Arch bridges - Computational Analysis and Design of Bridge Structures - page 282

The tied-arch bridge is an internally indeterminate structure so all the
parameters will affect the hangers' stress state. The factors that cause the
hangers' fatigue include the size and material properties of the hangers
themselves or the loads applying on the hangers. This section discusses
how the arrangement of hangers affects the fatigue (Pellegrino et al. 2010).
An example of a concrete-filled steel tube tied-arch bridge was studied
by Yao (2007) and is used here to explain the fatigue effect. Span is 61 m
(200′), carriageway width is 15.2 m (50′), and the ratio of rise to span is
1:5. The original spacing of hangers is 5.1 m (16.7′). Hot-extruding PE
high-tensile cable PES7-55 is used. The load will use normal vehicle design
load in this example.

9.3.2.1 Positions of hangers
First, the difference among the stress state of different hangers will be dis-
cussed. The tied-arch bridge and the numbers of the hangers are shown in
Figure 9.15. After analysis, the result is shown in Table 9.2. The stress range
(SR) ratio of a hanger is its stress range over that of the middle hanger. The
result in Table 9.2 shows that the middle hanger has a higher stress range,
thus more prone to fatigue damage than the side hangers without consider-
ing the flexural rigidity.

1 2 3 4 5 6 5 4 3 2 1

b d d

y

x

Figure 9.15 Study of a tied-arch bridge with different middle and side spaces.

Table 9.2 Study of baseline tied-arch bridge with side spaces b = 5.1 m (16.7 ′ )
Hanger numbers

1 2 3 4 5 6

Maximum stress (ksi) 60.83 63.57 64.38 65.00 65.41 65.41

Minimum stress (ksi) 51.78 53.42 53.69 53.77 53.77 53.77

Average stress (ksi) 49.05 58.49 59.04 59.38 59.60 59.60

Stress range (ksi) 9.05 10.15 10.69 11.24 11.64 11.64

SR ratio 0.776 0.871 0.918 0.965 1.000 1.000