Model of Strain-related Prestress Losses in Pretensioned Simply Supported Bridge Girders PDF Download
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Author: José Manuel Gallardo Méndez Publisher: ISBN: Category : Languages : en Pages : 608
Book Description
Prestressed concrete construction relies on the application of compressive stresses to concrete elements. The prestressing force is typically applied through the tensioning of strands that react against the concrete and induce compression in the concrete. Loss of prestress is the decrease of this pre-applied stress. The conservative estimation of the prestress losses is imperative to prevent undesired cracking of the prestressed element under service loads. A large fraction of the prestress losses is a consequence of concrete deformations. This fraction of the losses can be identified as strain-related losses, and these occur due to instantaneous elastic shortening, and time-dependent creep and shrinkage. Creep and shrinkage of concrete depend on many factors that are extremely variable within concrete structures. The time-dependent behavior of concrete is not well-understood, but recent findings in the topics of concrete creep and shrinkage provide a better understanding of the underlying mechanisms affecting the nature of these two phenomena. However, current design practices and prestress loss estimation methods do not reflect the state-of-the-art knowledge regarding creep and shrinkage. The main objective of this dissertation was the study and estimation of strain-related prestress losses in simply supported pretensioned bridge girders. Simply supported pretensioned girders are widely designed, produced and frequently used in bridge construction. Due to this common use, pretensioned concrete bridge girders has become fairly standardized elements, which results in a reduced variability in the behavior of pretensioned bridge girders, as compare to that of less standardized concrete structures. Hence, a simplified method was calibrated to estimate prestress losses within pretensioned girders to an adequate level of accuracy. To achieve an acceptable accuracy experimental data from the monitoring of pretensioned simply supported girders was used for the calibration of the method. The accuracy of this simplified method is comparable to that achievable using more elaborate methods developed for generic concrete structures.
Author: José Manuel Gallardo Méndez Publisher: ISBN: Category : Languages : en Pages : 608
Book Description
Prestressed concrete construction relies on the application of compressive stresses to concrete elements. The prestressing force is typically applied through the tensioning of strands that react against the concrete and induce compression in the concrete. Loss of prestress is the decrease of this pre-applied stress. The conservative estimation of the prestress losses is imperative to prevent undesired cracking of the prestressed element under service loads. A large fraction of the prestress losses is a consequence of concrete deformations. This fraction of the losses can be identified as strain-related losses, and these occur due to instantaneous elastic shortening, and time-dependent creep and shrinkage. Creep and shrinkage of concrete depend on many factors that are extremely variable within concrete structures. The time-dependent behavior of concrete is not well-understood, but recent findings in the topics of concrete creep and shrinkage provide a better understanding of the underlying mechanisms affecting the nature of these two phenomena. However, current design practices and prestress loss estimation methods do not reflect the state-of-the-art knowledge regarding creep and shrinkage. The main objective of this dissertation was the study and estimation of strain-related prestress losses in simply supported pretensioned bridge girders. Simply supported pretensioned girders are widely designed, produced and frequently used in bridge construction. Due to this common use, pretensioned concrete bridge girders has become fairly standardized elements, which results in a reduced variability in the behavior of pretensioned bridge girders, as compare to that of less standardized concrete structures. Hence, a simplified method was calibrated to estimate prestress losses within pretensioned girders to an adequate level of accuracy. To achieve an acceptable accuracy experimental data from the monitoring of pretensioned simply supported girders was used for the calibration of the method. The accuracy of this simplified method is comparable to that achievable using more elaborate methods developed for generic concrete structures.
Author: Maher K. Tadros Publisher: Transportation Research Board ISBN: 030908766X Category : Technology & Engineering Languages : en Pages : 73
Book Description
"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.
Author: Thomas E. Cousins Publisher: ISBN: Category : Concrete Languages : en Pages : 67
Book Description
Effective determination of long-term prestress losses is important in the design of prestressed concrete bridges. Over-predicting prestress losses results in an overly conservative design for service load stresses, and under-predicting prestress losses, can result in cracking at service loads. Creep and shrinkage produce the most significant time-dependent effect on prestress losses, and research has shown that high performance and high strength concretes (HPC and HSC) exhibit less creep and shrinkage than conventional concrete. For this reason, the majority of traditional creep and shrinkage models and methods for estimating prestress losses, over-predict the prestress losses of HPC and HSC girders. Nine HPC girders, with design compressive strengths ranging from 8,000 psi to 10,000 psi, and three 8,000 psi lightweight HPC (HPLWC) girders were instrumented to determine the changes in strain and prestress losses. Several creep and shrinkage models were used to model the instrumented girders. For the HPLWC, each model over-predicted the long-term strains, and the Shams and Kahn model was the best predictor of the measured strains. For the normal weight HPC, the models under-estimated the measured strains at early ages and over-estimated the measured strains at later ages, and the B3 model was the best-predictor of the measured strains. The PCI-BDM model was the most consistent model across all of the instrumented girders. Several methods for estimating prestress losses were also investigated. The methods correlated to high strength concrete, the PCI-BDM and NCHRP 496 methods, predicted the total losses more accurately than the methods provided in the AASHTO Specifications. The newer methods over-predicted the total losses of the HPLWC girders by no more than 8 ksi, and although they under-predicted the total losses of the normal weight HPC girders, they did so by less than 5 ksi.
Author: R. G. Oesterle Publisher: Transportation Research Board National Research ISBN: Category : Technology & Engineering Languages : en Pages : 108
Book Description
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.
Author: Edward G. Nawy Publisher: ISBN: Category : Technology & Engineering Languages : en Pages : 968
Book Description
Of Step-by-Step Trial-and-Adjustment Procedure for the Service-Load Design of Prestressed Members -- Design of Composite Post-Tensioned Prestressed Simply Supported Section -- Ultimate-Strength Flexural Design -- Load and Strength Factors -- ACI Load Factors and Safety Margins -- Limit State in Flexure at Ultimate Load in Bonded Members: Decompression to Ultimate Load -- Preliminary Ultimate-Load Design -- Summary Step-by-Step Procedure for Limit at Failure Design of the Prestressed Members -- Ultimate Strength Design of Prestressed Simply Supported Beam by Strain Compatibility -- Strength Design of Bonded Prestressed Simply Supported Beam Using Approximate Procedures -- SI Flexural Design Expression -- Shear and Torsional Strength Design -- Behavior of Homogeneous Beams in Shear -- Behavior of Concrete Beams as Nonhomogeneous Sections -- Concrete Beams without Diagonal Tension Reinforcement -- Shear and Principal Stresses in Prestressed Beams -- Web-Shear Reinforcement -- Horizontal Shear Strength in Composite Construction -- Web Reinforcement Design Procedure for Shear -- Principal Tensile Stresses in Flanged Sections and Design of Dowel-Action Vertical Steel in Composite Sections -- Dowel Steel Design for Composite Action -- Dowel Reinforcement Design for Composite Action in an Inverted T-Beam -- Shear Strength and Web-Shear Steel Design in a Prestressed Beam -- Web-Shear Steel Design by Detailed Procedures -- Design of Web Reinforcement for a PCI Standard Double Composite T-Beam -- Brackets and Corbels.
Author: Paul Barr Publisher: ISBN: Category : Girders Languages : en Pages : 244
Book Description
The design procedure to calculate the shear capacity of bridge girders that was used forty years ago is very different than those procedures that are recommended in the current AASHTO LRFD Specifications. As a result, many bridge girders that were built forty years ago do not meet current design standards, and in some cases warrant replacement due to insufficient calculated shear capacity. However despite this insufficient calculated capacity, these bridge girders have been found to function adequately in service with minimal signs of distress. The objective of this research was to investigate the actual in service capacity of prestressed concrete girders that have been in service over an extended period of time.
Author: Mehdi Saiidi Publisher: ISBN: Category : Bridges Languages : en Pages : 52
Book Description
A post-tensioned, simply-supported, concrete bridge structure in northern Nevada was instrumented in 1988 during construction, and the variation of its response was monitored over a 30-month period. The measured data consisted of tendon strain on four strands, concrete surface strain on two girders, and the deflection of the mid span relative to the ends of the superstructure. The measured losses on the tendons were due to creep and shrinkage. The data showed that the actual total creep and shrinkage losses are 30 percent higher than those predicted using a time-step analysis and 60 percent higher than those predicted by AASHTO. The results also indicate that the prestress forces continue to change due to seasonal variation in temperature and humidity, but the average stress becomes nearly stable
Author: Di Hu Publisher: Elsevier ISBN: 0323859984 Category : Technology & Engineering Languages : en Pages : 462
Book Description
Prestressing concrete technology is critical to understanding problems in existing civic structures including railway and highway bridges; to the rehabilitation of older structures; and to the design of new high-speed railway and long-span highway bridges. Analysis and Design of Prestressed Concrete delivers foundational concepts, and the latest research and design methods for the engineering of prestressed concrete, paying particular attention to crack resistance in the design of high-speed railway and long-span highway prestressed concrete bridges. The volume offers readers a comprehensive resource on prestressing technology and applications, as well as the advanced treatment of prestress losses and performance. Key aspects of this volume include analysis and design of prestressed concrete structures using a prestressing knowledge system, from initial stages to service; detailed loss calculation; time-dependent analysis on cross-sectional stresses; straightforward, simplified methods specified in codes; and in-depth calculation methods. Sixteen chapters combine standards and current research, theoretical analysis, and design methods into a practical resource on the analysis and design of prestressed concrete, as well as presenting novel calculation methods and theoretical models of practical use to engineers. Presents a new approach to calculating prestress losses due to anchorage seating Provides a unified method for calculating long-term prestress loss Details cross-sectional stress analysis of prestressed concrete beams from jacking to service Explains a new calculation method for long-term deflection of beams caused by creep and shrinkage Gives a new theoretical model for calculating long-term crack width
Author: José Manuel Gallardo Méndez
Author: José Manuel Gallardo Méndez
Author: Maher K. Tadros
Author: Thomas E. Cousins
Author: R. G. Oesterle
Author: Edward G. Nawy
Author: 
Author: Paul Barr
Author: Mehdi Saiidi
Author: Di Hu
Author: Osamah Ibrahim Mahmood