Friday, July 16, 2010

The magic of Anchor Ties

This is the view from my kitchen, at the back of my Dutch apartment.  I look out across rooftops, taking in a few steeples and lanterns, tiled roofs and brick walls (and the bothel, out of sight to the left).  And, over breakfast one morning, I started musing about the iron bars, some with curlicued ends, scattered over the walls (close-up, right).

What are they; why are they there?

Okay, I’ve done my research, and they’re kind of cool.  Bear with me.

These are wall anchors (also called anchor ties or anchor stays), and I’ve found them everywhere since I started looking for them.

Consider the  brick-wall facade (left).  It’s really just a thin veneer laid against the the building behind it.  It doesn’t have any particular structural strength (it’s just a stack of bricks), so how does it stay up against the rest of the building?

The answer is to extend a bar from the building structure through the brick wall, then fix it in place with a wide, flat crosspiece that distributes the restraining force across a broad area of brick facing.

Look at the example (right) from Ghent.  See the loop at the center of the bar, which is the tip of a rod extending back into the building.  The iron crosspiece has been pushed through the end of the tip and is pulled back flat against the wall, holding it against the building.

And pulling the wall against the structure behind it.

Well, I think it’s cool…

Lines of anchor stays trace out the structural elements of the building behind it.  So, where the building has a floor, the joists are extended through the facing wall and tied in place with a row of anchors.  Looking at the face or a building (below), I can trace the floors within.

Same thing holds for unusual places: a roof at the top of a belltower is held in place with a ring of anchor bolts; the slanted roof is behind a diagonal line of them.

And once I start to notice, I see lots of them, in enormous decorative variety, on bridges, walls, everywhere.  I find that they tell a lot about the buildings and structures behind them.

They are also wonderful little grace notes applied by builders like signatures to their work, sometimes with numbers, artisan signs, or decorative whorls.

‘really worth noticing.


Amanda said...

Remarkable. I've been wondering about these too, but hadn't gotten around to looking them up. Thanks for getting to it first. :)

patti said...

Cool! The lack of them on building around here must be why the bricks tumble off sometimes. There are a lot of old brick buildings being repaired this summer.

Dave Hampton said...

Thanks, Amanda -- If I've gotten it wrong, let me know?

Patti, about old buildings: I've been trying to see if I can determine when Anchor Ties stopped being used widely. Lots of brick buildings have dates on them, and it looks like use falls off in brick construction after the early 1900's?