Evaluation of the need for negative moment reinforcing in prestressed concrete bridges in the view of service loads. (15th March 2020)

• Record Type: Journal Article
• Authors: Liu, Zhengyu; Freeseman, Katelyn; Phares, Brent M.
• Is Part Of: Engineering structures. Volume 207(2020)
• Publication Date: 2020-03-15
• Subjects: Additional negative moment reinforcing steel (b2 bar) -- Secondary moment -- Finite element modeling -- Field test; Structural engineering -- Periodicals; Structural analysis (Engineering) -- Periodicals; Construction, Technique de la -- Périodiques; Génie parasismique -- Périodiques; Pression du vent -- Périodiques; Earthquake engineering; Structural engineering; Wind-pressure; Periodicals; 624.105
• DOI: 10.1016/j.engstruct.2020.110206
• Languages: English
• ISSNs: 0141-0296

Abstract

Highlights: Little research has been conducted on the performance of the additional negative reinforcing steel. The main objective of the research is to evaluate the effect of different amounts of b2 bars on resisting the negative moment over the pier on a continuous prestressed concrete girder. The results of this research filled the gap on the study of the effectiveness of negative moment resisting reinforcement. The results indicated that the additional longitudinal reinforcing steel provides minimal effect on resistance to the negative moment prior to the formulation of deck cracking. The current design approach determines the b2 bars requirement for the strength level based on the live load, it may be necessary to include the secondary moment in the design. Abstract: It is common practice to put additional longitudinal reinforcement (b2 bars) over intermediate supports to resist any negative moment induced by the superimposed dead loads and live loads on bridges. However, little research has been conducted on the performance of the additional negative reinforcing steel. Requirements for the termination of the additional negative moment reinforcing steel have largely been based upon the engineering judgement, previous performance, and existing practice. The main objective of the research is to evaluate the effect of different amounts of b2 bars on resisting the negative moment over the pier on a continuous prestressed concrete girder bridge when it subject to the live load generated moment and secondary moment. To achieve this objective, a live load field test was performed on a bridge designed with different amounts of b2 bars to allow for comparison of the varying levels of negative moment reinforcement present. A full-scale finite element model was developed and validated against the field-collected data to study the b2 bar performance subjected to live loads. An evaluation was performed, utilizing an analytical approach by calculating the time-dependent secondary moment using mRESTRAINT and loading the beam-line FE model with the maximum negative moment. It was found that the negative moment induced by the live load and secondary moment does appear through the service life of the bridge. The high differential shrinkage rate between the fresh deck concrete and the girder concrete is the main source of the negative moment over the supports. The magnitude of the secondary moment was found to be highly influenced by the time when the continuity established. The results also indicated that the additional longitudinal reinforcing steel provides minimal effect on resistance to the negative moment prior to the formulation of deck cracking, regardless of whether the negative moment was induced by live loads or secondary moment. The current design approach determines the b2 bars requirement for the strength level based on the live load, it may be necessary to include the secondary moment in the design.