Load transfer in steel box beam

[ozziz]

I have a 3 ft deep steel box beam slotted into a steel tubular column. How is the load from the beam being transfer to the column? Is the load being carried by the side plates of the box beam or the bottom flange to the pipe column?

Some recommended a half round pipe at the slot to reduce the concentration stress. This is only true if the beam is bottom flange bearing onto the column. But it would not be necessary if the side plates are transferring the shear loads.

So what is the actual behaviour?

 

[kslee1000]

You may want to provide a sketch to make people understand the beam-column connection to generate more responses.

 

[BAretired]

ozziz,

Yes, a sketch might help.

What is the width of the box beam? What is the size of the tubular column? What is the size of the slot? What is the reaction to be transferred? Is it a hinged or a moment connection?

The load transfer from beam to column is completely dependent on your connection detail.

If you connect the side plates to the wall of the column, the beam reaction will tend to be transferred through the sidewalls. If, in addition, the bottom flange bears on the HSS wall, a small portion of the load may be transferred by bearing.

If you bear the beam on the wall of the column and do not connect the sidewalls, you will have a concentrated load acting under each sidewall of the beam, but the bottom flange will try to spread the load over the width of the flange.

Your connection detail seems a bit unusual. Have you considered options other than slotting the column?


Best regards,

BA

 

[ozziz]

It is a trestle in the water. The box beam is 1.5 ft wide and the depth is 3 ft. The width is 1.5 ft wide to allow 2 end to end concrete planks to sit on top. The pile is about 3 ft in diameter. Instead of the box beam sitting directly on top of the pile head, the pile head is slotted (in U shape) for the box beam to slide in. The reason is that the level of the box beams can be accurately adjusted even though the cut off level of the pile head may be wrong cut.

Because of the slot in pile, does the load (on top of the beam) transferred to the pile via the side plates or the bottom flange plates. The engineer asked for a U shape slot as he claims that the loads are transferred to the beam bottom flange plates with a half round piece (pipe) welded to the box beam to avoid having high stress concentration in sharp corners of a cut slot.

If hope they are clear.

 

[BAretired]

ozziz,

Could be one or the other or a combination of the two, depending on connection details.

If the beam elevation is adjusted after sliding it into the slot, the beam will not be bearing on anything, so the load would have to be carried entirely by shear on the sidewalls.

If the beam is bearing on the pipe wall and the side walls are not connected, the entire load must be transferred by bearing.

If the beam is bearing on the pipe wall and the side walls are connected, the load would be shared in a way which could only be determined by strain compatibility of the various parts. Ordinarily this would require a finite element analysis to determine precisely.







Best regards,

BA

 

[civilperson]

End plate on the pile and shims are easier to get to the correct elevation.

 

[kslee1000]

As BA pointed out, the mechanism of load transfer is really a matter of the connection design.

Simply puts, if the beam freely sits in the slot, the load will be carried by the side walls to the half-circular pipe, which will be in bearing (point bearing, if the curve is not fitted).

If connections are made through the side walls, the matter is complicated by the degree of slippage allowed by the connections (the load could be handled entirely by the side walls through using slip critical connections, or the half-circular pipe may pick up some load after the beam has slipped).

If high stress concerntration in the side walls is a serious concern, then the addition of the half-circular pipe has its merit. However, since this is an under water construction, have you considered the buoyancy, which may reduce the support reactions significantly (especially for closed box structures), thus affecting the connection type and design for this application.

Also, the duribility and constructability (costs) of the connections should be looked closely.