25-08-2017, 09:32 PM
DEVELOPMENT OF SEISMIC RETROFITTING TECHNOLOGIES FOR EXISTING FOUNDATIONS
DEVELOPMENT OF SEISMIC RETROFITTING TECHNOLOGIES FOR EXISTING FOUNDATIONS.pdf (Size: 539.11 KB / Downloads: 53)
Abstract
Seismic retrofitting and liquefaction prevention measures on an existing
bridge foundation are performed under severe execution conditions. For example, in
cities, they are done close to other structures and in narrow spaces under girders.
Model experiments, analyses and trial executions have been carried out to develop
seismic retrofitting technologies that are economical and can be used easily under
such severe conditions. As a result, the authors have developed five rational seismic
retrofitting technologies with superior execution properties under severe conditions.
Introduction
Since the Seismic Design Specifications for Highway Bridges were revised
after the Hyogo-ken Nanbu Earthquake of 1995, the need for seismic retrofitting of
existing structures has been increasing. For bridge piers, reinforcement methods
using steel plate lining and so on had been established, but it is necessary to retrofit
bridge foundations in order to improve the seismic performance of a whole bridge.
When an existing foundation is retrofitted, it is difficult to obtain sufficient working
space, because of restrictions by under-girder space and nearby structures.
Consequently, it is difficult to apply usual methods such as increasing additional
piles or ground improvement. For three years since 1999, Public Works Research
Institute has, with 13 private companies, carried out the joint research to develop
seismic retrofitting methods and liquefaction prevention measures that are not
restricted by site conditions, even when executed directly below an existing bridge.
As a result, the authors have developed five rational seismic retrofitting
technologies with superior execution properties under severe execution conditions.
This report introduces these five seismic retrofitting technologies that were
established by the joint research.
Outline of Seismic Retrofitting Technologies for Existing Foundations
Through the joint research, design and execution methods for three methods,
micropile methods, Small Pipe Drain method and SSP method, were developed as
seismic retrofitting technologies for use in places with severe execution conditions.
1 Senior Research Engineer, Foundation Engineering Team, PWRI
2 Research Engineer, Foundation Engineering Team, PWRI
3 Team Leader, Foundation Engineering Team, PWRI
The micropile methods includes High Capacity Micropile, ST Micropile and
Multi-Helix Micropile methods.
Micropile Methods
A micropile is a pile with steel pipes that has a diameter of 300 mm or less.
Figure 1 shows an image of retrofitting for an existing foundation by a micropile
method. The followings are the features of the micropile methods developed by the
joint research.
1 Because the methods are executed