Design and Assessment of Bridges in Regions of Low to Moderate Seismicity: The Hong Kong Context

Abstract

This design guide has been prepared in response to the recent adoption of Structures Design Manual for Highways and Railway 2013 (SDMHR 2013), aiming to facilitate a smooth transition to the state-of-the-art seismic design methodology as introduced by the structural Eurocodes and to encourage a holistic approach from the initial conceptual design stage for compliance with the current requirements. It compares the performance requirements and the corresponding design seismic hazard levels currently adopted by SDMHR 2013 in relation to those used by other countries and regions. It organizes the seismic bridge design specifications as prescribed in the Eurocodes BS EN 1998-1 and BS EN 1998-2 with modifications by SDMHR 2013, where relevant, in a logical manner and also provides guidance on the choice of earthquake-resisting systems, articulations and intended seismic behaviour based on the established engineering practices in other countries and regions as well as some additional findings of this project. The topics covered in each chapter are as follows: Chapter 1 introduces the background of this design guide, highlighting the major revisions of SDMHR 2013 on seismic bridge design as compared to the earlier SDMHR 3rd edition, and identifies the typical characteristics of existing bridges in Hong Kong that form the basis of this design guide. Chapter 2 presents a general introduction to the seismic design of bridges based on a comprehensive review of several major seismic bridge design codes from other countries and/or regions, including their development history, design philosophy, major compliance approaches, methods of seismic demand analysis, and representation of seismic action. Chapter 3 summarizes the seismic bridge design specifications for Hong Kong, including those for highway and railway bridges, in a sequential order of seismic design procedures followed by a flowchart. Chapter 4 provides guidance on the seismic design of new bridges at the conceptual design stage in respect of the selection of earthquake-resisting systems, articulations, configurations and intended seismic behaviour, i.e. elastic, limited-ductile or ductile behaviour, by examining the relation between the choices and the design and response of structures under seismic actions. Chapter 5 describes the preliminary compliance assessments of typical existing highway bridges (previously designed to older codes) with reference to the current requirements of SDMHR 2013 in regard to the design seismic actions and structural details. It then presents the methodologies for performance-based seismic structural assessment of bridges and the development of fragility curves of some typical classes of bridges in Hong Kong for the purpose of rating of existing bridges. Chapter 6 presents some of the latest trends of bridge engineering in respect of material, construction method and structural system, with special emphasis on the implications of these developments on seismic bridge design and retrofitting.