Gen Training Series Pushover Analysis as per EC8:2004
MIDAS Information Technology Co., Ltd.
Program Version V7.4.1
Program License Registered, Trial
Revision Date 2008.12.26
Pushover Analysis of steel structure
as per EC8:2004
DL SD NC
Gen Training Series Pushover Analysis as per EC8:2004
MIDAS Information Technology Co., Ltd.2
Pushover analysis is one of the performance-based design
methods, recently attracting practicing structural engineers
engaged in the field of seismic design. The objective of a
performance-based design is achieved after the owner and the
designer collectively select a target performance for the
structure in question. The engineer carries out the conventional
design and subsequently performs a pushover (elasto-plastic)
analysis to evaluate if the selected performance objective has
been met.
In midas Gen V741, pushover analysis as per EN1998:2004
is newly added, and analysis performance and usability are
significantly improved. This tutorial explains the method and
procedure for pushover analysis of 3-dimensional Steel
structures as per EN1998:2004. For this reason, the procedure
for modeling and analysis were not explained in detail. For the
users who are not familiar with the basic functions for modeling
and analysis, it is recommended to review “Application 1”
tutorial before following this tutorial.
The pushover analysis procedure is as follows:
Modeling & Design
- Details of Building
- Perform analysis
- Perform steel code checking
Pushover Analysis
- Pushover Global Control
- Pushover Load Cases
- Define Hinge Properties
- Assign Hinge Properties
- Perform Pushover Analysis
- Pushover Curve
- Pushover Hinge Status Results
- Safety Verification Table
Optimal Design ProcedureOverview
Gen Training Series Pushover Analysis as per EC8:2004
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Details of the example structure
Figure 3. Elevation
Figure 1. Three-dimensional structural model
6,000
10,000
2,500 2,500 2,500 2,500
A
B
1 2 3
G2
G2
G2G2
C2 C2
C2C2 C1
C1
G1
G1
G1
BR
BR
3,000
3,000
3,000
9,000
BR1
BR1
BR2
Figure 2. Structural plan
Section Name Section ID Section DB Section Size
C1 1 UNI HEA240
C2 2 UNI HEA300
G1 21 UNI HEA280
G2 22 UNI IPE240
Brace1 31 UNI HEA160
Brace2 32 UNI HEA120
Gen Training Series Pushover Analysis as per EC8:2004
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Materials
•Eurocode3:2005
Gravity loads
•Dead load: 4.9kN/m2
•Live load : 2.5kN/m2
Static Wind Loads
•Applied code: Eurocode1:2005
•Terrain Category : II
• Fundamental Basic Wind Velocity (Vb,o): 26m/s
Static Seismic Loads
•Applied code: Eurocode8:2004
•Ground Type: B
•Design Ground Acceleration: 0.08g
•Behavior Factor (q): 1.5
•Lower Bound Factor (b): 0.2
•Importance Factor (I) : 1
Applied Loads
Load Name Details
Static
Load
Cases
1 DL Dead Load
2 LL Live Load
3 WXWind Load
(X-direction in the global coordinates)
4 XYWind Load
(Y-direction in the global coordinates)
5 EXSeismic Load
(X-direction in the global coordinates)
6 EYSeismic Load
(Y-direction in the global coordinates)
Unit Load Cases
•Column: S235
•Beam: S235
•Brace: S235
Applied Design Code
Gen Training Series Pushover Analysis as per EC8:2004
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Step 1. Open the model file and perform analysis
1. Open “Steel pushover analysis.mgb”
2. Select Works tab in the Tree Menu.
3. Check the entered section data and boundary condition in
Properties and Boundaries.
4. In the tree menu, select Static Loads>Static Load Case 1
and then right click Floor Loads:3.
5. In the context Menu, select Display and then check the
applied loads.
6. By this way, check the applied seismic loads and wind
loads.
7. Click icon to perform analysis.
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Pushover analysis is carried out in the post-processing mode
after completing elastic analysis.
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Gen Training Series Pushover Analysis as per EC8:2004
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Step 2: Check Steel Design Code
1. Design > Steel Design Parameter > Design Code
2. Specify the code as „Eurocode3:05‟.
3. Check [OK] button.
Design Code specified in the Steel Design Code dialog is
applied to calculate the capacity of members in pushover
analysis.
Gen Training Series Pushover Analysis as per EC8:2004
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Step 3: Steel Code Checking
1. Design > Steel Code Checking
Rotation capacity at the end of steel beams
or columns depends on the class of cross
section. In order for the program to
automatically determine the class of cross
section for the pushover analysis, select
„Auto‟. For the automatic classification
Steel Code Checking should be performed
first.
Gen Training Series Pushover Analysis as per EC8:2004
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Step 4-1: Pushover Global Control
1. Design > Pushover analysis > Pushover Global Control
2. Select DL in the combo box and click [Add] button.
3. Select LL in the combo box and enter the Scale Factor as 0.25.
4. Click [Add] button.
5. Click [OK] button.
2,3
2,4
5
In this step, we will define the initial load cases, which
will be applied prior to pushover analysis such as dead
load and live load.
Gen Training Series Pushover Analysis as per EC8:2004
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Step 4-2: Pushover Global Control„Reference Design code (Eurocode 8:2004)‟ option is displayed when
the design code (in the main menu, Design > Concrete Design
Parameter or Steel Design Parameter > Design code) is specified as
Eurocode and Design code in preferences (in the main menu, Tools >
Preferences) is specified as Eurocode.
Scale Factor for Ultimate Rotation
1) Wall: In calculating the total chord rotation capacity at ultimate , θu, for wall , the value is divided
by 1.6 as per EN1998-3:2004 A.3.1.1.
2) Cold-worked brittle steel: If cold-worked brittle steel is used the total chord rotation capacity is
divided by 1.6 as per EN1998-3:2004 A.3.1.1.
3) Without Detailing for earthquake resistance: In members without detailing for earthquake
resistance the total chord rotation capacity is multiplied by 0.85 as per EN1998-3:2004 .
4) Smooth longitudinal bars: in members with smooth (plain) longitudinal bars without lapping in
the vicinity of the end region where yielding is expected, the total chord rotation capacity may be
multiplied by 0.575 as per EN1998-3:2004.
Gen Training Series Pushover Analysis as per EC8:2004
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Secondary Seismic Elements
In order to calculate the total chord rotation capacity at ultimate, θu, the factor „γel’ is used. Since γel is differently applied for primary and
secondary seismic elements (γel = 1.5 for primary seismic elements, γel = 1.0 for secondary seismic elements as per EN1998-3:2004
A.3.1.1), the user can define Secondary Seismic Elements group. If Secondary Seismic Elements are not defined, all the elements are
considered as Primary Seismic Elements.
In this tutorial, Secondary Seismic Elements are not defined since pushover hinge properties are assigned to primary elements only.
Step 4-3: Pushover Global Control
Gen Training Series Pushover Analysis as per EC8:2004
1. Design > Pushover analysis > Pushover Load Cases
2. Click [Add] button.
3. Enter the pushover load case name as „Accel_X‟.
4. Enter the Increment Steps as „30‟.
5. Check on „Use Initial Load‟ option.
6. Check on „Consider P-Delta Effect‟ option.
7. Select „Displacement Control‟ in the Increment Method.
8. Select „Mater Node‟ option.
9. Click the entry field and click the node no. 20 with the
mouse in the model view.
10. Enter the Max. Displacement as 0.12m.
11. Check off „Limit inter-Story Deformation Angle‟
option.
12. Specify the Load Pattern as „Uniform Acceleration‟.
13. Specify the Direction as „DX‟ in the combo box and click
[Add] button.
14. Click [OK] button.
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Step 5-1: Pushover Load Case
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Gen Training Series Pushover Analysis as per EC8:2004
1. Design > Pushover analysis > Pushover Load Cases
2. Click [Add] button.
3. Enter the pushover load case name as „EY_Y‟.
4. Enter the Increment Steps as „30‟.
5. Check on „Use Initial Load‟ option.
6. Check on „Consider P-Delta Effect‟ option.
7. Select „Displacement Control‟ in the Increment Method.
8. Select „Mater Node‟ option.
9. Click the entry field and click the node no. 20 with the
mouse in the model view.
10. Enter the Max. Displacement as 0.3m.
11. Check off „Limit inter-Story Deformation Angle‟ option.
12. Specify the Load Pattern as „Static Load Cases‟.
13. Specify the Load Case as „EY‟ in the combo box and
click [Add] button.
14. Click [OK] button.
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Step 5-2: Pushover Load Case
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Step 6-1: Define Pushover Hinge Properties for beams 2
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In order to check or modify the hinge properties, click [Properties…]
button of the desired component.
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1. Design > Pushover analysis > Define Pushover Hinge Properties
2. Click [Add] button.
3. Enter the pushover hinge properties name as „Beam‟.
4. Select the Material Type as „Steel / SRC(Filled)‟
5. Check on „Fz‟ & „Mz‟ components.
6. Click [Properties…] button for My component.
7. Select the Class of cross section as „Auto‟.
8. Click [Apply] button.
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Gen Training Series Pushover Analysis as per EC8:2004
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Step 6-2: Define Pushover Hinge Properties for Columns
1. Enter the pushover hinge properties name as „Column‟.
2. Select the Material Type as „Steel / SRC(Filled)‟
3. Select „P-M-M in Status Determination‟ option for Interaction Type.
4. Check on „Fy‟, „Fz‟ & „My‟ components.
5. Click [Yield Surface Properties…] button.
6. Click [Y-Axis…] button for My component.
7. Select the Class of cross section as „Auto‟.
8. Click [OK] button.
9. Click [z-Axis…] button for My component.
10. Select the Class of cross section as „Auto‟.
11. Click [OK] button.
12. Click [OK] button.
13. Click [Apply] button.
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Coupled axial force-biaxial moment behavior is reflected by
calculating the flexural yield strength of a hinge considering the
effect of axial force.
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Step 6-3: Define Pushover Hinge Properties for braces
1. Enter the pushover hinge properties name as „Brace‟.
2. Select the Element Type as „Truss‟.
3. Select the Material Type as „Steel / SRC(Filled)‟
4. Check on „Fx‟ component.
5. Click [Properties…] button for Fx component.
6. Select the Class of cross section as „Auto‟.
7. Click [OK] button.
8. Click [OK] button.
9. Click [Close] button.
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Gen Training Series Pushover Analysis as per EC8:2004
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Pushover Hinge Properties
Shear
HingeEurocode3:2005, equation (6.18)
*θy= MyL/6EI
Where, My: Yield moment, L: Length of a member, E: Elasticity of Modulus, I: moment of inertia
Yield strength of Steel structures
Flexural
Hinge
Class Class 1 Class 2
DL 1.0θy 0.25 θy
SD 6.0 θy 2.0 θy
NC 8.0 θy 3.0 θy
Yield rotation of Steel structures
Gen Training Series Pushover Analysis as per EC8:2004
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Step 7-1: Assign Pushover Hinge Properties for columns
1. Select column members (Material ID 1:Column) from the Tree Menu.
2. Design > Pushover analysis > Assign Pushover Hinge Properties
3. Select Hinge Properties Type as „Column‟ in the combo box.
4. Click [Apply] button.
5. Click [Close] button.
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4 5
Right-click
Gen Training Series Pushover Analysis as per EC8:2004
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Step 7-2: Assign Pushover Hinge Properties for Beams
1. Select beam members (Material ID 2:Girder) from the Tree Menu.
2. Drag and drop the „Beam’ hinge property from the Tree Menu to the
Model Window .
Right-click
1
2
Pushover hinge properties can be simply assigned to the
selected elements by Drag & Drop.
Gen Training Series Pushover Analysis as per EC8:2004
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Step 7-3: Assign Pushover Hinge Properties for braces
1. Select brace members from the Tree Menu.
2. Drag and drop the „Brace‟ hinge property from the Tree Menu to the
Model Window .
Right-click1
2
Pushover hinge properties can be simply assigned to the
selected elements by Drag & Drop.
Gen Training Series Pushover Analysis as per EC8:2004
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Step 8: Check assigned hinge properties
1. Right-click „B1_Column‟ from the Tree Menu.
2. Select „Properties‟ from the context menu.
3. Check the calculated yield strength and yield strain.
4. Click [Detail] button to check the calculated values in detail.
1Right-click
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Before assigning hinge properties
Before assigning hinge properties (while defining hinge
properties), Yield Strength and Yield Strain are displayed
as „1‟. After assigning hinge properties, calculated values
for each element are displayed.
By clicking [Detail] button, the user can check the
detailed equation and values.
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Gen Training Series Pushover Analysis as per EC8:2004
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Step 9: Perform pushover analysis
1. Click „Task Pane‟.
2. Click „▼‟ icon and select „Analysis‟.
3. Click „Perform Pushover Analysis’.
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Task Pane displays work procedure for
advanced analysis functions and
description on input items so as to enable
the user to work more easily.
midas program provides 4 types of
advanced analysis features - Pushover
Analysis, Nonlinear Time History
Analysis, Time History Analysis and
Material Nonlinear Analysis.
In addition, Task Pane data can be
saved in the html format in the User
Folder, so that the user can directly write
or add the required input items for
analysis.
Gen Training Series Pushover Analysis as per EC8:2004
For the detailed formula of the Target Displacement, refer to „ANNEX B DETERMINATION OF THE
TARGET DISPLACEMENT FOR NONLINEAR STATIC (PUSHOVER) ANALYSIS, EN 1998-1:2004‟. The
target displacement, which is obtained from the above, corresponds to the seismic demand of the Limit State of
Significant Damage (SD). Target displacement of the Limit State of Near Collapse (NC) is taken equal to that
of SD multiplied by 1.5. Target displacement of the Limit State of Damage Limitation (DL) is taken equal to
that of SD divided by 2.5.
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Step 10-1: Pushover Curve
1. Click „Pushover Curve‟ in the Task Pane.
2. Select the Pushover Load Case as „Accel_X‟.
3. Select „For Target Displacement
(EC8/Masonry)‟.
4. Select the Spectrum Type as „Horizontal Design
Spectrum‟.
5. Enter the Design Ground Acc.(Ag) as „0.5‟.
6. Enter the Behavior Factor (b) as „1.5‟.
7. Click [Draw] button.
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Gen Training Series Pushover Analysis as per EC8:2004
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For the detailed formula of the Target Displacement, refer to „ANNEX B DETERMINATION OF THE
TARGET DISPLACEMENT FOR NONLINEAR STATIC (PUSHOVER) ANALYSIS, EN 1998-1:2004‟. The
target displacement, which is obtained from the above, corresponds to the seismic demand of the Limit State of
Significant Damage (SD). Target displacement of the Limit State of Near Collapse (NC) is taken equal to that
of SD multiplied by 1.5. Target displacement of the Limit State of Damage Limitation (DL) is taken equal to
that of SD divided by 2.5.
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Step 10-2: Pushover Curve
1. Select the Pushover Load Case as „EY_Y‟.
2. Select „For Target Displacement
(EC8/Masonry)‟.
3. Select the Spectrum Type as „Horizontal Design
Spectrum‟.
4. Enter the Design Ground Acc.(Ag) as „0.5‟.
5. Enter the Behavior Factor (b) as „1.5‟.
6. Click [Draw] button.
7. Click [Close] button.
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Step 11-1: Hinge Status Results
1. Click „Hinge Status Results‟ in the Task Pane.
2. Select the Pushover Load Cases Name as
„Accel_X‟.
3. Select „Status of Yielding (EC8:2004)‟.
4. Select the Components as „Ry‟.
5. Check on „Legend‟ and „Deform‟.
6. Specify the desired step in the combo box.
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The user can also check hinge status results for
each step by clicking on the step box and scroll
or clicking on the pushover graph which is
displayed in the black background.
Clicking and scrolling
Clicking on the graph
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Gen Training Series Pushover Analysis as per EC8:2004
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Step 11-2: Hinge Status Results
1. Select the Pushover Load Cases Name as
„EY_Y‟.
2. Select „Status of Yielding (EC8:2004)‟.
3. Select the Components as „Ry‟.
4. Check on „Legend‟ and „Deform‟.
5. Specify the desire step in the combo box.
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Step 12-1: Safety Verification Table
1. Click „Safety Verification Table‟ in the Task Pane.
2. Select „Show All Elements’.
3. Click [OK] button.
4. Select Pushover Load Case as „Accel_x‟.
5. Select „Significant Damage (SD)‟.
6. Check on „My‟ and „Fz‟.
7. Click [OK] button.
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Safety Verification Table displays the comparison results between the demand and
capacities of the elements as per EN1998-3:2004 Table 4.3. Safety verification shall be
conducted for both ductile and brittle elements respectively. For ductile elements,
verification will be conducted in terms of deformation using mean values of properties
divided by CF. For brittle elements, verification shall be conducted in terms of strength
using mean values of properties divided by CF and by partial factor.
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Gen Training Series Pushover Analysis as per EC8:2004
MIDAS Information Technology Co., Ltd.27 MIDAS Information Technology Co., Ltd.27
Step 12-2: Safety Verification Table
1. Right-click on the table and select „Set Safety
Verification‟ in the Context menu.
2. Select Pushover Load Case as „EY_Y‟.
3. Select „Significant Damage (SD)‟.
4. Check on „My‟ and „Fz‟.
5. Click [OK] button.
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Safety Verification Table displays the comparison results between the demand and
capacities of the elements as per EN1998-3:2004 Table 4.3. Safety verification shall be
conducted for both ductile and brittle elements respectively. For ductile elements,
verification will be conducted in terms of deformation using mean values of properties
divided by CF. For brittle elements, verification shall be conducted in terms of strength
using mean values of properties divided by CF and by partial factor.
2
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*For ductile elements, mean values of properties divided by CF are used. For brittle members, mean values of properties
divided by CF and by partial factor.
*θy= MyL/6EI
Where, My: Yield moment, L: Length of a member, E: Elasticity of Modulus, I: moment of inertia
Capacity of Steel structures for assessment in the Safety Verification Table (Eurocode8-3:2004, Annex A.3.1)
Plastic rotation
capacity
Class Class 1 Class 2
DL 1.0θy 0.25 θy
SD 6.0 θy 2.0 θy
NC 8.0 θy 3.0 θy
Shear capacity - Eurocode3:2005, equation (6.18)
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