Solving for reactional forces in a Tower
Solving for reactional forces in a Tower
(OP)
I have Tower Assembly, it has four columns and cross Bracings. As the columns of the Tower are fixed at the bottom, I was wondering if the assembly can be considered as a Statically indeterminate structure. If so, being a Mechanical Engineer I am clueless about how to solve for the reactions forces and moments at the bottom and resolving the force.
can someone please suggest how to solve this ?
Please find the attachment
http://files.engineering.com/getfile.aspx?folder=2...
can someone please suggest how to solve this ?
Please find the attachment
http://files.engineering.com/getfile.aspx?folder=2...






RE: Solving for reactional forces in a Tower
RE: Solving for reactional forces in a Tower
RE: Solving for reactional forces in a Tower
RE: Solving for reactional forces in a Tower
RE: Solving for reactional forces in a Tower
RE: Solving for reactional forces in a Tower
Here is the link: http://files.engineering.com/getfile.aspx?folder=2...
That is my exact situations while viewing the tower from front.
RE: Solving for reactional forces in a Tower
RE: Solving for reactional forces in a Tower
RE: Solving for reactional forces in a Tower
RE: Solving for reactional forces in a Tower
RE: Solving for reactional forces in a Tower
RE: Solving for reactional forces in a Tower
(1) 1st Diagonal Brace only
(2) 2nd Diagonal Brace only
Then I'd simply take the average of the two forces in the diagonals. In practice I'd resort to a simple FE model with bar/beam elements as appropriate, and examine the deflected shape/check reactions and axial forces are reasonable.
Good luck!
RE: Solving for reactional forces in a Tower
Thank you
RE: Solving for reactional forces in a Tower
RE: Solving for reactional forces in a Tower
And if you're coding the equations can't you just make a proper stiffness matrix and have it do the FEA analysis for you?
RE: Solving for reactional forces in a Tower
RE: Solving for reactional forces in a Tower
As ukbridge indicated, it may also be prudent to check the bracing as compression bracing as well, one way or the other the simple solution is to pretend like one of the braces doesn't exist, and that there is zero moment transfer at any of the connections. We operate with these assumptions all the time.
RE: Solving for reactional forces in a Tower
for the load shown, member 1 is in bending (SS beam), members 2 and 3 in compression, member 4 has zero acting.
curiously if you have 4 and 5 (ie both diagonals) then 1 could be a beam-column, and members 4 and 5 would be reacting load, and there'd be equal and opposite horizontal reactions at the ground.
if there is a lateral load applied, then the member 4 would react this, and the load in members 2 and 3 would change. If a lateral load applied with members 4 and 5 then you could assume that the load is reacted either ...
a) equally by both members 4 and 5, or
b) only by the tension loaded diagonal, or
c) only by the compression loaded diagonal.
another day in paradise, or is paradise one day closer ?
RE: Solving for reactional forces in a Tower
As I said, there are a few different ways people would analyze it. My way is not the only way, nor is it necessarily the easiest. But it does work and I'm comfortable with it. Perhaps my sketch doesn't fully give my whole intent. I was thinking of the bracing as tension only. Therefore the member 1 would be in bending and compression. The bracing only sees tension (and self weight bending) and the columns only compression.
RE: Solving for reactional forces in a Tower
(missed your very large Fh !?)
another day in paradise, or is paradise one day closer ?
RE: Solving for reactional forces in a Tower
1) Is the column a true "fixed" connection to the top "beam"? Or has it been designed as a simple connection permitting rotation?
2) Is everything going to node out, or will there be additional local moments exerted due to joint eccentricities?
3) How are you going to deal with the design of the connections (which can often be the critical case) if everything's welded together?
4) How many different load patterns are there going to be - if theres a lot it sounds like you're going to have to make a very complicated spreadsheet if you're implementing some kind of analysis which deals with statically indeterminate trusses like http://www.sut.ac.th/engineering/Civil/CourseOnlin...
5) Will the provision of an extra brace outweigh the additional fabrication cost, for what may be a frame using modest standardised hot rolled sections.
If you absolutely insist on analysing it to the extent you want to, download a free frame analysis package like 2D frame and do it for a test-run. Ideally it should be a portable program so whoever else has to use it doesnt have to install the program also! Examine the output/datafile and with a bit of tooling you can use Excel and a few concenate functions to get excel to generate a handy script with little/no knowledge of programming.
I think the above idea is much better than programming your own spreadsheet; it will be less prone to errors and will be far more flexible than a spreadsheet could ever be for this type of thing. I don't think I've used a spreadsheet that doesn't have an error in it somewhere, and I don't think this project will be any different.
I think very often as structural engineers we're expected to produce perfectly working, validated spreadsheets; in reality we're not software engineers and don't have all day to make test cases and see if theres any errors in it somewhere.
RE: Solving for reactional forces in a Tower