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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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