In a world in which climate change is increasing the frequency and intensity of global disasters, there is an ever-greater focus within the architecture, engineering, and construction industry on creating infrastructure that is resilient and that can withstand unexpected events and continue serving and safeguarding communities. Every viaduct, bridge, or building designed with foresight acts more than just a structure, but rather a prominent promise of safety, continuity, and hope.

In February 2023 in Türkiye, that promise was tested in dramatic fashion. Two consecutive earthquakes, including the strongest ever recorded in Türkiye, struck the southern region with devastating force. The first, a Mw 7.8 event, erupted at 4 a.m. and was followed just six hours later by a Mw 7.5 shock.

Close to the East Anatolian Fault that triggered the earthquakes runs the Tarsus–Adana–Gaziantep (TAG) motorway, one of the country’s most important transportation routes. Passing through low mountains, the motorway includes 14 viaducts, carrying three lanes of traffic in each direction. Of these, five bridges were all within 225 metres of the fault rupture line. The five bridges were all constructed before 2000 and two of them – the Ataturk Viaduct and the Turgut Ozal Viaduct – were designed by Dar.

 In an  article for the September 2025 issue of the leading, global Structure Magazine, Dr. Cenan Ozkaya, Dr. Robert Dowell, and Faruk Yildiz described how the viaducts’ “very advanced and innovative original seismic designs and details” allowed these structures to withstand a historic earthquake that was far more powerful than the earthquake accounted for in the original design and original specifications. The fact that these viaducts survived with relatively minimal damage – despite the strength of the earthquake and their proximity to the rupture line – was testimony to Dar’s original design and demonstrated that resilience, when embedded from the beginning, endures through disaster and makes it easier for communities to recover and rebuild.

Moreover, the authors argue, as the tallest building in the world to withstand its maximum considered earthquake, the Ataturk Viaduct in particular offers insights for the global community on how infrastructure can perform under such conditions.

Tested beyond expectations

Southern Turkey lies along the East Anatolian Fault, the country’s second most active seismic system and one of the world’s most earthquake-prone zones. For this reason, the TAG motorway viaducts were designed to meet strict seismic requirements. For the Ataturk and the Turgut Ozal viaducts, the seismic design was calibrated to a Peak Ground Acceleration (PGA) of 0.4g – which would be triggered by an earthquake that would happen once every 500 years. At the time, this represented the maximum credible load for the viaducts’ lifetime and required advanced engineering solutions for flexibility, stability, and strength.

The February 2023 earthquakes exceeded these expectations and met estimates for the region’s Maximum Considered Earthquake (MCE) which is the most severe event that could be expected along a given fault line. In this case, the MCE was predicted to come around once within a rough 1,000-year return period.

Ground accelerations near the viaducts reached 0.607g, around 50% beyond their original design level.

Yet the Dar-designed superstructures resisted. They sustained only minor damage, avoided collapse, and preserved their function. Their performance under these extreme conditions has since guided plans for retrofitting to withstand even higher PGA thresholds, extending their brilliant design, service, and resilience for decades to come.

• Ataturk Viaduct

When completed, the Ataturk Viaduct was the tallest in Turkey, with columns rising over 130 meters and a length of 802 m. Located only 75 metres from the fault rupture line of the 2023 earthquakes, it was directly exposed to the full impacts the February 2023 earthquakes.

In their assessment of the Ataturk Viaduct’s performance, the authors highlighted Dar’s original seismic design, which included multiple shock-absorbing bumpers added to the expansion joints at both ends of the bridge. These unique, elastic, high-force-capacity bumpers acted in tension and compression to provide a self-centring behaviour to the viaduct after the earthquake. The bridge was also restrained from movement in the transverse direction by steel seismic braces. With the one-in-a-thousand-year event, the bumpers and expansion joints as well as the sliding surfaces off the bearings were all damaged, the approaches to the viaduct settled, concrete slab was locally damaged at the expansion joins, and the asphalt concrete overlay buckled causing potholes, bumps, and undulations on the driving surface. However, despite these damages, the steel superstructure, columns, footings, and bent cap were left intact – keeping the viaduct standing and demonstrating the resilience of the design and construction, even though the design capacity was for a much weaker earthquake. 

• Turgut Ozal Viaduct

Similar in concept to the Ataturk Viaduct but smaller in scale, the Turgut Ozal Viaduct has columns reaching 76 meters and a total length of 424 meters. Located 225 meters from the fault rupture line of the earthquakes, it was still exposed to severe shaking.

Like the Ataturk Viaduct, the Turgut Ozal Viaduct used elastic, high-force-capacity bumpers at the end expansion joints as well as at the bents with shorter columns. Pot bearings with sliding surfaces were used at interior bents and abutments. Steel beams also restrained the longitudinal movement of the tall columns. Though these original design features were also damaged during the earthquake, they played their role in ensuring that the main reinforced-concrete and steel elements remained intact.

 “The high quality of both (1) the original design details and (2) the construction, are important features that helped save the viaducts during the February 2023 Mw 7.8 earthquake.” 

Committing to resilience by design

The TAG motorway viaducts remind us that resilience is measured in the structures that stand when tested by forces greater than anticipated. Designed for a force of 0.4g PGA but subjected to 0.607g, the Ataturk and Turgut Ozal viaducts endured seismic forces 50% beyond their original capacity and continue to serve. Moreover, following the earthquake, the viaducts underwent ongoing seismic retrofitting to ensure that they would not be damaged in the event of a future similar earthquake. The retrofitting process was unobtrusive, allowing traffic to continue uninterrupted. Yet, the authors note that an earthquake of this magnitude is unlikely to hit these structures again in their remaining service life. That means Dar’s design, despite accounting for a weaker earthquake, was nevertheless resilient enough to allow the viaducts to experience and withstand the largest earthquake they could have experienced.

Dar’s approach to engineering is rooted in designing for communities; for endurance, safety, and the ability to thrive in a world where resilient infrastructure is essential and vital.