Steel Joist Girder Connection at Existing Tilt Panel Wall

[NewbieStruct]

I have a situation where a joist girder sits on a WT that is welded to embed on an existing tilt panel wall. Does the embed take only shear? My senior engineer says since everything is attached, the deck, the joist are in place the connection will only take shear. I feel that the joist girder load will cause an eccentric load on the WT and therefore induce moment on the embed. We are planning to increase the capacity of the floor deck for the building and the general loading will increase by 10 psf. If I account for eccentric load the existing embed fails. If the connection is pure shear it is ok. If I need to design for moment, how should I tackle the problem?

 

[JAE]

I guess I'd see that there is eccentricity unless the joist girder seat and the WT work together adequately for the bending.

Usually the weld from the seat to the WT isn't enough to deal with the moment there.
Either there is moment in the joist girder seat/WT assembly or there is moment on the WT-to-wall connection.
You can't ignore both.

 

[NewbieStruct]

The actual studs attached to the embed are fine in shear,tension and interaction. However, the embed itself is relatively thin. I need it to be 3/4" thick it is 1/2" thick. If I ignore the tension, the plate is fine.

 

[ztengguy]

Did you see the replies to this:

http://www.eng-tips.com/viewthread.cfm?qid=363202

Dont ignore load that is there. If you boss insists you do, find a new boss.

now, have you checked to see if there is any live load reduction you can take, that was not taken before?

 

[CELinOttawa]

This has more to do with stiffness than anything else... If your girder and beam are effectively rigid, and your WT will not rotate, then you MAY have a case for shear only.

This is so rare that many codes make it illegal. In NZ3404 you MUST include a nominal eccentricity.

If you are in seismic zone, this argument is moot as well.

If you see high winds, I'd never consider this argument.

Effectively this is an abuse of St. Venant's principle. Local effects and Global effects at least INTERACT in almost every situation.

Don't design this to be dependent on no e, you'll be in for trouble IMHO.

 

[steellion]

The eccentricity needs to be considered. It's there. How old is the building? Based on ASCE standards for renovations of existing buildings, you may be permitted to assume an increase in f'c. If your loads are close, that may get you there.

 

[NewbieStruct]

Ztengguy, I read through the various post and I believe there is eccentricity. The eccentricity I assumed was half the bearing length of the girder. I have reduced the live loads.

The building is a non seismic 90 mph wind zone. It was built in 2009. The concrete and studs are fine, I am more concerned about the thickness of the embed. How can I increase the thickness of the embed? I don't think it is possible.

 

[CELinOttawa]

You can through- fasten the plate to a far side (exterior) plate, if visually acceptable.

 

[ztengguy]

Can you weld some stiffeners onto the plate beside the WT section to stiffen the plate and take the load?

 

[steellion]

You can weld plates with post-installed anchors to existing embed plate as necessary to increase capacity.