Journal of Structural Engineering & Applied Mechanics

Zeynep Fırat Alemdar Erdal Gül

The most important reasons for the usage of steel as a building material are its high strength and ductile behavior, which can be defined as inelastic deformation or displacement capacity under a certain load. Steel frames are required to sustain the horizontal loads during an earthquake. The steel frames are classified as moment-resisting steel frames, concentric steel braced frames, eccentric braced steel frames, and buckling restrained braced frames. These steel frames can be designed with a high ductility level frame, limited ductility level frames, and ductility level mixed frames. In this study, stress concentrations due to the maximum compression force that may occur during an earthquake have been examined by the finite element method at the connection point of the circular cross-sectional braces of the central X-type braced steel frame with a high ductility level. Stress concentrations in the X-type brace were investigated depending on the variation of the cut surface required for the connection plate due to the change in the angle between the braces and the differences in the weld thickness applied in this region. In the models, the angle between the braces is designed as 60°, 75°, and 90° and the weld thicknesses are defined as 3.5 mm, 5 mm, and 7 mm. The results are obtained by applying the same compressive and tensile forces to the braces under the same boundary conditions and compared for these different models. It is obtained that the highest stress values occur along the direction of the tensile force in the tension profile and nearly at a distance of 5 mm after the cut. The maximum stress values decrease when the intersection angle between the braces increases from 60° to 90°.

https://doi.org/10.31462/jseam.2024.01001023

Okan Bakbak Özgen Ümit Çolak

Creep behavior is observed even at room temperature in polymers and polymer composites under constant stress. In the design of structural elements using these materials, the determination of creep compliance for structural strength and performance analysis is crucial in terms of reliability and usability. In this study, the creep compliance of pure epoxy and functionalized graphene-reinforced epoxy nanocomposites were experimentally investigated and compared at room temperature at constant stress levels of 50, 100, and 200 MPa representing the viscoelastic region, yielding region and viscoplastic region, respectively. To reveal the effect of temperature as well as stress level on this behavior, the creep compliance of epoxy and graphene-epoxy nanocomposites was investigated at 65°C in addition to room temperature after the pure graphene used as a reinforcement element was functionalized with Triton X-100, nanocomposite production was carried out. In 2h creep tests, it was observed that as the constant stress level increased, the creep compliance increased and the creep compliance of the nanocomposite was lower than that of the epoxy at all stress levels. The creep compliance of the epoxy was improved by 65% with the addition of functionalized graphene at room temperature and a stress level of 100 MPa. As the temperature increased, the creep compliance of both epoxy and functionalized graphene-epoxy nanocomposite increased due to molecular mobility and viscous flow. However, at high temperatures, the positive effect of functionalized graphene on the compliance of the epoxy is higher. At 65°C and a stress level of 100 MPa, the improvement rate of creep compliance is 78%. Functionalized graphene exhibited a more effective behavior on creep resistance at high temperatures. The obtained results showed that creep compliance was significantly affected by stress level and temperature.

https://doi.org/10.31462/jseam.2024.01024033

Adnan Kıral Ali Gürbüz

As a way to reduce structural vibration, many buildings are initially intended to be base-isolated. However, because of the base isolators' inherent nonlinear behavior, particularly in earthquake-prone areas, buildings equipped with base isolation systems may experience significant displacement demands. Therefore, in certain situations, it might be required to use additional damping devices to control the seismic response of base-isolated buildings. This study examines three different building models: Fixed Base (FB), Isolated Base (IB), and Isolated Base with installed Viscous Dampers (IB&VD) in the base layer of the building. Sosokan, a nine-story structure on Keio University's Yagami Campus, is utilized for this purpose. The building is modeled in MATLAB. A state-space representation of the building with a Maxwell-type viscous damper model is used. The responses of the building models with FB, IB, and IB&VD are evaluated by time history analyses using eight ground motion records. Certain engineering requirements criteria, such as inter-story drift ratios and absolute acceleration, are taken into consideration while evaluating the findings of the analysis. Based on one of this study's main findings, a base-isolated building with passive viscous damping in the base layer could significantly reduce both maximum seismic displacement and acceleration. Maximum acceleration and inter-story drift are lowered by up to 92% and 89%, respectively, when IB&VD is scaled to the FB model. Based on the results of this study, passive viscous dampers combined with building base isolation are not only useful for multi-objective optimization (i.e., reducing acceleration as well as inter-story drift) but they can also be used to reduce high-frequency accelerations, which could be important for building equipment that is sensitive to acceleration.

https://doi.org/10.31462/jseam.2024.01034050

Zekai Angın

This study investigated the suitability of Trabzon stone, which is used as a building stone in many areas in and around Trabzon province, as an aggregate. It was found that the uniaxial compressive strength values of the samples taken from the quarry were 87-130 MPa, P-wave velocities were 5048-5642 m/s, density value was 2.58 g/cm3, apparent porosity values were 2.77-4.54%, water absorption values by weight were 1.04-1.78% and water absorption value by mass was 2.0%. Weight loss in the freeze-thaw test was 0.36%, weight loss in the wet-dry test was 0.22%, loss in the magnesium sulfate test was 13%, Los Angeles fragmentation resistance in coarse aggregate was 22%, abrasion resistance value was 18% and methylene blue value was 0.9%. When the results were analyzed, it was found that the mass water absorption rate and the magnesium sulfate test results were above the values required by the standards. Although these rocks are used as marble, it has been determined that the waste material is not suitable for use as ballast, crushed stone, stone fill, pere, and masonry for road and concrete construction. Despite this result, it is necessary to investigate the usability of materials from other marble quarries in the region as aggregates.

https://doi.org/10.31462/jseam.2024.01051057

Rafail Mehtiyev

In the reviewed paper, the case of a transverse displacement plane with two pairs of biperiodic (corresponding to the X and Y axes) cohesive cracks of unequal size, weakened by biperiodic circular holes, is considered. The circular holes are filled with reinforcing fibers and the surface is covered with a thin homogeneous non-metallic material of the same thickness. In this case, boundary issues between filler and coating, coating and matrix, and boundary issues along cohesion cracks are determined. For both cases, the solution to the problem is sought in the form of an analytical function with complex variables. According to the boundary conditions of the case, a system of unequal algebraic equations is found along the holes, and singular integral equations are constructed along the cohesion cracks. Currently, the singular integral equations are brought to the system of finite linear algebraic equations with the help of mathematical transformations. Both systems are solved together using the Gaussian method and the crack growth is determined using the stress intensity factor formulas at the crack tips. During the solution of the problem, the stress intensity coefficients at the end are found by the variation of the length of the cracks based on the radius of the circular holes.

https://doi.org/10.31462/jseam.2024.01058068

C.C. Hong

The effects of shear deformation theory and improved shear correction factors on the advanced computation of frequencies by using the fully homogeneous equation for thick functionally graded material (FGM) circular cylindrical shells are studied. It is quite reasonable to consider the extra advanced effect of third-order shear deformation theory (TSDT) of displacements on the varied shear correction coefficient. The values of advanced nonlinear shear correction coefficient are usually functions of the nonlinear coefficient term in TSDT, power-law exponent parameter, and environment temperature. The main achievements in the nonlinear case of displacements and with the varied value of shear correction coefficients, the non-dimensional fundamental frequencies are estimated, investigated, and compared with the values in the linear case. This paper aims to study the fundamental frequencies of very thick FGM cylindrical shells under the advanced effects of shear deformation theory and improved shear correction factors.

https://doi.org/10.31462/jseam.2024.01069083