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April - June 1997


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Earthquakes: How Can We Design Structures Less Likely to Fail
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Improving Piston Engines Through Better Ring Design
[Abstract] [References]

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Earthquakes: How Can We Design Structures Less Likely to Fail


During the past decade, earthquakes in California and in Japan have caused the dramatic collapse of freeways, bridges, and other structures built according to stringent earthquake-resistant design codes. A new Energy Laboratory study shows that today's building codes may be inadequate because they are based on incorrect assumptions about earthquake motions--assumptions derived when seismic data were relatively scarce. An MIT team has analyzed earthquake records gathered during the past decade and found that ground motions are more intense than previously thought possible. Moreover, they can vary substantially over short distances, producing differential motions that can endanger and even collapse large-span structures such as freeways and bridges. While theoretical simulations and scale models have been useful in earthquake engineering, they cannot accurately predict how strong ground motions cause structures to fail, hence what building codes and retrofitting techniques will prevent damage. Therefore, the MIT researchers have designed a 30-by-30-meter "shake table" that can hold a full-sized 10-story building or other large structure. Novel electromagnetic "pistons" move individual panels in the table so as to replicate the complex ground motions of an earthquake. A table-top model of the "electromagnetic seismic simulator" (EMSS) has demonstrated the feasibility of the concept. The EMSS is planned to be located at the Idaho National Engineering and Environmental Laboratory as part of a major facility for testing the responses of full-scale structures to earthquakes, wind, and aging.


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Improving Piston Engines Through Better Ring Design


Amajor challenge for designers of internal combustion engines is how to seal shut the "combustion chamber" at the top of the cylinder while the piston is moving up and down. Three rings are mounted on each piston and extend to the cylinder wall to form a seal. But as the piston moves, the rings shift in ways that can contribute to three major engine problems: friction, wear, and oil consumption. A detailed model developed by Energy Laboratory researchers can help engine designers identify new piston and ring designs that will reduce those problems. For a given engine design and operating conditions, the model describes how the rings move, how much friction and wear occur as they encounter other metal surfaces, and how much lubricating oil escapes into the combustion chamber, especially when the rings become unseated. Experimental studies have verified the model's ability to predict ring and oil film behavior. Using the model, the MIT researchers have defined a new friction-reducing shape for the grooves in which the rings are mounted. They have also identified a type of ring behavior that may contribute significantly to oil consumption--a behavior that can be altered by changing the shape of the rings.


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