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CONTENTS
Volume 16, Number 6, June 2019
 

Abstract
This paper investigates the seismic response of a typical non-navigable continuous girder bridge isolated with friction sliding bearings of the Hong Kong-Zhuhai-Macao link projects in China. The effectiveness of the friction pendulum system (FPS) and accuracy of the numerical model were evaluated by a 1/20 scaled bridge model using shaking table tests. Based on the hysteretic properties of friction pendulum system (FPS), double concave friction pendulum (DCFP), and triple friction pendulum system (TFPS), seismic response analyses of isolated bridges with the three sliding-type bearings are systematically carried out considering soil-pile interaction under offshore soft clay conditions. The fast nonlinear analysis (FNA) method and response spectrum are employed to investigate the seismic response of isolated offshore bridge structures. The numerical results show that the implementation of the three sliding-type bearings effectively reduce the base shear and bending moment of the reinforced concrete pier, at the cost of increasing the absolute displacement of the bridge superstructure. Furthermore, the TFPS and DCFP bearings show better isolation effect than FPS bearing for the example continuous girder bridge.

Key Words
friction sliding bearing; offshore bridge; seismic response; hysteretic model; isolation effect

Address
Baofu Wang: Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education, Beijing University of Technology, Beijing, China; Department of Civil Engineering, North China Institute of Science and Technology, Hebei, China
Qiang Han and Junfeng Jia: Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education, Beijing University of Technology, Beijing, China

Abstract
Behavior factor of a structure plays a crucial role in designing and predicting the inelastic responses of it. Recently, irregular buildings have been interested in many designers. To design irregular structures, recognizing the inelastic behavior of them is necessary. The main objective of this study is to determine the behavior factor of irregular Reinforced Concrete Moment Resisting Frames (RCMRFs) via nonlinear Incremental Dynamic Analysis (IDA). To do so, first, several frames are designed according to the regulations of the Iranian national building code. Then the nonlinear incremental dynamic analysis is performed on these structures and the behavior factors are achieved. The acquired results are compared with those obtained using pushover analysis and it is shown that the behavior factors acquired from the nonlinear incremental dynamic analysis are somewhat larger than those obtained from pushover analysis. Eventually, two practical relations are proposed to predict the behavior factor of irregular RCMRFs. Since these relations are based on the simple characteristics of frames such as: irregularity indices, the height and fundamental period, the behavior factor of irregular RCMRFs can be achieved efficiently using these relations. The proposed relations are applied to design of four new irregular RCMRFs and the outcomes confirm the accuracy of the aforementioned relations.

Key Words
behavior factor; irregular frames; incremental dynamic analysis; pushover analysis; reinforce concrete

Address
Alireza Habibi: Department of Civil Engineering, Shahed University, Tehran, Iran
Reza Gholami: Department of Civil Engineering, Kurdistan University, Sanandaj, Iran
Mehdi Izadpanah: Department of Civil Engineering, Kermanshah University of Technology, Kermanshah, Iran

Abstract
This study utilizes large-scale shake table test to investigate the seismic performance of an isolated bridge with lead rubber bearings crossing an active fault. Two transverse restraining systems with and without shear keys are tested by applying spatially varying ground motions. It is shown that the near-fault span exhibits larger bearing displacement than the crossing-fault span. Bridge piers away from the fault rupture are more vulnerable than those adjacent to the fault rupture by attracting more seismic demand. It is also verified that the shear keys are effective in restraining the bearing displacement on the near-fault span, particularly under the large permanent ground displacement.

Key Words
isolated simply supported bridge; fault rupture; shear keys; seismic performance; shake table testing; spatially varying ground motions

Address
Nailiang Xiang: State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, 1239 Siping Rd, Shanghai 200092, China; Department of Civil Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan
Huaiyu Yang: China Railway 15 Bureau Group CO, LTD, Shanghai 200070, China
Jianzhong Li: State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, 1239 Siping Rd, Shanghai 200092, China

Abstract
This paper presents machine learning methods using Support Vector Machine (SVM) and Multilayer Perceptron (MLP) to analyze optimal damper distribution for structural vibration control. Regarding different building structures, a genetic algorithm based optimization method is used to determine optimal damper distributions that are further used as training samples. The structural features, the objective function, the number of dampers, etc. are used as input features, and the distribution of dampers is taken as an output result. In the case of a few number of damper distributions, multi-class prediction can be performed using SVM and MLP respectively. Moreover, MLP can be used for regression prediction in the case where the distribution scheme is uncountable. After suitable post-processing, good results can be obtained. Numerical results show that the proposed method can obtain the optimized damper distributions for different structures under different objective functions, which achieves better control effect than the traditional uniform distribution and greatly improves the optimization efficiency.

Key Words
damper distribution; optimization; support vector machine; multilayer perceptron; genetic algorithm; machine learning

Address
Luyu Li and Xuemeng Zhao: School of Civil Engineering, State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, Liaoning 116024, China

Abstract
This study simulates the responses of large-scale bridge piers under pseudo-dynamic tests to investigate the performance of four types of numerical models that consider the nonlinear behavior of the pier and the rocking behavior of the footing. In the models, beam-column elements with plastic hinges are used for the pier, two types of foundation models (rotational spring and distributed spring models) are adopted for the footing behavior, and two types of viscous damping models (Rayleigh and dashpot models) are applied for energy dissipation. Results show that the nonlinear pier model combined with the distributed spring-dashpot foundation model can reasonably capture the behavior of the piers in the tests. Although the commonly used rotational spring foundation model adopts a nonlinear moment-rotation property that reflects the effect of footing uplift, it cannot suitably simulate the hysteretic moment-rotation response of the footing in the dynamic analysis once the footing uplifts. In addition, the piers are susceptible to cracking damage under strong seismic loading and the induced plastic response can provide contribution to earthquake energy dissipation.

Key Words
damping; plastic hinges; rocking; seismic design; spread footings; Winker models

Address
Jiunn-Shyang Chiou, Yi-Wun Jheng: Department of Civil Engineering, National Taiwan University, No. 1, Section 4, Roosevelt Rd., Taipei, Taiwan 10617, Republic of China
Hsiao-Hui Hung: National Center for Research on Earthquake Engineering, 200, Section 3, Xinhai Rd., Taipei, Taiwan 10668, Republic of China

Abstract
Seismic assessment of underground structures is one of the challenging problems in engineering design. This is because there are usually many sources of uncertainties in rocks and probable earthquake characteristics. Therefore, for decreasing of the uncertainties, seismic response of underground structures should be evaluated by sufficient number of earthquake records which is scarcely possible in common seismic assessment of underground structures. In the present study, a practical risk-based approach was performed for seismic risk assessment of an unsupported tunnel. For this purpose, Incremental Dynamic Analysis (IDA) was used to evaluate the seismic response of a tunnel in south-west railway of Iran and different analyses were conducted using 15 real records of earthquakes which were chosen from the PEER ground motion database. All of the selected records were scaled to different intensity levels (PGA=0.1-1.7 g) and applied to the numerical models. Based on the numerical modeling results, seismic fragility curves of the tunnel under study were derived from the IDAcurves. In the next, seismic risk curve of the tunnel were determined by convolving the hazard and fragility curves. On the basis of the tunnel fragility curves, an earthquake with PGA equal to 0.35 g may lead to severe damage or collapse of the tunnel with only 3% probability and the probability of moderate damage to the tunnel is 12%.

Key Words
seismic response; fragility curve; incremental dynamic analysis; underground structures

Address
Arsham Moayedifar, Hamid Reza Nejati, Kamran Goshtasbi: Rock Mechanics Division, School of Engineering, Tarbiat Modares University, Tehran, Iran
Mohammad Khosrotash: Donya Tunnel Saze Consulting Engineering Company, Tehran, Iran

Abstract
Several municipal seismic vulnerability investigations have been identified pounding of adjacent structures as one of the main hazards due to the constrained separation distance between adjacent buildings. Consequently, an assessment of the seismic pounding risk of buildings is superficial in future adjustment of design code provisions for buildings. The seismic lateral oscillation of adjacent buildings with eccentric alignment is partly restrained, and therefore a torsional response demand is induced in the building under earthquake excitation due to eccentric pounding. In this paper, the influence of the eccentric seismic pounding on the design demands for adjacent symmetric buildings with eccentric alignment is presented. A mathematical simulation is formulated to evaluate the eccentric pounding effects on the seismic design demands of adjacent buildings, where the seismic response analysis of adjacent buildings in series during collisions is investigated for various design parameters that include number of stories; in-plan alignment configurations, and then compared with that for no-pounding case. According to the herein outcomes, the effects of seismic pounding severity is mainly depending on characteristics of vibrations of the adjacent buildings and on the characteristics of input ground motions as well. The position of the building wherever exterior or interior alignment also, influences the seismic pounding severity as the effect of exposed direction from one or two sides. The response of acceleration and the shear force demands appear to be greater in case of adjacent buildings as seismic pounding at different levels of stories, than that in case of no-pounding buildings. The results confirm that torsional oscillations due to eccentric pounding play a significant role in the overall pounding-involved response of symmetric buildings under earthquake excitation due to horizontal eccentric alignment.

Key Words
eccentric pounding; adjacent buildings; time history analysis; horizontal eccentric alignment; design demands; earthquake characteristics

Address
Shehata E. Abdel Raheem: Civil Engineering Department, College of Engineering, Taibah University, Madinah 41411, KSA; Civil Engineering Department, Faculty of Engineering, Assiut University, Assiut 71516, Egypt
Mohamed Y.M. Fooly: Civil Engineering Department, Faculty of Engineering, Assiut University, Assiut 71516, Egypt
Mohamed Omar: Civil Engineering Department, Faculty of Engineering, Aswan University, Egypt; Civil Engineering Department, Faculty of Engineering, Cairo University, Giza, Egypt
Ahmed K. Abdel Zaher: Civil Engineering Department, College of Engineering, Taibah University, Madinah 41411, KSA; Civil Engineering Department, Faculty of Engineering, Cairo University, Giza, Egypt

Abstract
A reinforced concrete water tank is a typical functional liquid storage structure and cracks are the greatest threat to the liquid storage structure. Tanks are readily cracked due to seismic activity, thereby leading to the leakage of the stored liquid and a loss of function. In order to study the effect of cracks on liquid storage tanks, self-healing and leakage tests for bending cracks and through cracks in the walls of a reinforced concrete water tank were conducted. Material performance tests were also performed. The self-healing performance of bending cracks in a lentic environment and through cracks in a lotic environment were tested, thereby the self-healing width of bending micro-cracks in the lentic environment in the short term were determined. The through cracks had the capacity for self-healing in the lotic environment was found. The leakage characteristics of the bending cracks and through cracks were tested with the actual water head on the crack. The effects on liquid leakage of the width of bending cracks, the depth of the compression zone, and the acting head were determined. The relationships between the leakage rate and time with the height of the water head were analyzed. Based on the tests, the relationships between the crack characteristics and self-healing as well as the leakage were obtained. Thereby the references for water tank structure design and grading earthquake damage were provided.

Key Words
bending crack; leakage; reinforced concrete water tank; self-healing; through crack

Address
Lin Gao, Mingzhen Wang: College of Architecture Engineering, Chongqing University of Arts and Sciences, Chongqing 402160, China
Endong Guo: Key Laboratory of Earthquake Engineering and Engineering Vibration, Institute of Engineering Mechanics,
China Earthquake Administration, Harbin 150080, China
Yazhen Sun: School of Transportation Engineering, Shenyang Jianzhu University, Shenyang 110168, China

Abstract
In this paper, a new system of seismic isolation for buildings - called suspended columns - is introduced. In this method, the building columns are placed on the hinged cradle seats instead of direct connection to the foundation. In this system, each of the columns is put on a seat hung from its surrounding area by a number of cables, for which cavities are created inside the foundation around the columns. Inside these cavities, the tensile cables are hung. Because of the flexibility of the cables, the suspended seats vibrate during an earthquake and as a result, there is less acceleration in the structure than the foundation. A Matlab code was written to analyze and investigate the response of the system against the earthquake excitations. The findings showed that if this system is used in a building, it results in a significant reduction in the acceleration applied to the structure. A shear key system was used to control the structure for service and lateral weak loads. Moreover, the effect of vertical acceleration on the seismic behavior of the system was also investigated. Effect of the earthquake characteristic period on the system performance was studied and the optimum length of the suspension cables for a variety of the period ranges was suggested. In addition, measures have been taken for long-term functioning of the system and some practical feasibility features were also discussed. Finally, the advantages and limitations of the system were discussed and compared with the other common methods of seismic isolation.

Key Words
seismic isolation; base isolation; suspended columns; passive control; cable hanger

Address
Ali Beirami Shahabi, Gholamreza Zamani Ahari: Department of Civil Engineering, Faculty of Engineering, Urmia University, Urmia, Iran
Majid Barghian: Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran

Abstract
The seismic performance of a coupled shear wall system is governed by the shear resistances of its coupling beams. The plate-reinforced composite (PRC) coupling beam is a newly developed form of coupling beam that exhibits high deformation and energy dissipation capacities. In this study, the shear capacity of plate-reinforced composite coupling beams was investigated. The shear strengths of PRC coupling beams with low span-to-depth ratios were calculated using a softened strut-and-tie model. In addition, a shear mechanical model and calculating method were established in combination with a multistrip model. Furthermore, a simplified formula was proposed to calculate the shear strengths of PRC coupling beams with low span-to-depth ratios. An analytical model was proposed based on the force mechanism of the composite coupling beam and was proven to exhibit adequate accuracy when compared with the available test results. The comparative results indicated that the new shear model exhibited more reasonable assessment accuracy and higher reliability. This method included a definite mechanical model and reasonably reflected the failure mechanisms of PRC coupling beams with low span-to-depth ratios not exceeding 2.5.

Key Words
shear strength; plate-reinforced composite coupling beam; low span-to-depth ratio; softened strut-and-tie model; softened effects

Address
Jianbo Tian, Shen Li, Zheng Jian, Yunhe Liu: School of Civil Engineering and Architecture, Xi\'an University of Technology, No. 5,Jinhua Road, Xi\'an, Shaanxi, China;
State Key Laboratory Base of Eco-hydraulic Engineering in Arid Area, Xi\'an University of Technology, No. 5,Jinhua Road, Xi\'an, Shaanxi, China
Dandan Shen, Wengeng Ren: School of Civil Engineering and Architecture, Xi\'an University of Technology, No. 5,Jinhua Road, Xi\'an, Shaanxi, China


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