Arch bridges - Computational Analysis and Design of Bridge Structures - page 288

bridge contain complicated construction stage analyses, and cables or hangers
need to be tuned to reach an ideal design state. These analyses are all spe-
cific topics in cable-stayed bridge analyses. Therefore, a special-purpose FEA
package that can perform multistage construction analysis and cable-tuning
is required. As the arch is under compression, nonlinear effects such as initial
stress problem, stability, and even large displacement are often needed in arch
bridge analyses. Basic principles in modeling an arch bridge, such as whether
a three-dimensional (3D) model is necessary or not and how fine the mesh is
adequate, are the same as those in modeling a cable-stayed bridge. Detailed dis-
cussion in Chapter 11 for a cable-stayed bridge can be applied to an arch bridge.
9.4.1 Arches
The cross section of an arch varies from solid-reinforced concrete to steel
box, from steel truss to concrete-filled steel tubes. Compression is predomi-
nated in the arch under dead loads; however, live loads will also cause
bending moment. 2D/3D frame elements are used to model an arch. The
curvature of arch geometry can be simulated by straight elements, and the
curve element is not quite necessary. Like girders in a cable-stayed bridge,
initial stress effect may be considered in arch elements.
9.4.2 deck
The deck of an arch bridge usually contains floor beams and stringers as in
most half-through thrust arch bridges or tied cables/girders and floor beams
as in most tied-arch bridges. 3D model is always encouraged so as to better
simulate the stiffness of each deck component. Taking an example shown in
Figure 14.15, floor beams and tied girders are modeled as 3D frame elements.
When tied cables are separated, truss elements are used to model tied cables.
9.4.3 hangers
Like cables in a cable-stayed bridge, hangers are usually modeled as truss
elements. No sag effect exists in a hanger, and one hanger can be modeled
as one truss element. Initial stress effect should be considered in analyses
for lateral load cases and stability analysis.
9.4.4 stability
Due to high compression in the arch under dead loads and the height of
the crown from the deck, global stability, either in the arch plane or in the
horizontal plane, is more important in an arch bridge than other types
of bridges. Stability analysis is inevitable when designing an arch bridge.
For a tied-arch bridge without lateral bracings on arches or a long-span
arch bridge, lateral stability usually has a lower critical load than in-plane