Just-in-Time Structures

Conventional structures are sized for maximum loads, but maximum loads don't happen very often.  Wouldn't it be great if we could save material by strengthening structures only during emergencies, so to speak?  At the University of Stuttgart, they're experimenting with hydraulic drives that respond to unusual loads, which permits a structure to be made much thinner and lighter than usual.  In this prototype, a curved wooden shell touches down at four points, three of which end at moveable hydraulic cylinders.  A control system reads the load status at multiple points in the structure and moves the three free-floating points to counteract variable loads resulting from wind or snow.  As a result, the shell can be much thinner than what you'd expect for its huge span:  only four centimeters thick for 100 square meters of structure.

Imagine a bridge built with this system.  You really wouldn't want to lose power to the control system while traffic was on the bridge.


douglas said...

That's very cool, and I suppose a natural extension of where technology is going, and probably arose from active suspensions in cars. The problem I see with it is this: How does an engineer build in the 10-15% (perhaps more cumulatively) safety margins normally built into a structure if the structure doesn't have static numbers to pin down? Perhaps I'm unimaginative, but I can't see how this gets applied to conventional structures- perhaps under specialized conditions like military applications or a Moon base or something like that.

MikeD said...

The biggest problem I see is that such a system works best in a perfect world. We already know that needed maintenance is something that existing infrastructure already doesn't receive. Now, we're adding in an additional point of failure that means that the margins of error are effectively smaller than before. So if there's a loss of power (or pressure), the structure is then woefully inadequate to the needs of load.

douglas said...

Oh, absolutely- Modernists loved the idea of the new industrial materials and methods being used to better regulate the interior spaces conditions, and so started doing things like moveable bris-soleils (basically large vertical louvers usually) or banks of mechanically operated windows. Of course, they would break down, and then the benefits would be gone, and since they were what you were relying on to mediate light and temperature, you ended up with worse conditions than a traditional structure would have given you.

On the other hand, we've gotten better at doing these sorts of things economically, so perhaps in time it can be resolved to be practicable- seismic and high snow/wind load areas would seem to be the most logical uses- increasing load carrying ability rather than using the device to allow reductions of load.

I don't know if loss of power is that great a concern- it's not like an air-supported arch structure (like the Metrodome) where if you lose power the roof collapses even under ideal conditions- in this case, the structure would still stand (unless you've cut structural dimensions to razor thin and are now reliant on the post-loading effect of the hydraulics for structural integrity), but wouldn't have the increased ability to withstand additional loads- so there would be a danger, requiring evacuation.