• Steel and Composite Structures
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• v.38 no.6
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• pp.637-656
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• 2021

The component-based method is widely used to analyze the initial stiffness of joint in steel structures. In this study, an analytical component model for determining the column face stiffness of square or rectangular hollow section (SHS/RHS) subjected to tension was established, focusing on endplate connections. Equations for calculating the stiffness of the SHS/RHS column face in bending were derived through regression analysis using numerical results obtained from a finite element model database. Because the presence of bolt holes decreased the bending stiffness of the column face, this effect was calculated using a novel plate-spring-based model through numerical analysis. The developed component model was first applied to predict the bending stiffness of the SHS column face determined through tests. Furthermore, this model was incorporated into the component-based method with other effective components, e.g., bolts under tension, to determine the tensile stiffness of the T-stub connections, which connects the SHS column, and the initial rotational stiffness of the joints. A comparison between the model predictions, test data, and numerical results confirms that the proposed model shows satisfactory accuracy in evaluating the bending stiffness of SHS column faces.

• Earthquakes and Structures
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• v.23 no.5
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• pp.403-417
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• 2022

Reinforced concrete (RC) structures with low-strength RC columns are rampant in several countries, especially those constructed during the early 1960s and 1970s. The weakness of these structures due to overloading or some natural disasters such as earthquakes and building age effects are some of the main reasons to collapse, particularly with the scarcity of data on the impact of aspect ratio and corner radius on the confinement effectiveness. Hence, it is crucial to investigate if these columns (with different aspect ratios) can be made safe by strengthening them with carbon fiber-reinforced polymers (CFRP) sheets. Therefore, experimental and numerical studies of CFRP-strengthened low-strength reinforced concrete short rectangular, square, and circular columns were studied. In this investigation, a total of 6 columns divided into three sets were evaluated. The first set had two circular cross-sectional columns, the second set had two square cross-section columns, and the third set has two rectangular cross-section columns. Furthermore, FEM validation has been conducted for some of the experimental results obtained from the literature. The experimental results revealed that the confinement equations for RC columns as per both CSA and ACI codes could give incorrect results for low-strength concrete. The control specimen (unstrengthened ones) displayed that both ACI and CSA equations overestimate the ultimate strength of low-strength RC columns by order of extent. For strengthened columns with CFRP, the code equations of CSA and ACI code overestimate the maximum strength by around 6 to 13% and 23 to 29%, respectively, depending on the cross-section of the column (i.e., square, rectangular, or circular). Results of finite element models (FEMs) showed that increasing the layer number of new commonly CFRP type (B) from one to 3 for circular columns can increase the column's ultimate loads by around eight times compared to unjacketed columns. However, in the case of strengthened square and rectangular columns with CFRP, the increase of the ultimate loads of columns can reach up to six times and two times, respectively.

• Steel and Composite Structures
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• v.52 no.2
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• pp.145-163
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• 2024

This paper presents six novel hybrid machine learning (ML) models that combine support vector machines (SVM), Decision Tree (DT), Random Forest (RF), Gradient Boosting (GB), extreme gradient boosting (XGB), and categorical gradient boosting (CGB) with the Harris Hawks Optimization (HHO) algorithm. These models, namely HHO-SVM, HHO-DT, HHO-RF, HHO-GB, HHO-XGB, and HHO-CGB, are designed to predict the ultimate strength of both rectangular and circular reinforced concrete (RC) columns. The prediction models are established using a comprehensive database consisting of 325 experimental data for rectangular columns and 172 experimental data for circular columns. The ML model hyperparameters are optimized through a combination of cross-validation technique and the HHO. The performance of the hybrid ML models is evaluated and compared using various metrics, ultimately identifying the HHO-CGB model as the top-performing model for predicting the ultimate shear strength of both rectangular and circular RC columns. The mean R-value and mean a20-index are relatively high, reaching 0.991 and 0.959, respectively, while the mean absolute error and root mean square error are low (10.302 kN and 27.954 kN, respectively). Another comparison is conducted with four existing formulas to further validate the efficiency of the proposed HHO-CGB model. The Shapely Additive Explanations method is applied to analyze the contribution of each variable to the output within the HHO-CGB model, providing insights into the local and global influence of variables. The analysis reveals that the depth of the column, length of the column, and axial loading exert the most significant influence on the ultimate shear strength of RC columns. A user-friendly graphical interface tool is then developed based on the HHO-CGB to facilitate practical and cost-effective usage.

• Journal of the Korean Society of Visualization
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• v.20 no.3
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• pp.49-57
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• 2022

The interaction of planar shock wave with rectangular water column is investigated numerically. The flow phenomenon like reflection, transmission, cavitation, recirculation of shock wave, and large negative pressure due to expansion waves was discussed qualitatively and quantitatively. The numerical simulation was performed in a shock tube with a water column, and planar shock was initiated with a pressure ratio of 10. Three cases of the water column with different thicknesses, namely 0.5D, 1D, and 2D, were installed and studied. Water naturally has a higher acoustic impedance than air and mitigates the shock wave considerably. The numerical simulations were modelled using Eulerian and Volume of fluids multiphase models. The Eulerian model assumes the water as a finite structure and can visualize the shockwave propagation inside the water column. Through the volume of fluids model, the stages of breakup of the water column and mitigation effects of water were addressed. The numerical model was validated against the experimental results. The computational results show that the installation of a water column significantly impacts the mitigation of shock wave.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.3
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• pp.152-159
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• 2006

An experimental research has been performed to investigate capacity of CFCST(Concrete Filled Carbon Sheet Tube) columns because column member is one of the most important structural members. Generally, two shapes of column sections, rectangular and circular shapes, are designed but the circular shape which has constant curvature was chosen for this study. Total 17 column specimens confined by carbon sheet tube were tested using 10,000kN universal test machine(UTM).

• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.149-160
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• 1999

This paper is a part of a research aimed at the verification of basic design rules of high-strength concrete columns. A total of 32 column specimens were tested to investigate structural behavior and strength of eccentrically loaded reinforced concrete tied columns. Main variables included in this test program were concrete compressive strength. steel amount, eccentricity, and slenderness ratio. The concrete compressive strength varied from 356 kg/$cm^2$ to 951 kg/$cm^2$ and the longitudinal steel ratios were between 1.13 % and 5.51 %. Test results of column sectional strength are compared with the results of analyses by ACI rectangular stress block, trapezoidal stress block, and modified rectangular stress block. Axial force-moment-curvature analysis is also performed for predicting axial load-moment strength and compared with the test results. The ACI rectangular stress block provides over-estimated column strengths for the lightly reinforced high strength column specimens. The calculated strengths by moment-curvature analyses are highly affected by $k_3$ values of the concrete stress-strain curve. Observed failure mode. concrete ultimate strain, and stress block parameters are discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.4
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• pp.895-904
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• 1998

This paper presents the results of experimental investigation of the buckling behavior of thin-walled box-section column. The experiments for finding the buckling stress and bifurcation slenderness ratio are performed by the method from AISC. The sets of boundary conditions are both end simply supported, one end simply supported and the other end clamped, and both ends clamped. The types of specimens are clssified by thickness to width ratio. The experiments for the thin-walled rectangular tubes are closely concurrent with the theoretical values of overall buckling load and bifurcation slenderness ratio that are suggested by the part (I) of this paper.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.209-214
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• 2001

Most reinforce concrete Columns of Building structure are subjected to both axial load and biaxial bending. However, It is hard to estimate the moment capacity of biaxial bending by exact solution. Thus, columns under biaxial bending are designed by approximate methods in practice. The purpose of this study is to compare experimental result with approximate methods and exact solution by computer. Parameters of the present test are compressive strength of concrete (350, 585, 650kgf/$\textrm{cm}^2$) and shape ratio of rectangular section. Ultimately, an experimental shape factor for rectangular RC column section is obtained through the test program. The shape of load contour is dominated by this shape factor obtained experimentally. So, reasonable design of RC columns subjected to both axial compression and biaxial bending depends on load contour.

• Structural Engineering and Mechanics
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• v.10 no.6
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• pp.577-587
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• 2000

A 3D nonlinear finite element computation model is presented in order to analyze the concrete filled rectangular tubular (CFRT) composite structures. The concrete material model is based on a hypo-elastic orthotropic approach while the elasto-plastic hardening model is employed for steel element. The comparisons between experimental and analytical results show that the proposed model is a relatively simple and effective one. The analytical results show that the capacity of inner concrete of CFRT column mainly depends on the two diagonal zones, and the confining effect of CFRT section is mainly concentrated on the corner zones. At the ultimate state, the side concrete along the section cracks seriously, and the corner concrete softens with the increase of compressive strains until failure.

• Journal of the Korean Society of Safety
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• v.21 no.2 s.74
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• pp.70-79
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• 2006

many plumbing system are needed in the ceiling of the building as it becomes advanced more and more. This leads to make effective space between ceiling level and slab less. Also, piping system is not suitably arranged and operated if it is bent around the columns which they are a lot. But this system can be more effective if it passes through the columns directly. Most people think that those columns should not be damaged with such as holes. But actually this is existed in a hotel building in switzerland. This study is to fing out how much capacity the columns become damaged and low using model size of $20cm{\times}30cm$ rectangular section, and 160cm long, in the structural test. it's compressive strength is focused on $240kg/cm^{2}$ design strength, commonly used in korea. Compressive test for them was done at Hanyang University using UTM one thousand tone(1000t) capacity. Variable numbers for the study are one hole of dia 3cm with distance 20cm or 40cm, two holes of dia 3cm with 20cm and 40cm distance, one hole of dia 5cm with distance 20cm and 40cm, two holes of dia 5cm with 20cm and 40cm distance, me eccentric hole with 20cm and 40cm distance, Normal(without hole). two test specimens of each variable are made for the test. ED5H20 capacity was 16.7% decreased, compared to normal one. While ED5H40 distant 40cm from the end of column top showed 19.5% capacity decrease, compared to normal one. Strain of ED5H20 diameter 5cm, in distance of 20cm form the top of the column was less 5% than the one of diameter 3cm. Finally, conclusions are that in case of hole diameter 3cm, located at 20cm from the end of the column top, capacity was decreased down to 3, percent only compared to the same diameter hole with 20cm distant from the end of it.