Responsive Structures

As a proud and unabashed geek, the marriage of computer technology to my chosen field of profession is of particular interest to me. In an article I read recently from Science Daily, “Sensor Sensibility: Better Protection for Concrete Coastal Structures” they introduce a technology that will open the door for a whole new generation of civil engineering.

The article talks about a new sensor technology that can be deployed long-term, semi-permanently into concrete structures to monitor such metrics as pH and chloride levels.  The real news here is not the sensor, those have been around for some time. Instead the real hero here is the extended lifespan. The new sensor has an estimated lifespan of several years, up from just weeks due to the harsh chemical environment found in concrete. This extended lifespan makes practical real-world applications of concrete monitoring a reality.

This is particularly important for the applications of steel reinforced concrete, for example, in a road.  Concrete itself is not susceptible to water corrosion; however, the steel rebar within it is very much so susceptible to oxidation or rust.  This is particularly important in roadways where the use of salt in ice abatement is common practice. Salt and water both will permeate the concrete and reach the steel within. Sensors like these will provide maintenance managers and engineers warning of a decaying structure before it fails instead of waiting for the tell tale sign of cracked concrete and exposed steel reinforcing to make costly repairs.

Although the sensor and the implication of early warning information are both important technological advances, the true future of this technology, the way I see it reaches out much, much farther.

Enter – the integrated world.  Yes, I used a buzzword, but in this case it is actually the correct one. In my opinion the future of almost every field is simply this: integration. The sensors mentioned in this article combined with others such as extensometers, capable of measuring strain on structural members can be combined.

Communication technology has come far enough now that is reasonable to expect devices to communicate effectively between each other. I believe the future of construction, and therefore structural engineering, is in responsive structures.

I define a responsive structure as one that is integrated by a computer system such that it is capable of responding to conditions intelligently.

 Imagine for a moment a busy downtown bridge fitted with strain, corrosion and load sensors. On some random, so –far uneventful day a computer integrated with the bridge’s sensors and a database of historical traffic data determines that: at current corrosion levels of a specific structural member, combined with expected rush-hour traffic that the bridge will likely exceed its safe structural operating threshold. The computer responds by automatically closing the bridge, working in tandem with the systems operating city street lights to re-route traffic while at the same time notifying the necessary people regarding the situation.

These sensors bring us one step closer.

Structural Engineering

What is a structural engineer you ask?  Well, in short it is a civil engineer that has chosen to set his or her focus on solving the problems related to humanity’s impact on the natural world. To further appreciate what constitutes a structural engineer you must define what civil engineering is.

Civil engineering is the profession of understanding and ultimately changing the natural and man-made world. All things related to the environment within which humanity lives out its respective lives fall under the purview of a civil engineer; from the playground swing set a child enjoys to the solid waste management systems aboard the International Space Station (IIS).

Civil engineering, the eldest of all engineering disciplines, finds its history in the artisans of the ancient world.  For millennia man has been, for better or worse, “improving” the world around him. Until relatively recently, we as a species have relied solely upon intuition and experience to construct our society.  Take for example the builders of the Great Pyramids at Giza and the Temple at Karnak. Those responsible for the construction of these once great and still very impressive structures were not engineers, but their works are still standing thousands of years later, how?  It is because their designs were based on their own experience and intuition, a skill that has set humans apart from all other species on the planet.  For example, if I asked you to place a ruler on a table such that it extends as far out from the edge of the table as possible without falling off, you would most likely move the ruler quickly about half-way over the edge, then more slowly until it starts to tip and then lastly, move it back just a tiny bit.  How did you know to do that?  It was because of your understanding of balance. How about if I asked you to build a tower that is wider at one end than the other, which end would you put on the ground? The wider end, naturally. Intuition and experience will get you far, but they can lead to unexpected results when things aren’t exactly what they seem; e.g., the (leaning) Tower of Pisa.

Modern structural engineering takes these observations and intuitions about the physical world and applies scientific methods of identifying the forces at work followed by mathematics to describe and predict the behaviors.  The primary difference between an artisan builder of the past and a modern structural engineer is proof, by way of mathematics.  The artisan will build his house in a fashion he believes will be sturdy against the snow and wind, while the structural engineer will design his house such that he knows exactly how much snow and wind the house can withstand before yielding, and if it does yield he can predict exactly where and how it will break.

Amongst structural engineers there is a little joke that circulates that describes the profession, like most professional jokes, it is likely lost on the uninitiated but it goes like this, “Our job is simple, civil engineers simply balance all forces to zero, because nobody likes a building that accelerates.” We can thank Sir Isaac Newton for this exhibit of dry humor.