Focus on Research
Penn State Intercom......February 14, 2002

New approach
steadies flexible floors

By Barbara Hale
Public Information

An architectural engineer has developed a less-disruptive, more cost-effective, active-control approach to steadying floors that move excessively and annoy or frighten people who walk, work, exercise or dance on them.

Linda M. Hanagan, assistant professor of architectural engineering, said, "People don't think floors should move, and when they do, this motion can be perceived as annoying or even dangerous. This perception of danger can persist, even though no danger is present."

Stiffening or thickening the floors in an existing building to decrease excessive motion is costly and can take months to complete, disrupting the building's occupants, she added. However, Hanagan's new approach can be more effective than other structural retrofits and often takes less than a week to fix the problem.

Hanagan's approach, for which the University recently filed a provisional patent application, uses active control systems installed on the floor or in the ceiling cavity below it to damp the vibrations.

For example, if people are doing the bunny hop, the hop, hop, hop can cause a long-span, steel floor to begin to vibrate in response to the up and down motion of the dancers. Each time the dancers hop, the regular "beat" can cause the floor's up and down motion to increase. Hanagan said, "This happens because a component of the 'beat' is in resonance with the natural frequency of the floor."

Hanagan's solution is to use strategically placed "smart" counterweights that sense the magnitude of the floor's motion and move to apply opposing forces to damp or diminish the vibrations. The active-control system detects when the floor is moving up and down and when to react in the opposite direction to counter the movement.

The architectural engineer notes that her active floor vibration control system is similar in concept to the tuned mass damper approach that is sometimes used to correct floor motion. Both Hanagan's approach and the damper approach rely on a moving mass to dissipate the energy in the floor system. The advantage of the active system, which uses floor velocity measurements to generate the amount of force needed to damp the floor motion, is that it requires less moving mass to get the same degree of control as a damper system. One study showed that a damper system would have to weigh 30 times more than the active control system.

The active system also is cost effective. "As recently as a few years ago, 20 pounds of force cost about $30,000 to generate. Today, thanks to the improved capabilities of commercially available linear motors, we can generate 500 pounds for about $50,000," she noted.

The researcher is currently working on a non-exclusive basis with a commercial partner to apply her approach. She also measures and assesses floors on a consulting basis. In addition, she conducts research to provide design engineers with better tools to predict vibration behavior and prevent vibration problems before a building is constructed.

Barbara Hale can be reached at bah@psu.edu.

Countries with economic ties
are less likely to go to war, researchers say

By Paul Blaum
Public Information

Countries that maintain in-depth financial and economic ties with each other are less likely to engage in military conflict, according to a University study.

"Political analysts have observed for several centuries that international trade inhibits interstate war between countries by raising the cost of military violence," said Quan Li, assistant professor of political science. "Recent studies by John Oneal, Bruce Russett and several others evolve along this liberal reasoning. Our study, however, shows mathematically that it is not the prospective loss of trade, but the costly signaling of resolve by manipulating economic ties that render exchanges of violence unnecessary. Furthermore, we show statistically that compared with trade ties, capital market and monetary policy linkages are more effective in inhibiting conflict behaviors. In short, monetary ties allows countries to fight with money rather than with bullets."

Li, Erik Gartzke, assistant professor of political science at Columbia University and Charles Boehmer, doctoral candidate in political science, collaborated on the research.

The researchers constructed a game theoretic model to compare the opportunity cost and costly signaling arguments. The model shows that the benefits of interdependence have no discernible effect on the probability of conflict, but a country's willingness to signal costly resolve by manipulating the interdependent ties decreases the probability of fighting. The authors also argue for a notion of interdependence that covers not just trade ties but also capital market and monetary policy linkages. The researchers examined a sample of political relevant dyads from 1951 to 1985.

A country on the verge of hostilities with another country already knows the monetary value of its trade with that other country. Therefore, the researchers said, the risk factor in terms of trade is not an unknown. However, what each country doesn't know is how strongly the other country is willing to fight over some other issue beside trade: a slice of territory coveted by both countries, a military build-up perceived as a threat or the mistreatment of an ethnic or religious minority, they noted.

"Interdependent countries are in a better position to test the resolve of economic partners because they can more effectively exert non-violent (i.e. economic) pressure, and then observe the consequences," Li noted. "By taking commercial measures that represent both a clear and credible threat, a state can signal to economic partners that it is prepared to make considerable sacrifices. If, however, these sacrifices are too critical, the country could lose bargaining power in future conflicts.

Paul Blaum can be reached at pblaum@psu.edu.

Maranas to develop
research with grant

Janna K. Maranas, assistant professor of chemical engineering, has received a five-year grant from the National Science Foundation's Faculty Early Career Development (CAREER) program. The CAREER program is designed to help scientists and engineers develop their research and teaching simultaneously as their careers get under way.

Maranas' research will focus on understanding the relationship between intermolecular packing and short-time dynamic behavior in polyolefins, a class of polymers used to make everything from plastic bags to milk bottles to children's toys. Short-time dynamic behavior underlies the glass transition; whether a material is above or below this transition is the single most important physical property when considering applications of polymers.

For the educational component of the grant, Maranas will develop research-oriented activities for students who would not otherwise have such experiences. She will introduce experimental simulation problems into core chemical engineering courses and develop a class in which students learn how to use and interpret simulation data. She will develop a research program for undergraduate students at California State Polytechnic University, Pomona, an industrially oriented university with no formal research program. Selected Cal Poly Pomona students will spend a summer at Penn State working on research in her lab as part of their senior thesis projects.

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