• Structural Engineering and Mechanics
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• v.86 no.5
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• pp.589-605
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• 2023

This paper investigates the ductility demands of steel frames equipped with self-centring fuses under near-fault earthquake motions considering multiple yielding stages. The study is commenced by verifying a trilinear self-centring hysteretic model accounting for multiple yielding stages of steel frames equipped with self-centring fuses. Then, the seismic response of single-degree-of-freedom (SDOF) systems following the validated trilinear self-centring hysteretic law is examined by a parametric study using a near-fault earthquake ground motion database composed of 200 earthquake records as input excitations. Based on a statistical investigation of more than fifty-two (52) million inelastic spectral analyses, the effect of the post-yield stiffness ratios, energy dissipation coefficient and yielding displacement ratio on the mean ductility demand of the system is examined in detail. The analysis results indicate that the increase of post-yield stiffness ratios, energy dissipation coefficient and yielding displacement ratio reduces the ductility demands of the self-centring oscillators responding in multiple yielding stages. A set of empirical expressions for quantifying the ductility demands of trilinear self-centring hysteretic oscillators are developed using nonlinear regression analysis of the analysis result database. The proposed regression model may offer a practical tool for designers to estimate the ductility demand of a low-to-medium rise self-centring steel frame equipped with self-centring fuses progressing in the ultimate stage under near-fault earthquake motions in design and evaluation.

• Earthquakes and Structures
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• v.22 no.6
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• pp.585-595
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• 2022

Using the nonlinear static procedures has become very common in seismic codes to achieve the nonlinear response of the structure during an earthquake. The capacity spectrum method (CSM) adopted in ATC-40 is considered as one of the most known and useful procedures. For this procedure the seismic demand can be approximated from the maximum deformation of an equivalent linear elastic Single-Degree-of-Freedom system (SDOF) that has an equivalent damping ratio and period by using an iterative procedure. Data from the results of this procedure are plotted in acceleration- displacement response spectrum (ADRS) format. Different improvements have been made in order to have more accurate results compared to the Non Linear Time History Analysis (NL-THA). A new procedure is presented in this paper where the iteration process shall not be required. This will be done by estimation the ductility demand response spectrum (DDRS) and the corresponding effective damping of the bilinear system based on a new parameter of control, called normalized yield strength coefficient (η), while retaining the attraction of graphical implementation of the improved procedure of the FEMA-440. The proposed procedure accuracy should be verified with the NL-THA analysis results as a first implementation. The comparison shows that the new procedure provided a good estimation of the nonlinear response of the structure compared with those obtained when using the NL-THA analysis.

• International Journal of High-Rise Buildings
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• v.3 no.2
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• pp.107-120
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• 2014

A Reinforced concrete (RC) shear wall system with coupling beams has been known as one of the most promising structural systems for high-rise buildings. However, significantly large flexural and/or shear stress demands induced in the coupling beams require special reinforcement details to avoid their undesirable brittle failure. In order to solve this problem, one of promising candidates is frictional hysteretic energy dissipating devices (HEDDs) as an alternative to the coupling beams. The introduction of frictional HEDDs into a RC shear wall system increases energy dissipation capacity and maintains the frame action after their yielding. This paper investigates the strength demands (specifically yield strength levels) with a maximum allowable ductility of frictional HEDDs based on comparative non-linear time-history analyses of a prototype RC shear wall system with traditional RC coupling beams and frictional HEDDs. Analysis results show that the RC shear wall systems coupled by frictional HEDDs with more than 50% yield strength of the RC coupling beams present better seismic performance compared to the RC shear wall systems with traditional RC coupling beams. This is due to the increased seismic energy dissipation capacity of the frictional HEDD. Also, it is found from the analysis results that the maximum allowable ductility demand of a frictional HEDD should increase as its yield strength decreases.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.6
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• pp.65-76
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• 2001

Determination of ductility demand and prediction of nonlinear seismic responses of a structure under the earthquake ground motions have become a very important subject for evaluation of seismic performance in the performance based seismic design. In this study, the system ductility demand and nonlinear seismic responses of the steel moment framed structures by the nonlinear time history analysis are estimated and compared with those obtained from the capacity spectrum method suggested in ATC-40 and proposed method that is an improvement on the capacity spectrum method using the equivalent responses derived directly from a multi degree of freedom system. the adequacy and validity of the proposed method is verified by comparing the results evaluated by the method proposed in this study and the results obtained from method suggested in ATC-40 to the nonlinear seismic responses of the example structures from the nonlinear time history analysis.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.229-234
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• 2000

As the level of earthquake intensity in Korea is considered to be moderate, some structures or structural elements may be subjected to the reduced ductility demand, in contrast to the structures in high seismicity, due to the large inherent strength induced by gravity loads. New Zealand Standard(NZS) deals with there structures within the category of structures of limited ductility. This paper briefly reviews the applicability of the code, regarding limited ductility, for frame strucures which are commonly used as the office building structural system. The difference of the loading condition is considered. Details of the plastic hinge region are compared between NZS and Korean standard.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.205-210
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• 2007

The existing capacity spectrum method (CSM) is based on the displacement based approach for seismic performance and evaluation. Currently, in the domestic and overseas standard concerning seismic design, the CSM to obtain capacity spectrum from capacity curve and demand spectrum from elastic response spectrum is presented. In the multistory building, collapse is affected more by drift than by displacement, but the existing CSM does not work for story drift. Therefore, this paper proposes an improved CSM to estimate story drift of structures through seismic performance and evaluation. It uses the ductility factor in the A-T domain to obtain constant-ductility response spectrum from earthquake response of inelastic system using the drift and capacity curve from capacity analysis of structure.

• Structural Engineering and Mechanics
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• v.39 no.5
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• pp.683-701
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• 2011

In this study, inelastic displacement ratios and ductility demands are investigated for SDOF systems with period range of 0.1-3.0 s. with elastoplastic behavior considering soil structure interaction. Earthquake motions recorded on different site conditions such as rock, stiff soil, soft soil and very soft soil are used in analyses. Soil structure interacting systems are modeled with effective period, effective damping and effective ductility values differing from fixed-base case. For inelastic time history analyses, Newmark method for step by step time integration was adapted in an in-house computer program. Results are compared with those calculated for fixed-base case. A new equation is proposed for inelastic displacement ratio of interacting system ($\tilde{C}_R$) as a function of structural period of interacting system ($\tilde{T}$), strength reduction factor (R) and period lengthening ratio ($\tilde{T}/T$). The proposed equation for $\tilde{C}_R$ which takes the soil-structure interaction into account should be useful in estimating the inelastic deformation of existing structures with known lateral strength.

• Structural Engineering and Mechanics
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• v.41 no.3
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• pp.365-378
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• 2012

In this study, strength reduction factors are investigated for SDOF systems with period range of 0.1-3.0 s with elastoplastic behavior considering soil structure interaction for 64 different earthquake motions recorded on different site conditions such as rock, stiff soil, soft soil and very soft soil. Soil structure interacting systems are modeled and analyzed with effective period, effective damping and effective ductility values differing from fixed-base case. For inelastic time history analyses, Newmark method for step by step time integration was adapted in an in-house computer program. Results are compared with those calculated for fixed-base case. A new equation is proposed for strength reduction factor of interacting system as a function of structural period of system (T), ductility ratio (${\mu}$) and period lengthening ratio (T/T). It is concluded that soil structure interaction reduces the strength reduction factors for soft soils, therefore, using the fixed-base strength reduction factors for interacting systems lead to non-conservative design forces.

• Wind and Structures
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• v.7 no.3
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• pp.145-158
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• 2004

The evaluation of the accumulation of permanent set for inelastic structures due to wind action is important in establishing a criterion to select a reduced design wind load and in incorporating the beneficial ductile behaviour in wind engineering. A parametric study of the accumulation of the permanent set as well as the ductility demand for bilinear single-degree-of-freedom (SDOF) systems is presented in the present study. The dynamic analysis of the inelastic SDOF system is carried out using the method of Newmark for artificially generated time history of wind speed. Simulation results indicate that the mean of the normalized damage rate is highly dependent on the natural frequency of vibration. This mean value is relatively insensitive to the damping ratio if the damping ratio is larger than 5%. The scatter associated with the accumulation of the permanent set is very significant. The consideration of the postyield stiffness can significantly reduce the accumulation of the permanent set if the ratio of the yield strength to the expected peak response is small. The results also show that the ductility demand due to the wind action over a period of one hour for flexible structures can be much less than that for rigid structures or structures with larger damping ratio if the SDOF systems are designed with a reduced peak response caused by the fluctuating wind.

• Journal of the Korea Concrete Institute
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• v.19 no.5
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• pp.529-537
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• 2007

The purpose of this study is to discuss how strength and ductility of each system in low-rise reinforced concrete buildings composed of extremely brittle, shear and flexural failure lateral-load resisting systems have influence on seismic capacities of the overall system, which is based on nonlinear seismic response analyses of single-degree-of-freedom structural systems. In order to simulate the triple lateral-load resisting system, structures are idealized as a parallel combination of two modified origin-oriented hysteretic models and a degrading trilinear hysteretic model that fail primarily in extremely brittle, shear and flexure, respectively. Stiffness properties of three models are varied in terms of story shear coefficients, and structures are subjected to various ground motion components. By analyzing these systems, interaction curves of demand strengths of the triple system for various levels of ductility factors are finally derived for practical purposes. The result indicates that demand strength levels derived can be used as a basic information for seismic evaluation and design criteria of low-rise reinforced concrete buildings having the triple lateral-load resisting system.