Okan Özcan

Precise and continuous monitoring of thermal effects are critical for ensuring the structural safety of bridges and preventing potential failures. This study presents a methodology integrating unmanned aerial vehicle (UAV)-based thermal measurements with interferometric synthetic aperture radar (InSAR) satellite data to assess and monitor the thermomechanical response of bridges. A three-dimensional (3D) finite element model (FEM) of a prestressed concrete (PC) bridge was developed and validated using in situ displacement measurements. High-resolution, 3D temperature distributions of bridge elements were obtained daily and seasonally using UAV-based infrared thermography (UAV–IRT). Thermal maps were validated with point temperature measurements on the structure. Simultaneously, long-term wide-area deformation trends were investigated using satellite-based InSAR observations. The thermo-mechanical displacement behavior derived from UAV–IRT measurements was compared with historical InSAR-derived seasonal deformation patterns to develop an integrated multi-source structural monitoring framework. The behavior of the bridge in daily and seasonal temperature cycles was simulated and analyzed by integrating UAV–IRT thermal load data into FEM. Maximum stress levels occurring under the most adverse thermal loading conditions and over a one-year period were calculated, taking into account stress limits. The FEM revealed a maximum vertical displacement of 12.3 mm under extreme thermal loading, with tensile stresses in the deck mid-depth exceeding the 3.5 MPa limit, signaling a potential risk for thermally induced cracking. Integration of UAV–IRT thermal observations and historical InSAR deformation measurements revealed vertical temperature gradients of up to 24 °C during summer conditions and indicated that the observed structural response was predominantly governed by thermo-elastic deformation. UAV-satellite methodology offers a rapid, economical, and comprehensive solution for the structural health monitoring of bridges exposed to thermal effects.

Construction of offshore concrete platforms involves considerable challenges due to the transportation and installation of heavy monolithic reinforced concrete structures. Modular or segmental construction offers a promising alternative by reducing construction time and cost while enabling deployment in deeper waters. This study proposes a novel segmental design and analysis approach for Condeep platforms through comparison with monolithic construction. Three-dimensional finite-element models were developed and validated against available experimental data to accurately capture load–displacement behaviour, crack width distribution, submerged natural frequencies, and corresponding mode shapes. The Draugen Condeep platform was analysed in monolithic and segmental configurations under service and ultimate limit states, considering relevant loading conditions. The results indicate greater ductility of the segmental platform than the monolithic design. Prestressing tendon stresses increased by ∼18%–30%, while the maximum crack width was significantly reduced from 3.21 to 0.34 mm, demonstrating improved stress redistribution and crack control. Moreover, the shear capacity of segmental joints was found to be comparable with, and in some cases up to 15% higher than, that of the corresponding cross-sections. Findings confirm that segmental modular construction can ensure reliable structural performance while improving flexibility, serviceability, and constructability of offshore concrete platforms under demanding marine conditions.

Coastal dune systems are dynamic landforms shaped by aeolian processes, in which onshore winds transport and deposit sediments behind natural or artificial barriers. The Çukurova Delta Plain, Turkey’s largest delta along the Eastern Mediterranean, contains extensive dune fields, particularly within the Seyhan and Ceyhan Deltas. Despite technological advances in UAV photogrammetry and Structure-from-Motion (SfM) techniques, studies on coastal dune dynamics in Turkey remain scarce. This study demonstrates the first comprehensive assessment of the spatiotemporal evolution of coastal dunes in the Çukurova Delta Plain. Historical aerial photographs and high-resolution UAV imagery were analyzed to evaluate long-term and seasonal morphological changes. The results indicate notable spatial and temporal variability in sediment budgets, with distinct erosion and accretion patterns across the two deltas. While some dune segments remained stable over decades, others displayed strong seasonal responses to wind and sediment dynamics. These findings enhance the understanding of deltaic coastal geomorphology and provide critical insights for sustainable management of vulnerable dune ecosystems under increasing human and climatic pressures.

Coastal dune systems are dynamic landforms primarily shaped by aeolian processes, where onshore winds transport and deposit dry beach sediments behind natural or anthropogenic obstacles along the shoreline. The Çukurova Delta Plain, representing Turkey's most extensive deltaic formation along the Eastern Mediterranean coast, encompasses the largest coastal dune fields, extending approximately 100 kilometers. These dune ridges are prominently developed within the eastern sector of the Seyhan Delta and across the Ceyhan Delta. While recent advancements in Unmanned Aerial Vehicle (UAV) photogrammetry and Structure-from-Motion (SfM) techniques have significantly enhanced the generation of high-resolution digital elevation models (DEMs) for geomorphological studies, research focusing on coastal dune dynamics remains notably limited in Turkey. This study addresses this critical gap by presenting the first comprehensive investigation into the spatiotemporal evolution of coastal dunes in the Çukurova Delta Plain, the second-largest delta system in the Eastern Mediterranean after the Nile Delta. The research employs a multitemporal approach, integrating historical aerial photographs and contemporary UAV-derived imagery to analyze both decadal-scale and seasonal morphological changes. For long-term change detection, the study utilizes archival aerial photographs acquired by the General Directorate of Maps (HGM) at 20-year intervals spanning from 1950 to 2016. High-resolution UAV surveys conducted at 3-month intervals during the study period enable the assessment of short-term seasonal variations in dune morphology. The results demonstrate significant spatial and temporal variability in sediment budgets across the study area, with distinct patterns of erosion and accretion observed in different sectors of the Seyhan and Ceyhan Delta dune systems. The analysis reveals that while certain dune segments exhibit remarkable stability over multi-decadal timescales, others show pronounced sensitivity to seasonal variations in wind regimes and sediment supply. This study contributes to the broader understanding of deltaic coastal geomorphology by quantifying the response of dune systems to both long-term and short-term environmental forcings. The findings provide valuable insights for coastal management strategies and highlight the importance of integrated monitoring approaches in vulnerable dune ecosystems facing increasing anthropogenic pressures and climate change impacts.

Earthquakes inflict extensive damage on urban settlements, posing significant risks to human life and infrastructure. This study investigates the destruction caused by the Mw=6.7 Sivrice earthquake, which struck on January 24, 2020. It focuses on its impact within the city center via remote sensing (RS) and geographic information system (GIS) methodologies for damage assessment. In the study, post-earthquake building damage data and building inventory, collected through field surveys and provided by the Ministry, were compared with the collapsed areas which were identified using Sentinel-2 optical imagery. The surface velocity rates of the study area over the past five years have been derived using advanced InSAR techniques, specifically Persistent Scatterer (PS) and Small Baseline Subset (SBAS) methods. Moreover, a comprehensive analysis of factors influencing building damage was conducted by integrating geological maps, active fault maps, Coulomb stress distribution, Vs30 velocities, and surface velocity rates in the city center with the building inventory. It was revealed that the damage estimation map produced by analyzing pre-earthquake data and the damage map produced by field studies carried out after the earthquake showed a similar pattern. The findings demonstrate that buildings constructed on alluvial soils having low Vs30 velocities with high surface velocity rates experienced the most severe damage. This analysis highlights critical geological and structural parameters that exacerbate earthquake-induced structural damage, offering valuable insights for urban planning and seismic risk mitigation.

The Çukurova Delta Complex, which is located in the south of Turkey along the northeastern corner of the Mediterranean Sea, is the second-largest delta system in the Mediterranean. The Seyhan River flowed 10 km east from its current course until at least the 16th Century, and shifted to its current course in the west and began to build the modern delta and the youngest foredune ridges were formed by a combination of aeolian and littoral processes. Morphometrics of foredunes greatly contributes to understanding the relationship between aeolian and marine dynamics. High-resolution digital elevation models (DEMs) are important in examining the geomorphic features of foredune ridges because the low-relief delta environment makes it difficult to use standard topographic maps. Therefore, in the study, the morphometric features, including foredune height, foredune slope, foredune width, the space between foredune ridges, and beach width of the ridges within the study area were extracted from the DEM and orthophotograph of historical and recent aerial photographs. Structure from Motion (SfM) techniques allow for the reconstruction of present and past landforms, and to detect long-term topographic changes in the low-relief areas using historical and modern aerial images. A total of 27 aerial photographs were acquired from flights in AD 2016 covering the study area with a ground sampling distance of 0.3 m, while 13 archive analog aerial photographs with a ground sampling distance of 0.7 m were available from flights in AD 1950. Analysis of SfM-derived high-resolution DEM for the Seyhan Delta shows at least 25 foredune ridges inland for 4 km. It is very important to know the origin and morphodynamics of ridges in terms of revealing the coastal evolution of the Seyhan Delta. Since these ridges preserve past shoreline positions Holocene foredune ridges in the study area can be used to help reconstruct the nature of paleoenvironmental change.

The use of plain (smooth and undeformed) rebars as longitudinal and transverse reinforcement in RC members is one of the most encountered practices in old construction technology. Thus, probable vulnerabilities due to plain rebar implementation should be considered in the seismic evaluation of RC buildings. It is known that reduced bond stresses distributed along the plain rebar surface due to the absence of the ribs leads to a resultant reduction in effective stiffness and an increase in rotation capacities for RC members. Therefore, RC buildings that were constructed according to the older design codes using plain rebars were expected to deform laterally beyond the anticipated deformation capacities that were determined based only on the RC members reinforced with deformed rebars. In this study, the modeling strategies were examined and verified with the results from an existing building test in the literature, and then the seismic performance of a five-story RC framed building, which was reinforced with plain rebars, was evaluated under nonlinear time-history analysis (NTHA). In order for code comparison, the nonlinear characteristics of the RC members were determined according to the previously suggested model for members reinforced with plain rebars and the current Turkish earthquake code regulations. The parameters investigated were (1) the number of members at each damage state, (2) the maximum interstory drift ratios, and (3) the normalized story shears by building weight considering the earthquake type (pulse type or non-pulse type) and predamage effects. The analysis results emphasized the importance of rebar characteristics in seismic performance assessment, because the use of plain rebars reduced the number of plastic hinges while leading to higher drift ratios. This phenomenon is analogous to the behavior of RC beams reinforced with plain rebars which fail with a smaller number of wide cracks rather than a greater number of narrow cracks as in the case of deformed rebars.

Seismic assessment of reinforced concrete (RC) buildings heavily relies on the deformation capacity predictions of members. Similarly, the prediction of the deformation capacity of retrofitted RC columns has the utmost importance for seismic retrofit design. In this paper, a new unified drift model is proposed in order to estimate the rotation capacity of RC columns retrofitted with concrete jacketing, steel jacketing and fibre-reinforced polymer (FRP) wrapping. In order to generate the model, an extensive database was compiled consisting of 269 columns composed of 39 concrete-jacketed, 91 steel-jacketed and 139 FRP-wrapped RC columns failing in flexure mode. In the proposed drift model, the key model parameters are the confinement stress ratio, the axial load ratio and the lap splice length. The accuracy and scatter of the estimations with regard to the previous models were studied. For all of the column retrofitting options, the proposed unified model was observed to have rotation predictions better than the previous models in terms of the mean of the predicted to experimental rotation capacity ratios and with a reduced standard deviation.