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Chapter 16 — REFERENCED STANDARDS

Section A403

California Existing Building Code (Title 24, Part 10) · 2019 edition · updated 2026-09-10 · California

Italicized text is a California amendment to the model code, as printed in the official publication.

ANALYSIS AND DESIGN

[BS] A403.1 General. Modifications required by the provisions in this chapter shall be designed in accordance with the California Building Code provisions for new construction, except as modified by this chapter.

Exception: Buildings for which the prescriptive measures provided in Section A404 apply and are used.

Alteration of the existing lateral force-resisting system or vertical load-carrying system shall not reduce the strength or stiffness of the existing structure, unless the altered structure would remain in conformance to the building code and this chapter.

[BS] A403.2 Scope of analysis. This chapter requires the alteration, repair, replacement or addition of structural elements and their connections to meet the strength and stiffness requirements herein. The lateral load-path analysis shall include the resisting elements and connections from the wood diaphragm immediately above any soft, weak or open-front wall lines to the foundation soil interface or to the uppermost story of a podium structure comprised of steel, masonry, or concrete structural systems that supports the upper, woodframed structure. Stories above the uppermost story with a soft, weak, or open-front wall line shall be considered in the analysis but need not be modified. The lateral load-path analysis for added structural elements shall include evaluation of the allowable soil-bearing and lateral pressures in accordance with the building code. Where any portion of a building

Copyright © 2019 ICC. ALL RIGHTS RESERVED. Accessed by Kevin Day (kevin.day@dgs.ca.gov), (California Building Standards Commission) Order Number #100735044 on Jul 24, 2019 03:54 PM (PDT) pursuant to License Agreement with ICC. No further reproduction or distribution authorized. Single user only, copying and networking prohibited. ANY UNAUTHORIZED REPRODUCTION OR DISTRIBUTION IS A VIOLATION OF THE FEDERAL COPYRIGHT ACT AND THE LICENSE AGREEMENT, AND SUBJECT TO CIVIL AND CRIMINAL PENALTIES THEREUNDER.

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APPENDIX A

within the scope of this chapter is constructed on or into a slope steeper than one unit vertical in three units horizontal (33-percent slope), the lateral force-resisting system at and below the base level diaphragm shall be analyzed for the effects of concentrated lateral forces at the base caused by this hillside condition.

Exception: Where an open-front, weak or soft wall line exists because of parking at the ground floor of a twostory 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.

[BS] A403.3 Design base shear and design parameters. The design base shear in a given direction shall be permitted to be 75 percent of the value required for similar new construction in accordance with the building code. The value of R used in the design of the strengthening of any story shall not exceed the lowest value of R used in the same direction at any story above. The system overstrength factor, 0, and the deflection amplification factor, Cd, shall be not less than the largest respective value corresponding to the R factor being used in the direction under consideration.

Exceptions:

  1. For structures assigned to Seismic Design Category B, values of R, 0 and Cd shall be permitted to be based on the seismic force-resisting system being used to achieve the required strengthening.

  2. For structures assigned to Seismic Design Category C or D, values of R, 0 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.

  3. For structures assigned to Seismic Design Category E, values of R, 0 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.

[BS] A403.4 Story drift limitations. The calculated story drift for each retrofitted story shall not exceed the allowable deformation compatible with all vertical load-resisting elements and 0.025 times the story height. The calculated story drift shall not be reduced by the effects of horizontal diaphragm stiffness but shall be increased where these effects produce rotation. Drift calculations shall be in accordance with the building code.

[BS] A403.4.1 Pole structures. The effects of rotation and soil stiffness shall be included in the calculated story drift where lateral loads are resisted by vertical elements whose required depth of embedment is determined by pole formulas. The coefficient of subgrade reaction used in

deflection calculations shall be based on a geotechnical investigation conducted in accordance with the building code.

[BS] A403.5 Deformation compatibility and P Δ effects. The requirements of the building code shall apply, except as modified herein. Structural framing elements and their connections not required by design to be part of the lateral forceresisting system shall be designed and detailed to be adequate to maintain support of expected gravity loads when subjected to the expected deformations caused by seismic forces. Increased demand caused by P Δ effects and story sidesway stability shall be considered in retrofit stories that rely on the strength and stiffness of cantilever columns for lateral resistance.

be part of the lateral forceresisting system shall be designed and detailed to be adequate to maintain support of expected gravity loads when subjected to the expected deformations caused by seismic forces. Increased demand caused by P Δ effects and story sidesway stability shall be considered in retrofit stories that rely on the strength and stiffness of cantilever columns for lateral resistance.

[BS] A403.6 Ties and continuity. All parts of the structure included in the scope of Section A403.2 shall be interconnected as required by the building code.

[BS] A403.7 Collector elements. Collector elements shall be provided that can transfer the seismic forces originating in other portions of the building to the elements within the scope of Section A403.2 that provide resistance to those forces.

[BS] A403.8 Horizontal diaphragms. The strength of an existing horizontal diaphragm sheathed with wood structural panels or diagonal sheathing need not be investigated unless the diaphragm is required to transfer lateral forces from vertical elements of the seismic force-resisting system above the diaphragm to elements below the diaphragm because of an offset in placement of the elements.

Rotational effects shall be accounted for where asymmetric wall stiffness increases shear demands.

[BS] A403.9 Wood-framed shear walls. Wood-framed shear walls shall have strength and stiffness sufficient to resist the seismic loads and shall conform to the requirements of this section.

[BS] A403.9.1 Gypsum or cement plaster products. Gypsum or cement plaster products shall not be used to provide lateral resistance in a soft or weak story or in a story with an open-front wall line, whether or not new elements are added to mitigate the soft, weak or open-front condition.

[BS] A403.9.2 Wood structural panels.

[BS] A403.9.2.1 Drift limit. Wood structural panel shear walls shall meet the story drift limitation of Section A403.4. Conformance to the story drift limitation shall be determined by approved testing or calculation. Individual shear panels shall be permitted to exceed the maximum aspect ratio, provided that the allowable story drift and allowable shear capacities are not exceeded.

[BS] A403.9.2.2 Openings. Shear walls are permitted to be designed for continuity around openings in accordance with the building code. Blocking and steel strapping shall be provided at corners of the openings to transfer forces from discontinuous boundary elements into adjoining panel elements. Alternatively, perforated shear wall provisions of the building code are permitted to be used.

188 2019 CALIFORNIA EXISTING BUILDING CODE

Copyright © 2019 ICC. ALL RIGHTS RESERVED. Accessed by Kevin Day (kevin.day@dgs.ca.gov), (California Building Standards Commission) Order Number #100735044 on Jul 24, 2019 03:54 PM (PDT) pursuant to License Agreement with ICC. No further reproduction or distribution authorized. Single user only, copying and networking prohibited. ANY UNAUTHORIZED REPRODUCTION OR DISTRIBUTION IS A VIOLATION OF THE FEDERAL COPYRIGHT ACT AND THE LICENSE AGREEMENT, AND SUBJECT TO CIVIL AND CRIMINAL PENALTIES THEREUNDER.

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[BS] A403.9.3 Hold-down connectors.

[BS] A403.9.3.1 Expansion anchors in tension. Expansion anchors that provide tension strength by friction resistance shall not be used to connect holddown devices to existing concrete or masonry elements.

[BS] A403.9.3.2 Required depth of embedment. The required depth of embedment or edge distance for the anchor used in the hold-down connector shall be provided in the concrete or masonry below any plain concrete slab unless satisfactory evidence is submitted to the code official that shows that the concrete slab and footings are of monolithic construction.

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▸Contents — California Existing Building Code (Title 24, Part 10)
California Existing Building Code (Title 24, Part 10)
  1. Chapter 2 — DEFINITIONS
  2. Appendix A — GUIDELINES FOR
  3. Appendix B — SUPPLEMENTARY
  4. Appendix C — GUIDELINES FOR THE
  5. Chapter 1 — SCOPE AND ADMINISTRATION
  6. Chapter 3 — PROVISIONS FOR ALL COMPLIANCE METHODS
  7. Chapter 4 — REPAIRS
  8. Chapter 5 — PRESCRIPTIVE COMPLIANCE METHOD
  9. Chapter 6 — CLASSIFICATION OF WORK
  10. Chapter 7 — ALTERATIONS - LEVEL 1
  11. Chapter 8 — ALTERATIONS - LEVEL 2
  12. Chapter 9 — ALTERATIONS - LEVEL 3
  13. Chapter 10 — CHANGE OF OCCUPANCY
  14. Chapter 11 — ADDITIONS
  15. Chapter 12 — HISTORIC BUILDINGS
  16. Chapter 13 — PERFORMANCE COMPLIANCE METHODS
  17. Chapter 14 — RELOCATED OR MOVED BUILDINGS
  18. Chapter 15 — CONSTRUCTION SAFEGUARDS
  19. ▸Chapter 16 — REFERENCED STANDARDS
    Overview
    1. Section A100
    2. Section A101
    3. Section A102
    4. Section A103
    5. Section A104
    6. Section A105
    7. Section A106
    8. Section A107
    9. Section A108
    10. Section A109
    11. Section A110
    12. Section A111
    13. Section A112
    14. Section A113
    15. Section A114
    16. Section A201
    17. Section A205
    18. Section A202
    19. Section A203
    20. Section A204
    21. Section A206
    22. Section A207
    23. Section A301
    24. Section A302
    25. Section A303
    26. Section A304
    27. Section A401
    28. Section A402
    29. Section A403
    30. Section A404
    31. Section A405
    32. Section A406
    33. Section A407
    34. Section B101
    35. Section B102
    36. Section B103
    37. Section B104
    38. Section C101
    39. Section C102
    40. Section C103
    41. Section C104
    42. Section C201
    43. Section C202

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