Calculation by Phases - Case Study

 

In this case study, the Calculation by Phases function is used for running a seismic analysis considering mass eccentricity
The objective is to run the seismic analysis of a structure considering no eccentricity/+X +Y eccentricity for dynamic modal mass using Advance Design.
Displacements and efforts will be determined for a concrete building subjected to gravitational and lateral loads considering two cases of modal mass distribution: 

• Phase 1: modal mass with no eccentricity
• Phase 2: modal mass with +Y +X mass eccentricity

Structure configuration

Load cases 2-EX, 3-EY and 5-EX, 6-EY have the identical definition. A seismic loads family must be created for each modal analysis to be studied. In this example, two modal analysis set ups will be studied, therefore two seismic families were created. Load cases 2-EX, 3-EY will provide results for Case 1 when no mass eccentricity is defined. Load cases 5-EX and 6-EY will provide results for Case 2 when mass eccentricity is defined.

The analysis model is created by clicking the Analysis button in the Project Browser; in the Calculation sequence window only Verify, Mesh and Evaluate are checked:

After creating the analysis model, the Calculation by Phases button is enabled on the Analysis tab.

In the Calculation Sequence window only Load cases are listed. After each Phase is calculated, all Combinations that can be computed will be automatically identified and solved. Two phases will be added by using the Add Button. The following loads will be included in each phase:

Loads distribution by phases

Load cases 1-D, 4-L are required for computing dynamic mass in each phase. If not added by the user in a phase, they will be automatically added during Calculation for dynamic mass calculation, and results will be available only for seismic cases and Combinations related to those. Therefore, it is recommended that static load cases be added in the first Phase.

Check the Enable calculation by phases and Pause calculation after every phase, to be able to make changes between phases. 

In the Properties window of the Modal analysis, the set up for Phase 1, mass eccentricity disabled, must be made.

After defining Calculation by Phases, because the Analysis model is created, only FEM analysis will be performed:

During calculation of Phase 1, in Console are printed the computed load cases. After completion, only the computed cases and related combinations are available in the Results tab.
Level modal mass and rigidity centers reports can be generated, and lateral loads per level can be visualized:

For Phase 2, dynamic mass eccentricity must be set:

Phase 2 - Eccentricity enabled

The FEM analysis is performed for the second time, only for load case included in Phase 2, 5-EX_+Y ecc, 6-EY_+X_ecc.

Results for Phase 2 become available.

Phase 2 Level lateral forces on Y direction

Related Topics

 

• Defining Calculation by Phases
• Calculation Sequences
• Verify the Descriptive Model 
• Meshing
• FEM Analysis