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CONTENTS
Volume 27, Number 3, September 2024
 

Abstract
In this study, a direct Lagrangian-based three-dimensional computational procedure is developed to evaluate the seismic performance of reinforced concrete liquid-containing circular tanks (RC-LCT). In this approach, fluid-structure interaction (FSI), material nonlinearity, and liquid-structure large deformations are formulated realistically. Liquid is modeled using Mie-Grüneisen equation of state (EOS) in compressible form considering the convective and impulsive motions of fluid. The developed numerical framework is validated based on a previous study. Further, nonlinear analyses are carried out to assess the seismic performance of RC-LCT with various diameter-to-liquid height ratios ranging from 2.5 to 4.0. Based on observations, semi-deep tanks (i.e., D⁄Hl=2.5) show low collapse ductility due to their shear failure mode while shallow tanks (i.e., D⁄Hl=4.0) behave in a more ductile manner due to their dominant wall membrane action. Furthermore, the semi-deep tanks provide the least over-strength and ductility due to their catastrophic failure with little energy dissipation. This study shows that LCTs can be categorized as between immediately operational and life safety levels and therefore a drift limiting criterion is necessary to prevent probable damages during earthquakes.

Key Words
circular liquid-containing tank; direct Lagrange method; fluid-structure interaction; reinforced concrete; seismic performance assessment

Address
Erfan Shafei: Faculty of Civil Engineering, Urmia University of Technology, Urmia, Iran
Changiz Gheyratmand and Saeed Tariverdilo: Faculty of Civil Engineering, Urmia University, Urmia, Iran

Abstract
Accurately predicting the failure modes of reinforced concrete (RC) columns is essential for structural design and assessment. In this study, the challenges of imbalanced datasets and complex feature selection in machine learning (ML) methods were addressed through an optimized ML approach. By combining feature selection and oversampling techniques, the prediction of seismic failure modes in rectangular RC columns was improved. Two feature selection methods were used to identify six input parameters. To tackle class imbalance, the Borderline-SMOTE1 algorithm was employed, enhancing the learning capabilities of the models for minority classes. Eight ML algorithms were trained and fine-tuned using k-fold shuffle split cross-validation and grid search. The results showed that the artificial neural network model achieved 96.77% accuracy, while k-nearest neighbor, support vector machine, and random forest models each achieved 95.16% accuracy. The balanced dataset led to significant improvements, particularly in predicting the flexure-shear failure mode, with accuracy increasing by 6%, recall by 8%, and F1 scores by 7%. The use of the Borderline-SMOTE1 algorithm significantly improved the recognition of samples at failure mode boundaries, enhancing the classification performance of models like k-nearest neighbor and decision tree, which are highly sensitive to data distribution and decision boundaries. This method effectively addressed class imbalance and selected relevant features without requiring complex simulations like traditional methods, proving applicable for discerning failure modes in various concrete members under seismic action.

Key Words
Borderline-SMOTE oversampling algorithm; class imbalanced dataset; feature selection; reinforced concrete columns; seismic failure mode

Address
College of Civil Engineering, Nanjing Tech University, 30 South Puzhu Road, Nanjing 211816, China

Abstract
Due to the many advantages of concrete-filled double steel tube (CFDT) columns, they are highly recommended for use in heavy-load structures such as bridges, subway stations, and high-rise buildings. This study was carried out with the aim of numerically investigating and comparing the performance of CFDT columns under cyclic and seismic loads and providing innovative strengthening methods for CFDT columns. Hollow circular steel sections have been used for internal and external tubes. To make the circular CFDT columns stronger against seismic loads, stiffeners with different shapes (rectangular and Tshaped sheets) have been welded to the outside and inside tubes. The validated finite element (FE) model of the ABAQUS program is used to look into the behavior of CFDT columns numerically. Two frames of 10 and 20 floors with strengthened CFDT columns were modeled. The results showed that the use of stiffeners in the CFDT column has a significant effect on seismic performance, so that the maximum lateral load of the column is increased up to 32.74% under the effect of cyclic load. Also, the results revealed that the use of stiffeners in the columns of moderate and high-rise building frames causes a significant increase in the shear of the base and consequently the stiffness. Among the other important results that followed, it reduced the drift of floors and increased energy absorption.

Key Words
base shear load; concrete filled double steel tube column; cyclic load; energy absorption; rectangular stiffeners; seismic loads; T-shaped stiffeners

Address
Department of Civil Engineering, Faculty of Civil Engineering and Architecture, Shahid Chamran University of Ahvaz, Ahvaz, Iran

Abstract
The susceptibility of Reinforced Concrete (RC) buildings to earthquake-induced damage is a critical concern, primarily attributed to their inadequate seismic performance. The existing earthquake-resistant design code of India prescribes guidelines to minimize seismic damage but does not provide any means for evaluating the actual seismic performance and damage. To ascertain the seismic performance of the structures quantitatively, it is crucial to classify damage into measurable damage states. Damage Index (DI) acts as an important tool for this purpose. Among various procedures for computation of DI, the modified Park and Ang Damage Index appears to be highly accurate. However, the major drawback of this method is that it is lengthy and time-consuming. On the other hand, structural performances can be evaluated using various performance parameters such as interstory drift ratio (IDR), inelastic deformation, etc., as described in FEMA-356 and ASCE-41 17. The present study explores the correlation between seismic DI and structural performance in RC frame buildings designed according to IS code. Sixteen building models, incorporating diverse configurations, are examined using nonlinear static and time history analyses. A simplified equation is developed by regression analysis to predict DI based on IDR, offering a computationally efficient alternative. Validation tests are done to confirm the equation's accuracy. Furthermore, a unified damage scale integrating DI and seismic performance is also proposed for seismic damage evaluation of buildings designed by IS code.

Key Words
interstory drift; IS code method; performance levels; seismic damage index

Address
Department of Civil Engineering, National Institute of Technology Silchar, Silchar, Assam 788010, India

Abstract
The incidence angle of seismic excitation relative to the two orthogonal major axes of structures has been a subject of considerable research interest. Previous studies have primarily focused on single-storey symmetric and asymmetric structures, suggesting a minimal effect of incidence angle on structural behavior. This research extends the investigation to multi-storey structures, including vertically irregular configurations, using a comprehensive set of 20 near fault and 20 far field seismic excitation. The study employs nonlinear time-history analysis with a bidirectional hysteresis model to capture inelastic deformations accurately. Various structural models, including one-storey and two- storey regular structures (R1, R2) and vertically irregular structures with setbacks in one direction (IR1) and both directions (IR2), are analysed. The analysis reveals that the incidence angle has no discernible impact over the response of regular multi-storey structures. However, vertically irregular structures exhibit notable responses at corner columns, which decrease towards central columns, irrespective of the incidence angle. This response is attributed to the inherent mass distribution and stiffness irregularities rather than the angle of seismic excitation. The findings indicate that for both near fault and far field seismic excitation, the incidence angle's impact remains marginal even for complex structural configurations. Consequently, the study suggests that the angle of incidence of seismic excitation need not be a primary consideration in the seismic design of both regular and vertically irregular structures. These conclusions are robust across various structural models and seismic excitation characteristics, providing a comprehensive understanding the impact of incidence angle on seismic response.

Key Words
buildings; complex analytical method; dynamic analysis; earthquake/seismic analysis; seismic hazard/mitigation

Address
Md. Ghousul Ansari, Sekhar C. Dutta and Ishan Jha: Department of Civil Engineering, Indian Institute of Technology (ISM) Dhanbad, Dhanbad - 826004, India
Aakash S. Dwivedi: Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai - 400076, India

Abstract
Traditional immovable cultural assets are significant in terms of societal memory and cultural continuity. Therefore, it is essential to preserve their original qualities without alteration while also assessing their resilience under various influences. This study aims to document the Kirklareli Museum building and conduct a performance analysis for potential earthquake scenarios. To this end, surveys of the structure were conducted, on-site inspections were carried out, and ground and material properties were determined for use in the analysis. The 3D model of the structure was prepared to understand its behavior during earthquakes. The analysis results indicate that there will be no damage to the structure. However, it should be noted that damage could occur in the event of a more severe earthquake than the design earthquake specified by the regulations. This study is significant not only for encompassing the museum structure but also for providing a comprehensive evaluation by determining all material properties.

Key Words
earthquake analysis; masonry structures; museum; preservation; restoration

Address
Ercan Aksoy: Eha Construction & Architecture, Çankaya, Ankara, Turkey
Ali Ural: Department of Civil Engineering, Aksaray University, Adana Yolu Üzeri E-90 Karayolu 7. km Aksaray, Turkey

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