2 Important Failure Case Studies of Long-Span Steel Structures

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Space structures are generally utilized in the construction of airport terminals, stockrooms, historical centers, and shopping centers where huge transverse space is required. They are architecturally appealing and structurally adaptable. Moreover, space structures are light in weight, which reduces the construction cost and help cover large zones of continuous spans effectively.

In recent years, space structures have developed and discovered their utility in the cutting-edge world of construction. Hollow steel section members and nodes with improved properties have altogether affected their application in storage spaces. 

In comparison with the ordinary column-beam structure, long-range space structures are unpredictable in design and need explicit design rules. Thus, the chances of the generation of inaccurate data for mathematical models are high. Also, because of their simplicity, grid uniformity, and redundancy, structural engineers and contractors tend to assume their strength and stability.

Primary codes for the design of long-span steel structures lack procedural rules as the codes assume the behavior of a steel structure. Thus, experience in their planning, designing, construction, and assembly plays a fundamental role in avoiding failure.  

The collapse of space structure has distinctive mechanisms due to variance in their structural form. Multi-layer framework structures (MLFS) have exceptionally large statistic redundancy and indeterminacy. Therefore, they are not inclined to progressive failure even after the collapse of an individual part. But, the progressive failure of the structure may occur if the critical members fail during service loading.  

Likewise, progressive failure can occur in structures if the critical members are subjected to higher wind and snow load. Thus, to prevent the progressive failure of the structures, an additional factor of safety is to be utilized in critical members. Sensitivity analysis can be used to determine the critical members subjected to high loading and can be susceptible to failure.

On the other hand, the collapse of single-layer framework structures (SLFS) might be initiated due to the buckling of a single member. Therefore, examining the stability of the individuals is very vital. SLFS shows more sensitivity to buckling than MLFS because of the transfer of the forces through just only one layer. The local buckling in SLFS may occur due to the snap-through buckling of single members in a localized area. Whereas the global buckling happens when a bigger region of instability is considered in the space structure. 

In this article, we discuss various causes of failure and investigation methodology and two failure case studies specifically for long-span steel structures. 

1. Ceiling Collapse of Charles De Gaulle Airport-Terminal 2E, France

On 23^rd May 2004, the ceiling of Terminal 2E of the Charles De Gaulle Airport collapsed near gate E50. A 300 mm thick curved reinforced concrete precast slab was designed for the structure of 30 m width. Researchers suggested that a 30 m long concrete precast slab collapsed on to the boarding footpath. Four people lost their lives and three were critically injured. 

1.1 Investigation Findings

The design concept used to construct the ceiling of the terminal was somewhat unusual. It was complex to understand and evaluate the force distribution since the 2D model made by the design office was not adequate as per code provisions. Redistribution of local forces from the struts to the panel was absent. Thus, the failure of a single member due to punching shear produced the collapse of domed concrete. 

In the zone of concrete failure, the composite panels seemed to be loaded by a higher level of roof loads, increasing the punching shear by 50%. Also, the structural model failed to take into account the long-term effects of terminal structure. 

More than 400 firms were engaged with the venture, and a serious level of inefficient complexity was observed in the management of the project. A high likelihood of coordination error was inescapable because of the collective individual errors and mistakes. Thus, it played a pivotal role in amounting to failure. 

The quality of the assembled panels was affected due to the delay in executing the work. Also, the delay caused the misalignment between the composite panels of concrete. Therefore, the stresses were getting accumulated due to the eccentric loading on the composite panels. 

It was observed that the design error of the slab thickness was a trade-off due to the architectural requirement. The airport authorities themselves acted as the financier and the project manager. Thus, there was no external authority to check and regulate the project. 

Reports and investigations confirmed that the terminal ceiling failed due to the poor practice of construction, low-quality concrete, and lack of structural design knowledge.  

1.2 Causes of Failure

The following points describe the leading causes of the progressive collapse: 

1. Inadequate shear stiffness was developed due to the insufficient design of shear reinforcement. 
2. Dowel bars were deeply embedded inside the concrete shell and created cracks in the concrete roof. 
3. Several cracks were formed as a result of higher-than-expected construction loads and differential moisture and thermal movements.
4. Investigation reports suggested that the margin of safety was lesser than anticipated during the design. 
5. Cracks in concrete developed due to the misplacement of tensile reinforcement. Thus, the tensile stresses were not resisted effectively. 
6. The horizontal column ties and longitudinal support beams were inadequate to provide enough support to the structural members. 

2. Collapse of Roof of Sultan Mizan Zainal Abidin Stadium, Malaysia

The Sultan Mizan Zainal Abidin Stadium was constructed for hosting multi-purpose games in Kuala Lumpur, Malaysia. The seating capacity of the stadium was 50,000. The stadium was intended to have two-shell like rooftops. The support for rooftops was provided in the form of concrete buttresses and space framework structure. The stadium was comprised of a curved double-layer space network made of cylinders and steel ball joints. 

On 3^rd June 2009, a tragic collapse of the roof of the stadium occurred soon after it had opened for one year. Luckily, there were no lives lost after the failure of the long-span space structure. 

2.1 Investigation Findings

After the failure of the roof of the stadium, an investigation committee was formed. The committee reported that the design of the stadium was not as per the codal provisions. 

The structural engineer didn't consider the support conditions while modeling the roof of the stadium. The span of the roof was very large and hence the roof was susceptible to the movements at the supports. 

The roof was constructed ineffectively and prompted additional stresses in the members at support because of misalignment. The quality of materials, nature of workmanship, and testing of preliminary materials were far below the standard prerequisites. 

The structural engineer didn't take the stiffness of supports into account, which is very sensitive for large span roof structures. The complexity of the space structure was of a higher degree; therefore, a detailed structural analysis was needed to prepare working drawings for constructing the stadium. However, the designers didn't analyze the structure considering the complex architectural shape of the stadium. 

2.2 Causes of Failure

The following points describe the main reasons behind the collapse of the roof of the Sultan Mizan Zainal Abidin Stadium:

1. After the failure of the structure, it was evident from the site debris that the steel components were defectively welded. Therefore, quality control in the pre-fabrication stage was lacking.
2. The design for temporary supports was not adequate. Thus, additional construction loads were applied to the supports. 
3. No internal checks were conducted on the strength of the structure during the erection process. 
4. During the modeling of the stadium, the critical factors for wind speed, wind direction, risk factor, and importance factor were not considered. 
5. The orientation of the stadium was not based upon the topological conditions of the site. Moreover, the stadium was not designed for critically identified wind loads.
6. Due to the use of poor-quality material and improper design, the overall factor of safety of the structure was reduced. 
7. Incorporation of poorly conceived plans, strategies, and faulty implementation of quality control checks and control systems by the management contributed to the collapse
8. Desired skills and competency of the project manager and his team members were questionable. They were not trained to handle an endeavor of such magnitude and complexity.   

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