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Engineers investigate Jadwin floor after hoops fans shake bleachers

During the last three home basketball games, enthusiastic students and sellout crowds have rocked Jadwin – literally.

Following last week's Penn-Princeton game – during which students jumped up and down in unison causing the court and ceiling to shake visibly – the University called in an outside consultant to observe the floor during Friday's contest against Harvard.

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Director of Engineering Tom Nyquist called Allen Roth, vice president of Joseph B. Callaghan Inc., an engineering firm located in Philadelphia.

Roth and Nyquist monitored the tennis court ceiling – which lies directly below the basketball floor – during Friday night's game. Roth said he has just begun to look into the structural implications of the vibration, a process that will take several weeks.

"Every structure deflects to some degree," he explained. "The issue seems to be what impact the stands have on the court." Roth said the floor vibrated about half an inch during Friday night's game.

"I did see some of the beams deflecting on the underside," he noted. "But I did not see any of the distress that would signify any structural damage."

The referee's decision to assess a technical foul against the fans on Friday for shaking the court cut short their observation because the fans stopped jumping, Nyquist added.

No danger

Both Roth and Nyquist emphasized that there is no danger to Jadwin itself, only concern about the amount of vibration in the floor.

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"We will review what impact structural changes would make," Roth said, noting that he could not speculate as to what his recommendations would be.

Bouncin' history

This is not the first time in the building's 30-year history that Jadwin's floor has been a source of concern to University officials. In the late 1970s, the University installed diagonal reinforcement braces beneath the basketball court after the floor vibrated during a Beach Boys concert.

"There was a lot of analysis done then," Nyquist said, adding that the evidence overwhelmingly showed that the floor was safe.

However, according to Roth, the University did not place reinforcement braces beneath the area behind the baskets, leading him to hypothesize that fans in those bleachers were primarily responsible for causing the floor to bounce. "The side bleachers seem to be worse," he said.

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Because of Jadwin's unique structure, it has often been the object of research – one student even wrote his senior thesis on the building, Roth said. He added that past analyses of the floor report vibrations of up to six inches.

"What makes this structure so unique is the span underneath," he explained. "What's uncommon is that you have column-free areas." This structure, he added, "can be conducive to vibration."

In addition to investigating the floor, Nyquist said he checked to make sure the bleachers themselves were safe. "The bleachers are in good shape," he said. "There is no structural reason to replace them."

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