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