THE STEEL'S FISH TRAP BRIDGE IN MISSOURI ALMOST CERTAINLY IS NOT ONE OF THE SIX WHIPPLE ARCH
BRIDGES FROM THE BEALE ROAD. IT IS A BOWSTRING AS ARE ALL THE WHIPPLE ARCHES. (THERE ARE
MANY OTHER TYPES OF BOWSTRINGS THAT DIFFER FROM WHIPPLE'S IN THE DETAILS.)
THE ARCH CROSS SECTIONS IN WHIPPLES VARY IN WIDTH FROM SAY 11" AT MID-SPAN TO SAY 33" AT
THE ENDS (USING NORMANSKILL AS AN EXAMPLE). THE TOP FLANGE IN THE MID-SPAN PANEL IS SOLID,
BUT IN THE OTHER PIECES VOIDS ARE PROVIDED ALONG THE MEMBERS. THE MATERIAL IS CAST IRON.
IN THE STEEL'S FISH TRAP THE ARCH IS BUILT-UP TWO CHANNEL WEBS AND A TOP PLATE. THESE SHAPES
ARE RIVETED TOGETHER AND LACING BARS ARE RIVETED ALONG THE BOTTOM. THE MATERIAL IS WROUGHT
IRON. MADE BY THE PUDDLING PROCESS AND FURTHER SHAPED IN A STRUCTURAL ROLLING. NOT AT ALL
DIFFERENT FROM LATER FABRICATION IN STEEL.