2003 INTERNATIONAL BUILDING CODE® 321

STRUCTURAL DESIGN

FIGURE 1615(10)MAXIMUM CONSIDERED EARTHQUAKE GROUND MOTION FOR GUAM AND TUTUILLA

OF 0.2 AND 1.0 SEC SPECTRAL RESPONSE ACCELERATION(5 PERCENT OF CRITICAL DAMPING), SITE CLASS B

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321aR 2003 INTERNATIONAL BUILDING CODE®

STRUCTURAL DESIGN

FIGURE 1615(11)

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2003 INTERNATIONAL BUILDING CODE® 321bR

STRUCTURAL DESIGN

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1615.1.1 Site class definitions. The site shall be classifiedas one of the site classes defined in Table 1615.1.1. Wherethe soil shear wave velocity,v s , is not known, site class shallbe determined, as permitted in Table 1615.1.1, from stan-dard penetration resistance, N , or from soil undrained shearstrength, su , calculated in accordance with Section1615.1.5. Where site-specific data are not available to adepth of 100 feet (30 480 mm), appropriate soil propertiesare permitted to be estimated by the registered design pro-fessional preparing the soils report based on known geo-logic conditions.

When the soil properties are not known in sufficient detailto determine the site class, Site Class D shall be used unlessthe building official determines that Site Class E or F soil islikely to be present at the site.

1615.1.2 Site coefficients and adjusted maximum con-sidered earthquake spectral response acceleration pa-rameters. The maximum considered earthquake spectralresponse acceleration for short periods, SMS, and at 1-secondperiod, SM1, adjusted for site class effects, shall be deter-mined by Equations 16-38 and 16-39, respectively:

SMS = FaSs (Equation 16-38)

SM1 = FvS1 (Equation 16-39)

where:

Fa = Site coefficient defined in Table 1615.1.2(1).

Fv = Site coefficient defined in Table 1615.1.2(2).

SS = The mapped spectral accelerations for short periodsas determined in Section 1615.1.

S1 = The mapped spectral accelerations for a 1-secondperiod as determined in Section 1615.1.

1615.1.3 Design spectral response acceleration parame-ters. Five-percent damped design spectral response acceler-ation at short periods, SDS, and at 1-second period, SD1, shallbe determined from Equations 16-40 and 16-41, respec-tively:

S SDS MS= 23

(Equation 16-40)

S SD 1 M1= 23

(Equation 16-41)

where:

SMS = The maximum considered earthquake spectral re-sponse accelerations for short period as determinedin Section 1615.1.2.

SM1 = The maximum considered earthquake spectral re-sponse accelerations for 1-second period as deter-mined in Section 1615.1.2.

1615.1.4 General procedure response spectrum. Thegeneral design response spectrum curve shall be developedas indicated in Figure 1615.1.4 and as follows:

1. For periods less than or equal to TO, the design spec-tral response acceleration, Sa, shall be determined byEquation 16-42.

2. For periods greater than or equal to TO and less than orequal to TS, the design spectral response acceleration,Sa, shall be taken equal to SDS.

322 2003 INTERNATIONAL BUILDING CODE®

STRUCTURAL DESIGN

TABLE 1615.1.1SITE CLASS DEFINITIONS

SITECLASS

SOIL PROFILENAME

AVERAGE PROPERTIES IN TOP 100 feet, AS PER SECTION 1615.1.5

Soil shear wavevelocity,v S , (ft/s)

Standard penetrationresistance,N

Soil undrainedshear strength, s u , (psf)

A Hard rock vs > 5,000 N/A N/A

B Rock 2,500 < vs ≤ 5,000 N/A N/A

C Very dense soil and soft rock 1,200 < vs ≤ 2,500 N > 50 su ≥ 2,000

D Stiff soil profile 600 ≤ vs ≤ 1,200 15 ≤ N ≤ 50 1,000 ≤ su ≤ 2,000

E Soft soil profile vs < 600 N < 15 su < 1,000

E —

Any profile with more than 10 feet of soil having the following characteristics:1. Plasticity index PI > 20,2. Moisture content w ≥ 40%, and3. Undrained shear strength su < 500 psf

F —

Any profile containing soils having one or more of the following characteristics:1. Soils vulnerable to potential failure or collapse under seismic loading such as liquefiable

soils, quick and highly sensitive clays, collapsible weakly cemented soils.2. Peats and/or highly organic clays (H > 10 feet of peat and/or highly organic clay where

H = thickness of soil)3. Very high plasticity clays (H >25 feet with plasticity index PI >75)4. Very thick soft/medium stiff clays (H >120 feet)

For SI: 1 foot = 304.8 mm, 1 square foot = 0.0929 m2, 1 pound per square foot = 0.0479 kPa. N/A = Not applicable

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