HSS Truss Runway for Crane

[LowLax]

I have a client that basically wants a 90ft span runway beam for a 7.5 ton crane. I'm thinking of making it out of an HSS truss. I know I have to add lateral bracing, but other than that are there any major pitfalls anyone sees? Has anyone done something similar to this before?

I'm a little worried about fatigue, although this isn't a huge crane and not in constant use.

 

[dik]

HSS is OK... connections can be a bit of a problem and I would typically not design members for more than about 70% of their capacity, else connections become even a bigger problem. 90' span is a bit big, but a 4' or 5' truss should do it. It should be pretty easy to model and there are very good texts for connection design. Fatigue can be accommodated fairly easily, but may not be an issue with infrequent useage. For crane design I usually try to provide a bit of a histogram of the useage. Jeff Packer's book is pretty good.

Dik

 

[hokie66]

I wouldn't use hollow members for a crane runway truss because of the issues with getting full penetration welds, which I regard as essential with any crane runway. Why not use rolled wide flange sections?

 

[BAretired]

I agree that rolled sections are preferable to HSS. Chords could be tee sections. Webs could be double angles fillet welded each side of the stem of tee.

BA

 

[dik]

Hokie... the reason for designing about 70% is that full penetration welding is generally eliminated... I've done a few crane assemblies using HSS, generally longer spans; most, however, have been with W shapes and a C cap...

Dik

 

[hokie66]

dik,
I know it can be done, but for crane runways, I just don't want to depend on welds which can't be seen from both sides.

 

[paddingtongreen]

I don't like HSS for major trusses because I can't see inside them, I can see pretty well all of the surfaces and connections with shapes.


Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[asixth]

Is the fabricator going to transport the 90'x5' to site? Will it be as one member or will it require splicing? Also, will there be any issues involve with galvanizing a truss that big.

With the welding, would it be possible to use a thicker thickness HSS and specify butt-welds?

 

[hokie66]

Instead of a truss, why not use a welded girder? Maybe a bit heavier, but a lot less fabrication.

 

[dik]

and, one of the earliest long span crane beams assemblies I recall used a 'castellated' beam. Spans were long and shears were relatively light...

 

[LowLax]

I appreciate all the responses. The fabricator is also working closely with the owner on this project and preferred HSS trusses. I will definitely need to work with him on constructibility. If a splice is required I think HSS is out.

I don't see the need for CJP welds. What is wrong with using fillets? I know the connections might require the chord and web member sizes to change somewhat. I still have to go through all the HSS truss connection stuff in Chapter K. For now this is just preliminary for feasibility.

 

[BAretired]

If you want to use HSS sections, a bolted field splice should not be a problem.

BA

 

[dik]

Fillet welds are OK... just don't size the members to limit capacity... else CJP's are required...

 

[apsix]

Fillet welds are not good for fatigue.
You will have to do the fatigue analysis to determine if they will be adequate. (Or determine that fatigue is not an issue due to the low duty cycle.)