leobertolo
Civil/Environmental
- May 9, 2013
- 1
[highlight #A40000]Hello to everyone, i´m new in the forum so i hope i can find it helpful for all matter.
First of all sorry if i make any grammatical mistake, that would be because english is not my mother tongue.
Now going straight to the point, i´m having some trouble modeling a steel structure for oilseed industry of about 24 feet wide 17 feet long and 30 feet tall. It has 3 levels which two of them are accesible. At the top of it (30 feet) a 2637 lbs seed Screener hangs from four steel cables and moves elliptically at a frecuency of 4Hz. All this information is given by the screener manufacturer.
Therefore, i believe the load cases acting at that level are those two: a vertical static load due to self weight and an horizontal dynamic load due to equipment operating.
I modeled the dynamic load based on a steady state function starting at zero frecuency and increasing by reason of (2*pi*f)^2 until it reaches 4 Hz.
Everything goes right up to this point, but when i run the model and analyze the outputs, i find that displacements and element forces for steady state case are reasonable, but in the modal case find absurds values for almost all the modes found.
I find it hard to understand how to relate the steady state and modal cases and why they show such different behaviours.
I would appreciate some advice, comments, links or anything that might be helpful.
Thank you all and i look forward to see your posts.[/highlight]
First of all sorry if i make any grammatical mistake, that would be because english is not my mother tongue.
Now going straight to the point, i´m having some trouble modeling a steel structure for oilseed industry of about 24 feet wide 17 feet long and 30 feet tall. It has 3 levels which two of them are accesible. At the top of it (30 feet) a 2637 lbs seed Screener hangs from four steel cables and moves elliptically at a frecuency of 4Hz. All this information is given by the screener manufacturer.
Therefore, i believe the load cases acting at that level are those two: a vertical static load due to self weight and an horizontal dynamic load due to equipment operating.
I modeled the dynamic load based on a steady state function starting at zero frecuency and increasing by reason of (2*pi*f)^2 until it reaches 4 Hz.
Everything goes right up to this point, but when i run the model and analyze the outputs, i find that displacements and element forces for steady state case are reasonable, but in the modal case find absurds values for almost all the modes found.
I find it hard to understand how to relate the steady state and modal cases and why they show such different behaviours.
I would appreciate some advice, comments, links or anything that might be helpful.
Thank you all and i look forward to see your posts.[/highlight]