Download or read book Estimating Camber Deflection and Prestress Losses in Precast Prestressed Bridge Girders written by Ahmed Almohammedi and published by . This book was released on 2019 with total page 85 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Prestress Losses in Pretensioned High strength Concrete Bridge Girders written by Maher K. Tadros and published by Transportation Research Board. This book was released on 2003 with total page 73 pages. Available in PDF, EPUB and Kindle. Book excerpt: "The HCM includes three printed volumes (Volumes 1-3) that can be purchased from the Transportation Research Board in print and electronic formats. Volume 4 is a free online resource that supports the rest of the manual. It includes: Supplemental chapters 25-38, providing additional details of the methodologies described in the Volume 1-3 chapters, example problems, and other resources; A technical reference library providing access to a significant portion of the research supporting HCM methods; Two applications guides demonstrating how the HCM can be applied to planning-level analysis and a variety of traffic operations applications; Interpretations, updates, and errata for the HCM (as they are developed);A discussion forum allowing HCM users to ask questions and collaborate on HCM-related matters; and Notifications of chapter updates, active discussions, and more via an optional e-mail notification feature."--Publisher.
Download or read book Predicting Camber Deflection and Prestress Losses in Prestressed Concrete Members written by S. H. Rizkalla and published by . This book was released on 2011 with total page 153 pages. Available in PDF, EPUB and Kindle. Book excerpt: Accurate predictions of camber and prestress losses for prestressed concrete bridge girders are essential to minimizing the frequency and cost of construction problems. The time-dependent nature of prestress losses, variable concrete properties, and problems related to production variables make it difficult to predict camber accurately. The recent problems experienced by NCDOT during construction are mainly related to inaccurate prediction of camber. In this report, several factors related to girder production are shown to have a significant impact on the prediction of camber. A detailed method and an approximate method for predicting camber that both utilize adjustments to account for the production factors are proposed. The detailed method uses time-dependent losses calculations and creep factors to predict camber, while the approximate method uses multipliers. The current NCDOT method and the proposed methods are analyzed and compared using an extensive database of field measurements. The proposed methods are shown to provide significant improvements to the camber predictions in comparison to the current NCDOT method. Recommendations for design and production practices are provided.
Download or read book Predicting Prestress Losses Camber and Deflection in Prestressed Concrete Members written by Sami Rizkalla and published by . This book was released on 2011 with total page 153 pages. Available in PDF, EPUB and Kindle. Book excerpt: Accurate predictions of camber and prestress losses for prestressed concrete bridge girders are essential to minimizing the frequency and cost of construction problems. The time-dependent nature of prestress losses, variable concrete properties, and problems related to production variables make it difficult to predict camber accurately. The recent problems experienced by NCDOT during construction are mainly related to inaccurate prediction of camber. In this report, several factors related to girder production are shown to have a significant impact on the prediction of camber. A detailed method and an approximate method for predicting camber that both utilize adjustments to account for the production factors are proposed. The detailed method uses time-dependent losses calculations and creep factors to predict camber, while the approximate method uses multipliers. The current NCDOT method and the proposed methods are analyzed and compared using an extensive database of field measurements. The proposed methods are shown to provide significant improvements to the camber predictions in comparison to the current NCDOT method. Recommendations for design and production practices are provided.
Download or read book Improving Predictions for Camber in Precast Prestressed Concrete Bridge Girders written by Michael A. Rosa and published by . This book was released on 2007 with total page 358 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Validation of Prestressed Concrete I beam Deflection and Camber Estimates written by Cullen R. OʹNeill and published by . This book was released on 2012 with total page 205 pages. Available in PDF, EPUB and Kindle. Book excerpt: The camber at the time of bridge erection of prestressed concrete bridge girders predicted by the Minnesota Department of Transportation (MnDOT) was observed to often overestimate the measured cambers of girders erected at bridge sites in Minnesota, which, in some cases, was causing significant problems related to the formation of the bridge deck profile, the composite behavior of the girders and bridge deck, delays in construction and increased costs. Extensive historical data was collected from two precasting plants and MN counties and it was found that, on average, the measured cambers at release and erection were only 74% and 83.5%, respectively, of the design values. Through data collection, analysis, and material testing, it was found that the primary causes of the low camber at release were concrete release strengths that exceeded the design values, the use of an equation for concrete elastic modulus that greatly under-predicted the measured values, and thermal prestress losses not accounted for in design. Fourteen girders were instrumented and their camber measured and the program PBEAM was used to evaluate the influence of various time-dependent effects (i.e., solar radiation, relative humidity, concrete creep and shrinkage, length of cure and bunking/storage conditions) on long-term camber. Once investigated, these effects were included in long-term camber predictions that were used to create sets of both time-dependent and singlevalue camber multipliers. The use of these multipliers, along with modifications made to the elastic release camber calculations, greatly reduced the observed discrepancy between measured and design release and erection cambers.
Download or read book Extending Span Ranges of Precast Prestressed Concrete Girders written by Reid Wilson Castrodale and published by Transportation Research Board. This book was released on 2004 with total page 603 pages. Available in PDF, EPUB and Kindle. Book excerpt: At head of title: National Cooperative Highway Research Program.
Download or read book Behavior of Prestressed Concrete Bridge Girders written by Franklin B. Angomas and published by . This book was released on 2009 with total page 109 pages. Available in PDF, EPUB and Kindle. Book excerpt: For this research, prestress losses were monitored in six HPC bridge girders. These measured losses were compared to predicted losses according to four sources. Prestress loss predictive methods considered for this research were: 1- AASHTO LRFD 2004, 2- AASHTO LRFD 2004 Refined, 3- AASHTO LRFD 2007, and 4- AASHTO LRFD Lump Sum method. On the other hand, the camber prediction methods used in the present research were: 1- Time dependent method described in NCHRP Report 496, 2- PCI multiplier method, and 3- Improved PCI Multiplier method. For the purpose of this research, long-term prestress losses were monitored in select girders from Bridge 669 located near Farmington, Utah. Bridge 669 is a three-span prestress concrete girder bridge. The three spans have lengths of 132.2, 108.5, and 82.2 feet long, respectively. Eleven AASHTO Type VI precast prestressed girders were used to support the deck in each span. The deflection of several girders from a three-span, prestressed, precast concrete girder bridge was monitored for 3 years. Fifteen bridge girders were fabricated for the three span-bridge. Ten girders from the exterior spans had span length of 80 feet, and five girders from the middle span had span length of 137 feet. From the results of this research, in both the 82- and 132-foot-long, the AASHTO LRFD 2004 Refined Method does a better job predicting the prestress loss and it can be concluded that all the prediction methods do a better job predicting the loss for the larger girders. The Lump Sum method predicted very accurately the long term prestress loss for the 132-foot-long girders.
Download or read book Prestress Losses in Concrete and the Estimation of Long term Deflections and Camber for Prestressed Concrete Bridges written by Hema Jayaseelan and published by . This book was released on 2007 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt: Findings and conclusions. The results from the research showed that the proposed method shows strong correlation with the losses predicted using the NCHRP 496 method. The method also computed the long term deflection and camber that were comparable with the results obtained using the PCI Design Handbook multipliers. The results proved that the reduction in long term losses can be achieved by varying the material and design properties of prestressed concrete.
Download or read book Prestress Losses and the Estimation of Long term Deflections and Camber for Prestressed Concrete Bridges written by Hema Jayaseelan and published by . This book was released on 2007 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book AASHTO LRFD Bridge Design Specifications Customary U S units written by and published by . This book was released on 1998 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Improving Predictions for Camber in Precast Prestressed Concrete Bridge Girders written by Hang Thi Nguyet Nguyen and published by . This book was released on 2014 with total page 124 pages. Available in PDF, EPUB and Kindle. Book excerpt: Most of the modern medium-span bridges in the United States are constructed with precast, prestressed concrete girders. An accurate estimate of girder camber is important for all parties involved in the precast concrete industry for several reasons. The most important reason is that achieving vertical alignment, and casting the deck, becomes much more difficult if the cambers of two adjacent girders in the bridge are not the same, since the girders are generally too large to make the correction by brute force. In addition, any uncertainty of the estimated camber in the precast, prestressed concrete girders can lead to construction delays and can increase material and labor costs. However, the prediction and control of camber over time is difficult, because camber varies with many parameters, such as the concrete properties, curing methods, and temperature variations. The goal of this research is to improve the methods to predict camber in precast, prestressed concrete girders, with an emphasis on determining the effect of temperature on camber both during curing and in service. The research focused on monitoring and collecting fabrication camber to calibrate the current models for predicting camber. Temperature histories at release and service were also recorded to examine the effect of fabrication temperatures on initial camber and the effect of daily temperature variations on service camber. Two models were developed to predict daily camber changes under solar radiation based on ambient temperature data. The predictions of the models correlate well with the data collected during the research.
Download or read book Prestress Loss and Creep Camber in a Highway Bridge with Reinforced Concrete Slab on Pretensioned Prestressed Concrete Beams written by Howard L. Furr and published by . This book was released on 1968 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Evaluation of Time dependent Camber and Deflections in Bridge Girders written by Furkan Cakmak and published by . This book was released on 2021 with total page 554 pages. Available in PDF, EPUB and Kindle. Book excerpt: A methodology to predict each stage of camber and displacements in composite prestressed concrete and steel bridge superstructures from inception to end of service life including a prediction of rebound in deck replacement projects is presented. The methodology invokes the use of multiple creep curves and allows the proper simulation of various construction activities each of which feature unique loading events. The proposed method captures the influence of several factors, such as creep and shrinkage of beam and deck concrete as well as prestresses losses induced because of these phenomena. Additionally, the prediction methodology offers the capability to quantify the influence of temperature gradients on beam camber and displacements at any point in time. The proposed method can be used to predict beam rebound during a deck replacement activity by considering the removal of the deck as well as the removal of the locked-in time dependent internal forces. The overall framework for the prediction methodology is based on principles of engineering mechanics, although components of the methodology are based on empirical models such as the estimation of the modulus of elasticity at prestress release and 28 days, its variation with time, prediction of creep and shrinkage properties, and relaxation of prestressing strands. The proposed methodology has been evaluated using measured pre-erection and service camber data. An alternative simplified method suitable for preliminary design and based on time-dependent multipliers is presented. Pre-erection camber predictions based on the proposed methodology and the Time-Dependent Multiplier Method are more accurate than those based on the PCI Multiplier Method and the MDOT multiplier method. A computer program called MDOTCamber was developed to facilitate data input and summarize essential output.
Download or read book Effect of Temperature on Prestressed Concrete Bridge Girder Strand Stress During Fabrication written by and published by . This book was released on 2015 with total page 185 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Minnesota Department of Transportation has reported erection cambers of many prestressed concrete bridge girders that were much lower than anticipated. A previous University of Minnesota study (O’Neill and French, MN/RC 2012-16) attributed the discrepancies to inaccurate estimates of the concrete strength and stiffness at release and strand force loss due to temperature during fabrication. The objective of this study was to further investigate the effects of temperature on strand force and camber during precast, prestressed girder fabrication and to make recommendations for the design and fabrication processes to reduce the potential loss of prestress due to temperature effects during fabrication and to improve the release camber estimation. A thermal effects analysis was developed based on four key steps in the girder fabrication process: tensioning, concrete-steel bond, release, and normalization. The study included fabricating six short prestressed concrete segments released at early ages to determine the time/temperature associated with bonding the prestressing strand to the concrete. To investigate the non-recoverable prestress losses during girder fabrication, four sets of girders (MN54 and 82MW) were instrumented with thermocouples, strain gages, and in some cases load cells, that were monitored during the fabrication process to separate the thermal and mechanical strain components. Effects investigated included casting during a cold season, casting during a warm season, casting with the free length of strand covered, and casting with different bed occupancy during any season. A recommended procedure for adjusting strand force during tensioning was proposed to account for non-recoverable strand force changes due to temperature changes between tensioning and bond.
Download or read book Field Measurement and Evaluation of Time dependent Losses in Prestressed Concrete Bridges written by Okey U. Onyemelukwe and published by . This book was released on 1997 with total page 360 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Design of Precast Prestressed Bridge Girders Made Continuous written by R. G. Oesterle and published by Transportation Research Board National Research. This book was released on 1989 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
