welding a beam-tee

huangyhg

welding a beam-tee
hi fellow
now i am considering weld a beam-tee to a existing beam to increasing the section's property(ixx,zxx, etc). so, should i butt weld the beam-tee with full length, or can weld sections with spacing to achieve the same result. where i can find some information about these topic.
thanks for your time.
i suggest you first investicgate welding the t to the beam with fillet welds, preferable intermittant welds (stich welds).
to size the welds, one needs to develop adequate shear capacity between the t and the beam.  the formula to use is:
shear force = (shear force)x(area of t)x (dist. from centroid of combined section to centroid of t)/(moment of inertia of the combined section) = vq/i.
this force is then used to determine the area of weld required each side of the max. shear force.
i usually add a few stiffeners between the t and the beam to stabilize the t (to keep it from "rolling over").
regards,
jeff
very well said jec67.
use a fillet weld if you can.  it's cheaper and easier.  the vq/i equation will give you shear flow, force/length.  you can calculate the unit capacity of different size fillet welds based on the code that you follow.  then you pick how much weld per foot, say 2 inches every 12 inches for example.  i suggest you use the minimum weld size.  it is usually easier to fabricate longer smaller welds than less length of a larger weld.
stiffeners sound like a good idea also.
i agree that a fillet weld is preferreable.  however, depending on the environment, a continuous fillet weld may be preferable to an intermittent fillet weld to reduce the risk of corrosion.  perhaps you could have a 3mm seal weld between between the "stiches".
i agree with dbuzz and would only add (hopefully obviously) that the fillet weld must be on both sides of the leg.
the amount of weld required reduces towards the centre of the beam as the shear force reduces (for dead and uniformally distributed loads).
marcolegs - if this question is related to your other thread,
fillet weld is the way to go. the can be done fast, can be done in any position (overhead, horizontal, etc.) and intermittent is the way to go this way you can reduce the heat effect.
also, you may want to evaluate the effects of heat since it sounds like the beam is already loaded. avoid welding perpendicular to the tension flow! make sure the steel is in good condition, no corrosion, and abnormalities before welding.
jec67 done an excellent job explaining.
regards,
  
lutfi