Deck (and future Mezzanine) Beam structural calculator

[xanth]

Hi Everyone,

Hoping to build a deck this summer. Put together a plan and, after a couple weeks, submitted it today. Thought I had it all the requirements according to the 2018 ICC, but apparently my County had different ideas.

They require "Beams | Joists | Headers over 6ft. in length or Structural Calculations prepared + stamped by an Idaho Engineer *IF APPLICABLE". After seeking some clarification, they stated it did NOT need stamped by an engineer, but they required the beam "however, if any of the beams are longer than 6’ we will need the load calcs for them".

All the beams (and joists) for the deck are longer than six feet. I'm lost on how to do the load calculations for them. Beams are standard 2 ply 2x12's, joists 2x12s or 2x10's depending on location.

I've followed all spacing and span lengths requirements for the construction in the 2018 Idaho Residential Code, but apparently still need load calculations per the county.

Anyone have an easy (and understandable) calculator that someone who is NOT an engineer can use?

I've spent a lot of time looking, and have come up pretty empty handed. Seems like it is a requirement here to require a structural engineer, without outright saying the plan needs a structural engineer...

Once my shop is built, I'll building a mezzanine in it (and how it relates to garage journal!), and figure, my county will require these calculations for that too, so I might as well figure out how to do them.

Thanks,

 

[bb29510]

also think about flinch beams

 

[vavet]

For a simply supported beam, the equation is
deflection = (load *length)/(48*I*E)

A simply supported beam just means there are two posts with a beam across them.

load is the weight placed in the center of the beam, also include the weight of the beam here.
length in the length of the beam in inches.
I is moment of inertia. This is a little more complicated. Are you using standard dimensional lumber or an I beam. For standard dimensional lumber, it will be I=(bh^3)/12.
b is the width of it, h is the height of it. So a 2x6 will be (1.5*5.5^3)/12 = 20.8 inches^4
E is determined by the material. For SPF #2, we use a value is 1.35 x10^6 PSI. It'll be different depending on the wood species, type of steel, aluminum, etc..

Put it all in the deflection equation and you'll have the deflection at the center of the beam. Compare that to your modulus of rupture.

There are probably online calculators on the web, but this is the basics.

 

[billconner]

It's not clear to me what they want, starting with just beams or joists also. I think you should ask for an example. There are beam calculators on line. I used one in my permit application (rural NY) for a big beam in my garage. And maybe just print the tables from the code and key number and highlight each beam.

Consider asking same question on the buildingcodeforum.com. A lot of code officials and a deck maven.

 

[theoldwizard1]

First, it would be nice if we had some dimensions !

If the beam is going to span the width of a typical garage (20'-24') standard tables will give you the answer. Depending on the width (front edge to back wall) two 2x12s may NOT be enough. Adding another beam in the middle will help.

The biggest mistake most DIYers make is NOT properly supporting the ends of the beams. The need to have vertical support down to the foundation.