Civil Engineering Reference
In-Depth Information
Figure 15.9
Grid of deck frame elements for PC beam bridge.
connected to joints along the prestressed concrete beam centerlines. Four
frame elements are defined, two in the transverse direction and two in the
longitudinal direction.
The width of the deck sections are calculated via the beam tributary area.
The distance between joints along the centerline of the concrete beams in
the longitudinal direction is designated as
b
and equal to 3.05 m (10′). The
spacing between the concrete beams in the transverse direction is desig-
nated as
s
and equal to 2.18 m (7′-2″). The overhang distance between the
exterior concrete beams and the edge of the bridge is designated as
o
and
equal to 0.58 m (1′-11″). Figure 15.9 shows the deck
grid
model.
Figure 15.8 shows that the AASHTO type III beams have 20 prestressing
tendons. The tendons are modeled as truss elements. Four of these tendons
are deflected strands that vary along the beam length. The remaining 16
strands are straight through the beam length. The four deflected tendons are
modeled together as one at their centroid location, with a cross-sectional
area equal to four times the area of one tendon, or 0.612 in
2
(395 mm
2
).
The straight tendons are also modeled as one tendon group, with a cross-
sectional area equal to 2.448 in
2
(1579 mm
2
). The two top
tendons
are used
to resist tension on the
top
of the beam at release and are not modeled in
this analysis. Figure 15.10 illustrates the tendon layout in SAP2000 (2007).
15.4.2 attack scenarios
The five attack scenarios for the PC beam bridge are restated in Table 15.9.
Each scenario is characterized by a charge weight of TNT and location
Search WWH ::
Custom Search