Redundancy analysis - Computational Analysis and Design of Bridge Structures - page 485

All structural steel sections are A36 (248-MPa) carbon steel, and the con-
crete deck is lightweight concrete. The stringers are W16 × 40 rolled beams,
and the PG sections vary along the bridge length. There are three different
PG sections, each having a constant web plate depth of 120″ (3048 mm). The
web thickness varies along the PG from 9.5 mm (3/8″) to 11 mm (7/16″).
The PG flange plates are 762 mm (30″) wide, with a thickness ranging from
8 mm (1 5/16″) to 57 mm (2 1/4″).
15.5.1 Bridge model
A model of the three-span continuous PG bridge is created by SAP2000
(2007). As this example is concerned with the response of the major
structural elements (e.g., PGs, stringers, deck), the deck is modeled using
frame elements. By defining the deck as frame elements, nonlinear hinges
can be assigned at the ends, so the deck will exhibit nonlinear plastic
behavior. To properly model the bridge deck and show transverse and
longitudinal stiffness, a grid of frame elements is created. The deck frame
elements are connected to the joints along the PG and stringer centerlines.
The modeling details are similar to the PC bridge example discussed in
Section 15.4.1.
The width of the deck sections are calculated via the girder tributary area.
The distance between joints along the centerline of the PGs and stringers in
the longitudinal direction is designated as b and equal to 2.6 m (8.5′). The
distance between the PGs and exterior stringers is designated as s 1 and equal
to 1.4 m (4′-7″). The spacing between the PGs and interior stringers in the
transverse direction is designated as s 2 and equal to 2.1 m (7′). The overhang
distance between the exterior stringers and the bridge edge is designated as
o and equal to 0.2 m (7″).
Deck section 1 is along the end of the bridge in the transverse direction.
The width of this section is equal to half the distance between joints along
the PGs and stringers, or b /2. Deck section 2 is also in the transverse direc-
tion, with a width equal to the spacing between joints, or b . Deck section 3
falls in the longitudinal direction along the exterior stringers, so the width
is defined as the overhang distance plus half the beam spacing, or ( o + s 1 /2).
Deck section 4 elements, also in the longitudinal direction, are along the
PGs, with a width equal to ( s 1 + s 2 )/2. Deck section 5 elements are in the lon-
gitudinal direction along the interior stringers, with a width equal to their
center-to-center spacing, or s 2 . Figure 15.14 shows a plan view of the deck
grid at the left end of the bridge model.
15.5.2 attack scenarios
The five attack scenarios for the steel PG bridge are restated in Table 15.12.
Each scenario is characterized by a charge weight of TNT and location