Civil Engineering Reference
In-Depth Information
• Allowable side shear and base bearing stresses
• Downdrag and uplift conditions
Also, specific dynamic soil investigations may be required in areas of high seis-
mic activity to determine soil strength, foundation settlement, and stability under
earthquake motions.
In some cases it is possible that, due to geotechnical conditions, foundations must
berelocated.Thiswillresultinsignificantchangesintheproposedbridgearrangement
and should be carefully and comparatively cost estimated. A geotechnical engineer
experienced in shallow and deep bridge foundation design and construction should
be engaged to manage geotechnical site investigations and provide recommendations
for foundation design.
3.2.4 G
EOMETRY OF THE
T
RACK AND
B
RIDGE
Railway horizontal alignments consist of simple curves (
Figure 3.5)
and a tangent
track connected by transition or spiral curves. Track profile, or vertical alignment, is
composed of constant grades connected by parabolic curves. Many high-density rail
lineshavegradesof
<
1%andrestrictcurvaturetosafelyoperateathighertrainspeeds.
3.2.4.1
Horizontal Geometry of the Bridge
If curved tracks traverse a bridge, the consequences for steel superstructure design
are effects due to the:
• Centrifugal force created as the train traverses the bridge at speed,
V
(force
effect)
I
T
100 ft
M
C
R
I
/2
D
FIGURE 3.5
Simple curve geometry.
