Frequency of Industrial Structure
Frequency of Industrial Structure
(OP)
I am doing an estimate of the weight of an Industrial Structure, with cranes in all spans.
As usual I modeled the tranverse frames as moment frames, and the longitudinal frames as braced frames, with the end of connections hinged.
The dimensions of the building are approximately 540 Ft width, 1000ft lengtht, and 66 ft height to the eave. The Isometric of the building is in attach.
My question is about the influence of the hinges in the period/frequency of the structure response.When I considered everything continuous, including angles of the Truss, I got T=3.29 sec, but if I considered the structural normal. ( rigid in the transverse direction) , braced with hinges in the longitudianl direction and also the diagonals of the trusses hinged, I got T =30 sec. !!
I am using RISA 3D. Obviously do not exist perfect hinges in a truss, the value of the restriction is between fixed and hinged.
Some one can give me an idea?. there is any paper talking about this issue?
I will thanks your comments.
jatfuentes
As usual I modeled the tranverse frames as moment frames, and the longitudinal frames as braced frames, with the end of connections hinged.
The dimensions of the building are approximately 540 Ft width, 1000ft lengtht, and 66 ft height to the eave. The Isometric of the building is in attach.
My question is about the influence of the hinges in the period/frequency of the structure response.When I considered everything continuous, including angles of the Truss, I got T=3.29 sec, but if I considered the structural normal. ( rigid in the transverse direction) , braced with hinges in the longitudianl direction and also the diagonals of the trusses hinged, I got T =30 sec. !!
I am using RISA 3D. Obviously do not exist perfect hinges in a truss, the value of the restriction is between fixed and hinged.
Some one can give me an idea?. there is any paper talking about this issue?
I will thanks your comments.
jatfuentes






RE: Frequency of Industrial Structure
Typically in a linear FEA rather than modelling a hinge with kr=0 we use a small non zero positive value. Unfortunately this can be a crucial tuning parameter aka fudge factor in the model. If you perform an experimenatl modal analysis on a real assembly you can see this, as your frequencies shift with different excitation levels. As you turn the force level up hinges unstick and things start to flap.
So, if you are interested in earthquaake response, you'd better assume that the hinges are indeed free to rotate, whereas in normal use they might be jammed solid.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Frequency of Industrial Structure
RE: Frequency of Industrial Structure
I dont know, because I sent the attach. Any way I send it again.
Really the modeling the bolt connections as hinges is a problem , because you cant use your same static model for a dynamic model.
I dont know if there is any research or PHD tesis for this problem. I have a book written by W. F chen about partially restrained connections, but is not focsed for seismic cases.
RE: Frequency of Industrial Structure
There are times when a localized stiffness issue will a mode with very little mass participation to have a very large period. When this happens, you can look at the mode shape to see the "near instability", so it should be easy to correct.... as long as you have only one or two.
RE: Frequency of Industrial Structure
In your model, I see a hinge at the intersection of X-B. Try making your XB as tension only member( truss member) and make it continuous from one end to other.
Try this and it may solve your problem.
RE: Frequency of Industrial Structure
RE: Frequency of Industrial Structure
I am interested. What is an example?
RE: Frequency of Industrial Structure
I don't have Blevins to hand but I think even with clamped ends the frequency is lower than free free.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Frequency of Industrial Structure
Thanks for your atention. Yes, this is only a part of the . The building is Huge !. But now, the client is interested only in an estimate of weight, yhe most closer possible to the final weight. really I´m working a lot because, i have to buildings more, that allready I finish.
Yes, I will put bracings at end of the building.
LOKSTR,
I will take a look to the model.
You know, to analise concrete structures is very diferent that analise steel structures. Concrete structures are 99% monolitic. Steel structures, depend on if the structures is braced or not, if the connection is flexible or not, etc.
I think, i dont know, but I didnt reading nothing about this issue.
If some body have something talking about this problem, please let me know
Maybe a PHD thesis ???
thanks.
jatfuentes