Checking defl'n on a multi-material beam

[Signious]

Hello,

I have a funky beam that I have been tasked at checking, it is a 3Ply 1.75" x 14" 2.0E LVL where the contractor went ahead and bolted a steel plate to each side.

The LVL alone can handle moment & shear requirements but doesn't quite cut it for defl'n. I checked the deflection through method of multiple materials by transforming the sections of steel to LVL by:

(E_steel=2x10⁶psi)
(E_LVL=29x10⁶psi)
n = E_steel / E_LVL

then multiply the thickness of the steel plate (3/8 inch) by the n value to get a modified beam of: 1.75" x 3 + 5.4" x 2 =~ 16" wide, ran deflection and it all checked out.

I haven't done anything like this since mechanics of materials class 10 odd years ago - so just want to make sure!

Thanks

 

[Signious]

woups, mixed up my E values - steel is 29x10⁶, LVL is 2x10⁶

 

[jayrod12]

How much deficient are the lvl. My bet is that it's likely ok. Provided the fastening of the steel beam to the lvl is sufficient.

I normally size steel reinforcement to support the entire load and just have the wood transfer the force into the support.

 

[Signious]

The LVL ended up at L/286 for live defl'n and L/160 for total defl'n

I was shooting for L/360 and L/ 240 respectively. When taking the steel into account the total deflection was L/480.

 

[Signious]

It is a fairly long residential span, but they sheeted drywall 1" off of the bottom of the beam & under full load conditions the beam deflected around 1.5" without the steel. Was concerned about serviceability and the beam cracking out the drywall around the beam (dropped beam supporting roof loading).

 

[kushal2944]

your knowledge on mechanics seems fine sir