Innovation in Seismic Bracing Design

Over the last decade, one new seismic design technology has been rapidly adopted in the US.  The Buckling Restrained Braced Frame (BRBF) system is one of those rare innovations that radically improves the ability of structures to resist earthquakes, while at the same time is completely backwards compatible with previous technology.  (See MSC articles from Sabelli & Lopez and Robinson for more information)

The ability of this system to resist earthquakes comes from a dramatically simple idea:  decouple bending and compression.  To show how easy this concept is, let us review how the inventor came up with it.  An engineer, Benne Narasimhamurthy Sridhara from Bangalore, wanted to get more strength out of his braces (see my earlier post on braces for more info).  He created a simple physical model using a small rod and a plastic pipe.  He put the rod inside of the pipe and applied force on each end of the rod.  Instead of the rod buckling out of shape and failing, the pipe held it in place.  Brilliant!

A typical column buckling under applied load

Because the pipe (or sleeve) is not participating in resisting compression, it is "decoupled" from the rod.  This means that the rod is continuously braced and will develop full material capacity.  The implications of this small change are huge.  It allows engineers to specify braces that:

1. Will fit easily into existing designs, allowing retrofits and new construction
2. Will act similarly in tension and compression, eliminating the need for paired braces at every location
3. Help dissipate destructive seismic energy by steel yielding (like a car's crumple zone)
4. Remain stiff and strong even after the initial event
5. Cost much less than comparable technologies

It's a really awesome invention (patent info).  The rapid uptake of this technology shows how important it is to the future of seismic resistant buildings.  A recent article from India uncovered a little more of the interesting story behind its creation.  It makes me wonder what structural engineering inventions will be discovered in the coming years. It goes to show that the simplest solutions are sometimes the best, and they are hiding in plain sight.

This technology can be applied in even more interesting applications as engineers grow familiar with its use.  I am anxiously awaiting the first use of this in a bridge application.  Congratulations to Mr. Sridhara for figuring out how to do more with less.