[BS] ASPECT RATIO.
The span-width ratio for horizontal diaphragms and the height-length ratio for shear walls.
[BS] GROUND FLOOR.
Any floor whose elevation is immediately accessible from an adjacent grade by vehicles or pedestrians. The ground floor portion of the structure does not include any floor that is completely below adjacent grades.
[BS] NONCONFORMING STRUCTURAL MATERIALS.
Wall bracing materials other than wood structural panels or diagonal sheathing.
[BS] OPEN-FRONT WALL LINE.
An exterior wall line, without vertical elements of the lateral force-resisting system, that requires tributary seismic forces to be resisted by diaphragm rotation or excessive cantilever beyond parallel lines of shear walls. Diaphragms that cantilever more than 25 percent of the distance between lines of lateral force-resisting elements from which the diaphragm cantilevers shall be considered excessive. Exterior exit balconies of 6 feet (1829 mm) or less in width shall not be considered excessive cantilevers.
An improvement of the lateral force-resisting system by alteration of existing structural elements or addition of new structural elements.
[BS] SOFT WALL LINE.
A wall line whose lateral stiffness is less than that required by story drift limitations or deformation compatibility requirements of this chapter. In lieu of analysis, a soft wall line may be defined as a wall line in a story where the story stiffness is less than 70 percent of the story above for the direction under consideration.
A story as defined by the building code, including any basement or underfloor space of a building with cripple walls exceeding 4 feet (1219 mm) in height.
[BS] STORY STRENGTH.
The total strength of all seismic-resisting elements sharing the same story shear in the direction under consideration.
[BS] WALL LINE.
Any length of wall along a principal axis of the building used to provide resistance to lateral loads. Parallel wall lines separated by less than 4 feet (1219 mm) shall be considered one wall line for the distribution of loads.
[BS] WEAK WALL LINE.
A wall line in a story where the story strength is less than 80 percent of the story above in the direction under consideration.
Exception: Buildings for which the prescriptive measures provided in Section A404 apply and are used.
No alteration of the existing lateral force-resisting system or vertical load-carrying system shall reduce the strength or stiffness of the existing structure, unless the altered structure would remain in conformance to the building code and this chapter.
Exception: When an open-front, weak or soft wall line exists because of parking at the ground floor of a two-story building and the parking area is less than 20 percent of the ground floor area, then only the wall lines in the open, weak or soft directions of the enclosed parking area need comply with the provisions of this chapter.
- For structures assigned to Seismic Design Category B, values of R, Δ0 and Cd shall be permitted to be based on the seismic force-resisting system being used to achieve the required strengthening.
- For structures assigned to Seismic Design Category C or D, values of R, Δ0 and Cd shall be permitted to be based on the seismic force-resisting system being used to achieve the required strengthening, provided that when the strengthening is complete, the strengthened structure will not have an extreme weak story irregularity defined as Type 5b in ASCE 7 Table 12.3-2.
- For structures assigned to Seismic Design Category E, values of R, Δ0 and Cd shall be permitted to be based on the seismic force-resisting system being used to achieve the required strengthening, provided that when the strengthening is complete, the strengthened structure will not have an extreme soft story, a weak story, or an extreme weak story irregularity defined, respectively, as Types 1b, 5a and 5b in ASCE 7 Table 12.3-2.
Rotational effects shall be accounted for when asymmetric wall stiffness increases shear demands.
- Diaphragm aspect ratio L/W is less than 0.67, where W is the diaphragm dimension parallel to the soft, weak or open-front wall line and L is the distance in the orthogonal direction between that wall line and the rear wall of the ground floor open area.
- Minimum length of side shear walls = 20 feet (6096 mm).
- Minimum length of rear shear wall = three-fourths of the total rear wall length.
- No plan or vertical irregularities other than a soft, weak or open-front wall line.
- Roofing weight less than or equal to 5 pounds per square foot (240 N/m2).
- Aspect ratio of the full second floor diaphragm meets the requirements of the building code for new construction.
Notes shall show required edge distance for fasteners on structural wood panels and framing members; required flush nailing at the plywood surface; limits of mechanical penetrations; and the sill plate material assumed in the design. The limits of mechanical penetrations shall also be detailed showing the maximum notching and drilled hole sizes.
Structural testing and inspection for new construction materials shall be in accordance with the building code, except as modified by this chapter.