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    Constitutive Model and Mechanical Properties of Grade 8.8 and 10.9 High-Strength Bolts at Elevated Temperatures
    (Asce-Amer Soc Civil Engineers, 2024) Saglik, Huseyin; Etemadi, Ali; Chen, Airong; Ma, Rujin
    This paper presents an experimental study on the determination of the mechanical behaviors of Grade 8.8 and 10.9 high-strength bolts at elevated temperatures. Strength reduction coefficients are obtained based on test results at temperatures ranging from 20 degrees C to 900 degrees C, for both yield and ultimate stresses. Simplified expressions are presented to identify the strength reduction factors at considered temperatures. At 400 degrees C, the yield and ultimate strengths of bolts decrease by 30%-35% for both grades compared to those in ambient temperature. Yield strengths are 30% and 20% of yield strengths of Grade 8.8 and 10.9 bolts at ambient temperature, respectively, when the temperature exceeds 500 degrees C. The ultimate strength decreases slightly slower than the yield strength at high temperatures. Although the decrease in ultimate strength follows the decrease in yield strength at elevated temperatures, it is slightly slower. About 3%-6% of yield and ultimate strengths at ambient temperature remain for both grades at 700 degrees C. Moreover, a series of expressions are provided to obtain the full range stress-strain curve of high-strength bolts at elevated temperatures. Comprehensive literature studies are taken into consideration to propose a more generalized description of the stress-strain curves. The proposed model can be fully drawn by only using elastic modulus, yield, and ultimate stresses at ambient temperature. It is shown that the proposed model has enough efficiency to describe the general material behavior at elevated temperatures.
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    Öğe
    Direct Displacement Based Design of RDC Frame-Shear Wall Structures
    (İstanbul Gelişim Üniversitesi, 2021) Balkaya, Can; Etemadi, Ali; Genç, Öznur
    A large part of Turkey's urban region is located in the seismic prone zone and in terms of population, the majority of densely populated cities are located close to near-fault regions. It is very important to determine the behaviors of structures against external forces after destructive earthquakes. Structural and non-structural damages that occur during the earthquake usually arise from lateral displacements occurring in the structural system. This is why, in recent years, the displacement-based design has become more important when compared to the force based design. In this study, the Direct Displacement Based Design method under earthquake forces are explained. The process steps of this method on a frame-wall structure are clarified. The dynamic behavior of a moment resistant structures and a combined system with shear walls are compared. The finite element method used to analysis of reinforced concrete building models. Some model with moderate and high vibration period is adopted for dynamic analysis. An arrangement of the shear walls is changed in story plan of models. The dynamic analysis has shown quite different response among the structural systems. The difference in dynamic behavior is coming from the interaction of dynamic response between shear walls and moment resistant frames. Furthermore, the important role of shear walls displacements in transferring lateral loads is clarified with numerical examples. The positive role of RC shear walls on the combined structures under earthquake forces has been emphasized.
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    Öğe
    Shaping Effects on Long Span Bridge Deck Aerodynamics
    (İstanbul Gelişim Üniversitesi, 2023) Etemadi, Ali
    An aerodynamic circumstance of wind pressure surrounding the long-span bridge allocates many theoretical and experimental research to this topic. Determination of the materials and optimal cross-sectional shape of bridge decks that affected a dynamic behavior of long span bridge deck is still included in current research issues and works to be continued in this path. These include the Lack of sufficient awareness of wind forces, stemming from complex nature, and the unpredictability of the wind nature. In this study, in addition to recognizing the aerodynamic behavior of the flutter, the acting pressure forces on the bridge deck are investigated. The geometrical shape of decks, wind velocity, and flutter conditions are adopted as design variables that affected the dynamic forces exerted on bridge decks. A common type of geometric sections of the long-span bridge deck and effective aerodynamic phenomena are examined. The hollow box steel suspended deck and double cells box girder linked via upper flanges and cells linked via the top and bottom flanges are adopted for Computational Fluid Dynamic (CFD) approach. Thus, aerodynamic instability and turbulent torsional flutter flows, as well as a trail of shedding vortices around the bridge decks, are investigated. By changing some geometrical parameters of commonly used bridge sections, the optimal cross-section in terms of turbulence created above and below the deck section is examined and an optimal cross-sectional shape variable is proposed. The shape variable and section dimensions adopted for CFD-Simulations are similar to the dimensions and materials used in previous laboratory specimens of wind tunnels to be able to interpret the results and possibly verify them with the result of the current study.
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    Öğe
    Static Response of Functionally Graded Porous Circular Plates via Finite Element Method
    (Springer Heidelberg, 2024) Doori, Silda Ghazi Mohammed; Noori, Ahmad Reshad; Etemadi, Ali
    The main purpose of this paper is to investigate the axisymmetric bending response of functionally graded porous (FGP) circular plates. The material properties are changed continuously in the thickness direction of the plate. Three distinct porosity distributions uniform, symmetric and monolithic are employed. The effect of porosity on the axisymmetric bending analysis of circular plates is examined parametrically. In this study, clamped and roller supports which commonly serve to achieve ideal boundary conditions in numerous engineering applications are used. The finite element method is employed for numerical analysis. The principal of the potential energy is used to obtain the governing equations. To generate the model of the FGP circular plates, an eight-node quadratic quadrilateral element with two degrees of freedom on each node is utilized. The results of this study are confirmed by the existing published literature. A good agreement between the results of the presented model and the previous literature has been observed. The results of the present study show that plate deflection increases with the increase of the porosity coefficient and the ratio of radius to thickness of circular plates. By increasing the porosity coefficient, the displacement values of the plates made of uniform porosity distribution is effected more than those of other porosity distributions.
  • Küçük Resim
    Öğe
    The role of masonry infills on the interstory drift demand of reinforced concrete frames
    (Elsevier Sci Ltd, 2024) Etemadi, Ali; Balkaya, Can
    Most frame buildings, especially those with shear -type moment resistance frames, are affected by masonry infill panels, which change the mechanical properties of whole systems in a big way. In turn, seismic performance varies depending on the infill panel and frame interactions. In conventional structural design practice, such interaction has been overlooked. This study looks at the range of local displacement demands in shear -type frames with and without infill panels. Generic frames are developed by tuning the story stiffness and mass to produce a reasonable period range between 0.2 and 2.0 s. The masonry infill panels are simulated through equivalent diagonal struts. A Bouc-Wen-based hysteretic model is applied to incorporate the post -yielding hysteresis degradations of both columns and masonry panels. The hysteresis loop control parameter values are also given for incorporating masonry infill properties. The correlation analysis between the strength and stiffness of RC frames and masonry infills is supplied as an instrument for calibrating the hysteretic model. In the collection of records, there are a lot of near -fault ground motions, which puts a lot of seismic demands on the buildings. The modification factors via regression analysis are proposed using over 1254 nonlinear response history analyses. This modification factor is figured out by looking at the difference between the mean drift spectrum for a set of generic frames that are both bare and filled. The nonlinear analysis shows that residual drift demands can be reduced in the case of panel effects that exist for masonry-infilled mid -rise RC shear -type frames.