Double angles as beams

[nuche1973]

Has anyone used double angles to support concrete slab and metal deck? Looking at 2" deck with 3 1/2" of concrete (5 1/2") total. I'm getting conflicing advise: been told using anlges as beams is against AISC, but 13th ed has provisions for checking in biaxial flexure. 9th (green book) does a well. My max span would be 6' with a live load of 100psf. The archy is pushing this system citing the old "we have done this before" clause. My original plan was to use W8's (for easier bolted connections), but the project is being VE'd. My gut feeling is that this design is inherent to problems in the future. Any thoughts or suggestions would be greatly appreciated. Thanks.

 

[nutte]

Who told you AISC prohibits using angles as beams? Ever seen a loose lintel? Angles at framed openings in the metal roof deck?

 

[nuche1973]

I've seen those situations, but I haven't seen angles used with metal deck and concrete, except as deck edge and not the supporting beam.

 

[spats]

Your architect is right... it's done all the time. A similar standard detail is to use a double angle beam across corridors in multistory hotel construction to support hollowcore planks, and corridors can definitely be wider than 6 feet.

 

[hokie66]

Why would the architect want double angles? They are generally not as efficient as other sections. Angles have their uses, but as beams supporting a floor slab?

 

[DaveAtkins]

Double angles and single angles are used all the time as flexural members. Walk into many stairwells, look up, and you will see single angle members supporting a concrete slab at the landing above.

I agree with the Architect--why overkill with a W8?

DaveAtkins

 

[KootK]

What will the connection of these single angles look like? Coped vert leg with horiz leg used as bearing? That scenario always bother me when significant loads are involved.

 

[hokie66]

Dave,
Why would you say using a single member rather than two angles is overkill? If a W8 is too big, use a W6.

 

[haynewp]

Angles are used all the time to support RTU's and to frame penetrations in floor slabs. The vertical leg provides a pour stop.

 

[hokie66]

But I think these are floor beams where the vertical legs are down. Probably because the structure soffit is exposed, and the architect wants to dictate the look.

 

[haynewp]

If that is the case, then of course the W section is preferable for efficiency.

 

[nuche1973]

Thanks guys.

 

[BAretired]

Double angles (or single angles for that matter) are inefficient flexural members but they can sustain minor flexural loads over short spans.

BA