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CONTENTS
Volume 26, Number 1, January 2024
 

Abstract
Isolation technology has been proven effective in reducing the seismic response of superstructures, where most of the deformation is concentrated in the isolation layer. However, in cases of earthquakes with intensities surpassing the fortification level of the area, or severe near-fault earthquakes, the isolation layer may experience excessive deformation, resulting in damage to the isolation bearings or collisions with the retaining wall or surrounding buildings. In this study, a finite element model using ABAQUS is established and compared with experimental test results to deeply investigate the influence of limit devices on the isolation layer and its response to the superstructure. The findings reveal that a larger limiter stiffness and a smaller reserved gap can achieve a more effective limiting effect. Nevertheless, a smaller reserved gap and a larger limiter stiffness may result in increased response of the superstructure. Therefore, rational selection of the reserved gap and limiter stiffness is crucial to reduce the acceleration response.

Key Words
base-isolated structure; collision mode; deformation limitation; simulation analysis

Address
School of Civil and Transportation Engineering, Beijing University of Civil Engineering and Architecture,Beijing 100044, China

Abstract
Earthquakes can lead to substantial damage to buildings, with long-period ground motion being particularly destructive. The design of high-performance building structures has become a prominent focus of research. The double-story isolated structure is a novel type of isolated structure developed from base isolated structure. To delve deeper into the building performance of double-story isolated structures, the double-story isolated structure was constructed with the upper isolated layer located in different layers, alongside a base isolated structure for comparative analysis. Nonlinear elastoplastic analyses were conducted on these structures using different ground motion inputs, including ordinary ground motion, near-field impulsive ground motion, and far-field harmonic ground motion. The results demonstrate that the double-story isolated structure can extend the structural period further than the base isolated structure under three types of ground motions. The double-story isolated structure exhibits lower base shear, inter-story displacement, base isolated layer displacement, story shear, and maximum acceleration of the top layer, compared to the base isolated structure. In addition, the double-story isolated structure generates fewer plastic hinges in the frame, causes less damage to the core tube, and experiences smaller overturning moments, demonstrating excellent resistance to overturning and a shock-absorbing effect. As the upper isolated layer is positioned higher, the compressive stress on the isolated bearings of the upper isolated layer in the double-story isolated structure gradually decreases. Moreover, the compressive stress on the isolated bearings of the base isolated layer is lower compared to that of the base isolated structure. However, the shock-absorbing capacity of the double-story isolated structure is significantly increased when the upper isolated layer is located in the middle and lower section. Notably, in regions exposed to long-period ground motion, a double-story isolated structure can experience greater seismic response and reduced shock-absorbing capacity, which may be detrimental to the structure.

Key Words
base isolated structure; double-story isolated structure; elastoplastic analysis; long-period ground motion; seismic response

Address
Liang Gao, Dewen Liu, Yuan Zhang, Yanping Zheng, Jingran Xu and Zhiang Li: College of Civil Engineering, Southwest Forestry University, Kunming 650000, China
Min Lei: College of Civil Engineering, Southwest Jiaotong University, Chengdu 610000, China

Abstract
In order to get a better understanding of seismic performance of exterior beam-column joint, reciprocating loading tests with variable loading speeds or axial forces were carried out. The main findings indicate that only few cracks exist on the surface of the joint core area, while the plastic hinge region at the beam end is seriously damaged. The damage of the specimen is more serious with the increase of the upper limit of variable axial force. The deflection ductility coefficient of specimen decreases to various degrees after the upper limit of variable axial force increases. In addition, the higher the loading speed is, the lower the deflection ductility coefficient of the specimen is. The stiffness of the specimen decreases as the upper limit of variable axial force or the loading speed increase. Compared to the influence of variable axial force, the influence of the loading speed on the stiffness degradation of the specimen is more obvious. The cumulative energy dissipation and the equivalent viscous damping coefficient of specimen decrease with the increase of loading speed. The influence of variable axial force on the energy dissipation of specimen varies under different loading speeds. Based on the truss model, the biaxial stress criterion, the Rankine criterion, the Kent-Scott-Park model, the equivalent theorem of shearing stress, the softened strut-and-tie model, the controlled slip theory and the proposed equations, a calculation method for the shear capacity is proposed with satisfactory prediction results.

Key Words
axial force; calculation method; exterior beam-column joint; loading speed; seismic performance

Address
Guoxi Fan, Wantong Xiang and Zichen Dou: College of Engineering, Ocean University of China, Qingdao, Shandong, 266404, China
Debin Wang: School of Civil Engineering, Dalian Jiaotong University, Dalian, Liaoning, 116028, China
Xiaocheng Tang: School of Civil Engineering, Jilin Jianzhu University, Changchun, Jilin, 130000, China

Abstract
The purpose of this study was to develop a system capable of restoring the seismic performance of a precast concrete (PC) connection damaged by an earthquake. The developed PC connection consists of a top-and-seat angle, posttensioning (PT) tendons, and U-shaped steel. The PC beam can be replaced by cutting the PT tendons in the event of damage. In addition, the seismic performance of the developed PC beam-column connection was evaluated experimentally. A PC beamcolumn connection specimen was fabricated, and a quasistatic cyclic loading test was conducted to a maximum drift ratio of 2.3%. Subsequently, the PC beam was replaced by a new PC beam, and the repaired PC connection was loaded to a maximum drift ratio of 5.1%. The structural performance of the repaired PC connection was then compared with that of the original PC connection. The difference in the load at the drift ratio of 2.3% between the original and the repaired PC specimens was only 0.2%. The residual drift ratio in the repaired PC specimen did not exceed 1.0% at the 2.0 % drift ratio cycles, which satisfies the life safety performance level specified in ACI 374.2R-13. When the developed PC connection system is used, structural performance can be restored by rapidly replacing the damaged elements.

Key Words
beam-column joint; precast concrete; replaceable; seismic performance

Address
Seung-Ho Choi: Department of Disaster Management and Fire Safety Engineering, University of Seoul, 163 Siripdae-ro, Dongdaemun-gu, Seoul 02504, Korea
Sang-Hoon Lee and Kang Su Kim: Department of Architectural Engineering and the Smart City Interdisciplinary Major Program, University of Seoul, 163 Siripdae-ro, Dongdaemun-gu, Seoul 02504, Korea
Jae-Hyun Kim, Inwook Heo and Hoseong Jeong: Department of Architectural Engineering, University of Seoul, 163 Siripdae-ro, Dongdaemun-gu, Seoul 02504, Korea

Abstract
This paper presents a dam-reservoir interaction model that includes, water compressibility, sloshing of surface water, and radiation damping at the far-end reservoir, to investigate the influence of concrete deterioration on seismic behavior along with seismic performance of gravity dams. Investigations on seismic performance of the dam body have been conducted using the linear time-history responses obtained under six real and 0.3 g normalized earthquake records with time durations from 10 sec to 80 sec. The deterioration of concrete is assumed to develop due to mechanical and chemical actions over the dam lifespan. Several computer programs have been developed in FORTRAN 90 and MATLAB programming languages to analyze the coupled problem considering two-dimensional (2D) plane-strain condition. According to the results obtained from this study, the dam structure shows critical responses at the later ages (75 years) that could cause disastrous consequences; the critical effects of some earthquake loads such as Chi-Chi with 36.5% damage and Loma with 56.2% damage at the later ages of the selected dam body cannot be negligible; and therefore, the deterioration of concrete along with its effects on the dam response should be considered in analysis and design.

Key Words
ageing of concrete gravity dams; dam-reservoir interaction; infinite fluid elements; Lagrangian approach; seismic performance assessment

Address
Department of Civil Engineering, Engineering Faculty, Atatürk University, 25240 Erzurum, Turkey

Abstract
To investigate the seismic performance of steel pipe-aeolian sand recycled concrete columns, this study designed and produced five specimens. Low-cycle repeated load tests were conducted while maintaining a constant axial compression ratio. The experiment aimed to examine the impact of different aeolian sand replacement rates on the seismic performance of these columns. The test results revealed that the mechanical failure modes of the steel pipe-recycled concrete column and the steel pipe-aeolian sand recycled concrete column were similar. Plastic hinges formed and developed at the column foot, and severe local buckling occurred at the bottom of the steel pipe. Interestingly, the bulging height of the damaged steel pipe was reduced for the specimen mixed with an appropriate amount of wind-deposited sand under the same lateral displacement. The hysteresis curves of all five specimens tested were relatively full, with no significant pinching phenomenon observed. Moreover, compared to steel tube-recycled concrete columns, the steel tube-aeolian sand recycled concrete columns exhibited improved seismic energy dissipation capacity and ductility. However, it was noted that as the aeolian sand replacement rate increased, the bearing capacity of the specimen increased first and then decreased. The seismic performance of the specimen was relatively optimal when the aeolian sand replacement rate was 30%. Upon analysis and comparison, the damage analysis model based on stiffness and energy consumption showed good agreement with the test results and proved suitable for evaluating the damage degree of steel pipe-wind-sand recycled concrete structures.

Key Words
aeolian sand concrete; column; recycled concrete; seismic performance; steel pipe

Address
Yaohong Wang and Kangjie Chen: 1) School of Civil Engineering, Inner Mongolia University of Technology, Hohhot 010051, China, 2) Key Laboratory of Civil Engineering Structure and Mechanics of Inner Mongolia Autonomous Region, Hohhot 010051, China
Bin Wu: Key Laboratory of Civil Engineering Structure and Mechanics of Inner Mongolia Autonomous Region, Hohhot 010051, China
Zhiqiang Li: School of Water Conservancy and Construction Engineering, Shihezi University, Shihezi, Xinjiang 832003, China
Wei Dong: Civil Engineering, Inner Mongolia University of Science and Technology College of Engineering, Baotou, Inner Mongolia 014010, China

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