Coninuous steel beams over columns

[haynewp]

I have a situation where my beam runs continuous over my column and cantilevers about 2' to pick up a small load. I usually try to avoid this detail but this time I cannot.

I have placed stiffener plates on each side of the beam, to help potential rolling over of the beam under earthquake load. I am considering the top of my column adequately braced in this situation. It seems that all this will work if the roof is adequately braced against moving (with small enough deflection).

I understand this detail is pretty common, but I am looking for any add'l opinions and this detail's success under seismic loading.

 

[JAE]

Do you have any members running perpendicular to this beam near the column. Sometimes simply extending a bottom chord/flange angle to further prevent rotation might be a prudent detail in a seismic zone.

That said, we just completed a warehouse project in Los Angeles where we had continuous beams over columns everywhere; used stiffener plates at all columns and did not use these extra angle braces.

 

[flamby]

One add'l opinion. If torsion due to unequal rolling is feared, the stiffeners will not be resisting. In that case you have to check the beam for the torsional effects as well.

 

[haynewp]

Thanks guys!

 

[dik]

I generally try to use continuous steel beams where possible and, except for very light loadings, always use stiffener plates. The stiffener plates, in conjunction with 4 high strength bolts, normally provide sufficient resistance against 'tipping'. I'm not sure why the reluctance to use beams over columns; it's a simple connection to design and analyze.

In addition, with continuous spans, the stiffeners provide additional assurance that the cross section will remain stable at the initial plastic hinge locations (even if not required, although there's not much redistribution with a cantilever <G>). The continuity generally makes for more economical construction (smaller members and fewer pieces to handle). It also provides an increased stiffness for deflection considerations.

I also almost never check for web crippling at supports, preferring stiffener plates; I use stiffeners almost all the time (except for very light loadings).

 

[JAE]

I would second dik's comments. Our policy is to always use stiffeners when beams run continuous over columns. flame's comment above makes sense, but it discounts the fact that the column has stiffness running into the joint as well so the torsional stiffness of a wide flange is really nothing to consider. If the beam tries to roll then the &quot;continuity&quot; between the column, cap plate, bolts, and beam-with-stiffeners will resist the rolling.

Every structural collapse that I've investigated (about 4) has been in part due to the lack of stiffeners over columns. In one case, there were concrete columns supporting steel beams continuous over the columns. Heavy snow (in Texas) initiated a collapse....the roof came down but there still standing were all the concrete columns...nothing but ornamental poles reaching for the sky.

The beams simply rolled off the columns and the columns punched through the deck.