Function
- Define load cases for pushover analysis.
Call
From the nain nenu, select [Poshover] tab > [Load Case] group > [Load Case]
Input
Pushover Load Cases dialog
Name
Enter the load case name pertaining to Pushover analysis.
Description
Enter the load case name pertaining to Pushover analysis.
General Control
Increment Steps (nstep) : Number of steps to reach the estimated collapse load. The number of steps must be an integer and enter at least 20.
Consider P-Delta Effect : Consider the P-Delta effect simultaneously.
P-Delta effect is very important in pushover analysis. Lateral displacement caused by the lateral load can be magnified by the gravitational load and this effect can reduce the lateral stiffness of the structure. Especially when plastic hinges occur at the lower part of the columns, which are under large axial forces, the reduced lateral stiffness can cause the collapse of the structure.
The stiffness rapidly decreases after reaching peak strength in case of FEMA and Eurocode type hinge, while geometric stiffness is neglected after reaching ultimate strength, i.e. Collapse Prevention (CP) and Near Collapse (NC), respectively.
Initial Load
Pushover analysis is divided into load control and displacement control.
Load Control : A method of defining the expected collapse load (Qud) of a structure and performing an analysis by increasing the load by an equivalent series.
Displacement Control : A method by which the user pre-set the target displacement that may occur on the structure and increase the displacement until the target displacement is achieved on the structure.
When PMM interaction is considered, the user needs to apply the initial load<></> In the case of static analysis (ST) and construction stage analysis (CS), cumulative output of reaction force and displacement is impossible.
Increment Method
Pushover analysis is divided into load control and displacement control.
Load Control : method of defining the expected collapse load (Qud) of a structure and performing an analysis by increasing the load by an equivalent series.
Displacement Control : A method by which the user pre-set the target displacement that may occur on the structure and increase the displacement until the target displacement is achieved on the structure.
Stepping Control Option [when Load Control is selected]
Specify the control data for the load increment.
Auto-Stepping Control : The applied load (Qud) is divided by the automatically calculated load parameters. The first step is loaded up to 90% of the elastic limit of the structure. Further steps are automatically divided by the ratio of
Elastic limit means the estimated load under which the first yield occurs.
Equal Step (1/nstep) : The applied load (Qud) is equally divided by the number of nstep.
Incremental Control Function : The applied load (Qud) is divided by the user-defined function.
Analysis Stopping Condition [when Load Control is selected]
Specify the condition of termination of Pushover analysis.
Current Stiffness Ratio (Cs) : If the Current Stiffness Ratio (Cs) is entered and the ratio of the stiffness at the current an incremental step to the initial stiffness reaches the specified value, the analysis is terminated.
In addition to the above conditions for termination of analysis, analysis is also terminated if the maximum number of increments is reached, or negative values are encountered in the stiffness matrix.
Control Option [when Displacement Control is selected]
Specify the Target Displacement to be applied to pushover analysis
Global : Target displacement is specified with respect to the node where the maximum translational displacement occurs.
Max. Translational Displacement : Specify the max. target translational displacement.
For any structure with an irregular plan the node and direction of maximum displacement can be changed at each increment.
Master Node : Target displacement is specified relative to the master node.
Node : Master Node number
Direction : Select one of the three translational directions for the target displacement in the GCS.
Max. Displacement : Max. target displacement
Load Case(Qud) / Load Pattern
Define the type of load pattern (ratio of magnitude) to be applied to pushover analysis
Load Type
In a pushover analysis by displacement control, relative proportions are of importance for the distribution pattern rather than the magnitudes of the loads.
Static Load Cases : Use the load pattern of static load cases that have been defined.
The combination of load cases multiplied by the corresponding scale factors is used as the load pattern.
Uniform Acceleration : The load is distributed relative to the inertia forces developed in the structure, which has been subject to a uniform acceleration. If the acceleration is uniform, the load pattern is determined proportionally to the mass at each story level.
Mode Shape : The pushover load pattern retains a mode shape and as such, eigenvalue analysis is a prerequisite. The user can select the orders of natural modes that are applied to determining the pushover load pattern.
For the Static Load Cases: All the static load cases are activated. For the Uniform Acceleration: Load distribution directions (DX, DY, DZ) are activated. For the Mode Shape: The user directly enters the mode. For this option, eigenvalue analysis must precede pushover analysis.
Click the "Add" button to add the entered load type to the list at the bottom. Click the "Modify" button to modify the specified load type or the "Delete" button to delete.