Seismic loadcases
On completion of the Seismic Wizard process, seismic loadcases are automatically created and applied in the two building directions, Dir1 and Dir2. Seismic torsion loadcases are also created.
Equivalent Lateral Force (ELF) Loadcases
For structures not requiring application of accidental seismic torsion (eg ASCE7 SDC A)
The following lateral seismic loadcases are created:
- Seismic Dir1 - loadcase type: Seismic
- Seismic Dir2 - loadcase type: Seismic
For all other structures:
The following lateral seismic
loadcases are created:
- Seismic Dir1 - loadcase type: Seismic
- Seismic Dir2 - loadcase type: Seismic
The following seismic torsion
loadcase is also created:
- Seismic Torsion - loadcase type: Seismic
Note:
+ and - factors are applied in the combinations to achieve the possible permutations - +Dir, -Dir, +torsion and -torsion.
Viewing the Seismic Forces
After analysis, the magnitudes and distributions of the seismic forces can be viewed directly in the Results View via the “Seismic” button on the Results ribbon after selecting the required a seismic loadcase.
Note that, for seismic torsion
loadcases created by the ELF method, a system of lateral, radial “push-pull”
forces are applied to the structure to produce the overall torsion.
The Seismic Design report includes a table giving the total level loads Fi and eccentricity values Ecc used to calculate these forces.
Response Spectrum Analysis (RSA) Loadcases
The following lateral seismic loadcases are created:
- Seismic Dir1 - loadcase type: Seismic RSA
- Seismic Dir2 - loadcase type: Seismic RSA
The following seismic seismic torsion loadcase
is also created:
- Seismic Torsion - loadcase type: Seismic
Note: In Tekla Structural Designer the seismic torsion loading and analysis is static, even for the RSA method;
only the lateral RSA analysis is 'dynamic' i.e. a modal analysis + RSA. This is a
common method of seismic analysis i.e. dynamic lateral analysis + static
torsion.
Note:
Enveloping is used in the combinations to achieve the possible permutations - +Dir, -Dir, +torsion and -torsion.
Viewing the Seismic Forces
After analysis, the magnitudes and distributions of the seismic forces can be viewed directly in the Results View via the “Seismic” button on the Results ribbon after selecting the required a seismic loadcase.
Note that, for seismic torsion loadcases created by the RSA method, the application
of these forces depends on the diaphragm options that have been applied.
- For a rigid diaphragm single point torsion loads are applied.
- For semi-rigid diaphragms or for levels with no diaphragms, radial “push-pull”
forces are applied to the structure to produce the overall torsion.
The Seismic Design report includes a table giving the total level loads Fi and eccentricity values Ecc used to calculate these forces.