[Nils]

Working on a new project. The customer wants a metal walkway built that he can suspend over an area that floods when it rains, then be able to remove it and store it during the dry months. It is 4 feet by 24 feet long. Made up of three 8 foot spans interlocked together. The construction of each span will be a 8 foot pair of 2x2x1/4 angles, capped by 1/4x2 flat bar, with five 8 foot lengths of the same material running longitudinally and spread evenly across the center. They will be reinforced with 12 each cross members spread out evenly. Then covered on a single side with a sheet of standard expanded metal. The center span will have two 4 foot wide, concrete, parking bumpers mounted to its underside, while the adjacent spans will only have one bumper mounted at their ends mating to the center span.

Each span will need to be fabricated in a way that maintains as much flatness as possible. I intend to tack as much together as possible before running the finished beads. Also, keeping heat spread out evenly, I will alternate ends being welded, with a short bead here, and then a short bead on the opposite end. Since I'll be constructing the spans at home, I'll be using the Millermatic 250 for most of the welding.

Got any suggestions on how to maintain and assure a minimum of distortion (flatness)?????????????? Fixtures and stress relieving heat treat are not desired.

[Otto Nobedder]

You'll get surprisingly little distortion MIGging it, especially with the order of operations you've described.

I take it the 2X2 1/4 angles are to be stitched together to form a 5" channel? Or will there be some trusswork between? As long as you can assure flatness and straightness fabbing these, they'll be so rigid you'll lose more flatness to gravity when installed than from weld distortion.

Steve S

[Nils]

Thanks for the input, Steve! You d'man.

Let me clarify the design. One 2x2 angle will be used on each side of the 8 foot length. To provide additional stiffening, five 2x 1/4 flat bar lengths will run parallel to the angles. The two angles and five flat bars will all be tied to a 50 inch 2 x 1/4 flat bar length cap. The structure will have 12 short flat bar members tied in perpendicular to the 8 foot lengths. I believe the total of seven 2 inch rails will be sufficient to bear the weight of foot traffic. I was originally considering 3x3 angles, but thinking it might be over-design, went to the 2x2's.

What are your thoughts, Steve? Do you think I have sufficient structure?

Also, this job is in the bidding stage. I submitted my bid for the job last night, as the it was due today. I had compiled my data and was ready to submit it on Friday, but decided to hold off and use my time allotted. This was a wise decision on my part and afforded me the opportunity to make several revisions making the bid more attractive. Whether or not I get this order is TBD. With that being said, the learning process is still always relevant.

Thanks

[WerkSpace]

My car hauler plans are using a 3"X5" outside frame (angle facing upwards)
and 2"X3" welded cross-members (angle facing downward) on 24" centers.
This allows for 2" thick lumber to be anchored to the flat face of the cross-members.
The resulting structure is 5" in height, including the wood decking.
This design is rated for 12,000lb gross weight.

For a foot traffic bridge, you could easily get away with 2"X2" frame (angle facing upwards)
and 1"X1" welded cross-members (angle facing downwards) plus 1" wood decking.
I estimate that this bridge design would easily support 2,000lbs.

[Otto Nobedder]

Okay, now I can visualize it. You're aiming for a total depth of 2", plus the walking surface of expanded metal, for the structure. 50" total width, with 2X1/4 flatbar vertical on 8 1/3" centers. (Lay out 10" centers, you'll only fit four between angles 50" apart).

I still think you can maintain "flat", but unless you include a handrail, you may want to build a very slight arch in each 8' section.

Steve S