40 M TRUSS

[ENGRRA]

I HAVE 40 M PRATT TRUSS IN A ROOF SYSTEM AND I NEED SOME HELP WHERE TO PUT THE SPLICES
THE MAXIMUM LENGTH OF HOT ROLLED SECTION IS 12 M SO I NEED 3 POINTS OF SPLICES IN THE TOP AND BOTTOM CHORD
WHERE IS THE BEST 3 POINTS TO PUT THE SPLICES
THNX FOR ALL

 

[steellion]

Axial stress is maximized in the center. As a rule of thumb, we keep splices out of the middle third of the chord span.

 

[BAretired]

I designed Warren trusses with low pitch top chord of similar span for an arena about thirty years ago. The EOR left the truss design up to the Contractor. I was working for the steel fabricator. He wanted just one splice at midspan. At first, I thought it was a crazy idea but it turned out to be very easy to erect and very economical.

The top and bottom chords consisted of HSS members, I think they were 10"x10". The middle diagonals sloped downward and away from the splice point (i.e. compression members under uniform load). This meant that the bottom chords had no web members cluttering up the tension splice.

Both chords were fitted with square end plates which were field bolted together. The bolts were in a square pattern around the HSS. The top chord splice was in compression under snow load, so the bolts were designed to take uplift tension and shear due to unbalanced snow load (which did not occur simultaneously).

End plates on the bottom chord splice were designed for prying action and the bolts were A490 bolts.

BA

 

[MiketheEngineer]

If it is a pitched truss - axial forces are less in the middle - a flat truss has higher forces in middle.

 

[ENGRRA]

the truss is flat and members have local bending from the joists

 

[dik]

also check with the rolling mills... some produce lengths of 18m.

Dik

 

[Ron]

As BAretired noted, sometimes a center moment connection in a truss is easier to fabricate and erect than two shear splices. I have designed aluminum trusses in this way as well.

 

[BAretired]

A shallow slope on a longspan roof truss makes sense to avoid ponding. Does the roof really have to be flat?

Local top chord bending can be avoided by ensuring that each joist bears at a truss panel point. The Warren configuration with a vertical member at each bottom chord panel point is likely the most economical for such a long span.

With 12m maximum length of material, chords can be shop spliced at or near the quarter and three quarter points with a field splice at midspan.

BA

 

[paddingtongreen]

The 12M shop length does not limit your shipping length. On one job I worked, the fabricator built a similar length truss in three pieces, two had shop welded splices. The three pieces were assembled on a specially designed low bed transporter/jig. These welded splices were made in the fabricator's yard and the complete truss shipped as a "Long Load". It worked very well.

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