Civil Engineering Reference
In-Depth Information
Figure 17.21
Tied arch
laterally so much that its stabilising effect is reduced. Any normal continuous highway
deck is likely to fulfi l these conditions, but light footbridges may not. If the hangers
are effectively triangulated transversally, meeting at an apex at the arch, and if the deck
has suitable torsional stiffness, the arch may be completely stabilised against lateral
buckling, Figure 17.21 (c), allowing the most slender of structures. Even a narrow
angle of triangulation will be effective in providing this stability, as the fi rst incremental
sideways movement of the arch immediately encounters a horizontal component of
hanger force.
The bridge must of course be capable of carrying concentrated live loads which, if
applied to the arch, would generate bending moments in it and signifi cantly increase
its required depth and weight. The logic of the tied arch is to provide a stiff deck that
carries the moments, allowing the arch to be as light as possible.
