Libin
Yin, William R. Spillers, and M Ala
Saadeghvaziri
Department of Civil and Environmental Engineering, New Jersey Institute of Technology, Newark, NJ 07102
Bridges composed of simple-span, precast, prestressed concrete girders made continuous via cast-in-place decks and diaphragms are continuous only for live loads and superimposed dead loads. The continuity diaphragms often crack due to time dependent effects in the girders. These cracks not only impair bridge aesthetics and durability, but also reduce “degree of continuity”. A related issue is that joint construction is time consuming and expensive due to reinforcement congestion. This research presents a series of field tests, analytical studies, and laboratory experiments concerning the design and performance of this type of bridge.
To improve structural efficiency of multi-span simply supported bridges, partial and/or full continuity is provided through cast- in-place concrete diaphragms and decks. These bridges, known as Simple-Span Precast Prestressed Bridge Girders Made Continuous, are continuous for live loads. This continuity connection is also beneficial from maintenance point of view by eliminating open joints. However, continuity connections also have their own structural, construction, and maintenance shortcomings. Development of positive moments and diaphragm cracking at the internal pier due to time dependent effects of prestressing is a major structural problem that also affects bridge durability and esthetics. Another issue is that due to reinforcement congestion joint construction is time consuming and thus expensive. Furthermore, the degree of continuity varies depending on structural and construction conditions. These problems are common to various design details used by many states in the US.
In addition to collecting design data from other states and transportation agencies, under this study field performance of bridges is monitored and the results are compared to detailed analytical studies (including finite element analysis) to better understand the behavior and load transfer mechanism of continuity connections. Using these results, recommendations for changes to existing design and detailing practice are made. Also, an effective analysis program (CONTINUITY) is developed that can be used by engineers to check the restraint moments caused by the time dependent effects and to examine the degree of continuity of simple span girders made continuous. Furthermore, an innovative continuity connection using Carbon Fiber Reinforced Polymer has been developed and laboratory tested. To provide continuity, Carbon Fiber Reinforced Polymer reinforcement is attached to the top of the girders over the cast in place diaphragm. The negative moment over the supports caused by the deck weight balances the positive restraint moment caused by creep in the prestressed girders thus eliminating positive moment cracking. Structural efficiency is also increased since the girders are continuous under the deck dead load too. It is shown that the new continuity connection is a viable option and that it addresses the problems and shortcomings associated with the existing design while further enhancing structural integrity and design effectiveness. Standard design plates and construction sequences are provided and areas for further research are identified.
Department of Civil and Environmental Engineering, New Jersey Institute of Technology, Newark, NJ 07102
Bridges composed of simple-span, precast, prestressed concrete girders made continuous via cast-in-place decks and diaphragms are continuous only for live loads and superimposed dead loads. The continuity diaphragms often crack due to time dependent effects in the girders. These cracks not only impair bridge aesthetics and durability, but also reduce “degree of continuity”. A related issue is that joint construction is time consuming and expensive due to reinforcement congestion. This research presents a series of field tests, analytical studies, and laboratory experiments concerning the design and performance of this type of bridge.
To improve structural efficiency of multi-span simply supported bridges, partial and/or full continuity is provided through cast- in-place concrete diaphragms and decks. These bridges, known as Simple-Span Precast Prestressed Bridge Girders Made Continuous, are continuous for live loads. This continuity connection is also beneficial from maintenance point of view by eliminating open joints. However, continuity connections also have their own structural, construction, and maintenance shortcomings. Development of positive moments and diaphragm cracking at the internal pier due to time dependent effects of prestressing is a major structural problem that also affects bridge durability and esthetics. Another issue is that due to reinforcement congestion joint construction is time consuming and thus expensive. Furthermore, the degree of continuity varies depending on structural and construction conditions. These problems are common to various design details used by many states in the US.
In addition to collecting design data from other states and transportation agencies, under this study field performance of bridges is monitored and the results are compared to detailed analytical studies (including finite element analysis) to better understand the behavior and load transfer mechanism of continuity connections. Using these results, recommendations for changes to existing design and detailing practice are made. Also, an effective analysis program (CONTINUITY) is developed that can be used by engineers to check the restraint moments caused by the time dependent effects and to examine the degree of continuity of simple span girders made continuous. Furthermore, an innovative continuity connection using Carbon Fiber Reinforced Polymer has been developed and laboratory tested. To provide continuity, Carbon Fiber Reinforced Polymer reinforcement is attached to the top of the girders over the cast in place diaphragm. The negative moment over the supports caused by the deck weight balances the positive restraint moment caused by creep in the prestressed girders thus eliminating positive moment cracking. Structural efficiency is also increased since the girders are continuous under the deck dead load too. It is shown that the new continuity connection is a viable option and that it addresses the problems and shortcomings associated with the existing design while further enhancing structural integrity and design effectiveness. Standard design plates and construction sequences are provided and areas for further research are identified.
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