Redundancy analysis - Computational Analysis and Design of Bridge Structures - page 482

Figure 15.11 Attack scenario 1 (674-lb TNT) static equivalent joint loads.
on an open-air hemispherical explosion calculates the static pressure at
each joint. The influence surface is the surface area expanding radially
from the explosion centroid. As the blast magnitude increases, the influ-
ence surface increases. Trial and error aided in deciding that the blast
loads may be cut off at pressures less than 200 psi (1.38 MPa). Using
the tributary area method, the pressure is resolved into joint loads. In
Table 15.10, the pressures that appear in bold are greater than or equal
to 200 psi (1.38 MPa), so the corresponding joint loads of these pressures
are applied to the PC beam bridge model. Figure 15.11 shows the static
equivalent joint loads for attack scenario 1 applied to the prestressed con-
crete beam bridge model.
15.4.3 analyze structural response
The nonlinear static analysis output shows the performance of struc-
tural members' plastic hinges with nodes color-coded showing the
hinge's state on the moment-rotation or force-deformation curve. The
analysis generated responses for multiple steps. Figure 15.12 demon-
strates the final response step for one of the attack scenarios, which
reveals that the PC beam bridge experiences total failure in every attack
scenario. Therefore, the bridge under attack has no additional redun-
dancy and will have to be replaced. This result simplifies the quantifica-
tion of damaged areas by performance levels. Table 15.11 summarizes
the structural damage under IO, LS, and CP. With all attack scenarios
under the category of (≥CP), there is no redundancy left for this type
of bridges.