Concrete Products

MAR 2016

Concrete Products covers the issues that attract producers of ready mixed and manufactured concrete focusing on equipment and material technology, market development and management topics.

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56 • March 2016 www.concreteproducts.com TECHNICAL TALK BY TOM KUENNEN A new longitudinal joint detailing design for popular double-tee concrete girders in South Dakota bridges quells water intru- sion and enhances girder performance, say Nadim Wehbe, South Dakota State Universi- ty-Brookings; Michael Konrad, Kiewit Engi- neering Co., Omaha; and Aaron Breyfogle, South Dakota Department of Transportation, in their TRB paper, Joint Detailing Between Double Tee Bridge Girders for Improved Ser- viceability and Strength. "Precast/prestressed double tee bridge girders are widely used for accelerated bridge construction on local roads in South Dakota," the authors note. Deteriorated joints allow moisture and de-icing chemicals to reach the deck reinforcement, leading to premature corrosion of reinforcing steel and spalling of concrete, they add. Detailing of longitudinal joints between precast bridge girders for ade- quate shear transfer remains a major concern especially in "decked" precast girders, such as double tee members, which do not require cast-in-place bridge decks. The conventional joint detailing used for double tee girder bridges in South Dako- ta consists of discrete welded connections spaced along a grouted longitudinal joint (shear keyway) between adjacent girders, Wehbe, Konrad and Breyfogle observe. A com- mon issue among existing double tee bridges is that the longitudinal joints deteriorate with time, most likely due to inadequate shear connection between adjacent girders. It is only a matter of time before the grout begins to crack along the joint, creating a path for moisture and de-icing chemicals to reach the steel reinforcement in the deck, and leading to corrosion, concrete spalling, and structural degradation of the bridge. To see if the structural performance of conventional and proposed longitudinal joints between precast double tee bridge girders could be improved, both versions were examined experimentally under cyclic and monotonic loading. For the proposed specimen's joint details, the longitudinal joint was 4 in. wider than that of the con- ventional specimen, and was reinforced with overlapping 4 x 8-D8.0 X D4.0 welded wire mesh that extended from the deck reinforce- ment for a distance of 6 in., with the wire mesh extension provided during fabrication of the girders. "Thus, the joint reinforcement consisted of 0.319 in.-diameter deformed wires spaced at 4 in. center-to-center, for a total steel NEW JOINT DETAILING IMPROVES DOUBLE-TEE GIRDER PERFORMANCE Deterioration of double tee bridge girders at longitudinal joints. PHOTOS, DRAWING: Wehbe, Konrad and Breyfogle Give your savings a lift The DCG90–180 is designed for superior uptime, lower fuel consumption and reduced maintenance costs. DCG90-180 is avaliable with the latest generation of engines from both Volvo or Cummins. They both meet the requirments of Tier 4 emission standard. The DCG90-180 is eqipped with a variable hydraulic pumps as standard. The variable pump signifcantly lowers the strain on the hydraulic system and allows the forklift to fully perform when its needed. This features has also proven to lower the fuel consumption of the machine but at the same time raise the performance. www.kalmarglobal.com/G

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