structural steel connection design 1

[rfd23]

I am working in North America. client/upper management hires a korean detailing company for structural steel connection. Their typical shear connection detail is close to shear tab/ beam splice connection. We can use this type of connection as per AISC-ASD manual if we incorporate eccentricity moment in connections(refer.pg3-123- vol.2).
I will explain the detailas follows:
beam stops at the edge of girder flange,shear plate is welded to full depth of girder like a stiffener(it is on both side of web). Two plates similar to splice connection(both side of webs) make a connection between girder and beam using bolts to fulldepth of beam. (this is 100% similar to splice connection).45 mm is distance between beam bolts and face of girder flange.
koreans are using e=45mm eccentricity (for all beams) and Mcon= R*45 KN-mm. My opinion is that eccentricity should be equal to the 1/2 of flange width of girder (Mconn=.5*gider flange width*R) as beam stops outside of girder flange face.
Now this moment should be resolved into components and victorically added to shear to get max bolt forces.

Please give me your feed back. I would be greatfull to all of you.

 

[slickdeals]

It appears that the beam bolts are being designed for the 45mm eccentricity.

The eccentricity should be calculated from the girder CG. If you want to be a 100% accurate, then

actual eccentricity = distance of CG of beam bolt group from the girder centroid.

If the 45mm eccentricity is from beam bolt CG to the face of the girder flange, then

eccentricity = ( 45mm + 0.5*girder flange width ) * R

 

[burtonSTR]

It depends on the the stiffeness of girder and the connetion plate.

Girder support was torsion resistance. If you consider girder length=0, it's the situation of Korea's calculation.

 

[rfd23]

thanks both of you. 45mm is distance between beam bolts CG and flange face of girder. e= (45+.5*flange width)is it not too conservative.
I am at home and will attach connection detail and some calculations tomorrow to discuss futher.

Girder is modeleld as simple pin connections both sides. Moreover w sections has very little or no torsional resistance. Torsion will act on girder as Mconn (as per AISC) but it would not be resisted by girder instead will be resisted by connection. once again thanks for your time.

 

[BAretired]

Is there a beam framing into the plate on the other side of the girder web? If so, the two reactions will tend to remove or at least reduce torsion on the girder.

Best regards,

BA

 

[rfd23]

some time beam is on both side of girder and some time not. It is a typical shear connection configration either beam is there or not.

I can imagine that torsion is there, but it is taken by connection, not by a girder. My basic worry is this eccetricity moment(how much) and how to resolve it into connection bolts shears.

 

[BAretired]

rfd23,

If the girder cannot take torsion and the beam is connected on one side only the connection must be designed for an eccentric moment of R(b/2 + 45) as noted earlier by both you and slickdeals.

Bolt shears for eccentric loads on bolt groups are readily available.

Best regards,

BA

 

[rfd23]

thanks. BAretired an slicdeals.
please see attached connection detail and calculation.
review and discuss.

 

[rfd23]

connection calculation is attached

 

[BAretired]

rfd23,

I do not recognize the beam sizes you are using. The girder is H390 x 300 with bf = 300. Does that mean a 390 mm deep member weighing 300 kg per meter with a flange width of 300 mm? If that is correct, it seems to me that your eccentricity is greater than 150 mm. There seems to be something wrong with the dimensions shown.

Assuming the distance from the center of the girder to the centerline of the three bolts connecting the beam is 150 mm, then I agree with your calculation, but I suspect it is more.

Best regards,

BA

 

[DaveAtkins]

I agree with the comments above. The Korean calculation is treating the shear plate like a splice plate, which is incorrect, because it introduces torsion into the supporting girder. The three bolts at the supported beam should be designed for a much larger eccentricity.

DaveAtkins

 

[asixth]

I would be calculating the moment that is required to transmit through the splice and resolve the moment into bolt shears. One of the first designs I ever did was a splice very similar to this, I see if I can did it out at work tomorrow.

 

[BAretired]

rfd23,

The bolt spacing is 60 and 70 in your calculation and drawing respectively. That will help. Also, the bolts are in double shear which will help a lot.

This detail would not have been my first choice. I would prefer to extend the beam into the web of the girder, coping the top as necessary, then use an end plate on the beam and bolt through the girder web. That avoids eccentricity.

Best regards,

BA

 

[hokie66]

I agree with the others that the eccentricity, or lever arm as I would call it, is the distance from the girder web to the bolts in the supported beam. The connection has to resist the resulting moment and shear.

The only reason for using this detail is to simplify shop fabrication and to reduce slightly the length of rolled steel beams required. It will be a nightmare to erect, as you have to install all the bolts, including those in the supported beam, while holding the beam in position. The fabricator is attempting to pass on his costs to the erector.

 

[rfd23]

thanks every body for this usefull discussion. sorry I could not participate earlier.
BA
Beam sizes are as per JIS (Japanese hot rolled section)
beam d=390 bf=300, tf=16, tw=10 mm. weight 107kg/m.

asixth
please check at your work how you did this in past.

hokkie66
it appears to me that this type of connection is normal practice in Korea and Japan. Actually in this particular job fabricator is subcontractor for erector.

I also had a discussion on this in my office and just share with all of you that this type of connection is also recomended in Japenese code.

Please look at pg3-123 vol.2 ASD manual and discuss. after lot of discussion with you guys and in my office,
I am in favour of taking eccentricity as distance between last bolt line (in this case girder bolts) and weld line (weld to the web of girder). this should be our Mconn as per AISC. e for this particular case would be (15+45)
bolts on both should take this moment and also all plates must be design for this moment.
Please review and discuss.
Thanks

 

[BAretired]

What is the vertical spacing of bolts...60 mm or 70 mm? Do you agree that the bolts are in double shear? What is the distance between the center of girder and the three bolts supporting the beam? Why am I repeating myself? Am I having fun? What other fun stuff could I be doing?

Best regards,

BA

 

[hokie66]

rfd23,
Firstly, for a 300 wide girder, I think the bolt to web distance is greater than that. It would have to be (150-5-40=105) per your detail.

But that would just give you the moment in the web stiffener, which is OK by inspection, as it is welded to the flanges. The lever arm for the connection bolts has to be at least the distance between the bolts, which is at least 90 per your detail, but about 200 if you take it to the center of the beam.

If your design is to American standards, you should be dictating the connections, rather than relying on foreign practice. Where is the actual project located?

 

[BAretired]

hokie66,

The eccentricity has to be approximately (bf/2 + 45) which would be about 195 mm. The drawing does not reflect this.

I don't believe we are getting very up to date information on this thread.

So how are things in Australia? Have the fires all died down? Is anyone waltzing with Matilda? Have you had any emu stew lately?

Best regards,

BA

 

[hokie66]

BA,

Yes, the fires are gone for now. Most of those areas have had some rain, so we hopefully won't have any more bad fires until next year. I see they have reduced the official death toll from over 200 to around 175. The problem now is flooding in areas on the east coast. They call it the "Land of fire and water".

Come on down, I'll introduce you to some of the strange local wildlife, the ones we eat and the ones we avoid.

 

[BAretired]

hokie,

Sounds like a plan. I'd love to come. We could enjoy some of the local wildlife and maybe a bit of 'bush tucker'.

Best regards,

BA