Practical Examples employing the International Building Code (IBC) regulations and the New Seismic Hazard Maps for the Eastern Caribbean
June 2011Walter Salazar Richard Robertson Lloyd Lynch Joan Latchmanwww.uwiseismic.com
Carlo Lai Francesca Bozzoni Mirko Corigliano Elisa Zuccolo Laura Scandella
Practical Examples Get the design response spectra and the seismic coefficients Cs for the following sites at rock conditions: 1) Scarborough -Tobago (Building 20 stories) 2) Indian River Dominica (Bridge 30 m multispan intermediate columns with height H = 15 m)
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Design spectral acceleration parameters IBC ASCE 7_05
SDS = 2/3*Fa * Ss SD1 = 2/3*Fv * S1
Spectral acceleration for 0.2 s
Obtained in the Seismic Spectral acceleration for 1.0 s Hazard maps
Fa and Fv: depends on soil conditionsFor rock site conditions CLASS B It Corresponds to a shear wave velocity Vs = 760 m/s:
Fa = 1.0 and Fv = 1.03
SDS
ELASTIC DESIGN RESPONSE SPECTRUM COMPATILE WITH THE IBC
Sa =
S D1 T
SD1
Ts To4
EXAMPLE 1: Scarborough -Tobago Building 20 stories
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1.85 g
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0.375 g
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Reading from the maps
S S = 1.85 g S1 = 0.375 g
S DS = (2 / 3) *1.85 g = 1.23 g S D1 = (2 / 3) *0.375 g = 0.25 g
S D1 0.25 To = 0.2 = 0.2* = 0.04 s 1.23 S DS T T Sa = SDS 0.4 + 0.6 = 1.23* 0.4 + 0.6 = 0.492 + 18.45T 0.04 To T : the fundamental period of the structure in s8
S a = S DS = 1.23 g
Flat spectral response
S D1 0.25 TS = = = 0.20 s Period to which begin S DS 1.23 the exponential decay
S D1 0.25 g Sa = = T T
Spectral exponential decay
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Sa = 0.492 + 18.45T
The Seismic Coefficient Cs Fundamental Period: T = 2.0 s (after dynamic analysis)
S a = S DS = 1.23g
Sa =
S D1 0.25 g = T T
SA = 0.13g (elastic spectral acceleration) Reduction factor R= 8.0 considering ductility and overstrength Seismic design coefficient:
0.13 g0.04s
0.20s
Cs = SA/R=0.13g/8=0.016g
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SAP MODEL FOR THE 20 STORY BUILDING11
EXAMPLE 2: MULTI SPAN BRIDGE INDIAN RIVER - DOMINICA
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MULTI SPAN BRIDGE INDIAN RIVER - DOMINICA
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Indian River
1.55g
Indian River
0.47g
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Reading from the maps
S S = 1.55 g S1 = 0.47 g
S DS = (2 / 3) *1.55 g = 1.03 g S D1 = (2 / 3) *0.47 g = 0.31g
S D1 0.31 To = 0.2 = 0.2* = 0.06 s 1.03 S DS T T Sa = SDS 0.4 + 0.6 = 1.03* 0.4 + 0.6 = 0.41 + 10.3T 0.06 To T : the fundamental period of the structure in s15
S a = S DS = 1.03 g
Flat spectral response
S D1 0.31 TS = = = 0.30 s Period to which begin S DS 1.03 the exponential decay
S D1 0.31g Sa = = T T
Spectral exponential decay
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Sa = 0.41 + 10.3T
S a = S DS = 1.03g
The Seismic Coefficient Cs Design of a column Fundamental Period (after dynamic analysis):
Sa =
S D1 0.31g = T T
T = 0.75 s (H=15 m and 30 m span) SA = 0.42g (elastic spectral acceleration)) Reduction factor R= 8.0 Considering ductility and overstrength
0.42 g
0.30s 0.06s
Cs = SA/R =0.42g/8=0.053g17
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