• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2010년도 춘계 학술대회 제22권1호
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• pp.257-258
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• 2010

본 연구는 매스 콘크리트의 수화열 저감을 위해 혼화재를 다량 치환한 사용한 배합(LHC)에 대하여 실험을 실시하였으며, 그 결과는 다음과 같다. 동일 유동성을 만족하기 위한 감수제량은 약 50% 정도 감소하였으며, 압축강도는 OPC의 약 95% 정도를 발현하였다. 또한 수화열에 의한 온도상승은 OPC 및 FA25에 비해 36~48% 저하하는 것으로 나타나 매스 콘크리트의 수화열 저감에 큰 효과가 있을 것으로 판단된다.

• Earthquakes and Structures
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• 제21권5호
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• pp.477-487
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• 2021

This study focuses on the influence of strong ground motion duration on the response and collapse probability of reinforced concrete walls with a predominant response in flexure. Walls with different height and mass were used to account for a broad spectrum of configurations and fundamental periods. The walls were designed following the specifications of the Chilean design code. Non-linear models of the reinforced concrete walls using a distributed plasticity approach were performed in OpenSees and calibrated with experimental data. Special attention was put on modeling strength and stiffness degradation. The effect of duration was isolated using spectrally equivalent ground motions of long and short duration. In order to assess the behavior of the RC shear walls, incremental dynamic analyses (IDA) were performed, and fragility curves were obtained using cumulative and non-cumulative engineering demand parameters. The spectral acceleration at the fundamental period of the wall was used as the intensity measure (IM) for the IDAs. The results show that the long duration ground motion set decreases the average collapse capacity in walls of medium and long periods compared to the results using the short duration set. Also, it was found that a lower median intensity is required to achieve moderate damage states in the same medium and long period wall models. Finally, strength and stiffness degradation are important modelling parameters and if they are not included, the damage in reinforced concrete walls may be greatly underestimated.

• Steel and Composite Structures
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• 제24권1호
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• pp.113-128
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• 2017

This paper highlights a study undertaken on the free vibration of a precast steel-concrete composite slab panel for track support. The steel-concrete composite slab track is an evolvement from the slab track, a form of ballastless track which is becoming increasingly attractive to asset owners as they seek to reduce lifecycle costs and deal with increasing rail traffic speeds. The slender nature of the slab panel due to its reduced depth of construction makes it susceptible to vibration problems. The aim of the study is driven by the need to address the limited research available to date on the dynamic behaviour of steel-concrete composite slab panels for track support. Free vibration analysis of the track slab has been carried out using ABAQUS. Both eigenfrequencies and eigenmodes have been extracted using the Lanczos method. The fundamental natural frequencies of the slab panel have been identified together with corresponding mode shapes. To investigate the sensitivity of the natural frequencies and mode shapes, parametric studies have been established, considering concrete strength and mass and steel's modulus of elasticity. This study is the world first to observe crossover phenomena that result in the inversion of the natural orders without interaction. It also reveals that replacement of the steel with aluminium or carbon fibre sheeting can only marginally reduce the natural frequencies of the slab panel.

• Steel and Composite Structures
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• 제25권4호
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• pp.427-442
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• 2017

This paper presents unprecedented damped oscillation behaviours of a precast steel-concrete composite slab panel for track support. The steel-concrete composite slab track is an innovative slab track, a form of ballastless track which is becoming increasingly attractive to asset owners as they seek to reduce lifecycle costs and deal with increasing rail traffic speeds. The slender nature of the slab panel due to its reduced depth of construction makes it susceptible to vibration problems. The aim of the study is driven by the need to address the limited research available to date on the dynamic behaviour of steel-concrete composite slab panels for track support. Free vibration analysis of the track slab has been carried out using ABAQUS. Both undamped and damped eigenfrequencies and eigenmodes have been extracted using the Lancsoz method. The fundamental natural frequencies of the slab panel have been identified together with corresponding mode shapes. To investigate the sensitivity of the natural frequencies and mode shapes, parametric studies have been established, considering concrete strength and mass and steel's modulus of elasticity. This study is the world first to observe crossover phenomena that result in the inversion of the natural orders without interaction. It also reveals that replacement of the steel with aluminium or carbon fibre sheeting can only marginally reduce the natural frequencies of the slab panel.

• Structural Engineering and Mechanics
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• 제61권5호
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• pp.663-674
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• 2017

The determination of the fundamental period of vibration of a structure is essential to earthquake design. Current codes provide formulas for the approximate estimation of the fundamental period of earthquake-resistant building systems. These formulas are dependent only on the height of the structure or number of storeys without taking into account the presence of infill walls into the structure, despite the fact that infill walls increase the stiffness and mass of the structure leading to significant changes in the fundamental period. Furthermore, such a formulation is overly conservative and unable to account for structures with geometric irregularities. In this study, which comprises the companion paper of previous published research by the authors, the effect of the vertical geometric irregularities on the fundamental periods of masonry infilled structures has been investigated, through a large set of infilled frame structure cases. Based on these results, an attempt to quantify the reduction of the fundamental period due to the vertical geometric irregularities has been made through a proposal of properly reduction factor.

• Steel and Composite Structures
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• 제42권1호
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• pp.123-137
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• 2022

The fundamental period (FP) is one of the most critical parameters for the seismic design of structures. In the reinforced concrete (RC) infilled frame, the infill walls significantly affect the FP because they change the stiffness and mass of the structure. Although several formulas have been proposed for estimating the FP of the RC infilled frame, they are often associated with high bias and variance. In this study, an efficient soft computing model, namely the group method of data handling (GMDH), is proposed to predict the FP of regular RC infilled frames. For this purpose, 4026 data sets are obtained from the open literature, and the quality of the database is examined and evaluated in detail. Based on the cleaning database, several GMDH models are constructed and the best prediction model, which considers the height of the building, the span length, the opening percentage, and the infill wall stiffness as the input variables for predicting the FP of regular RC infilled frames, is chosen. The performance of the proposed GMDH model is further underscored through comparison of its FP predictions with those of existing design codes and empirical models. The accuracy of the proposed GMDH model is proven to be superior to others. Finally, explicit formulas and a graphical user-friendly interface (GUI) tool are developed to apply the GMDH model for practical use. They can provide a rapid prediction and design for the FP of regular RC infilled frames.

• 한국도로학회논문집
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• 제17권2호
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• pp.47-53
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• 2015

PURPOSES: The scaling of a concrete surface caused by the combined effects of frost and de-icing salts is one of the main reasons for the need to repair transportation infrastructures in cold-climate regions. This study describes the results of attempts to determine the scaling resistance of concrete incorporating mineral admixtures such as fly ash, GGBFS, and silica fume, and subjected to the actions of frost and salt. METHODS : Conventionally, to evaluate the fundamental properties of concrete, flexural and compressive strength measurements are regularly performed. Based on the ASTM C 672 standard, concrete is subjected to 2%, 4%, and 8% $CaCl_2$ salt solutions along with repeated sets of 50 freeze/thaw cycles, and the scaling resistance was evaluated based on the mass of the scale and a visual examination. RESULTS : It was observed that silica fume is very effective in enhancing the scaling resistance of concrete. Meanwhile, concrete incorporating GGBFS exhibited poor resistance to scaling, especially in the first ten freeze/thaw cycles. However, fly ash concrete generally exhibited the maximum amount of damage as a result of the frost-salt attack, regardless of the concentrations of the solutions. CONCLUSIONS: It can be concluded that the scaling resistance of concrete is highly dependent on the type of the mineral admixture used in the concrete. Therefore, to provide a durable concrete pavement for use in cold-climate regions, the selection of a suitable binder is essential.

• Earthquakes and Structures
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• 제3권1호
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• pp.17-35
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• 2012

Simplified equations for fundamental period of vibration of skeletal structures provided by most seismic design provisions suffer from the absence of any associated confidence levels and of any reference to their empirical basis. Therefore, such equations may typically give a sector of designers the false impression of yielding a fairly accurate value of the period of vibration. This paper, although not addressing simplified codes equations, introduces a set of mathematical equations utilizing the theory of error propagation and First-Order Second-Moment (FOSM) techniques to determine bounds on the relative error in theoretically calculated fundamental period of vibration of skeletal structures. In a complementary step, and for verification purposes, Monte Carlo simulation technique has been also applied. The latter, despite involving larger computational effort, is expected to provide more precise estimates than FOSM methods. Studies of parametric uncertainties applied to reinforced concrete frame bents - potentially idealized as SDOF systems - are conducted demonstrating the effect of randomness and uncertainty of various relevant properties, shaping both mass and stiffness, on the variance (i.e. relative error) in the estimated period of vibration. Correlation between mass and stiffness parameters - regarded as random variables - is also thoroughly discussed. According to achieved results, a relative error in the period of vibration in the order of 19% for new designs/constructions and of about 25% for existing structures for assessment purposes - and even climbing up to about 36% in some special applications and/or circumstances - is acknowledged when adopting estimates gathered from the literature for relative errors in the relevant random input variables.

• 한국건축시공학회지
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• 제9권6호
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• pp.113-119
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• 2009

본 연구는 양생요인 및 PP 섬유 혼입율 변화에 따른 고강도 콘크리트의 기초적 특성 및 내화특성을 분석하였는데, 그 결과를 요약하면 다음과 같다. 콘크리트의 기초적 특성으로 유동성은 PP 섬유 혼입율이 증가 할수록 감소하는 경향을 나타내었고, 압축강도는 PP 섬유 혼입율 증가에 따라 약간 감소하였으나 재령 7일에서 모두 60 MPa 이상 재령 28일에서 90 MPa이상으로 고강도 범위를 나타내었다. 함수율 변화에 따른 폭렬성상으로 함수율 3.0 %에서 PP 섬유를 혼입하지 않은 플레인을 제외한 모든 배합에서 폭렬이 방지되는 것으로 나타났다. 이때 폭렬이 방지된 경우 잔존압축강도율은 22~41%, 질량감소율 5~7 %로 비교적 양호한 것으로 분석되었다. 양생방법 변화에 따른 폭렬성상으로 표준양생의 경우 PP 섬유 혼입율 0.05 % 이상, 증기 양생 및 오토클레이브의 경우 PP 섬유 혼입율 0.10 %에서 폭렬이 방지되는 것으로 나타났다. 이때 폭렬이 방지된 경우 잔존압축강도율은 23~42 %, 질량감소율은 7~11 % 전후로 나타났다. 이상을 종합하여 볼때 고강도 콘크리트는 함수율이 작을수록 폭렬방지가 용이하고, 양생방법에 따라서는 표준양생이 PP섬유 0.05 % 이상, 증기양생 및 오토클레이브의 경우 PP 섬유 혼입율 0.1 %이상을 혼입해 주어야 폭렬이 방지됨을 알수 있었다.

• Smart Structures and Systems
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• 제24권4호
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• pp.447-457
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• 2019

The use of Tuned mass dampers (TMD) has proved to be effective in reducing the effects of vibrations caused by wind loads and far-field seismic action. However, its effectiveness in controlling the dynamic response of structures under near-fault earthquakes is still under discussion. In this case, the uncertainty about the TMD performance arises from the short significant duration of near-fault ground motions. In this work, the TMD effectiveness for increasing the safety margin against collapse of structures subjected to near-fault earthquakes is investigated. In order to evaluate the TMD performance in the proposed scenario, the nonlinear dynamic response of two reinforced concrete (RC) frames was analyzed. TMDs with different mass values were added to these structures, and a set of near-fault records with frequency content close to the fundamental frequency of the structure was employed. Through a series of nonlinear dynamic analysis, the minimum amplitude of each seismic record that causes the structural collapse was found. By comparing this value, called collapse acceleration, for the case of the structures with and without TMD, the benefit produced by the addition of the control device was established.