I've written a number of articles on fireplace mantels and mantel design. A few of these articles I have posted on Hub pages. The first in the series of articles deal with some of the design considerations (or I should say restrictions) related to fire safety. But the second part of the article considers designing mantel surrounds with columns.  The second article on Hubpages consider mantel surrounds with pilasters.  The following link is to the first article: Mantel Design