12-15-2009, 05:40 PM
(12-11-2009, 05:21 AM)RICARDI Wrote: Hi!
I have a doubt!
I´am modeling a group of buildings (three buildings whit diferents heights and shapes , they have a comon basement (it is the parking lot) like a table, when i did the modal analisys and checked the global base shear (on the comon first floor of the three buildings) and then i compare whit the sum of the shear of the colums the sum of the colums are greater than the global base shear. I did a simple model like a table and two towers ( 4 columns and 2 story) and i did the same comparisons and both values are equal bot when a did the same model with two tawers one whit 2 storys and the other with 3 storys the results are different (like the big model).
Can you help me?
P.D. Sorry for the bad English
Hi there!
When you have a structure like you do, with multiple towers with a comon basement, you perform the modal and seismic analysis for every tower individually. So, you "cut out" one tower from the top of the basement and you run the modal and seismic analysis.
Practically you can make "2" different models:
- static model - you analyze the whole structure, without a modal and seismic analysis. And here you design the horizontal elements: beams, plates...(90% of the time).
- dynamic model - you make as many models as needed, and you perform the modal and seismic analysis. Here you design the vertical elements: walls, columns.
The problem that occurs in your case, is in that every tower has its own modal shapes and periods, and i think the program cannot recognize that you have multiple towers, so it doesn't distribute the forces as it should.
I hope I could help!