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Section 5 
5-305
 
algebraic summation of higher modes. ASCE & CQC are more 
sophisticated and realistic methods and are recommended. 
The specifier EURO is mandatory to denote that the applied 
loading is as per the guidelines of Eurocode 8. 
 
The response spectrum loading can be based on either ELASTIC 
or DESIGN response spectra. 
 
Within the scope of Eurocode 8 the earthquake motion at a given 
point of the surface is generally represented by an elastic ground 
acceleration response spectrum termed as “Elastic Response 
Spectrum”. STAAD generates the Elastic Response Spectra using 
the guidelines of section 4.2.2 and Table 4.1 of Eurocode 8. 
 
The capacity of structural systems to resist seismic actions in the 
nonlinear range generally permits their design for forces smaller 
than those corresponding to a linear elastic response. To avoid 
explicit nonlinear structural analysis in design, the energy 
dissipation capacity of the structure through mainly ductile 
behavior of its elements and/or other mechanisms, is taken into 
account by performing a linear analysis based on a response 
spectrum which is a reduced form of the corresponding elastic 
response spectrum. This reduction is accomplished by  introducing 
the behavior factor Q and the reduced response spectrum is termed 
as “Design Response Spectrum”. STAAD generates the Elastic 
Response Spectra using the guidelines of section 4.2.4 and Table 
4.2 of Eurocode 8. 
 
So, if the structure is supposed to resist seismic actions in the 
nonlinear range the Design Response Spectra is to be used.  
  
X Y Z  f1, f2, f3 are the factors for the input spectrum to be 
applied in X, Y, & Z directions.  Any one or all directions can be 
input.  Directions not provided will default to zero. 
 
ACC indicates that the Acceleration spectra will be entered. 
Eurocode 8 does not provide displacement response spectra.