Box trusses using square hollow sections 1

[MX009]

Hi everyone,
I have been employed to design a stacker which will include a box truss for the conveyor, constructed from square hollow sections instead of the usual WB, angles and channels.
The intention seems to be to bevel the ends and full penetration butt weld the perpendiculars to the main chords, and then add the diagonals in he same plane.
Is this the usual way to constructed a mobile structure fully from square sections?
I would prefer to slot the sections and use fin plates.
The sections would then be fillet welded to the fins.
Does anyone have any experience with this ?
Thanks.

 

[dik]

You may want to design the members for about 80% of their capacity and run with regular welds and not CJPs... likely less expensive. HSS trusses work well.

Dik

 

[BAretired]

It is usual to place web members in the same plane. In some cases there are "gap" connections and in others, "overlap" connections.

"Hollow Structural Section Connections and Trusses" by J.A. Packer and J.E. Henderson provides valuable information on the design of HSS trusses, including factored resistances for various types of connections, including T, Y, X and K, N connections with gap or overlap of web members. If you have not designed HSS trusses before, this book should prove helpful.

BA

 

[hokie66]

The CIDECT Design Guides are probably the bible for hollow section connections. The authors of the book referenced by BAretired were also involved in the CIDECT Guides.

http://www.cidect.org/design-guides/

 

[Ron]

Good info hokie66....thx.

 

[dhengr]

MX009:
Truss design and fabrication using square or rectangular HSS (round CHS too) is always fairly difficult because of all the joint preparation required to provide top quality joints. It is not a particularly good idea to assume you need CJP welds any time you don’t really need them. They are just time consuming and expensive without really improving the final product. They may need backing bars, specially qualified welders and procedures, special attention and details at the four radiused corners of rectangular shapes, and along them, the acute side of a skewed joint is always a real dog to detail and weld well. The flare-bevel-groove welds and the transitions at the corners to a different weld detail are really difficult to do well. Then, fabricating is particularly tricky in terms of which are the best sub-assemblies, weld sequencing, positioning for welding, and final assembly, etc. But, they sure do look nice when they are done.

 

[SAIL3]

If possible, upfront,I usually try and design the diagonals with the same width as the chords and then lap the joints with gusset pls.....this eliminates any need for CJP welds and endless design effort in designing the connections....if this is not viable, then one has to slog thru the design of the connections as per the CIDECT Design guides....

 

[BAretired]

If web members have the same width as the chords, a special weld is required at the radius of the chord. It is usual to use web members narrower than the chord width to avoid this problem.

BA

 

[dik]

BART: Yup

Should have added, we had one of the company 'constructability experts' review one of my projects and the only 'fault' was that I had a mile or so of 'T' cable tray supports and that I had used 6x6 HSS for the top and 5x6 HSS for the stem... he thought I should have used 6x6 for all... I guess he has to do something to earn the 'big buks'.

Sail3: It is likely a lot less costly to avoid gussets.

Dik