Like most of these Architect’s Glossary posts, this one was generated from a misunderstanding between myself and a client. When they expressed a desire for piers instead of posts, my mind went in a very different direction than they had intended. A quick meeting resolved the issue, but started me wondering on the various terms we use for vertical supports of structures.
I think most of us would describe the elements in the above photo as columns. You could call them posts - they are doing the work of posts - but these guys look entirely too fancy to be mere posts. These are posts:
In terms of structural engineering, there is not a difference between a column and a post. Both are vertical supports that carry a load downward. It does seems that all columns are posts, but not all posts are columns. Columns are the country club cousins of poor posts. Similarly, all pillars are posts, although pillar seems to imply not fancier but certainly larger. Is there such a thing as a small, slender pillar?
These stumpy columns (or maybe pillars?) are in a Frank Furness designed bank building in Philadelphia. They are maybe more like pistons than either columns, posts or pillars, but that’s another topic. In any case, the large stone bases that they sit on are almost too large to be bases and start to fall into the category of piers.
The image above clearly shows what we would call piers, supporting the bridge, spanning the river and extending down into the earth. It may be that direct connection with the earth that sets piers apart from the smaller, more refined cousins of columns, posts and pillars. Again, the piers are doing the same work as their smaller relations, but there is no clearly defined threshold beyond which a pillar or post becomes a pier. There is no Body Mass Index telling us if we are in pier or post territory (although there is a slenderness ratio...).
I think we likely can agree that a number of columns bunched together is called a pier, although that may be more easily agreed upon in a church than the house above.
Finally, we come to the lowly pilaster. The definition of a pilaster is easy to describe - it is an engage column, or rather, it looks like a column embedded in a wall with just a portion exposed.
These pilasters are really just part of the wall, but the architect wants to define and articulate the wall, making the wall look like it is a structure made up of columns that have been filled in between.
So, even those these are really just my own musings on these definitions, it does feel like although post, pillar, column, pier and pilaster are all doing the same work, they differ on their context and intentions. In either case, just don’t call any of these a beam - that would cause enough confusion that the building may not recover.