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CONTENTS
Volume 8, Number 1, January 2023
 

Abstract
To consider the effects of the increasing speed of next-generation high-speed trains, the existing traffic safety code for railway bridges needs to be improved. This study suggests a numerical method of evaluating the new effects of this increasing speed on railway bridges. A prestressed concrete (PSC) box bridge with a 40 m span length on the Gyeongbu track sector is selected as a representative example of high-speed railway bridges in Korea. Numerical models considering the inertial mass forces of a 38-degree-of-freedom train and the interaction forces with the bridge as well as track irregularities are presented in detail. The vertical deflections and accelerations of the deck are calculated and compared to find the new effects on the bridge arising with increasing speed under simply and continuously supported boundary conditions. The ratios between the static and dynamic responses are calculated as the dynamic amplification factors (DAFs) under different running speeds to evaluate the traffic safety. The maximum deflection and acceleration caused by the running speed are indicated, and regression equations for predicting these quantities based on the speed are also proposed.

Key Words
dynamic amplification factors; next-generation high-speed train; PSC box bridge; traffic safety; vertical deflections and accelerations

Address
Soon T. Oh, Dong J. Lee and Byeong J. Jeong: Civil and Environmental Engineering, Seoul National University of Science and Technology, Seoul 01811, Republic of Korea

Seong T. Yi: Department of Civil and Environmental Engineering, Inha Technical College, Incheon 22212, Republic of Korea


Abstract
The Puebla-Morelos Earthquake (Mw 7.1) occurred in Mexico in 2017 causing 44 buildings to collapse in Mexico City. This work evaluates the non-linear response of a 6-story reinforced concrete (RC) frame prototype model with masonry infill walls on upper floors. The prototype model was designed using provisions prescribed before 1985 and was subjected to seismic excitations recorded during the earthquakes of 1985 and 2017 in different places in Mexico City. The building response was assessed through a damage index (DI) that considers low-cycle fatigue of the steel reinforcement in columns of the first floor, where the steel was modeled including buckling as was observed in cases after the 2017 earthquake. Isocurves were generated with 72 seismic records in Mexico City representing the level of iso-demand on the structure. These isocurves were compared with the location of 16 collapsed (first-floor column failure) building cases consistent with the prototype model. The isocurves for a value greater than 1 demarcate the location where fatigue failure was expected, which is consistent with the location of 2 of the 16 cases studied. However, a slight increase in axial load (5%) or decrease in column cross-section (5%) had a significant detrimental effect on the cumulated damage, increasing the intensity of the isocurves and achieving congruence with 9 of the 16 cases, and having the other 7 cases less than 2 km away. Including column special detailing (tight stirrup spacing and confined concrete) was the variable with the greatest impact to control the cumulated damage, which was consistent with the absence of severe damage in buildings built in the 70s and 80s.

Key Words
cumulative damage; damage index; frame buildings; infill walls; low-cycle fatigue; Puebla-Morelos earthquake; reinforced concrete buildings; soft-story

Address
Leonardo M. Massone and Diego Aceituno: University of Chile, Blanco Encalada 2002, Santiago, Chile

Julian Carrillo: Universidad Militar Nueva Granada, UMNG, Cra. 11, Bogotá, Colombia

Abstract
Squat reinforced concrete (SRC) shear walls are a critical part of the structure for both office/residential buildings and nuclear structures due to their significant role in withstanding seismic loads. Despite this, empirical formulae in current design standards and published studies demonstrate a considerable disparity in predicting SRC wall shear strength. The goal of this research is to develop and evaluate hybrid and ensemble artificial neural network (ANN) models. State-of-the-art population-based algorithms are used in this research for hybrid intelligence algorithms. Six models are developed, including Honey Badger Algorithm (HBA) with ANN (HBA-ANN), Hunger Games Search with ANN (HGS-ANN), fitness-distance balance coyote optimization algorithm (FDB-COA) with ANN (FDB-COA-ANN), Averaging Ensemble (AE) neural network, Snapshot Ensemble (SE) neural network, and Stacked Generalization (SG) ensemble neural network. A total of 434 test results of SRC walls is utilized to train and assess the models. The results reveal that the SG model not only minimizes prediction variance but also produces predictions (with R2 = 0.99) that are superior to other models.

Key Words
ensemble learning methods; optimization algorithm; shear strength; squat reinforced concrete wall

Address
Mohammad Sadegh Barkhordari: Department of Civil and Environmental Engineering, Amirkabir University of Technology, Tehran, Iran

Leonardo M. Massone: Department of Civil Engineering, University of Chile, Blanco Encalada 2002, Santiago, Chile

Abstract
Fiber reinforced polymer (FRP) columns are increasingly being used in various engineering fields due to its high strength to weight ratio and corrosion resistance. Being a thin-walled structure, their designs are often governed by buckling. Buckling strength depends on state of stress of elements which is greatly influence by stacking sequence and various inaccuracies such as geometric imperfections and imperfections due to eccentricity of compressive load and non-uniform boundary conditions. In the present work, influence of load eccentricity on buckling strength of FRP column has been investigated by conducting parametric study. Numerical analyses were carried out by using finite element software ABAQUS. The finite element (FE) model was validated using experimental results from the literature, which demonstrated good agreement in terms of failure loads and deformed shapes. The influence of load eccentricity on buckling behavior is discussed with the help of developed graphs.

Key Words
buckling; eccentric load; finite element analysis; FRP laminate; stability

Address
M Kasiviswanathan: Department of Civil Engineering, Sona College of Technology, Salem 636005, India

M Anbarasu: Department of Civil Engineering, Government College of Engineering, Salem 636011, India

Abstract
Calculating size-dependent mechanical properties of the nano-scale materials usually involves cumbersome numerical and theoretical works. In this paper, we aim to present a closed-form relation to calculate the length-dependent Young's modulus of carbon nanotubes (CNTs) based on nonlocal elasticity theory. In this regard, a single wall carbon nanotube (SWCNT) is considered as a rod structure and the governing nonlocal equations are developed under uniaxial tensile load. The equations are solved using analytical methods and strain distribution, total displacement and the size-dependent equivalent Young's modulus are obtained. Further, the results are compared with the molecular dynamics results from the literature. The outcome indicates that the calculated relations are coincident with the molecular dynamics results.

Key Words
carbon nanotube; nanocomposite; nonlocal elasticity; size-dependent properties; stability; Young's modulus

Address
Jiangjiang Li: Social Science Foundation Department, Zhejiang College of Security Technology, Wenzhou 325016, Zhejiang, China


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