NEHRP Revised

8/10/2019 NEHRP Revised

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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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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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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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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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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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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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Shear Wave Velocity



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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.



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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)

Documents

NEHRP Revised