Arched truss bridge

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Just as the arch design is a solution to inefficient post and lintel construction, it also offers

a solution to the inefficiencies of long span beam or truss bridge designs.  Like their solid

wood or masonry counterparts, arch trusses are able to collect the downward acting

compressive stresses induced in a structure and displace them laterally around the legs of

the arch to the abutments on which the structure rests.  This makes them an ideal design

for supporting the mid-span of a bridge and countering the bending moment there.

 

arch_truss.gif

arch_truss.gif

trussed_deck_arch_bridge.gif

(static demonstration models)

(scale visualization model)

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Fig. 181 - Arch truss designs                               click image to enlarge

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In another variation, called the bowstring arch, the deck of the bridge is suspended by

cables or struts from a superstructure of arched trusses located on both sides.  The vertical

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bowstring_arch_bridge.jpg

 

bowstring_arch_bridge.jpg

Fig. 182 - Bowstring arch bridge

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(static demonstration model)

  (scale visualization model)

 

click image to enlarge

 

load on the deck is displaced to the cables as tensile stresses.  These are then transferred to

the arches where they are further displaced to the abutments on which the arches rest. The

many cables reduce the bending moment of the load by breaking the arm of the moment

into shorter segments.  Another unique feature of the design is that the legs of the arches

are tied together by the deck thereby resisting their outward thrust on the abutments.  The

bridge's foundations only have to support the load of the bridge and its traffic.  The

bowstring arch is an integral, self-

bowstring_arch_bridge.jpg

contained structure that can be

repeated in series for long distances.

This makes it ideal for causeways.

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Fig. 183 - Series of bowstring arches ►

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