thi I beam is a lamination in the center of the riser that is verticle to the limbs. It usually shoes on the belly of the riser and in the site window. Looks depend entirely on how it is done. God Bless and hope this helps , Steve PS if you click on my seb site all the bows on there have an ibeam. The good is that it tremendously strenthens and stffens the riser. The only bad is that it cost more to build because it takes a lot more time to make the riser.
In this riser the resish brown wood (Tigerwood) in the back of the riser is the I beam. It is seen in the site window. Notice that the striping continues through it . I will be building all the Talon Takedowns with a phenolic I beam now. It should make an awsome target and 3 D bow with the extra weight and stiffness. This bow is an Eaglewing D and R Longbow. god Bless and hope this helps . Steve