Unfortunately, we often learn more from a structural failure than from a project’s success. The cause of such failures can vary from human misjudgments to flawed materials and acts of nature. However, we must glean something positive from each occurrence to improve our practice of engineering.
Several 20th-century calamities have markedly contributed to improving engineering and construction practices in the United States. For example, the deadly molasses tank failure (1919, Boston) and collapses of the Knickerbocker Theater (1922, Washington, D.C.) and Mosholu Parkway Apartments (1936, New York) emphasized the need for designers and builders of major structures to be registered professional engineers (P.E.s). These three disasters advanced a national push to have all structural drawings stamped.
They also spotlighted the need for construction document reviewers to be qualified and for designers to be involved and consulted during construction.
The collapse of the Tacoma Narrows bridge (1940, Bremerton, Wash.), was one of the most spectacular structural mishaps in American history.
The Tacoma Narrows—the most flexible bridge built up to its time—exceeded previous designs in terms of its length, depth, and width ratios. But by exceeding previous parameters, the designers took an unprecedented risk, completely unaware of the implications of dynamic forces. After the structure twisted itself apart, its main designer Leon Moisseiff commented, “I’m completely at a loss to explain the collapse.” It wasn’t until after the failure that engineers understood the significance of aerodynamic forces on long, thin structures—and the danger of exceeding time-tested design paradigms without understanding the impact of all secondary and primary forces.
In more modern times, early computer programs and programmers sometimes overlooked the effects of secondary stresses and other factors. For instance, the roof failures of the Civic Center Coliseum (1978, Hartford, Conn.) and the Kemper Arena (1979, Kansas City, Mo.), alerted the design community to the dangers of totally relying on computer analysis when cutting structural sizes for long-span construction to a bare minimum.
The design community received another abrupt educational experience when it was learned that slab-to-column connection inadequacies and progressive failure were the culprits behind the crash of the Skyline Plaza Apartments (1973, Bailey’s Crossroads, Va.), the Harbour Cay Condominiums (1981, Cocoa Beach, Fla.), and the L’Ambiance Plaza (1987, Bridgeport, Conn.). Progressive failure also played a major part in the collapse of the two World Trade Center towers (2001, New York).
Specifically, both Skyline and Habour Cay structures were made of cast-in-place construction while L’Ambiance was a liftslab design.When the shoring for upper floors of the cast-in-place projects was removed before the concrete reached sufficient strength, the slabs failed in punching shear. The domino effect ensued from the top down. Similarly, the lift-slab problem occurred when the steel-to-steel erection connections proved inadequate. Today, verifying punching shear in thin slabs and stresses in connections between lift-slabs and columns are major design concerns.
The significance of changing details on contract drawings and not having designers involved in field inspections were factors in three different types of failures on three different types of projects.
West Virginia’s Willow Creek cooling tower formwork collapse (1978), which killed 51 workers, prompted the re-analysis of the parameters and reassessed accountability for formwork design. The Hyatt Regency Hotel walkways collapse (1981, Kansas City, Mo.) that resulted in the deaths of 114 people highlighted the long-standing problem of responsibility for the design and construction of steel connections. The Walnut Street Bridge girder collapse (1985, Denver) occurred because no designers were hired to observe construction, and the designer’s drawings were unclear. (Forms were removed before the concrete topping had developed its required strength.) Studying the intricacies of structural failures provides engineers with valuable lessons. Every structural engineer’s library should have books on structural failures. Books such as When Technology Fails, To Engineer is Human, and Why Buildings Fall Down: How Structures Fail should be as frequently consulted as the latest, greatest design textbooks and manuals.
Richard Weingardt, P.E., is CEO and chairman of Richard Weingardt Consultants, Inc., a Denver-based structural engineering firm. He can be reached via e-mail at firstname.lastname@example.org.