Well, that is going at the problem from the wrong direction - you should use a 3D printer not to print everything, rather to print tools and fittings to manufacture what you need from local resources.
In this case for example a saw making tool & make the beam from local wood using 3D printed gauges.
Wood you harvest and cut yourself is not going to match an I beam on strength, you need engineered wood for that, which involves adhesives and composites.
Not to mention, lots of places on earth don't have local wood suitable for construction...
Or, I'd wager, dropped a 3D printed resin part on a hard floor and watched it shatter like glass.