Precast alternative for flat slab bridges : final report.

Final reportPDFTech ReportFHWA-SC-13-04SPR 682Alternatives analysisBeamsBridge constructionBridge designHigh performance concreteLongitudinal crackingPrecast concreteSurveysUnited StatesSouth CarolinaClemson University. Glenn Department of Civil EngineeringNielson, Bryant G.Schiff, Scott D.Pang, WeichiangSheng, HuanClemson University. Glenn Department of Civil EngineeringSouth Carolina. Dept. of TransportationUnited States. Federal Highway AdministrationUS Transportation CollectionThe cast-in-place (CIP) concrete slab bridge and the hollow core flat slab bridge are two very common bridge types utilized by theSouth Carolina Department of Transportation (SCDOT). The CIP bridge is durable but has a long construction time while the hollowcorebridge has a short construction time but produces durability concerns. Trying to balance the speed of construction for hollow-coreand the durability of CIP, the SCDOT commissioned this study to provide a recommendation for an alternative bridge type that could:1) eliminate or minimize longitudinal cracking, 2) have a shorter erection time than the CIP flat slab system, and 3) have no restrictionon ADTT and can be used on the National Highway System.There were two distinct phases in this research. In Phase 1, a thorough online survey and telephone interviews were conducted toinvestigate the pros and cons of existing short-span bridge systems used by other state departments of transportation. In addition,feedback from contractors and precast element fabricators in the Southeast region was also solicited. Based on this work, a precastbridge system known as the NEXT-D (Northeast Extreme Tee) beam was selected by the SCDOT for further testing and validation.The experimental and analytical validation along with the design of a 6 ft. wide section (NEXT-6) and an 8 ft. wide section (NEXT-8),with span lengths from 22 ft. to 40 ft., was the focus of Phase 2.The results of the experimental study indicated that U-shaped reinforcing bars and poly-vinyl alcohol (PVA) fiber reinforced ultrahighperformance concrete (UHPC) were an effective combination when used for the shear key located between precast NEXTelements. These results were also used to calibrate analytical models which were used to better understand and quantify the loaddemands associated with this beam type. Using this new understanding, a set of new design guidelines for the new NEXT-6 andNEXT-8 bridge systems was developed. For the beam design, the AASHTO live load distribution factors for tee beams arerecommended to be used. For the deck design, the AASTHO strip method is recommended with some modification. A simplified fourstepprocedure was developed to assist bridge engineers in determining the design demands (positive and negative moments) on a onefootstrip of deck for Strength I and Service I limit states.The results of this study, field experience with existing cast-in-place and precast bridges and sound engineering judgment allow theinvestigators to believe with a reasonable degree of confidence that the construction of a bridge using the provided recommendationsand new system will lead to durable bridges that are cost effective and can be constructed using an accelerated schedule. One of theimmediate needs is to now share the results of this study with neighboring states, so that the investment of needed steel forms byprecasters can result in similar precast pieces sold to multiple states