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Multi Hazard Building Design
Earthquake Loads
Consulting Engineers Partnership Ltd
Grenville W Phillips IIBSc, BEng, MASc, MURP, CEng, MIStructE, MIHT, MAPM, MCSCE, MBAPE
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Design Spectral Response
Acceleration SDS = 5% damped design spectral
response acceleration at short periods =2/3 SMS
SMS = Maximum considered earthquake
spectral response accelerations for shortperiods = Fa.Ss
Fa = Site Coefficient Ss = Mapped spectral accelerations for
short periods.
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Site Classification
Note: Top soil layer to be continuous 30 m (100 ft)
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Site Coefficient
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Seismic Use Group II
Those that have a substantial public hazard due to occupancy or use including:
1. Covered structures whose primary occupancy is public assembly with acapacity greater than 300 persons
2. Educational structures through the 12th grade with a capacity greater than250 persons
3. Day care centers with a capacity greater than 150 persons
4. Medical facilities with greater than 50 resident incapacitated patients nototherwise designated a Seismic Use Group III structure
5. Jails and detention facilities
6. All structures with a capacity greater than 5,000 persons
7. Power generating stations and other public utility facilities not included inSeismic Use Group III and required for continued operation
8. Water treatment facilities required for primary treatment and disinfection forpotable water
9. Waste water treatment facilities required for primary treatment.
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Seismic Use Group III
Essential facilities required for post-earthquake recovery and those
containing substantial quantities of hazardous substances including:1. Fire, rescue, and police stations
2. Hospitals
3. Designated medical facilities having emergency treatment facilities
4. Designated emergency preparedness centers
5. Designated emergency operation centers
6. Designated emergency shelters
7. Power generating stations or other utilities required as emergency back-up facilities for Seismic Use Group III facilities
8. Emergency vehicle garages and emergency aircraft hangars9. Designated communication centers
10. Aviation control towers and air traffic control centers
11. Structures containing sufficient quantities of toxic or explosivesubstances deemed to be hazardous to the public
12. Water treatment facilities required to maintain water pressure for firesuppression.
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1. Seismic Design Category A
Minimum Lateral Force at level x (Fx)
Fx = 1%.wx ; w = effective seismic weight
Connections between separation joints Fp = 5%.weight of smaller portion
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2.2 Seismic Use Group I
V = Seismic base shear
W = effective seismic weight
R = Response modification factor
SDS = Design elastic response acceleration at short periods.
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2.3 Seismic Use Group I
Minimum Lateral Force at level x (Fx)
Design Storey Drift = 1% Storey Height
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VERTICAL FORCE
DISTRIBUTION
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3.1 Equivalent Lateral Force
Procedure
V = seismic base shear
Cs = seismic response coefficient
R = Response modification factor
SDS = Design elastic response acceleration at short periods.
I = Occupancy Importance Factor
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Seismic Use Group I
Occupancy Importance FactorsThose not assigned to Seismic Use Groups
III or II
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The Four Main Types
Bearing Walls?
Shear Walls?
Braced Frame?
Moment Frame?
25% Moment frame
+ shear walls or
braced frame?
Bearing wall system
Building frame system
Moment resisting
frame system
Dual system
Yes
Yes
YesNo
No
No
No
Yes
Yes
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3.2 Equivalent Lateral Force
Procedure
T = the fundamental period of the structure (in seconds) = 0.1N
TL = Long-period transition period (in seconds)
N = Number of storeys above ground level.
Cs shall not be taken less than 0.01.
For regular structures 5 stories or less
with max period, T, of 0.5 sec, Cs, can becalculated using values of 1.5 and 0.6,
respectively, for the mapped maximum
considered earthquake spectral response
acceleration parametersSS
and S1.
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3.3 Equivalent Lateral Force
Procedure
Cvx = vertical distribution factor,
V = total design lateral force or shear at the base of the structure,
wi and wx = the portion of the total gravity load of the structure,W, located or assigned to Level i orx,
hi and hx = the height from the base to Level i orx, and
k= an exponent related to the effective fundamental period ofthe structure as follows: T =2.5, k = 2
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3.4 Equivalent Lateral Force
Procedure
Mx= Overturning moments at Level
x,Fi = the portion of the seismic base shear, V, induced at
Level i, and
hi and hx = the height from the base to Level i orx.
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3.5 Equivalent Lateral Force
Procedure
x= deflections of Level
x,Cd= the deflection amplification factor,
xe = the deflections determined by an elastic analysis, and
I = the occupancy importance factor
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3.6 Equivalent Lateral Force
Procedure Allowable Storey Drift (inches)
Seismic Use Group
Building I II III
Buildings other than masonry shear
wall, 4 storeys or less
0.025 hx 0.02 hx 0.015 hx
Masonry cantilever shear wallbuildings
0.01 hx 0.010 hx 0.010 hx
Other masonry shear wall buildings 0.007 hx 0.007 hx 0.007 hx
Masonry wall frame 0.013 hx 0.013 hx 0.010 hx
All other buildings 0.020 hx 0.015 hx 0.010 hx
hx = storey height below level x
DISCONTINUOUS SOIL LAYER
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DISCONTINUOUS SOIL LAYER
Shear Wave Velocity
DISCONTINUOUS SOIL LAYER
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DISCONTINUOUS SOIL LAYER
Standard Penetration ResistanceNi = the Standard Penetration Resistance determined in
accordance with ASTM D 1586, as directly measured in thefield without corrections, and shall not be taken greater than
100 blows/ft. Where refusal is met for a rock layer,Ni shall be
taken as 100 blows/ft.
DISCONTINUOUS SOIL LAYER
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DISCONTINUOUS SOIL LAYER
Undrained Shear Strength sui = the undrained shear strength in psf
(kPa), determined in accordance withASTM D 2166 or D 2850, and shall not be
taken greater than 5,000 psf (250 kPa)