About web opening in S beam or W-beam 1

[Staed79]

If there is a web opening in W section we normally design it using the formulae or methods specified by Steel Design guide 2 "Steel and composite beam with web opening" but if the W beam is cut to T section somewhere along the length, could we still use the method an formulae.
Secondly could we use the method for S-shaped beams too.

Thanks for reading and I appreciate your response.

 

[csd72]

To make it into a T then you have to remove the flange so it is no longer a web opening. You need to provide a new bottom flange and then analyse it as a built up beam.

I see no reason why S-shapes would not use the same formula though you should check the formula assumptions before using them.

 

[rday]

I believe the guide goes over the theory behind the formulae provided. It seems the theory would hold for tees and s shapes, though the formulae may change slightly. I would have to look at the design guide. It's been awhile.

 

[Staed79]

In the design examples they consider only web openings..so when we have a built up section using angles..can use the formulaes give by the guide..or should be go around the basic steps of beam design and say if the section modulus provided by the built up section is adequate.. the cut T- section is adequate to bear the required loading and no other checks are required...

Last question : If angles are provided how to determine how much development is required at both ends..

Thanks for the response..

 

[Staed79]

I wanted to restate my statements :
1) Can i use the formulae from " Design guide 2 "Steel and composite beam with web opening"", if the W -beam is cut to a t-beam along the length for a duct to pass through.

2) what checks do i need to consider in the design?

 

[csd72]

1) No - these formuli are for a completely different situation It is not called "Steel and composite beam with WEB opening" by accident.

2) Check bending, shear, longitudinal shear capacity in reinforced reduced section (and the welds). The angles need to be sufficiently long so that the bottom flange force can be transferred to the original flange via longitudinal shear of the web. You also need to check overall buckling, and this is where it may get interesting.

 

[Staed79]

csd72: thanks for valuable comment, The book is called "Steel and composite beam with web opening".
It is Steel design guide series 2
2) How do i check the length of the angle member is sufficient and check for overall buckling. Is there any good reference material.
Thanks again for the comment.

 

[JKStruct]

Are you speaking about the two "T" sections created by the WEB opening if you cut a section through the beam at the opening? If so, then yes, the Design Guide 2 formulae are applicable.

 

[JKStruct]

Okay, I reread your question, and I'm confused about what you mean exactly. If the penetration is through the web, leaving both flanges intact, the two flanges with the portion of the web that is still there form a T and an inverted T in section (separated by the opening). Design Guide 2 is the correct resource for this case.

If you are lopping off a flange somewhere along the length, this is a different scenerio, and you need to analyze it as csd suggested.

 

[Staed79]

JkStruct:
The duct that is passing through cuts through the bottom part of flange and web. So the bottom part of the flange is cut just for short distance...

 

[apsix]

Do you mean 'bottom part of flange' or 'bottom flange'?

 

[Staed79]

I hope this drawing makes the matter more clear.

 

[csd72]

Staed79,

1) my comment is that they did not use the word WEB by accident in the title, this publication refers to openings in the WEB not the flanges and therefore is not directly applicable.

2) If this beam is simply supported and the compression flange is restrained then buckling should not be a problem as long as the stresses are within the allowable section stresses. If this is a continuous or framed beam then this is a much more complicated matter the cutout constitutes a discontinuity in the effective length of the bottom flange - the easiest way to rectify this is to provide fly braces each side. Keep in mind that this discontinuity issue applies even if the cutout section is in tension as this still effect the effective length for the end moments.

This is something that should not have been done, dont feel guilty about going a little over the top to make yourself comfortable that it will work.

 

[Staed79]

Thanks csd72;
for your comments