THE CONCRETE BRIDGE MAGAZINE

FALL 2016

ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.

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ASPIRE Fall 2016 | 31 increasing the width of the bearings under a seated girder, and providing bracing or other means to restrict rotation of the girder. Recommendations on the successful implementation of these strategies are included in the document. General criteria provide guidance in establishing assumed design and construction loads, material properties, fabrication tolerances for construction, stress limitations, and overall factors of safety. Tolerances to be considered for stability include strand and prestressing force eccentricity, sweep and lateral deflection (fabrication tolerance), camber variation from design camber, and transverse and longitudinal location of lifting devices. Design loads that may be applied to the girder before full incorporation into the bridge include permanent loads such as dead load and effective prestress, and transient loads such as dynamic impact, centrifugal force, wind loads, and construction live loads. Additional considerations for stability are also presented to describe construction processes affecting stability during girder manufacture, transportation to the bridge site, erection at the bridge site, and stability during the construction of the bridge deck. As an example, the addition of temporary post-tensioning to add compression into the top flange is described, which will increase the factor of safety against cracking. For girders supported on elastomeric bearings, the degradation of the roll stiffness due to bearing uplift or skewed bearing orientation is described. This degradation significantly reduces the roll stiffness and stability factors of safety. Example calculations are provided to illustrate many of the conditions encountered including lifting with vertical cables, lifting with inclined cables, seated during transport, single girder seating on bearings, and stability during deck construction. In the lifted condition, varying degrees of wind load and dynamic impact are calculated to show the sensitivity of these factors on the resulting factors of safety including a comparison of the factors of safety between lifting with vertical cables. The PCI Recommended Practice for Lateral Stability of Precast, Prestressed Concrete Bridge Girders is an essential resource for stability engineers to aid fabricators, transporters, erectors, and engineers for the evaluation of stability at all phases of the girders life from bed-to-bridge. ____________ Glenn Myers is the vice president, director of structural engineering for bridges and ports with Atkins in Fort Lauderdale, Fla. EDITOR'S NOTE Recommended Practice for Lateral Stability of Precast, Prestressed Concrete Bridge Girders is available through the PCI bookstore in hard-copy and as an e-Pub at www.pci.org. Lifting of a 209-ft-long Florida I-beam. Photo: Lane Construction. Environmentally Safe VpCI ® /MCI ® Technologies EXCELLENCE Q U A I T Y ® C O R P O R AT I O N www.CortecMCI.com White Bear Parkway St. Paul, MN 55110 USA 1-800-4-CORTEC productinfo@cortecvci.com Durability Matters Dual functioning MCI ® increases chloride threshold and reduces corrosion once initiated to dramatically increase service life of structures

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