Section A111 — SPECIAL PROCEDURE — 2025 California Existing Building Code (Title 24, Part 10)

[BS] A111.1 Limits for the application of this procedure. The special procedures of this section shall be applied only to buildings having the following characteristics:

Flexible diaphragms at all levels above the base of the structure.
Vertical elements of the seismic force-resisting system consisting predominantly of masonry or a combination of masonry and concrete shear walls.
Except for single-story buildings with an open front on one side only, not fewer than two lines of vertical elements of the seismic force-resisting system parallel to each axis of the building (see Section A111.8 for open front buildings).

[BS] A111.2 Seismic forces on elements of structures. With the exception of the provisions in Sections A111.4 through A111.7, elements of structures shall comply with Sections A110.2 through A110.4.

[BS] A111.3 Crosswalls. Crosswalls shall meet the requirements of this section.

[BS] A111.3.1 Crosswall definition. A crosswall is a wood-framed wall sheathed with any of the materials described in Table A108.1(1) or Table A108.1(2) or other system as defined in Section A111.3.5. Crosswalls shall be spaced not more than 40 feet (12 192 mm) on center measured perpendicular to the direction of consideration, and shall be placed in each story of the building. Crosswalls shall extend the full story height between diaphragms.

Exceptions:

Crosswalls need not be provided at all levels where used in accordance with Section A111.4.2, Item 4.
Existing crosswalls need not be continuous below a wood diaphragm at or within 4 feet (1219 mm) of grade, provided that:

2.1. Shear connections and anchorage requirements of Section A111.5 are satisfied at all edges of the diaphragm. 2.2. Crosswalls with total shear capacity of 0.5 S D1 Σ W d interconnect the diaphragm to the foundation. 2.3. The demand-capacity ratio of the diaphragm between the crosswalls that are continuous to their foundations does not exceed 2.5, calculated as follows:

Equation A1-6

DCR = (-----------------------------------------2.1 S D1 W d + V ca - ) 2 v u D

on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

[BS] A111.3.2 Crosswall shear capacity. Within any 40 feet (12 192 mm) measured along the span of the diaphragm, the sum of the crosswall shear capacities shall be not less than 30 percent of the diaphragm shear capacity of the strongest diaphragm at or above the level under consideration.

[BS] A111.3.3 Existing crosswalls. Existing crosswalls shall have a maximum height-to-length ratio between openings of 1.5 to 1. Existing crosswall connections to diaphragms need not be investigated as long as the crosswall extends to the framing of the diaphragms above and below.

[BS] A111.3.4 New crosswalls. New crosswall connections to the diaphragm shall develop the crosswall shear capacity. New crosswalls shall have the capacity to resist an overturning moment equal to the crosswall shear capacity times the story height. Crosswall overturning moments need not be cumulative over more than two stories.

[BS] A111.3.5 Other crosswall systems. Other systems, such as moment-resisting frames, may be used as cross-walls provided that the yield story drift does not exceed 1 inch (25 mm) in any story.

[BS] A111.4 Wood diaphragms.

[BS] A111.4.1 Acceptable diaphragm span. A diaphragm is acceptable if the point ( L,DCR ) on Figure A111.4.1 falls within Region 1, 2 or 3.

[BS] FIGURE A111.4.1—ACCEPTABLE DIAPHRAGM SPAN

540

480

420

360

300

240

180

120




1








	3

		2

0 2

3 3 4 5 6

DEMAND-CAPACITY RATIO, DCR

Region of demand-capacity ratios where crosswalls may be used to increase h/t ratios.
Region of demand-capacity ratios where h/t ratios of “buildings with crosswalls” may be used, whether or not crosswalls are present.
Region of demand-capacity ratios where h/t ratios of “all other buildings” shall be used, whether or not crosswalls are present.

For SI: 1 foot = 304.8 mm.

[BS] A111.4.2 Demand-capacity ratios. Demand-capacity ratios shall be calculated for the diaphragm at any level according to the following formulas:

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

Equation A1-7 DCR = 2.1 S D1 W d /Σ v u D 2. For a diaphragm in a single-story building with qualifying crosswalls, or for a roof diaphragm coupled by crosswalls to the diaphragm directly below:

Equation A1-8 DCR = 2.1 S D1 W d /Σ v u D + V cb

DCR = 2.1 S D1 W d /Σ v u D

DCR = 2.1 S D1 W d /Σ v u D + V cb

APPENDIX A-12 2025 CALIFORNIA EXISTING BUILDING CODE

on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

For diaphragms in a multiple-story building with qualifying crosswalls in all levels:

Equation A1-9 DCR = 2.1 S D1 ΣW d / ΣΣ( v u D + V cb )

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 meet the requirements of Equation A1-10. 4. For a roof diaphragm and the diaphragm directly below, if coupled by crosswalls:

Equation A1-10 DCR = 2.1 S D1 Σ W d /ΣΣ v u D

[BS] A111.4.3 Chords. An analysis for diaphragm flexure need not be made, and chords need not be provided.

[BS] A111.4.4 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.

[BS] A111.4.5 Diaphragm openings.

Diaphragm forces at corners of openings shall be investigated and shall be developed into the diaphragm by new or existing materials.
In addition to the demand-capacity ratios of Section A111.4.2, the demand-capacity ratio of the portion of the diaphragm adjacent to an opening shall be calculated using the opening dimension as the span.
Where an opening occurs in the end quarter of the diaphragm span, the calculation of v u D for the demand-capacity ratio shall be based on the net depth of the diaphragm.

[BS] A111.5 Diaphragm shear transfer. Diaphragms shall be connected to shear walls and new vertical seismic force-resisting elements with connections capable of developing the diaphragm-loading tributary to the shear wall or new seismic force-resisting elements given by the lesser of the following formulas: Equation A1-11 V = 1.2 S D1 C p W d using the C p values in Table A111.5, or Equation A1-12 V = v u D

DCR = 2.1 S D1 ΣW d / ΣΣ( v u D + V cb )

DCR = 2.1 S D1 Σ W d /ΣΣ v u D

V = 1.2 S D1 C p W d

V = v u D

[BS]TABLE A111.5—HORIZONTAL FORCE FACTOR, C
p

CONFIGURATION OF MATERIALS	Cp
Roofs with straight or diagonal sheathing and roofing applied directly to the sheathing, or floors with straight tongue-and- groove sheathing.	0.50
Diaphragms with double or multiple layers of boards with edges offset, and blocked plywood systems.	0.75
Diaphragms of metal deck without topping:
Minimal welding or mechanical attachment.	0.6
Welded or mechanically attached for seismic resistance.	0.68

[BS] A111.6 Shear walls (in-plane loading).

[BS] A111.6.1 Wall story force. The wall story force distributed to a shear wall at any diaphragm level shall be the lesser value calculated as:

Equation A1-13 F wx = 0.8 S D1 W ( wx + W d /2)

but need not exceed

Equation A1-14 F wx = 0.8 S D1 W wx + v u D

[BS] A111.6.2 Wall story shear. The wall story shear shall be the sum of the wall story forces at and above the level of consideration.

Equation A1-15 V wx = Σ F wx

[BS] A111.6.3 Shear wall analysis. Shear walls shall comply with Section A112.

[BS] A111.6.4 New seismic force-resisting elements. New seismic force-resisting elements such as moment frames, braced frames or shear walls shall be designed as required by the building code, except that the seismic forces shall be as specified in Section A111.6.1, and the story drift ratio shall be limited to 0.015, except as further limited by Section A112.4.2 for moment frames.

[BS] A111.7 Out-of-plane forces—unreinforced masonry walls.

[BS] A111.7.1 Allowable unreinforced masonry wall height-to-thickness ratios. The provisions of Section A110.2 are applicable, except the allowable height-to-thickness ratios given in Table A110.2 shall be determined from Figure A111.4.1 as follows:

In Region 1, height-to-thickness ratios for buildings with crosswalls may be used if qualifying crosswalls are present in all stories.
In Region 2, height-to-thickness ratios for buildings with crosswalls may be used whether or not qualifying crosswalls are present.

F wx = 0.8 S D1 W ( wx + W d /2)

F wx = 0.8 S D1 W wx + v u D

V wx = Σ F wx

on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

In Region 3, height-to-thickness ratios for “all other buildings” shall be used whether or not qualifying crosswalls are present.

[BS] A111.7.2 Walls with diaphragms in different regions. Where diaphragms above and below the wall under consideration have demand-capacity ratios in different regions of Figure A111.4.1, the lesser height-to-thickness ratio shall be used.

[BS] A111.8 Open-front design procedure. A single-story building with an open front on one side and crosswalls parallel to the open front may be designed by the following procedure:

Effective diaphragm span, L i, for use in Figure A111.4.1 shall be determined in accordance with the following formula: Equation A1-16 L i = 2[( W w / W d ) L + L ]
Diaphragm demand-capacity ratio shall be calculated as:

Equation A1-17 DCR = 2.1 S D 1 ( W d + W w )/[( v u D ) + V cb ]