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Steel Beam to Concrete Wall Connection

Steel Beam to Concrete Wall Connection

Steel Beam to Concrete Wall Connection

(OP)
I have searched but no real answer. We traditionally use 3/4" embedded plates with 1"x7" studs embedded into the 8" concrete to attach steel beams to the concrete walls. The problem is the connection from the steel beam to the plate. The concrete walls were moved in by 2 inches so we want to weld the two 4x4x3/8 angles to the beam web and fully weld it to the plate. I have heard some concerns about moment transfer and pull out of the embedded plate studs. I have seen this fully welded connection on several projects. Can someone advise if there is a reference and is this a major concern. The beam is a W30x90 and it will extend no more than 1/4" from the face of concrete wall and the top flange will not be welded.  

RE: Steel Beam to Concrete Wall Connection

If you have a double clip angle connection and want it to remain as a simple connection, you can't have a weld return on the top of the greater than 4 times the weld leg or half the width of the part (See ASIC 360-05 J2.2b under the fillet weld terminations - it's item 2 on page 16.1-97).

If you weld the angles all the way around to the embed plate, it will attract some moment and will be a problem for the anchors.

RE: Steel Beam to Concrete Wall Connection

Perhaps I am reading too much into the original post, but if you attach a 7" long stud to a 3/4" plate and embed that into an 8" wall, you only have 1/4" of concrete cover over the studs.  

Other than above, what SEIT states is typical.  Having only a small return will allow the angles to "flex" allowing some rotation.

RE: Steel Beam to Concrete Wall Connection

Why not just bolt them with normal bolts and it will behave more like a single plate shear connection.

RE: Steel Beam to Concrete Wall Connection

(OP)
Sorry the studs are only 5" long and we can't bolt them any more because the holes dom't fit since the wall has moved in.

thanks SEIT..how about I spec. that they only weld the vertical leg of the angle to the beam web. There is sufficient capacity in the vertical welds to hold.

RE: Steel Beam to Concrete Wall Connection

Not welding the top[ flange of the W30 to the plate is a big step toward minimizing the moment transferred to the wall.  

I just don't understand why you are apparently welding the bottom flange.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Steel Beam to Concrete Wall Connection

(OP)
Sorry just to be clear, we are not welding any of the flanges.

RE: Steel Beam to Concrete Wall Connection

If you are welding only the tips of the outstanding legs to the embed plate, the connection should be sufficiently flexible.  I would suggest no return top or bottom.  

If you can decrease the thickness of the angles, flexibility will improve substantially.

BA

RE: Steel Beam to Concrete Wall Connection

AISC recommends a return at the top of the angles equal to twice the weld size, no return on bottom.  Look at Table 10-3 on page 10-47 of the 13th edition Manual.  That's what I would use.

RE: Steel Beam to Concrete Wall Connection

Why not weld a shear plate to the cast in plate and bolt the beam web to the plate?

RE: Steel Beam to Concrete Wall Connection

A beam of that size might be quite long (or maybe just heavily loaded) - Don't forget about thermal changes...

RE: Steel Beam to Concrete Wall Connection

Mike has a good point about thermal changes, I was on a project a while ago that was approximately 250 long without an expansion joint in the middle.  On either sides of the building the steel framed into concrete walls with pockets. Both sides were welded during a hot summer day on july, after the first cool day in september the studs welded on the plates in the pockets made the concrete spall.  If one didnt realize this was the effect of contraction it almost look like the pocket had failed.  The EOR thought with a spacing of about 25' for columns, about 9 columns would allow for enough movement in the connection from the beam to the column.  What was ironic is that his detail actually called for a bolt on the beam pocket but the detailer just called for the weld.   

RE: Steel Beam to Concrete Wall Connection

StructuralEIT describes the corrected welded/welded angle connection.  With a return only at the top of the outstanding legs, the connection is flexible and transfers shear only to the embed.  Welding completely across  the top is not prohibited.   

http://www.FerrellEngineering.com

RE: Steel Beam to Concrete Wall Connection

Welding completely across the top would render it not very flexible.

BA

RE: Steel Beam to Concrete Wall Connection

Welding across the top in excess of a return only, can create a stress concentration in the weld and a crack can occur.   

http://www.FerrellEngineering.com

RE: Steel Beam to Concrete Wall Connection

In that case, why would welding completely across the top not be prohibited?

BA

RE: Steel Beam to Concrete Wall Connection

I don't have my book, but I think it is prohibited.  I have read research that suggests no return is better than a return greater than 4 times the weld size.   

http://www.FerrellEngineering.com

RE: Steel Beam to Concrete Wall Connection

I am inclined to favor no return, top or bottom, but nutte says that AISC recommends a return of 2 times weld size on top only.

BA

RE: Steel Beam to Concrete Wall Connection

Yes. AISC recommends a return of at least 2 times the welds size and not more than 4 times the weld size.   

http://www.FerrellEngineering.com

RE: Steel Beam to Concrete Wall Connection

Sorry. BA.
I just noticed that I said "not" prohibited in the earlier post.  I was thinking not allowed and typing prohibited.  

http://www.FerrellEngineering.com

RE: Steel Beam to Concrete Wall Connection

Both csd72 and I suggested a single plate shear connection, welded to the embed and bolted to the beam.  No one commented.  Is that because you guys don't like that type connection?  

RE: Steel Beam to Concrete Wall Connection

I suppose this is primarily related to earthquake design.  We do most of our connections this way in Australia.  Never seen a double angle connection here.

RE: Steel Beam to Concrete Wall Connection

connectengr,

Okay, I was wondering about that.  The part I still don't get is why AISC wants a return of two times weld size on the top.  Zero return would be my preference.  Is there something wrong with that?

hokie,

I have no particular objection to a single plate shear connection welded to the embedded plate and bolted to the beam web, provided the wall can sustain the moment of R*e where R is the reaction and e is the eccentricity.

BA

RE: Steel Beam to Concrete Wall Connection

BA,

Yes, the wall has to take that moment locally, but usually the studs (or drilled in anchors) are controlling.  Our code actually classifies this type connection as flexible.

RE: Steel Beam to Concrete Wall Connection

BA-

I remember one of my professors from school talking about the return helping to keep the stress concentration away from the weld that we're actually relying on for strength.  I can't say I've actually looked into that, but I do remember that from class.

RE: Steel Beam to Concrete Wall Connection

BA -

The Canadian code also calls for this same return. See CSA S16-01 page 3-65 "Welded Double Angle Beam Connections".

RE: Steel Beam to Concrete Wall Connection

I just checked out the commentary in AISC and it says that the static strength of the connection is not affected by the presence or absence of the return and that it's optional(it doesn't appear optional per the spec), but if it is used the length is restricted to 4x the weld size (as noted in an earlier post).

RE: Steel Beam to Concrete Wall Connection

(OP)
Thank you everyone...I'm planning on requiring a bolted connection for the W30, for all the other beams I will allow welded but with no more than 2x the weld size return  as per AISC. I think the return will help with the stress at the ed of the weld. Any comments on whether the shear plate is better than the double angle in the future.

RE: Steel Beam to Concrete Wall Connection

This is just a personal preference, but for your condition I prefer the double angle because I believe the shear tab will want to dump a moment (equal to the beam reaction times the distance from the face of wall to first line of bolts) into the embed plate.

RE: Steel Beam to Concrete Wall Connection

(OP)
StructuralEIT....I agree

RE: Steel Beam to Concrete Wall Connection

You can use double angles with a bolted/welded knife angle connections.  We frequently using knife angles to embeds, with long slots in the back-to-back legs (requires cover plates) or in the beam web (no cover plate).  Due to the increased eccentricity of the long slots, the bolted connection must consider this eccentricity.  The angles can be erected one at a time, or the bottom flange of the beam can be coped and the web slid between the two angles field welded to the embed.  I do not recommend shop welding the angles to the embed.  The embed plates are rarely located precisely.     

http://www.FerrellEngineering.com

RE: Steel Beam to Concrete Wall Connection

I have used bolted connections for this type application in the past with limited success.  The plate embedded into the concrete often is not flush with the wall, and the walls are typically not cast to tight enough tolerances to allow for easy fit up.

Since you the shear plates or angles will need to be field welded to the plate, field welding to the beam web is not that big a deal.

My preference is angles with a return weld to the embedded and welds with a nearly full return to the beam web.

RE: Steel Beam to Concrete Wall Connection

Why not specify horizontal, short slotted holes if you are concerned about transfering end moments to the embed plate? You still need to design for the eccentricity from the centerline of the bolts to the face of the wall but at least there will not be a mechanism for restraining the ends of the beam.

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