Thursday, January 10, 2013

Siobhan Roberts's "Wind Wizard"

Siobhan Roberts is a Toronto journalist and author whose work focuses on mathematics and science. Her first book, King of Infinite Space: Donald Coxeter, The Man Who Saved Geometry, won the Mathematical Association of America's 2009 Euler Prize for expanding the public's view of mathematics.

She applied the “Page 99 Test” to her latest book, Wind Wizard: Alan G. Davenport and the Art of Wind Engineering, and the Rule of the Many, and reported the following:
Wind engineer Alan Davenport’s story begins in the 1960s in New York City, where he set the template for modern wind science by conducting pioneering boundary layer wind tunnel tests on the Twin Towers, then just in the planning stages with structural engineer Les Robertson.

Today, Davenport’s story continues to play out in New York, where the Bronx-Whitestone Bridge, a suspension bridge crossing the East River and connecting Queens and The Bronx, underwent full-scale tests during the onslaught of Hurricane Sandy. The Whitestone, a sister bridge of the ill-fated Tacoma Narrows Bridge that so spectacularly collapsed in 1940, has made numerous visits to Davenport’s Lab at the University of Western Ontario since the late 1960s. The bridge underwent numerous tests and pricey aerodynamic renovations, such as the addition of wind fairings — just as a race car’s spoiler system of fins is meant to “spoil” unfavorable airflow across the vehicle, these aerodynamic devices on bridges reduce drag and lift. The last of the retrofits concluded last year, with the addition of a $136.7million new orthotropic steel deck. But an essential part of the rehabilitation program continued…

From page 99:
Perhaps the most essential principle of wind tunnel testing, Davenport always argued, is to check the results of wind tunnel model studies with actual observations of full-scale performance once the structure is built — test the results, so to speak.
In the 1990s, the Bronx-Whitestone had been put under full-time full-scale monitoring to ensure that the Lab had the best possible measure of its vital signs and the full-scale tests informed the retrofits — the installation of fairings and the deck, among others. And with laudable insight and foresight, the bridges and tunnels division of the Metropolitan Transportation Authority agreed to the Lab’s recommendation that the bridge continue to be monitored for the foreseeable future— just for the sake of the Lab’s and the MTA’s own erudition.

Full-scale monitoring is the Holy Grail of wind testing. The purpose of full-scale testing, Davenport cautioned, was not so much to measure whether the theoretically or experimentally predicted behavior of a bridge held true in reality, especially since one might wait tens or hundreds of years for the design wind to occur. Neither was full-scale monitoring tantamount to testing in a gigantic wind tunnel. Instead, he felt this line of inquiry should be used in ironing out the remaining wrinkles in theoretical models. Theory is innately embedded with uncertainties and unknowns, even in the building blocks, the sometimes still blurry building blocks that scientists perpetually strive to pull into sharper focus. Perhaps not surprisingly, the nature of the wind itself is still the building block of greatest variability.

Prior to the latest round of retrofits, the Bronx-Whitestone endured Hurricane Floyd in 1999, holding its own against 60mph peak winds. With Hurricane Sandy, winds reached peaks of 74-85mph. The Lab and the MTA are currently analyzing the data, but all indications are that the bridge weathered the storm without suffering any troublesome instabilities.
Learn more about the book and author at Siobhan Roberts' website.

The Page 69 Test: King of Infinite Space.

--Marshal Zeringue