Journal of Structural Engineering & Applied Mechanics

Umit Necmettin ARIBAS Mehmet Hakkı OMURTAG

This paper investigates the internal forces of sandwich exact conical helices using the mixed finite elements based on Timoshenko beam theory and a numerical method of cross-sectional warping inclusion. The exact conical axis geometry is derived over Archimedean and logarithmic planar curves. The exact curved mixed finite element has two nodes and twenty-four degrees of freedom in total. The constitutive equations of sandwich sections are derived by modifying the constitutive equations of an orthotropic continuum based on the classical rod theory. The cross-sectional warping included torsional rigidity is taken into account using a numerical method in the mixed finite element formulation. A convergence analysis for the support reactions of sandwich exact conical helices having fixed-fixed boundary conditions is performed. The results are compared with the displacement type finite element results of computer aided design programs. Finally, the internal forces of sandwich exact conical helices over Archimedean and logarithmic planar curves are obtained for various conicity ratios, pitch angles and the number of active turns. In order to investigate the influence of cross-sectional warping on precision, the warping included results are compared to the conventional torsional rigidity results. In the scope of the investigated internal forces, the maximum influence of cross-sectional warping on the results is obtained for the normal force. The influence of cross-sectional warping on the normal force increases as the pitch angle or the conicity ratio decreases. Besides, the maximum influence of the conical helix geometry on the warping included internal forces is obtained for the torque.

https://doi.org/10.31462/jseam.2019.04153163

Ali Mortazavi

Fuzzy logic is widely used as the fundamental platform for the many artificial intelligence systems. In the theory of fuzzy set, membership functions (MFs) provide an infrastructure for determining the degree of truth in a fuzzy model. So, they can play important role in the performance of these logical mechanisms. Different types of MF can be defined to fuzzification-difuzzification process (i.e. converting Boolean input to a fuzzy output and vise-versa). They are categorized and named based on the shape of their diagrams as triangular, Gaussian, trapezoidal and so forth. In the current study the effect of MF’s type on the search capability of the fuzzy-reinforced metaheuristic optimization algorithms is assessed. To meet this aim, a metaheuristic technique strengthen with fuzzy adjustment mechanism is tested on solving a number of benchmark problems involving different types of MFs. The results indicate that due to stochastic essence of metaheuristic approaches the type of MF does not seriously affect the search capability of these techniques. So, the MFs in the field of metaheuristic should be selected based on the simplicity criterion. It means the simplest MF which provides the designers requirements can be the best choice.

https://doi.org/10.31462/jseam.2019.04164173

Mehmet Aydın KÖMÜR İbrahim Özgür DENEME Ramazan Oruç

Seismic isolation systems can be used in new structures to reduce the negative effects of the earthquake on the building. The lead rubber bearing (LRB) is one of the most commonly used seismic isolators. This study focused on the behavior of Reinforced Concrete (RC) frame systems with fixed-base and Lead Rubber Bearing systems under Near-Fault (NF) and Far-Fault (FF) records. For this purpose, two-plane frame systems with 4 and 8 story were designed. Nonlinear behavior of both superstructure and isolation system was taken into consideration in modeling. The nonlinear time history analysis method was used in the seismic analysis of reinforced concrete frame systems. Finally, story acceleration, interstory drift ratio, base shear force and distribution of plastic hinges and their damage conditions were evaluated. The results of the analysis showed that the effects of the NF earthquake record on the frame system had generally greater according to the effects of the FF earthquake records.

https://doi.org/10.31462/jseam.2019.04174189

Ali İhsan KARAKAŞ Ayse Daloglu

A graded harmonic solid ring finite element model (FEM) is developed from the three-dimensional theory of elasticity using Fourier series expansion in circumferential direction to investigate free vibration characteristics of functionally graded (FG) thin and thick-walled cylinders parametrically. The mechanical properties of the finite length FG cylinders composed of metal (stainless steel) and ceramic (silicon nitride) are assumed to vary in radial direction according to a power law variation as a function of the volume fractions of the constituents. The frequency characteristics of the FG cylinders depending on various parameters such as circumferential harmonic number, power law exponent, thickness to radius ratio, length to radius ratio, and constituent material configuration are investigated through numerical simulations. When the graded harmonic model is compared with the previous models in the literature the agreements are found to be excellent. Also, a reduction in computational effort is provided using a smaller number of graded elements required for a fair estimation of vibrational behavior of such axisymmetric structures. As far as the numerical results are considered it is observed that thin and thick-walled cylinders behave in a different way for increasing circumferential harmonic number. The influence of the power law exponent on the frequency depends on the constituent material position and it does not affect the circumferential harmonic number at which the fundamental natural frequency occurs. As a conclusion, it can be stated that the free vibration behavior of FG cylinders can be regulated arbitrarily by altering material configuration and power law function as well as geometrical parameters.

https://doi.org/10.31462/jseam.2019.04190206

Önder Halis Bettemir Kâzım Türk

In this study, structural analysis software is developed to analyze buildings by slope-deflection method with minimum data entry requirement. It is adequate to define the dimensions of the columns and beams for one floor and the developed software replicates the assigned dimensions for the remaining floors. Similarly, vertical loads on the beams are also replicated for each floor. Aforementioned design approach expedites the data entry process without affecting the reliability of the analysis for preliminary design stage. Structural analysis software forms the slope-deflection equations and computes the rotations of the nodes and horizontal displacements of floors by matrix inversion. The software gives feedback on the suitability of the dimensions of the beams and columns by considering the obtained moments, shear forces, and normal forces. The designer can update the dimensions of the columns as well as beams and repeat the analysis until the dimensions are optimized. Henceforth the structure can be analyzed on robust structural analysis software with a few modifications. This approach would save important amount of time and work hours at design offices. Because state-of-the art building information modeling software require many attribute data about each structural elements and materials. Therefore, updating any section of the structure may cause revision of the attribute data as well. Developed software is tested on 20 floor structure with four spans. Utilization of a simple design approach decreases the allocation of robust design software and reduces the required number of structural analysis software for the design offices. In addition to this, the structural analysis software is freeware and can be used by civil engineering students for validation of their solutions.

https://doi.org/10.31462/jseam.2019.04207218