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...