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Microstran Response Spectrum Analysis to AS 1170.4

   
  Applies To 
   
  Product(s): Microstran
  Version(s): V8i
  Environment:  N/A
  Area:  Analysis
  Original Author: Richard Collins
   

An Excel spreadsheet, shown below, is available to assist in the use of Microstran Response Spectrum Analysis of structures to AS 1170.4. The procedure is described briefly in notes at the top of the spreadsheet. The spreadsheet calculates scale factors that have to be entered in Microstran dialog boxes during the response spectrum analysis. Values shown in the spreadsheet relate to this structure:

Earthquake Example

The spreadsheet is available at Microstran Excel Spreadhsheet Extensions.

MICROSTRAN RESPONSE SPECTRUM ANALYSIS - AS1170.4        
         
PROCEDURE:        
1. Do dynamic analysis without RSA box checked.        
2. File > List/Edit File command, then choose Dynamic Log.        
3. Find fundamental period for direction of interest.        
4. Enter the values shown in red. Do not change anything else.        
5. Do static analysis with empty load case for RSA results.        
6. Repeat dynamic analysis with…        
a. RSA box checked.        
b. Green value entered in Response Spectrum dialog.        
7. Check dynamic log for 90% mass participation.        
8. Analyse > Response Spectrum then:        
In Dynamic Load Case Scale Factors dialog…        
- transfer Reaction value to blue value below        
- transfer magenta value below to Scale Factor.        
9. Create Input/Analysis report and check base shear        
for earthquake case.        
         
Acceleration coefficient, a = 0.10   (Hobart=0.05 to Newcastle=0.11)  
         
Height, hn = 12.0 m    
Eq. 6.2.4(1):        
Fundamental period = 0.26 sec.    
Frequency (1) = 3.83 Hz.    
C(1) = 0.306      
Eq. 6.2.4(2):        
Period for the orthogonal direction = 0.21 sec.    
Frequency (2) = 4.83 Hz.    
C(2) = 0.357      
Minimum earthquake design coeff., C = 0.286      
         
Structure period, T = 0.81   (Fundamental period from dynamic analysis)  
         
Importance factor, I = 1   (1.00 or 1.25)  
Eq. 6.2.3 = 0.144      
Earthquake design coefficient, C = 0.286      
Site factor, S = 0.67   (Rock=0.67 to Soft clay=2.0)  
Structural response factor, Rf = 3.0   (Masonry=1.5 to MRF=8.0)  
Gravity load, Gg = 5766 kN (9.81 x sum mass matrix diagonal - see dynamic log.)  
         
Earthquake base shear force, V:        
V, Eq. 6.2.2 = 368 kN    
V, lower limit = 58 kN    
V, upper limit = 481 kN    
V = 368 kN    
         
Microstran Response Spectrum dialog:        
Scale factor = 0.327      
Microstran Dynamic Load Case Scale Factors dialog:        
Reaction = 165 kN (Value to be scaled according to Cl. 7.4.2.4)  
Percentage of Section 6 horiz. base shear force = 90%   (Irregular=100%, Regular=90%)  
Required base shear = 331 kN    
Scale Factor = 2.004   (RSA values will be factored by this value)  

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