Moment magnifiers for masonry beam-columns

The 2005 MSJC Code does not have consistent provisions for addressing the effects of slenderness. In its strength-design provisions, compressive capacities are reduced by a slenderness-related factor. This approach, while not illogical, is not the best way of handling the problem. In theory, moments should be increased by a moment magnifier.

In the allowable-stress provisions, the compressive capacity of unreinforced masonry is decreased by a slenderness-related factor, and is also checked against elastic buckling using a severe penalty factor that rapidly decreases the allowable capacity as the effective eccentricity increases. This approach, while also not illogical, is also not the best way of handling the problem. It was originally proposed as a conservative substitute for a moment magnifier.

Now that moment magnifiers have been commonly accepted in reinforced-concrete design provisions, and the computational aids available to the designer are much more powerful, there seems to be no good reason to avoid the use of moment magnifiers in masonry design provisions. Work should continue to introduce consistent moment magnifiers into masonry design provisions. If necessary, these magnifiers should be checked using focused research.