Civil Engineering Reference
In-Depth Information
Readers should be aware that, here and there, we give our views, a few
of them controversial, on the directions in which we think bridge building
and infrastructure policy should go. Where we express opinions (informed
ones, we believe), the reader will be able to detect that from the way we
write. Our most forceful claim is for the millennial bridge—but let us not
reveal too much yet. We invite readers to find out what we mean.
We begin in the next chapter by counting America's bridges. We also
estimate the number of sites, in a year, for which decisions have to be made
about new construction or rehabilitation.
Then four chapters that follow should be read in a row: they are our
engineering chapters. Chapter 3 provides the basics on the forces that bridge
spans must resist to stay aloft. The next (chapter 4) explains how basic prin-
ciples guide the engineer to design the types of bridges all of us observe on
our travels. Though bridges are remarkably safe, their design cannot be based
on certainty. Chapter 5 introduces the ways in which engineers manage to
keep bridges strong, despite uncertainties. The most serious uncertainties
arise from the possibility of extreme events, such as floods and earthquakes.
These are the greatest challenges to bridge safety, and chapter 6 illustrates
the ways in which engineers and other professionals strive to meet them.
Our series of chapters on bridge planning begins with the question:
is the bridge worth building in the first place? Chapter 7 seeks to answer
the question by introducing cost-benefit analysis for a bridge. This and
subsequent chapters can be read in any order. The next (chapter 8) is on
transportation planning and uses an extended example to analyze whether
traffic pressures justify a new bridge.
The bridge to be built or rebuilt may well raise possibilities of envi-
ronmental harm. Chapter 9 explains the process by which environmental
impact is assessed and asks what could be meant by a “sustainable bridge.” In
chapter 10, our series on bridge planning ends by investigating a sometimes
intractable problem: why a project often creeps along for a decade or more
to get from initial studies to the day the ribbon is cut. We conclude the
topic with what we have already hinted about, our appeal for you to join
us in advocating for bridges that span a millennium.
