• Geomechanics and Engineering
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• 제13권5호
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• pp.743-756
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• 2017

Laboratory investigation reveals that rockfills exhibit significant stress-path-dependent behavior during shearing, therefore realistic prediction of deformation of rockfill structures requires suitable constitutive models to properly reproduce such behavior. This paper evaluates the capability of a strain hardening model proposed by the authors, by comparing simulation results with large-scale triaxial stress-path test results. Despite of its simplicity, the model can simulate essential aspects of the shear behavior of rockfills, including the non-linear stress-strain relationship, the stress-dependence of the stiffness, the non-linear strength behavior, and the shearing contraction and dilatancy. More importantly, the model is shown to predict the markedly different stress-strain and volumetric behavior along various loading paths with fair accuracy. All parameters required for the model can be derived entirely from the results of conventional large triaxial tests with constant confining pressures.

• Geomechanics and Engineering
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• 제29권2호
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• pp.171-182
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• 2022

Reusing the used pile has not yet been implemented due to the unpredictability of the bearing capacity evolution. This paper presents an analytic approach to estimate the sides shear setup after the dissipation of pore pressure. Long-term evolution of adjacent soil is simulated by viscoelastic-plastic constitutive model. Then, an innovative concept of quasi-overconsolidation is proposed to estimate the strength changes of surrounding soil. Total stress method (α method) is employed to evaluate the long term bearing capacity. Measured data of test piles in Louisiana and semi-logarithmic time function are cited to validate the effectiveness of the presented method. Comparisons illustrate that the presented approach gives a reasonably prediction of the side shear setup. Both the presented method and experiment show the shaft resistance increase by 30%-50%, and this highlight the potential benefit of piles reutilization.

• Structural Engineering and Mechanics
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• 제60권6호
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• pp.1021-1038
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• 2016

Considerable part of reinforced concrete building has suffered from destructive earthquakes in Turkey. This situation makes necessary to determine nonlinear behavior and seismic performance of existing RC buildings. Inelastic response of buildings to static and dynamic actions should be determined by considering both flexural plastic hinges and brittle shear hinges. However, shear capacities of members are generally neglected due to time saving issues and convergence problems and only flexural response of buildings are considered in performance assessment studies. On the other hand, recent earthquakes showed that the performance of older buildings is mostly controlled by shear capacities of members rather than flexure. Demand estimation is as important as capacity estimation for the reliable performance prediction in existing RC buildings. Demand estimation methods based on strength reduction factor (R), ductility (${\mu}$), and period (T) parameters ($R-{\mu}-T$) and damping dependent demand formulations are widely discussed and studied by various researchers. Adopted form of $R-{\mu}-T$ based demand estimation method presented in Eurocode 8 and Turkish Earthquake Code-2007 and damping based Capacity Spectrum Method presented in ATC-40 document are the typical examples of these two different approaches. In this study, eight different existing RC buildings, constructed before and after Turkish Earthquake Code-1998, are selected. Capacity curves of selected buildings are obtained with and without considering the brittle shear capacities of members. Seismic drift demands occurred in buildings are determined by using both $R-{\mu}-T$ and damping based estimation methods. Results have shown that not only capacity estimation methods but also demand estimation approaches affect the performance of buildings notably. It is concluded that including or excluding the shear capacity of members in nonlinear modeling of existing buildings significantly affects the strength and deformation capacities and hence the performance of buildings.

• 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.

• 대한기계학회논문집A
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• 제30권7호
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• pp.857-864
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• 2006

Various compressive specimens were fabricated using autoclave do-gassing moulding to find out the compressive characteristics of the carbon/epoxy plain weave fabric composites with respect to the bias and shear angles. The stacking angles of the bias specimens are $[0]_{10T,}\;[3]_{10T,}\;[6]_{10T,}\;[9]_{10T,}\;[12]_{10T,}\;[15]_{10T,}\;[30]_{10T,}\;[45]_{10T}$ and those of the sheared specimens are $[{\pm}37]_{10T,}\;[{\pm}32]_{10T,}\;[{\pm}28]_{10T,}\;[{\pm}22]_{10T,}$ respectively. In order to verify the effect of micro-tow structures on compressive strength and modulus of the composites, compressive test specimens of uni-directional carbon/epoxy composites with the same materials and the same stacking conditions were fabricated. The modulus and strength of both types of composite specimens were compared with the prediction results based on the CLPT and a proposed strength formula. The tow deformation and fracture modes were investigated by microscopic observation.

• Steel and Composite Structures
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• 제23권1호
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• pp.17-29
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• 2017

The seismic performance of steel beam to concrete-encased composite column with unsymmetrical steel section joints is investigated and reported within this paper. Experimental and analytical evaluation were conducted on a total of 8 specimens with T-shaped and L-shaped steel section under lateral cyclic loading and axial compression. The test parameters included concrete strength, stirrup ratio and axial compression ratio. The response of the specimens was presented in terms of their hysterisis loop behavior, stress distribution, joint shear strength, and performance degradation. The experiment indicated good structural behavior and good seismic performance. In addition, a three-dimensional nonlinear finite-element analysis simulating was conducted to simulate their seismic behaviors. The finite-element analysis incorporated both bond-slip relationship and crack interface interaction between steel and concrete. The results were also compared with the test data, and the analytical prediction of joint shear strength was satisfactory for both joints with T-shaped and L-shaped steel section columns. The steel beam to concrete-encased composite column with unsymmetrical steel section joints can develop stable hysteretic response and large energy absorption capacity by providing enough stirrups and decreased spacing of transverse ties in column.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1993년도 가을 학술발표회 논문집
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• pp.195-200
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• 1993

This paper develops practical and realistic reliability models and methods for the evalusion of system reliability and system reliability-based rating of R.C box-girder bridge superstructures. The precise prediction of reserved carrying capacity of bridge as a system is extremely difficult expecially when the bridges are highly redundant and significantly deteriorated or damaged. This paper proposes a new approach for the evaluation of reserved system carrying capacity of bridges in terms of equivalent system-strength, which may be defined as a bridge system-strength corresponding to the system reliability of the bridge. This can be derived from an inverse process based on the concept of FOSM form of system reliability index. The strength limit state models for R.C box-girder bridges suggested in the paper are based on the basic bending and shear strength. and the system reliability problem of box-girder superstructure is formulated as parallel-series models obtained from the FMA(Failure Mode Approach) based on major failure mechanism or critical failure states of each girder. AFOSM and IST(Importance Sampling Technique) simulation algorithm is used for the reliability analysis of the proposed models.

• 한국지반공학회논문집
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• 제24권6호
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• pp.37-44
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• 2008

낮은 응력 상태에서 모래의 인장강도는 포화도 또는 흡입력에 따라 증가하다 최대값이 이른 후 감소한다. 최대인장 강도는 어느 포화도에서든 발생될 수 있다. 선행 연구에서는 이와 같은 습윤 모래의 인장강도를 정확히 표현한 이론이 제시되었다. 본 연구에서 세 가지 종류의 모래(워싱턴 주 시애틀의 검정 Esperance모래, 오스트리일리아 서부 Perth 해변 모래, Ottawa 모래)에 대해 실시된 일축인장실험, 함수특성실험, 직접전단실험 결과를 이용하여 제안된 이론을 검증하였다. 제안된 닫힌 형식의 식으로 표현된 이론은 이들 모래들로부터 얻어진 실험결과와 비교 시 전체 포화도 영역에서 인장강도 변화양상, 인장강도 크기, 최대인장강도, 최대인장강도가 발생할 때의 해당 포화도 등을 잘 예측하는 것으로 나타났다.

• Composites Research
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• 제17권5호
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• pp.39-46
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• 2004

본 연구에서는 공간적으로 보강된 복합재(SRC)의 강도를 예측하였다. 각 방향의 라드(rod)와 라드의 체적에 비례하는 기지의 강성으로 표현되는 구조요소(structural element)를 정의하고, 이 구조요소에 파손판단식을 적용하여 SRC의 강도를 예측하였다. 라드의 파손판단식의 경우는 최대파손변형률을, 기지의 경우는 수정된 Tsai-Wu 파손판단식을 각기 적용하였다. 또한 SRC의 강도를 예측하기 위해서 라드와 SRC의 물성치를 측정하였다. 측정된 물성치는 라드의 인장 파손변형률, 3D SRC의 압축 파손변형률, $45^{\cir}$ 회전된 방향에서의 인장 및 압축 강도와 전단강도들이다. 3D/4D SRC의 강도분포는 각 SRC의 라드방향에서 크게 나타나고 라드에서 벗어날수록 작은 강도 값을 보였다. 강도의 전체분포를 보다 빠르게 계산하기 위해서 하중증분을 유동적으로 사용하였고, 하중이력을 구할 때는 균일한 하중이력을 사용하였다. 3D SRC의 라드방향 압축실험결과 해석의 비교에서 초기 기울기는 서로 잘 일치하였고, 강도값은 18% 정도의 차이를 보였다.

• Computers and Concrete
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• 제28권5호
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• pp.507-519
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• 2021

In this study, a new procedure was proposed in order to predict the crack pattern and failure mode of steel fiber reinforced concrete (SFRC) corbels. Moreover, an experimental study was carried out in order to investigate the effect of several parameters, such as compressive strength, tensile strength, steel fiber ratio, shear span on the mechanical behavior of SFRC corbels in detail. Totally, 24 RC and SFRC corbels were prepared for the experimental study. Experimental results indicate that each investigated parameter has noticeable effect on the load capacity and failure mode of SFRC corbels. Moreover, finite element (FE) model of the tested corbels were prepared and efficiency of FE model was investigated for further studies. Comparison of FE and experimental results show that there is an acceptable fit between them regarding load capacity and crack patterns. Thereafter, parametric study was carried out via FE analyses in order to obtain a methodology for crack pattern and failure mode prediction of SFRC corbels. As a result of parametric studies, a new procedure was proposed as flowcharts in order to predict the failure mode of SFRC corbels for normal and high strength concrete class separately.