Steel splice 3

[Mohamed Maher]

Hi all

I have two beams with box section members , we want make splice for it and the suggested splice from architect to insert box in between
With length 400 mm from each side and we will add only some bolts for fixation between the main outside beam boxes and the inserted box .

The gap between the inserted box and the outer beam 8s 1 mm from each side.

My question is the inserted box should be designed based on the same moment on the external beams

Thanks

 

[dik]

I would try to avoid a connection of that type for anything but the smallest loads. I don't know what the effects of that type of flexure on HSS tubes are. If necessary to have a sliding connection in the span, I would be looking at one for one of the supports.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[HTURKAK]

Dear MAHER,

In this case ,I would prefer welded splices .. The following doc is useful to see connection details for the HSS members. (By Steel Tube Institute )

 

[kingnero]

1 mm gap? how is that, relative to the outer HSS size? And is that consistent?
In order to mitigate any tolerance issues, I prefer 2 L sections, so you can snug them up against 2 sides. Might need to grind away the outside corner to fit in the inside radii. Or 4 plates, one side prebolted in the factory, the other side drilled and tapped for field bolting.

As Dik said, those splices aren't worth much (unless designed and executed meticulously). And I don't have much faith in field welding either, again, unless you work with reliable contractors.

 

[dik]

HTURKAK... thanks for the link.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Brad805]

HTURKAK, great reference.

 

[Mohamed Maher]

Thank you all that was very useful..
Thanks HTURKAK

 

[KootK]

There certainly are better & easier moment connections available per HTURKAK's excellent document but, yeah, in reference to your original question:

1) The inner box would have to be designed for the beam moment at that location and, more critically;

2) The connections on both sides of the joint would have to be designed for that same moment.

I've actually seen this done successfully in some AESS applications. Obviously, the challenge is getting a snug yet erectable fitup. I've also seen some recommendations for tube in tube moment connections that suggest that an insertion of as little as 1.5 X Member Depth is sufficient to get the job done.

I agree with the other folks, however, in that pretty much any other type of connection is preferable is you can sell it to your architect.

 

[Mohamed Maher]

@Kootk ,

Did you mean that may be we don't need to much bolts or only some little bolts for only make sure for sufficient minimum election between bolts

And if we make only little bolts how can we justify it by codes

Thsnks

 

[dik]

Do you have a sketch of what you are trying to do?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Mohamed Maher]

Actually we need to add only bolts from top only and depth of embedded box can be 800 mm 400 from each side

We need to depend on bearing for transferring forces not bolts

 

[dik]

Is it a tension member? if not, why so many fasteners?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Mohamed Maher]

Actually this is a continuous beam which has moment in both direction and shear both direction and axial compression

 

[dik]

thanks...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[KootK]

Did you mean that may be we don't need to much bolts or only some little bolts for only make sure for sufficient minimum election between bolts

Yes, that is what I meant. For purely flexural loads, the bolts aren't strictly required. Obviously, and consistent with your thoughts, some nominal, positive, axial connection is still required.

And if we make only little bolts how can we justify it by codes

Not by way of the North American building codes. At least, not as far as I know. This issue of tube in tube moment connection has been discussed in detail here on this forum. And much of what I think I know about these things comes from that discussion. My vague recollection of it:

1) There might be stuff in the telecom codes.

2) It works better with round tube.

3) It works better still with telescoping tube.

Actually this is a continuous beam which has moment in both direction and shear both direction and axial compression

That sounds like a tall order for a rectangular tube. Assuming that gravity moments dominate and that you'd use blind bolts, I might abandon any attempt at a snug fit in the lateral direction and attempt a connection like this, wherein the bolts are structural for both strong and weak axis moment transfer if possible.