Modelling machine foundation on top roof concrete slab 1

[Refaatfaraj]

Dear colleagues
I am designing a machine foundation for the rotary machine (HVAC outdoor unit) . The foundation will be executed on the top roof slab. The top roof slab is a concrete ribbed slab with stiff beams. So, there is no embedment impedance
I have assumed modulus of subgrade for the machine foundation (Kz = 50000 KN/m3 , Kx = 5000 KN/m3 and Ky = 5000 KN/m3 ). Since mesh size = 0.50 m then (Kv = (50000*0.50*0.5 ) = 12500 KN/m while as (Kh = 12500*0.10 = 1250 KN/m).
However, I assume the damping ratio for the machine foundation (5% ) is in the vertical direction while I considered the damping ratio less in the horizontal direction (2%) because the foundation will be contracted on a concrete roof slab.
But I am unsure about the material damping value ( as in the attached capture00).
I selected the empirical method to calculate the dynamic loading.
The file .sfa and calculation report are attached for reference.
I am a beginner with this software (STAAD Foundation Advanced ) if someone can help to answer the following inquiries:
- What is damping ratio value shall be used for material ( please take a look to capture 00)?
- Resonance check, what is the correct value of resonance limit for machine and foundation frequencies?
- Why does the frequency of modes (9and 10 ) equal to (Zero) and still the mass participation for (X&Y) direct less than (90%) ? (capture 01)
- What is the meaning of Machine Frequency is within 20.00 % of Foundation Frequency? how I can overcome this issue? since I have noted some values of foundation frequency higher and lower the machine frequency (capture 02).
- How I do cancel the pier above the foundation? since the machine will fix directly on the foundation.
- Are the values of the modulus of subgrade reaction for the foundation reasonable? (Kz =5000 KN/m3 ) .
Any help will be highly appreciated

 

[Aswathi_A]

1.What is damping ratio value shall be used for material
As per 351.3R-19 code, a material damping ratio of 5% is used by practioners in general.
2. Resonance check, what is the correct value of resonance limit for machine and foundation frequencies?
The acting frequencies of the machine should not be within (+-)20% of the resonance frequency.
3. Why does the frequency of modes (9and 10 ) equal to (Zero) and still the mass participation for (X&Y) direct less than (90%) ?
Seems like an issue with the version of SFA you are using. Try using the latest version of SFA where you can get mass participation facotr of 100% of modes 9 and 10. The latest version is 9.7.2.99
4. What is the meaning of Machine Frequency is within 20.00 % of Foundation Frequency? how I can overcome this issue? since I have noted some values of foundation frequency higher and lower the machine frequency (capture 02).
Since you have specified in the input that the resonance limit is 20%, when the program finds that that if the machine frequency and foundation frequency falls within 20%, this warning has been reported. You may want to change the foundation sizes.