Pushover Load Case



Enter, modify or delete load cases and analysis conditions for pushover analysis. 



From the Main Menu select Pushover > Load Cases > Pushover Load Case. 


Click the to create new load cases. Click the to confirm or modify and the to delete the data entry. ■ If Load Control is selected If Load Control is selected, pushover analysis is carried out to reach the estimated collapse load (Qud) through the load increments. Load Case Name Enter the load case name pertaining to Pushover analysis. Description State a brief description related to the pushover load case. General Control Incremental Steps (nstep) : Number of steps to reach the estimated collapse load Note The incremental steps must be entered as a positive integer value (nstep≥1), and minimum 20 steps are recommended. (Default = 20) Consider PDelta Effect : Check on to consider PDelta geometric nonlinear effects. Note 1 PDelta 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.
Note 2 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 Use Initial Load : Accumulate the reaction/story shear/displacement due to the initial load to the pushover analysis result.
Reaction / Story Shear by Initial Load : Accumulate the reaction/story shear due to the initial load
Displacement by Initial Load : Accumulate the displacement due to the initial load
Note When PM interaction is considered, the user needs to apply the initial load. Stepping Control Option Specify the control data for the load increment. AutoStepping 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 . Note 1 Elastic limit means the estimated load under which the first yield occurs. Note 2 Analysis method and example for the AutoStepping Control option Example Equal Step (1/n step) : The applied load (Qud) is equally divided by the number of nstep. Incremental Control Function : The applied load (Qud) is divided by the userdefined function. Refer to Design>Pushover Analysis>Pushover Increment Functions to see how to define userdefined function. Analysis Stopping Condition 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. For example, if the user specifies the Current Stiffness Ratio as 5%, analysis will be terminated when the ratio of the current stiffness to the initial stiffness becomes 0.05. Note 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.
Limit InterStory Deformation Angle : If the Limit InterStory Deformation Angle is entered and the maximum InterStory Deformation Angle reaches the specified value, the analysis is terminated. (Default=1/10) Load Case (Qud) Define the type of load pattern (ratio of magnitude) to be applied to pushover analysis Load Type Static Load Case : Use the load pattern of static load cases that have been defined. Note The combination of load cases multiplied by the corresponding scale factors is used as the load pattern. Uniform Acceleration : he 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. Normalized Mode Shape* Mass: The Load pattern for the pushover analysis is obtained by the normalized mode shape x mass. Example:
Load Case/Direction/Mode: Specify the load cases/directions/mode related to the specified load type. Note 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.
Note 2 If the following temperature loads are entered in the Load Pattern input box, pushover analysis cannot be performed. 1. Beam Section Temperature 2. Temperature Gradient 3. System Temperature 4. Nodal Temperature 5. Element Temperature
■ If Displacement Control is selected If Displacement Control is selected, pushover analysis is carried out to reach the target displacement through the incremental displacements.
Load Case Name Enter the load case name pertaining to Pushover analysis. Description State a brief description related to the pushover load case. General Control Specify the general control data for nonlinear analysis. Incremental Steps (nstep) : Number of steps to reach the prescribed displacement Note The incremental steps must be entered as a positive integer value (nstep≥1), and minimum 20 steps are recommended. (Default = 20) Consider PDelta Effect : Check on to consider PDelta geometric nonlinear effects. Note 1 PDelta 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.
Note 2 The stiffness rapidly decreases after reaching peak strength in case of FEMA type hinge, while geometric stiffness is neglected after reaching ultimate strength, i.e. Collapse Prevention (CP) and Near Collapse (NC), respectively. Initial Load Accumulate the reaction/story shear/displacement due to the initial load to the pushover analysis result. Use Initial Load Reaction / Story Shear by Initial Load : Accumulate the reaction/story shear due to the initial load Displacement by Initial Load : Accumulate the displacement due to the initial load Note When PM interaction is considered, the user needs to apply the initial load
Control Option Specify the Target Displacement to be applied to pushover analysis Global Control Target displacement is specified with respect to the node where the maximum translational displacement occurs.
Maximum Translational Displacement: Specify the max. target translational displacement.
Note For any structure with an irregular plan the node and direction of maximum displacement can be changed at each increment.
Master Node Control Target displacement is specified relative to the master node.
Master Node: Master Node number
Master Direction: Select one of the three translational directions for the target displacement in the GCS.
Maximum Displacement: Max. target displacement Analysis Stopping Condition Specify the condition of termination of Pushover analysis. Limit InterStory Deformation Angle : If the Limit InterStory Deformation Angle is entered and the maximum InterStory Deformation Angle reaches the specified value, the analysis is terminated. (Default=1/10) Load Pattern Define the type of load pattern (ratio of magnitude) to be applied to pushover analysis Load : 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 Case : Use the load pattern of static load cases that have been defined. Note The combination of load cases multiplied by the corresponding scale factors is used as the load pattern. Uniform Acceleration : he 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. Load Case/Direction/Mode : Specify the load cases/directions/mode related to the specified load pattern Note 1 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.
Note 2 If the following temperature loads are entered in the Load Pattern input box, pushover analysis cannot be performed. 1. Beam Section Temperature 2. Temperature Gradient 3. System Temperature 4. Nodal Temperature 5. Element Temperature 
