural-use panel sheathing in diaphragms shall have all unsupported edges blocked. Wood structural-use panel sheathing for both stories of shear walls shall have all unsupported edges blocked and, for the lower story, shall have a minimum thickness of 15/32 inch (12 mm).
1997 Provisions, Chapter 12
FIGURE 12.3.4.2-1 Diaphragm length and width for plan view of open front building.
e. There shall be no out-of-plane horizontal offsets between the first and second stories of wood structural-use panel shear walls.
12.3.4.2 Horizontal Distribution of Shear: Diaphragms shall be defined as flexible for the purposes of distribution of story shear and torsional moment when the maximum lateral deformation of the diaphragm is more than two times the average story drift of the associated story determined by comparing the computed maximum in-plane deflection of the diaphragm itself under lateral load with the story drift of adjoining vertical-resisting elements under equivalent tributary lateral load. Other diaphragms shall be defined as rigid. Design of structures with rigid diaphragms shall include the structure configuration requirements of Sec. 5.2.3.1 and the horizontal shear distribution requirements of Sec. 5.3.5.
Open front structures with rigid wood diaphragms resulting in torsional force distribution shall be permitted provided the length, l, of the diaphragm normal to the open side does not exceed 25 feet (7620 mm), the diaphragm sheathing conforms to Sec. 12.4.3.1 through 12.4.3.4, and the l/w ratio (as shown in Figure 12.3.4.2-1) is less than 1/1 for one-story structures or 1/1.5 for structures over one story in height.
Exception: Where calculations show that diaphragm deflections can be tolerated, the length, l, normal to the open end shall be permitted to be increased to a l/w ratio not greater than 1.5/1 when sheathed in conformance with Sec. 12.4.3.1 or 12.4.3.4, or to 1/1 when sheathed in conformance with Sec. 12.4.3.3.
Rigid wood diaphragms shall be permitted to cantilever past the outermost supporting shear wall (or other vertical resisting element) a length, l, of not more than 25 feet (7620 mm) or two thirds of the diaphragm width, w, whichever is the smaller. Figure 12.3.4.2-2 illustrates the dimensions of l and w for a cantilevered diaphragm.
Structures with rigid wood diaphragms having a torsional irregularity in accordance with Table 5.2.3.2, Item 1, shall meet the following requirements: The l/w ratio shall not exceed 1/1 for one-story structures or 1/1.5 for structures greater than one story in height, where l is the dimension parallel to the load direction for which the irregularity exists.
Exception: Where calculations demonstrate that the diaphragm deflections can be tolerated, the width is permitted to be increased and the l/w ratio may be increased to 1.5/1 when
FIGURE 12.3.4.2-2 Diaphragm length and width for plan view of cantilevered diaphragm.
sheathed in conformance with Sec. 12.4.3.1 or to 1/1 when sheathed in conformance with Sec.
12.4.3.3 or 12.4.3.4.
12.3.4.3 Framing and Anchorage Limitations: All framing used for shear wall construction shall conform to Ref. 12-7 for 2-by (actual 1.5 in., 38 mm) or larger members. Boundary elements shall be tied together at all corners by lapping the members and nailing with 2-16d ( 0.162 by 2½ in., 4 by 64 mm) common nails or an equivalent capacity connection. Diaphragm and shear wall sheathing shall not be used to splice boundary elements. Diaphragm chords and drag struts shall be placed in, or tangent to, the plane of the diaphragm framing unless it can be demonstrated that the moments, shears, and deflections and deformations, considering eccentricities resulting from other configurations, can be tolerated without exceeding the adjusted resistance and drift limits.
12.3.4.4 Shear Wall Anchorage: Where net uplift is induced, tie-down (hold-down) devices shall be used. Tie-down (hold-down) devices attached to the end post with nails are permitted. All devices shall only be used where the uplift resistance values are based on cyclic testing of wall assemblies and the test results indicate that the tie-down device does not reduce the stiffness, ductility, or capacity of the shear wall when compared to nailed-on devices.
Foundation anchor bolts shall have a plate washer under each nut. The minimum plate washer sizes are as follows:
Bolt size Plate washer size for shear walls
1/2 and 5/8 inch (13 and 16 mm) 1/4 x 3 x 3 inch (6 x 75 x 75 mm) 3/4, 7/8, and 1 inch (19, 22, and 25 mm) 3/8 x 3 x 3 inch (10 x 75x 75 mm)
1997 Provisions, Chapter 12
Hole diameters in the plate washer 3/16 in. (5 mm) larger than the bolt diameter are permitted provided that a standard cut washer is placed between the plate washer and the nut. Foundation anchor bolt embedment shall conform to the requirements of Chapters 6 and 8.
Bolts shall be placed a maximum of 2 inches (50 mm) from the sheathed side of walls sheathed on one face . Walls sheathed on both faces shall have the bolts staggered with the bolt a maximum of 2 in. (50 mm) from either side of the wall. Alternatively, for walls sheathed on both faces the bolts shall be placed at the center of the foundation sill with the edge of the plate washer within ½ in. (13 mm) of each face of the wall. The plate washer width shall be a minimum of 3 in (75 mm) and the plate thickness shall be determined by analysis using the upward force on the plate equal to the tension capacity of the bolt.
Anchor bolt and tie-down nuts shall be tightened without crushing the wood, and provision for preventing nuts from loosening shall be made just prior to covering the framing.