• Computers and Concrete
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• 제21권6호
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• pp.697-703
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• 2018

Compressive strength is one of the most important engineering properties of concrete, and testing of the compressive strength of concrete specimens is often costly and time consuming. In order to provide the time for concrete form removal, re-shoring to slab, project scheduling and quality control, it is necessary to predict the concrete strength based upon the early strength data. However, concrete compressive strength is affected by many factors, such as quality of raw materials, water cement ratio, ratio of fine aggregate to coarse aggregate, age of concrete, compaction of concrete, temperature, relative humidity and curing of concrete. The concrete compressive strength is a quite nonlinear function that changes depend on the materials used in the concrete and the time. This paper presents an adaptive neuro-fuzzy inference system (ANFIS) for the prediction of concrete compressive strength. The training of fuzzy system was performed by a hybrid method of gradient descent method and least squares algorithm, and the subtractive clustering algorithm (SCA) was utilized for optimizing the number of fuzzy rules. Experimental data on concrete compressive strength in the literature were used to validate and evaluate the performance of the proposed ANFIS model. Further, predictions from three models (the back propagation neural network model, the statistics model, and the ANFIS model) were compared with the experimental data. The results show that the proposed ANFIS model is a feasible, efficient, and accurate tool for predicting the concrete compressive strength.

• 콘크리트학회논문집
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• 제25권2호
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• pp.225-232
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• 2013

최근 건설시장의 세계적인 흐름은 방법 및 수행 절차보다는 최종 성과물의 성능을 제시하는데 초점을 맞춘 성능중심 설계기준으로 변화하고 있는 실정이다. 또한, 콘크리트 재료 및 구조물의 성능 검증을 위하여 재령효과에 따른 콘크리트 강도를 검토할 경우 적절한 모델을 사용하여야 한다. 따라서 이 논문에서는 국내 재료 특성을 반영한 콘크리트 강도발현 상수를 제안하고, 그 적합성을 평가하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 가을 학술발표회 논문집
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• pp.542-549
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• 2004

The compressive strength of concrete is commonly used criterion in producing concrete. However, the tests on the compressive strength are complicated and time-consuming. More importantly, it is too late to make improvement even if the test result does not satisfy the required strength, since the test is usually performed at the 28th day after the placement of concrete at the construction site. Therefore, accurate and realistic strength estimation before the placement of concrete is being highly required. In this study, the estimation of the compressive strength of concrete was performed by probabilistic neural network (PNN) on the basis of concrete mix proportions. The estimation performance of PNN was improved by considering the correlation between input data and targeted output value. Adaptive probabilistic neural network (APNN) was proposed to automatically calculate the smoothing parameter in the conventional PNN by using the scheme of dynamic decay adjustment algorithm. The conventional PNN and APNN were applied to predict the compressive strength of concrete using actual test data of a concrete company. APNN showed better results than the conventional PNN in predicting the compressive strength of concrete.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2007년도 추계 학술논문 발표대회
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• pp.1-4
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• 2007

Because reinforced concrete structures were being high more and more in recent year, concrete was being demanded high performance of high strength and high fluidity. But various characteristics must be confirmed besides guarantee of demand strength in ultra-high strength concrete. In ultra-high strength concrete, autogenous shrinkage and drying shrinkage grow big because of a low water cement ratio and much quantity of binder. So dangerousness of crack generation grow big in early ages. And ultra-high strength concrete is influenced by use materials more than ordinary strength concrete. In this study we were examined mix design, atuogenous shrinkage and pumpability of ultra-high strength concrete to apply on the ground.

• Advances in concrete construction
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• 제9권4호
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• pp.413-421
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• 2020

For steel-concrete girders made composite using shear studs, initial damage on studs induced by weld defect, unexpected overloading, fatigue and others might degrade the service performance and even threaten the structural safety. This paper conducted a numerical study to investigate the static behavior of damaged stud shear connectors that were embedded in ultra high performance concrete (UHPC). Parameters included damage degree and damage location. The material nonlinear behavior was characterized by multi-linear stress-strain relationship and damage plasticity model. The results indicated that the shear strength was not sensitive to the damage degree when the damage occurred at 2/3d (d is the stud diameter) from the stud root. An increased stud area would be engaged in resisting shear force as the distance of damage location from stud root increased and the failure section becomes inclined, resulting in a less reduction in the shear strength and shear stiffness. The reduction factor was proposed to consider the degradation of the shear strength of the damaged stud. The reduction factor can be calculated using two approaches: a linear relationship and a square relationship with the damage degree corresponding to the shear strength dominated by the section area and the nominal diameter of the damaged stud. It was found that the proposed method is preferred to predict the shear strength of a stud with initial damage.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2016년도 추계 학술논문 발표대회
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• pp.81-82
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• 2016

The present study aims to derive optimal interface treatment conditions for emulating a monolithic construction. The joints in this construction are formed through the bonding shear evaluation method during the placement of ultra-high-performance concrete (UHPC) and normal strength concrete (NSC). The evaluation items include push-off tests for homogeneous UHPC + UHPC and heterogeneous NSC + UHPC. The experimental samples comprised a monolithic placement as the baseline, two levels for the separated placement according to the compression strength of concrete, and five levels for the interface treatment. The increase in the number of grooves and their cross-sectional areas only slightly influenced the bonding shear performance. The optimal interface treatment method for the homogeneous UHPC + UHPC construction grooves was at least 30mm. The heterogeneous NSC + UHPC construction should utilize waterjet roughening to expose the aggregate for the increased roughness.

• Computers and Concrete
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• 제22권5호
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• pp.461-468
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• 2018

In this paper, to access the suitability of recycled aggregate for structural applications, concrete strength i.e., compressive, tensile and flexural strength were evaluated and compared with those specimens made of natural aggregates. Test results indicated that 30 to 42% of the mentioned strength decreases. To study the performance of frame structures made of recycled aggregate concrete (RAC) two reinforced RAC frames were prepared and tested under monotonic loading. The joint regions of one of the RAC frame were casted with micro-concrete. A reference specimen was also prepared using natural aggregate concrete (NAC) and subjected to a similar loading condition. The RAC frame resulted in a brittle mode of failure as compared to NAC frame. However, the presence of a micro-concrete at the joint region of an RAC frame improved the damage tolerance and load resisting capacity. Seismic parameter such as energy dissipation, ductility and stiffness also improves. Conclusively, strengthening of joint region using micro-concrete is found to have a significant contribution in improving the seismic performance of an RAC frame.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.695-702
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• 2002

Shotcrete (or Sprayed concrete) has been used as an important support material in New Austrian Tunnelling Method (NATM). Since the mid of 1990, permanent shotcrete tunnel linings such as Single-shell, NMT (Norwegian Method of Tunnelling) has been constructed in many countries for reducing the construction time and lowing construction costs instead of conventional in-situ concrete linings. Among essential technologies for successful application of permanent shotcrcte linings, high performance shotcrete providing high strength, high durability, better pumpability has to be developed in advance as an integral component. This paper presents the Ideas and first experimental attempts to increase early strength and bond strength of wet-mixed Steel Fiber Reinforced Shotcrete(SFRS) in sump water condition. In order to increase early strength, a new approach using high-early strength cement with liquid alkali-free accelerator has been investigated From the results, wet-mix SFRS with high-early strength cement and alkali-free accelerator exhibited excellent early strength improvement compared to the ordinary portland content and good bond strength even under sump water condition.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.897-902
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• 2001

Recently, structure performance is maximized by using high strength concrete. In design of structure, concrete need combination with reinforcement, but use of common strength reinforcement make member complex bar placement, so high strength concrete members require increased strength reinforcement. If common strength reinforcement replaced by equal tension area of high strength reinforcement, reinforcement ratio increase and brittle failure of member may occur by material change. So, adequate upper limit of strength ratio is required to affirm ductile behavior in application of high strength reinforcement. In this study, ductility behavior was analysed by factor of reinforcement ratio, strength of concrete and reinforcement. The result indicate that ductile failure is shown under 0.35 $\rho_{b}$ in any reinforcement strength of same section and high strength concrete of 800kg/$cm^{2}$ used commonly is compatible with reinforcement of 5500kg/$cm^{2}$.

• 한국화재소방학회논문지
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• 제25권1호
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• pp.78-84
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• 2011

최근 콘크리트 내화 연구는 대부분 고강도 콘크리트의 내화성능 확보에 많은 초점이 맞추어져 있다. 그러나 국내의 콘크리트 수요를 살펴보면 40MPa 이하의 일반강도 콘크리트의 수요가 전체 콘크리트 수요량의 대부분을 차지한다. 따라서 고강도 콘크리트의 내화성능에 대한 연구뿐만 아니라 일반콘크리트의 내화성능에 관한 연구도 필요하다. 본 연구에서는 40MPa 콘크리트 기둥을 대상으로 콘크리트 피복 두께와 단면크기를 변수로하여 내화성능을 평가하였으며, 연구 결과 단면크기가 커질수록, 피복두께가 두꺼워질수록 내화성능은 향상되는 것으로 나타났다.