Restoring moment of inertia and area of beam with web opening

[CHARLESCOSTA]

A lifting tackle beam is to be designed which has 4 circular holes in the web(centers coinciding with mid point of web height)symmetrically placed with respect to mid point of beam length.Two holes will be used to suspend load through hangers connected to pins passing through the holes and two holes will be used to lift the tackle with crane hook holding pins passing through the holes.At the vertical section passing through center of holes,i weld bearing bosses(pins will bear on these)and use stiffeners welded above and below these bosses to the web such that moment of inertia and area at these sections become equal to those at sections not having holes.Is this method good for practical purposes.I am aware ofNCCI design rules for web opening in beams ,but i haven't used it.The above method which i have read in some old book seems easy to me,since in any case i am going to use bearing bosses to reduce bearing stresses on pin.

 

[rb1957]

sounds reasonable to me ... holes in webs close to the neutral axis have a very small effect on the bending strength of the beam. local stiffening of the web to support the new loads being introduced sounds reasonable.

 

[DTGT2002]

For our Lifting beams, we have moved away from I sections and now use tube steel members exclusively due to their stronger weak axis bending capability. I beams must be chosen carefully to use a member with sufficient strength in both axes to both carry the load and adequately brace the strong axis against buckling.

The article "Design and Construction of Lifting Beams" by David T. Ricker has been very helpful for our designs even with the change from W-shapes to Tube Steel.

That said, if you are dead set on using the W shape, lifting points aligned with the web of the member might be a simple detail to design and construct with the major fault being the inability to lay the beam flat to the ground. Depending on your fabricator, large holes in the midspan of a beam can be difficult to do the right way.

Best of luck,

Daniel Toon

 

[CHARLESCOSTA]

Daniel
I am sorry I didn't mention that the beam is box section having ry=0.6rx.Also the effective length is taken as 3 times the nominal length for transverse stability corresponding to the case of beam with no torsional restraint at ends and ,oad as well as beam being free to move(taken from standards ). My exact question is that is the method of restoring moment of inertia and area correct or at least acceptable as a crude method?