STEEL FRAME DEFLECTION
STEEL FRAME DEFLECTION
(OP)
Hi everybody,
I have two questions.
1. How to apply the lateral force to get the true deflection of the frame?
e.g.
ASSUMING a single storey frame with 7 bays, with tension only bracing in 1st, 3rd & 5th bay)
If I have 400kN lateral force, I get different lateral deflection values if I apply 400kN at
a. 400kn at one END ONLY
b. 200KN EACH AT BOTH ENDS
2. What would be the best location to put the brace in a frame, near the ends or centre? And why? ( assuming no obstruction for bracing).
Thanks
I have two questions.
1. How to apply the lateral force to get the true deflection of the frame?
e.g.
ASSUMING a single storey frame with 7 bays, with tension only bracing in 1st, 3rd & 5th bay)
If I have 400kN lateral force, I get different lateral deflection values if I apply 400kN at
a. 400kn at one END ONLY
b. 200KN EACH AT BOTH ENDS
2. What would be the best location to put the brace in a frame, near the ends or centre? And why? ( assuming no obstruction for bracing).
Thanks






RE: STEEL FRAME DEFLECTION
2) In many cases, the braces are placed in the center of the frame - especially for freezer type warehouses, where the temperature differential won't cause the separated braces to fight each other.
RE: STEEL FRAME DEFLECTION
RE: STEEL FRAME DEFLECTION
As to where to put the bracing - JAE's comments are or course correct but for a different take:- Put the bracing where you expect the erector to commence the erection. They generally will want to start at a corner or end of a building so first bay would be good.
RE: STEEL FRAME DEFLECTION
Frame geometry is as follows:
ht.=8.7m, bay width=11.2m, no. of bays=7, single storey
Tension only brace in 1st,3rd & 5th bay.
Lateral force applied=400Kn at one end or 200kn at each end.
Properties of all frame members are:
Area=6452 mm², I=1.05e+08mm^4, Z=2.95e+06mm^3.
Model this in any software and see the deflection at each end. It is different.
I got the values as 8.6mm & 1.3mm when 400kn applied at one end only.
Def= 4.93mm & 6.67mm when 200kn applied at each end.
Which is correct value of deflection?
Thanks,
RE: STEEL FRAME DEFLECTION
I modeled the frame and obtained the same results as you got. To get the properties the section is either 330x330x5 (in mm) square tube or 350x6 pipe. The walls are very thin and not typically used (as I know), the local buckling should be checked or you can used only an effective sectional area.
The different deflections are caused by the different axial deformations of the strut beams and the diagonal bracings. You raised an interesting one storey frame case, the axial deformation plays a big role like a truss.
RE: STEEL FRAME DEFLECTION
The properties of section is not important. I used the default properties of my software. You can put different properties for columns, beams & brace but the deflection results will still vary.
My question remains the same. How to get the actual deflection of frame? Where should we apply the lateral force to get actual deflection?
Also, position of brace does affect the value of deflection. So what is the best location to minimizereduce lateral deflection?
Thanks,
RE: STEEL FRAME DEFLECTION
Back to your original questions. 1) consider whether you have to use three anchor bays. If the frame is exposed, you will have big temperature stress. One anchor bay should be enough if the foundation is sufficient. 2) apply loads where they initiate. You can change the locations of bracings to adjust the deflections. But the deflection/height ratios are small in the braced frame.
RE: STEEL FRAME DEFLECTION
I must say that I would be suprised too with the difference in deflection you obtained. I believe if you used sections that are actually strong enough for that geometry and loading the cross sectional area would be greater and therefore the axial deformations less.