Light weight truss - spool fabrication

[MoreAC]

I have to design/build, lift and install offshore, a trussed arrangement. The requirement is to have a box of 1.2 m wide and any suitable depth. So, I have come up with two trussess spaced at 1.2 m and depth of 400mm (something like steel joists). To minimize weight and as per requirement, the truss is composed of 2 EA 100x100x8 top and bottom members. The digonals and verticals of truss are made up of 16dia and 25 dia steel rods.

The two trusses are separated by a transverse at every meter by 100 x 65 x 7mm. And diagonals are attached at every two meters.

Currently, I am looking at around 35m of this box section to be lifted and installed in one piece. Can somebody suggest/guide if there is any technical issue while using angles or the arrangement considered. The structure is checked with SACS considering Lb of 2m and Lx/Ly of 2 m for top and bottom members of EA 100x100x8mm.

The sections considered are

Two EA 100 x 100 x 8 mm @ top and bottom

Top transverse brace UEA 100 x 65 x 7 mm - transverse

Diagonal chords EA 60 x 60 x 6 mm

The truss diagonals and verticals are 16 dia and 25 dia round bars.

Attached sketch shows the proposed arrangement.

Thanks & Regards,

Anurag

 

[Ussuri]

Assuming you plan to lift this using a four point lift, have you considered the racking effect during the lift which will tend to twist your structure?

 

[BigInch]

No lateral diagonal bracing?

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"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[MoreAC]

Yes for racking, I will add a small EA 60x60x6 @ every 2 meters. So, it will be seen in the top view as shown in the attached file.

But again, won't the diagonal bracing as shown in the section next to plan help for racking effect?

Currently I am planning to develop a plated detail for lifting point. It will be like a plate welded at an angle of 60 deg between 4 chord members. The plate will be strengthened by back-up plates to distribute loads to the chord angles EA 100x100x8.

 

[BigInch]

That appears to be a lot stiffer than what you had before. The spacing and length of those red diagonals will depend on the allowable stress for their kl/r.

BTW, in general L, T, WT sections are not preferred for offshore construction due to their high surface area vs crossectional area ratio and their resulting increased succeptibility to corrosion. Ever noticed how many things are made of tubes out there, which also happen to have the highest kl/r ratio of any x-sect shape enabling a high strength to weight ratio.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/