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CONTENTS
Volume 7, Number 4, December 2020
 


Abstract
In this paper, an adaptive MEMD based modal identification technique for linear time-invariant systems is proposed employing multiple vibration measurements. Traditional empirical mode decomposition (EMD) suffers from mode-mixing during sifting operations to identify intrinsic mode functions (IMF). MEMD performs better in this context as it considers multi-channel data and projects them into a n-dimensional hypercube to evaluate the IMFs. Using this technique, modal parameters of the structural system are identified. It is observed that MEMD has superior performance compared to its traditional counterpart. However, it still suffers from mild mode-mixing in higher modes where the energy contents are low. To avoid this problem, an adaptive filtering scheme is proposed to decompose the interfering modes. The Proposed modified scheme is then applied to vibrations of a reinforced concrete road bridge. Results presented in this study show that the proposed MEMD based approach coupled with the filtering technique can effectively identify the parameters of the dominant modes present in the structural response with a significant level of accuracy.

Key Words
hilbert transform; Multi-variate Empirical Mode Decomposition; intrinsic mode function; operational modal analysis; modal parameters of bridge

Address
(1) Swarup Mahato:
Department of Components and System, Gustave Eiffel University, Bouguenais - 44340, France;
(2) Budhaditya Hazra, Arunasis Chakraborty:
Department of Civil Engineering, Indian Institute of Technology Guwahati, Assam - 781039, India.

Abstract
Investigation of the stability of arch dam abutments is one of the most important aspects in the analysis of this type of dams. To this end, the Bakhtiari dam, a doubly curved arch dam having six wedges at each of its abutments, is selected. The seismic safety of dam abutments is studied through time history analysis using the design-based earthquake (DBE) and maximum credible earthquake (MCE) hazard levels. Londe limit equilibrium method is used to calculate the stability of wedges in abutments. The thrust forces are obtained using ABAQUS, and stability of wedges is calculated using the code written within MATLAB. Effects of foundation flexibility, grout curtain performance, vertical component of earthquake, nonlinear behavior of materials, and geometrical nonlinearity on the safety factor of the abutments are scrutinized. The results show that the grout curtain performance is the main affecting factor on the stability of the abutments, while nonlinear behavior of the materials is the least affecting factor amongst others. Also, it is resulted that increasing number of the contraction joints can improve the seismic stability of dam. A cap is observed on the number of joints, above which the safety factor does not change incredibly.

Key Words
dam; finite element analysis of structures; modeling of structures; non-linear time-series analysis; seismic analysis; structural damage

Address
Hasan Mostafaei and Farhad Behnamfar: Department of Civil Engineering, Isfahan University of Technology, Isfahan 8415683111, Iran
Mohammad Alembagheri: Department of Civil and Environmental Engineering, Tarbiat Modares University, Tehran, Iran

Abstract
Inverse analysis of non-linear reinforced concrete bridge pier using recursive Gaussian filtering for in-situ condition assessment is the main theme of this work. For this purpose, minimum variance unbiased estimation using unscented sigma points is adopted here. The uniqueness of this inverse analysis lies in its approach for strain based updating of engineering demand parameters, where appropriate bound and constrained conditions are introduced to ensure numerical stability and convergence. In this analysis, seismic input is also identified, which is an added advantage for the structures having no dedicated sensors for earthquake measurement. First, the proposed strategy is tested with a simulated example whose hysteretic properties are obtained from the slow-cyclic test of a frame to investigate its efficiency and accuracy. Finally, the experimental test data of a full-scale bridge pier is used to study its in-situ condition in terms of Park & Ang damage index. Overall the study shows the ability of the augmented minimum variance unbiased estimation based recursive time-marching algorithm for non-linear system identification with the aim to estimate the engineering damage parameters that are the fundamental information necessary for any future decision making for retrofitting/rehabilitation.

Key Words
bouc-wen hysteresis; minimum variance unbiased estimation; condition assessment of bridge pier; shake table test; Park & Ang damage index

Address
Pranjal Tamuly, Arunasis Chakraborty and Sandip Das: Department of Civil Engineering, Indian Institute of Technology Guwahati, Assam, India- 781039

Abstract
At present, many machine leaning and data mining methods are used for analyzing and predicting structural response characteristics. However, the platform that combines big data analysis methods with online and offline analysis modules has not been used in actual projects. This work is dedicated to developing a multifunctional Hadoop-Spark big data platform for bridges to monitor and evaluate the serviceability based on structural health monitoring system. It realizes rapid processing, analysis and storage of collected health monitoring data. The platform contains offline computing and online analysis modules, using Hadoop-Spark environment. Hadoop provides the overall framework and storage subsystem for big data platform, while Spark is used for online computing. Finally, the big data Hadoop-Spark platform computational performance is verified through several actual analysis tasks. Experiments show the Hadoop-Spark big data platform has good fault tolerance, scalability and online analysis performance. It can meet the daily analysis requirements of 5s/time for one bridge and 40s/time for 100 bridges.

Key Words
structural health monitoring; bridge; big data; Hadoop-Spark platform; data processing

Address
Manya Wang, Youliang Ding, Chunfeng Wan and Hanwei Zhao: Key Laboratory of C&PC Structures of the Ministry of Education, Southeast University,
Nanjing 210096, China;
Department of Civil Engineering, Southeast University, Nanjing 210096, China


Abstract
The specific characteristics of near-field earthquake records can lead to different dynamic responses of bridges compared to far-field records. However, the effect of near-field strong ground motion has often been neglected in the seismic performance assessment of the bridges. Furthermore, damage to horizontally curved multi-frame RC box-girder bridges in the past earthquakes has intensified the potential of seismic vulnerability of these structures due to their distinctive dynamic behavior. Based on the nonlinear time history analyses in OpenSEES, this article, assesses the effects of near-field versus far-field earthquakes on the seismic performance of horizontally curved multi-frame RC box-girder bridges by accounting the vertical component of the earthquake records. Analytical seismic fragility curves have been derived thru considering uncertainties in the earthquake records, material and geometric properties of bridges. The findings indicate that near-field effects reasonably increase the seismic vulnerability in this bridge sub-class. The results pave the way for future regional risk assessments regarding the importance of either including or excluding near-field effects on the seismic performance of horizontally curved bridges.

Key Words
curvature radius; curved bridges; seismic fragility; near and far-field; probabilistic vulnerability; damage monitoring system

Address
Ali Naseri: Structural Engineering, Babol Noshirvani University of Technology, Iran
Alireza MirzaGoltabar Roshan: Babol Noshirvani University of Technology, Iran
Hossein Pahlavan: Earthquake Engineering, Shahrood University of Technology, Iran
Gholamreza Ghodrati Amiri: Center of Excellence for Fundamental Studies in Structural Engineering, Univ. of Science and Technology, School of Civil Engineering, Iran


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