flitch plate beam for porch

[dgc]

I have a 8' x 65' back porch with a shed roof of tounge-in-groove pine and asphalt shingles. It has a post every 10 feet supporting 4x6 beams. I'd like to join every 2nd and 3rd beam with a flitch plates sandwich, then eliminate those posts, and thereby create two 30' spans - for a better view from the porch. Can this be done with flitch plates? I'm not an engineer/architect and the local ironworks says it doesn't normally create flitch plates form spans over 20 feet or so. There's a photo of the porch at

http://www.nbdigital.com/photos/porch.jpg

if that would help.

 

[ishvaaag]

You can have 30' spans as long as properly engineered. This normally will mean a quite deep beam between the 30' separated columns and maybe the substitution / reinforcing of the columns. Integrity of the beam is paramount.

 

[LPPE]

30' is long for wood. You can make a deep wide flitch work, but I would be concerned with crushing at the supports.

 

[dgc]

Both replies indicate that a deep beam would be needed. That sounds as if I cannot just sandwich the existing 4"x6" beams (which are each 10' long). Also, if I should to this, would I need a single 30' flitch plate on each side, or would flitch plates of say 6' over each of the two joints work? Note: in ref to the last comment, I don't have a problem with doubling the thickness of the support posts (above and below the posts) to avoid compression.

 

[ishvaaag]

In one or another way, you can get your 30' span as you are ready to accept that bigger beam and posts are required. Then you can rescue some of the capacity of the extant members through connections (maybe even gluing as well) to your added structural parts.

So my advice is engage a local structural designer in your area to produce the particular design that suits more your taste, for the additional work can be designed in different ways.