Fundamentals of posttensioning for clamping design in structures with precast components.

摘要

There are more than 600,000 bridges in U.S. alone. The Federal Highway Administration statistics indicate that more than 20 percent of the National Highway System (NHS) bridges and 27 percent of non-NHS bridges are structurally deficient or functionally obsolete. Rehabilitation and replacement of large number of existing bridges cause safety, environmental, and socioeconomic problems. Prefabricated bridge elements/systems are widely used to accelerate the construction and assure the quality; thus, increase service life. Accelerated construction as well as the use of prefabricated elements has many inherent advantages including minimum traffic disruption and increased work zone safety. Yet, the failure of empirically designed field implemented joint details for connecting precast components is a major durability concern.;The motivation behind this study is the inconsistency involved in various stages of the design of connections of precast bridge superstructure systems. Development of joint details to assure monolithic structural behavior with no cracks and no water leakage under service loads require fundamental understanding of the joint behavior against design parameters. The most common joint detail is to use grouted keyways and posttension that resembles the behavior of a multi-layer plate compressed with concentrated loads.;This study investigates the clamping stress distributions in precast bridge superstructure systems. Understanding the stress profile caused by the clamping loads plus investigating ways to be able to create uniform compression is the primary objective of this dissertation. To accomplish this goal, various design parameters; namely, the elasticity mismatch between layers, friction between interfaces, stiffeners, restraints and aspect ratio are considered. Using the available analytical models, finite element models are developed and verified. Finite element models are further modified for cases where employment of analytical models is not sufficient. The stress distribution under the presence of multiple clamping loads is also investigated. The research describes the interaction of posttension design parameters and present design recommendations for optimum joint performance utilizing numerical investigation results as well as pertinent literature.