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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.
The design of prestressed concrete bridge girders has changed significantly over the past several decades. Specifically, 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. The actual capacity was compared with calculated values using the AASHTO LRFD Specifications.
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.
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The main aim of the book is to evaluate the safety level of Turkish type precast prestressed concrete bridge girders designed according to AASHTO LRFD based on reliability theory. Two types of design truck loading models are taken into account: H30S24-current design live load of Turkey and HL93-design live load model of AASHTO LRFD. The statistical parameters of both load and resistance components are estimated from local data and published data in the literature. The girders are designed according to the requirements of both Service III and Strength I limit states. The reliability indexes are calculated by different methods for both Strength I and Service III limit states. The reliability level of typical girders of Turkey is compared with those of others countries. Different load and resistance factors are intended to achieve the selected target reliability levels. For the studied cases, a set of load factors corresponding to different levels of reliability index are suggested for the two models of truck design loads.
Tests of two prestressed concrete composite bridge girders which were continuous over two spans are reported. Both were I-section girders with cast-in-place decks, and had spans of about 37 ft (11 m), and were approximately 1/3 scale models of structures spanning 125 ft (38 m). Each girder was constructed from three segments which were joined end-to-end by cast-in-place concrete splices. Modell was post-tensioned after erection of the girders and casting of the deck and splice concrete. The two end segments, each supported on the final abutments and on temporary supports located about 1/3 of the span from the central pier, were pretensioned for their dead loads plus the deck concrete. The central segment, which was supported on the central pier of the structure plus the two temporary supports was precast reinforced concrete, plus a small amount of pre= tensioned reinforcement. Model 2 was externally similar, but was not post-tensioned. The segments were pretensioned for the final moments, and were joined by splicing reinforcing bars which extended into the splice region. Both structures were subjected to a series of loadings to the service load, design ultimate, and high over-load levels. Both had capacities which were significantly higher than the design ultimate values. The capacities were generally predictable on the basis of flexural strength calculations, and shear did not cause major problems. Joint details in Modell lead to difficulties in two tests, and this aspect of the design is discussed in detail.