I want to design a cantilever addition. Over the driveway so I can't add supports.

I want to use the calculator here https://calcresource.com/moment-of-inertia-rect.html

But I'm having trouble figuring out the inputs. Specially the Young's Module and moment of inertia. What would those values be for a 3.5 inch x 12 inch glue laminate beam?

The load on the beam will be part uniform and part point load. Can I calculate the deflection for each and add the results together?

  • 2
    $\begingroup$ You shall looking for professional (structural engineer) help in the formal setting for your own good. Good luck. $\endgroup$
    – r13
    Mar 12, 2021 at 3:28

1 Answer 1


It seems their solver is okay, I tested it with a bunch of beams and the answers were correct.

You have to enter the exact values of your beam usually something like 3 7/16" by 11 7/8" or sometimes in decimal fractions. You need to find the manufacturer's datasheet which will give you pertinent info like the $f_c,$ service moisture content, shear values, fasteners, A whole bunch of information.

And On the loads even though you can add them, there are loads that are a bit complicated, such as wind loads and seismic loads.

Not to intimidate you, but all these loads have an effect on the existing structure and need to be accounted for. You may well have to add new Posts, shear walls, shear transfer beams, a new foundation.

Things may seem easy at the beginning but quickly turn into a totally different ball game. Many cities will have you upgrade part of the existing structure affected by this job to the most recent applicable code.

Many cities will advise you for free, and may even give you some handouts as to what to do.


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