Response Spectrum
The Response Spectrum analysis tool is part of the seismic module add-in and is used to determine the design forces on a structural due to seismic loading. This part of the seismic module allows building to be analysed using a Response Spectrum analysis. The seismic module also includes an analysis of building structures using the Lateral Force method. Since the Lateral Force method is based on equivalent static forces, it does not depend upon a mode shape analysis, so it is used through MasterFrame directly rather than through the dynamic analysis. The Response Spectrum analysis uses a code defined elastic response spectrum to model the effective peak ground accelerations.
The Response Spectrum analysis can be carried out in accordance with Eurocode 8, the International Building Code IBC 2012, the Uniform Building Code UBC 1997, or alternatively for a user defined response spectrum. In each case the response spectra relate to horizontal ground movements only; no vertical ground accelerations are included. The method employed in the software is suitable for use where vertical ground accelerations are less than 2.5 m/sĀ². Vertical acceleration is not likely to exceed this value where the horizontal accelerations are less that 2.7 m/sĀ². The IStructE guide "Manual for the seismic design of steel and concrete buildings to Eurocode 8" notes that in most cases, vertical accelerations may be considered to be adequately accounted for in the partial factors on gravity loads. However, vertical accelerations to seismic events must be covered in the following cases:
- Horizontal or nearly horizontal members with spans of 20m or greater
- Horizontal or nearly horizontal cantilever components of span 5m or more
- Prestressed components of any length or orientation
- Transfer beams supporting columns
- Base isolated structures
The software is not suitable for use with ground conditions not covered by those given in Eurocode EC8. It is also not suitable for use with structures which require analysis by either a analysis by 'push-over' non-linear methods, or requiring a full non-linear time-history analysis.
On first entering the Response Spectrum Analysis tab, the initial screen layout is as show below.
.png)
To add a seismic Response Spectrum Load Case, click on the .png)
icon. Multiple seismic load cases can be created, to allow for the analysis with different parameters. Each of the seismic load cases can then be added to the Masterframe analysis. Each load case is named automatically..