Seismic loading

During an earthquake, the subsoil bearing a structure moves. The structure tries to follow this movement and as a result, the masses in the structure begin to move. Subsequently, these masses subject the structure to inertial forces.

The method which is implemented in SCIA Engineer is based on modal superposition, aka Response Spectrum Method. The user defines the loading by spectrums in the 3 global directions X, Y and Z (in a 3D model).The program computes the modal deformation and modal forces.

Two methods are implemented to consider the missing mass into the seismic analysis.

Depending on the selected modal superposition method, the modal results are combined to obtain the final results.

The results (deformations, internal forces, reactions) are displayed in the standard way. A dedicated service is available for displaying both modal and combined deformations and accelerations.

This section gives general information about seismic loading in SCIA Engineer. Read also the chapter dedicated to the seismic analysis of buildings.

The theoretical background about seismic loading is presented in the following chapters:

• Bases of modal analysis
• Modal superposition (incl. multiple eigenshapes)
• Mass in the seismic analysis
• Signed results
• Mode filtering
• Mathematical formulation & Calculation protocol

Additionally, the following features are detailed separately in the chapter related to seismic analysis of buildings:

• Reduced analysis model IRS (Improved Reduced System)
• Equivalent Lateral Forces (ELF)
• Accidental eccentricity