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CONTENTS
Volume 21, Number 3, September 2021
 


Abstract
This paper presents a mainshock-aftershock seismic fragility and collapse capacity assessment of reinforced concrete (RC) structures retrofitted with a hybrid damper composed of a steel slit plate and friction pads. Three and eight-story RC buildings are designed and assessed before and after retrofit considering the aftershocks effect. Non-linear time-history response analysis (NLTHA) using twelve natural earthquake sequences are used to produce incremental dynamic analysis (IDA) curves to obtain the median collapse capacity of the structures. Three different damage state (DS) levels are used for the mainshock ground excitation to quantify the scale factors required for conducting the aftershock IDAs. The maximum inter-story drift ratio (MIDR) is used as the main engineering demand parameter. The study shows the importance of considering the aftershock in the seismic assessment process of RC structures. The un-retrofitted structures are found to experience a high level of deterioration under aftershock event which is not considered in the design stage. The findings of the study reveal that the mainshock-aftershock sequence responses of the retrofitted structures show better performance in terms of the median collapse capacity and the seismic fragility compared to the un-retrofitted ones.

Key Words
energy dissipation devices; incremental dynamic analysis; mainshock-aftershock; seismic fragility; seismic retrofit

Address
Mohamed Noureldin: Department of Civil and Architectural Engineering, Sungkyunkwan University, 2066 Seobu-Ro, Jangan-Gu, Suwon, Gyeonggi-Do, Korea

Michael Adane: Department of Civil and Architectural Engineering, Sungkyunkwan University, 2066 Seobu-Ro, Jangan-Gu, Suwon, Gyeonggi-Do, Korea

Jinkoo Kim: Department of Civil and Architectural Engineering, Sungkyunkwan University, 2066 Seobu-Ro, Jangan-Gu, Suwon, Gyeonggi-Do, Korea

Abstract
Shear wave velocity (Vs) profile is one of the critical geotechnical measurements of soil layers for seismic hazard assessment and liquefaction potential evaluation. Enhancing the effectiveness of in-situ Vs profiling by reducing time and cost is of great interest. For that reason, this study aims at assessing Vs profile generation from a single-station three-component geophone with additional borehole log data for constraining parameter space. Based on multichannel analysis of surface waves (MASW), and microtremor array Measurements (MAM) conducted previously at seven sites located in Bukit Timah Granite, Singapore, this study utilized HVSR signals for Rayleigh wave ellipticity (ellipticity curve) inversion with additional inversion constraint using borehole log data. The resulting Vs profiles and reference Vs profiles from MASW and MAM were quantitatively compared using average Vs of 30 m (Vs30). The profiles generated from ellipticity curve inversion revealed a good agreement with Vs reference profiles. Vs30 based site classification results also indicated a good fit of two test results. Therefore, HVSR measurements for further ellipticity curve inversion, with already available borehole log data for constraint, is considered as a promising cost and time-effective site classification approach.

Key Words
ellipticity curve; HVSR; shear wave velocity; site classification; surface waves

Address
Shynggys Abdialim: Department of Civil and Environmental Engineering, School of Engineering and Digital Sciences,
Nazarbayev University, Kabanbay Batyr Ave. 53, Nur-Sultan 010000, Kazakhstan

Farkhod Hakimov: RWTH Aachen University, Neotectonics and Natural Hazards, Lochnerstrabe 4–20, 52056 Aachen, Germany

Jong Kim: Department of Civil and Environmental Engineering, School of Engineering and Digital Sciences,
Nazarbayev University, Kabanbay Batyr Ave. 53, Nur-Sultan 010000, Kazakhstan

Taeseo Ku: Department of Civil and Environmental Engineering, National University of Singapore, 1 Engineering Drive 2, Singapore, 117576

Sung-Woo Moon: Department of Civil and Environmental Engineering, School of Engineering and Digital Sciences,
Nazarbayev University, Kabanbay Batyr Ave. 53, Nur-Sultan 010000, Kazakhstan


Abstract
The seismic performance of a steel frame base-isolated structure with steel spiral spring limiters is experimentally investigated under near-fault ground motions. A series of shake table simulator tests are carried out to analyze the dynamic response of isolation layer and superstructure. The test setup consists of a one-eighth scale five-story steel frame with steel spiral spring limiters that are designed and modeled in different parameters and stiffness, as well as various reserved gap sizes between the testing structure and limiters. The main output parameters are the maximum deformation at the isolation level, the maximum vertical force of isolation bearings, and inter-story drift. The results further reveal the seismic impact on the isolation layer and superstructure dynamic response caused by the limiter stiffness and reserved gap size.

Key Words
base isolation; base limiter; near-fault ground motions; shake table tests; vibration mode

Address
Miao Han: Beijing Advanced Innovation Center for Future Urban Design, Beijing University of Civil Engineering and Architecture, Beijing, China

Yuandong Wang: The Dennis Group, Salt Lake City, U.S.A.

Hongkai Du: Beijing Advanced Innovation Center for Future Urban Design, Beijing University of Civil Engineering and Architecture, Beijing, China/ Department of Civil and Environmental Engineering, University of Utah, Salt Lake City, U.S.A.

Xiangyang Chu: Beijing Advanced Innovation Center for Future Urban Design, Beijing University of Civil Engineering and Architecture, Beijing, China

Mingzhu Cui: Hefei University of Technology, Anhui, China

Lingshuai Meng: China State Decoration Group Co. Ltd., Beijing, China



Abstract
Dams are constructed across the river to confine the water and utilize it for various purposes such as hydroelectricity generation, flood control, irrigation, etc. Failure of dams causes huge loss to property and lives. Dams, designed to be built in high seismicity areas, are prone to damage due to intensive earthquake events. Strong ground motions recorded in the vicinity of fault planes are generally considered as near fault (or near source) ground motions. Near fault ground motions possess considerably different features which have high damage potential. In last few decades, a lot of studies have been conducted on the identification, characterization and simulation of pulse-type and non pulse-type ground motions. However, researchers have paid attention to the seismic safety assessment of dams under near fault and far fault ground motions since the last decade. In this context, this present study reports a state-of-the-art review on the seismic behaviour of various types of dams under different ground motions, based on available literature. This study also describes existing modelling techniques of the dam-reservoir-foundation system, failure modes, seismic analysis method and seismic response of different kinds of dams to near fault and far fault earthquakes. Finally, the study attempts to find the research gaps, which should be given proper attention in the future.

Key Words
dam-reservoir-foundation system; dams; dynamic behaviour; far fault ground motions; near fault ground motions; seismic safety assessment

Address
Soumya Gorai: Department of Civil Engineering, Indian Institute of Technology Kharagpur, West Bengal, India

Damodar Maity: Department of Civil Engineering, Indian Institute of Technology Kharagpur, West Bengal, India


Abstract
The Combined pile raft foundation (CPRF) is considered to be an efficient type for tall buildings since it accounts for raft contribution to both vertical and lateral loads. Traditionally, in a pile raft foundation, the contribution of raft to resist loads is ignored due to the fact that its analysis requires complicated soil-structure interaction. Hence this simplification may lead to an uneconomical design. While research on vertical resistance of raft in CPRF is considerable, research on its horizontal resistance is yet very limited. To address this issue, in this research the contribution of the components of pile-raft foundation to lateral loads is evaluated experimentally. Ten small scale combined piled raft models were fabricated and instrumented with load cells at pile top to find raft contribution in resisting vertical and lateral load. Load cells were composed of strain gauge rosettes in Wheatstone bridge arrangements. The vertical static load of 5350 N was applied through steel plates and the lateral incremental load of 1500 N was applied using the hydraulic machine. The number of piles was varied from 1 to 25 with s/d ratio of 6.67 and 3.44. The results show that raft in a piled raft system is contributing in resisting 10-60% of the applied lateral load which is highly dependent on the number of piles. The percentage contribution of the raft to the lateral load decreases with the increase in the number of piles. Furthermore, it was also shown that in case of piled raft, the rear piles are resisting more lateral load than the front piles depending on the vertical load level.

Key Words
contribution; lateral response; piled raft foundation; piles; raft

Address
Irfan Jamil: Department of Civil Engineering, University of Engineering & Technology, Peshawar, Pakistan

Irshad Ahmad: Department of Civil Engineering, University of Engineering & Technology, Peshawar, Pakistan

Wali Ullah: Department of Civil Engineering, University of Engineering & Technology, Peshawar, Pakistan

Abstract
Precast reinforced concrete (RC) frames have been rapidly developed in structural engineering due to their various advantages, such as high efficiency and low environmental pollution. However, the construction quality of precast RC frames is difficult to guarantee, and the interface of new and old concrete and the bond-slip effects of additional steel bars may lead to different performance levels of precast RC frames. Therefore, it is necessary and important to investigate and assess the seismic performance of precast RC frames that adopt the conformation of Chinese code. In this paper, a numerical simulation method for precast RC frames is developed based on OpenSEES software, in which the Joint2D element is used to simulate the beam-to-column connections to consider the shear and bond-slip effects. Two prototype structures of precast RC frames are designed, and the nonlinear time history analysis is performed to explore the seismic performance of the precast RC frames according to the Chinese code. Meanwhile, the incremental dynamic analysis and fragility analysis are conducted to study the differences in seismic performance and collapse resistance between precast RC frames and cast-in-situ RC frames.

Key Words
bond-slip effects; fragility analysis; incremental dynamic analysis; Joint2D; nonlinear dynamic analysis; OpenSEES; precast RC frames

Address
Zhun Wang: Key Laboratory of Concrete and Prestressed Concrete Structures of the Ministry of Education, National and Local Joint Engineering Research Center for Intelligent Construction and Maintenance, Nanjing 210096, P.R. China

De-Cheng Feng: Key Laboratory of Concrete and Prestressed Concrete Structures of the Ministry of Education, National and Local Joint Engineering Research Center for Intelligent Construction and Maintenance, Nanjing 210096, P.R. China

Xuyang Cao: Key Laboratory of Concrete and Prestressed Concrete Structures of the Ministry of Education, National and Local Joint Engineering Research Center for Intelligent Construction and Maintenance, Nanjing 210096, P.R. China

Gang Wu: Key Laboratory of Concrete and Prestressed Concrete Structures of the Ministry of Education, National and Local Joint Engineering Research Center for Intelligent Construction and Maintenance, Nanjing 210096, P.R. China

Abstract
The friction and viscous damping actions always cause nonlinear responses of a seismic isolation system under earthquakes. Their influence on the seismic responses needs investigation in detail. In order to analyze the effects of nonlinear phenomenon on the seismic isolation system, a mathematical model was built for such a nonlinear isolation system, and the nonlinear responses were calculated and analyzed. The numerical results indicate that an appropriate combination of spring, Coulomb friction and viscous damper is able to achieve an optimal seismic performance. The stiffness and natural period of system are significantly influenced by the friction action. Both the friction action and the viscous damping action can dissipate earthquake energy, and the optimal value of one depends on the value of the other in the seismic isolation system. All of the values of spring, Coulomb friction and viscous damper should be accurately evaluated before the design of seismic isolation system.

Key Words
coulomb friction; mathematical model; seismic isolation; spring; viscous damper

Address
Shanshan Li: School of Civil Engineering, Central South University, Changsha 410075, China/ National Engineering Laboratory for High Speed Railway Construction, Changsha 410004, China

Ping Xiang: School of Civil Engineering, Central South University, Changsha 410075, China/ National Engineering Laboratory for High Speed Railway Construction, Changsha 410004, China

Biao Wei: School of Civil Engineering, Central South University, Changsha 410075, China/ National Engineering Laboratory for High Speed Railway Construction, Changsha 410004, China

Hao Tan: School of Civil Engineering, Central South University, Changsha 410075, China/ National Engineering Laboratory for High Speed Railway Construction, Changsha 410004, China

Yunji Fu: School of Civil Engineering, Central South University, Changsha 410075, China/ National Engineering Laboratory for High Speed Railway Construction, Changsha 410004, China

Abstract
Reinforced Concrete (RC) structural wall is widely used in the lateral force resisting system for multistoried RC frame buildings located in earthquake-prone regions. In such buildings, the wall is connected to the RC slab at every floor level. The junction region of shear wall and floor slab constitutes an important link in the load path from slab to wall during earthquake shaking, thereby influencing the pattern of lateral load distribution in the shear wall. In case of multistoried building, the maximum elastic drift is estimated by carrying out linear static analysis for different load combinations as recommended by the Indian Earthquake Code IS 1893 (Part 1): 2016. However, during strong earthquake shaking, the inelastic lateral drift needs to be monitored to avoid undesirable levels of damage in structural members. The inelastic drift level of an isolated slender shear wall considering the behaviour of wall-slab junction has not been studied in the past. The present study aims to investigate the possible lateral drift limit of RC wall frame building considering the effect of floor slabs.

Key Words
drift criteria; seismic analysis; wall-frame building; wall-slab junction

Address
Snehal Kaushik: Department of Civil Engineering, Girijananda Chowdhury Institute of Management and Technology, Guwahati, 781017, India

Kaustubh Dasgupta: Department of Civil Engineering, Indian Institute of Technology Guwahati, Guwahati, 781039, India


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