Inclined Brace Design for Horizontal Load 5

[elfstein123]

Hi everyone. I am working on a steel member design problem and wanted to clarify my thought process for calculating the member forces. The member is a brace and there is a horizontal load P on it. The brace is pinned to the floor and is connected to another member via gusset plate. The load transfer through the gusset will be P.
I originally thought that I would resolve it based on the angle of the member and get the axial and shear force on the member as shown in Option 1 on the image but that means that the member has significant moment (since we have shear and the member length) and that threw me off. I can't imagine this bending but of course buckling is possible and is checked under the axial load. Is this correct? Will we actually have moment in the member?
The second thing that popped up was to resolve it differently as shown in Option 2. We have a higher axial load then but in this case what happens to the vertical component? Does the gusset take it only not the brace? Will this case have any moment? I'd really appreciate any feedback that would help me understand this. Thank you.

 

[ProgrammingPE]

What does the entire frame look like? Normally, the brace is designed with pinned ends so it only ever sees axial loads.

The horizontal load, P, results in an axial load for the brace of P/cos(theta). This creates a vertical component of P*tan(theta) that must be resolved. It usually gets transferred down through the column (assuming you have one).

Structural Central

http://www.structuralcentral.com

http://www.youtube.com/channel/UCOj2mXXf3ZbZtgxTc6BtkGg

 

[KootK]

The second thing that popped up was to resolve it differently as shown in Option 2.

You want the second model but with your vertical component as P x tan(theta).

We have a higher axial load then but in this case what happens to the vertical component?

It depends on what your structure surrounding the frame is but, most commonly:

a) the vertical at the low end goes into the foundation.

b) the vertical at the high end gets dragged down into a column below that joint and then into the foundation.

Does the gusset take it only not the brace? Will this case have any moment?

No and no.

Check out this thread for some additional information that you may find useful:Link.

 

[elfstein123]

Thank you both. About the connecting member point both of you raised, the brace is connected to a gusset which is connected to a curved beam which is supported on hangars that connect to other structures. There is no vertical support at the brace location, just the brace. That was why I assumed the vertical component would go through the gusset into the curved beam. Is this a point of concern, that we have no other vertical support at this location? The brace is there to provide support against the horizontal movement from the horizontal force.

 

[BAretired]

Use a horizontal roller support at the left and a pinned support at the right.

The way you show it, the applied force goes into the pinned support at the left and no force goes to the brace.

BA

 

[KootK]

The vertical load has to go somewhere but it can certainly be carried by the curved beam en route to columns etc. For me, if there's a concern, it's for the vertical stiffness of the curved beam where the brace hits it. The brace is going to try to kick the beam upwards or downwards at that location depending on the direction of that horizontal force. How much will depend, in large measure on the stiffness of that curved beam.

 

[KootK]

If I understand the situation correctly, I see the free body diagram on the curved beam as shown below. The horizontal forces at the joint cancel out but the vertical force does not. Hence the beam tries to kick upwards.

 

[BAretired]

BA[/color]]Hi everyone. I am working on a steel member design problem and wanted to clarify my thought process for calculating the member forces. The member is a brace and there is a horizontal load P on it. The brace is pinned to the floor and is connected to another member via gusset plate. The load transfer through the gusset will be P.
Unfortunately, that is not possible if P is horizontal and the brace is sloping, unless you change the boundary conditions.

I originally thought that I would resolve it based on the angle of the member and get the axial and shear force on the member as shown in Option 1 on the image but that means that the member has significant moment (since we have shear and the member length) and that threw me off.
I remember your previous post. You either deleted it, or someone else did. But, in any case, as I recall, your free body diagram did not satisfy statics. Specifically, the member was not in equilibrium, i.e. the sum of the moments was not zero.

I can't imagine this bending but of course buckling is possible (yes, it is) and is checked under the axial load. (I don't know what that means) Is this correct? Is what correct? Will we actually have moment in the member? Not if both ends are pinned.


The second thing that popped up was to resolve it differently as shown in Option 2. Option 2 is no better than Option 1. The left support is pinned, which means that any force applied as shown will be resisted by the left support. It will not reach the member, so the member will be unstressed (no axial and no moment). We have a higher axial load then but in this case what happens to the vertical component? It goes into the support. Does the gusset take it only not the brace? No, of course not. Will this case have any moment? No!!! I'd really appreciate any feedback that would help me understand this. Thank you.

If the gusset is to feel only a horizontal force, there are only two ways that could be accomplished: 1) place the brace horizontally and 2) Use a sloping brace with a horizontal roller at the left support which takes the vertical component from the brace. (see below)

BA

 

[JoshPlumSE]

I haven't looked at this in any real detail. But, BAretired's sketch looks correct.

I did a lot of "tech support" back in the day on people who had trouble resolving Joint Loads into member forces and making them balance. For a simple model like this, my approach would be:
1) Solve for horizontal reactions (Sum of horizontal forces = zero)
2) Solve for vertical reaction (Sum of moments about a point = zero)
3) That means the other vertical reaction will be the opposite (i.e. sum of vertical forces = 0)
4) Do a vector sum of the various applied loads / reactions and you will be able to convince yourself that it's only an axial load and does not result in any shear.

 

[elfstein123]

Hi everyone, thanks so much for your help! I understand this now. Thank you for sharing your tips and links, much appreciated.