Civil Engineering Reference
In-Depth Information
Transverse vibration
Flexural cracks
initiated
Propagation of flexural cracks
to reduce effective concrete
section for shear force
1/3 Main steel
reinforcement
interrupted
Extensive diagonal cracks
initiated and propagated
a. earthquake-induced vibration
b. flexural crack initiation
c. flexural and shear cracks
When columns overturned,
longitudinal reinforcement
moved outwards
Shear cracks reached
the other side because
of the tilting of columns
in mountain side
Tilting increased
due to P-
Failure of tie reinforcement,
rupture of longitudinal
reinforcement and rupture
of gas-pressure weld were
developed
Δ
effects
d. crack spreading and pier tilting
e. global collapse
Figure B.48
Flexural failure above column base of columns of the Hanshin expressway, due to premature termina-
tion of longitudinal reinforcement and inadequate confi nement in the 1995 Kobe (Japan) earthquake: observed failure
(
top
) and mechanism of failure (
bottom
) (
courtesy of
Dr. Kazuhiko Kawashima)
Failure may also occur without yielding of vertical reinforcement, due to an inadequate lap- splice
length or failure in welded bars as displayed in Figure B.49 .
(ii) Column Shear Failure
Elastically designed structures may suffer failure by shear, since the shear strength corresponding
to the maximum fl exural strength would not have been considered. Shear failure mechanisms are
not usually suitable for ductile seismic response, because of the low levels of deformation
corresponding to failure. Short columns are particularly susceptible to such effects. A high percentage
of bridges lane collapsed during recent earthquakes because of shear failure. Two cases are shown in
Figure B.50 .
