Aydin Demir

This study investigates the shear damage mechanisms in reinforced concrete (RC) beams through non-linear numerical modeling. Using the Finite Element Method (FEM) in ABAQUS, a Concrete Damaged Plasticity (CDP) framework was validated against experimental results and subsequently utilized for a 36-model parametric investigation. The study isolated the influence of stirrup spacing, diameter, and yield strength to evaluate their roles in ultimate shear capacity. The results indicated that while increasing stirrup diameter yielded modest capacity enhancements of approximately 7%, the impact of increasing yield strength was negligible, as the failure modes were primarily governed by concrete web crushing before reinforcement yielding could occur. These physical limit states were compared against the linear Truss Analogy adopted by major design standards—including ACI 318-19, Eurocode 2, and TS 500—to quantify discrepancies in heavily reinforced sections. The findings reveal that, strictly within the investigated parameter space (a/d = 2.67, f’_c = 28.5 MPa), current linear equations can significantly overestimate the physical capacity gains provided by reinforcement modifications. These observations are configuration-specific and highlight the need for cautious application of linear models in heavily reinforced scenarios. Furthermore, the study suggests that utilizing 3D beam elements for transverse reinforcement provides a more nuanced representation of shear transfer mechanisms, such as dowel action, compared to standard truss models.

The February 6, 2023, Kahramanmaraş earthquakes in Türkiye caused severe structural failures, particularly in older reinforced concrete (RC) buildings. A key factor in these collapses was the presence of pre-existing column cuts on ground floors, significantly compromising structural integrity. This study investigates the progressive collapse (PC) behavior of older RC buildings with pre-cut columns under gravity and seismic loads. Two numerical models, representing a low-rise (5- story) and mid-rise (10-story) RC structure, were developed based on the Turkish Earthquake Codes of 1975 and 1998. The PC analysis employed nonlinear dynamic simulations using SAP2000, considering three ground-floor column removal scenarios: exterior corner, edge, and interior columns. Findings reveal that TEC1998 structures exhibited improved PC resistance under gravity loads compared to TEC-1975 designs, yet both remained highly vulnerable at exterior columns. Under a simulated Mw 7.7 magnitude earthquake, all models experienced ground-floor column failures, leading to total collapse. These results highlight the inadequacy of outdated seismic codes and the urgent need to retrofit pre-2000 RC buildings to meet modern seismic standards. This study contributes to seismic engineering by emphasizing the impact of structural modifications in older RC buildings and advocating for advanced retrofitting strategies to enhance resilience against PC and earthquake-induced failures.

This paper provides a comprehensive examination of post-earthquake structural damage assessment efforts following the Kahramanmaras, Turkey, earthquakes that occurred on February 6, 2023. Drawing on global damage assessment protocols, the study compares and analyzes the methods implemented in the aftermath of the earthquakes, offering insights into lessons learned and challenges faced. The analysis of objections raised regarding the assessment efforts reveals significant changes in structures with moderate and severe damage, emphasizing the need for continuous improvement in assessment strategies. The paper advocates for a realistic and two-stage application method, consideration of crack type and cause, and active involvement of local communities in the assessment process. Furthermore, the study identifies key issues in the current earthquake damage assessment methodology and proposes solutions, including a more precise classification system, regular volunteer training, consideration of secondary disaster risks, and effective communication methods. The paper concludes by underscoring the importance of effective damage assessment in disaster management, addressing objections from the affected population, and continual enhancement of strategies to improve resilience in earthquake-prone regions.

In the year 1999, two devastating earthquakes (M_w 7.4 Kocaeli earthquake in August and M_w 7.2 Düzce earthquake in November) occurred in Northwest Türkiye. These two earthquakes led to a very large number of casualties and building collapses. When the 1999 earthquakes occurred, most of the structures in the earthquake-impacted region were not designed according to modern seismic design codes. During the 25 years following those earthquakes, there have been significant advances in building construction in the light of earthquake engineering, including adequate seismic codes, new regulations, and effective code enforcement in the earthquake impacted region. These advances have been reflected in the construction of new structures in the region and the retrofitting of existing ones. As a result, 70–80% of the current building stock in Düzce was designed, constructed, or retrofitted after the 1999 earthquakes. Almost 23 years later, in 2022, an M_w 6.1 earthquake occurred in Düzce, with ground shaking close to the seismic design code life safety performance level. The 2022 earthquake provided a great opportunity to evaluate the effectiveness and consequences of the advances in earthquake engineering and the relevant policy-making and regulations. This paper provides a comparative overview of the 1999 and 2022 earthquakes that struck the city of Düzce in terms of hazard, vulnerability, and consequences. Furthermore, other key lessons learned from the 2022 Düzce earthquake are documented based on field reconnaissance and numerical simulations. The lessons learned are expected to provide useful guidance for the reconstruction efforts after the 2023 Kahramanmaraş Türkiye earthquake sequence or in similar efforts in other parts of the world.

Two successive earthquakes with moment magnitudes of M_w = 7.7 (focal depth = 8.6 km) and M_w = 7.6 (focal depth = 7 km) occurred approximately within 9 h on February 6, 2023, in Türkiye, respectively. The epicenters were the Pazarcık and Elbistan districts of Kahramanmaraş. Both earthquakes occurred in the East Anatolian Fault Zone, one of Türkiye’s two major active fault systems. Between these two severe earthquakes, there was one more big aftershock with a moment magnitude of 6.6, the epicenter of which was in the Nurdağı District of Gaziantep. Then, on February 20, 2023, another aftershock earthquake with a magnitude of M_w = 6.4 occurred in Yayladağı district of Hatay. As a result of the earthquakes, severe damage occurred in several provinces and districts with a population of around 15 million, and more than 50,000 people have lost their lives. This study presents on-site geotechnical and structural investigations by a team of researchers after the Kahramanmaraş earthquakes. It summarizes the performance of the building environments as a result of on-site assessments, taking into account observed structural damage, local site conditions, and strong ground motion data. The possible causes of the observed damage are addressed in detail. These earthquakes once again revealed the common deficiencies of existing reinforced concrete structures in Türkiye, such as poor material quality, poor workmanship, unsuitability of reinforcement detailing, and inadequate earthquake-resistant construction techniques. Precast concrete and masonry structures in the region were also severely damaged during the earthquakes due to insufficient engineering service, poor materials, deficiencies during construction, etc.

In this study, a numerical progressive collapse response evaluation was performed on a 40-story high-rise building designed according to the Turkish Earthquake Code of 2018 (TEC-2018). The alternate path method specified in the General Services Administration of 2016 (GSA2016) and the Unified Facilities Criteria (UFC 4-023-03) was used for the evaluation. A total of 18 scenarios were investigated for column and shear wall removals. In the cases where hinges were observed, the extent of damage was evaluated using the performance criteria given in the Turkish Seismic Code and the American Society of Civil Engineers (ASCE) 41-17. In this study, the most damage was observed when the corner column was removed at the bottom floor, while the least damage was observed on the shear walls close to the center and core of the building. For all the scenarios evaluated, no collapse was observed. The study deduced that the high-rise building designed according to TEC-2018 showed sufficient resistance to progressive collapse.