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At head of title: National Cooperative Highway Research Program.
Prestressed concrete decks are commonly used for bridges with spans between 25m and 450m and provide economic, durable and aesthetic solutions in most situations where bridges are needed. Concrete remains the most common material for bridge construction around the world, and prestressed concrete is frequently the material of choice. Extensively illustrated throughout, this invaluable book brings together all aspects of designing prestressed concrete bridge decks into one comprehensive volume. The book clearly explains the principles behind both the design and construction of prestressed concrete bridges, illustrating the interaction between the two. It covers all the different types of deck arrangement and the construction techniques used, ranging from in-situ slabs and precast beams; segmental construction and launched bridges; and cable-stayed structures. Included throughout the book are many examples of the different types of prestressed concrete decks used, with the design aspects of each discussed along with the general analysis and design process. Detailed descriptions of the prestressing components and systems used are also included. Prestressed Concrete Bridges is an essential reference book for both the experienced engineer and graduate who want to learn more about the subject.
This report documents and presents results of a study to determine time-dependent behavior and relevant design criteria for simple-span precast, prestressed bridge girders made continuous. A questionnaire was used to determine current practice. Creep and shrinkage tests of steam-cured concrete loaded at an early age were made. Computer simulations were used to investigate the effects of time-dependent material behavior and variation in design parameters on the effective continuity for live load plus impact. The findings suggest that positive moment connections in the diaphragms at the piers are not required and provide no structural advantages. The findings also suggest that effective continuity for live load plus impact can vary from 0 to 100% dependent on the design parameters and timing of construction. Computer analyses were also used to determine an upper limit for the amount of negative moment reinforcement over the supports to insure full moment redistribution and attainment of maximum bridge strength. New computer programs were developed for simplified analysis to determine time-dependent effects and service moments. Recommendations for design procedures were presented and design examples given.
Introduction and Research Approach -- Findings -- Interpretation, Appraisal, and Application -- Interpretation, Appraisal, and Application -- References -- Appendixes.
At head of title: National Cooperative Highway Research Program.
This report establishes a user's manual for the acceptance, repair, or rejection of precast/prestressed concrete girders with longitudinal web cracking. The report also proposes revisions to the AASHTO LRFD Bridge Design Specifications and provides recommendations to develop improved crack control reinforcement details for use in new girders. The material in this report will be of immediate interest to bridge engineers.
The 2011 PCI Bridge Design Manual provides preliminary design charts for selecting the girder size and number of prestressing strands for a given span length and beam spacing but only for [small leter f with hook]ʹ[subscript c] = 8,000 psi (55.2 MPa). This single strength limits the use of the charts, particularly for states considering ultra-high performance concrete (UHPC). Accordingly this dissertation presents a simplified procedure to develop preliminary design charts for prestressed concrete bulb-tee girders considering service load stress limits, flexural strength and stresses at release. The results for a BT-72 beam are first compared with the 2003 PCI design charts originally developed based on the AASHTO Standard Specifications. The procedure is then adapted to the AASHTO LRFD Bridge Design Specifications and verified with the prevailing 2011 PCI design charts. Finally, new LRFD charts are generated for NSC, HPC, and UHPC with 0.5, 0.6, and 0.7-in. (13, 15 and 18 mm) strands for simple and two-span continuous bridges to illustrate the simplified procedure and potential impact of UHPC, larger strand size, and continuity on bridge girders. The new LRFD charts are shown to be accurate for the design assumptions made since an excellent agreement (within 2% and 4%) resulted between the preliminary design charts developed in this study and those given in the 2003 and 2011-PCI Bridge Design Manuals. The "transition point" is identified which provides the information needed for a designer to distinguish the zones between fully prestressed (uncracked), partially prestressed, and non-prestressed (cracked) members. The preliminary design charts demonstrate the effect of using UHPC and/or larger strand size and/or two-span continuous layouts. The effect of implementing continuity with the combination of UHPC and a larger strand diameter was shown to be much more significant than just increasing the concrete compressive strength or the strand diameter or using two-span continuous layouts. However, the use of longer full-span girders poses significant challenges for fabrication, transportation, erection, span-to-depth ratios, and live and dead load deflections of prestressed concrete bridges and, consequently, should be considered carefully for the final design of the bridge.