Development of LRFD Procedures for Bridge Piles in Iowa—Volume IV: Design Guide and Track Examples

With the goal of producing engineered foundation designs with consistent levels of reliability as well as fulfilling the Federal Highway Administration (FHWA) mandate that all new bridges initiated after October 1, 2007 be designed according to the Load and Resistance Factor Design (LRFD) approach, the Iowa Highway Research Board (IHRB) sponsored three research projects on driven piles (TR-573, -583 and -584). The research outcomes are presented in three reports entitled Development of LRFD Design Procedures for Bridge Piles in Iowa, Volumes I, II, and III, and other research information is available on the project web site at http://srg.cce.iastate.edu/lrfd/. Upon incorporating the regional LRFD recommendations from the completed research into the Iowa DOT Bridge Design Manual (2010) as it is being rewritten under the new title of LRFD Bridge Design Manual (December 2011), and adopting the American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specifications (2010), this Volume IV for driven piles in Iowa was developed. Following the layout of a design guide, the application of the LRFD approach is demonstrated using various pile design examples in three different tracks, which depend on the construction control method used for establishing the pile driving criteria. Piles are designed using the Iowa Blue Book method. The pile driving criteria are established using the Wave Equation Analysis Program (WEAP) in Track 1, the modified Iowa Engineering News Record (ENR) formula in Track 2, and the combination of WEAP and the Pile Driving Analyzer (PDA) with a subsequent pile signal matching analysis using the CAse Pile Wave Analysis Program (CAPWAP) in Track 3. The track examples cover various pile types, three different soil profiles (cohesive, non-cohesive, and mixed) and special design considerations (piles on rock, scouring, downdrag, and uplift)

Improving the Accuracy of Camber Predictions for Precast Pretensioned Concrete Beams

The discrepancies between the designed and measured camber of precast pretensioned concrete beams (PPCBs) observed by the Iowa DOT have created challenges in the field during bridge construction, causing construction delays and additional costs. This study was undertaken to systematically identify the potential sources of discrepancies between the designed and measured camber from release to time of erection and improve the accuracy of camber estimations in order to minimize the associated problems in the field. To successfully accomplish the project objectives, engineering properties, including creep and shrinkage, of three normal concrete and four high-performance concrete mix designs were characterized. In parallel, another task focused on identifying the instantaneous camber and the variables affecting the instantaneous camber and evaluated the corresponding impact of this factor using more than 100 PPCBs. Using a combination of finite element analyses and the time-step method, the long-term camber was estimated for 66 PPCBs, with due consideration given to creep and shrinkage of concrete, changes in support location and prestress force, and the thermal effects. Utilizing the outcomes of the project, suitable long-term camber multipliers were developed that account for the time-dependent behavior, including the thermal effects. It is shown that by using the recommended practice for the camber measurements together with the proposed multipliers, the accuracy of camber prediction will be greatly improved. Consequently, it is expected that future bridge projects in Iowa can minimize construction challenges resulting from large discrepancies between the designed and actual camber of PPCBs during construction