Presence of hoist trolley load adjacent to bolt hole

[PEVT]

I have a very specific check I want to make where the wheel from a hoist trolly is located adjacent to an existing bolt hole. A two ton hoist is attached to a trollye which rolls on a S6X12.5 beam and passes by an old bolt pattern of 4 @ 9/16" holes. I want to evaluate/model the stresses at the exact point when the trolley wheel is adjacent to the thin section of the bottom flange outside the hole. This relatively thin (.3 inch) exterior section of the flange is supporting the wheel and has been for the last 20 years. I need to now make the case that this is still ok or I have to tell them not to allow the hoist to pass through this area. The trolley is moved along the beam with hand run chain gears, so the speed is very low. I have attached an image which shows the design problem in greater detail.

 

[SlideRuleEra]

PEVT - One way to approach this problem is to make simplifying assumptions that will result in a reasonable, approximate answer. I'll go over how do this my hand, using old style ASD (9th Ed. AISC) - perhaps the calcs can be speeded up with software. Be warned, the method is tedious :

1. Based on published dimensions and properties of S6x12.5, make a simplified shape from three rectangles - two flanges plus web. See Page 1 of the attachment.

2. Calculate accuracy of the area and section modulus of the simplified shape. Results (98.5%+ accurate) are summarized on Page 1. Note: Since the shape is symmetric about the X-axis, section modulus can be calculated directly - this will be important later.

3. Subtract the diameter of the pair of 9/16" holes from the width of the bottom flange. Then assume that this reduced width flange is continuous (the holes are now gone). See Page 2.

4. Calculate the section modulus for the equivalent, modified S6x12.5. Since this section is NOT symmetric about the X-axis, section modulus cannot be calculated directly. Compute the area, moment of inertia, then the section modulus.

5. Assuming the S6x12.5 is simply supported, the reduced section bottom flange is the tension flange. Therefore the beam can be loaded to full allowable bending stress (say, 24 KSI for A36 steel).

6. To calculate bending stress at the location of the holes, position the trolley so that one wheel is directly over the holes. The other wheel is to the side that puts it closest to the center of the beam. This will give maximum bending stress at that spot compared to ANY location of the trolley along the length of the beam. Also include bending stress, at the location of the holes, from the the beam's self weight (a uniform distributed load). See Page 3 of the attachment.

The result should give a reasonable estimate of bending stress, at the location of the holes.

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[ToadJones]

I don't think this method will help with your local flange bending checks

 

[dhengr]

PEVT:
Look to see where on the flg. tip the wheel wear line is, that sets your load location. Look to see at each hole if that wear line doesn’t move to or toward the inner edge of the hole, nearest the bm. web. The flg. tip could be deflecting enough, not yielding, to move the wheel load line toward the bm. web. The flg. tip is spanning across the hole discontinuity 9/16", in the length direction of the bm. to two cantilevered sections of flg. off of the bm. web. If you don’t see any permanent deformation of the flg. tips around the holes, check with a straight edge, you are probably O.K. You have less than 1.5" canti. to the flg. tip and the contour of the wheel may just be riding right over these holes, although I wouldn’t drill them there for the fun of it.