jetboat
Structural
- Jan 7, 2009
- 19
I am Wondering how others use Risa for doing frequency checks? I compared Risa frequency with hand calc frequency and the two were not comparable. I have tried a few different modeling techniques as listed below.
1. One model I used a sub meshed plate and assigned each node a spring constant calculated from the sub grade modulus. Also, on each of the corner nodes I placed a restraints ineach of the plan directions for stability issues.
2. Second model was same as first model but instead of restraints on each corner node I placed spring constants on all nodes simulating the soil to concrete frictional resistance in the plan directions.
3. The third and fourth models were similar to models one and two but instead of using plates I used solids.
What have others done or what is the best way to obtain realistic frequencies from Risa? Has anyone been able to compare Risa Calculated frequencies with their own?
1. One model I used a sub meshed plate and assigned each node a spring constant calculated from the sub grade modulus. Also, on each of the corner nodes I placed a restraints ineach of the plan directions for stability issues.
2. Second model was same as first model but instead of restraints on each corner node I placed spring constants on all nodes simulating the soil to concrete frictional resistance in the plan directions.
3. The third and fourth models were similar to models one and two but instead of using plates I used solids.
What have others done or what is the best way to obtain realistic frequencies from Risa? Has anyone been able to compare Risa Calculated frequencies with their own?