I'm not sure if you are going to find any code provision that requires a certain bearing length onto masonry. However, other checks may govern the length of bearing such as bearing stresses, the capability of the masonry structure to support the eccentric load from a small bearing length, and the anchorage of said structural steel to masonry. A few places to check would be the Masonry Standards Joint Committee (MSJC) if in the U.S. Also, the attached website could have some valuable information.
Section 5.3 of the steel joists specs requires that joists have a minimum bearing of 4" on masonry unless a detailed bearing analysis is performed. Steel beams generally have more load than joists. 4" would be a minimum for bearing. I generally use 250 psi bearing pressure and size my bearing plate to keep the average stress below this level. Because of beam rotation due to deflection it is a good idea to set your bearing plates back from the edge of the masonry by about 1/2" since the actual bearing stress is closer to a triangular load with the highest pressure at the edge of the masonry. If you don't do this you will frequently see the edge or the block bust off.
