• Computers and Concrete
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• 제10권5호
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• pp.489-505
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• 2012

This paper presents a simplified grid beam model for simulating the nonlinear response of reinforced concrete flat-plate structures. The beam elements are defined with nonlinear behavior for bending moment and torsion. The flexural stiffness and torsional strength of the beam elements are defined based on experimental data to implicitly account for slab two-way bending effects. A failure criterion that considers the interaction between the punching strength and slab flexural behavior is incorporated in the model. The effects of bond-slip of slab reinforcement on connection stiffness are examined. The proposed grid beam model is validated by simulating large-scale tests of slab-column connections subjected to concentric gravity loading and unbalanced moment. This study also determines the critical parameters for a hysteretic model used to simulate flat-plates subjected to cyclic lateral loading.

• 한국공간구조학회논문집
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• 제22권2호
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• pp.29-37
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• 2022

The collapse of reinforced concrete (RC) frame buildings is mainly caused by the failure of columns. To prevent brittle failure of RC column, numerous studies have been conducted on the seismic performance of strengthened RC columns. Concrete jacketing method, which is one of the retrofitting method of RC members, can enhance strength and stiffness of original RC column with enlarged section and provide uniformly distributed lateral load capacity throughout the structure. The experimental studies have been conducted by many researchers to analyze seismic performance of seismic strengthened RC column. However, structures which have plan and vertical irregularities shows torsional behavior, and therefore it causes large deformation on RC column when subjected to seismic load. Thus, test results from concentric cyclic loading can be overestimated comparing to eccentric cyclic test results, In this paper, two kinds of eccentric loading pattern was suggested to analyze structural performance of RC columns, which are strengthened by concrete jacketing method with new details in jacketed section. Based on the results, it is concluded that specimens strengthened with new concrete jacketing method increased 830% of maximum load, 150% of maximum displacement and changed the failure modes of non-strengthened RC columns.

• Computers and Concrete
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• 제10권4호
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• pp.331-347
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• 2012

This paper describes the varying material model, the analysis method and the software development for reinforced concrete circular columns confined by spiral or hoop transverse steel reinforcement and subjected to eccentric loading. The widely used Mander model of concentric loading is adapted here to eccentric loading by developing an auto-adjustable stress-strain curve based on the eccentricity of the axial load or the size of the compression zone to generate more accurate interaction diagrams. The prediction of the ultimate unconfined capacity is straight forward. On the other hand, the prediction of the actual ultimate capacity of confined concrete columns requires specialized nonlinear analysis. This nonlinear procedure is programmed using C-Sharp to build efficient software that can be used for design, analysis, extreme event evaluation and forensic engineering. The software is equipped with an elegant graphics interface that assimilates input data, detail drawings, capacity diagrams and demand point mapping in a single sheet. Options for preliminary design, section and reinforcement selection are seamlessly integrated as well. Improvements to KDOT Bridge Design Manual using this software with reference to AASHTO LRFD are made.

• Earthquakes and Structures
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• 제22권6호
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• pp.539-548
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• 2022

Steel plate shear walls (SPSWs) are one of the most important and widely used lateral load-bearing systems. The reason for this is easier execution than reinforced concrete (RC) shear walls, faster construction time, and lower final weight of the structure. However, the main drawback of SPSWs is premature buckling in low drift ratios, which affects the energy absorption capacity and global performance of the system. To address this problem, two groups of SPSWs under cyclic loading were investigated using the finite element method (FEM). In the first group, several series of circular rings have been used and in the second group, a new type of SPSW with concentric circular rings (CCRs) has been introduced. Numerous parameters include in yield stress of steel plate wall materials, steel panel thickness, and ring width were considered in nonlinear static analysis. At first, a three-dimensional (3D) numerical model was validated using three sets of laboratory SPSWs and the difference in results between numerical models and experimental specimens was less than 5% in all cases. The results of numerical models revealed that the full SPSW undergoes shear buckling at a drift ratio of 0.2% and its hysteresis behavior has a pinching in the middle part of load-drift ratio curve. Whereas, in the two categories of proposed SPSWs, the hysteresis behavior is complete and stable, and in most cases no capacity degradation of up to 6% drift ratio has been observed. Also, in most numerical models, the tangential stiffness remains almost constant in each cycle. Finally, for the innovative SPSW, a relationship was suggested to determine the shear capacity of the proposed steel wall relative to the wall slenderness coefficient.

• Steel and Composite Structures
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• 제34권6호
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• pp.909-927
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• 2020

This paper addresses the results of an experimental study involving 10 partially encased composite columns under concentric and eccentric compressive loads. Parameters such as slenderness ratio, ordinary reinforced concrete and fiber reinforced concrete, load eccentricity and bending axis were investigated. The specimens were tested to investigate the effects of replacing the ordinary reinforced concrete by fiber reinforced concrete on the load capacity and behavior of short and slender composite columns. Various characteristics such as load capacity, axial strains behavior, stiffness, strains on steel and concrete and failure mode are discussed. The main conclusions that may be drawn from all the test results is that the behavior and ultimate load are rather sensitive to the slenderness of the columns and to the eccentricity of loading, specially the bending axis. Experimental results also indicate that replacing the ordinary reinforced concrete by steel fiber reinforced concrete has no considerable effects on the load capacity and behavior of the short and slender columns and the proposed replacement presented very good results.

• Steel and Composite Structures
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• 제46권2호
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• pp.153-173
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• 2023

Rectangular concrete-filled steel tubular (RCFST) column, a type of concrete-filled steel tubular (CFST), is widely used in compression members of structures because of its advantages. This paper proposes a robust machine learning-based framework for predicting the ultimate compressive strength of RCFST columns under both concentric and eccentric loading. The gradient boosting neural network (GBNN), an efficient and up-to-date ML algorithm, is utilized for developing a predictive model in the proposed framework. A total of 890 experimental data of RCFST columns, which is categorized into two datasets of concentric and eccentric compression, is carefully collected to serve as training and testing purposes. The accuracy of the proposed model is demonstrated by comparing its performance with seven state-of-the-art machine learning methods including decision tree (DT), random forest (RF), support vector machines (SVM), deep learning (DL), adaptive boosting (AdaBoost), extreme gradient boosting (XGBoost), and categorical gradient boosting (CatBoost). Four available design codes, including the European (EC4), American concrete institute (ACI), American institute of steel construction (AISC), and Australian/New Zealand (AS/NZS) are refereed in another comparison. The results demonstrate that the proposed GBNN method is a robust and powerful approach to obtain the ultimate strength of RCFST columns.

• 한국소음진동공학회논문집
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• 제24권1호
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• pp.45-53
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• 2014

For the time integration solution of the impulsive dynamic contact problem of high-speed rotating disks formulated by the finite element technique, the velocity and acceleration contact constraints as well as the displacement contact constraint are imposed for the numerical stability without spurious oscillations. The solution of the present technique is checked by the numerical simulation using the concentric high-speed rotating disks with the clearance and impulsive loading. It is shown that the almost steady state solution agrees with the corresponding analytical solution of the elasticity and that the differentiated constraints are crucial for the numerical stability of such high-speed contact problems of the disks under impulsive loading.

• Steel and Composite Structures
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• 제13권6호
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• pp.521-537
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• 2012

In this study, an experimental study is performed to understand the effect of spalling on the structural behavior of fire damaged steel reinforced high strength concrete (SRHSC) columns, and the test results of temperature distributions and the displacements at elevated temperature are analyzed. Toward this goal, three long columns are tested to investigate the effect of various test parameters on structural behavior during the fire, and twelve short columns are tested to investigate residual strength and stiffness after the fire. The test parameters are mixture ratios of polypropylene fiber (0 and 0.1 vol.%), magnitudes of applied loads (concentric loads and eccentric loads), and the time period of exposure to fire (0, 30, 60 and 90 minutes). The experimental results show that there is significant effect of loading on the structural behaviors of columns under fire. The loaded concrete columns result more explosive spalling than the unloaded columns under fire. In particular, eccentrically loaded columns are severely spalled. The temperature distributions of the concrete are not affected by the loading state if there is no spalling. However, the loading state affects the temperature distributions when there is spalling occurred. In addition, it is found that polypropylene fiber prevents spalling of both loaded and unloaded columns under fire. From these experimental findings, an equation of predicting residual load capacity of the fire damaged column is proposed.

• Steel and Composite Structures
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• 제33권6호
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• pp.793-803
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• 2019

Concrete-filled steel tubular (CFST) beam-columns are widely used owing to their good performance. They have high strength, ductility, large energy absorption capacity and low costs. Externally stiffened CFST beam-columns are not used widely due to insufficient design equations that consider all parameters affecting their behavior. Therefore, effect of various parameters (global, local slenderness ratio and adding hoop stiffeners) on the behavior of CFST columns is studied. An experimental study that includes twenty seven specimens is conducted to determine the effect of those parameters. Load capacities, vertical deflections, vertical strains and horizontal strains are all recorded for every specimen. Ratio between outer diameter (D) of pipes and thickness (t) is chosen to avoid local buckling according to different limits set by codes for the maximum D/t ratio. The study includes two loading methods on composite sections: steel only and steel with concrete. The case of loading on steel only, occurs in the connection zone, while the other load case occurs in steel beam connecting externally with the steel column wall. Two failure mechanisms of CFST columns are observed: yielding and global buckling. At early loading stages, steel wall in composite specimens dilated more than concrete so no full bond was achieved which weakened strength and stiffness of specimens. Adding stiffeners to the specimens increases the ultimate load by up to 25% due to redistribution of stresses between stiffener and steel column wall. Finally, design equations previously prepared are verified and found to be only applicable for medium and long columns.

• 터널과지하공간
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• 제8권3호
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• pp.226-233
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• 1998

자연적으로, 혹은 인위적으로 발생된 균열들은 현지암반의 공학적 거동에 대한 중요한 자료를 제공한다. 일정한 방향으로 분포하는 미세균열들은 암반의 물성에 현저한 영향을 미치게 되지만, 다른 요인들에 의한 이방성이 큰 경우에는 이들의 영향은 감소한다. 본 연구에서는 초음파속도의 이방성과 점하중 재하에 의한 인공균열의 진행방향을 기초로, 암석조직이 암석의 물성에 미치는 영향에 대하여 조사하였다. 암석시료는 우백질의 포천화강암 석재에서 코어링한 NX 시험편과 현장 시추코어를 사용하였다. 시료에 분포하는 균열들의 주 방향을 기준으로 설정한 후, 초음파속도의 이방성을 측정한 결과, 균열에 수직한 방향에서 초음파속도의 최소치가 측정되었다. 속도측정에 사용한 NX코어로부터 EX크기의 원판형 시험편을 성형한 수 점하중 재하실험을 수행하였으며, 점하중재하에 의한 인공균열의 진행방향은 기존의 미세균열의 방향과 거의 일치하였다.