long beam with camber and beam splice

[delagina]

I have a very long beam 120 feet that will be spliced 2 times. I have a big deflection and may need to camber the beam.
I'm worried about camber affecting the splice. Also since it will be spliced 2 times, I will have middle beam.
I don't know how cambering works with the middle beam.

 

[TehMightyEngineer]

What's the beam size?

Maine EIT, Civil/Structural.

 

[paddingtongreen]

If your beam is anything like normal depth, you will have to make up the "camber" in the splices. This is not that difficult if it is jigged out properly. On one job, a truss of similar length, the fabricator built his jig on a long trailer base, assembled and welded the splices and the sent it to the site as an oversize load. There were a number of these trusses, so the expense was shared.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[dhengr]

Delagina:
Talk to a couple local fabricators who might end up involved in the project, and ask them how they would do it. More than likely, they will cut the camber into the webs, assuming some sort of a plate girder, and then just press the flanges to the web for welding. You lay the splice out on/about the radial line which goes through the joint. On bolted joints, I believe we usually drilled the flange and web splice plates and used them as templates for the girder flanges and web drilling. Many times we laid the girders on the shop floor in a surveyed relative position or stood them at their relative elevations and completed the connection drilling.

 

[delagina]

can I just put in the drawing the camber height and let the steel detailer worry about the connection?
or do I have to do the connection to compensate the camber?

 

[delagina]

can anyone give me sample drawing, how is this presented for detailer. thanks,

 

[steellion]

For a beam of that length, you probably want to give camber "spot elevations" every so often along the beam and let the fabricator figure out how to achieve it. If you have a uniform load along the beam, it won't be hard to figure out the expected deflection at any point.

 

[delagina]

can someone comment on this. I know the deflection at all locations of the beam. I don't know how to present it in the drawing for the detailer.
I saw some online how it is presented.

Can someone comment on attached pic.

 

[hokie66]

I would just set Points 1 and 3, and leave the centre section straight.

 

[dhengr]

Delagina:
Below you beam elevation, draw a horiz. line and divide it into at least 10' increments (maybe 5' increments). Plot the camber (Camber Diagram) in an exaggerated scale above this horiz. line and show the camber at each increment, on the curve; not tabular, P1, P2, etc. Comment on whether this is a circular curve or can be essential straight lines/segments btwn. your defined locations. Defined camber points should occur at the splice points. Since this is made up of WF shapes, it will either be heat cambered, or more likely ‘bump formed’ on a bull dozer. That’s a large horiz. hydraulic press, a 3 point press, 2 reaction points, and a center load application cylinger, which yields the WF shape at the center force application point.

 

[delagina]

dhengr, how about something like this?

 

[dhengr]

If you are going to do it Hokie’s way, if that is acceptable for your needs.... then set the three beams, 30',60', & 30' with their mill tolerance camber up, and provide all the adjustment in the splice detail.

 

[delagina]

I'm now confused. I don't plan on doing any adjustment on splice detail due to camber. I was going to detail it as if it was a [pre][/pre]straight beam and let the detailer or fabricator do all the connection adjustment.

 

[hokie66]

The suggestion of placing the upward deflection at the splice points was just to make it simpler. It is easier to jig three sections into a shape and weld them together than it is to weld them first and then bend. Probably more accurate as well. Why do you need to be so precise with the camber?

 

[delagina]

hokie66,

I don't have to be precise with camber.

1. So I only need to put to camber heights located at 2 splice points?

2. If the beam length becomes 140 ft and I need 3 splice, I can put camber heights at 3 locations where the splices are?

3. Also my splice will be bolted splice, do I need to do anything to compensate for camber with the bolted splice detail?

 

[hokie66]

1. Yes
2. Yes
3. I don't see why you can't use bolted splices.

As these are really not beams, but rather truss chords, the splices are primarily for axial forces. You could put the splices at the panel points and incorporate the truss web member connections. You don't need full moment connections in the chords.

 

[paddingtongreen]

The towers are a complication. Without the towers, it is easier to simply make the top chords of the center truss segment longer than the bottom, but with the towers there, deformation starts at the ground. If you start with the towers vertical, your cambered full length truss, bottom chord will be short. There are a number of decisions to be made and they all have consequences.

At the splices, you might consider welding a splice plate to each of the members on opposite sides. Drill the holes in the unwelded side of the plate before shop fitting and use as a template for holes in the truss member, after the chords have been shop fitted in the correct relationship, separate them for shipping. This way you know they will fit properly at site.

I think now that you should simply put in a finished camber requirement and then check/negotiate the method preferred by your Erector and Fabricator, but with a shop fitting prior to shipping.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin