Mass Transit magazine features agency profiles, industry trends, management tips and new product information.
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70 | Mass Transit | MassTransitmag.com | SEPTEMBER/OCTOBER 2014 800.477.7275 www.atkinsglobal.com/northamerica Innovative transit solutions Rapid urbanization, aging infrastructure, and federal def cits— is your system ready for what the future holds? Atkins is leading the way in future proof ng transit by delivering systems engineering, asset management, and public-private partnership solutions. Our global experience and thought leadership in managing legacy assets and upgrading systems deliver insight that drives increased resiliency and eff ciency for our transit clients. Driving innovation for the future For more information, visit www.MassTransitmag.com/10735344 • 2012: Te Carlsbad Double Track and Bridge Project fnishes and both main tracks are open for revenue-generating train service. Te two main tracks stand side by side across the Agua Hedionda Lagoon, exhibiting the next evo- lution of bridge design. DEVELOPING THE GIRDERS Te frst concrete bridge (2006) has spans made from standard concrete bulb-tee girders, which are beams that look like elongated "I" letters. Te girders — four per span — support a ballast bridge deck, where the train track fas- tens to ties that are in a bed of stable ballast material on top of the bridge deck. Te outermost girders on both sides support the ballast retainers. Te structural bridge de- signer on the Carlsbad Double Track and Bridge Project makes a unique design improvement. He notices that two diferent components of the 2006 con- crete bridge perform the same function. Why not eliminate one? He decides to eliminate the separate bridge deck altogether from the new concrete bridge. He redesigns the standard bulb-tee girders, widening and thicken- ing the top edges. Te redesigned top edges now support the ballast directly, eliminating the need for an intermediate bridge deck. As before, the outermost girders on both sides support the ballast retainers. Te short girders have the ballast retainers precast, and the long girders have the ballast retainers cast in place afer setting. Te redesigned bulb-tee gird- ers are the highlight of the Carls- bad Double Track and Bridge Project, saving about $750,000 of construction costs and two months of construction time. Te savings are the estimated con- struction costs and time of build- ing a separate bridge deck. As a result, the overall project is under budget and ahead of schedule.