• Steel and Composite Structures
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• 제42권6호
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• pp.733-745
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• 2022

This study proposed a robust artificial intelligence (AI) model based on the social behaviour of the imperialist competitive algorithm (ICA) and artificial neural network (ANN) for modelling the deflection of reinforced concrete beams, abbreviated as ICA-ANN model. Accordingly, the ICA was used to adjust and optimize the parameters of an ANN model (i.e., weights and biases) aiming to improve the accuracy of the ANN model in modelling the deflection reinforced concrete beams. A total of 120 experimental datasets of reinforced concrete beams were employed for this aim. Therein, applied load, tensile reinforcement strength and the reinforcement percentage were used to simulate the deflection of reinforced concrete beams. Besides, five other AI models, such as ANN, SVM (support vector machine), GLMNET (lasso and elastic-net regularized generalized linear models), CART (classification and regression tree) and KNN (k-nearest neighbours), were also used for the comprehensive assessment of the proposed model (i.e., ICA-ANN). The comparison of the derived results with the experimental findings demonstrates that among the developed models the ICA-ANN model is that can approximate the reinforced concrete beams deflection in a more reliable and robust manner.

• Advances in materials Research
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• 제11권3호
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• pp.171-190
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• 2022

In this paper, the problem of interfacial stresses in steel cantilever beams strengthened with bonded composite laminates is analyzed using linear elastic theory. The analysis is based on the deformation compatibility approach, where both the shear and normal stresses are assumed to be invariant across the adhesive layer thickness. The original study in this paper carried out an analytical solution to estimate shear and peel-off stresses, as, interfacial stress analysis concentration under the uniformly distributed load and shear lag deformation. The theoretical prediction is compared with authors solutions from numerous researches. This phenomenon of deformation of the members, which gives probably approach on the study of interface of the reinforced structures, is called "shear lag effect". The resolution in this paper shows that the shear stress and the normal stress are significant and, are concentrated at the end of the composite plate of reinforcement, called "edge effect". A parametric study is carried out to show the effects of the variables of design and the physical properties of materials. This research is helpful for the understanding on mechanical behaviour of the interface and design of such structures.

• 한국터널지하공간학회 논문집
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• 제4권3호
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• pp.175-184
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• 2002

일반적으로 터널 굴착시 지보재의 설치시기에 대한 예측을 위하여서는 지반반응곡선 (Ground reaction curve)을 활용하고 있다. 이 지반반응곡선은 굴착에 따른 지반의 변위 특성을 나타내며, 일반적으로 원형단면이고 등방상태 (K = 1.0)로 가정하여 단순화시킨 Closed Form Solution을 통해서 구해진다. 그러나, 원형단면이 아니고, 비등방 응력상태인 실질적인 현장조건을 고려해 본다면, 이 지반반응특성 예측식을 현장조건에 적용함에 있어서 어떠한 한계점을 갖는지에 대하여 규명할 필요가 있다. 이를 위해, 본 논문에서는 굴착단면 형상에 따른 측벽에서의 초기탄성변위 및 임계지보압의 변화 특성에 대하여 연구하였다. 터널굴착 형상은 단면의 높이 (b)와 폭 (a)의 비, 즉 굴착형상 계수 S (=b/a)값이 1.0, 0.8, 0.6, 0.4로 변화하도록 하였으며, 각각의 굴착형상마다 초기등방응력을 5~30 MPa사이에서 변화시켜가면서 수치해석을 통해 지반반응곡선을 얻었다. 수치해석을 통해 얻어진 측벽에서의 지반반응곡선을 분석하여 그에 따른 특성을 제시하였다. 검토결과 지반의 자립성을 평가하는데 있어서 Closed form solution의 사용에는 한계가 있는 것으로 판단된다.

• 한국지반환경공학회 논문집
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• 제18권7호
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• pp.37-47
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• 2017

본 연구에서는 강관매입말뚝의 하중-침하 및 전단응력 전이 특성을 분석하기 위하여 시험시공 및 수치해석을 수행하였다. 동재하시험 및 정재하시험을 수행한 결과 EOID 및 Restrike 시험을 통해 평가된 말뚝의 설계지지력은 정재하시험에서 평가된 설계 지지력에 비해 각각 약 56~105% 및 65~121%의 범위를 보였으며, 말뚝재하시험 이전에 수행된 Class-A type 수치해석의 경우 38~142%의 범위를 보였다. 또한 Restrike 시험에서 평가된 설계지지력은 EOID 시험의 설계지지력에 비해 12~60% 증가된 것으로 평가되었다. EOID에서는 선단지지력이 크게 측정되는 데 비해, Restrike 시험에서는 주면마찰력이 크게 측정되었는데 Restrike 시험의 타격에너지가 충분하지 않은 경우 말뚝의 선단지지력이 과소평가될 가능성이 있는 것으로 분석되었다. 본 연구의 분석에 의하면 동재하시험을 통해 말뚝의 지지력을 합리적으로 평가하기 위해서는 주면지지력은 Restrike 시험 결과를, 선단지지력은 EOID 시험 결과를 적용하는 것이 합리적인 것을 알 수 있었다. 정재하시험 실측값과 수치해석으로부터 예측된 하중-침하 관계는 탄성범위까지는 어느 정도 유사하지만 항복이 발생한 이후의 거동은 크게 벗어났다. 즉 실측값은 항복 이후 경화현상이 거의 없이 마치 탄성-완전소성(elastic-perfectly plastic) 재료와 유사하게 파괴에 도달되는 반면에, 수치해석에서는 변형경화(strain hardening)과정을 거치면서 파괴에 점진적으로 도달되는 경향을 보였다. 말뚝의 하중-침하 특성은 지반의 강성에 영향을 받으며, 축력분포는 지반의 전단 강도상수에 영향을 받는 것으로 나타났다.

• 한국지반공학회논문집
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• 제18권6호
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• pp.33-42
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• 2002

지반 굴착시 지반의 변위특성과 지보재의 설치시기에 대한 중요한 정보를 제공하는 지반반응곡선(Ground reaction curve)을 구하는 방법은 일반적으로 원형단면이고 측압계수 K＝1.0인 상태를 가정한 closed from solution을 통해서 구해지지만, 실제 현장에서는 주로 마제형 굴착단면이 사용되며 $K\neq$1.0인 경우 대부분이다. 지반 굴착시 측압계수와 굴착 형상에 따라 측벽에서의 초기탄성변위 및 임계지보압이 변화하는 경향을 알아보기 위하여 측압계수 값을 0.5～3.0 사이에서 변화시키고, 각 측압계수마다 초기연직응력을 5～30MPa 사이에서 변화시켜가면서 원형단면과 마제형 단면인 경우를 구분하여 수치해석을 통해 지반반응곡선을 얻었다. Closed form solution에 의해 얻어진 지반반응곡선은 측압계수와 굴착단면의 형상을 고려하지 못하기 때문에 $K\neq$1.0인 실제 지반에 대한 변위거동과 지반의 자립성을 평가하는 데 큰 오차를 유발할 수 있는 것으로 나타났다. 따라서, Closed from solution에 의해 지보재의 설치시기를 예측하는 것은 많은 오차를 수반하는 과정이므로, 수치해석을 통한 지보설치 시기와 자립성에 대한 검토를 수행하는 것이 바람직 할 것으로 판단된다.

• 한국농공학회지
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• 제37권3_4호
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• pp.61-71
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• 1995

Natural ground is a composite consisted of the three phases of water, air and soil paircies. Among the three components, water as a material is weU understood but soil particles are not in foundation engineering. Especially, weathered granite soil generally shows a large volumetric expansion when they freeze. And, the stability and durability of the soil have shown decreased with repetitive freezing and thawing processes. These unique charcteristics may cause various construction and management problems if the soil is used as a construction material and foundation layers. This project was initiated to investigate the soil's physical and engineering characteristics resulting from freezing and freezing-thawing processes. Research results may be used as a basic data in solving various problems related to the soil's unique characteristics. The following conclusions were obtained: The degree of decomposition of weathered granite soil in Kangwon-do was very different between the West and East sides of the divide of the Dae-Kwan Ryung. Soil particles distributed wide from very coarse to fine particles. Consistency could be predicted with a function of P200 as LL=0.8 P200+20. Permeability ranged from 10-2 to 10-4cm/sec, moisture content from 15 to 20% and maximum dry density from 1.55 to 1.73 g /cmΥ$^3$ By compaction, soil particles easily crushed, D50 of soil particles decreased and specific surface significantly increased. Shear characteristics varied wide depending on the disturbance of soil. Strain characteristics influenced the soil's dynamic behviour. Elastic failure mode was observed if strain was less than 1O-4/s and plastic failure mode was observed if strain was more than 10-2/s. The elastic wave velocity in the soil rapidly increased if dry density became larger than 1.5 g /cm$^3$ and these values were Vp=250, Vg= 150, respectively. Frost heave ratio was the highest around 0 $^{\circ}C$ and the maximum frost heave pressure was observed when deformation ratio was less than 10% which was the stability state of soil freezing. The state had no relation with frost depth. Over freezing process was observed when drainage or suction freezing process was undergone. Drainage freezing process was observed if freezing velocity was high under confined pressure and suction frost process was occurred if the velocity was low under the same confined process.

• Structural Engineering and Mechanics
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• 제37권4호
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• pp.385-399
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• 2011

The aim of this research is to model the behaviour of recently developed high force to volume (HF2V) passive energy dissipation devices using a simple finite element (FE) model. Thus, the end result will be suitable for use in a standard FE code to enable computationally fast and efficient analysis and design. Two models are developed. First, a detailed axial model that models an experimental setup is created to validate the approach versus experimental results. Second, a computationally and geometrically simpler equivalent rotational hinge element model is presented. Both models are created in ABAQUS, a standard nonlinear FE code. The elastic, plastic and damping properties of the elements used to model the HF2V devices are based on results from a series of quasi-static force-displacement loops and velocity based tests of these HF2V devices. Comparison of the FE model results with the experimental results from a half scale steel beam-column sub-assembly are within 10% error. The rotational model matches the output of the more complex and computationally expensive axial element model. The simpler model will allow computationally efficient non-linear analysis of large structures with many degrees of freedom, while the more complex and physically accurate axial model will allow detailed analysis of joint connection architecture. Their high correlation to experimental results helps better guarantee the fidelity of the results of such investigations.

• Structural Engineering and Mechanics
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• 제41권2호
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• pp.183-204
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• 2012

Several issues regarding the structural idealization of steel buildings with perimeter moment resisting steel frames (MRSFs) and interior gravity frames (GFs) are studied. Results indicate that the contribution of GFs to the lateral structural resistance may be significant. The contribution increases when the stiffness of the connection of the GFs is considered and is larger for inelastic than for elastic behavior. The interstory shears generally increase when the connections stiffness is taken into account. Resultant stresses at some base columns of MRSFs also increase in some cases but to a lesser degree. For columns of the GFs, however, the increment is significant. Results also indicate that modeling the building as planes frames may result in larger interstory shears and displacements and resultant stresses than those obtained from the more realistic 3-D formulation. These differences may be much larger when semi-rigid (SR) connections are considered. The conservativism is more for resultant stresses. The differences observed in the behaviour of each structural representation are mainly due to a) the elements that contribute to strength and stiffness and b) the dynamics characteristics of each structural representation. It is concluded that, if the structural system under consideration is used, the three-dimensional model should be used in seismic analysis, the GFs should be considered as part of the lateral resistance system, and the stiffness of the connections should be included in the design of the GFs. Otherwise, the capacity of gravity frames may be overestimated while that of MRSFs may be underestimated.

• Steel and Composite Structures
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• 제4권5호
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• pp.385-402
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• 2004

Nearly 400 composite railway bridge decks of a new kind belonging to the trough type with U-shaped cross section have been constructed in Belgium over the last fifteen years. The construction of these bridge decks is rather complex with the preflexion of precambered steel girders, the prestressing of a concrete slab and the addition of a 2nd phase concrete. Until now, they have been designed with a classical computation method using a pseudo-elastic analysis with modular ratios. Globally, they perform according to the expectations but variability has been observed between the measured and the computed camber of these bridge decks just after the transfer of prestressing and also at long-term. A statistical analysis of the variability of the relative difference between the measured camber and the computed camber is made for a sample of 36 bridge decks using no less than 10 variables. The most significant variables to explain this variability at prestressing are the ratio between the maximum tensile stress reached in the steel girders during the preflexion and the yield strength and the type of steel girder. For the same sample, the long-term camber under permanent loading is computed by two methods and compared with measurements taken one or two years after the construction. The camber computed by the step-by-step method shows a better agreement with the measured camber than the camber computed by the classical method. The purpose of the paper is to report on the statistical analysis which was used to determine the most significant parameters to consider in the modeling in order to improve the prediction of the behaviour of these composite railway bridge decks.

• Steel and Composite Structures
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• 제35권5호
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• pp.611-625
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• 2020

Experimental investigation and finite element analysis of corroded cold-formed steel (CFS) columns are presented. 11 tensile coupon specimens and 6 stub columns of corroded CFS that had a channel section of C160x60x20 were subjected to monotonic tensile tests and axial compression tests, respectively. The degradation laws of the mechanical properties of the tensile coupon specimens and stub columns were analysed. An appropriate finite element model for the corroded CFS columns was proposed and the influence of local corrosion on the stability performance of the columns was studied by finite element analysis. Finally, the axial capacity of the experimental results was compared with the predictions obtained from the existing design specifications. The results indicated that with an increasing average thickness loss ratio, the ultimate strength, elastic modulus and yield strength decreased for the tensile coupon specimens. Local buckling deformation was not noticeable until the load reached about 90% of the ultimate load for the non-corroded columns, while local buckling deformation was observed when the load was only 40% of the ultimate load for the corroded columns. The maximum reduction of the ultimate load and critical buckling load was 57% and 81.7%, respectively, compared to those values for the non-corroded columns. The ultimate load of the columns with web thickness reduced by 2 mm was 53% lower than that of the non-corroded columns, which indicates that web corrosion most significantly affects the bearing capacity of the columns with localized corrosion. The results predicted using the design specifications of MOHURD were more accurate than those predicted using the design specifications of AISI.