Like their masonry counterparts, arched trusses are extremely stable.  As many as three

flexible hinge points, or fractures, can develop in the structure without it failing.  In fact,

some arch trusses are specifically designed to have one, two, or three hinge points in order

to relieve the build up of stresses in the arch.  This allows it to conform more readily to

changes in its shape induced by temperature fluctuations or asymmetrical loads.

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Cantilever bridge

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Another solution to the problem that most of the dead weight of the deck is concentrated

mid-span, is to cantilever the roadbed either from the end abutments or from a support that

is located center span.  Cantilevering the deck from the end abutments entails extending a

diagonal bracing strut from the abutment to a point near the mid-point of the deck.  The

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A deck that is cantilevered from a central support extends outwards in both directions in a

balanced fashion like the limbs of a tree.   This centers the mass of the structure over the

support rather than in the middle of the span.  A bending moment force applied to one end

of the dual-cantilever is countered by the moment exerted by the weight of the other end,

like two masses being weighed on a balance scale.

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