Response spectrum analysis of Building frame

- September 17, 2019 at 3:46 am
  
  VinayN
  Subscriber
  
  Hi all. NOOB alert !
  
  I wanted to do a response spectrum analysis of a building frame. I'm comparing results from STAAD.pro and ANSYS.
  
  I have a RCC building. with damping ratio 0.05, seismic acceleration is 0.036 (depending on building type and zone). My eigen values, in modal analysis, don't seem to match up with the results from STAAD.pro and response spectrum analysis says it doesn't support damped analysis.
  
  I put the entire mass of building at corresponding levels as point loads.
  
  Thank You.
  
  What is happening ?
- September 17, 2019 at 9:56 am
  
  peteroznewman
  Subscriber
  
  Hi VinayN,
  
  In a Response Spectrum analysis, the damping is included in the acceleration spectrum data, so the Modal analysis must be undamped or you would be double counting the damping.
  
  The damping is included in the acceleration data when the transient acceleration time history is converted to a Response Spectrum using a Q value in the conversion. A Q value of 10 equals 5% damping.
  
  Regards,
  Peter
- September 17, 2019 at 3:09 pm
  
  VinayN
  Subscriber
  
  Thank you, Mr. Peter.