replace flitch beam with steel I beam 1

[jgrasmehr]

what size steel I beam would I need to replace a flitch beam that is constructed of 2 doug fir 2x12x20ft with steel plate bolted inbetween. this beam supports roof truss's on 24" centers and are approx 30' long with support in center.

Jgrasmehr

 

[Trussdoc]

For a meaningful answer, we would need:

The span of the beam to be replaced
the code loading on the roof trusses
Constraints on depth, deflection etc.
Is this beam at the internal bearing of the roof trusses or in an exterior wall?

 

[boo1]

Why not use the classic approach of designing to the load; sizing the new beam for Bending, Shear, Deflection, and Bearing instead of sizing an equivalant beam.

 

[jgrasmehr]

the span is 20 ft and support roof truss's on 24" centers and load requirements are 20 lb live load. this beam is open in the garage and sets on exterior walls. The garage door is located approx 2 ft out from this beam. The depth of the beam max would be 10" but I have a 4 1/2 x 8" I beam available.

 

[boo1]

You still have not provided the beam loading (only the LL/sqft), or the available I beams weight. The following is my estimate

Assuming:
LL=20psf
DL=10psf
span=20'
Lu (Unbraced lenght)=20'
tributary area=30/2 + 2/2 = 16' using 1/2 the 30' span + 1/2 the 2' between the beam and garage
steel= A36
pinned end conditions
load duration factor=1
W flange
deflection allowable L/360

Summary
W8x28 is the min size
12,530 psi bending stress
2,210 shear stress
Max def .664"

You can of course, determine the bearing and attachment methods.

 

[sc]

jgrasmehr,

How about you contact a local engineer to look at your specific problem, this site is not really the place to get a specific answer.


regards
sc

 

[boo1]

Of course SC is correct. Its cheaper to do it right the first time. To correctly design a beam and commections here would be ..... JGRasmehr the sizing is accurate only if my assumptions are correct. the connections, support and foundations are just as important as the beams load carring capacity. With all that said ... cheers