Challenge Journal Publications (TULPAR Academic Publishing)
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Examining the effects of different seismic base isolators on the seismic behavior of a real-size steel truss structure
Full text linkIn this study, the seismic behavior of a real-size steel truss structure is examined for elastomeric isolator, double friction pendulum isolator, and fixed support conditions. Hence, the main aim of the study is to examine which type of support is safer for seismic response of a real-size steel truss structure, considering the structural reactions under earthquake and other acting load effects. To do this, the structural models generated with three different support conditions are examined in detail in terms of earthquake characteristic according to conducted structural seismic analyzes. The real-size steel truss structures are modeled in SAP2000 structural analysis program and are designed in accordance with the Turkish Building Earthquake Code-2018 specifications. The snow and wind loads acting on the truss structures are calculated in the direction of TS EN 1991-1-3 and TS EN 1991-1-4 specifications, respectively. The earthquake forces are implemented to the truss structure through mode superposition method. Finally, the truss structure is comparatively examined in terms of the structural weight, base shear force, natural vibration period, and relative drift. As regards to the obtained results, it has been observed that the seismic responses of the steel truss structure are remarkable better when the seismic base isolator is implemented into the structure
Influence of damage state threshold variability on the seismic vulnerability analysis of masonry aqueducts
Full text linkThe accuracy of fragility curves, a key outcome of seismic vulnerability studies, directly influences rational seismic risk assessments. In this study, analytical-based fragility curves for a masonry aqueduct were derived using tested earthquake-based Intensity Measure (IM) parameters and various threshold limit values for specific damage states, as commonly used in the literature. The Maximum Intensity Damage Ratio (MIDR) thresholds for specific damage states proposed by FEMA 356, GERMHS, and ASCE 41-13 standards were considered. Additionally, damage state thresholds were determined through a capacity curve obtained via nonlinear static analysis and empirical relationships found in the literature. The effect of damage thresholds on the Probability of Exceedance (PoE) values for a specific damage state was analyzed using the reference MIDR values determined in this study. Based on earthquake ground motion records, PoE values corresponding to different damage states were evaluated separately for each IM parameter. The results demonstrate that the damage threshold value significantly impacts the developed fragility curves. Therefore, when developing fragility curves for the seismic risk assessment of masonry structures, it is crucial to analyze and determine the appropriate threshold levels for each structure individually, rather than directly applying the threshold values used in the literature
Long-term durability of red mud-modified cement mortars: Effects of high temperature and freeze-thaw cycles
Full text linkThe use of industrial by-products such as red mud in cementitious materials addresses sustainability by reducing environmental impact and improving performance. As a hazardous waste from aluminium production, red mud offers a promising solution for waste management and improves the mechanical and durability properties of mortar when used as a partial cement replacement. This study investigates the long-term mechanical and durability properties of cement mortars modified with red mud, a by-product of alumina production. Red mud was incorporated at substitution percentages of 5%, 10%, 15%, 20%, 25%, 30% and 35% by weight of cement. The mortars were subjected to harsh environmental conditions such as high temperatures (200°C to 600°C), freeze-thaw cycles (50 and 100 cycles), and normal curing conditions at 365 days of age. The study showed that partial replacement of cement with red mud significantly affected the mechanical and durability properties of the mortars. The optimum red mud replacement level of 10% showed that microstructural compactness and hardness were improved by increasing the ultrasonic pulse velocity, dynamic modulus of elasticity and flexural strength. Durability tests showed improved thermal resistance at moderate levels of red mud content, while higher levels adversely affected freeze-thaw performance. These findings confirm that a 10% red mud substitution offers the best balance between strength, durability, and sustainability
Photocatalytic activation of fibrous lightweight polymer concrete surfaces under artificial light source
Full text linkIn general, surface contamination of building materials is caused by pollution, which can be divided into human-made and natural sources. Building materials whose surfaces are exposed to pollutants from these sources for a long time show chemical and physical degradation and lose their function over time and their service life is shortened. Due to photocatalytic feature provided to the material surfaces, organic pollutants on the surface are degraded as a result of oxidation and reduction reactions under the influence of light. In this study, the self-cleaning performance was measured on the surfaces of fibrous lightweight polymer concretes with titanium dioxide (TiO2) reinforcement incorporated into the structure. Perlite-based concrete specimens with TiO2/resin ratios of 0%, 3%, 6% and 9% and fiber/resin ratios of 0%, 0.5% and 1% were prepared. When the results of the self-cleaning test with Rhodamine B dye were examined, the samples with a TiO2/resin ratio of 9% had the highest degradation percentages of about 67%. This study shows that photocatalytic properties can be imparted to lightweight polymer concretes with different structures from conventional concrete by TiO2 reinforcement
Enhancing the mechanical performance of perforated steel plates through fiber-reinforced composite reinforcement: A finite element analysis study
Full text linkReinforced concrete and steel plates are widely used in civil engineering and are important components of many structural systems and ground reinforcement projects. These plates effectively carry different loads, enhance ground support, and improve the durability of structures. Moreover, the proper selection and use of these materials during the design and planning stages of construction projects have a direct impact on cost and time efficiency. In addition to their structural contributions, the effective use of reinforced concrete and steel plates is critical for the safety and success of construction projects. In order to transfer loads to the frame system, reinforced concrete plates serve as horizontal load-carrying components. Load-bearing capacity, stiffness, fire resistance, and sound insulation are important properties of reinforced concrete plates. Perforated plates are widely used in structural applications but suffer from stress concentration around openings, reducing their mechanical performance. This study investigates the reinforcement of perforated steel plates using fiber-reinforced polymer (FRP) composites around holes to enhance structural integrity. The research employs finite element analysis (FEA) to assess the effects of different reinforcement widths under varying loads. A detailed comparison of stress and deformation distributions before and after reinforcement is presented. The findings indicate that FRP reinforcement significantly reduces stress concentration and improves the load-bearing capacity of perforated plates, providing practical insights for industrial and construction applications
Levobupivacaine versus bupivacaine for spinal anesthesia in jackknife position: A randomized trial in pilonidal sinus surgery
Full text linkBackground: This study aimed to compare the efficacy and clinical characteristics of levobupivacaine and bupivacaine for spinal anesthesia in the jackknife position during pilonidal sinus surgery.Materials and Methods: The onset and maximum level of sensory block were similar between groups. Regression to S2 occurred significantly earlier in the levobupivacaine group (139.7 ± 7.3 min) compared with the bupivacaine group (165.2 ± 8.0 min, p=0.001). The duration of motor block was also shorter in the levobupivacaine group (125.8 ± 6.5 vs. 148.5 ± 7.2 min, p=0.001). Hemodynamic stability and side-effect profiles were comparable between groups.Results: The onset and maximum level of sensory block were similar between groups. Regression to S2 occurred significantly earlier in the levobupivacaine group (139.7 ± 7.3 min) compared with the bupivacaine group (165.2 ± 8.0 min, p=0.001). The duration of motor block was also shorter in the levobupivacaine group (125.8 ± 6.5 vs. 148.5 ± 7.2 min, p=0.001). Hemodynamic stability and side-effect profiles were comparable between groups.Conclusions: Levobupivacaine provides shorter motor block duration and faster recovery compared with bupivacaine, making it particularly suitable for short procedures performed in the jackknife position. Larger multicenter trials are warranted to validate these findings
Triple threat: Anesthetic approach to IVF twin gestation, pre-eclampsia and peripartum cardiomyopathy in caesarean section
Full text linkPeripartum cardiomyopathy (PPCM) is a rare idiopathic condition frequently presenting with heart failure secondary to left ventricular systolic dysfunction towards the end of pregnancy or in the months following delivery. Can present as acute life-threatening pulmonary oedema in late pregnancy or early puerperium, its diagnosis is mainly by exclusion of other causes of cardiac dysfunction. Anaesthetic management of such cases poses a challenge; due to the increased risk of various perioperative complications. Morbidity is high due to the reduced physiological reserve in pregnancy. PPCM and severe pre-eclampsia can co-exist and their clinical presentation may overlap, making the diagnosis more difficult and often delayed, with potentially devastating consequences. We report the successful anaesthetic management of lower segment caesarean section in a patient with PPCM with preeclampsia of IVF twin gestation
Behavior of multi-cell steel columns under impact loading
Full text linkThis study investigates the behavior of multi-cell steel columns (MCCs) under impact loading through both experimental and numerical analysis. Twelve specimens, including single-cell columns (SCC) and four-cell MCC configurations, were tested in empty and concrete-filled conditions. The specimens were categorized into three groups based on a fixed height-to-width ratio (R). A nonlinear finite element model was developed using ABAQUS and validated against experimental data. Key parameters, including peak deflection, failure modes, deflection-time relationships, maximum impact forces, energy absorption and the rectangularity ratio effect, were examined to provide insights into impact-resistant structural design. The results demonstrate that the internal partitioning of the column into cells significantly reduces local buckling under impact loading by enhancing the section’s local stiffness. In addition, internal partitioning improves energy absorption for empty models. On the other hand, concrete-filled models do not show the same behavior although concrete filling significantly improves resistance to impact forces. The results also provides that increase of the R ratio results in an increase in impact force and a decrease in mid-point displacement. For empty single-cell columns, an increase in R results in a decrease in energy absorption, which may be due to energy dissipation through local buckling under the falling impactor. These findings contribute to the advancement of impact-resistant column designs for applications in structural and transportation engineering
Impact of wrap quantity on strength of damaged and undamaged CFRP-reinforced structural members
Full text linkIn this study, the effect of carbon fiber reinforced polymer (CFRP) wrapping on the compressive and bending behavior of damaged reinforced concrete structural elements located in high earthquake risk areas was investigated in detail. The main objective was to evaluate the potential of CFRP wraps as an effective strengthening technique for improving the mechanical performance of concrete members that have already sustained damage. During the experimental phase, concrete specimens in the form of 15×15×15 cm cubes and 10×10×50 cm prisms were prepared using CEM IV 32.5 pozzolanic cement, which is commonly used in structural applications due to its durability and environmental benefits. After subjecting these specimens to controlled damage to simulate real-life structural degradation, they were reinforced using single and double layers of CFRP wrapping. The mechanical performances of these wrapped specimens were then assessed through compressive and bending strength tests. The results demonstrated that CFRP wrapping significantly enhanced the compressive strength of the specimens, with double-layer applications showing the greatest improvements. However, the effect on flexural strength was found to be more limited, indicating that although CFRP is 60.83% effective in resisting compressive loads, its contribution to flexural capacity may require additional considerations. Furthermore, double-layer CFRP wrapping not only improved strength but also increased deformation capacity, indicating enhanced ductility and energy absorption. Despite the relatively high cost of CFRP materials, these findings highlight the technique as a practical and efficient solution for the rehabilitation and strengthening of compression load-bearing members, particularly in regions vulnerable to seismic activity
