Redundancy analysis - Computational Analysis and Design of Bridge Structures - page 465

15.3 3d exaMPle with Redundancy analysis
of a Pony tRuss, Pennsylvania

This illustrated example is to demonstrate the redundancy capacity check
using nonlinear finite element analysis. A truss configuration was selected
to represent the 142′-8 1/2″ (43.5-m) Foxstop Road Bridge, shown in
Figures 15.2 and 15.3, where all designs are fabricated using grade 50
(345-MPa) steel. The 3D model in ANSYS is shown in Figure 15.4. Following
the flowchart shown in Figure 15.1, the first step is to identify FCMs.
After the finite element model is made by the first-level linear analysis, the
FCMs are identified. Seventeen (17) FCMs are identified per truss panel (where
A as the left truss panel and B as the right truss panel): nine on truss A are bot-
tom chord members (elements 1 through 9) and eight are diagonal members
(elements 28, 31, 34, 37, 40, 43, 46, and 49). Due to symmetry and simplifi-
cation, only three bottom chord members (L1L3, L5L7, and L9L11) and two
diagonal member-cut cases (U2L3 and U4L5) and one uncut case were ana-
lyzed for each load case. Specifically, a series of code checks are required for
these bottom chord and diagonal members of the truss bridge in the uncut and
cut conditions, which are shown in Table 15.2. Figure 15.5a shows the semi-
box section for the bottom chord with two channels, and Figure 15.5b shows
the wide flange section for the diagonal members, both shown in ANSYS
plastic section designation prepared to the second-level nonlinear analysis.

W12 × 96 L Truss

W 12 × 87

7/8″ ϕ
A325 high-
strength bolts
at field connections

2-MC12 × 40

2-C12 × 50 2-C12 × 50 2-MC12 × 40

2-MC12 × 40

L Bearing 15′ 10 1/4″ 15′ 10 1/4″ 15′ 10 1/4″

9 Panels @ 15′ 10 1/4″ (±) = 142′ 8 1/2″

15′ 10 1/4″ 15′ 10 1/2″

Figure 15.2 USB 43.5-m (142 ′ -8 1/2 ″ ) Foxstop Road Bridge detail.

Field bolted connections

U 8 U 10 U 12

U 6 U 14

U 4

U 16

U 2

U 18

L 1 L 3 L 5 L 7 L 9 L 11 L 13 L 15 L 17 L 19

9 Panels @ 15′ 10 1/4″ (±) = 142′ 8 1/2″ C/C BRGS
Total camber = 3 3/16″

Figure 15.3 USB 43.5-m (142 ′ -8 1/2 ″ ) Foxstop Road Bridge elevation view of truss.