extending stanchion legs

[dellboy]

So its a work shop shed im building for myself i have 2nd hand steel for stanchions. its to be 59 feet wide. i want to make it a little higher only by 4 to 5 feet as i have crane and gantry that will be going in it and dont want to make it too low. stanchions are currently 25.5 feet long 605x305x149kg. steel size for the rafters that i was going to buy was 305x165x40kg. so the current stations have a 20mm plate on top with 8 20mm holes in it as in left of picture. not sure what way i would increase height. crane rails will be sitting on lower section so extension part would not be any different than any 60ft shed wide shed. A and B show some options. But as its only going to be 4 to 5 feet would you just weld the short stanchion extension to the rafter all together ? i thought about just not extending the stanchions and just design the rafters like in option B and but directly on top of stanchion that way i would save a 1ft in height or do like in option C and gain 2ft in height. I have never seen option A or C done so would like any ideas or suggestions. thanks

 

[dannewhouse]

I assume the crane is attached to the big stations? why do you want even more height above or are you moving the crane up as well? so the "extra" height will appear below the crane so useful.
bring your conc foundations as high up as possible? like 6" below FFL?
if you were extending the big section best to do it at bottom, if adding to top like A or B you need to transfer both flanges forces to the flanges below.

 

[dellboy]

I assume the crane is attached to the big stations? why do you want even more height above or are you moving the crane up as well? so the "extra" height will appear below the crane so useful.
bring your conc foundations as high up as possible? like 6" below FFL?
if you were extending the big section best to do it at bottom, if adding to top like A or B you need to transfer both flanges forces to the flanges below.

correct crane will be attached to big stanchions and its more height under crane im looking for. i dont want to extend the heavy stanchions or do i think i need to either for my requirements. crane rails are 2ft high and crane probably 5 ft high. so in theory i could extend the top extensions by over 7ft and still have crane sitting on heavy stanchions. i even thought of sitting the crane rails directly on top of heavy stanchions (as opposed to them hanging on a leg out the side) with the lighter stanchions right beside them. but i think i would have too much height then. ya agree 6inches below the FFL is what i was thinking too so will have to do pads. but was always planing on doing pads anyway.

 

[dannewhouse]

You should really be doing something like this to continue your flanges down. (it may be easier to have 2 sections on top of the heavy 1 to fill it flange to flange.
You could put a flat plate on top of the heavy section then bolt the light section above that but make a gusset to fill it out to the full width of the heavy section.