Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 107
107
action plays a critical role in the evaluation of the effect of seis-
mic loading for both flexible and rigid culverts and pipes. A
unified evaluation procedure is developed in this chapter to
provide a rational and reliable means for seismic evaluations as
well as realistic design for buried culvert and pipe structures.
9.3.1 Ground Shaking
Ground shaking refers to the vibration of the ground pro-
duced by seismic waves propagating through the earth's crust.
The area experiencing this shaking may cover hundreds of
square miles in the vicinity of the fault rupture. The intensity
of the shaking attenuates with distance from the fault rupture.
Ground shaking motions are composed of two different
types of seismic waves, each with two subtypes:
· Body waves travel within the earth's material. They may be
either longitudinal compressional (P-) waves or transverse
shear (S-) waves, and they can travel in any direction in the
ground.
· Surface waves travel along the earth's surface. They may be Figure 9-2. Ovaling and racking deformations.
either Rayleigh waves or Love waves.
The axial and curvature deformations are induced by com-
As stable ground is deformed by the traveling waves, any ponents of seismic waves that propagate along the culvert or
culverts or pipelines in the ground also will be deformed. The pipeline axis. Figure 9-1 shows the idealized representations of
shaking or wave traveling induced ground deformations are axial and curvature deformations. The general behavior of the
called transient ground deformations. linear structure is similar to that of an elastic beam subject to
When subject to transient ground deformations, the re- deformations or strains imposed by the surrounding ground.
sponse of a buried linear culvert or pipe structure can be de- Current design and analysis methodologies for pipeline
scribed in terms of three principal types of deformations: systems were developed typically for long, linear structures.
(1) axial deformations, (2) curvature deformations (refers The principal failure modes for long, continuous pipeline struc-
to Figure 9-1), and (3) ovaling (for circular cross section) or tures consist of (1) rupture due to axial tension (or pull out for
racking (for rectangular cross section) deformations (refers jointed segmented pipelines), and (2) local bucking (wrinkling)
to Figure 9-2). due to axial compression and flexural failure. If the pipelines
are buried at shallow depth, continuous pipelines in com-
pression also can exhibit beam-buckling behavior (that is,
global bucking with upward buckling deflections). If the axial
stiffness of the structures is large, such as that for a large sec-
tional concrete pipe, then the buckling potential in the longi-
tudinal direction is small for both local buckling and global
buckling. The general failure criteria for the above-mentioned
potential failure modes have been documented by previous
studies (O'Rourke and Liu, 1996).
It should be noted, however, that typical culvert structures
for transportation applications are generally of limited length.
For this condition, it is in general unlikely to develop signifi-
cant transient axial/curvature deformations along the culvert
structures. The potential failure modes mentioned above are
not likely to take place during the earthquake. The main focus
of this chapter will not be on the effects of axial/curvature de-
formations. Instead, the scope of this chapter will concentrate
Figure 9-1. Axial and curvature deformations. on transverse deformations of culverts and pipes.
