TR.32.10.1 Response Spectrum Analysis
Various methods for performing response spectrum analysis have been implemented in STAAD.Pro. They include a generic method that is described in most text books, as well as code based methods like those required by the IBC, Eurocode 8, IS 1893, etc. These are described in the following sections.
| Country | Code | Title |
|---|---|---|
| Canada | NRC 2005 | National Building Code(NRC/CNRC) of Canada |
| NRC 2010 | National Building Code(NRC/CNRC) of Canada | |
| China | GB 50011-2010 | Code for seismic design of buildings GB50011-2010 (2016 Edition) |
| India | IS:1893 (Part 1) 2002 | Criteria for Earthquake Resistant Design of Structures - Part 1: General Provisions and Buildings and Part 4: Industrial structures including Stack-like structures |
| IS:1893 (Part 1) 2016 | Criteria for Earthquake Resistant Design of Structures - Part 1: General Provisions | |
| IS:1893 (Part 4) 2015 | Criteria for Earthquake Resistant Design of Structures Part 4 Industrial Structures Including Stack-Like Structures | |
| Europe | ENV 1994-1:1996 (withdrawn) | Eurocode 8: Design of structures for earthquake resistance – Part 1: General rules, seismic actions and rules for buildings (published 1996) |
| EN 1998-1:2004 | Eurocode 8: Design of structures for earthquake resistance – Part 1: General rules, seismic actions and rules for buildings (published 2004) | |
| Russia | SNiP II-7-81 | Строительство в сейсмических районах (Construction in Seismic Regions) |
| SP 14.13330.2011 | Строительство в сейсмических районах (Construction in Seismic Regions) | |
| US | IBC 2006 | International Building Code, 2006 edition |
| IBC 2012 | International Building Code, 2012 edition | |
| IBC 2015 | International Building Code, 2015 edition | |
| IBC 2018 | International Building Code, 2018 edition |
Torsion Effects
A number of provided design codes include an option for including torsion effects by specifying parameters DEC, to account for the difference between the centre of mass and the centre of rigidity, and ECC for accounting for accidental eccentricity. To use either or both of the factors, requires that the model be defined with Floor Diaphragms. See TR.28.2 Floor Diaphragm. Note that this feature is not supported with the SET Z UP setting.
Missing Mass
Each response spectrum definition allows for the mass that has not been captured in the model extraction to be accounted for using a parameter MISS as a static effect. The spectral acceleration for this missing mass mode can then be specified otherwise taken to be that at 33 Hz.
It is important to note that when response spectra are defined in multiple load cases, if this option is specified in any case, then it is applied to all other cases until the analysis command (including those specified before). If there are load cases defined after the analysis command (which should include the CHANGE command) that have a response spectrum defined, then if the missing mass option is required here, then one of these load cases should include the parameter.Individual Modal Responses
The option to generate load cases of each mode using the IMR parameter is provided in a number of codes. This essentially creates additional primary load cases, one for each of the modes, which have the forces that apply to that mode. This means that it is currently not possible to define a model which has load combinations as these need to be defined after all primary load cases.
A current limitation is that the IMR option should be specified in the last response spectrum load case before the analysis command. At this time the output file will report the IMR details for the first set only, although results for all sets will be available in the post processing workflow.
If it is required to include combinations, then they should be defined as primary load cases and use the REPEAT LOAD command, see TR.32.11 Repeat Load Specification.
Mass Model
- load specified in the first dynamic load case entered, otherwise
- if the first dynamic load case does include any load data, then all reference load cases defined as LOADTYPE MASS will be used, otherwise
- then all reference load cases defined as LOADTYPE GRAVITY will be used, otherwise
- then all load cases defined as LOADTYPE DEAD and LIVE. At least one load case must be defined as DEAD
Refer to G.17.3.2 Mass Modeling for additional details.