Single Angle Flexural Design question...

[Hemi79]

Hi everyone, First let me say that I have been reading a lot of the posts in here regarding single angle design. I have looked into the steel manual and examples. I just would like if someone can help me clarify one thing. Let me explain, I am adding 2 single angles of equal legs to a girder which spans 46' in a building done in 1912 (Yeah the owners want to keep almost everything), now I don't know if this will work obviously but I want to see what my design results are. Now being that I will be adding bolts to connect both angles on each side of the girder, this is a 2nd floor by the way,and I have the joists connecting to the girders @ 18" O.C. I figure that I can design this angle as "continuous lateral-torsional restraint". Yes? So am I to use F10-2 or F10-3 equation and simply use my 18" as the "laterally unbraced length of a member"?

Thanks in advance.

 

[CANPRO]

If the joist line up on each side of the girder you can remove remove the existing beam, splice across to make the joists continuous and then add the new steel beam to the underside of the splice.

Probably easier to just add a new beam on each side and leave the existing in place.

 

[TLHS]

If the issue is maintaining the appearance, install a new steel beam, take out the wood beam and use the wood from the existing beam to build a sort of facade box around the new steel beam.

 

[TDIengineer]

I suggest a nice HSS member. You wont have to worry about bracing the top flange, and you could just put it to one side or the other and get the full bending capacity of the element. Then use a long threaded rod thru-bolt with a plate washer to grab all those wood beams.

Ignore the beams altogether, design the new beam for all the loads. Check the wall for the loads and get the wall connx to work.

 

[HermanLJ]

Adding those angles won't do anything. What I suggest is removing the beam, installing an I-section of sufficient capacity, and then cladding the I-section using shaped pieces of the original beam to maintain the appearance.

 

[dhengr]

Hemi79:
In your previous thread about deflection calcs., the 2x10 joists spanned 20' btwn. beams and were spaced at 16" on center. Now they are spaced at 18" o/c, and it seems to me there was some mention of the jst. end bearing on the beam being notched. And, you have not really shown us a good section of the girder and the jsts. bearing on it, to scale, so we can understand the relative locations, sizes, etc. Rather than pick a WF off the self, I might be tempted to fab a box beam, where I can very the width and the depth to better fit this situation. Then, I might extend the bot. flg. on this box beam 4" beyond the two webs, as a seat for a 2x4 or 4x4 onto which the old jsts. can now bear. I would support the existing jsts. on either side of the existing girder, shore them up, remove the existing girder, snap a line on the jsts. and cut them to a new, slightly shorter length, getting rid of the notching. I would nail a new rim jst. to the ends of the existing jsts., then move my new box beam up into position. All we’ve seen so far is some photos which show a whole bunch of junk going on around the existing girder, so you have to really study the details and how you will clean this mess up. So, you can finally get a new girder in there, and properly support it. Also, you still have to study the existing jsts., they might have actually checked under older versions of the bldg. codes, for 2nd floor loadings, but may need some exceptions/exemptions under the latest codes.

 

[hokie66]

dhengr,
In the sketch in his previous thread, he does give a good idea of how the 'girder' is configured. With spacers/splices, the wooden beam is probably 24" wide. Thus my comment above that he will need headers under the wood, over the steel, to bring the load to the steel beam...if he only uses one beam. A box beam might be a bit much. The joists are poorly supported, but that can probably be accommodated with joist hangers. May be simpler, as CANEIT suggested, just to provide a steel beam on each side. Whichever solution is adopted, there will need to be a lot of jacking and shimming to level everything up.

 

[Hemi79]

dhengr: I apologize for the O.C. mistake. They are actually @ 18" O.C. My calculations reflect the 18".

CANEIT: It seems like a great idea. I will look into it. Its not easy adding vertical supports at the ends of the girder because at the end of the 46' span there are rooms on each side. I say this regarding the idea of adding the beams beside the girder. It would put my connection too far from the new girders.

hokie66: I will be implementing headers. thanks.

I have not looked into an HSS member to be honest. I have thought about adding at least one plate over the steel girder for bearing improvement, but the H21x55 works without the plate (except for bearing). As for the facade, the box (fake beam) that is exposed in the ceiling is framed from the girder down to the ceiling height. There is a few ft. difference between the loaded girder and the exposed molding.

I appreciate all the help. I am going to propose the existing girders be considered for removal. I will recommend a thorough inspection to all parties for deflection confirmation. I don't see how the steel girders will eliminate the existing deflection of the wooden girders. Yes it will not deflect for years to come but what about all the movement that has happened. I agree that all this is pretty messy. I have reiterated that to, well I should say WE, we have voiced our concerns strongly in not having complete access to the whole structure. I have personally mentioned it might even end up costing more for them if we end up over designing due to wrong assumptions. I don't like the idea of keeping the existing joists. All that notching is just a hard NO for me. We will propose appropriate connections for all joist to headers over steel girder.

Thanks again.