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Lateral load in CFS truss

Lateral load in CFS truss

Lateral load in CFS truss

Hi guys!

I have a big problem with lateral load from the trusses in the case below.
If I make the support pinned-pinned on the wall, I get a large lateral force, which the beam, and the wall can't support.

We thought about getting a roller support on the right side(details below) and pinned on the other side so in this way we can get rid off the lateral load, making it a simply supported truss.

So as you can see, where the roller is, the whole structure is supported by the 8mm M8.8 metric screw because we elevated the truss with 15 mm of the wall, and the truss is fixed into a U shaped profile with an oval hole of the dimension 25 mm + 9 mm (25 mm is the maximum horizontal displacement from vertical loads)

We are using C75x1,5 mm for the truss and 2C100x1,5 mm for the walls.

Do you think this is a good idea and can really work like a true roller in reality?

RE: Lateral load in CFS truss

We deal with this issue in light frame wood structures all the time. In summary:

1) They do make off the shelf connectors that allow the kind of "roller" slip that you envision. The consensus seems to be that we don't have much faith in that solution however. One does not want that joint to be a roller when it comes to the out of plane load response of the walls attached to the truss. And it's tough to justify trying to have it both ways.

2) Friction between the truss and the wall plate probably hinders any real "rolling".

3) Away from wall corners and returns, the walls can probably accommodate a fair bit of lateral movement without distress. Where that is not the case, the most practical solution seems to be to:

a) Design the truss as pin-roller and;

b) Make the truss stiff enough with respect to lateral deflection that it won't damage the walls where the walls would be sensitive to the movement.

RE: Lateral load in CFS truss

You don't need to provide an idealized frictionless roller or something, you need to allow for that lateral movement. I think the slotted bolted connection is a reasonable way to allow for that movement. I am curious how well that little bolt is transferring the vertical forces at this joint but that is for you to design.

RE: Lateral load in CFS truss

I think you just design it pin-roller, and detail it pin-pin. Like Koot indicates, except at super stiff corners, the top of the wall will be flexible enough generally to allow for the movement required to realize the pin-roller assumption. And in the stiff areas, Nothing bad ever really seems to happen.

RE: Lateral load in CFS truss

Quote (jayrod12)

And in the stiff areas, Nothing bad ever really seems to happen.

For what it's worth, I was once a designer of metal plate connected wood trusses. jayrod12 is quite right, in my experience, in saying that nothing bad ever really does seem to happen.

RE: Lateral load in CFS truss

I see, thank you all for the feedback.

Below you can see my calculations with vertical + horizontal loads from the pinned-pinned trusses applied to the wall.

As you can see, I also get pretty big horizontal reaction in the right corner and a tearing out vertical force in the bottom of the column on the left. My question is, even if I design the trusses as pinned-roller, I do have to consider these reactions in the corners?

RE: Lateral load in CFS truss

How much lateral deflection do your trusses have if you ignored the stiffness of the supporting structure? (i.e. ran them pinned-roller)

RE: Lateral load in CFS truss


Quote (XR250)

How much lateral deflection do your trusses have if you ignored the stiffness of the supporting structure? (i.e. ran them pinned-roller)

Max. 25 mm. The problem is, it's not uniform, so I get 25mm from one truss and 14 mm from the other and so on...

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