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CONTENTS
Volume 15, Number 1, July 2018
 

Abstract
A new site classification system and site coefficients based on local site conditions in Korea were developed and implemented as a part of minimum design load requirements for general seismic design. The new site classification system adopted bedrock depth and average shear wave velocity of soil above the bedrock as parameters for site classification. These code provisions were passed through a public hearing process before it was enacted. The public hearing process recommended to modify the naming of site classes and adjust the amplification factors so that the level of short-period amplification is suitable for economical seismic design. In this paper, the new code provisions were assessed using dynamic centrifuge tests and by comparing the design response spectra (DRS) with records from 2016 Gyeongju earthquake, the largest earthquake in history of instrumental seismic observation in Korea. The dynamic centrifuge tests were performed to simulate the representative Korean site conditions, such as shallow depth to bedrock and short-period amplification characteristics, and the results corroborated with the new DRS. The Gyeongju earthquake records also showed good agreement with the DRS. In summary, the new code provisions are reliable for representing the site amplification characteristic of shallow bedrock condition in Korea.

Key Words
site classification system; design response spectrum; dynamic centrifuge test; 2016 Gyeongju earthquake

Address
Dong-Soo Kim: Department of Civil and Environmental Engineering, Korean Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
Satish Manandhar: Renewable Energy Group, Korea Electric Power Corporation Research Institute, 105 Munji-ro, Yuseong-gu, Daejeon 34056, Republic of Korea
Hyung-Ik Cho: Earthquake Research Center, Korea Institute of Geoscience and Mineral Resources 124 Gwahak-ro, Yuseong-gu, Daejeon 34132, Republic of Korea

Abstract
This paper provides recommendations for setting performance requirements for the seismic design of building structures in Hong Kong. Fundamental issues relating to the required level of structural safety will be addressed, which is then followed with a recommended seismic action model for structural design purposes in Hong Kong. The choice of suitable performance criteria of structures and the return period of the design seismic actions are first discussed. The development of the seismic hazard model for Hong Kong is then reviewed. The determination of the design response spectrum and the choice of design parameters for structures of different importance classes will also be presented.

Key Words
seismic design; building structures; performance requirements; response spectrum; return period

Address
Hing-Ho Tsang: Department of Civil & Construction Engineering, Swinburne University of Technology, Melbourne, VIC 3122, Australia (formerly with The University of Hong Kong)


Abstract
On 12 September 2016, ML 5.1 (foreshock) and ML 5.8 (mainshock) earthquakes occurred about 48 minutes apart in the historic city of Gyeongju. Among the numerous aftershocks within the Yangsan Fault System, the largest aftershock of ML 4.5 occurred on 19 September 2016. In particular, the ML 5.8 earthquake with the focal depth of 13 km is the largest seismic event observed in South Korea since instrumental earthquake monitoring began in 1978. Up to now (January 2018), more than 600 aftershocks (> ML 1.5) have followed. The focal mechanism showed a right-lateral strike-slip fault plane with a strike of 26o (or 118o), a dip of 68o (or 85o), a rake of 175o (22o), and the moment magnitude (MW) was deduced into MW 5.5. The strikes of major events match the trend of the distribution of aftershock epicenters with depths ranging 11 to 16 km. According to the on-site survey, the fault-plane, which caused the Gyeongju earthquakes, did not extend to the surface. Finally, seismic site classification B and C, are primarily distributed near damaged buildings, where low-rise structures and non-structural members were damaged due to energy concentration of Gyeongju earthquakes on the high-frequency band.

Key Words
2016 Gyeongju earthquakes; engineering seismology; characteristics in hypocenters; geological and geophysical survey; seismic site effect

Address
Chang-Guk Sun, Hyung-Ik Cho and Han-Saem Kim: Earthquake Research Center, Korea Institute of Geoscience and Mineral Resources, 124 Gwahak-ro, Yuseong-gu, Daejeon, 34132, Republic of Korea


Abstract
A ground-motion prediction equation (GMPE) for the Korean Peninsula, especially for South Korea, is developed based on synthetic ground motions generated using a ground motion model derived from instrumental records from 11 recent earthquakes of ML>4.5 in Korea, including the Gyeongju earthquake of Sept. 12. 2016 (ML5.8). PSAs of one standard deviation from the developed GMPE with MW 6.5 at hypocentral distances of 15 km and 25 km are compared to the design spectrum (soil condition, SB) of the Korean Building Code 2016 (KBC), indicating that: (1) PSAs at short periods around 0.2 sec can be 1.5 times larger than the corresponding KBC PSA, and (2) SD\'s at periods longer than 2 sec do not exceed 8 cm. Although this comparison of the design spectrum with those of the GMPE developed herein intends to identify the characteristics of the scenario earthquake in a lower-seismicity region such as South Korea, it does not mean that the current design spectrum should be modified accordingly. To develop a design spectrum compatible with the Korean Peninsula, more systematic research using probabilistic seismic hazard analysis is necessary in the future.

Key Words
ground motion prediction equation; ground motion model; lower-seismicity region; Korean Peninsula

Address
Ki-Hyun Jeong and Han-Seon Lee: School of Civil, Environmental and Architectural Engineering, Korea University, Seoul 02841, Korea

Abstract
Over the last three decades, Performance-based Earthquake Engineering (PBEE) has been mainly developed for high seismicity regions. Although information is abundant for PBEE throughout the world, the application of PBEE to lower-seismicity regions, such as those where the magnitude of the maximum considered earthquake (MCE) is less than 6.5, is not always straightforward because some portions of PBEE may not be appropriate for such regions due to geological differences between high- and low-seismicity regions. This paper presents a brief review of state-of-art PBEE methodologies and introduces the seismic hazard of lower-seismicity regions, including those of the Korean Peninsula, with their unique characteristics. With this seismic hazard, representative low-rise RC MRF structures and high-rise RC wall residential structures are evaluated using PBEE. Also, the range of the forces and deformations of the representative building structures under the design earthquake (DE) and the MCE of South Korea are presented. These reviews are used to propose some ideas to improve the practice of state-of-art PBEE in lower-seismicity regions.

Key Words
performance-based earthquake engineering; lower-seismicity regions; Korean Peninsula

Address
Han-Seon Lee and Ki-Hyun Jeong: School of Civil, Environmental and Architectural Engineering, Korea University, Seoul 02841, Korea

Abstract
Malaysia and Singapore have adopted Eurocode 8 (EC8) for the seismic design of building structures. The authors studied the seismic hazard modelling of the region surrounding Malaysia and Singapore for a long time and have been key contributors to the drafting of the Malaysia National Annex (NA). The purpose of this paper is to explain the principles underlying the derivation of the elastic response spectrum model for Malaysia (Peninsular Malaysia, Sarawak and Sabah). The current EC8 NA for Singapore is primarily intended to address the distant hazards from Sumatra and is not intended to provide coverage for potential local intraplate hazards. Hence, this paper recommends a reconciled elastic response spectrum for Singapore, aiming to achieve a more robust level of safety. The topics covered include the modelling of distant interplate earthquakes generated offshore and local earthquakes in an intraplate tectonic setting, decisions on zoning, modelling of earthquake recurrences, ground motion and response spectrum. Alternative expression for response spectrum on rock, strictly based on the rigid framework of EC8 is discussed.

Key Words
Eurocode 8; seismic hazard; response spectrum; PSHA; intraplate local earthquake

Address
Daniel T.W. Looi:Department of Civil Engineering, The University of Hong Kong, Pokfulam, Hong Kong; Working Group 1, Technical Committee on Earthquake, The Institution of Engineers Malaysia
H.H. Tsang: Department of Civil and Construction Engineering, Swinburne University of Technology, Melbourne, Australia
M.C. Hee: Working Group 1, Technical Committee on Earthquake, The Institution of Engineers Malaysia
Nelson T.K. Lam: Department of Infrastructure Engineering, The University of Melbourne, Parkville, Victoria, Australia

Abstract
Most buildings feature core walls (and shear walls) that are placed eccentrically within the building to fulfil architectural requirements. Contemporary earthquake design standards require three dimensional (3D) dynamic analysis to be undertaken to analyse the imposed seismic actions on this type of buildings. A static method of analysis is always appealing to design practitioners because results from the analysis can always be evaluated independently by manual calculation techniques for quality control purposes. However, the equivalent static analysis method (also known as the lateral load method) which involves application of an equivalent static load at a certain distance from the center of mass of the buildings can generate results that contradict with results from dynamic analysis. In this paper the Generalised Force Method of analysis has been introduced for multi-storey buildings. Algebraic expressions have been derived to provide estimates for the edge displacement ratio taking into account the effects of dynamic torsional actions. The Generalised Force Method which is based on static principles has been shown to be able to make accurate estimates of torsional actions in seismic conditions. The method is illustrated by examples of two multi-storey buildings. Importantly, the black box syndrome of a 3D dynamic analysis of the building can be circumvented.

Key Words
generalised force method; static analysis method; plan irregularity; torsion

Address
Elisa Lumantarna: Department of Infrastructure Engineering, The University of Melbourne, Parkville 3030, Victoria, Australia; Bushfire and Natural Hazards Cooperative Research Centre, Melbourne Australia
Nelson Lam and John Wilson: Swinburne University of Technology, Sarawak Campus, Kuching, Sarawak, Malaysia; Bushfire and Natural Hazards Cooperative Research Centre, Melbourne Australia

Abstract
Buildings featuring a transfer structure can be commonly found in metropolitan cities situated in regions of lower seismicity. A transfer structure can be in the form of a rigid plate or an array of deep girders positioned at the podium level of the building to support the tower structure of the building. The anomalous increase in the shear force demand on the tower walls above the podium is a major cause for concern. Design guidance on how to quantify these adverse effects is not available. In this paper a simplified method for quantifying the increase in the shear force demand on the tower walls is presented. In view of the very limited ductile nature of this type of construction the analysis presented herein is based on linear elastic behaviour.

Key Words
displacement-controlled behaviour; transfer structures; transfer plate; transfer girder; tower walls

Address
Mehair Yacoubian, Nelson Lam, Elisa Lumantarna: Department of Infrastructure Engineering, The University of Melbourne, Parkville, Victoria 3010, Australia
John L. Wilson: Centre for Sustainable Infrastructure, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia


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