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Chapter 16 — STRUCTURAL DESIGN

Section 1613

California Building Code (Title 24, Part 2) · 2022 edition · updated 2026-09-12 · California

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

1613.1 Scope.

Every structure, and portion thereof, including nonstructural components that are permanently attached to structures and their supports and attachments, shall be designed and constructed to resist the effects of earthquake motions in accordance with Chapters 11, 12, 13, 15, 17 and 18 of ASCE 7, as applicable. The seismic design category for a structure is permitted to be determined in accordance with Section 1613 or ASCE 7.

Exceptions:

  1. Detached one- and two-family dwellings, assigned to Seismic Design Category A, B or C, or located where the mapped short-period spectral response acceleration, SS, is less than 0.4 g.

  2. The seismic force-resisting system of wood-frame buildings that conform to the provisions of Section 2308 are not required to be analyzed as specified in this section. [OSHPD 1R, 2 & 5] Not permitted by OSHPD, see Section 2308.

  3. Agricultural storage structures intended only for incidental human occupancy.

  4. Structures that require special consideration of their response characteristics and environment that are not addressed by this code or ASCE 7 and for which other regulations provide seismic criteria, such as vehicular bridges, electrical transmission towers, hydraulic structures, buried utility lines and their appurtenances and nuclear reactors.

  5. References within ASCE 7 to Chapter 14 shall not apply, except as specifically required herein.

6. [OSHPD 1R, 2 & 5] Seismic Design Category shall be in accordance with exception to Section 1613.2.5. 1613.1.1 Scope. [SL] For applications listed in Section 1.12 regulated by the State Librarian, only the provisions of ASCE 7 Tables 13.5-1 and 1607.1, as amended, of this code shall apply.

1613.1.2 State-owned buildings. [BSC] State-owned buildings, including those of the University of California, CSU and Judicial Council, shall not be constructed where any portion of the foundation would be within a mapped area of earthquake-induced liquefaction or landsliding or within 50 feet of a mapped fault rupture hazard as estab- lished by Section 1803.7.

1613.1.3 Existing state buildings. [BSC] Additions, alter- ations, repairs or change of occupancy category of existing buildings shall be in accordance with the Califor- nia Existing Building Code, Part 10.

1613.2 Seismic ground motion values.

Seismic ground motion values shall be determined in accordance with this section.

1613.2.1 Mapped acceleration parameters. The parameters SS and S 1 shall be determined from the 0.2 and 1second spectral response accelerations shown on Figures

STRUCTURAL DESIGN

1613.2.1(1) through 1613.2.1(10). Where S 1 is less than or equal to 0.04 and SS is less than or equal to 0.15, the structure is permitted to be assigned Seismic Design Category A.

Exception: [OSHPD 1R, 2 & 5] Seismic Design Cate- gory shall be in accordance with exception to Section 1613.2.5.

1613.2.2 Site class definitions. Based on the site soil properties, the site shall be classified as Site Class A, B, C, D, E or F in accordance with Chapter 20 of ASCE 7.

Where the soil properties are not known in sufficient detail to determine the site class, Site Class D, subjected to the requirements of Section 1613.2.3, shall be used unless the building official or geotechnical data determines that Site Class E or F soils are present at the site.

Where site investigations that are performed in accordance with Chapter 20 of ASCE 7 reveal rock conditions consistent with Site Class B, but site-specific velocity measurements are not made, the site coefficients Fa and Fv shall be taken at unity (1.0).

1613.2.3 Site coefficients and adjusted maximum considered earthquake spectral response accelera- tion parameters. The maximum considered earthquake spectral response acceleration for short periods, SMS, and at 1-second period, SM1, adjusted for site class effects shall be determined by Equations 16-20 and 16-21, respectively:

SMS = FaSS (Equation 16-20)

SM1 = Fv S 1 (Equation 16-21)

but SMS shall not be taken less than SM1 except when determining the seismic design category in accordance with Section 1613.2.5.

where:

Fa = Site coefficient defined in Table 1613.2.3(1). Fv = Site coefficient defined in Table 1613.2.3(2). SS = The mapped spectral accelerations for short periods

as determined in Section 1613.2.1. S 1 = The mapped spectral accelerations for a 1-second

period as determined in Section 1613.2.1. Where Site Class D is selected as the default site class per Section 1613.2.2, the value of Fa shall be not less than 1.2. Where the simplified design procedure of ASCE 7, Section 12.14 is used, the value of Fa shall be determined in accordance with ASCE 7, Section 12.14.8.1, and the values of Fv, SMS and SM1 need not be determined.

1613.2.4 Design spectral response acceleration parame- ters. Five-percent damped design spectral response acceleration at short periods, SDS, and at 1-second period, SD1, shall be determined from Equations 16-22 and Equation 16-23, respectively:

2

SDS = 3 - - SMS (Equation 16-22)

Copyright © 2022 by, or licensed to, International Code Council, Inc. (ALL RIGHTS RESERVED); licensed to California Building Standards Commission pursuant to License Agreement. No further reproductions is authorized. 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.

STRUCTURAL DESIGN

SD1

2 = 3 - - SM1

(Equation 16-23)

site-specific procedures of ASCE 7. Each building and structure shall be assigned to the more severe seismic design category in accordance with Table 1613.2.5(1) or 1613.2.5(2), irrespective of the fundamental period of vibration of the structure, T .

Exception: [OSHPD 1R, 2 & 5] Structures not assigned to Seismic Design Category E or F above shall be assigned to Seismic Design Category D.

1613.2.5.1 Alternative seismic design category deter- mination. Where S 1 is less than 0.75, the seismic design category is permitted to be determined from Table 1613.2.5(1) alone where all of the following apply:

  1. In each of the two orthogonal directions, the approximate fundamental period of the structure, Ta, in each of the two orthogonal directions determined in accordance with Section 12.8.2.1 of ASCE 7, is less than 0.8 Ts determined in accordance with Section 11.8.6 of ASCE 7.

  2. In each of the two orthogonal directions, the fundamental period of the structure used to calculate the story drift is less than Ts .

where:

SMS = The maximum considered earthquake spectral

response accelerations for short period as determined in Section 1613.2.3. SM1 = The maximum considered earthquake spectral

response accelerations for 1-second period as determined in Section 1613.2.3.

1613.2.5 Determination of seismic design category. Structures classified as Risk Category I, II or III that are located where the mapped spectral response acceleration parameter at 1-second period, S 1, is greater than or equal to 0.75 shall be assigned to Seismic Design Category E. Structures classified as Risk Category IV that are located where the mapped spectral response acceleration parameter at 1-second period, S 1, is greater than or equal to 0.75 shall be assigned to Seismic Design Category F. Other structures shall be assigned to a seismic design category based on their risk category and the design spectral response acceleration parameters, SDS and SD1, determined in accordance with Section 1613.2.4 or the

TABLE 1613.2.3(1) [OSHPD 1R, 2 & 5]

a

VALUES OF SITE COEFFICIENT Fa a

SITE CLASS MAPPED RISK TARGETED MAXIMUM CONSIDERED EARTHQUAKE (MCE )
R
SPECTRAL RESPONSE ACCELERATION PARAMETER AT SHORT PERIOD
SITE CLASS Ss ≤ 0.25 Ss = 0.50 Ss = 0.75 Ss = 1.00 Ss = 1.25 Ss ≥ 1.5
A 0.8 0.8 0.8 0.8 0.8 0.8
B 0.9 0.9 0.9 0.9 0.9 0.9
C 1.3 1.3 1.2 1.2 1.2 1.2
D 1.6 1.4 1.2 1.1 1.0 1.0
E 2.4 1.7 1.3 1.2c 1.2c 1.2c
F Note b Note b Note b Note b Note b Note b

a. Use straight-line interpolation for intermediate values of mapped spectral response acceleration at short period, Ss . b. Values shall be determined in accordance with Section 11.4.8 of ASCE 7. c. See requirements for site-specific ground motions in Section 11.4.8 of ASCE 7. These values of Fa shall only be used for calculation of Ts, determination of

Seismic Design Category, linear interpolation for intermediate values of Ss, and when taking the exception under Item 2 within Section 11.4.8 of ASCE 7.

TABLE 1613.2.3(2) VALUES OF SITE COEFFICIENT FV a
SITE CLASS **MAPPED RISK TARGETED MAXIMUM CONSIDERED EARTHQUAKE (MCER) **
SPECTRAL RESPONSE ACCELERATION PARAMETER AT 1-SECOND PERIOD		 **MAPPED RISK TARGETED MAXIMUM CONSIDERED EARTHQUAKE (MCER) **
SPECTRAL RESPONSE ACCELERATION PARAMETER AT 1-SECOND PERIOD		 **MAPPED RISK TARGETED MAXIMUM CONSIDERED EARTHQUAKE (MCER) **
SPECTRAL RESPONSE ACCELERATION PARAMETER AT 1-SECOND PERIOD		 **MAPPED RISK TARGETED MAXIMUM CONSIDERED EARTHQUAKE (MCER) **
SPECTRAL RESPONSE ACCELERATION PARAMETER AT 1-SECOND PERIOD		 **MAPPED RISK TARGETED MAXIMUM CONSIDERED EARTHQUAKE (MCER) **
SPECTRAL RESPONSE ACCELERATION PARAMETER AT 1-SECOND PERIOD		 **MAPPED RISK TARGETED MAXIMUM CONSIDERED EARTHQUAKE (MCER) **
SPECTRAL RESPONSE ACCELERATION PARAMETER AT 1-SECOND PERIOD
SITE CLASS _S_1 ≤ 0.1 _S_1 = 0.2 _S_1 = 0.3 _S_1 = 0.4 _S_1 = 0.5 _S_1 ≥ 0.6
A 0.8 0.8 0.8 0.8 0.8 0.8
B 0.8 0.8 0.8 0.8 0.8 0.8
C 1.5 1.5 1.5 1.5 1.5 1.4
D 2.4 2.2c 2.0c 1.9c 1.8c 1.7c
E 4.2 3.3c 2.8c 2.4c 2.2c 2.0c
F Note b Note b Note b Note b Note b Note b

a. Use straight-line interpolation for intermediate values of mapped spectral response acceleration at 1-second period, S 1. b. Values shall be determined in accordance with Section 11.4.8 of ASCE 7. c. See requirements for site-specific ground motions in Section 11.4.8 of ASCE 7. [OSHPD 1R, 2 & 5] These values of Fv shall only be used for calculation of

TS, determination of Seismic Design Category, linear interpolation for intermediate values of S1, and when taking the exceptions under Items 1 and 2 of Section 11.4.8 for the calculation of SD1.

16-36 2022 CALIFORNIA BUILDING CODE

Copyright © 2022 by, or licensed to, International Code Council, Inc. (ALL RIGHTS RESERVED); licensed to California Building Standards Commission pursuant to License Agreement. No further reproductions is authorized. 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.

  1. Equation 12.8-2 of ASCE 7 is used to determine the seismic response coefficient, Cs .

  2. The diaphragms are rigid or are permitted to be idealized as rigid in accordance with Section 12.3.1 of ASCE 7 or, for diaphragms permitted to be idealized as flexible in accordance with Section 12.3.1 of ASCE 7, the distances between vertical elements of the seismic force-resisting system do not exceed 40 feet (12 192 mm).

Exception: [OSHPD 1R, 2 & 5] Seismic design cat- egory shall be determined in accordance with exception to Section 1613.2.5.

1613.2.5.2 Simplified design procedure. Where the alternate simplified design procedure of ASCE 7 is used, the seismic design category shall be determined in accordance with ASCE 7.

Exception: [OSHPD 1R, 2 & 5] Seismic design cat- egory shall be determined in accordance with exception to Section 1613.2.5.

1613.3 Ballasted photovoltaic panel systems.

Ballasted, roof-mounted photovoltaic panel systems need not be rigidly attached to the roof or supporting structure. Ballasted nonpenetrating systems shall be designed and installed only on roofs with slopes not more than one unit vertical in 12 units horizontal. Ballasted nonpenetrating systems shall be designed to resist sliding and uplift resulting from lateral and vertical forces as required by Section 1605, using a coefficient of friction determined by acceptable engineering principles. In structures assigned to Seismic Design Category C, D, E or F, ballasted nonpenetrating systems shall be designed to accommodate seismic displacement determined by nonlinear response-hi story or other approved analysis or

STRUCTURAL DESIGN

shake-table testing, using input motions consistent with ASCE 7 lateral and vertical seismic forces for nonstructural components on roofs. [OSHPD 1R, 2 & 5] Ballasted photo- voltaic panel systems shall be considered as an alternative system.

1613.4 Component Importance Factors. [OSHPD 1R, 2 &

5] Nonstructural components designated below shall have a component importance factor, Ip, equal to 1.5:

1. For components that are required for life-safety pur- poses after an earthquake, including emergency and standby power systems, mechanical smoke removal sys- tems, fire protection sprinkler systems and fire alarm control panels.

2. For medical equipment required for patient life sup- port.

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▸Contents — California Building Code (Title 24, Part 2)
California Building Code (Title 24, Part 2)
  1. Chapter 2 — DEFINITIONS AND ABBREVIATIONS
  2. Appendix G — FLOOD-RESISTANT
  3. Appendix L — EARTHQUAKE RECORDING
  4. Appendix M — TSUNAMI-GENERATED
  5. Appendix N — REPLICABLE
  6. Appendix O — PERFORMANCE-BASED
  7. Chapter 1 — SCOPE AND ADMINISTRATION
  8. Chapter 3 — OCCUPANCY CLASSIFICATION AND USE
  9. Chapter 4 — SPECIAL DETAILED REQUIREMENTS BASED ON OCCUPANCY A…
  10. Chapter 5 — GENERAL BUILDING HEIGHTS AND AREAS
  11. Chapter 6 — TYPES OF CONSTRUCTION
  12. Chapter 7 — FIRE AND SMOKE PROTECTION FEATURES
  13. Chapter 7A — MATERIALS AND CONSTRUCTION
  14. Chapter 8 — INTERIOR FINISHES
  15. Chapter 9 — FIRE PROTECTION AND LIFE SAFETY SYSTEMS
  16. Chapter 10 — MEANS OF EGRESS
  17. Chapter 11A — HOUSING ACCESSIBILITY
  18. Chapter 11B — ACCESSIBILITY TO PUBLIC BUILDINGS, PUBLIC ACCOMM…
  19. Chapter 12 — INTERIOR ENVIRONMENT
  20. Chapter 14 — EXTERIOR WALLS
  21. Chapter 15 — ROOF ASSEMBLIES AND ROOFTOP STRUCTURES
  22. ▸Chapter 16 — STRUCTURAL DESIGN
    Overview
    1. Section 1601
    2. Section 1602
    3. Section 1603
    4. Section 1604
    5. Section 1605
    6. Section 1607
    7. Section 1606
    8. Section 1608
    9. Section 1609
    10. Section 1610
    11. Section 1611
    12. Section 1612
    13. Section 1613
    14. Section 1614
    15. Section 1615
    16. Section 1616
    17. Section 1617
  23. Chapter 16A — STRUCTURAL DESIGN
  24. Chapter 17 — SPECIAL INSPECTIONS AND TESTS
  25. Chapter 18 — SOILS AND FOUNDATIONS
  26. Chapter 19 — CONCRETE
  27. Chapter 20 — ALUMINUM
  28. Chapter 21 — MASONRY
  29. Chapter 22 — STEEL
  30. Chapter 23 — WOOD
  31. Chapter 24 — GLASS AND GLAZING
  32. Chapter 25 — GYPSUM BOARD, GYPSUM PANEL PRODUCTS AND PLASTER
  33. Chapter 26 — PLASTIC
  34. Chapter 27 — ELECTRICAL
  35. Chapter 28 — MECHANICAL SYSTEMS
  36. Chapter 30 — ELEVATORS AND CONVEYING SYSTEMS
  37. Chapter 31 — SPECIAL CONSTRUCTION
  38. Chapter 31B — PUBLIC POOLS
  39. Chapter 31C — RADIATION
  40. Chapter 31D — FOOD ESTABLISHMENTS
  41. Chapter 31F — MARINE OIL TERMINALS
  42. Chapter 32 — ENCROACHMENTS INTO THE PUBLIC RIGHT-OF-WAY
  43. Chapter 33 — SAFEGUARDS DURING CONSTRUCTION
  44. Chapter 35 — REFERENCED STANDARDS
  45. Appendix A — EMPLOYEE QUALIFICATIONS
  46. Appendix B — BOARD OF APPEALS
  47. Appendix C — GROUP U – AGRICULTURAL BUILDINGS
  48. Appendix D — FIRE DISTRICTS
  49. Appendix F — RODENTPROOFING
  50. Appendix H — SIGNS
  51. Appendix I — PATIO COVERS
  52. Appendix J — GRADING
  53. Appendix K — GROUP R-3 AND GROUP R-3.1 OCCUPANCIES
  54. Appendix P — EMERGENCY HOUSING

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