Steel lintel beam exceeding Lu

[ACE58]

I have a 14" reinforced masonry wall with a 42'-0" opening. I am investigating spanning the opening with a wide-flanged steel lintel beam W36x135 with a bottom plate. If I consider the opening length of 42' to be the unbraced length of the compression flange, the moment capacity is not adequate by the ASD Method, Section F1.3. I realize that the concrete masonry being carried supplies a measure of bracing to the beam, but how much? I haven't found any sources that give me a length reduction factor or a procedure for calculating the reduced Fb other than Section F1.3. I can go a little deeper on beam size, but not much.

 

[jike]

Section F1.3 is what you need to use. I would not count on the wall providing lateral support. If there is a floor or roof within a reasonable distance from the lintel, you might consider bracing to that to reduce the unbraced length of the lintel. For such a large lintel, you might consider two spans with an intermediate column. Another idea is to add a cap channel on a beam to increase the Lu.

Don't forget to limit the deflection per code. Also, don't forget to include lateral load if in a seismic zone or wind load for an exterior wall.

I hope these ideas may help!

 

[miecz]

I don't think you can count on the wall providing lateral support. You may consider the plate as acting composite with the beam, but that makes the unbraced length calculations messy and probably won't help much with a W36. If most of your load is dead load, LRFD may help (did I say that?).

 

[UcfSE]

I agree with jike about not using the masonry to support the compression flange.

I've not used it myself but I've seen details in which a steel lintel is cast into a concrete beam so that it all fits inside the wall. It might be an idea. You may be able to then use some of the concrete cast above the steel as composite to help you out. I don't know how well this turns out in the field.

Then again, with a 14-inch wall, you could probably get a big concrete honker beam to work.

 

[JAE]

A 42 ft. long lintel sounds.....really....long.

I agree with the above. Don't count on the masonry for lateral support. Use additional cap plates...or a cap channel.....or external braces, etc. There is also consideration for lateral wind, seismic, or the minimum 5 psf interior partition loads that may apply. (at least one of them will apply).

 

[JLNJ]

I believe that the 13th Edition has more liberal values for unbraced length allowable stresses than the 9th Edition. You might have a look there.

If this is an exterior lintel you'll be fighting weak axis bending in the beam as well.

 

[dik]

What is above the masonry wall? Can you use the wall as a deep beam? and reinforce it? can you use a shallow beam and tie it up into the wall... I've done a 40' opening supporting double tees at a parkade entrance by hanging the opening into the wall above...

Dik