• Structural Engineering and Mechanics
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• 제45권6호
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• pp.741-758
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• 2013

In this study, inelastic displacement ratios are investigated for existing systems with known lateral strength considering soil structure interaction. For this purpose, SDOF systems for period range of 0.1-3.0 s with different hysteretic behaviors are considered for a number of 18 earthquake motions recorded on soft soil. The effect of stiffness degradation on inelastic displacement ratios is investigated. The Modified Clough model is used to represent structures that exhibit significant stiffness degradation when subjected to reverse cyclic loading and the elastoplastic model is used to represent non-degrading structures. Soil structure interaction analyses are conducted by means of equivalent fixed base model 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. A new equation is proposed for inelastic displacement ratio of system with SSI with elastoplastic or degrading behavior as a function of structural period ($\tilde{T}$), 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.

• Earthquakes and Structures
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• 제20권3호
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• pp.279-293
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• 2021

Most of the existing seismic codes for RC buildings consider only a scenario earthquake for analysis, often characterized by the response spectrum at the specified location. However, any real earthquake event often involves occurrences of multiple earthquakes within a few hours or days, possessing similar or even higher energy than the first earthquake. This critically impairs the rehabilitation measures thereby resulting in the accumulation of structural damages for subsequent earthquakes after the first earthquake. Also, the existing seismic provisions account for the non-linear response of an RC building frame implicitly by specifying a constant response modification factor (R) in a linear elastic design. However, the 'R' specified does not address the changes in structural configurations of RC moment-resisting frames (RC MRFs) viz., building height, number of bays present, bay width, irregularities arising out of mass and stiffness changes, etc. resulting in changed dynamic characteristics of the structural system. Hence, there is an imperative need to assess the seismic performance under sequential earthquake ground motions, considering the adequacy of code-specified 'R' in the representation of dynamic characteristics of RC buildings. Therefore, the present research is focused on the evaluation of the non-linear response of medium-rise 3D RC MRFs with and without vertical irregularities under bi-directional sequential earthquake ground motions using non-linear dynamic analysis. It is evident from the results that collapse probability increases, and 'R' reduces significantly for various RC MRFs subjected to sequential earthquakes, pronouncing the vulnerability and inadequacy of estimation of design base shear by code-specified 'R' under sequential earthquakes.

• Steel and Composite Structures
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• 제45권1호
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• pp.51-66
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• 2022

This paper presents the axial compression behavior of partially encased composite (PEC) columns using H-shaped structural steel. In the experimental program, a total of eight PEC columns with H-shaped steel sections of different flange and web slenderness ratios were tested to investigate the interactive mechanism between steel and concrete. The test results showed that the PEC columns could sustain the load well beyond the peak load provided that the flange slenderness ratio was not greater than five. In addition, the previous analytical model was extended to predict the axial load-strain relationships of the PEC columns with H-shaped steel sections. A good agreement between the predicted load-strain relationships and test data was observed. Using the analytical model, the effects of compressive strength of concrete (21 to 69 MPa), yield strength of steel (245 to 525 MPa), slenderness ratio of flange (4 to 10), and slenderness ratio of web (10 to 25) on the interactive mechanism (K_h = confinement factor for highly confined concrete and K_w = reduction factor for steel web) and ductility index (DI = ratio between strain at peak load and strain at proportional load) were assessed. The numerical results showed that the slenderness of steel flange and yield strength of steel significantly influenced the compression behavior of the PEC columns.

• 한국전산구조공학회논문집
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• 제20권3호
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• pp.255-264
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• 2007

다층구조물의 경우 변위보다 층간변위에 의해 구조물의 파괴가 발생되나 현행 국 내외 내진설계 규준에 제시된 역량스펙트럼 법에서는 변위에 의한 응답산정으로 층간변위를 정확히 예측할 수가 없었다. 따라서 본 논문에서는 다층구조물의 가장 기본적인 모델인 전단빌딩(Shear Building)에 대하여 기존의 역량해석법의 간편성과 장점을 변함없이 유지하면서, 구조물의 파괴에 직접적인 영향을 미치는 층간변위를 실제에 가깝게 예측하고 구조물의 내진성능을 평가할 수 있는 개선된 역량스펙트럼 법을 제안하고자 한다. 나아가 제안된 방법을 예제구조물에 적용하고 시간이력 해석결과와 비교함으로서 제안된 방법의 신뢰성에 대한 검증을 수행하였다.

• 콘크리트학회논문집
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• 제26권2호
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• pp.159-169
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• 2014

이 연구에서는 철근콘크리트 전단벽의 횡하중 거동과 연성을 합리적으로 평가하기 위해서 모멘트-곡률관계를 정립하고 이로부터 단순화된 횡하중-횡변위관계를 제시하였다. 최초 휨 균열, 인장철근 항복, 최대내력, 최대내력의 80% 및 인장철근파단시점에서 모멘트와 곡률은 힘의 평형조건과 변형적합조건으로부터 정립되었다. 최대내력 이후의 곡률평가를 위한 압축측연단 콘크리트 변형률은 Razvi and Saatcioglu의 구속된 콘크리트의 응력-변형률 관계를 이용하여 최대응력의 감소계수와 횡보강근 체적지수의 함수로 제시하였다. 모멘트 평가모델은 변수연구를 통하여 인장철근지수, 수직철근지수 및 축력지수의 함수로 일반화하였다. 횡변위는 전단벽의 높이에 따라 분포된 이상화된 곡률로부터 모멘트 면적법을 이용하여 환산하였다. 제시된 횡하중-횡변위관계는 기존 실험 결과와 잘 일치하였으며, 특히 최대내력 이후의 거동을 잘 평가하였다.

• 한국지진공학회논문집
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• 제9권3호
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• pp.77-85
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• 2005

2001년 9월 11일 세계무역센터 붕괴 후. 그리고 지진발생시 빈번히 발생하는 건물의 화재피해 때문에 구조부재의 내화에 대한 사회적 관심이 증대되었다. 최근에는 전통적인 방법이 아니라 콘크리트의 내화성능과 철골의 구조적 특성을 복합한 내화성능이 향상된 합성구조에 대한 연구가 진행 중이다. 본 논문에서는 내화성능향상을 목적으로 개발된 부분적으로 철근콘크리트로 채워진 H형강-국부 콘크리트 합성 보의 상온에서의 휨 거동을 조사하기 위하여 몇 가지 합성상세를 갖는 실험체들의 휨실험을 실시하였다. 실험결과 $6\~8$의 변위 연성계수를 얻었다. 콘크리트와 철골의 일체화를 위한 합성상세간의 횡 거동 차이는 미미하였고, 극한 휨 강도에 가장 영향을 주는 것은 배근된 주철근 양임을 알 수 있었다. 따라서 중진 지역의 내진설계시 이 타입의 합성보를 사용하면 단일 H형강에 철근배근만 달리하여 상당부분의 층에서의 보의 춤을 동일하게 유지할 수 있다.

• Earthquakes and Structures
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• 제18권1호
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• pp.27-44
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• 2020

This work presents a comparison of three performance-based seismic design methods (PBSD) as applied to plane steel frames having eccentric braces (EBFs) and buckling restrained braces (BRBFs). The first method uses equivalent modal damping ratios (ξ_k), referring to an equivalent multi-degree-of-freedom (MDOF) linear system, which retains the mass, the elastic stiffness and responds in the same way as the original non-linear MDOF system. The second method employs modal strength reduction factors (${\bar{q}}_k$) resulting from the corresponding modal damping ratios. Contrary to the behavior factors of code based design methods, both ξ_k and ${\bar{q}}_k$ account for the first few modes of significance and incorporate target deformation metrics like inter-storey drift ratio (IDR) and local ductility as well as structural characteristics like structural natural period, and soil types. Explicit empirical expressions of ξ_k and ${\bar{q}}_k$, recently presented by the present authors elsewhere, are also provided here for reasons of completeness and easy reference. The third method, developed here by the authors, is based on a hybrid force/displacement (HFD) seismic design scheme, since it combines the force-base design (FBD) method with the displacement-based design (DBD) method. According to this method, seismic design is accomplished by using a behavior factor (q_h), empirically expressed in terms of the global ductility of the frame, which takes into account both non-structural and structural deformation metrics. These expressions for q_h are obtained through extensive parametric studies involving non-linear dynamic analysis (NLDA) of 98 frames, subjected to 100 far-fault ground motions that correspond to four soil types of Eurocode 8. Furthermore, these factors can be used in conjunction with an elastic acceleration design spectrum for seismic design purposes. Finally, a comparison among the above three seismic design methods and the Eurocode 8 method is conducted with the aid of non-linear dynamic analyses via representative numerical examples, involving plane steel EBFs and BRBFs.

• 한국지진공학회논문집
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• 제3권2호
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• pp.55-66
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• 1999

본 연구는 철도, 도시고속화도로 및 고속도로 교량의 교각으로 많이 이용디고 있는 철근콘크리트 기둥으 내진성능 평가에 관한 quasi-static 실험으로서 사용된 실험 변수는 축하중 내진설계유무에 따른 띠철근량 변위제어 하중형태 등을 채택하였다 RC 기둥시험체는 수원에 위치한 하갈교의 교각을 1/3.4의 축소모델로 하여 내진설계된 단면과 내진설계되지 않은 시험체를 각각 4개씩 총 8개를 제작하였으며 소성힌지구간에서 띠철근의 간격은 2.2cm 및 4.4cm 이다 실험변수에 따른 내진 및 비내진 시험체의 내진성능검토를 위하여 충진콘크리트 교각의 하중변위 이력특성 연성능력, 강도감소, 에너지 흡수능력, 등가점성계수 등을 실험적으로 분석조사하였다. '96년 개정된 도로교시방서의 RC기둥에 관한 내진설계기준은 AASHTO(1992)와 유사한 것으로서 중.약지진 지역으로 구분되는 국내의 실정에는 다소 과다설계로 판단된다. 실험결과 비내진설계된 콘크리트 교각도 어느 정도의 연성능력을 발휘한 것으로 조사되었으나 추가의 충분한 실험연구가 요구된다. 그러나 비내진설계교각도 적절한 내진보강방안을 강구한다면 우수한 내진성능을 발휘할수 있으리라판단된다.

• Structural Engineering and Mechanics
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• 제59권3호
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• pp.455-473
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• 2016

Methods for the seismic demands evaluation of structures require iterative procedures. Many studies dealt with the development of different inelastic spectra with the aim to simplify the evaluation of inelastic deformations and performance of structures. Recently, the concept of inelastic spectra has been adopted in the global scheme of the Performance-Based Seismic Design (PBSD) through Capacity-Spectrum Method (CSM). For instance, the Modal Pushover Analysis (MPA) has been proved to provide accurate results for inelastic buildings to a similar degree of accuracy than the Response Spectrum Analysis (RSA) in estimating peak response for elastic buildings. In this paper, a simplified nonlinear procedure for evaluation of the seismic demand of structures is proposed with its applicability to multi-degree-of-freedom (MDOF) systems. The basic concept is to write the equation of motion of (MDOF) system into series of normal modes based on an inelastic modal decomposition in terms of ductility factor. The accuracy of the proposed procedure is verified against the Nonlinear Time History Analysis (NL-THA) results and Uncoupled Modal Response History Analysis (UMRHA) of a 9-story steel building subjected to El-Centro 1940 (N/S) as a first application. The comparison shows that the new theoretical approach is capable to provide accurate peak response with those obtained when using the NL-THA analysis. After that, a simplified nonlinear spectral analysis is proposed and illustrated by examples in order to describe inelastic response spectra and to relate it to the capacity curve (Pushover curve) by a new parameter of control, called normalized yield strength coefficient (${\eta}$). In the second application, the proposed procedure is verified against the NL-THA analysis results of two buildings for 80 selected real ground motions.

• Steel and Composite Structures
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• 제46권4호
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• pp.497-512
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• 2023

Using light weight concrete as infill material in conventional cold-formed steel (CFS) shear wall systems can considerably increase their load bearing capacity, ductility, integrity and fire resistance. The compressive strength of the filler concrete is a key factor affecting the structural behaviour of the composite wall systems, and therefore, achieving maximum compressive strength in lightweight concrete while maintaining its lightweight properties is of significant importance. In this study a new type of optimum polystyrene lightweight concrete (OPLC) with high compressive strength is developed for infill material in composite CFS shear wall systems. To study the seismic behaviour of the OPLC-filled CFS shear wall systems, two full scale wall specimens are tested under cyclic loading condition. The effects of OPLC on load-bearing capacity, failure mode, ductility, energy dissipation capacity, and stiffness degradation of the walls are investigated. It is shown that the use of OPLC as infill in CFS shear walls can considerably improve their seismic performance by: (i) preventing the premature buckling of the stud members, and (ii) changing the dominant failure mode from brittle to ductile thanks to the bond-slip behaviour between OPLC and CFS studs. It is also shown that the design equations proposed by EC8 and ACI 318-14 standards overestimate the shear force capacity of OPLC-filled CFS shear wall systems by up to 80%. This shows it is necessary to propose methods with higher efficiency to predict the capacity of these systems for practical applications.