In 1987 the University of Washington hoped to add to their football team's home, Husky Stadium. This addition was to be a 17,000 seat addition to the North side of their stadium completed in time for the next season's opening game against Stanford on September 5th, but the events of February 25, 1987 would make that goal seem very unreasonable (Griffin). That morning was a sunny clear day at the University of Washington, but something unusual was noticed by some of the construction workers on site, a large crack in the steel frame had begun to form. At 10:07 AM a loud bang was heard all across the UW campus followed by the entire collapse of the North Stands Addition (Griffin). The entire 12 second collapse was documented in the time lapse photos shown below.

After an extensive investigation, the overall design of the structure was deemed sufficient and  collapse was caused by insufficient lateral bracing during the construction process. The roof structure included guy wires which kept the roof structure from experiencing unusual torsional forces on the structure, and the demolition process required cutting of these guy wires. This had to be done in a very controlled and methodical sequence. Unfortunately some of these wires were cut out of order. This resulted in the twisting of the structure which caused the original crack in the roof truss support beams mentioned earlier (Griffin). 

One contributing factor to the cause of the collapse was how the tubular guy wires were originally designed. Generally when tubular sections are designed it is assumed the section stays circular when subjected to deformations (Chen 1988 p. 1088). A report done on local and post-buckling behavior of tubular beam-columns shows that tubular sections with walls significantly thinner than the diameter of the section subjected to significant deformations can experience local buckling and distortion of the cross section. The local buckling and distortion of the cross section causes a reduction in the load carrying capacity and the energy absorption section of the guy wire (Chen 1988 p.1088). When the workers cut the guy wires out of order, they subjected the remaining guy wires to loads well above the original design loads. This could have caused large deformations which reduced the roof structure’s ability to resist the wind loads experienced on site. 

The engineer's field observations at the incident site revealed that neither temporary bracings necessary for the safe erection of systems-engineered metal buildings nor permanent wall bracings required to resist lateral loads as shown in the manufacturer's drawings were installed.

the subcontractor responsible for the erection of the systems-engineered metal building did not follow the guidelines indicated in the manufacturer's drawings and the procedures specified in the installation manual developed by the manufacturer to safely erect and maintain the structural stability of systems-engineered metal buildings during construction.

Had the erector followed the procedures specified in the installation manual developed by the Metallic Building Company with respect to temporary and permanent bracings and had the erector complied with the OSHA regulations pertaining to the erection of systems-engineered metal buildings, he would have avoided the collapse of the systems-engineered metal building and thereby prevented the resulting loss of life and injuries.

It is believed the site team had clocked off for the day just minutes before the collapse.

HSE investigators have still to determine what caused the steel frame structure on the Ashe Construction site to collapse, despite eyewitness speculation.

Ashe confirmed to the Enquirer that the steelwork contractor on the job is Norfolk based DGT Structures.
It is believed steel beams spanning the building’s main auditorium failed bringing down surrounding steel work.

A statement by Ashe said: “An Ashe rapid response team visited the scene and assisted the emergency services in securing the site last night.  A 60m exclusion zone has been put into place.
“The site has now been handed back to us by members of the emergency services, and the Health and Safety Executive and forensic experts will start investigations into how and why the collapse occurred.

“Ashe Construction is doing all it can to assist the HSE and other appropriate parties.”
Eye witness Mick Pandher told the Ilford Recorder: “I looked towards the building and I thought it was a thunder storm at first.

“Seconds later, I saw the whole building going to the floor.

“It was very sudden. It was like when you see a building being demolished. It came down in a straight line.”

A Fire Brigade statement said: “Our specialist urban search and rescue (USAR) crews were called to a collapsed building on Clements Road in Ilford. Six fire engines and four fire rescue units were also at the scene.

“The five storey building was under construction.

“The steel frame surrounding it collapsed and scaffolding from the construction site also fell into a nearby car park, damaging six cars.All 22 construction workers on the site escaped uninjured.
“USAR crews used specially trained dogs to complete a systematic search of the area and were able to confirm that no-one else was involved in the incident, although one passer by was treated for shock by London Ambulance Service.

“A crane on the site was left in a precarious position after the building collapsed and a 60 metre safety cordon was established.”

Work on the site started last June with construction due to last 16 months.

The Puerto Rico OSHA, thru Region II, requested the Directorate of Construction to provide engineering assistance for causal determination and to identify potential OSHA standard violations. A structural engineer from the Office of Engineering, Directorate of Construction, visited the incident site on November 8, 2005. At the time of his visit, all failed structural members were already removed from the site as per the demolition plan. Construction in the failed area was not renewed.

Until an official inquiry is completed, the precise cause of the collapse will be unclear. Theories range from design faults and construction errors to a rush to finish the job and budget constraints. Paul Andreu, the architect who designed the terminal for Aéroports de Paris (ADP), the state-owned airport company, and Hubert Fontanel, the chief engineer, each confirmed that there had been cracks early on, but insisted that the problems had been resolved. Mr Andreu said candidly that he “didn't think that he'd made a mistake” in the design, and added that the project had been under cost constraints. The possibility that the entire terminal might have to be pulled down has not been ruled out.

This is bad news for ADP. The company has been trying to build up Charles de Gaulle, the world's eighth-biggest airport, as a rival to London's Heathrow and to Frankfurt. The new terminal, with another satellite under construction, is due to serve the Airbus 380, the giant 555-seater aircraft scheduled to begin flying in 2006. ADP has also been winning lucrative design work for airports abroad, including new terminals at Abu Dhabi and Shanghai. Such ambitions may now be open to question, as will government plans to start privatising ADP next year. For Air France, too, the collapse is a setback. The terminal is critical to the airline's efforts to create a hub for its flights and for those of its partner airlines in the Sky Team alliance.

The investigation conducted by the Dutch Safety Board revealed that the roof structure’s insufficient stability, and therefore the risk of collapse, was caused by several factors. The main factor was the absence of essential coupling pipes at the back ends of the roof beams and stabilizing connections in the roof structure. During assembly of the roof beams, steel cables were used as a temporary stabilizing measure. The last stabilizing cable was removed on the day of the incident. In addition, the roof structure was already being subjected to additional loading by a video wall, suspension bridges, piles of roofing sheets and the workers present. The investigation also revealed that the roof structure was being subjected to additional loading as a result of dimensional differences between the concrete beams of the stand, the foundation of the steel structure and the steel structure itself. These dimensional deviations in combination with insufficient adjustment options mean that parts of the roof structure could only be inserted by exerting deforming forces. The deformation caused additional tension that reduced the load-bearing capacity. The combination of tensions in the structure as a result of its own weight, dimensional deviations, the load already present and the absence of stabilizing measures caused one of the roof beams to fail as a result of the forces to which it was subjected, which initiated a total collapse 

As a result of this accident, twelve workers fell from a great height. Two workers were killed and nine injured, a few of them critically. One worker escaped with bodily injury 

The Hyatt Regency Hotel walkway collapse did not occur as a result of innovative design, construction or material use, but rather as a product of numerous management errors. It was these fatal management errors that resulted in the flawed construction detail to be used in the support system of the walkways of the Hotel Atrium (Moncarz, Fellow, and Taylor 2000). Various events and disputed communications between G.C.E. engineers and Havens Steel Company resulted in the design change from a single to a double hanger rod box beam connection on the fourth floor walkways (Texas A&M University 2009). The original design detail of continuous threading of the nut through two stories of the building appeared to be impractical to the contractor and as such he changed the design drawings (Shop Drawing 30 and Erection Drawing E-3) and replaced the original single hanger rod design with a two rod system. In the two rod system, one rod goes from the lower to the upper bridge and the other goes from the upper bridge to the roof truss (Moncarz, Fellow, and Taylor 2000). This change in the hanger rod more or less doubled the load to be transferred on the 4th floor box beam-hanger rod connection (Marshall 1982). The design load for the fourth floor walkway was 20.3 kips (90 kN) when under the new design system the connection should have had a design load of double that, 40.7 kips (181 kN) (Texas A&M University 2009). The original hanger rod design would have been able to hold the load at the time of the collapse (Marshall 1982). Within a year, the box beams resting on the supporting rod nuts and washers were deformed, so that the box beam resting on the nuts and washers on the rods could no longer hold up the load, thus the box beams detached from the ceiling rods and the fourth and second floor walkways of the Hotel. Had this change in the hanger rod design not been made, the maximum capacity of the design connection would have been far short of Kansas City building code requirements which require a minimum value of 33.9 kips (151 kN). The value for the original connection would have been approximately 20.5 kips (91 kN) meaning that the original connection capacity would have been only 60% of what was expected by building codes (Texas A&M University 2009). Apart from the design change, poor management and decisions on the part of the construction firm and engineering firm, and the failure of the connection to meet building codes, other factors resulted in the collapse of the hotel. Quality of workmanship, improper welding and connections, inadequate building material, failure on the part of the hotel to hire building inspectors as well as failure of the building inspectors to allow the building to be occupied despite its hazards were also factors in the collapse (Kieckhafer, Moses, and Warta 2010).

As a result of the fatal miscommunication, the American Society of Civil Engineers has now set the precedent that responsibility lies with the engineer's seal. That is, that whoever places their seal of approval upon a set of plans carries the responsibility for the building and the outcome. It is now also required that all load bearing calculations must be checked by a city appointed engineer and that checks be formal and not “spot checks” (Luth 2000). As an industry, it is important for all responsible parties (architects, engineers, fabricators, etc.) to understand the challenge learned as a result of this fatality. Design presents the industry with a challenge to anticipate any failed detail and to correct it within the design process

In 1991, a new housing development project, known as Bukit Antarabangsa Development Project, commenced construction on the hilltop located behind the Highland Towers. The hill was cleared of trees and other land-covering plants, exposing the soil to land erosion that is the leading factor of causing landslides.

The water from the new construction site was diverted into the existing pipe system used to divert the flow of East Creek. This overloaded the pipe system and water, sand and silt from both East Creek and the construction site of Bukit Antarabangsa. infiltrated the pipes. The pipes burst at several locations on the hill, and the surrounding soil (behind Block 1) had to absorb the excessive water. The monsoon rainfall in Dec 1993 further worsened the situation.

The water content in the soil became over-saturated to the extent that the soil had turned viscous, in effect becoming mud. By the end of Nov 1993, the hill slope had been saturated with water, and water was seen flowing down the hill slopes and the constructed retaining walls.

Shortly thereafter, a landslide took place and destroyed the constructed retaining walls. The landslide contained an estimated 100,000 square metres of mud – a mass equivalent to 200 Boeing 747  jets. The soil rammed onto the foundation of Block 1, incrementally pushing it forward. After of that constant pressure, the foundations of Block 1 snapped and in December 1993, residents began to see cracks forming and widening on the road around the Highland Towers  a forewarning of collapse. Unfortunately, there was no further investigation before Block 1 collapsed on 11 December 1993.

After the crane was rigged to the steel frame, the workday ended.  Two ironworkers, who were exiting the job trailer, observed the structure fail. The failure occurred approximately 15 to 30 minutes after the crane was released from the paired joists.

The following assumption were made for the analyses:


Though the joists were interconnected with the bolted diagonal bridging at eight locations, the bridging lines were not anchored to any terminus point where the bridging forces could be transferred. In the absence of any viable load path for the bridging forces to be transferred and resisted, the bridging lines were considered inadequate to provide any effective translational restraint to the top chords of the joists and thus could not effectively brace the top chord. If the unbraced length is considered to be the entire span length of the joist as discussed above, the maximum capacity was determined to be minimal

On January 28, 2006, in the midst of a frigid Polish winter, the Katowice Trade Hall was hosting the 56th National Exhibition of Carrier Pigeons. What the 700 people attending didn’t know was that the managers of the building had not had the snow and ice removed from the roof. Damningly, the roof had buckled under the winter snow four years earlier and been rebuilt without being properly inspected or tested.

On this fateful day, the accumulation of snow overloaded the roof of the building by 100 percent, and the roof smashed down on the exhibition, trapping hundreds of people beneath its weight, and exposing them to dangerous sub-zero temperatures.

Rescue teams poured in from the surrounding areas, braving the terrible weather. The building, however, was still unstable, and a second section of the roof collapsed during the rescue effort.

The lacerated metal acted like a freezer, further endangering survivors. Still, rescuers couldn’t heat the air under the ruins because parts of the building were supported by nothing more than piles of snow.

In the end, 65 people died and more than 170 were injured. The architects and managers of the building all faced criminal charges.

Almost immediately the bridge began to wobble from side to side. The oscillations increased to a magnitude of nearly 70 mm near the middle, large enough to force people to cling to the banisters. The engineers were immediately notified and attempted to mitigate the bridge sway by controlling the number of pedestrians. However, even smaller crowds, well under the bridge’s 2,000 person operational capacity induced lateral movement in the bridge. The Millennium Bridge was closed 2 days later in order to diagnose and remedy the failure.

Several factors played into the unforeseen behavior of the bridge under pedestrian load. Arup engineers understood that the normal gait of humans generates a small lateral force for balancing purposes. However, engineers expected the random step of the pedestrians to largely offset this lateral force, and focused more on the vertical force caused by walking that has been understood and documented in design code and specifications.

What caused this underestimation to manifest itself in the Millennium Bridge more so than many other pedestrian bridges around the world had to do with the natural frequency of the bridge itself. Due to the sleek design of the bridge, the suspension cables run along side instead of well above the bridge as in the Golden Gate Bridge and other traditional suspension bridges. These suspension cables, therefore, were pulled more tightly between supports, increasing their tension and decreasing their length. These properties of the suspension cables along with the relatively light aluminum decking of the walkway, acted to raise the natural frequency of the bridge to very closely match the frequency of the human walk. 

The Arup engineers were correct in their assumption that people walk in a random fashion, but failed to understand that even in a random model, a portion of the people are destined to “match step.” In the case of the Millennium Bridge, the unintentional matching of step by a fraction of the crowd was able to induce lateral motion in the bridge. As the motion manifested itself, more and more people began to match step with the motion in order to balance themselves, therefore, magnifying the oscillation of the bridge. 

There were two options available to correct the failure. One option was to stiffen the bridge considerably to move the frequency outside of the excitation zone. The other option was to add a system of dampers to absorb and dissipate the lateral energy applied by the pedestrians. It was decided that stiffening the bridge would cause too serious a change to its physical appearance, and therefore, an extensive dampening system was designed. Arup underwent a $8.9 million dollar renovation installing 91 dampers in the bridge in order to disrupt the natural frequency and absorb the energy of the lateral movement. The Millennium Bridge reopened 18 months later. 

The media, and even occasionally highway agencies, have done a poor job of reporting exactly why the I-35W Bridge collapsed. This has led to additional misunderstanding about whether other truss bridges, whether or not similar to the I-35W Bridge, pose a collapse risk. Some explanations and thoughts about the I-35W Bridge collapse follow.

The I-35W Bridge collapsed because the gusset plates that formed the connections for the truss bridge members were not thick enough and as a result lacked the proper strength to bear the load the bridge was designed to bear. This problem was not detected when the bridge was first designed because the engineers failed to perform the calculations needed to check whether the gusset plates were the correct size.

The overall design of the I-35W Bridge was safe, reliable, and effective. Had the gusset plates been the correct thickness, the I-35W Bridge collapse would not have occurred. The gusset plates were the only problem with the bridge.

Sverdrup and Parcel, the designers of the I-35W Bridge, were experienced engineers who knew how to properly design a bridge and check the design calculations. While they failed to check the design calculations of the I-35W Bridge, they built many other truss bridges without making this mistake, and those bridges have proven to be safe and reliable bridges.

There is nothing about a "deck cantilever truss" type of bridge that is less safe or less reliable than other types of cantilever truss bridges.

Most truss bridges are considered "fracture critical" meaning that if one part of the bridge fails the entire bridge might collapse. While that sounds scary, the reality is that fracture critical bridges are safe and reliable as long as they are inspected routinely as required by law. A proper bridge inspection will detect problems with truss members long before they even come close to complete failure.

Bridge inspectors and highway agencies are now required to check truss bridges for the type of design errors that were present on the I-35W Bridge. As a result, truss bridges standing today and still open to traffic have been checked to make sure a similar problem does not exist.

The fact that a truss bridge is fracture critical should not be used to justify demolishing and replacing a truss bridge. If a truss bridge is to be replaced, additional reasoning should be present (deterioration, width of roadway, etc) to justify a replacement.

The fact that a bridge "looks like" the I-35W Bridge should not justify a demolition and replacement project. Unless the similar-looking bridge was found to have gusset plates that are too thin, such a bridge would not be at risk for an I-35W type of failure and subsequent collapse.

[1, 2, 3]

 

Failure: Rana Plaza Garment Factory Collapse
Location: Savar, near Dhaka, Bangladesh
Date: April 24, 2013
Type: 8-story Progressive Collapse

Architect & Structural Design: Massood Reza of Vastukalpa Consultants
Site Developer: Sohel Rana (currently in prison)

1,129 Dead
2,515 Rescued
*Deadliest accidental structural failure in history [e]

Major cracking shook the building the day before the collapse, alarming workers inside. A consultant structural engineer deemed the building unsafe and urged evacuation, along with local police. Garment factory owners forced employees to work anyway on April 24 by threatening to dock pay. [a] The building—already lacking structural integrity—was shaken to final collapse when generators and heavy machinery restarted after a power outage around 9:00AM. Cracks seen on the 7th floor propagated, causing collapse of the uppermost floor. A domino effect ensued, killing and entrapping thousands of workers in the rubble. [b]

After formal investigation, authorities concluded that the major contributing factors of failure were:      (i) a lot unfit for a multistory building, (ii) shoddy construction and poor materials, (iii) illegal expansion and use, and (iv) a lack of safety regulations or regular inspections.

(i) Investigators claim the building footprint is partially on what once was a swampy landfill, causing uneven settling of the foundation and unstable support of heavy loads. The owner bribed officials for construction permits and to avoid inspections. [b]

(ii) As is a common issue in developing countries, the construction was completed with very cheap materials. The high cost and unavailability of steel led to use of smooth reinforcement bars. After the collapse, officials cited underuse of proper steel rebar (to achieve redundancy) and bad cement in the reinforced concrete construction. Had there been more reinforcement, the collapse may have been localized rather than progressive. [c]

(iii) Though initially designed to be a 5 story building used for office spaces, the final occupation of the building was as an 8-story industrial garment factory. At the time of collapse, the building appeared to be undergoing even further expansion. [a] The heavy machinery and crowded conditions of the garment factories created extreme, uneven loading that surpassed the strength of the structure. There was blatant disregard for building codes by the owner.

(iv) Bangladesh has the lowest wages in the world for garment workers, with over 5,000 factories manufacturing for retailers worldwide paying its over 4 million workers an average of $38 USD per month. [b] Building codes are ignored and inspections are irregular—a consequence of bribery and the political clout of factory owners. Hundreds of others were also killed in factory fires or collapses that year. [d]

At 6:45 pm on July 2, 1983, a single story retail store, Magic Mart, was subject to a high amount of water from a surprise storm that occurred in the area. This retail store is part of a line of shops along the side of the road in Bolivar, Tennessee. The building was designed with steel wide flange girders and the roof consists of typical steel bar joists. The columns in the building that supported the girders were steel pipe columns. Through investigation, it was shown that the building was constructed differently than it was designed. Smaller, weaker members were used and oriented 90 degrees in comparison to the construction drawings, and the bar joists did not have sufficient bottom chord extensions and stiffener plates to create sufficient strength in the roof structure.

To make matters worst, the construction drawings were not stamped by an architect or engineer, but were prepared by an architectural firm. These drawings, like any drawings used, need to be stamped by a registered professional. While the investigators did not find any issues with the structural designs holding the design loads, there was no designer or structural design representative in the field at the time of construction, and this caused the construction to be sequenced in correctly and fabricated incorrectly and with the wrong sizes. These incorrect construction methods led to a structure that could not hold the design loads, and the roof work done added load and caused the ponding to be more severe, which initiated the collapse. The structure then progressively collapsed, a direct cause of the poor construction methods and incorrect structural members used in the building. The two figures below show the difference between the as designed, and as built contruction.
After the collapse on July 2, 1983 Simpson, Gumpertz & Heger, Inc. arrived on site about a month later, on August 4th, 1983. It was noted that even though a rescue attempt had occurred, the collapse site was still relatively undisturbed. After doing a survey of the collapsed building, SGH attempted to recreate the slope of the building and found that because of the incorrect beam size, the building was not sloped to drain to the rear correctly. There was a low spot towards the back of the building, but it allowed about 3 inches of rain to pond on the roof. It was determined through investigation of the materials that the roof had been patched and re roofed without properly removing the under layers. This only added to the dead load on the roof and the eminent collapse. This low point in the roof was the point where the collapse started. After the rain overloaded the roof, the improperly braced and structurally weak girders and joists progressively collapsed. The welds and connections were sufficiently strong, which helped with pulling the rest of the roof down once the collapse was initiated. (Bell and Parker, 1987)

 

Wolftrap Performing Arts Center - Weld Failure
Fairfax, VA - January 1985
Christopher Barlow, MAE/BAE, The Pennsylvania State University Class of 2017

Through the peaceful countryside, over grassy hills and tall forests, the sound of music resonates through Vienna in summertime. But this is not Vienna, Austria. This is Vienna, Virginia, a small town thirty miles west of Washington, DC. And of course this is not Julie Andrews and the beloved Von Trapp Family. This is the Wolftrap Performing Arts Center. For nearly fifty years, the Wolftrap Performing Arts center has dazzled its patrons with hundreds of musical guests including legendary world-renowned musicians of every genre as well as today's pop stars. Central to this cultural hub is the Filene Center, a large wooden indoor and outdoor auditorium with seating for 7,000. Truly, the experience offered by this venue is unique and inspiring.

Figure 1. Animation of the crack in girder G-1
However, this peaceful sanctuary was also once the source of a tremendous amount of panic and turmoil for those involved in its construction. Not long after its completion and totally without warning, a monstrous 8-foot crack appeared in a major steel roof girder above the Filene Center, resulting in a 9.5 inch deflection (Figure 1) (Feld & Carper 1996). The park was immediately closed and a lengthy investigation commenced to determine the source of the failure. The drama intensified as the architects, engineers, steel suppliers, fabricators, and contractors involved in the project waited anxiously to read the report that would determine who was at fault and who would pay the hefty cost for repairs. This wiki will summarize various theories regarding the cause of the failure, the final conclusion of the official report, subsequent legal ramifications, as well as lessons learned for future construction of large-scale outdoor venues such as this.

Weld Failure

Figure 2. Types of weld cracks (Credit: Wikimedia Commons)Welding is a complex procedure requiring a high level of skill that many designers often take for granted. The figure to the left shows the many different types of cracks that can occur as a result of insufficient welding (Figure 2). In the case of girder G-1, the initial defect was determined to be a fusion-line edge-type crack in the weld between the web plate of the box member and the backing bar (Kaminetzky 1993). The welding type was designed to be a full penetration weld; however, the backing bar used to create the full penetration weld was not itself continuously welded to the inside of the box, which likely introduced the flaw into the member.

As is the case with most building failures, there was not one definite cause but a number of mistakes or oversights made throughout the design and delivery process that ultimately triggered the failure. The official report of this failure cited three main causes: "weld flaws, extremely cold temperatures, and poor metallurgy (steel with insufficient fracture toughness," (Feld & Carper 1996). For a thorough discussion of the welding flaws, see above. Unusually low, sub-zero temperatures also played a role in the failure. The theater, used exclusively during the summer, was designed to be open to the elements and unheated. Investigators found that this factor was not taken into account by designers of the girder as the weld material used was not capable of maintaining its required toughness in this environment (ENR Mar. 1985).

Fracture toughness is an important property to be considered when designing any steel structure. A higher fracture toughness means a higher resistance to brittle fracture. Unfortunately, higher strength steel tends to have a lower fracture toughness. Therefore, designers must be careful with balancing these two properties. Simply designing a steel structural element using the highest strength steel available is never a good idea, especially when designing in cold environments. Unfortunately, in the case of the Wolftrap roof girder, there was no minimum requirement set for the fracture toughness of the material (Maranian 2010). This slight omission in the design process, in tandem with the weld flaws and cold temperatures, ultimately caused a failure.

Figure 3. Original design and corrective actions of girder G-1
The crack was first discovered during an inspection after a piece of copper flashing had fallen off the end of the girder (ENR Feb., 1985). Immediately following the discovery of the crack, scaffolding was placed around the structure to hold up the roof until a proper fix could be installed. According to the original designers of the building, the roof was in no danger of collapsing (ENR Feb., 1985). This is because the structure had a sufficient level of redundancy, allowing for the load to take alternate paths to the foundation (Maranian 2010).

The first fix introduced to the structure appointed the removal of all the plates which had been compromised by the crack. Next, new plates were added with more careful welding of the back up bars. Finally, to provide ultimate peace of mind, the entire girder was post-tensioned with cables (Feld & Carper 1996). The image to the left first shows the original design of the member followed by the fixes made after the failure (Figure 3). It is important to note the shop note provided, which states that the back-up bars must also be welded and continuous along the entire length of the beam.

Investigators also recommended that corrective work be applied to the remaining roof structure (ENR Mar. 1985). The roof structure consisted of two large inner girders, each carrying a third of the load, and two outer girders, each carrying a sixth of the load (ENR Feb. 1985). According to the firm coordinating the repairs, "There are many possibilities for similar flaws on the outside of the roof girders," (ENR Mar. 1985).

The final cost of repairs came to a staggering $1.5 million (Los Angeles Times 1985). The companies involved in the original construction include: Dewberry & Davis, the architect and engineers; Bethlehem Steel of Bethlehem, PA, the steel supplier; Globe Iron Construction of Norfolk, the beam fabricator; and G&C Construction of Vienna, the chief contractor. All four firms agreed to hire one forensic engineer, John W. Fisher, to determine the cause of the failure. Although Fisher did not explicitly place blame in his report, he did often gravitate toward the poor workmanship of the beam (Hockstader 1985).

 

 

[1,2,3]

The Metrodome was built in 1980 in Minneapolis, Minnesota and is home to the Minnesota Vikings, United FC, and the Golden Gophers.[a] The building will be demolished this year.[a] Hubert H. Humphrey Metrodome has been no stranger to failures involving its inflatable roof structure. “In fact, the December 12, 2010 roof collapse marks the fifth time in the Metrodome’s history the domed roof has failed. Three of the four previous roof collapses, in 1981, 1982, and 1983, have been attributed to snow, while the fourth failure, in 1986, was due to strong winds.” [b] A severe winter storm moved into the Minneapolis region on Saturday, December 11. The storm dumped more than seventeen inches of snow in the Minneapolis area. [b] Anticipating the approaching storm, maintenance crews at the Metrodome took preventative measures by heating the internal temperature of the dome to around 80 degrees while pumping warm air into the cavity separating the inner and outer layers of the roof structure.[c]

At approximately 5:03 A.M. on Sunday December 12, 2010, a sliding mass of snow and ice broke free and slid down the roof, slicing a gaping hole in fabric panel number 104, seen in Figure 3. Although the internal pressurization system of the Metrodome was designed to compensate for minor tears, a hole of this magnitude resulted in the depressurization of the space and ultimately the collapse of the dome. Upon impact with roof equipment, the sliding mass caused tears in fabric panel numbers 43 and 44, directly over midfield.[b]

“On December 12th, a series of firms were contacted to assess the damage that had been done to the Metrodome roof structure.According to the Metropolitan Sports Facilities Commission, it was unanimously accepted that the deflation of the dome was caused by sliding snow and ice impacting the ring beam along the perimeter of the roof structure, rupturing the roof fabric at panel number 104. The tear in this panel caused the loss of internal building pressure resulting in the deflation of the air supported fabric.”[b] Birdair Inc., reported numerous minor tears and abrasions in the fabric. Their examination revealed the loss of the Polytetrafluoroethylene (PTFE) protective coating on the fabric membrane and the formation of cavities at the intersection of glass yarns within the inner fabric. If these depressions reached the depth of the inner woven glass yarns they would have been exposed to the elements, and the infiltration of moisture would ultimately weaken them. The ring beam and columns, and cables were inspected and deemed useable for future use. [b]

Bab Berdieyinne Mosque suffered tragedy when the ceiling as well as part of the structural walls of its minaret collapsed into the courtyard on February 19, 2010 [a].

Officials blamed a series of heavy rains for weakening the structure just before the collapse [b], but further analysis revealed several characteristics that contributed to the minaret’s ultimate demise. The 400 year old mosque was composed of rammed earth, or man-made sedimentary rock, making it particularly sensitive to prolonged moisture exposure [c]. The foundation of the site lacked proper drainage, subjecting the structural walls to constant damp conditions—weakening their overall stability [d]. As seen in Figure 2 above, proof of further foundation instability could be seen by the slight tilt of the minaret [f]. In addition, the foundation had been described as insufficiently proportioned [e].

Officials had been criticized prior to the collapse for their negligence of the mosque; multiple cracks were visible in the exterior, one of which was estimated to be 10 meters long [e]. The Imam, or worship leader, of the mosque had requested the mosque be closed for a week for structural investigation but was denied.

On May 10, ten years ago, the worst factory fire in history took place at the Kader Industrial toy factory on the outskirts of the Thai capital of Bangkok. Officially 188 workers, most of them young women from impoverished rural families, died in the blaze. Another 469 were injured; many seriously and permanently, after they were forced to leap from second, third and fourth floors of the buildings to avoid being burnt to death.

Hundreds of workers were packed into each of the three buildings that collapsed. There were no fire extinguishers, no alarms, no sprinkler systems and the elevated walkways between the buildings were either locked or used as storage areas. The buildings themselves were death traps, constructed from un-insulated steel girders that buckled and gave way in less than 15 minutes. Those who attempted to flee through the narrow ground floor exits found them jammed shut.

There were many reactions to this terrible tragedy. The international media barely mentioned the fire. Inside Thailand, however, there was widespread anger. The toy factory, owned by Thai, Hong Kong and Taiwanese investors, was symbolic of the exploitation associated with globalised production. Major toy corporations such as Tyco, Kenner and Arco faxed their orders to Kader, complete with the detailed specifications required to market the goods in the US and Europe. None of them had the slightest interest, however, in the safety standards, wages or conditions for the factory workers who produced the plastic-moulded toys.

The International Committee of the Fourth International (ICFI) recognised the significance of the disaster and dispatched a reporting team to Thailand to investigate. A series of articles, which initially appeared in the newspapers of the ICFI and was later published as a book Industrial Inferno: The story of the Thai Toy Factory Fire, detailed the immediate causes of the fire, allowed survivors and the victims’ families to speak, and exposed the official cover-up and the inaction of various trade union leaders.

More fundamentally, the articles pointed to the underlying changes in world capitalist economy that made such tragedies inevitable. The previous worst industrial fire—at the Triangle Shirtwaist factory in New York in 1911—became the focus for struggles by working people that succeeded in placing limited restraints on the operations of capital. But under conditions where globally mobile investors were not tied to a particular country, let alone to one factory, the prospects for such piecemeal reform had become nil.

“Companies such as Kader Holdings need to move their operations rapidly to take advantage of the newest areas of low-cost labour. That it why the Kader factory outside Bangkok was never intended to be a permanent structure. Cheap shoddy buildings, which failed to meet even the minimal Thai construction requirements, were simply packed to overflowing with workers and machines. Elementary safety precautions were deemed to be unnecessary overheads.

“Thailand’s limited building and safety codes, minimal wage levels and factory regulations are not enforced. Indeed, the government in Thailand attracts foreign capital to its shores by openly advertising the lack of restrictions on the exploitation of workers. The Kader factory was no aberration. All the horrors of nineteenth century European capitalism—child labour, dirty and unsafe working conditions, shanty housing—are on display everywhere in Bangkok.” (1)

On December 15, 1967, the Silver Bridge collapsed while it was full of rush-hour traffic, resulting in the deaths of 46 people. Two of the victims were never found. Investigation of the wreckage pointed to the cause of the collapse being the failure of a single eyebar in a suspension chain, due to a small defect 0.1 inch (2.5 mm) deep. Analysis showed that the bridge was carrying much heavier loads than it had originally been designed for and had been poorly maintained.

The collapsed bridge was replaced by theSilver Memorial Bridge, which was completed in 1969.

The 2-story parking garage has eccentrically braced frames in both loading directions as its primary lateral resisting system. The steel braces are HSS sections with gusset plate connections. These braces were designed in a way that they were not allowed to buckle during an earthquake. However, plastic deformation was concentrated in the gusset plates in the short distance between the end of the brace and the overlap with the gusset plate from the columns 

At the interior brace foundations there was foundation uplift due to the unbalanced load that was delivered to the foundation due to gusset plate local buckling 

The parking garage was designed in 1991. In the EW loading directions all the top gusset plates fractured due to low cycle fatigue. 

 

 

Note that none of these gusset plate details included any stiffener to prevent the out-of-plane movement of the gusset. Fracture initiated at the tow of the weld in the heat affected zone and propagated along the length of the gusset plate. 

Due to gusset plate fracture outside the separation between the concrete slab and the top of the beam indicated unbalanced loading that was successfully delivered to the columns. Note that in the NS loading direction the primary damage was local buckling of the top gusset plates. However, none of them fractured because the ground motion component in this loading direction was not as strong as the one in the EW direction.