Y. Yang – Vehicle Bridge Interaction Dynamics with Applications to High-speed Railways

Автор: Y. Yang
Название книги: Vehicle Bridge Interaction Dynamics with applications to high-speed railways
Формат: PDF
Жанр: Железнодорожное дело
Страницы: 565
Качество: Изначально компьютерное, E-book

The commercial operation of the first high-speed (or bullet) train
in 1964 with a speed of 210 km/hr in the Japanese railways connecting
Tokyo and Osaka marked the beginning of a new era in
railway engineering. Since then, high-speed trains with speeds over
200 km/hr or higher have emerged as a competitive tool for intercity
transportation in several countries including Japan, Germany,
France, Italy, Spain, United Kingdom and Sweden. Such a trend
continues to spread in different parts of the world. While Japan
and many European countries have been working on expanding their
high-speed railway networks or improving their existing railway lines,
Asian countries, such as Korea, Taiwan and China, have reached the
stage of planning, constructing, or field-testing their high-speed railway
systems. Undoubtedly, high-speed train will become a key tool
for inter-city passenger transportation, at least in the aforementioned
countries.
Partly enhanced by the rapid expansion of high-speed railway systems,
research on the moving load problems in general, and vehicle–
bridge interactionsa in particular, has been booming in the past two
decades. Nevertheless, there is an apparent lack of a timely book
that can adequately address most of the problems encountered in
the design of high-speed railway bridges, which for the reasons stated below, are different from those encountered in traditional railway or
highway bridges. This book is intended to fill such a gap. It has been
developed as a result of the research works conducted by the authors
and their co-workers. In preparing this book, special attention was
paid to the problems that may be encountered by engineers in practice,
with clear physical meanings given for each of the phenomena
involved. It is hoped that the book in the present form can serve
as a most updated source of reference for engineers and researchers
working in high-speed railways, and possibly to those working in the
broad area of railway or bridge engineering.
One problem encountered in high-speed railways is the impact
and vibration of bridges caused by the moving trains. This problem
is substantially different from that encountered in highway bridges
for the following reasons. First, the loads induced by a moving train
on the bridge are repetitive in nature, as characterized by the sequentially
moving wheel loads, implying that certain frequencies of
excitation will be imposed on the bridge during the passage of a
train. In contrast, the loads implied by a highway traffic are random
in nature, when expressed in terms of the wheel loads and wheel
distance. Second, high-speed trains can travel at a speed much
higher than the vehicles moving on highways, making it possible
for the excitation frequencies to coincide with the vibration frequencies
of the bridge, resulting in the so-called resonance phenomenon.
Whenever the condition of resonance is reached, the bridge response
will be continuously amplified as there are more wheel loads passing
the bridge. Such a phenomenon can hardly be observed in highway
bridges. Third, the mass ratio of the vehicles to the bridge is
generally larger for railways than for highways, due to the fact that
a train consists of a number of cars in connection and the railway
bridge deck is relatively narrow, it carries no more than two tracks in
most cases. In contrast, a highway bridge deck may be so wide that
it can afford four or more lanes of running vehicles in each of the
two directions. For this reason, the interaction between the moving
vehicles and bridge appears to be much stronger for railways than
for highways. Finally, concerning the maneuverability of the train
in motion, the riding comfort or vehicle response is an issue that should be taken into account in the design of high-speed railways.
Moreover, the response of a moving vehicle is more sensitive to the
vehicle–bridge interaction (VBI) compared with that of the bridge.
However, the analysis of the dynamic behavior of a VBI system is
not straightforward as there are two subsystems, i.e., the moving
vehicles and the bridge, interacting with each other through the contact
forces existing between the wheels and rails surface, which, in
essence, is a nonlinear, coupled and time-dependent problem.
This book intends to give a broad and systematic coverage of the
vibration problems encountered in high-speed railway bridges, with
particular emphasis placed on the interaction between the moving
vehicles and supporting bridge. In general, the book is divided into
two parts, with Part I dedicated to the moving load problems and
Part II to the interaction dynamics problems. These two parts can
also be distinguished by the fact that the moving load problems (i.e.,
those treated in Part I) can generally be solved by analytical means,
for which closed form solutions are possible, while the interaction dynamics
problems (i.e., those treated in Part II) can only be solved by
numerical means, say, using the vehicle–bridge interaction elements
derived.
Starting with a general review of the related previous works
in Chapter 1, an analytical formulation was presented for simplysupported
beams subjected to a sequence of moving loads in
Chapter 2, from which the phenomena of resonance and cancellation
were identified, along with the optimal design criteria established for
bridges. The closed-form solution presented for simple beams allows
us to identify the key parameters involved. Conventionally, elastic
bearings are installed at the supports of bridge girders for isolating
the earthquake forces transmitted from the ground to the superstructure.
However, such devices may adversely result in amplification
of the response of the bridge during the passage of a train. The
problem of elastically supported beams subjected to moving loads
has received little attention in the literature, which was studied by
an analytical approach in Chapter 3. The envelope impact formulas
presented in Chapter 3 can be used as a useful aid for preliminary designs.
Moreover, the mechanism for the occurrence of resonance and cancellation was thoroughly investigated in Chapter 4, with which
the measured results obtained from the field test for two adjacent
bridges was interpreted with clear physical meanings.
The dynamic behavior of a horizontally-curved beam subjected to
a series of moving masses was formulated and studied in Chapter 5.
This problem was not well-treated before, due to the overlook of the
centrifugal forces induced by masses moving over a circular path,
which are functions of both the speed of the moving masses and
radius of the curved beam. In Chapter 5, a complete theory was
presented for the vertical and horizontal vibrations of a horizontallycurved
beam under the excitation of the gravitational and centrifugal
forces, respectively, that are induced by the moving masses. Particular
emphasis was placed on the impact effect caused by the moving
masses on the radial response of the curved beam.
One feature of the book is the derivation of a number of efficient
VBI elements by condensing the vehicle’s degrees of freedom to those
of the bridge in contact, based on the concept of dynamic condensation
in Chapter 6. These elements can be used to simulate problems
with bridges and moving vehicles of various complexities. The VBI
element presented in Chapter 6 was extended in Chapter 7 to include
the pitching motion of the moving vehicle. Using the VBI elements
derived, the dynamic properties of the vehicles and bridge, as well as
rail irregularities, can be duly taken into account, while the dynamic
response of the moving vehicle can be solved in addition to the bridge
response.
Another way to analyze the VBI dynamics is to treat the moving
vehicles and bridge as two separate systems, which interact with each
other through the contact forces. By solving for the contact forces
from the vehicles equations, one can treat them as external forces
acting on the bridge, which can then be solved using conventional
finite element procedures. Such a concept was utilized in developing
the VBI element in Chapter 8, which was then extended in Chapter 9
to include the effect of rails with profile irregularities that form part
of a railway track in the two-dimensional sense. Because of its versatility,
the VBI element derived, based on the concept of contact
forces, can be used in the simulation of various three-dimensional vehicle-rails-bridge systems considering, for instance, the crossing
of two trains on a bridge, the risk of derailment of a moving train
(Chapter 10), and the stability of trains moving over bridges simultaneously
shaken by earthquake (Chapter 11).
The authors wish to express their sincerest gratitude to their great
teacher in civil engineering and education, Dr. Chao-Chung Yu, the
former dean of the College of Engineering, National Taiwan University
(NTU) (1972–1979) and the former President of the NTU
(1981–1984), for his strong influence and continuous advice through
their careers of development, both as students and teachers. His experience
as a teacher, researcher, educationist, and in some sense as
an engineer, has always been a source of inspiration to all the young
fellows under his instruction or working with him.
A large portion of the research results presented in this book has
been sponsored through a series of research projects granted by the
National Science Council of the Republic of China on subjects related
to vehicle–bridge interactions, as well as on bridge dynamics. The
senior author has been the principal investigator of all these projects.
Without such a continuous support, it would be difficult to maintain
such a large research group at the NTU working on different aspects
of the VBI problem, ranging from the vibration of substructure and
superstructure of railway bridges to wave propagations in soils and
nearby buildings; the latter forms an independent subject that requires
further research, which was not covered in this book. Besides,
we are also grateful to the China Engineering Consultants, Inc., for
their continuous support to our research group, especially through
the 1st Structural Department previously led by Senior Vice President
Mr. Dyi-Wei Chang. Some research results presented in this
book have been made possible through such a support.
This book was prepared as part of the results of the research
group led by the senior author at the National Taiwan University.
Many of the graduate students have contributed directly or indirectly
to the success of this work, including Chia-Hung Chang, Chon-Min
Wu, Chin-Lu Lin, Bing-Houng Lin, Lin-Ching Hsu, Shyh-Rong Kuo,
Hsiao-Hui Hung, Chern-Hwa Chen, Jiann-Tsair Chang, Cheng-Wei
Lin, and Kuo-Wei Chang. The assistance from the administrative staff of the College of Engineering, NTU, especially Ms. Hong-Hua
Chang, during the preparation of this book is greatly appreciated.
Finally, a book can never be completed without the continuous support,
and expectation, from the families of the authors, colleagues,
friends, and the society in which they live in.