Static Seismic Loads

• Function

In MIDAS/Gen, the automatic data entry of equivalent static seismic loads according to various standards is applicable for common buildings where each story can be defined and can reasonably act as a rigid diaphragm. The following procedure is observed :

1. Model the structure. The structure must be modeled so that the gravity acts in the direction opposite to the GCS Z-direction.

2. Convert the self-weight of the structure included in the modeling into mass data, if the self-weight is to be considered for the equivalent static seismic load calculation. Use "Converting Type of Model weight to Masses" in Structure Type to assign the directions to be considered for the mass components and enter the value in the "Gravity Acceleration" field.

The procedure of converting the self-weight of the model into mass data by stories to calculate the equivalent static seismic load is as follows :

Calculate the self-weight of the members. Divide and assign the self-weight equally to the connection nodes, which then become the story mass data when the connection nodes are on a story plane (refer to step 4). If the connection nodes fall in between the stories, the nodal masses are considered to exist at the upper story.

3. Use Building > Control Data to enter the position of the ground level in GCS Z-axis coordinate.

Once the ground level is entered, the base shear is calculated at the ground level. The parts below this level are considered as underground floors. All the entered mass data are neglected in the equivalent static seismic load calculation. If the ground level is not defined, the lowest part of the structural model is assumed to be the ground level by default.

4. Use Story to define stories and their floor rigid diaphragm characteristics. Enter the eccentricities to consider the accidental eccentricity moments at each story. Use to auto-generate the data necessary for the stories and the application of seismic loading.

Once the floor diaphragm is defined in Story, the X-, Y-displacement degrees-of-freedom and the rotational degree-of-freedom about the Z-axis between all the nodes on the plane (plane parallel to the GCS X-Y plane) are constrained.

In addition, a part or all of constrained nodes can be separated from the floor rigid diaphragm using Floor Diaphragm Disconnect.

Note
If, at a specific story, Story Diaphragm is released, the Story Force at the corresponding story is considered to be ??  Even if the user specifies Additional Seismic Loads, the program considers the Story Force to be ??  

5. Use Nodal Masses, Floor Diaphragm Masses or Load to Masses to enter the mass components not included in the model.

6. Use Static Seismic Loads to select the desired standards and enter the data for the calculation of equivalent static seismic loads.

The built-in standards for the calculation of equivalent static seismic loads in MIDAS/Gen are as follows:

IBC2000: International Building Code 2000

UBC (1997): UBC 97 standards

UBC (1991): UBC 91 standards

ATC 3-06 (1982): ATC 3-06 Provision

NBC (1995): National Building Code of Canada

Eurocode-8 (1996): Design provisions for earthquake resistance of structures. General rules. Strengthening and repair of buildings.

Eurocode-8 (2003) Elastic: Design provisions for earthquake resistance of structures. General rules. Strengthening and repair of buildings.

IS1893 (2002): Indian Standard

Taiwan (2006): Seismic Design Specifications and Commentary of Buildings

Taiwan (1999): Seismic Design Specifications and Commentary of Buildings

(available upon request)

Japan (Arch, 2000): Japan, Arch. Assoc.- Building structure loading & comm.

Korean (KBC, 2005): Korea Building Code-Structural, KBCS

Korean (Arch, 2000): Buildings loading criteria and commentaries

Korean (Arch, 1992): Regulations related to structural criteria for buildings

China Shanghai (DGJ08-9-2003): Shanghai Code for Seismic Design of Buildings

China (GB50011-2001): Chinese Code for Seismic Design of Buildings

Once the data required for the calculation of seismic loads are defined, auto-calculate seismic loads for each story in connection with the story data generated in Story. Use to verify the auto-calculated seismic loads.

Equivalent static seismic load generation

• Call

From the Main Menu select Load > Static Seismic Loads.

Select Static Loads > Static Seismic Loads in the Menu tab of the Tree Menu.

• Usage

Access Seismic Loads to activate the dialog box defining the seismic loads. Click to display the dialog box shown below.

Add/Modify Seismic Load Design Code dialog box

Load Case Name

Select the load case name to be associated with the seismic load. Click to the right to enter or modify new load cases.

Seismic Load Code

Select the standards to be applied to the seismic load calculation.

IBC2000: International Building Code 2000

UBC (1997): UBC 97 standards

UBC (1991): UBC 91 standards

ATC 3-06 (1982): ATC 3-06 Provision

NBC (1995): National Building Code of Canada

Eurocode-8 (1996): Design provisions for earthquake resistance of structures. General rules. Strengthening and repair of buildings.

Eurocode-8 (2003) Elastic: Design provisions for earthquake resistance of structures. General rules. Strengthening and repair of buildings.

IS1893 (2002): Indian Standard

Taiwan (2006): Seismic Design Specifications and Commentary of Buildings

Taiwan (1999): Seismic Design Specifications and Commentary of Buildings

(available upon request)

Japan (Arch, 2000): Japan, Arch. Assoc.- Building structure loading & comm.

Korean (KBC, 2005): Korea Building Code-Structural, KBCS

Korean (Arch, 2000): Buildings loading criteria and commentaries

Korean (Arch, 1992): Regulations related to structural criteria for buildings

China Shanghai (DGJ08-9-2003): Shanghai Code for Seismic Design of Buildings

China (GB50011-2001): Chinese Code for Seismic Design of Buildings

Description

Enter a short description.

Seismic Load Parameters

Enter the parameters to be applied to the seismic load calculation.

IBC2000 (ASCE7-98)

Seismic Design Categories

Site Class

Mapped Spectral Response Acceleration at Short Periods (Ss)

Mapped Spectral Response Acceleration at 1 Second Periods (S1)

Importance Factor

UBC (1997)

Soil Profile Type

Seismic Zone Factor

Seismic Source Type

Closest Distance to Known Seismic Source: Distance to the verified epicenter

Importance Factor

UBC (1991)

Soil Profile Type

Zone Factor

Importance Factor

ATC3-06 (1982)

Soil Profile Coefficient

Effective Peak Velocity

NBC (1995)

Zonal Velocity Ratio (v): The specified zonal horizontal ground  velocity expressed as a ratio to 1 m/s

Acceleration Zone (Za): Acceleration-related seismic zone

Velocity Zone (Zv): Velocity-related seismic zone

Importance Factor (I)

Foundation Factor (F)

Eurocode-8 (2004)

Ground Type: Soil type (A, B, C, D, E, S1 and S2)

Soil Factor (S): Soil factor (range: S > 0)

Spectrum Parameters

Tb: Lower limit of the period of the constant spectrum acceleration branch

Tc: Upper limit of the period of the constant spectrum acceleration branch

Td: Value defining the beginning of the constant displacement response range of the spectrum

Design ground acceleration (Ag): Design ground acceleration (range: Ag > 0)

Behavior factor (q): Behavior factor (range: q> 0)

Lower bound factor (b): Lower bound factor for the design spectrum (range: b> 0)

Importance Factor (I): Importance factor (range: I > 0)

Eurocode-8 (1996)

Soil Class

Basic Behavior Factor (q0)

Ductility Class (Kd)

Elevation Regularity (Kr)

Failure Mode Factor (Kw)

Ratio of Design ground acceleration to gravity acceleration (alpha)

IS1893 (2002)

Seismic Zone Factor (Z)

Soil Type

Importance Factor(I)

Damping (%)

Damping Multiplying Factor:

Damping Multiplying Factor is automatically calculated by linear interpolation based on the table shown below.

Taiwan (2006): Seismic Design Specifications and Commentary of Buildings

Seismic Zone (Z)

Seismic Zone Related Data

General Zone

Horizontal Spectral Accel.  

Short Period (Ss): Horizontal Spectral Acceleration at short periods

1 Sec Period (S1): Horizontal Spectral Acceleration at 1 second periods

Site Magnify Factor

Soil Type

Short Period (Fa): Site Magnify Factor at short periods

1 Sec Period (Fv): Site Magnify Factor at 1 second periods

Near Fault Zone

Horizontal Spectral Accel.  

Short Period (Ss): Horizontal Spectral Acceleration at short periods

1 Sec Period (S1): Horizontal Spectral Acceleration at 1 second periods

Near Source Factor  

Short Period (Na): Near Source Factor at short periods

1 Sec Period (Nv): Near Source Factor at 1 second periods

Site Magnify Factor

Soil Type

Short Period (Fa): Site Magnify Factor at short periods

1 Sec Period (Fv): Site Magnify Factor at 1 second periods

Taipei Basin  

Sub Zone

Horizontal Spectral Accel.  

Short Period (Ss): Horizontal Spectral Acceleration at short periods

Trans. Period: Transfer period

T0: S1/Ss

Importance Factor(I)

Seismic Magnify Factor

Taiwan (1999)

Seismic Zone (Z)

Soil Type

Importance Factor (I)

Seismic Magnifying Factor

Japan (Arch, 2000)

Seismic Zone Factor (Z)

Soil Period (Tc)

Std. Base Shear Factor (C0)

Seismic Base Shear Distribution Factor (Ai)

Note
Ai is automatically calculated or entered by the user.

Korean (KBC. 2005)

         Design Spectral Response Acceleration

Seismic Zone

Site Class

Sds: Spectral response acceleration at short periods

Sd1: Spectral response acceleration at a period of 1 sec

Seis. Use Group

City Plan Region

Importance(Ie)

Seis. Design Category

Korean (Arch, 2000)

Soil Profile Type

Earthquake Zone

Importance Factor

Korean (Arch, 1992)

Soil Profile Type

Earthquake Zone

Importance Factor

China Shanghai (DGJ08-9-2003)

Seis. Fortification Intensity

Site Class

Structure Type

Damping ratio

Frequent Earthquake

Scarce Earthquake

Masonry Multistory, Framed 1st Story, Interior Frame - Exterior Masonry Structure

China (GB50011-2001)

Near Source Category

Seis. Fortification Intensity

Site Class

Structure Type

Damping Ratio

Frequent Earthquake

Scarce Earthquake

Masonry Multistory, Framed 1st Story, Interior Frame - Exterior Masonry Structure

Structural Parameters

Enter the parameters defining the characteristics of the structure.

IBC2000 (ASCE7-98)

Period (Analysis): Obtained by eigenvalue analysis

Period (Codr): Obtained by the Code method

Response Modification Coefficient (R)

UBC (1997)

Period: Periods of the structure calculated from the equation in the code

Ductility Coefficient (R): Numerical coefficients representative of the inherent overstrength and global ductility capacity of a lateral force resisting system

UBC (1991)

Period (Analysis): Natural periods of the structure from eigenvalue analysis

Period (Code): Natural periods of the structure calculated from the equations in the code

Ductility Coefficient (Rw): Numerical coefficients representative of the inherent overstrength and global ductility capacity of a lateral force resisting system

ATC3-06 (1982)

Period (Analysis): Natural periods of the structure from eigenvalue analysis

Period (Code): Natural periods of the structure calculated from the equations in the code

Response Modification Coeff.

NBC (1995)

Period (Analysis): Natural periods of the structure from eigenvalue analysis

Period (Code): Natural periods of the structure calculated from the equations in the code

Response Modification Factor (R)

: Auto-calculation of periods from the code equations

N: Number of Stories

H: Height of the building

Ds: Length of the wall or braced frame which constitutes the main lateral-force-resisting system in the direction parallel to the applied forces

Note
If the main lateral-force-resisting system does not have a well-defined length then D Shall be used in lieu of Ds
D: Length of  the building in a direction parallel to the applied  forces

Eurocode-8 (2004, 1996)

Fundamental Period

: Auto-calculation of periods from the code equations

H: Height of the building

Ac: Combined effective area of the shear walls in the first story of building

d: lateral displacement if the top of the building due to the gravity loads applied horizontally

IS1893 (2002)

Fundamental Period

: Auto-calculation of periods from the code equations

h: Height of the building (unit: m)

d: Width of the building in a direction parallel to the seismic load at the 1st floor

Response Reduction Factor

Taiwan (2006): Seismic Design Specifications and Commentary of Buildings

Analytical Period: Natural periods of the structure from Eigenvalue analysis

Approximate Period: Natural periods of the structure calculated from the equations in the code

Fundamental Period

Response Modification Factor

Taiwan (1999)

Analytical Period: Natural periods of the structure from Eigenvalue analysis

Approximate Period: Natural periods of the structure calculated from the equations in the code

Response Modification Factor

Japan (Arch, 2000) (available upon request)

Period (T)

Period Calculator

Korean (KBC, 2005) (available upon request)

Analytical Period: Natural periods of the structure from Eigenvalue analysis

Approximate Period: Natural periods of the structure calculated from the equations in the code

 : Auto-calculation of periods from the code equations

Fundamental Period

Response Modification Factor

Korean (Arch, 2000) (available upon request)

Period (Analysis): Natural periods of the structure from eigenvalue analysis

Period (Code): Natural periods of the structure calculated from the equations in the code

: Auto-calculation of periods from the code equations

Response Modification Coeff.

Korean (Arch, 1992) (available upon request)

Period (Analysis): Natural periods of the structure from eigenvalue analysis

Period (Code): Natural periods of the structure calculated from the equations in the code

: Auto-calculation of periods from the code equations

Response Modification Coeff.

China Shanghai (DGJ08-9-2003) (available upon request)

Fundamental Period

 : Auto-calculation of periods from the code equations

H: Height of the building

Bx: Width of building subjected to seismic load in the Global X-axis direction

By: Width of building subjected to seismic load in the Global Y-axis direction

n: Number of Stories

China (GB50011-2001) (available upon request)

Fundamental Period

: Auto-calculation of periods from the code equations

H: Height of the building

Bx: Width of building subjected to seismic load in the Global X-axis direction

By: Width of building subjected to seismic load in the Global Y-axis direction

n: Number of Stories

Seismic Load Direction Factor

Enter the directions and magnitudes of the seismic loads to be applied.

Scale Factor in Global X: Scale factor in GCS X-direction

Scale Factor in Global Y: Scale factor in GCS Y-direction

Eccentricity Direction

Assign the directions to be considered with accidental eccentricities in the structure.

If the 'None' option is selected, accidental eccentricity is not considered.

Torsional Amplification

Accidental Eccentricity: Check whether or not to apply amplification to torsion due to Accidental Eccentricity.

Inherent Eccentricity: Check whether or not to apply amplification to torsion due to the eccentricity between the center of mass and the center of stiffness of the building structure.  

Additional Seismic Loads

Enter additional seismic loads that the auto-calculation does not take into account

Press to enter the stories to apply additional seismic loads and the magnitudes for each direction.

: Display Tables and Graphs in a spreadsheet form for each loading direction and component of the auto-calculated seismic load.

Component: Assign the seismic loading direction for a graphic display

Select Profile: Select the items to be displayed

Story Force

Story Shear

Overturning Moment

: Display a spreadsheet Text Output file showing the seismic load calculation process. Text Editor is automatically executed.

: Apply the auto-calculated equivalent static seismic loads to the model.

Note
Refer to the relevant code for details regarding the equivalent seismic load calculation.