Engineering Disasters and the Weather

During the afternoon of July 14, 1999, the heavy lift crane dubbed Big Blue was hoisting a 400-ton roof section into place on the new Miller Park Stadium in Milwaukee, Wisconsin. During the lift, the crane's sudden failure triggered a chain reaction starting with Big Blue's collapse, and ending with the crane, the roof section being hoisted, and a second crane reduced to a massive pile of rubble. Tragically, three construction workers lost their lives and five other workers were seriously injured. The collapse also left behind extensive damage to the partially-built stadium.




On January 18, 1978, the roof of the Hartford Civic Center in Hartford, Connecticut, catastrophically failed, resulting in a near-total collapse of the roof. Miraculously, there were no deaths or injuries from the collapse, despite the fact that the collapse occurred just six hours after the arena was packed with over 4,000 spectators for the basketball match-up between the University of Connecticut and the University of Massachusetts.


After less than four months since its opening, the Tacoma Narrows Bridge experienced violent oscillations that culminated in a dramatic collapse of the main span on November 7, 1940. While there were no human deaths or serious injuries, the collapse claimed the life of a dog who was trapped in a car stranded on the bridge. In the aftermath, it would take 10 years for another fixed road crossing to be built across the Tacoma Narrows.





What is the common denominator these three engineering disasters all share? The weather was a major contributor to each. Strong winds were the major player in the Big Blue disaster and the Tacoma Narrows Bridge collapse, while heavy snowfall was the main contributor to the Hartford Civic Center collapse. To determine the root cause of each catastrophic failure, forensic meteorologists and forensic civil engineers worked hand-in-hand to reconstruct the weather conditions at the time and location of each event, and then determined how the weather conditions created excessive loading on the affected structures that resulted in their failure.


In the case of the Big Blue crane collapse in 1997, the investigation report cited that surface wind speeds at the time the 400-ton roof section was being hoisted varied between 26 mph and 35 mph. Big Blue--one of the largest cranes in the world--was rated for a maximum wind speed of 20 mph. Engineers on the project also did not consider the additional wind loading on the roof section being hoisted into place. Crane operators expressed concern about strong winds on the day of the collapse, but construction managers elected to proceed with the lift regardless.


Like the Big Blue crane collapse, the original Tacoma Narrows Bridge was a victim of excessive wind loading. The Tacoma Narrows Bridge collapse was due to improper design that never underwent any kind of wind tunnel testing prior to its construction. It was a new kind of suspension bridge for that era which featured a relatively thin bridge deck using plate girders. In contrast, traditional suspension bridges such as the George Washington Bridge near New York City and the Golden Gate Bridge near San Francisco, were built with a large open lattice design that provided stiffness for the roadway and allowed the wind to pass through the structure. The plate girder design of the Tacoma Narrows Bridge acted in a similar fashion to an airplane wing that trapped the wind instead of letting it pass through the structure resulting in lift. Because the amount of lift is proportional to the wind speed, the bridge deck would begin oscillating, first in a sinusoidal wave pattern with light breezes, but then in a twisting motion with higher wind speeds--a phenomenon known as aeroelastic flutter. Exacerbating the situation is that winds increase through the Tacoma Narrows due to the Venturi Effect, a phenomenon where a fluid's speed increases as it moves through a constricted environment. This was present on the morning of November 7, 1940 with winds reaching 42 mph in the Narrows around the time the bridge collapsed.


The replacement span that opened in 1950 had two major design features that were borne out of the lessons learned from the 1940 collapse: 1) the 1950 Tacoma Narrows Bridge was constructed using a traditional open steel lattice deck that allowed the wind to pass through the structure; and 2) the four-lane bridge deck was more than double the width of the original 1940 span that carried only two lanes of traffic, which provided additional structural stability. Moreover, a scale mockup of the 1950 Tacoma Narrows Bridge was subjected to extensive wind tunnel testing before its design was approved for construction.


Wind loads are not the only concern that engineers have when designing a sound structure. The winter of 1977-78 was a particularly brutal winter for the northeastern United States with intense cold outbreaks and several major winter storms, and notably the blizzard of February 5-7, 1978 (Blizzard of '78) that New Englanders regard as their "storm of the century" that all subsequent winter storms are compared against. The Hartford Civic Center's roof collapsed about three weeks before the Blizzard of '78--it was the result of another major snowstorm that struck the region and a roof system that was improperly designed such that it was insufficient to support its own weight, let alone the added snow and ice loads that come with a typical Connecticut winter. The subsequent investigation revealed that the improperly-designed roof began showing signs of deformation almost immediately following its construction in 1975, and deterioration of the roof progressed over the next three years to the point of failure on the night of January 18, 1978. The added load from 4.8 inches of wet snow was enough for the failed roof system to collapse on the morning of January 18, 1978.


In summary, meteorologists play a critical role in preventing engineering disasters like the collapse of Big Blue, the Hartford Civic Center, and the Tacoma Narrows Bridge. The climate data provided by meteorologists is a key piece of information to help civil engineers properly design structures to withstand all of the loads that will be imposed upon them by the weather. Moreover, the tailored weather forecasts meteorologists provide to engineers and construction managers with clear "Go/No-Go" criteria facilitates informed decision-making that will help prevent another Big Blue disaster.



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