This post will cover three different structural engineering disasters. These unfortunate incidents occur all to often. We as engineers need to learn about structural disasters and the failures that caused them to ensure that these occurrences never happen again.

Sampoong Department Store Collapse

On the 29th June 1995, Sampoong Department Store, Seoul, South Korea collapsed, 502 died and over 1440 people were injured. This was the worst structural disaster South Korea has ever seen, and hopefully ever will.

Sampoong Department Store, Seoul, South Korea

A major investigation was held by industry experts. As usual with disasters of any kind, many ideas are put into the mix and then narrowed down with evidence, eliminating each idea one by one, until the most probable cause is found. Originally, it was suspected that gas was the most probable cause since two other explosions occurred in Seoul. However, fire is a major by-product with gas and this was not the case. A terrorist attack from the North was also eliminated due to the way in which the building collapsed; it collapsed vertically and was contained. In explosions that would be expected by a terrorist attack or a significant explosion, debris would be hurled in many directions outwards.

A structural failure was found to be the cause of the collapse of the department store. The Sampoong department store was constructed from reinforced concrete columns using a flat slab arrangement. This means that the load is not transferred by beams but directly to the columns.

A phenomenon known as punching shear occurs when a concentrated load acts on a material. As the name suggests, the force wants to ‘punch’ through the member and this needs to be considered during member design. Punching shear was discovered to have not been considered in the design of the Sampoong department store. Thin flat slabs were present and they were not built to the requirements specified in the drawings. Additionally there was not enough reinforcement steel used, reducing the tensile capacity of the columns and slabs.

Design changes were also found to have increased the loads above what was originally designed. This is actually quite common as developers find more suited tenants to these types of buildings. However, the building is still designed with factors of safety or partial factors (1.35 and 1.5 for dead and live respectively in accordance with Eurocodes). As such, the building would still most likely have sufficient capacity.

Something must have occurred to trigger a response that caused the final fatal few seconds.

I came to find out about the disaster during my studies involving dynamic analysis and vibration. Air conditioning units are typically found on the roofs of these structures and they exhibit heavy loads. Due to the cyclic nature of the units, they can cause vibrations. The units in the Sampoong department store case were moved or dragged across the roof causing cracking to the reinforced concrete roof. The vibrations propagated the cracks and eventually caused the significantly weakened structure to collapse.

The key lessons from Sampoong department store collapse:

• All relevant design checks must be completed and punching shear cannot be ignored.
• Quality control on site is an absolute must. Checks must be done prior to concrete pours to ensure correct cover, concrete grade, concrete mix design and reinforcement bars all match the design.
• Maintenance for plant equipment requires solutions ahead of time. Proper planning could have actually prevented the demise of the structure.
• Major cracking in structures must be checked by a certified professional.
• It is normal for specifications and requirements to change, but this must be followed up by the design engineer to ensure compliance.

Zolitude Shopping Centre Roof Collapse

21 November 1013, in the Zolitude neighbourhood of Riga, Latvia, the roof structure of a Maxima building collapsed killing 54 people and injuring more than 40 others. It is the worst disaster in Latvia since the sinking of the Mayakovsky in 1950.

The structure in Zolitude was a Maxima shopping centre; a building that contained multiple businesses and a large shopping centre. The total cost of the development was in the region of 1.4 million euros and won the ‘Latvian Building of the Year’ award. An impressive feat with an unfortunate end.

Zolitude Shopping Centre Roof Collapse - (AP Photo/ Roman Koksarov)

An investigation was initiated immediately after the collapse. However, the structure was not stable and this hindered the investigation from the beginning. In order to gain access, the structure needed to be reinforced, incurring an additional cost but also potentially destroying critical evidence that could be used to find any structural problems.

The hypothesis initially pointed to the structural design, negligence of local authorities and the green roof. The latter was quickly disproved. Here’s why.

The collapse occurred in November 2013, but the structure was completed 2 years earlier in November 2011. During the harsh winters, Latvia has large amounts of snow. The snow exhibits a much greater weight than would be found from a green roof. Therefore, overloading of the roof structure due to the green roof could be the cause of failure. This doesn’t rule out that member weaknesses could have caused the collapse, but we will get onto that next.

Local authorities have a very important role in the construction industry. They ensure and aim to impose good quality working standards, working methods and health and safety practises. Local authorities in the United Kingdom and Europe check the structural designs and then use them to ensure the work on site is completed to the same specification. This includes correct reinforcement, foundation size, concrete grades etc. All of this is additionally checked by the site manager, contractors and civil/structural engineers. However, as we are all aware, little things can slip through the net at any stage and additional pairs of eyes are always welcome. A criminal investigation was completed and found the local authorities guilty of negligence for not checking the designs and following regulations. Several other members of the design team, including the construction engineer and architect, were also found guilty of negligence.

Forgery of documents was also discovered during the investigation. We will delve any further into this aspect as we want to understand the structural ramifications that caused the disaster and improve our knowledge to ensure these things never happen again.

However, the major reason for the collapse of the structure was found to be the structural design of the roof. The investigation in April discovered prolonged deformation of the roof structure well before the collapse. This means that the roof surpassed its elastic capacity due to stresses much greater than its capacity. A member will first undergo permanent deformation due to elastic failure and then fail due to plastic failure.

The final verdict was that the roof was built improperly and that the collapse was not sudden, but instead due to prolonged deformation. Metal fatigue may also have played a part, since it was  recorded that a fire broke out during the construction of the structure.

The key lessons from the Zolitude Shopping Centre, Riga, Latvia:

• A key aspect to quality control is local authorities. A good local authority can reduce any potential dangers which could arise due to poor workmanship or incorrect designs.
• The roof collapse was due to prolonged deformation. Inspections should have been completed on the structure and the deformations recorded. The green roof may however,  have played a part in hiding the deformations.
• Fires during construction can cause metal fatigue and problems with structures many years later.
• For a major disaster such as this to occur, multiple parties are at fault. It is not one single individual error, but multiple minor and occasionally major errors that accumulate.

CTV Building Collapse

22 February 2011, a 6.2 magnitude earthquake struck Christchurch, New Zealand. Within minutes the CTV Building collapsed, killing 115 people in the process. Many of the victims died due to the collapse, but fires broke out and attempts to put out the fires also caused more fatalities. The lift shaft and parts of the northern wall were all that remained of the structure following the disaster.

CTV Building Collapse, New Zealand
By Gabriel - Flickr: PGC building, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=14442523

The codes of practise in New Zealand have had many revisions, especially the Earthquake codes of practise. Due to the nature of an earthquake, the joints of a structure are allowed to yield which will cause large deformations, but at the same time prevents the structure from completely failing. It will render the building uninhabitable after a major earthquake, but is designed to save lives.

A lot of questions were raised by the council as to whether the building was designed to the codes of practise. Was the structure code-compliant. A consultant stepped up and stated that it was not designed to own standards they would expect but he trusted the design engineers judgement and had suitable credentials. As it owns out, the structural engineer in charge did not have adequate experience in the design of high-rise buildings and even had a fake engineering degree. We cannot solely blame the engineer however, all designs need to be checked thoroughly. It is worth mentioning that the building was declared safe for earthquakes on multiple occasions, even though it had errors in the design.

Mistakes are easy to make and hard to spot.

The key lessons from CTV Building collapse, New Zealand:

• Although the codes of practice and building regulations can be quite hard to digest, they must be followed, especially local or national annexes.
• Quality control begins in the office, during the design stage. We all need to work as a team, at all stages to ensure that any mistakes are caught.
• During any recruitment process, documents need to be certified.