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Prestress loss due to creep, shrinkage, and relaxation can cause serviceability issues, and in the case of structures post-tensioned with unbonded tendons, can reduce the flexural capacity. The accurate estimation of prestress losses is vital for making good decisions about the remaining life of a structure. The Varina-Enon Bridge is a post-tensioned concrete box-girder bridge near Richmond, Virginia. Flexural cracks in the bridge prompted an investigation into the magnitude of prestress loss experienced by the structure. Long-term prestress losses were estimated using two methods. First, a finite element model was created, and multiple code expressions for creep and shrinkage were applied to a time-step analysis of the structure. The code expressions investigated in this research were from the CEB-FIP 1978, CEB-FIP 1990, CEB-FIP 2010, and AASHTO (2017) codes. The second method utilized data from sensors installed on the bridge to back-calculate the effective prestressing force based on recorded openings of the flexural cracks. For the four spans monitored in this research, the field-determined effective prestress varied between 161 ksi and 166 ksi. Using the commercially available bridge design software, LARSA 4D, along with the creep and shrinkage model used in the original design, CEB-FIP 1978, the calculated effective prestress varied between 169 ksi and 171 ksi. This indicates that prestress losses were higher than anticipated in the original design, but the measured effective prestress was still, on average, about 96% of the design effective prestress. The more modern creep and shrinkage models of CEB-FIP 1990 and CEB-FIP 2010 also predicted higher than measured effective prestress, with both being very similar to CEB-FIP 1978. The effective prestress predicted by the AASHTO (2017) model was slightly higher. Calculation of flexural capacity using the effective prestress estimated by the field measurement system resulted in estimates of strength 1 to 4% smaller than using the effective prestress estimated by the original creep and shrinkage model used for design. Measured thermal gradients over the period studied in this project were smaller than the AASHTO LRFD design gradients; however, the restraint moment calculated for the worst case measured gradient was very similar to the restraint moment calculated using the design gradient.
The durability of post-tensioning tendons depends undoubtedly on the durability of the materials used, but there are design concept specifics which are also of major importance: the post-tensioning layout and layers of protection such as concrete cover and selected materials in view of the aggressivity of the environment for instance. It is well known that sustainability principles guide the Engineer from the very beginning, at the project conception, during construction and the service life of a structure. Decisions made during conceptual and design stage have the largest influence on the durability and sustainability of post-tensioning tendons. fibBulletin 33 addresses the specifics for prestressed concrete structures: the durability of post-tensioning tendons. It should be noted that it does not repeat topics that have been addressed in other fib bulletins and which is common for both reinforced concrete and prestressed concrete structures. Pre-tensioning, which is used extensively in the precast industry, is not considered here, although conclusions and recommendations herein may, in many cases, also be applicable. This recommendation was prepared by Working Party 5.4.2, Durability specifics for prestressed concrete structures, in cooperation with fib Commission 9,Reinforcing and prestressing materials and systems. A preliminary version of this recommendation served as the basic document for the second workshop on "Durability of post-tensioning tendons", held on 11-12 October 2004 in Zurich. This workshop was a follow-up to the first workshop held in Ghent in 2001. Bulletin 33 includes revisions corresponding to the agreed results of the Zurich workshop.
"This specification provides minimum requirements for the selection, design, and installation of cementitious grouts for steel post-tensioned systems used in concrete construction. The purpose of the grout is to provide corrosion protection to the prestressing steel and in bonded post-tensioning (PT) applications to develop bond between the prestressing steel and the surrounding concrete." -- From publisher
This English translation of the successful French edition presents the conception and design of steel and steel-concrete composite bridges, from simple beam bridges to cable supported structures. The book focuses primarily on road bridges, emphasizing the basis of their conception and the fundamentals that must be considered to assure structural safety and serviceability, as well as highlighting the necessary design checks. The principles are extended in later chapters to railway bridges as well as bridges for pedestrians and cyclists. Particular attention is paid to consideration of the dynamic performance.
Essential reading for researchers, practitioners, and engineers, this book covers not only all the important aspects in the field of corrosion of steel reinforced concrete but also discusses new topics and future trends. Theoretical concepts of corrosion of steel in concrete structures, the variety of reinforcing materials and concrete, including stainless steel and galvanized steel, measurements and evaluations, such as electrochemical techniques and acoustic emission, protection and maintenance methods, and modelling, latest developments, and future trends in the field are discussed. Comprehensive coverage of the corrosion of steel bars in concrete, investigating the range of reinforcing materials, and types of concrete Introduces the latest measuring methods, data collection, and advanced modeling techniques Second edition covers a range of new, emerging topics such as the concept of chloride threshold value, concrete permeability and chloride diffusion, the role of steel microstructure, and innovations in corrosion detection devices
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.
Reliability of Structures enables both students and practising engineers to appreciate how to value and handle reliability as an important dimension of structural design. It discusses the concepts of limit states and limit state functions, and presents methodologies for calculating reliability indices and calibrating partial safety factors. It also supplies information on the probability distributions and parameters used to characterize both applied loads and member resistances. This revised and extended second edition contains more discussions of US and international codes and the issues underlying their development. There is significant revision and expansion of the discussion on Monte Carlo simulation, along with more examples. The book serves as a textbook for a one-semester course for advanced undergraduates or graduate students, or as a reference and guide to consulting structural engineers. Its emphasis is on the practical applications of structural reliability theory rather than the theory itself. Consequently, probability theory is treated as a tool, and enough is given to show the novice reader how to calculate reliability. Some background in structural engineering and structural mechanics is assumed. A solutions manual is available upon qualifying course adoption.