Mehdi Öztürk

Due to Türkiye’s location in an active seismic zone, the safe design of load-bearing systems in reinforced concrete buildings is essential. Under seismic effects, factors such as plan aspect ratio, slab type, and soil class directly influence the structural behavior, including building stiffness, diaphragm action, and lateral load transfer. In this study, a total of 12 reinforced concrete building models were analyzed using the STA4CAD software in accordance with the Turkish Building Earthquake Code (TBEC-2018), considering three key parameters: slab system (beam-slab and two-way ribbed slab), plan aspect ratio (1 and 4), and soil class (ZB, ZC, ZD). The models were evaluated in terms of natural periods, modal mass participation ratios, base shear forces, inter-story drifts, and second-order effects. Additionally, concrete, formwork, and reinforcement quantities were compared. The results indicated that as the soil class deteriorates, the demand for shear walls increases, which in turn shortens the natural periods by increasing stiffness. It was found that ribbed slab systems exhibit lower lateral stiffness and result in greater displacements and longer periods compared to beam-slab systems. Moreover, buildings with ribbed slabs required approximately 18–22% more reinforcement. Increasing the plan aspect ratio to 4 significantly increased the displacement in the weak direction and the need for shear walls. The findings highlight that slab type, soil class, and plan geometry collectively play a decisive role in seismic performance.

Türkiye topraklarının yaklaşık %92’sinin aktif deprem kuşağında yer alması ve nüfusun %95’inin bu bölgelerde yaşaması, mevcut yapı stokunun önemli bir bölümünü oluşturan yığma yapıların deprem güvenliğinin değerlendirilmesini zorunlu kılmaktadır. Bu çalışmada, yığma yapıların sismik performansı, 2007 Deprem Bölgelerinde Yapılacak Yapılar Hakkında Yönetmelik (DBYBHY) ile 2018 Türk Bina Deprem Yönetmeliği (TBDY) esas alınarak makro modelleme yaklaşımıyla karşılaştırmalı olarak incelenmiştir. İlk aşamada, yığma yapılarda kullanılan taş, tuğla ve kerpiç gibi malzemelerin mekanik özellikleri ile deprem etkileri altındaki davranışları değerlendirilmiştir. Ardından, her iki yönetmelikte yer alan yığma yapılara ilişkin tasarım hükümleri; taşıyıcı sistem boyutlandırması, malzeme dayanımı ve deprem yüklerinin hesaplanması açısından karşılaştırılmıştır. Uygulama kapsamında, Diyarbakır’da bulunan tarihi bir yığma yapı ele alınmış, laboratuvar verilerine dayalı olarak mekanik özellikler belirlenmiş ve SAP2000 yazılımı kullanılarak makro modelleme yöntemiyle analizler gerçekleştirilmiştir. Elde edilen bulgular, TBDY 2018’in DBYBHY 2007’ye kıyasla daha yüksek güvenlik düzeyleri öngördüğünü ve daha güvenli bir tasarım yaklaşımı sunduğunu ortaya koymaktadır.

Masonry retaining walls constitute an essential component of historic and urban infrastructure in seismic regions; however, their seismic performance remains insufficiently quantified due to material heterogeneity, limited tensile capacity, and complex soil–structure interaction. This study investigates the seismic response of historic stone masonry retaining walls using a finite element-based anisotropic macro-modeling approach. The analysis focuses on the perimeter retaining walls of Emirgan Grove in Istanbul, which represent culturally significant heritage structures constructed from natural limestone and cement–lime mortar. Material properties were defined based on experimental test results and representative values reported in the literature, while composite anisotropic behavior was incorporated into the numerical models. Static loads, earth pressures, and seismic actions were applied in accordance with the Turkish Building Earthquake Code (TBEC-2018) using the equivalent static earthquake load method. Representative wall segments with heights of 2.5 m, 3.5 m, 4.0 m, and 6.30 m were analyzed. The numerical results show that maximum compressive stresses reached approximately 0.48 MPa, remaining well below the allowable limit of 4.50 MPa, while maximum tensile stresses of about 0.28 MPa did not exceed the allowable tensile limit of 1.00 MPa. In contrast, shear stresses locally reached approximately 0.25 MPa, exceeding the allowable shear limit of 0.10 MPa, particularly along the soil–wall interface in taller walls. Sliding stability was satisfied in all cases, whereas overturning and shear behavior governed seismic vulnerability. These findings confirm that wall height is the primary parameter controlling seismic response and demonstrate the effectiveness of the proposed framework for preservation-oriented seismic safety assessment of historic masonry retaining walls.

This study investigates the seismic performance of existing reinforced concrete (RC) buildings, focusing on the influence of near-fault ground motions caused by proximity to fault lines. Compared to ordinary or far-fault earthquakes, near-fault earthquakes may have diverse effects on the response of buildings resulting from directivity and intense velocity pulses, which significantly amplify seismic demands. For this purpose, nonlinear time history analyses were carried out on a seven-story RC residential building that was subjected to near-fault effects and sustained heavy damage during the Kahramanmaraş earthquakes on 6 February 2023. The analyses used both near-fault and far-fault ground motion records, and four structural models were developed by gradually reducing the number of shear wall elements to assess the impact of diminishing lateral-load-resisting capacity. The results revealed that near-fault ground motions led to significant increases in base shear, inter-story drift ratios, and structural damage levels. Furthermore, a reduction in shear wall content resulted in a noticeable decline in seismic performance. These findings underscore the necessity of accounting for near-fault effects in seismic design and the critical role of lateral stiffness. The study emphasizes that considering near-fault characteristics is essential for ensuring the seismic resilience of RC buildings located in active seismic zones.

Depremler, hem tarihi hem de modern betonarme ve çelik yapılar için büyük risk oluşturan doğal afetlerdir. Türkiye gibi aktif deprem kuşağında yer alan ülkelerde yapı güvenliğinin sağlanması kritik bir öneme sahiptir. Deprem hasarlarını minimize etmek amacıyla geliştirilen sismik izolasyon sistemleri, yapıların deprem yüklerine karşı dayanıklılığını artıran etkili mühendislik çözümlerindendir. Bu çalışmada, Türkiye Bina Deprem Yönetmeliği (TBDY) 2018’e göre, sürtünmeli sarkaç izolatörlerin sismik performans üzerindeki etkisi konu alınmıştır. Çalışma kapsamında bir hastane binası, geleneksel yaklaşım ve sismik izolatörlü olarak hedef sismik performansı sağlayacak şekilde ayrı ayrı tasarlanmıştır. Sayısal analizler sonucunda, sismik izolasyonun yapı periyodunu uzatarak deprem kuvvetlerini azalttığı, göreli kat ötelemelerini düşürdüğü ve yapısal deformasyonları minimize ettiği belirlenmiştir. Ayrıca, izolasyon sisteminin maliyet analizi yapılmış ve izolatörlü bina maliyetinin geleneksel betonarme binaya kıyasla %20 daha fazla olduğu tespit edilmiştir. Ancak sonuç olarak, sürtünmeli sarkaç izolatör sistemlerinin, hastane gibi kritik yapıların sismik dayanıklılığını artırmada önemli bir mühendislik çözümü olduğu vurgulanmıştır.

This study investigates the in-plane shear behavior of solid brick masonry walls, both unreinforced and retrofitted using Reinforced Khorasan Jacketing (RHJ), a traditional pozzolanic mortar technique rooted in Iranian and Ottoman architecture. Six one-block-thick English bond masonry walls were tested in three configurations: unreinforced with Horasan plaster (Group I), reinforced with steel mesh aligned to wall edges (Group II), and reinforced with mesh aligned diagonally (Group III). All the walls were plastered with 3.5 cm of Horasan mortar and tested after 18 months using diagonal compression, with load-displacement data recorded. A detailed 3D micro-modeling approach was employed in finite element simulations, with bricks and mortar modeled separately. The Horasan mortar was represented using an elastoplastic Mohr-Coulomb model with a custom softening law (parabolic-to-exponential), calibrated via inverse parameter fitting using the Nelder-Mead algorithm. The numerical predictions closely matched the experimental data. Reinforcement improved the shear strength significantly: Group II showed a 1.8 times increase, and Group III up to 2.7 times. Ductility, measured as post-peak deformation capacity, increased by factors of two (parallel) and three (diagonal). These enhancements transformed the brittle failure mode into a more ductile, energy-absorbing behavior. RHJ is shown to be a compatible, effective retrofit solution for historic masonry structures.

In this study, beams produced by geopolymer concrete (GC) with different properties such as compressive strengths, stirrups ratios, and shear-span to effective depth ratio (a/d) were tested up to the failure to attain the load-deflection behaviors. Then, tested damaged beams were retrofitted using Carbon Fiber Reinforced Polymer (CFRP) in both shear and flexure to examine the CFRP strengthening efficiency. A three-point flexural test was conducted on both reference and retrofitted GC beams. According to this study, applying the CFRP strengthening to damaged GC beams increased the load-carrying capacity between 4% - 72%, depending on the compressive strength, stirrups spacing, and a/d with reference to the reference GC beams. The area calculated under the load-deflection graph of the retrofitted GC beams was lower than the reference beams in all tested series. The initial stiffness in the tested retrofitted beams was generally obtained lower compared to the reference GC beams. The deflection capability of the retrofitted beams in the tested series was between 18% -80% lower than the reference beams.

Geopolymer concrete (GC) is an emerging alternative construction material due to it being eco-friendly in production with considerably low carbon emissions. Despite being an alternative material, the structural behavior of GC is a rarely studied subject in the literature. The studies concerning the mechanical behavior of structural members made from GC have established the foundations of its practical usability. The current structural codes are exclusively for ordinary Portland cement concrete (OPCC), and the utilization of these for GC constitutes an open question. In this study, 12 GC beams with different shear span-to-effective depth ratios of 2.5, 3.5 and 4.5 were manufactured and tested in a three-point bending test setup. The effect of the shear reinforcement ratio was also taken into account (0, 0.34, 0.45 and 0.67%). The results were compared with the predictive capabilities of four structural codes and two equations in the literature (all for OPCC). In addition, comparisons were made with a very limited number of studies, which included predictive tools for the strength of GC. All specimens’ cracking moments were calculated with flexural tensile strength predictions and compared with experimental cracking moments. Moreover, particularly for the beams that failed in flexure, the ultimate bending moments were compared with the predictions of two structural codes for OPCC. It was observed that the best predictions of the cracking moment could be made by the equation of Diaz-Loya et al. (2011), which resulted in the lowest coefficient of variation (COV) and consistently predicted on the safe side, whereas, even with a lower COV, EC2 consistently overestimated the cracking moment. For the ultimate moment capacity, it was observed that both ACI318 (2019) and TS500 (2000) delivered relatively good predictions and could be employed confidently.

Active research is ongoing regarding the mechanical behavior of structural members manufactured from geopolymer concrete (GC), as it lacks standardized/codified manufacturing and design procedures. This study aims to address the shear behavior of GC beams. First, a consistent trial–error-based approach was used to develop the optimal mixture ratio (102.38/234.0 for NaOH/Na₂SiO₃) in terms of workability and consistency for the production of six (6) test specimens with span-to-depth ratios of (a/d) of 2.5, 3.5, and 4.5 and transverse reinforcement intervals of 10, 15, and 20 cm. Then, shear failure tests using a three-point bending setup were conducted and analyzed statistically. As a first attempt in the literature, an empirical expression for shear capacity prediction that was specifically tuned for GC beams was given. This expression, along with seven other similar expressions for ordinary concrete beams from the literature, and various practice codes were tested against a pool of experimental shear failure results given by four (4) different researchers. As a measure of the predictive capability, coefficient of variation (COV = standard deviation/average) values were obtained, and the lowest COV value of 0.305 suggested that the expression obtained the highest predictive capability, whereas more common practice codes such as ACI318, EN1992, and ENV1992 produced COV values of 0.435, 0.374, and 0.627, respectively. Finally, this study provides a working expression for the shear capacity estimation of GC beams and a mixture ratio for the practical manufacturing conditions of workability and consistency, with a slump value of 270 mm and a 90 min setting time.