Seismic Base Shear Calculator

Per IBC 2006 and ASCE 7-05 Specifications
Using Equivalent Lateral Force Procedure for Regular Single-Level Building/Structural Systems

Input Data

Occupancy Category =  [?] IBC 2006, Table 1604.5, page 281
Importance Factor, I = ASCE 7-05 Table 11.5-1, page 116
Soil Site Class = IBC 2006 Table 1613.5.2, page 303
Location Zip Code =  
Spectral Accel., SS = ASCE 7-05 Figures 22-1 to 22-14
Spectral Accel., S1 = ASCE 7-05 Figures 22-2 to 22-14
Long. Trans. Period, TL = sec. ASCE 7 Fig's. 22-15 to 22-20
Structure Height, hn = ft.
Total Seismic Weight, W = kips  ASCE 7-05 Section 12.7.2
Actual Calc. Period, Tc = sec.  from independent analysis
Seismic Resist. System =  

Result Data

Site Coefficients:
Fa = IBC 2006 Table 1613.5.3(1), page 304
Fv = IBC 2006 Table 1613.5.3(2), page 304
 
Maximum Spectral Response Accelerations for Short and 1-Second Periods:
SMS = SMS = Fa*SS,  IBC 2006 Eqn. 16-37, page 303
SM1 = SM1 = Fv*S1,  IBC 2006 Eqn. 16-38, page 303
 
Design Spectral Response Accelerations for Short and 1-Second Periods :
SDS = SDS = 2*SMS/3,  IBC 2006 Eqn. 16-39, page 304
SD1 = SD1 = 2*SM1/3,  IBC 2006 Eqn. 16-40, page 304
 
Seismic Design Category:
Category(for SDS) = IBC 2006 Table 1613.5.6(1), page 306
Category(for SD1) = IBC 2006 Table 1613.5.6(2), page 306
Use Category = Most critical of either category case above controls
 
Fundamental Period:
Period Coefficient, CT = ASCE 7-05 Table 12.8-2, page 129
Period Exponent, x = ASCE 7-05 Table 12.8-2, page 129
Approx. Period, Ta = sec.,  Ta = CT*hn^(x),  ASCE 7-05 Section 12.8.2.1, Eqn. 12.8-7
Upper Limit Coef., Cu = ASCE 7-05 Table 12.8-1, page 129
Period max., T(max) = sec.,  T(max) = Cu*Ta,  ASCE 7-05 Section 12.8.2, page 129
Fundamental Period, T = sec.,  T = Ta <= Cu*Ta,  ASCE 7-05 Section 12.8.2, page 129
   
Ice Load Based on Perimeter of Member:  
Response Mod. Coef., R = ASCE 7-05 Table 12.2-1, pages 120-122
Overstrength Factor, Wo = ASCE 7-05 Table 12.2-1, pages 120-122
Defl. Amplif. Factor, Cd = ASCE 7-05 Table 12.2-1, pages 120-122
CS = CS = SDS/(R/I), ASCE 7-05 Section 12.8.1.1, Eqn. 12.8-2
CS(max) = For T<=TL, CS(max) = SD1/(T*(R/I)), ASCE 7-05 Eqn. 12.8-3
CS(min) = CS(min) = 0.044*SDS*I >= 0.01, ASCE 7-05 Eqn. 12.8-5 (Suppl. 2)
Use: CS = CS(min) <= CS <= CS(max) 
 
Seismic Base Shear:
V = kips, V = CS*W, ASCE 7-05 Section 12.8.1, Eqn. 12.8-1

Seismic Base Shear
(Regular Bldg. Configurations Only)

x
TABLE 1-1
Occupancy Category of Buildings and Other Structures for Flood, Wind, Snow, Earthquake, and Ice Loads
Nature of Occupancy
Occupancy Category
Buildings and structures that represent a low hazard to human life in the event of failure including, but not limited to:
- Agriculture facilities
- Certain temporary facilities
- Minor storage facilities
 I
Buildings and other structures except those listed in Categories I, III and IV II
Buildings and other structures that represent a substantial hazard to human life in the event of failure including, but not limited to:
- Buildings and other structures where more than 300 people congregate in one area
- Buildings and other structures with day-care facilities with capacity greater than 150
- Elementary or secondary school facilities with capacity greater than 250
- Colleges & adult education facilities with a capacity greater than 500
- Health care facilities with a capacity greater than 50 resident patients but not having surgery or emergency treatment facilities
- Jails and detention facilities
Buildings and other structures, not includes in Occupancy Category IV, with potential to cause substantial economic impact and/or mass disruption of day-to-day civilian life in event of failure, including, but not limited to:
- Power generating stations, water treatment facilities, sewage treatment facilities, and telecommunication centers
- Buildings and structures not included in Category IV containing sufficient quantities of toxic, explosive, or other hazardous materials dangerous to the public if released
 III
Buildings and other structures designated as essential facilities including, but not limited to:
- Hospitals and health care facilities having surgery or emergency treatment facilities
- Fire, rescue and police stations and emergency vehicle garages
- Designated earthquake, hurricane or other emergency shelters
- Designated emergency preparedness, communication, and operation centers and other facilities required for emergency response
- Power-generating stations and other public utility facilities required in an emergency
- Ancillary structures required foroperation of Category IV structures during an emergency
- Aviation control towers, air traffic control centers and emergency aircraft hangars
- Water storage facilities and pump structures required to maintain water pressure for fire suppression
- Buildings and other structures having critical national defense functions
- Buildings and structures containing extremelyhazardous materials where quantity of material exceeds a threshhold quantity established by authority having jurisdiction
 IV
(a) Cogeneration power plants that do not supply power on the national grid shall be designated Occupancy Category II.
ASCE 7-05 TABLE 11.5-1
IMPORTANCE FACTORS
IMPORTANCE FACTOR, I, (ICE LOADS)
Occupancy Category I
I or II 1.0
III 1.25
IV 1.5
*See Section 1.5 and Table 1-1.
ASCE 7-05 TABLE 20.3-1
SITE CLASSIFICATION
SITE CLASS Soil Shear Wave Velocity, vs, (ft/s) Standard Penetration Resistance, N Soil Undrained Shear Strength ,su, (psf)
A. Hard Rock vs > 5000 Not Applicable Not Applicable
B. Rock 2500 <= vs <= 5000 Not Applicable Not Applicable
C. Very Dense Soil & Soft Rock 1200 <= vs <= 2500 N > 50 su > 2000
D. Stiff Soil 600 <= vs <= 1200 15 <= N <= 50 1000 <= su <= 2000
E. Soft Clay Soil vs < 600 N < 15 su < 1000
    Any profile with more than 10 feet of soil having the following characteristics:
1. Plasticity Index, PI > 20
2. Moisture Content, w >= 40% and
3. Undrained shear strength, su < 500 psf
F. Soils requiring site response analysis per Section 21.1 See Section 20.3.1
*See Section 1.5 and Table 1-1.
'W' = The effective seismic weight of the structure, including the total dead load and other loads listed below:
  1. In areas used for storage, a minimum of 25% of the reduced floor live load (floor live load in public garages and open parking structures need not be included).
  2. Where an allowance for partition load is included in the floor load design, the actual partition weight or a minimum weight of 10 psf of floor area, whichever is greater.
  3. Total operating weight of permanent equipment.
  4. 20% of flat roof snow load where flat roof snow load > 30 psf.
IBC 2006 TABLE 1613.5.3(1)
VALUES OF SITE COEFFICIENT, Fa, AS A FUNCTION OF SITE CLASS
AND MAPPED SPECTRAL RESPONSE ACCELERATION AT SHORT PERIODS (Ss)(a)
SITE CLASS
MAPPED SPECTRAL RESPONSE ACCELERATION AT SHORT PERIODS
Ss<=0.25g Ss=0.50g Ss=0.75g Ss=1.00g Ss>=1.25g
A 0.8 0.8 0.8 0.8 0.8
B 1.0 1.0 1.0 1.0 1.0
C 1.2 1.2 1.1 1.0 1.0
D 1.6 1.4 1.2 1.1 1.0
E 2.5 1.7 1.2 0.9 0.9
F Note (b) Note (b) Note (b) Note (b) Note (b)
(a) - Use straight line interpolation for intermediate values of mapped spectral acceleration at short period, Ss.
(b) - Site-specific geotechnical investigation and dynamic site response analyses shall be performed to determine appropriate values. See ASCE 7-05 Section 11.4.7.
IBC 2006 TABLE 1613.5.3(2)
VALUES OF SITE COEFFICIENT, Fv, AS A FUNCTION OF SITE CLASS
AND MAPPED SPECTRAL RESPONSE ACCELERATION AT 1 SECOND PERIOD (S1)(a)
SITE CLASS
MAPPED SPECTRAL RESPONSE ACCELERATION AT 1 SECOND PERIOD
S1<=0.1g S1=0.2g S1=0.3g S1=0.4g S1>=0.5g
A 0.8 0.8 0.8 0.8 0.8
B 1.0 1.0 1.0 1.0 1.0
C 1.7 1.6 1.5 1.4 1.3
D 2.4 2.0 1.8 1.6 1.5
E 3.5 3.2 2.8 2.4 2.4
F Note (b) Note (b) Note (b) Note (b) Note (b)
(a) - Use straight line interpolation for intermediate values of mapped spectral acceleration at 1-second period, S1.
(b) - Site-specific geotechnical investigation and dynamic site response analyses shall be performed to determine appropriate values. See ASCE 7-05 Section 11.4.7.
'SMS' is the maximum considered earthquake spectral response accelerations for short period as determined from IBC 2006 Section 1613.5.3.
'SM1' is the maximum considered earthquake spectral response accelerations for 1-second period as determined from IBC 2006 Section 1613.5.3.
'SDS' is the design spectral response acceleration at short periods as determined in IBC 2006 Section 1613.5.4.
'SD1' is the design spectral response acceleration at 1-second period as determined in IBC 2006 Section 1613.5.4.
IBC 2006 TABLE 1613.5.6(1)
SEISMIC DESIGN CATEGORY BASED ON
SHORT-PERIOD RESPONSE ACCELERATIONS
VALUE OF SDS
OCCUPANCY CATEGORY
I or II III IV
SDS < 0.167g A A A
0.167g <= SDS < 0.33g B B C
0.33g <= SDS < 0.50g C C D
0.50g <= SDS D D D
IBC 2006 TABLE 1613.5.6(2) SEISMIC DESIGN CATEGORY BASED ON 1-SECOND PERIOD RESPONSE ACCELERATIONS
(a) - Occupancy Category I, II, and III structures located on sites with mapped maximum considered earthquake spectral response acceleration at 1-second period, S1, equal to or greater than 0.75g, shall be assigned to Seismic Design Category E, and Cccupancy Category IV structures located on such sites shall be assigned to Seismic Design Category F.
Seismic Design Category to be used shall be the the highest (most critical) category as determined from IBC 2006 Table 1613.5.6(1) using 'SDS' and IBC 2006 Table 1613.5.6(2) using 'SD1'.
'CT' is the building period coefficient, and is dependent on the type of seismic-force-resisting system that is used:
CT = 0.028 for moment-resisting frames of steel
CT = 0.016 for moment-resisting frame systems of reinforced concrete
CT = 0.030 for eccentrically braced steel frames
CT = 0.020 for all other building systems
'x' is the building period formula exponent, and is dependent on the type of seismic-force-resisting system that is used:
x = 0.80 for moment-resisting frames of steel
x = 0.90 for moment-resisting frame systems of reinforced concrete
x = 0.75 for eccentrically braced steel frames
x = 0.75 for all other building systems
'Ta' is the approximate fundamental period of the building, in seconds. Ta = CT*hn^(x), ASCE 7-05 Section 12.8.2.1, Eqn. 12.8-7
ASCE 7-05 TABLE 12.8-1 COEFFICIENT FOR UPPER LIMIT ON CALCULATED PERIOD
Design Spectral Response Acceleration
at 1 Second Period, SD1		Coefficient, Cu
>=0.4 1.4
0.3 1.4
0.2 1.5
0.15 1.6
<=0.1 1.7
The Response Modification Coefficient, "R", is determined from ASCE 7-05 Table 12.2-1.
The System Overstrength Factor, "Wo", is determined from ASCE 7-05 Table 12.2-1.
The Deflection Amplification Factor, "Cd", is determined from ASCE 7-05 Table 12.2-1.
'CS' is the seismic response coefficient.
'V' is the total Seismic Base Shear, and it may be minimized by any of the following means:
  1. Using a seismic-force-resisting system with a larger Response Modification Factor, 'R'. The total Seismic Base Shear, 'V', is inversely proportional to the the value of 'R'.
  2. Using a lower site class if possible
  3. Minimizing the weight of the structure.

 

Disclaimer: This calculator is not intended to be used for the design of actual structures, but only for schematic (preliminary) understanding of structural design principals. For the design of an actual structure, a competent professional should be consulted.

‘Calculations courtesy of Alex Tomanovich, PE ’