I hadn't heard of LVL beams. I've done a little bit of work on a home we sold and we were sistering 2x12s, 3 wide to cover a 24' span. Of course, this was in a humid 'mechanical' basement that had adjoining crawlspaces connected to it. I'll have to read about how LVL beams are created, can't see how they can be stronger than timber but I'm surprised every day.
The wood grain direction is really a huge variable in conventional lumber and its material properties and strength vary on several factors but mostly on the grain direction and and it what direction the load is applied realtive to the grain. Wood is strongest when load is applied parallel to the grain and parallel to the deeper dimenison so depending on your use you typically want a beam to be deep in the direction of the loading and with the grain parallel. With conventional wood this is not always 100% the case along the length of the member. LVL takes the grain direction and normalizes it along the length of a member and homogenizes it so the same strength and section properties occur along the whole length. There are no knots, loss of sections, wierd grain pattern changes etc. There are also significnat differences in the species of tree and their mechanical properties. Pre-engineered beams can be made to order to suit whatever you need wher eas conventional wood is based on the species and a whole lot of other factors you have to consider. I am very used to using Southern Yellow pine but if I had to use cedar or spruce I'd have to spend time becoming familiar with their properties.
The propblem is that LVL are glued and pressed together so sometimes there are failures in this part of the process. LVLs can be up to 2.5 x stronger than a conventional lumber of similar size though so its more bang for your buck especially if space is limited.
Laminated Veneer Lumber (LVL)
LVL is a widely used structural composite lumber product. It is produced by bonding thin wood veneers together in a large billet so that the grain of all veneers is parallel to the long direction. The LVL billet is then sawn to desired dimensions depending on the end-use application. Because LVL is made with scarfed or lapped jointed veneers, LVL is available in lengths far beyond conventional lumber lengths.
Popular LVL applications include headers and beams, hip and valley rafters, scaffold planking, and the flange material for prefabricated wood I-joists.