Welding question for built up beam

[gcs3pe]

I've got a 7.25" deep floor box into which I must shoehorn a steel beam. A W6x25 deflects too much on it's own, so I intend to build up the section with .25" x 4" plates welded to the top and bottom flanges.

The fabricator says a continuous fillet weld will cause heat damage the W6. Is that true? If so, how do I size stitched fillet welds to avoid the heat damage?

I am primarily a wood guy, so welds are not really my thing.

 

[csd72]

Its the heat from the welds that tends to warp the steel rather than actually damaging the beam.

You need to minimise the amount of weld and also get them to stagger the welds on alternat sides of each flange so any stress are evened out during the process.

A staggered weld is simply designed as a fillet weld with a hit and miss so you would call it as 6" on 6" off or as required for the particular fillet weld. so the weld would then be half as strong as the same size continuous weld.

 

[BAretired]

The welds are sized based on the horizontal shear between plate and shape, namely VQ/I.

BA

 

[ahmedhegazi]

Size of welding electrode should not be more than thickness of thinner plate ,even you should go bit less.

you have to alternate the weld and length of continuous weld should preferably kept 40times weld size,the weld is design by shear flow as BA said ,just his equation missed B(section width) it should VQ/IB

 

[BAretired]

ahmed,

VQ/IB gives a shear stress for the area of the plate. What we are interested in is the total shear between the plate and the flange which is VQ/I. Half of that is provided by welds on each side.

BA

 

[ahmedhegazi]

You are right BA my equation gives stress then will be multiplied by width (which is your equation) to give Force/Length

 

[gcs3pe]

Thanks for the lesson, guys - as always. A 20' beam with a 5k point requires impressively little welding.

 

[Lion06]

especially for cover plates. They are say far away from the neutral axis, that the shear flow is minimal there. I think that's more of a player than the 5k point load.