Posted on March 18, 2023
The recent earthquakes that hit Turkey on 6 February 2023, as well as the aftershocks during the course of the following month, leading to the loss of life and damage to buildings and other structures in the aftermath, have left the world in shock. During a public lecture on 9 March 2023, Prof George Markou of the University of Pretoria’s Department of Civil Engineering in the Faculty of Engineering, Built Environment and Information Technology shared his thoughts on what went wrong.
Prof Markou is a specialist in structural engineering with a particular interest in earthquakes. During his professional career as a civil engineer in Cyprus, he designed numerous structural engineering projects, which mainly involved seismically resistant residential and commercial reinforced concrete buildings with the use of the Cyprus, New Greek Earthquake Design Code and Eurocodes. In addition to that, Prof Markou developed a finite element analysis software, Reconan FEA, for the seismic assessment of structures such as bridges, wind turbine towers, nuclear reactor buildings and foundation systems through advanced numerical modelling, a software that he used to seismically evaluate different types of structures around the world. He is thus pre-eminently qualified to voice an opinion on the devastating earthquakes in Turkey and what could have been done to prevent the extensive damage to Turkey’s concrete structures.
He started his lecture by explaining what earthquakes are and how they occur. He then went on to provide the facts about the two main seismic events that took place. The first earthquake, which took place on 6 February, had a moment magnitude of 7.8 and struck southern and central Turkey, and northern and western Syria. The epicentre was 37 km from Gaziantep. This was followed by a second earthquake with a magnitude of 7.5 that occurred in Kahramanmaraş, 95 km from the primary event. More than 3 500 aftershocks followed the two main seismic events.
These natural disasters, together with their aftershocks, caused widespread damage over an area of 350 000 km2, which resulted in more than 50 000 fatalities. An estimated 14 million people (16% of Turkey’s population) were affected, and four million buildings in Turkey and Syria were damaged or collapsed entirely. The cause of the seismic sequence of events was determined to be shallow strike-slip faulting in the underlying geomorphology, which occurred at the juncture of three tectonic plates: the Anatolian, the African and the Arabian tectonic plates.
Following the events, the Turkish Ministry of Environment, Urbanisation and Climate Change inspected 763 000 buildings for damage. It revealed that more than 41 000 buildings collapsed and at least 60 000 buildings would have to be demolished. The direct physical damage amounted to $34.2 billion (4% of Turkey’s GDP).
According to Prof Markou, the question that inevitably arises is what could have been done differently to prevent the structural damage that left about 1.5 million people homeless. Working with data from the Engineering Strong Motion (ESM) database of Italy’s National Institute of Geophysics and Vulcanology, researchers were able to extract accelerograms and compile a response spectrum diagram of the main event, which could be used to illustrate the reinforced concrete behaviour of structures under seismic excitation.
What researchers sought to determine with this data was how structures could be expected to behave under different seismic loads. They first compared the behaviour of tall buildings between four and 15 storeys to those with only one to three storeys to determine whether one could expect to experience more failures in tall or short buildings. The resulting elastic spectrum diagrams were then compared to the expected behaviour of these structures according to the Eurocode standards for the reinforced concrete earthquake-resistant design of structures.
Another question that was considered related to the overall safety factor that derives from the design of a structure through Eurocode 8 (the European Union’s standard for the design of structures for earthquake resistance) and the Turkish design code. By means of a modelling exercise, varying loads were computed according to Eurocode 8, specifically to determine the behaviour of reinforced concrete buildings. The results of this exercise revealed that the maximum strength of a reinforced concrete building should have been able to withstand a force three times larger than the design seismic load, a phenomenon attributed to the partial safety factors that are used during the design of structures. Through the use of the developed spectrum acceleration diagram, it was found that shorter buildings were more likely to develop damages than taller buildings with a larger number of storeys as the shorter buildings were expected to develop a larger spectrum acceleration during the main earthquake event.
Following the earthquakes, some experts claimed that the quakes were so massive that no building code could have prevented the collapses that were witnessed during the events. However, upon examining the collapsed buildings, it was noted that there were isolated buildings that remained standing, despite the surrounding buildings crumbling to the ground. Contrary to the results of the modelling exercise, some of the buildings that remained standing were buildings with only a few storeys, while buildings of eight and more storeys directly behind them collapsed.
Upon further investigation, several disturbing factors came to light. One report determined that shop-owners had removed some of the structural columns in buildings to create more space for their wares, thus weakening the structural strength of buildings. An examination of the debris also determined that high-rise buildings that were purported to be constructed with reinforced concrete had, in fact, been constructed using sub-standard material that did not adhere to the building codes, while reinforcement was absent or not very prominently used. It appears that this was the result of a desire by the authorities to build low-cost housing to solve the housing problem in the cities of Kahramanmaraş and Hatay. Contractors profited from an arrangement such as this, which entailed no official site inspection or proper design code implementation.
An interesting case that came to light, which might prove the suspicions created following the examination of the debris in Kahramanmaraş, was the case of Ezrin City. This has become known as the “city that did not collapse”, and many consider it to be a miracle. Located only 80 km from the epicentre of the main earthquake event, it suffered no fatalities and no buildings collapsed, despite experiencing a quake with a magnitude of 7.8. Officials and residents attribute this to the city’s long-standing determination not to allow construction that violated the country’s building codes. In fact, when officials encountered buildings that had been built illegally, they were summarily demolished. This seems to be what saved Ezrin from destruction.
Concluding his lecture, Prof Markou acknowledged the fact that Turkey’s main seismic event, with a magnitude of 7.8, giving rise to a second event with a magnitude of 7.5 and more than 3 500 aftershocks, could not have been anticipated by any design code in the world. “Nevertheless, our current knowledge of designing earthquake-resistant structures allows civil engineers to prevent any failure, even for extreme events of this kind.”
The question of why the events of 6 February led to so many building collapses in Gaziantep and Kahramanmaraş points to building amnesties, construction companies not complying with the country’s building codes, illegal interventions to existing structures and poor-quality construction materials. In some cases, designers had inadequate know-how and a lack of fundamental earthquake-resistant design knowledge. “If the design codes had been properly implemented, the destruction of infrastructure and loss of life could have been significantly reduced.”
Reflecting on the latest trends in structural engineering research internationally, which is what Prof Markou and his research team are engaged in at the University of Pretoria’s Department of Civil Engineering, he emphasises that the design of buildings and other city infrastructure should be motivated first and foremost by a desire to create a safe built environment for the world’s urban population.
His work is focused on making use of artificial intelligence (AI) and machine learning to predict the strength of structural members and full-scale structures under different actions, including that of seismic loads. From data modelling to the design of algorithms to test the strength of concrete structures mathematically, and the smart monitoring of the built environment, the latest developments in the discipline of structural engineering can contribute to the solution of several emerging problems by describing the complex interactions among various input variables and their corresponding responses.
With this innovative approach, actual physical experimentation will soon be completely replaced by detailed 3D state-of-the-art mathematical simulations that can be used to generate millions of results for different types of reinforced concrete structures, assuming different material properties, while considering various geometries and reinforcement configurations. This will revolutionise the way civil engineers design their structures, given that new advanced AI-generated predictive models will be made available for the design of civil engineering structures, ensuring that they can withstand even the strongest forces of nature.
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