Siobhan Roberts - Wind Wizard: Alan G. Davenport and the Art of Wind Engineering

WIND WIZARD

WIND WIZARD

Alan G. Davenport and the Art of Wind Engineering

SIOBHAN ROBERTS

PRINCETON UNIVERSITY PRESS

PRINCETON AND OXFORD

Copyright 2013 by Siobhan Roberts

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Jacket photograph by Ron Nelson. Courtesy of the estate of Ron Nelson.

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Library of Congress Cataloging-in-Publication Data

Roberts, Siobhan.

Wind wizard : Alan G. Davenport and the art of wind engineering / Siobhan Roberts.

p. cm.

Includes bibliographical references and index.

ISBN 978-0-691-15153-3 (hardcover : alk. paper) 1. Wind-pressure. 2. Davenport, Alan G. 3. BuildingsAerodynamics. 4. BridgesAerodynamics. I. Title.

TA654.5.R636 2012

624.175dc23 2012015170

British Library Cataloging-in-Publication Data is available

This book has been composed in Minion Pro

Printed on acid-free paper.

Printed in the United States of America

1 3 5 7 9 10 8 6 4 2

In memoriam

Alan Davenport

19322009

WIND WIZARD

N o sooner did the Tacoma Narrows Bridgethe worlds third longest suspension bridge, and the pride of Washington Stateopen in July 1940 than it earned its epitaphic nickname, Galloping Gertie. The 4,000-foot structure, its main span reaching 2,800 feet, twisted and bucked in the wind. The pronounced heave, or more technically speaking the longitudinal undulation, caused some automobile passengers to complain of seasickness during crossings. Others observed oncoming cars disappearing from sight as if traveling a hilly country road. By November 7, amid 39-mile-an-hour winds, the $6,400,000 bridge wobbled and flailed, then rippled and rolled, then twisted like a roller coaster, until in its final throes it plunged, with a beastly roar, 190 feet into the waters of Puget Sound.

See for definitions

Speaking to a New York Times reporter the day after the collapse, Leon S. Moisseff, the bridges designer and engineer, was at a loss to explain the cause, placing blame on a peculiar wind condition.

Wind engineer Alan G. Davenport, founder of the Boundary Layer Wind Tunnel Laboratory at the University of Western Ontario, often summoned the memory of the Tacoma Narrows Bridge disaster as a cautionary tale. Most features of this disaster are too familiar to bear repeating, he told his audiences, whether assembled at technical lectures or at popular talks. Both occasions always included screenings of grainy film footage capturing the bridge misbehaving as though fashioned from rubberfootage now preserved, owing to its cultural, historical, and aesthetic import, in the United States National Film Registry, as well as on YouTube, with numerous clips garnering more than six million cumulative views. Nonetheless, Davenport noted, as familiar as this disaster may be to the collective consciousness, the consequences bear continued consideration. Whats past is prologue, Shakespeare observes in The Tempest (and said the jester Trinculo, Heres neither bush nor shrub to bear off any weather at all, and another storm brewing; I hear it sing i th wind). In broadening the moral of the Tacoma disaster and applying it to the behavior of all structuresbridges, buildings, and beyondDavenport made of this cautionary tale a professional credo that governed his lifelong fascination with the wind, and with balancing the winds fickle forces.

Figure 1A. The Tacoma Narrows Bridge displayed torsional oscillation and longitudinal undulation even before it opened on July 1, 1940. University of Washington Libraries, Special Collections, UW21413.

Figure 1B. Photographer Howard Clifford of the Tacoma News Tribune snapped a few shots and ran. University of Washington Libraries, Special Collections, UW20731.

Figure 1C. The bridges main span collapsed into the waters of the Tacoma Narrows on November 7, 1940. University of Washington Libraries, Special Collections, UW21422.

Figure 1D. The new and improved Tacoma Narrows Bridge, 1950. Courtesy of R. A. Dorton.

It was in 1965 that Davenport established the worlds first dedicated boundary layer wind tunnel designed to test civil engineering structures. The planetary boundary layer is the region of the atmosphere extending from the earths surface upward about 3,000 feet, the wind churning the air into turbulent eddies, average velocity increasing with height. A boundary layer wind tunnel mimics these marbled striations of airit mimics wind energyin order to test designs for buildings and bridges that will face the wind when built. Making its debut in the 1960s, Davenports wind tunnel arrived the same decade as the laser, the computer mouse and the Internet, handheld calculators and the ATM, Apollo 8, string theory, and Rachel Carsons Silent Spring. In the years to come, Davenports revolutionary lab would investigate the windworthiness of some of the worlds most innovative structures: many of the tallest buildings, including New York Citys World Trade Center and Citicorp Tower, Chicagos Sears Tower, Bostons John Hancock Tower, Shanghais World Financial Center, and Torontos CN Tower (which, strictly speaking, is not a building but rather a freestanding structure), and many of the longest bridges, among them Floridas Sunshine Skyway, the proposed Straits of Messina span in Italy, Frances Millau Viaduct and the Pont de Normandie, as well as the iconic Golden Gate Bridge and New Yorks Bronx-Whitestone Bridge. The Bronx-Whitestone Bridge, being very similar in design to the Tacoma Narrows crossing, has over the years required an extensive rehabilitation regime that continues to this day.

In addition to the buildings and bridges that came through the lab, there were also a few exceptions and eccentricities. Legend has it that in the early days the lab conducted tests on portable toilets, and later on Arctic tents to be deployed by the Canadian military. NASA commissioned a study on the ground wind loads for the Jupiter launch vehicle (occasionally Davenport said he wished hed been an astronaut). The 2,421-foot illuminated Glorious Cross of Dozul had its day in the tunnel, though it has yet to grace the countryside of Normandy. Sports Illustrated splurged on an investigation of Augusta Nationals twelfth hole, the lynchpin of the Masters famed Amen Corner, said to be among the toughest holes in golf, in part because of the seemingly indecipherable winds (see sidebar, Driving into the Wind, below).