Response Spectrum Analysis to AS 1170.4
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:
The spreadsheet is available at Free Stuff.
| 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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