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    Behaviour of steel cushions subjected to combined actions
    (Springer, 2018) Yuksel, Ercan; Karadogan, Faruk; Ozkaynak, Hasan; Khajehdehi, Arastoo; Gullu, Ahmet; Smyrou, Eleni; Bal, Ihsan Engin
    Mild steel is relatively low-cost and easily accessible material to fabricate some structural members. It would be a significant advantage if seismic energy dissipaters that are used in structures constructed in the earthquake prone areas, could also be produced on site. In this paper, a promising seismic energy dissipater made of mild steel, so-called steel cushion (SC) is presented. It is provided experimental and analytical responses of SCs subjected to bi-axial loadings. SC rolls under the lateral loading that allows relocation of the plasticized cross-section. Henceforth, SC dissipates considerable amount of seismic energy. A series of tests were performed to achieve experimentally the behavior of SC subjected to longitudinal and transversal loading. Finite Element Models (FEMs) were also generated to reproduce the experimental backbone curves and to predict the bi-directional response properties for discrete transversal forces and plate thicknesses. Closed-form equations were derived to determine yield and ultimate forces and the corresponding displacements as well as location of the plasticized sections. The behavior of SC could either be projected by the FEMs with the exhibited parameters or by means of the proposed closed-form equations and the normalized design chart.
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    Cyclic behavior of reinforced concrete cladding panels connected with energy dissipative steel cushions
    (Elsevier Sci Ltd, 2019) Karadogan, Faruk; Yuksel, Ercan; Khajehdehi, Arastoo; Ozkaynak, Hasan; Gullu, Ahmet; Senol, Erkan
    Precast concrete structures show damage after the destructive earthquakes and indicate that the connections of reinforced concrete (RC) cladding panels might be inadequate. RC cladding panels greatly increase the lateral stiffness and strength of the building when they are rigidly connected to the structural system. However, this also increases the seismic requirements. Consequently, a robust mechanical connection device with energy-dissipating capability was produced for RC cladding panels. Extensive experimental and numerical studies on an energy-dissipative steel cushion (SC) connection device were carried out in the framework of the SAFECLADDING project. Cladding panel tests were conducted with various connection configurations. The fundamental variables are the location, quantity, and thickness of SCs used in the cladding systems. The test results demonstrate that the SCs used in panel-to-panel and panel-to-support connections made large contributions to the total energy dissipation capacity. The parameters of a numerical model were also evaluated to reproduce the experimental results.
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    An improved input energy spectrum verified by the shake table tests
    (Wiley, 2019) Gullu, Ahmet; Yuksel, Ercan; Yalcin, Cem; Dindar, A. Anil; Ozkaynak, Hasan; Buyukozturk, Oral
    Input energy is the principal component of the energy balance equation. It is beneficial to determine, through its components, how the recoverable and irrecoverable energies are distributed within the structural elements. Several equations and attenuation relations to define mass-normalized input energy spectra exist in the literature. They are mainly proposed for elastic systems subjected to far-fault EQs. There is a lack of experimental verification of these proposed spectra. In this paper, experimental assessment was performed to the existing spectra, and further improvements were accomplished. For this purpose, steel cantilever columns were tested on the shake table for two specific historical EQs coincidently having similar spectral acceleration values. Based on the experimental results, a three-part mass-normalized relative input energy spectrum was formulated including soil type, EQ (corner period, intensity, duration, spectral acceleration, and velocity), and structural behavioral characteristics (period and structural damping). The proposed input energy spectrum was experimentally calibrated and numerically validated for various EQs featuring near-and far-field types. Analytical and experimental comparisons were made between the previously developed spectrum and the newly proposed one. The validation studies and the statistical evaluations exposed that the proposed spectrum yielded better agreement with the experimental and numerical results.
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    Investigation of the Effect of Reinforcement Type on the Flexural Performance of Slab Tracks
    (Asce-Amer Soc Civil Engineers, 2023) Durgun, Yavuz; Gullu, Ahmet; Calim, Furkan; Ozden, Bayezid; Ozcan, Ali; Olcer, Beyazit; Senol, Erkan
    This paper presents the results of a comprehensive experimental study on the flexural performance of ballastless discrete precast slab tracks with two alternative reinforcement types. These are the precast slab tracks produced using ordinary reinforcement [nonpost-tensioned (NPT)] and the precast slab tracks produced using post-tensioned (PT) reinforcement. The study aims to compare the flexural performances of NPT- and PT-type slab tracks using three-point bending tests, even though they continuously sit on the ground with different rigidities in real-life applications. The tests performed on four full-scale slab tracks in the longitudinal and transversal directions resulted in the first cracking and the ultimate loads were greater in PT specimens. Also, the maximum crack widths and residual displacements of PT specimens were smaller. Although the aforementioned performance parameters of NPT-type slab tracks are relatively behind those of PT-type slab tracks, their overall response is still acceptable, with the advantages of easier production and lower cost.
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    Numerical Modelling of Energy Dissipative Steel Cushions
    (Korean Soc Steel Construction-Kssc, 2019) Gullu, Ahmet; Smyrou, Eleni; Khajehdehi, Arastoo; Ozkaynak, Hasan; Bal, I. Engin; Yuksel, Ercan; Karadogan, Faruk
    Energy dissipative steel cushions (EDSCs) are simple units that can be used to join structural members. They can absorb a substantial amount of seismic energy due to their geometric shapes and the ductile behavior of mild steel. Large deformation capability and stable hysteretic behavior were obtained in monotonic and cyclic tests of EDSCs in the framework of the SAFECLADDING project. Discrete numerical modeling strategies were applied to reproduce the experimental results. The first and second models comprise two-dimensional shell elements and one-dimensional flexural frame elements, respectively. The uncertain points in the preparation of the models included the mesh density, representation of the material properties, and interaction between contacting surfaces. A zero-length nonlinear link element was used in the third attempt in the numerical modeling. Parameters are recommended for the Ramberg-Osgood and bilinear models. The obtained results indicate that all of the numerical models can reproduce the response, and the stiffness, strength, and unloading and reloading curves were fitted accurately.
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    Rapid and Easily Applicable Procedure for Full-Scale Laboratory Tests of Ballastless Slab Tracks
    (Asce-Amer Soc Civil Engineers, 2021) Gullu, Ahmet; Ozden, Bayezid; Olcer, Beyazit; Ozcan, Ali Ihsan; Binbir, Ergun; Durgun, Yavuz; Saruhan, Hakan
    Increasing demand for high speed railway lines necessitates reducing construction and maintenance costs. Accordingly, RC slab tracks are preferred due to their advantages such as being almost maintenance free and supplying uniform support conditions. However, new testing procedures are required for the performance evaluation of the slab tracks to identify possible failure modes which may not be observed in numerical analyses. Although there are some procedures in the literature, there still is no consensus on loading intensity, shape, frequency, or number of cycles. A testing procedure that greatly decreases experimental costs was adopted for the design approval tests of precast RC slab tracks. The procedure was evaluated experimentally through full-scale laboratory tests of intact and intentionally damaged specimens. The study demonstrated that the proposed testing procedure reduces experimental costs and identifies the mechanical properties of slab tracks.
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    Uni-axial behavior of energy dissipative steel cushions
    (Techno-Press, 2018) Ozkaynak, Hasan; Khajehdehi, Arastoo; Gullu, Ahmet; Azizisales, Faraz; Yuksel, Ercan; Karadogan, Faruk
    Seismic excitations may impart a significant amount of energy into structures. Modern structural design attitudes tend to absorb some part of this energy through special dissipaters instead of heavy plastic deformations on the structural members. Different types of dissipater have been generated and utilized in various types of structures in last few decades. The expected earthquake damage is mainly concentrated on these devices and they may be replaced after earthquakes. In this study, a low-cost device called energy dissipative steel cushion (EDSC) made of flat mild steel was developed and tested in the Structural and Earthquake Engineering Laboratory (STEELab) of Istanbul Technical University (ITU). The monotonic and cyclic tests of EDSC were performed in transversal and longitudinal directions discretely. Very large deformation capability and stable hysteretic behavior are some response properties observed from the tests. Load vs. displacement relations, hysteretic energy dissipation properties as well as the closed form equations to predict the behavior parameters are presented in this paper.