• International journal of steel structures
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• v.18 no.4
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• pp.1363-1372
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• 2018

Recently, there have been studies about the increasing effect on the local plate buckling strength of flat plates when longitudinally stiffened with closed-section ribs and an approximate solution to quantitatively estimate these effects were suggested for flat plates. Since there are few studies to utilize such increasing effect on curved panels and a proper design method is not proposed, thus, this study aims to numerically evaluate such effect due to the rotational stiffness of closed-section ribs on curved panels and to propose an approximate method for estimating the buckling strength. Three-dimensional finite element models were set up using a general structural analysis program ABAQUS and a series of parametric numerical analyses were conducted in order to examine the variation of buckling stresses along with the rotational stiffness of closed-section ribs. By using a methodology that combine the strength increment factor due to the restraining effect by closed-section ribs and the buckling coefficient of the panel curvature, the approximate solutions for the estimation of buckling strength were suggested. The validity of the proposed methods was verified through a comparative study with the numerical analysis results.

• Steel and Composite Structures
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• v.38 no.1
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• pp.67-78
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• 2021

The use of composite beams with partial interaction, with less shear connectors than those required for full interaction, may be advantageous in many situations. However, these beams tend to show higher deflections compared to beams with full interaction, and codified expressions for the calculation of such deflections are not fully developed and validated. Thus, this paper presents a comprehensive numerical study on the deflections of steel-concrete composite beams with partial interaction. Efficient numerical models of full-scale composite beams considering material nonlinearities and contact between their parts have been developed by means of the advanced software ABAQUS, including a damage model to simulate the concrete slab. The FE models were validated against experimental results, and subsequently parametric studies were developed to investigate the influence of the shear connection degree and the coefficient of friction in the deflection of composite beams. The comparison of predicted deflections using reference codes (AISC, Eurocode-4 and AS-2327.1) against numerical results showed that there are still inaccuracies in the estimation of deflections for the verification of the serviceability limit state, according to some of the analyzed codes.

• Structural Engineering and Mechanics
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• v.77 no.5
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• pp.673-689
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• 2021

This paper addresses the efficiency of thermal insulation layers applied to protect structural elements strengthened by fiber-reinforced polymers (FRP) in the case of fire event. The paper presents numerical modeling and nonlinear analysis of reinforced concrete (RC) columns externally strengthened by FRP and protected by thermal insulation layers when subjected to elevated temperature specified by standard fire tests, in order to predict their residual capacity and fire endurance. The adopted numerical approach uses commercial software includes heat transfer, variation of thermal and mechanical properties of concrete, steel reinforcement, FRP and insulation material with elevated temperature. The numerical results show good agreement with published results of full-scale fire tests. A parametric study was conducted to investigate the influence of several variables on the structural response and residual capacity of insulated FRP-confined columns loaded by service loads when exposed to fire. The residual capacity of FRP-confined RC column was affected by concrete grade and insulation material and was shown to improve substantially by increasing the concrete cover and insulation layer thickness. By increasing the VG insulation layer thickness 15, 32, 44, 57 mm, the loss in column capacity after 5 hours of fire was 30%, 13%, 7% and 5%, respectively. The obtained results demonstrate the validity of the presented approach for estimation of fire endurance and residual strength, as an alternative for fire testing, and for design of fire protection layers for FRP-confined RC columns.

• Structural Engineering and Mechanics
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• v.83 no.6
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• pp.757-770
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• 2022

In this paper, the vibration of a moderately thick plate to a moving mass is investigated. Pasternak foundation with a variable subgrade modulus is considered to tackle the shortcomings of Winkler model, and an analytical-numerical solution is proposed based on the eigenfunction expansion method. Parametric studies by using both CPT (Classical Plate Theory) and FSDT (First-Order Shear Deformation Plate Theory) are carried out, and, the differences between them are also highlighted. The obtained results reveal that utilizing FSDT without considering the rotary inertia leads to a smaller deflection in comparison with CPT pertaining to a thin plate, while it demonstrates a greater response for plates of higher thicknesses. Moreover, it is shown that CPT is unable to properly capture the variation of the plate thickness, thereby diminishing the accuracy as the thickness increases. The outcomes also indicate that the presence of a foundation contributes more to the dynamic response of thin plates in comparison to moderately thick plates. Furthermore, the findings suggest that the performance of the moving force approach for a moderately thick plate, in contrast to a thin plate, appears to be acceptable and it even provides a much better estimation in the presence of a foundation.

• Structural Engineering and Mechanics
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• v.78 no.4
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• pp.455-471
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• 2021

The present work focuses on experimental and numerical performance of the ferrocement RC walls reinforced with welded steel mesh, expanded steel mesh, fiber glass mesh and tensar mesh individually. The experimental program comprised twelve RC walls having the dimensions of 450 mm×100 mm×1000 mm under concentric compression loadings. The studied variables are the type of reinforcing materials, the number of mesh layers and volume fraction of reinforcement. The main aim is to assess the influence of engaging the new inventive materials in reinforcing the composite RC walls. Non-linear finite element analysis; (NLFEA) was carried out to simulate the behavior of the composite walls employing ANSYS-10.0 Software. Parametric study is also demonstrated to check out the variables that can mainly influence the mechanical behavior of the model such as the change of wall dimensions. The obtained numerical results indicated the acceptable accuracy of FE simulations in the estimation of experimental values. In addition, the strength gained of specimens reinforced with welded steel mesh was higher by amount 40% compared with those reinforced with expanded steel mesh. Ferrocement specimens tested under axial compression loadings exhibit superior ultimate loads and energy absorbing capacity compared to the conventional reinforced concrete one.

• Structural Monitoring and Maintenance
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• v.9 no.2
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• pp.107-127
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• 2022

Structural health monitoring (SHM) has been related to damage identification with either operational loads or other environmental loading playing a significant complimentary role in terms of structural safety. In this study, a non-parametric method of time frequency analysis on the measurement is used to address the time-frequency representation for modal parameter estimation and system damage identification of structure. The method employs the wavelet decomposition of dynamic data by using the modified complex Morlet wavelet with variable central frequency (MCMW+VCF). Through detail discussion on the selection of model parameter in wavelet analysis, the method is applied to study the dynamic response of both steel structure and reinforced concrete frame under white noise excitation as well as earthquake excitation from shaking table test. Application of the method to building earthquake response measurement is also examined. It is shown that by using the spectrogram generated from MCMW+VCF method, with suitable selected model parameter, one can clearly identify the time-varying modal frequency of the reinforced concrete structure under earthquake excitation. Discussions on the advantages and disadvantages of the method through field experiments are also presented.

• The Korean Journal of Applied Statistics
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• v.35 no.6
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• pp.755-764
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• 2022

This paper is concerned with power transformations in estimating GARCH volatility. To handle a semi-parametric case for which the exact likelihood is not known, quasi-likelihood (QL) rather than maximum-likelihood method is investigated to best estimate GARCH via maximizing the information criteria. A power transformation is introduced in the innovation generating QL estimating functions and then optimum power is selected by maximizing the profile information. A combination of two different power transformations is also studied in order to increase the parameter estimation efficiency. Nine domestic stock prices data are analyzed to order to illustrate the main idea of the paper. The data span includes Covid-19 pandemic period in which financial time series are really volatile.

• The Journal of the Korea Contents Association
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• v.22 no.2
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• pp.294-304
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• 2022

The purpose of this study is to examine the effects of a character education program based on self-reflection using a liberal arts course at university. To this end, a single treatment group pre- and post-design was conducted in which data were collected at the beginning and end of the semester for 18 students. For statistical estimation suitable for a small sample size, a non-parametric test was performed to examine the significant mean changes of the data. This program was found to significantly improve the level of self-compassion, life satisfaction, and mental well-being of university students. Based on the above results, it was discussed that the liberal arts course for character education based on self-reflection could be useful as a character education for university students, and the implications and suggestions of the results of this study were presented.

• Geomechanics and Engineering
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• v.37 no.6
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• pp.565-576
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• 2024

In this study, the earthquake risk assessment of single-story RC precast buildings in Turkey was carried out using loss curves. In this regard, Kocaeli, a seismically active city in the Marmara region, and this building class, which is preferred intensively, were considered. Quality and period parameters were defined based on structural and geometric properties. Depending on these parameters, nine main sub-classes were defined to represent the building stock in the region. First, considering the mean fragility curves and four different central damage ratio models, vulnerability curves for each sub-class were computed as a function of spectral acceleration. Then, probabilistic seismic hazard analyses were performed for stiff and soft soil conditions for different earthquake probabilities of exceedance in 50 years. In the last step, 90 loss curves were derived based on vulnerability and hazard results. Within the scope of the study, the comparative parametric evaluations for three different earthquake intensity levels showed that the structural damage ratio values for nine sub-classes changed significantly. In addition, the quality parameter was found to be more effective on a structure's damage state than the period parameter. It is evident that since loss curves allow direct loss ratio calculation for any hazard level without needing seismic hazard and damage analysis, they are considered essential tools in rapid earthquake risk estimation and mitigation initiatives.

• Geomechanics and Engineering
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• v.37 no.1
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• pp.31-48
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• 2024

To stabilize the excavations in urban area, soil anchorage is among the very common methods in geotechnical engineering. A more efficient deformation analysis can potentially lead to cost-effective and safer designs. To this end, a total of 116 three-dimensional (3D) finite element (FE) models of a deep excavation supported by tie-back wall system were analyzed in this study. An initial validation was conducted through examination of the results against the Texas A&M excavation cases. After the validation step, an extensive parametric study was carried out to cover significant design parameters of tie-back wall system in deep excavations. The numerical results indicated that the maximum horizontal displacement values of the wall (δ_hm) and maximum surface settlement (δ_vm) increase by an increase in the value of ground anchors inclination relative to the horizon. Additionally, a change in the wall embedment depth was found to be contributing more to δ_vm than to δ_hm. Based on the 3D FE analysis results, two simple equations are proposed to estimate excavation deformations for different scenarios in which the geometric configuration parameters are taken into account. The model proposed in this study can help the engineers to have a better understanding of the behavior of such systems.