angle profile bolted to the flange

[Andrew88]

Hello,

Could someone please give me some tips on how to size the bolt as per attached sketch? Can I assume the the rotation would occur around the corner of the angle profile and then the force in the bolt with specific level arm would need to be equal but with the opposite direction to this moment?

Thank you in advance!
Jed

 

[canwesteng]

I would probably assume a triangular compressive stress distribution, peaking at the heel of the angle and going to zero at the bolt. Somewhat more conservative than your assumption but I doubt you'll have an issue.

 

[12345abc6ttyui67]

Hey Jed,

You're right. The overturning moment at the base of the handrail must be resisted by a compression / tension force couple between the RSA and the bolt. The compression part of the couple is at either the heel or toe of the angle (depending on which way the load at the top of the handrail is applied). The tension part of the couple is the bolt. You can divide the overturning moment by the distance between the two couples (e.g. either the heel to the bolt, or the toe to the bolt) to get the tension / compression force.

Fun fact, you can do this quickly just by comparing the ratio of the two lever arms, e.g. (1.1m / 0.045m) * 0.76kN/m = 18.6kN/m. Depending on how many bolts you have per meter, you can easily get the tension in the bolt (and thus size appropriately).

Note that handrail loading in the opposite direction will be more critical as the bolt lever arm is only 30mm, not 45mm. You'll need to decide if it is credible that 0.76kN/m could also be applied 'inwards', rather than only 'outwards'

As an aside, 'technically' this will give you an infinitely high compressive stress where the heel (or toe) digs into the support beam flange (as it is applied along a line with zero width). I usually assume a 5mm strip of the heel (or toe) carries the compressive load to avoid this (that's just my own personal method though, havn't seen that written down anywhere).

Some other things you may need to consider:
-> Local bending in the legs of the RSA
-> Local flange bending in the supporting beams
-> Torsion in the supporting beam

In my company, we typically use either side mounted handrails which attach to a web stiffener, or top mounted handrails which fit into a socket welded to the supporting beam. We also specify a limit on how far away each handrail post can be from a transverse member spanning into the support beam. If this is exceeded, a transverse member is added to take out the torsion.

Of course, above may not be necessary if the supporting beam is of sufficient strength or restrained by deck plate etc.

 

[racookpe1978]

Is the HEB 250 truly a W shape (flat webs) or a I bean (13 deg angled flange interiors)? If the latter, you will need to verify the drilled location of the flange and web to be sure you have nut and washer room from the side of the web.

 

[12345abc6ttyui67]

HEB's have uniform thickness flanges across their breadth. There is a small rolling radius at the flange / web interface. Assuming you stick to (or close to) the standard bolt sizes and back marks there won't be an issue with washer clearance to the root.

 

[Andrew88]

Thank you everyone for the responses! Could you please give me some tips on how to check local buckling in the RSA? For the flange of the HEB I would just assume it is a cantilever fixed to the web, is it right? Then would check it with the triangular stress distribution in a similar way to the bolt calculation?

 

[12345abc6ttyui67]

Hi Jed,

If you draw your bending moment diagram you'll see that the 'long' (vertical) leg of the RSA continues to carry the bending moment at the bottom of the handrail post right down to the heel. At this point, the bending is split into the compression / tension couple at the heel (or toe) and bolt. You effectively have a very long beam (the handrail and RSA) which has two pinned supports placed very close together at one end (the heel (or toe) and bolt).

So, I would check the 'long' leg of the RSA for a moment of 0.76kN/m * 1.1m. I'm not sure what the bolt pattern is like where the handrail post attaches to the RSA, but you will have some distribution from the centre of the handrail post bolt group to the root radius of the RSA 'long' leg. e.g. assuming you had only two bolts here, one above the other as you have sketched, centered 90mm above the heel of the RSA, I might distribute the moment over approx. 315mm of the RSA leg (which is a 30deg distribution through the leg, you should check whether you are comfortable with this distribution). You can easily work out the (minor axis) elastic modulus (Z_yy in UK notation) for a 315mm long piece of the 8mm thk leg. Checking for M / Z_yy will give you the bending stress along that portion of the RSA leg, which you will need to limit to an appropriate value.

You can do a similar check for the 'short' leg using the bolt tension you have worked out back to the root radius.

The same thinking is applied to the flange as well. Treat it as a cantilever with an applied moment which acts over a specific length of the flange.

Note this assumes the HEB itself acts as a 'fixed' support, hence checking torsion in the HEB is prudent.