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Arched truss bridge |
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Just as the arch design is a solution to inefficient post and lintel construction, it also offers |
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a solution to the inefficiencies of long span beam or truss bridge designs. Like their solid |
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wood or masonry counterparts, arch trusses are able to collect the downward acting |
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compressive stresses induced in a structure and displace them laterally around the legs of |
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the arch to the abutments on which the structure rests. This makes them an ideal design |
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for supporting the mid-span of a bridge and countering the bending moment there. |
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In another variation, called the bowstring arch, the deck of the bridge is suspended by |
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cables or struts from a superstructure of arched trusses located on both sides. The vertical |
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load on the deck is displaced to the cables as tensile stresses. These are then transferred to |
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the arches where they are further displaced to the abutments on which the arches rest. The |
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many cables reduce the bending moment of the load by breaking the arm of the moment |
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into shorter segments. Another unique feature of the design is that the legs of the arches |
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are tied together by the deck thereby resisting their outward thrust on the abutments. The |
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bridge's foundations only have to support the load of the bridge and its traffic. The |
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Back to Knowhere |
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