Section 1613A — California Building Code (Title 24, Part 2)

EARTHQUAKE LOADS

1613 A .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 shall be determined in accordance with Section 1613 A .

1613 A .2 Seismic ground motion values. Seismic ground motion values shall be determined in accordance with this section.

1613 A .2.1 Mapped acceleration parameters. The parameters SS and S 1 shall be determined from the 0.2 and 1-second spectral response accelerations shown on Figures 1613 A .2.1(1) through 1613 A .2.1(8).

88 2019 CALIFORNIA BUILDING CODE

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1613 A .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 A .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 A .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, SM 1, adjusted for site class effects shall be determined by Equations 16 A -36 and 16 A -37, respectively:

SMS = FaSs (Equation 16 A -36)

SM1 = Fv S 1 (Equation 16 A -37)

STRUCTURAL DESIGN

but SMS shall not be taken less than SM 1 except when determining the seismic design category in accordance with Section 1613 A .2.5.

where: Fa = Site coefficient defined in Table 1613 A .2.3(1). Fv = Site coefficient defined in Table 1613 A .2.3(2). SS = The mapped spectral accelerations for short periods

as determined in Section 1613 A .2.1. S 1 = The mapped spectral accelerations for a 1-second

period as determined in Section 1613 A .2.1.

Where Site Class D is selected as the default site class per Section 1613 A .2.2, the value of Fa shall be not less than 1.2. 1613 A .2.4 Design spectral response acceleration parameters. Five-percent damped design spectral response acceleration at short periods, SDS, and at 1-second period, SD1, shall be determined from Equations 16 A -38 and 16 A -39, respectively:

SDS

SD1

2 = 3 ^- ^- ^SMS

2 = 3 ^- ^- ^SM1

(Equation 16 A -38)

(Equation 16 A -39)

where:

TABLE 1613 A .2.3(1) 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	Note b	Note b	Note b
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.

TABLE 1613 A .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.

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