511C.4 Wood Diaphragms.

511C.4 Wood Diaphragms.

511C.4.1 Acceptable diaphragm span. A diaphragm is acceptable if the point (L,DCR) on Figure 5C-1 falls within Regions 1, 2 or 3.

511C.4.2 Demand-capacity ratios. Demand-capacity ratios shall be calculated for the diaphragm at any level according to the following formulas:

1. For a diaphragm without qualifying crosswalls at levels immediately above or below:

DCR = 0.332 Wd/ΣvuD (5C-5)

2. For a diaphragm in a single-story building with qualifying crosswalls:

DCR = 0.332 Wd/(ΣvuD+Vcb) (5C-6)

3. For diaphragms in a multi-story building with qualifying crosswalls in all levels:

DCR = 0.332 ΣWd/(ΣΣvuD+Vcb) (5C-7)

DCR shall be calculated at each level for the set of diaphragms at and above the level under consideration. In addition, the roof diaphragm shall also meet the requirements of Formula (5C-6).

4. For a roof diaphragm and the diaphragm directly below if coupled by crosswalls:

DCR = 0.332 ΣWd/ΣΣvuD (5C-8)

511C.4.3 Chords. An analysis for diaphragm flexure need not be made and chords need not be provided.

511C.4.4 Collectors. An analysis of diaphragm collector forces shall be made for the transfer of diaphragm edge shears into vertical elements of the lateral force resisting system. Collector forces may be resisted by new or existing elements.

511C.4.5 Diaphragm openings.

511C.4.5.1 Forces. Diaphragm forces at corners of openings shall be investigated and shall be developed into the diaphragm by new or existing materials.

511C.4.5.2 Demand-capacity ratio. In addition to the demand-capacity ratios of Section 511C.4.2, the demand-capacity ratio of the portion of the diaphragm adjacent to an opening shall be calculated using the opening dimension as the span.

511C.4.5.3 End quarter of diaphragm. Where an opening occurs in the end quarter of the diaphragm span, vuD for the demand-capacity ratio calculation shall be based on the net depth of the diaphragm.