holes in crane girder tension zone

[aayvat]

I have a steel support structure for a retractable crane stopper which is to be installed to an existing crane girder. The support stucture consists of welded plates to which the pneumatic stopper is fixed above. The crane girder is simply supported by the building columns and the stopper will be installed near the center of the span.

The space for installation of the support structure to the existing girder is tight and construction prefers to bolt the structure to the web of the girder rather to minimize the field welds. The stiffener/transfer plates of the support would be welded to the top flange of the girder and bolted to the web.

My concern is introducing holes to the tension field of the existing girder without a complete verification of the girder itself. Is this a valid concern? Is it common to see web bolted stiffeners in practice?

Thanks for any comments or suggestions.

 

[BadgerPE]

A sketch would help, but it seems to me you are installing the stopper at midspan of the girder near or at the top flange. Depending on the size of the web in relation to the diameter of the bolts, bolting may not be a concern as the web is transferring shear and not bending related tension forces. However, without a sketch, it is difficult to understand what you are proposing.

 

[aayvat]

Thanks for your comments Crackerjack47. I've attached a sketch to better explain the question.

The stopper will be at/near midspan of the crane girder between building columns. The stiffeners of the support will be welded to the top flange of the girder as shown in the sketch.

 

[dhengr]

aayvat:
I don’t think I’d worry about a few holes in the web at the midspan of the girder either. But, it seems a funny argument that they want to save field welding, when they are already downhand welding to the flange tip and overhead welding to the underside of the flange. In fact, that looks like an awfully big bracket to support a few hundred pounds of crane stopper mechanism. And, more importantly, should that mechanism and bracket really be taking the stopping load in the first place? That’s pretty eccentric and awkward: arm length back to a hinge pin; through some base structure and base bolts; into the bracket top plate; then back into the girder.

What is the axial load (load along the rail axis) which you have to absorb? Is this load equally split with a stopper on the other girder, or 60/40? Is there any shock absorbing device in the system? Why don’t you take the load out along the length of the girder flange, by somehow clamping/wedging/locking to them? Then your bracket and stopper mechanism would only be for holding and positioning the mechanism, not taking the full load.

Why not fab. two mirror image angle shapes, one each side, and to fit up under the girder flange; with the vert. leg down and bolted through the girder web; length and number of bolts to be determined, but they are basically bolts in double shear absorbing the impact. The horiz. legs project out beyond the girder flange tip 1.5" and have a 6" long notch cut in this leg tip 1.5" deep. Maybe this horiz. leg could be welded to the girder flange tip. Your stopper mechanism would drop a couple shear lugs down into these 1.5 x 6" notches. The shear lugs would have to take some cantilever moment, depending upon the height of the applied impacting load, but this is better centered over the girder now.