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Structural Failure. Overview of the Construction Industry. Structural Failure. Strength of Materials Failure Engineering / Design Error Poor Construction Unauthorized Substitution Loadings Applied that were not Considered. Three Examples. John Hancock Tower, Boston
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Structural Failure Overview of the Construction Industry
Structural Failure • Strength of Materials Failure • Engineering / Design Error • Poor Construction • Unauthorized Substitution • Loadings Applied that were not Considered
Three Examples • John Hancock Tower, Boston • Hyatt Regency Hotel, Kansas City • Citicorp Tower, New York City
John Hancock Tower, Boston Pei Cobb Freed Associates, Architects
Citicorp Tower, • New York City
John Hancock Tower, Boston
The windows in the John Hancock Tower were not the only problem with the building • The shoring for the foundation work came very close to collapse • An engineer determined that the entire building could potentially collapse under certain wind conditions • The engineer who was contacted to save the structure was the same engineer who designed the Citicorp Tower in NYC
Excavation • Shoring Collapse can damage adjacent structures
The building was a much-anticipated landmark from the country's most respected design firm, but has been more notorious for its engineering flaws than for its architectural achievement. Its opening was delayed from 1971 to 1976, and the total cost is rumored to have rocketed to $175 million from $75 million. It was an embarrassment for the firm, modernist architects, and the architecture industry.[3] • During the excavation of the tower's foundation, temporary steel retaining walls were erected to create a void on which to build. The walls warped, giving way to the clay and mud fill of the Back Bay which they were supposed to hold back. The inward bend of the retaining walls damaged utility lines, the sidewalk pavement, and nearby buildings—including the historic Trinity Church across the street. Hancock ultimately paid for all the repairs. • Inventing a way to use the blue mirror glass in a steel tower came at a high price. Entire 4' x 11', 500-lb (1.2 x 3.4 m, 227 kg) windowpanes detached from the building and crashed to the sidewalk hundreds of feet below. Police had to close off surrounding streets whenever winds reached 45 mph (72 km/h). According to the Boston Globe, a scale model of the entire Back Bay was built in MIT's Wright Brothers Wind Tunnel to identify the problem. The research raised questions about the structural integrity of the entire building (due to unanticipated twisting of the structure), but it did not account for the loss of the glass panels. An independent laboratory eventually confirmed that the failure of the glass was due to oscillations and repeated thermal stresses caused by the expansion and contraction of the air between the inner and outer glass panels which formed each window; the bonding between the inner glass, reflective material, and outer glass was so stiff that it was transmitting the force to the outer glass (instead of absorbing it), causing the glass to fail.[4] • In October 1973, I.M. Pei & Partners announced that all 10,344 window panes would be replaced by a single pane, heat-treated variety,[5] costing between $5 million and $7 million. During the repairs, sheets of plywood replaced empty windows of the building, earning it the nicknames "Plywood Palace" and "Plywood Ranch" (the same name as a suburban lumber-yard chain at the time). The joke was that the Hancock Tower was "the world's tallest plywood building". • The building's upper-floor occupants suffered from motion sickness when the building swayed in the wind. To stabilize the movement, contractors installed a tuned mass damper on the 58th floor.[6] As described by Robert Campbell, architecture critic for the Boston Globe: • Two 300-ton weights sit at opposite ends of the 58th floor of the Hancock. Each weight is a box of steel, filled with lead, 17 feet (5.2 m) square by 3 feet (0.9 m) high. Each weight rests on a steel plate. The plate is covered with lubricant so the weight is free to slide. But the weight is attached to the steel frame of the building by means of springs and shock absorbers. When the Hancock sways, the weight tends to remain still, allowing the floor to slide underneath it. Then, as the springs and shocks take hold, they begin to tug the building back. The effect is like that of a gyroscope, stabilizing the tower. The reason there are two weights, instead of one, is so they can tug in opposite directions when the building twists. The cost of the damper was $3 million. The dampers are free to move a few feet relative to the floor. • The John Hancock Tower seen from the Prudential Tower; on the left is Copley Square (and Trinity Church), to the upper left is the Boston Common, on the right is the Massachusetts Turnpike (I-90) and to the top right is Logan International Airport. • According to Robert Campbell, it was discovered that—despite the mass damper—the building could have fallen over under a certain kind of wind loading. It was assessed as more unstable on its narrow sides than on the big flat sides. Some 1,500 tons of diagonal steel bracing, costing $5 million, were added to prevent such an event.[6]
The skybridges connecting the hotel rooms with the ballrooms collapsed when fully loaded with people • 111 people were killed, 200 others were wounded • It was the worst building collapse in United States history up to that time
Kansas City Hyatt Regency, 1981 • 1. Undersized Structural Members
Kansas City Hyatt Regency, 1981 • 2. Substitution of Design without Check
Kansas City Hyatt Regency, 1981 • 3. Insufficient Welds during Construction
Kansas City Hyatt Regency, 1981 • 4. Substitution meant deck carried 2x loading
Kansas City Hyatt Regency, 2007 • Skybridges have been removed / replaced
Citicorp Tower in NYC sits on four huge columns that are not at the corners
Citicorp Tower in NYC sits on four huge columns that are not at the corners
Citicorp Tower in NYC sits above a small church which sold them the air rights to the site. The design allows the tower to rise over the church.
Citicorp Tower in NYC. Every eight floors is supported by a huge truss.
Citicorp Tower • Under Construction • Note the Truss Construction on the Tower Shaft
Section thru the Atrium Space Adjacent to the Tower, indicates height. Imagine if this fell over.
Changes during construction led to a finished product that was structurally unsound. In June 1978, prompted by discussion between a Princeton University engineering student and design engineer Joel Weinstein, LeMessurier recalculated the wind loads on the building. In the original design, the engineer calculated for wind loads that hit the building straight-on, but he did not calculate for quartering wind loads, which hit the building at a 45-degree angle. This oversight revealed that quartering wind loads resulted in a 40% increase in wind loads and a 160% increase in the load at all connection joints. While this discovery was disturbing, LeMessurier was not overly concerned because the original design was padded by a safety factor (which in most cases was 1:2) and the design allowed for some leeway. • Later that month, LeMessurier met for an inquiry on another job where he mentioned the use of welded joints in the Citicorp building, only to find a potentially fatal flaw in the building's construction: the original design's welded joints were changed to bolted joints during construction, which were too weak to withstand 70-mile-per-hour (113 km/h) quartering winds. While LeMessurier's original design and load calculations for the special, uniquely designed "chevron" load braces used to support the building were based on welded joints, a labor- and cost-saving change altered the joints to bolted construction after the building's plans were approved. • Base of the Citigroup Center • View from the street • The engineers did not recalculate what the construction change would do to the wind forces acting on two surfaces of the building's curtain wall at the same time; if hurricane-speed winds hit the building at a 45-degree angle, there was the potential for failure due to the bolts shearing. The wind speeds needed to topple the models of Citigroup Center in a wind-tunnel test were predicted to occur in New York City every 55 years. If the building's tuned mass damper went offline, the necessary wind speeds were predicted to occur every 16 years. • This knowledge, combined with LeMessurier's discovery that his firm had used New York City's truss safety factor of 1:1 instead of the column safety factor of 1:2, meant that the building was in critical danger. The discovery of the problem occurred in the month of June, the beginning of hurricane season. The problem had to be corrected quickly. • It is reported that LeMessurier agonized over how to deal with the problem. If he made it known publicly, he risked ruining his professional reputation. He approached Citicorp directly and advised them of the need to take swift remedial action, ultimately convincing the company to hire a crew of welders to repair the fragile building without informing the public, a task made easier by the press strike at that time. • For the next three months, a construction crew welded two-inch-thick steel plates over each of the skyscraper's 200 bolted joints during the night, after each work day, almost unknown to the general public. Six weeks into the work, a major storm (Hurricane Ella) was off Cape Hatteras and heading for New York. With New York City hours away from emergency evacuation, the reinforcement was only half-finished. Ella eventually turned eastward and veered out to sea, buying enough time for workers to permanently correct the problem. • Because nothing happened as a result of the engineering gaffe, the crisis was kept hidden from the public for almost 20 years. It was publicized in a lengthy article in The New Yorker in 1995.[2] LeMessurier was criticized for insufficient oversight leading to bolted rather than welded joints, for not only not informing the endangered neighbors but actively misleading the public about the extent of the danger during the reinforcement process, and for keeping the engineering insights from his peers for two decades.[3] However, his act of alerting Citicorp to the problem inherent in his own design is now used as an example of ethical behavior in several engineering textbooks.
