Railway Track & Structures - April 2008 - (Page 44)

Bridge inspection ture fall” load combination generated relatively-high moments at the arch crown. What concrete strength should be assumed? This was a particularly interesting problem. Concrete modulus of elasticity was shown as two million pounds per square inch on 1911 stress sheets. From 1918 Concrete Engineers Handbook, a modulus of elasticity for concrete equal to 1/15 that of steel may be assumed when the strength of the concrete is taken as greater than 800 psi and less than 2,200 psi. Based on the above information, the load rating analysis assumed a design concrete strength fc’= 2,000 psi. Concrete core samples, however, all tested well in excess of 3m000 psi capacity. Still, the original design assumptions regarding elastic modulus were found to be most appropriate for obtaining rational and balanced results. Load ratings were computed in accordance with AREMA (2006) Chapter 8, Concrete Structures and Foundations, Section 19, Rating of Existing Concrete Structures. A twodimensional linear element analysis was performed using SAP 2000 Integrated Software for Structural Analysis and Design. Similar to the 1911 stress sheets, the arches were analyzed as independent spans. For the load rating evaluation of the arch rib and spandrel walls, ultimate strength axial force versus bending moment interaction diagrams were constructed and the main arch ribs and spandrel walls were rated by the load factor method. The deck sections were analyzed independently by hand calculation using the working stress method. Rolling Lift span. The bridge carries approximately 35 passenger and six freight trains per weekday. In recent years, the draw span of the bridge has experienced approximately 3,700 yearly openings to accommodate navigation on the Connecticut River. The bridge spans the Connecticut River near its mouth at Navigation MP 3.4 in the towns of Old Saybrook and Old Lyme, Conn. The approach span structures were designed by the New York, New Haven and Hartford Railroad. The bascule span was designed for the NYNH&H by the Scherzer Rolling Lift Bridge Company in 1905. The structure was constructed by American Bridge Company beginning in 1906. The structure is used primarily for passenger trains for the Amtrak Northeast Corridor, with one or more daily round trips for the Providence and Worcester freight train and the occasional maintenance rail cars. Hands-on inspection of the Connecticut River Bridge included working around 25,000-volt railroad electrification wires and feed lines. Safety rules require that inspectors maintain 15 feet Connecticut River Bridge The 100-year-old Connecticut River Bridge is part of the rail infrastructure that has served New England for many years. Conn Bridge is one of nine movable railroad bridges along the Connecticut coast main passenger line between Stamford in the west and Mystic in the east. The existing bridge, constructed circa 1907, is a two-track, open-deck, electrified railroad bridge, 1,564 feet long, consisting of seven through-truss spans, two deck-girder spans and one 158-foot Scherzer-type 44 Railway Track & Structures April 2008 www.rtands.com http://www.rtands.com

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Railway Track & Structures - April 2008 Contents On Track Industry Today Supplier News AREMA News NRC News TTCI R&D Railroads Seeking More Advanced Systems to Handle Materials SKOL Bounces Back From Summer Flood Landmark Railroad Bridges Need Inspection, Too Products and Literature People Calendar Sales Representatives Advertisers Index Website Directory Professional Directory Classified Advertising Chicago Perspective

Railway Track & Structures - April 2008

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