Skip to content

Seismic Loads

The Seismic Load module works through ASCE 7 Chapters 11 and 12 in two tabs. Seismic Design Criteria establishes the site: the mapped accelerations, the site class, the design spectral accelerations, and the seismic design category. Seismic Building Design describes the building, its levels and weights and its seismic force-resisting systems, and calculates the base shear and its vertical distribution by the equivalent lateral force procedure.

Features in Prose

  • Site parameters looked up from USGS for the project coordinates, or entered by hand
  • Site class, design spectral accelerations SDS and SD1, and the seismic design category per Chapter 11
  • The design response spectrum, drawn for the site
  • Building levels with elevations and seismic weights, and the total seismic weight W
  • The complete Table 12.2-1 library of seismic force-resisting systems, with R, Ω0, Cd, and the system limitations, including height limits, for Seismic Design Categories B through F
  • Approximate period, base shear, the vertical distribution of forces Fx, and the diaphragm forces Fpx for each system
  • A summary and report with every equation and code reference

Editions

This page shows the ASCE 7-22 module, used by IBC 2024 projects, which uses the multi-period design spectrum from the USGS lookup. Projects on ASCE 7-10 or 7-16 show the inputs those editions use. The Design Criteria and Building Design pages give the section and equation numbers for each edition.

Adding the Module

  1. Click the three-dot menu (⋮) next to the structure name in the sidebar
  2. Select Seismic Load

The module opens on the Seismic Design Criteria tab with the USGS lookup switched on and no coordinates yet, Site Class D, and the risk category read from the structure. The Building Design tab starts with two levels and one system.

Typical Workflow

  1. Enter the site latitude and longitude, or the mapped values by hand. See Design Criteria
  2. Choose the site class and read the design parameters and the seismic design category
  3. Enter the building levels with their elevations and seismic weights. See Building Design
  4. Name each seismic force-resisting system and pick it from Table 12.2-1
  5. Read the period, the base shear, and the force distribution for each system
  6. Export the report

PDF Export

  1. Click the Export PDF tab above the summary
  2. Review the report in the viewer
  3. Save the PDF from the viewer toolbar. In a narrow pane the Save button sits in the >> menu at the right end of the toolbar

The report carries both tabs: the design criteria with the spectrum, then each system with its period, base shear, and force distribution. The same pages appear in the project report.

Deleting the Module

  1. Hover the Seismic Load entry under the structure in the sidebar and click its three-dot menu (⋮)
  2. Select Delete Module
  3. Confirm with Delete Seismic Load

Code References

  • ASCE 7 Chapter 11: Seismic design criteria
  • ASCE 7 Chapter 12: Seismic design requirements for building structures
  • Section 12.8: Equivalent lateral force procedure
  • Table 12.2-1: Design coefficients and factors for seismic force-resisting systems
  • Chapter 22: Seismic Ground Motion, Long-Period Transition, and Risk Coefficient Maps in ASCE 7-10 and 7-16; Seismic Ground Motion and Long-Period Transition Maps in ASCE 7-22

Best Practices

  • Use the project's actual coordinates for the lookup, and keep the geotechnical report's site class
  • Enter the seismic weight of each level from the dead load module and the applicable portions of other loads per Section 12.7.2
  • Check the system's height limit for the seismic design category before you rely on its R value
  • Model each direction's system separately when the building uses different systems in the two directions