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CONTENTS
Volume 27, Number 5, November 2024
 

Abstract
Seismic performance evaluation of precast building frames is of great importance because precast buildings have failed during earthquakes in the past. The present work evaluates the seismic performance of a 10-story precast building frame using pushover analysis (POA). Three types of precast connections are incorporated in the study, and the corresponding monolithic connections in the frame are utilized to evaluate the relative performances of the precast frames. A pushover analysis is performed for frames with each type of connection, and three performance points (PP) are identified: one in the elastic range, the second in the elastoplastic range, and the third in the near collapse state. The PP is obtained using the average response spectrum of an ensemble of seven earthquake records belonging to three types of earthquakes: a far field, a near field with a directivity effect, and a near field with a fling step effect. At the PP, responses obtained from POA are compared with the average responses of the nonlinear time history analysis (NLTHA). The response quantities of interest include maximum base shear, maximum top displacement, and maximum inter-story drift ratio (MIDR). Additionally, performance evaluation includes the study of the characteristics of the fragility curves corresponding to four defined damage states similar to those defined by HAZUS for nonlinear static analysis. The fragility curves are developed based on peak ground acceleration (PGA). The results of the study indicate that depending on the performance points, a maximum of 30% difference in responses between POA and NLTHA is observed. Furthermore, the nature of the fragility curves of the precast and monolithic frame could be different in the higher damage state; however, the same may not be significant for the lower damage state.

Key Words
CSM; fragility curves; precast building frames; pushover analysis; seismic performance evaluation

Address
National Center for Disaster Mitigation and Management, Malaviya National Institute of Technology, Jaipur 302017, India

Abstract
Earthquake soil-structure interaction (ESSI) is the dynamic interaction between seismic waves, soil layers underlying structures, and the structures themselves during earthquakes, which affects the structures' response. This relationship impacts foundation behaviour, soil amplification, energy dissipation, nonlinear effects, resonance phenomena, and earthquake design considerations. Comprehending ESSI is crucial for evaluating structural performance, creating resilient structures and executing efficient seismic retrofitting procedures in earthquake-prone areas. Present seismic standards do not account for interbuilding dynamic interactions through the soil, and hence the associated seismic risk is ignored. However, due to recent population growth in cities and rising land costs, there has been a rise in city building surface density, resulting in buildings being more closely spaced. The seismic analysis of a city with high building surface density is very complex due to detailed requirement material and geometrical properties of historical as well as present structures. The construction of new building adjacent to preexisting building can either reduce or increase its structural response. This phenomenon of dynamic interaction between existing and newly built buildings is known as dynamic cross interaction (DCI) whereas site-city interactions (SCI) describe the effects of a group of structures on the overall seismic response of the site or city. This study covers the entire literature review of the pioneer findings in the field of ESSI considering different types of structures, mitigation techniques, ESSI modelling techniques, comparison between experimental and numerical techniques for earthquake analysis and latest concepts related to ESSI, DCI and SCI further the research gaps and future scope is also discussed.

Key Words
DCI; ESSI; machine learning; multi-hazard approaches; performance-based design; probabilistic methods; SCI

Address
Department of Civil Engineering, Maulana Azad National Institute of Technology, Bhopal, India

Abstract
Highway bridges usually extend over long distances and are vulnerable to the variation of ground motions. In this paper, a 5-link continuous bridge with a total length of 510 m was selected for seismic vulnerability analyses under consistent and multi-support excitations. Fragility curves for piers and bearings considering both the non-isolated and isolated conditions are generated through incremental dynamic analysis (IDA). The results show that for the non-isolated condition with elastomeric bearings (EBs), the junction piers between adjacent links are more vulnerable than interior piers within links under consistent excitation, whereas it is exactly the opposite for the bearings. Under the multi-support excitation, the fragility of the bearings at junction piers significantly increases due to the unsynchronized movement of adjacent links. For the isolated condition with lead-core rubber bearings (LRBs) and friction pendulum bearings (FPBs), the fragility of piers is effectively reduced compared to EBs, especially for FPBs and under multi-support excitation. The fragility of LRBs is lower than that of EBs under both excitation modes. The fragility of FPBs is apparently higher than that of the piers, controlling the vulnerability of the bridge. This study provides a reference for the seismic design of highway bridges.

Key Words
highway bridges; isolation bearings; multilink continuous bridges; seismic vulnerability analysis; spatially varying ground motions

Address
Yu Zhang: 1) School of Civil Engineering, Shandong University, 17923 Jingshi Rd., Jinan 250061, China, 2) State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, 2 Linggong Rd., Dalian 116024, China
Ruipeng Guo: Shandong Hi-speed Engineering Construction Group Co., Ltd., 14677 Jingshi Rd., Jinan 250014, China
Chen Liu, Li Tian and Chao Li: School of Civil Engineering, Shandong University, 17923 Jingshi Rd., Jinan 250061, China
Hanlin Dong: College of Civil Engineering, Shanghai Normal University, 100 Haisi Rd., Shanghai 201418, China

Abstract
This study presents a method for optimization of weighting matrices of the linear quadratic regulator (LQR) control algorithm in order to design an optimal active control system using metaheuristic algorithms. The LQR is a widely used control technique in engineering for designing optimal controllers for linear systems by minimizing a quadratic cost function. However, the performance of the LQR strongly depends on the appropriate selection of weighting matrices, which are usually determined by some thumb rule or exhaustive search method. In the present study, for the optimization of weighting matrices, four metaheuristic algorithms including, Particle Swarm Optimization (PSO), Genetic Algorithm (GA), Grey Wolf Optimizer (GWO) and, Whale Optimization Algorithm (WOA) are considered. To generate optimal weighting matrices, the objective function used consists of displacement and absolute acceleration. During the optimization process, a response effectiveness factor is also checked for displacement and acceleration as a constraint for the proper selection of weighting matrices. To study the effectiveness of optimized active control system to those for the exhaustive search method, the various controlled responses of the system are compared with the corresponding uncontrolled system. The optimized weighting matrices effectively reduce the displacement, velocity, and acceleration responses of the structure. Based on the simulation study, it can be observed that GWO performs well compared to the PSO, GA, and WO algorithms. By employing metaheuristic algorithms, this study showcases a more efficient and effective approach to finding optimal weighting matrices, thereby enhancing the performance of active control systems.

Key Words
active control system; genetic algorithm; grey wolf optimization; linear quadratic regulator; metaheuristic algorithms; optimization; particle swarm optimization; whale optimization algorithm

Address
Department of Civil Engineering, SVNIT Surat, India

Abstract
The safety and stability of bridges are critical to traffic safety. However, post-earthquake ground motion records often contain noise, which undermines the accuracy of seismic response analysis in bridge structures. To tackle this issue, we introduce a method that optimizes Variational Mode Decomposition (VMD) parameters using the Sparrow Search Algorithm (SSA) and combines it with Wavelet Thresholding (WT) to eliminate noise from strong motion signals. SSA is employed to identify the optimal VMD parameters [K, a], followed by the selection of effective modes based on the Variance Contribution Rate (VCR). These modes are then subjected to WT noise reduction, resulting in a high-quality reconstructed strong motion record. The method was validated using both simulated signals and ground motion records. In simulations, it demonstrated a 31.35% reduction in Root Mean Square Error (RMSE), a 31.6% decrease in the Smoothness Indicator (R), and a 1.17% improvement in the Correlation Coefficient (CC), compared to other methods. For ground motion records, it more accurately preserved seismic features than traditional wavelet denoising. When applied to the seismic response analysis of the Dahejia Bridge during the Jishishan earthquake, the denoised ground motion records obtained by this method produced force predictions on pier bearings that closely matched the field-observed damage, outperforming predictions based on traditional wavelet denoising. These findings confirm the accuracy and practicality of the proposed method.

Key Words
ground motion records; Jishishan earthquake; seismic response of bridge; sparrow search algorithm; variational mode decomposition

Address
Qin Xu, Shihu Zhou and Liqun Bao: LanZhou Institute of Technology, Lanzhou, Gansu, 730050, China
Haitao Min: Linxia Highway Development Center, Linxia, Gansu, 731100, China
Zhangrong Pan: Gansu Earthquake Agency, Lanzhou, Gansu, 730000, China

Abstract
In this study, shaking table tests were conducted to assess and analyze the seismic performance of the molded transformers used in actual hydropower plants. The test method was executed by adjusting the acceleration magnitude through the generation of artificial earthquakes that comply with the seismic performance criteria outlined in the ICC-ES AC 156 procedure. Additionally, a performance assessment for earthquakes with a magnitude of 5.0 or greater, recorded domestically in recent times, was concurrently conducted to analyze the dynamic behavioral characteristics. The test results indicated that there was no functional damage to the test specimen in all shaking table test procedures. However, structural damage began to be visually confirmed through a visual inspection when the artificial seismic intensity exceeded 100%, and at 150%, cumulative deformation was measured at the lower part. This is attributed to the nonlinear behavior caused by the structural characteristics of the heavy upper structure, its high centre of gravity, and the relatively small load and high flexibility of the lower frame. The excessive relative displacement between the upper and lower parts resulting from this phenomenon is anticipated to lead to potential damage, such as collisions with surrounding equipment or impact on adjacent facilities.

Key Words
analytical verification; earthquakes; molded transformer; seismic performance evaluation; shaking table tests

Address
Sang-Moon Lee: Institute for Smart Infrastructure, Gangneung-Wonju National University, 7 Jukheon-gil, Gangneung-si, Gangwon-Do, Republic of Korea
Bub-Gyu Jeon: Seismic Research and Test Center, Pusan National University, 49, Busandaehak-ro, Mulgeum-eup, Yangsan-si, Gyeongsangnam-do, Republic of Korea
Woo-Young Jung: Department of Civil and Environmental Engineering, Gangneung-Wonju National University, 7 Jukheon-gil, Gangneung-si, Gangwon-Do, Republic of Korea

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