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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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    Development of Earthquake Energy Demand Spectra
    (Sage Publications Inc, 2015) Dindar, Ahmet Anil; Yalcin, Cem; Yuksel, Ercan; Ozkaynak, Hasan; Buyukozturk, Oral
    Current seismic codes are generally based on the use of response spectra in the computation of the seismic demand of structures. This study evaluates the use of energy concept in the determination of the seismic demand due to its potential to overcome the shortcomings found in the current response spectra based methods. The emphasis of this study is placed on the computation of the input and plastic energy demand spectra directly derived from the energy-balance equation with respect to selected far-field ground motion obtained from Pacific Earthquake Engineering Research (PEER) database, soil classification according to National Earthquake Hazards Reduction Program (NEHRP) and characteristics of the structural behavior. The concept and methodology are described through extensive nonlinear time history analyses of single-degree-of-freedom (SDOF) systems. The proposed input and plastic energy demand spectra incorporate different soil types, elastic perfectly plastic constitutive model, 5% viscous damping ratio, different ductility levels, and varying seismic intensities.
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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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    Improvement of seismic performance of precast frames with cladding panels fastened by energy dissipative steel cushions
    (Springer, 2021) Ozkaynak, Hasan; Khajehdehi, Arastoo; Yuksel, Ercan; Karadogan, Faruk
    Precast reinforced concrete panels are commonly used as wall claddings in precast buildings. The cladding panels are generally evaluated as non-structural members and are joined to structural systems via mechanical, welding, and bolted dry connections. Several failures were observed in the last seismic events in Southern Europe, which demonstrate the deficiencies of the cladding connections in terms of strength and ductility. A comprehensive research activity named SAFECLADDING was conducted in Europe to provide knowledge for proper seismic design of precast structures with cladding panels. In this context, energy dissipative steel cushions were developed and evaluated through the extensive experimental and numerical studies. Steel cushions can provide robust interaction of the structural system with the cladding panels. This paper numerically evaluates the effects of cladding panels with steel cushions on the global seismic behaviour of the buildings. An existing representative industrial building is selected to perform intensive nonlinear dynamic analyses. Analyses performed on the bare and hybrid systems showed that the hybrid system has high performance in terms of story drifts, internal forces, and deformations with respect to the bare system. The overall drifts in longitudinal and transversal directions of the building are reduced by about 78 and 54%, respectively. Average residual drifts of cladding panels and steel cushions indicated that the applied steel cushion placement scheme has a promising re-centring capability during seismic action.
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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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    Seismic design of RC frame structures based on energy-balance method
    (Elsevier Sci Ltd, 2021) Yalcin, Cem; Dindar, Ahmet Anil; Yuksel, Ercan; Ozkaynak, Hasan; Buyukozturk, Oral
    The force- and displacement-based design methodologies have been widely used in current seismic design practice. In both methodologies, inelastic behavior is determined indirectly since the seismic demands are derived from elastic acceleration response spectra. In this study, a novel energy-based design (EBD) approach is proposed in the determination of both seismic demand and dissipation capacities of reinforced concrete (RC) frame members through their inelastic behavior directly. In the case of frame-type RC structures, the distribution of demand plastic energy throughout the structure is achieved. The proposed EBD is then accomplished by comparing the demand plastic energy with the energy dissipation capacity of members while integrating performance-based design guidelines. A cantilever column and a benchmark frame, both from the literature, are analyzed in verification of the proposed methodology. Comparisons are made between force, displacement and EBD methodologies in terms of soil condition, member, system and ductility performance requirements. Member and global performance targets are found to be comparable in displacement and EBD methodologies. However, owing to lack of ductility considerations in the prior design methodologies, the proposed EBD showed more reliable result in the determination of both cross-sectional geometry and its rebar configuration. The proposed methodology provides better understanding of damage state limits of RC members by incorporating the plastic energy spectrum, which includes cyclic action, duration, and frequency content of ground motions, as well as inherent ductility in both demand and capacity determinations. The sensitivity analyses between code compliantdesign and soft-story-mechanism buildings showed a distinct difference in the variations of seismic energy among the members and their corresponding damage distributions. EBD methodology provides better in depth understanding of the seismic design in terms of demand and capacity of member and overall structural system, and their corresponding performance.
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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.