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Seismic Shift Vice President Research, Office of the 2006

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8  December 2006  R BUILDING HOW WILL YOU THQUAKE? FARE IN AN EAR AS IS T E RJ E H A U K A G H OW INVESTIGATIN AND PROBABILITY SED 3-D COMPUTER-BA AN PROVIDE SIMULATIONS C URE A BETTER PICT  It happened in the early morning hours of January 17, 1994. A small rumble from the depths of the earth steadily grew in strength and intensity to unleash a tremor that would crack cement, crumble brick, bend steel and reduce many “earthquake resistant” buildings and overpasses to dust. Within minutes, 51 people were dead and 9,000 more injured. From San Fernando Valley to Anaheim to Santa Monica, just one shift in the earth’s crust left a path of destruction with few structures unscathed. Although it had a moderate magnitude of 6.7, the 1994 Northridge earthquake proved to be the most costly quake in US history based on the dollar amount of damage. With most earthquake design codes, damage is implied to allow the structure to dissipate seismic energy. How much damage, no design code is capable of predicting, leaving serious questions about their efficacy. “The Northridge earthquake in 1994 was interesting because the design codes did exactly what they were supposed to, namely ensure life safety because there wasn’t a lot of loss of life,” says Dr. Terje Haukaas, assistant professor at UBC Vancouver’s Department of Civil Engineering. “But the damage  was in the billions and this was at odds with owners’ and public’s expectations.” The financial repercussions of the damage sustained in the 1994 Northridge earthquake prompted researchers at the University of California, Berkeley, to pioneer a performance-based approach to seismic-engineering design. Haukaas was among this new generation of structural engineers who abandoned a complete reliance on design codes and began investigating how computer analysis could more accurately simulate the actual behaviour of a building in an earthquake. “I don’t think people realize just how  those analysis models much of an impact y portunity to actuall will have on our op ur of a building,” simulate the behavio “I’m interested in Haukaas explains. the building instead the performance of l orms to code. I fee of that it only conf g -based engineerin that performance t the codes by should complemen al requirements.” In adding to its minim his research partner 2006, Haukaas and a giant leap towards Dr. Ken Elwood took performance-based securing the future of e ocuring a real-tim engineering by pr el through a $0.9hybrid-testing mod dation for Innovation million Canada Foun grant. As one of the New Opportunities Canada, the hybrid first of its kind in g nes physical testin testing system combi ulations in the form and model-based sim models that enable of 3-D numerical structural systems. large-scale testing of nt communication Because there is insta ter and the real between the compu December 2006  9  Photo> Getty Images  “I’m interested in the performance of the building instead of that it only conforms to code.”  10  December 2006  structure in the lab, data can be calibrated from both the numerical model and the physical element for a more accurate account of a building’s global performance. Unlike the hybrid system, current earthquake-engineering experiments rely on data produced by shake tables or hydraulic actuator tests. Shake tables produce ground motion similar to an actual earthquake, but due to sheer size limitations these experiments can only consider individual structural components, like a column or a wall. Tests with hydraulic actuators are even more limited because they can only subject the structural component to varying static loads even though earthquakes subject entire structural systems to dynamic loads. The fact that traditional earthquake-engineering experiments don’t factor in uncertainty is of particular interest to Haukaas. Uncertainties in the structural properties of  a particular building, its material properties, its non-structural content such as furniture, and the amount of force created by the tremors all affect the probability of a reallife building behaving exactly as replicated in a lab. This limits the usefulness of deterministic simulations and predictions. Instead of taking a deterministic approach to seismic design, Haukaas’ research utilizes probability to link computer-simulated numerical models with reliability (the consideration of uncertainties); sensitivity (the response to change); and optimization (the balance between cost and safety). By taking these three aspects into account, Haukaas says models calibrated by hybrid testing provide a more complete and realistic picture of the extent of damage expected to a structure: “Instead of saying the building will behave in such and such a way, there’s a  probability distr ibution here. It may be less satisfying to tell the owner th at there is a five per cent chance of certain damage happening but in reality, you can ne ver be sure about the ac tual outcome.” Fo r those living on the Wes t Coast where ea rthquake hazard is ubiqui tous, building ow ners can benefit from more specific informatio n about how their buildin g will perform in the event treaded by Haukaas and his research team of an earthquake , allowing them to make is still relatively new to the engineering essential decisions about insurance co verage community; his research has been warmly and the necessity for structural up grades. but cautiously received. Haukaas is optimistic Haukaas’ research into performance -based his work will gain momentum as city engineering also provides a pres cription planners and building owners begin to to revise buildin g codes withou t having realize the advantage of understanding how to wait for an ea rthquake to high light the structures will react in an earthquake. For weaknesses of th e current system. “Imagine if that Northrid now, Haukaas is content to look to a future ge earthquake scenario happened here in where performance-based engineering will Vancouver, being the port to the massive As play a vital role in not only saving lives, ian market. It’s going to have ripple effec but saving critical infrastructure and ts from here to Chicago,” he suggests. “But avoiding business interruption as well. In earthquake haza rd isn’t something you addition to the $0.9-million grant from can touch and feel. As such, it can be the Canada Foundation for Innovation a nasty animal be cause it can suddenly jum New Opportunities, Dr. Terje Haukaas also p up and bite yo u. Then people realize, oh receives funding from the Natural Sciences darn, we should ’ve put some thought in and Engineering Research Council of to how we desig n our building to mak Canada (NSERC) and the British Columbia e it as safe as po ssible and avoid business in Knowledge Development Fund (BCKDF). terruptions.” Th e terrain December 2006  11  


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