Improving performance prediction of corroding concrete bridges with field monitoring
This paper provides an approach based on the monitoring of life cycle performance of concrete bridges exposed to chlorides, and demonstrates its application in a case study. It is first shown that some of the data, which are commonly used by engineers as input values into service life prediction models, can be different from actual field values, because these parameters vary widely in space and time. It is then demonstrated that service life predictions can be improved by updating the models with field monitoring data. (National Research Council of Canada Institute for Research in Construction report NRCC-53245,
July 2010, 16p.)
Modelling RC Bridge Columns Under the Combined Effects of Traffic and Reinforcement Corrosion
Significant increase in strength and stiffness of construction materials in the past five decades has led to a considerable reduction of bridge elements size and weight, resulting in more slender bridge structures that could have inadequate dynamic characteristics. For slab-on-girder bridges, the bridge superstructure traffic-induced vibration is reduced through dampers and discontinuity in the superstructure/substructure joints before affecting the bridge substructure. However, significant level of traffic vibration is observed in the substructure. On the other hand, reinforced concrete (RC) bridge columns in cold regions are affected by chloride-induced reinforcement corrosion from the application of de-icing salts in the winter, and their serviceability and strength capacity can be reduced over time. This paper presents a numerical model of individual and compound effects of traffic and corrosion-induced damage in RC bridge columns on the dynamic performance of the bridge superstructure. The procedure includes two time-dependent cycles presenting each process: an external cycle, which represents the corrosion process, and an internal cycle, which performs time-history analysis of the bridge under traffic load. The slab-on-girder bridge is modelled as a beam-on-two-columns system (BOTC) using a two-dimensional finite element method, and the truck is modelled as a two-degree of freedom dynamic system integrated with the bridge model. Corrosion-induced damage is introduced through the reduction of the reinforcing steel area and spalling of the concrete cover. It is found that the model is efficient in simulating the static and dynamic behaviour of slab-on-girder bridges. From the case study, it is found that although reinforcement corrosion of the bridge columns significantly reduces their capacity, it only causes a marginal increase in the bridge superstructure dynamic deflection under the dynamic movement of the truck.
(National Research Council of Canada Institute for Research in Construction report NRCC-53536,
August 2010, 11p.)
Structural performance of laminated FRP box girder bridge deck compared to slab on prestressed concrete girder bridge
A promising advance in the use of advanced composites in civil-structures is the development of a bridge superstructure with all-advanced composite elements. However, one of the critical obstacles to extensive use of advanced composites in construction is the lack of simplified and practical design approaches, specifications or guidelines. In this paper, an iterative performance based multi-scale analysis and design approach for all-advanced composite bridge superstructure is proposed. The bridge superstructure is formed from laminated FRP box girder and chopped FRP top surface layer or “deck slab”. Several laminate designs are examined and the performance of the most efficient material and structural designs of the proposed bridge are compared to a traditional slab on prestressed concrete bridge. The results show that the proposed procedure leads to an efficient use of the materials with higher structural performance and significantly lower superstructure weight. However, further research is needed to investigate manufacturing and construction procedures and long term performance.
(National Research Council of Canada Institute for Research in Construction report NRCC-53572,
July 2010, 13p.)
Benefits of internal curing on service life and life-cycle cost of high-performance concrete bridge decks - a case study
This paper investigates the impact of internal curing on the service life of high-performance concrete (HPC) bridge decks by using analytical models to predict the times to onset of corrosion, onset of corrosion-induced damage, and failure of decks. Three bridge deck design options were compared: (i) normal concrete deck; (ii) HPC deck with supplementary cementing materials (SCM); and (iii) HPC deck with SCM and internal curing. It was found that the use of internal curing can extend the service life of high-performance concrete bridge decks by more than twenty years, which is mainly due to a significant reduction in the rate of penetration of chlorides in concrete as a result of reduced early-age shrinkage cracking and reduced chloride diffusion. Compared to normal concrete, HPC with SCM and internal curing was predicted to add more than 40 years to the service life of bridge decks in severe environmental conditions. Life-cycle cost reductions of 40% and 63% were estimated when conventional HPC and internally-cured HPC were used in bridge decks instead of normal concrete, respectively, despite the fact that the in-place unit cost of internally-cured HPC can be 4% higher than that of conventionally-cured HPC, which in turn can be up to 33% higher than that of normal concrete. This is due to a longer service life and less frequent maintenance activities offered by low-permeability HPC bridge decks.
(National Research Council of Canada Institute for Research in Construction report NRCC-52661,
July 2010, 43p.)
Effect of Chloride-based Deicers on Reinforced Concrete Structures
We conducted an extensive literature review and performed laboratory tests to assess the effect of chloride-based deicers on the rebars and dowel bars in concrete and to determine whether or not deicer corrosion inhibitors help preserve the transportation infrastructure. The laboratory investigation exposed concrete samples to four common chloride-based deicers for approximately one year or less, for natural diffusion at room temperature or for cyclic exposure with wet/dry and temperature cycling. Under the experimental conditions in this study, the corrosion inhibitors in deicers helped to preserve the strength of concrete undergoing temperature and wet/dry cycles. While they also slowed down the chloride ingress and subsequent corrosion initiation of steel in concrete, such benefits seem to diminish once the active corrosion of the rebar is initiated.
(Washington State Department of Transportation report WA-RD 741.1,
July 2010, 174p.)
Strategic Evaluation of Different Topical Protection Systems for Bridge Decks and the Associated Life-Cycle Cost Analysis
Topical protection systems act as barriers to protect bridge decks from corrosion damage by preventing water, oxygen, and chloride ions from reaching the reinforcement. This study evaluated topical protection systems commonly used on highway bridge decks in Colorado, including low-permeability concrete overlays and waterproof membranes with asphalt overlays. Five bridges were selected for inspection in the project. Concrete cores were taken from the selected bridge decks, and chloride concentration profiles were obtained at various depths. Chloride concentration is an important indicator for the corrosion damage of rebars in concrete deck.
(Colorado Department of Transportation report CDOT-2010-6,
August 2010, 73p.)
Impact of Overhang Construction on Girder Design
Economical constraints on the design of bridges usually necessitate the use of as few girders as possible across the bridge width. The girders are typically uniformly spaced transversely with the deck extending past the fascia girders, thereby resulting in an overhang. While designers commonly employ rules of thumb with regard to the geometry of the overhang, these rules of thumb generally address only the deck in-service strength and deflection requirements, and the effect due to construction load is not considered. In particular, the impact of the overhang on fascia girder behavior during construction is not well understood. Overhang construction often leads to a torsional load on the girder system that can lead to problems in steel and concrete girder bridges during construction. The main issue with concrete girder bridges is excessive lateral rotation in the fascia girder, which can cause potential problems of construction safety and maintenance. The objective of this study was to improve the understanding of the bridge behavior due to the unbalanced loading from the overhangs and to identify critical factors affecting the girder behavior. The study was also aimed at developing simple design methodologies and design recommendations for overhang construction. The research included field monitoring, laboratory tests, and parametric finite element analyses.
(Texas Department of Transportation Report FHWA/TX-10/0-5706-1,
May 2010, 205p.)
Determining More Effective Approaches and Materials for Grouting Shear Keys
The objective of this project was to evaluate improved design and construction practices that have the potential to reduce shear key grout failure (cracking) in PennDOT precast box beam bridges. This objective was met by conducting a state-of-the-practice literature review, numerical parametric studies, and experimental verification tests. The literature review presented four possible parameters that have the potential to reduce cracking: (i) shear key configuration; (ii) grouting material; (iii) transverse post-tensioning, and; (iv) bearing pad details. Experimental tests of shear key connections were conducted. Results from these tests were used to validate finite element models of the shear key region. A grillage analysis of a selected bridge configuration was conducted to determine the maximum live-load effects experienced by the shear key. A parametric study using finite element analysis showed that a full-depth, epoxy-grouted shear key could significantly reduce the likelihood of cracking. Moreover, the amount of post-tensioning and the effect of bearing pad at supports also play an important role in reducing the maximum tensile stress and thus cracking.
(Pennsylvania Department of Transportation report FHWA-PA-2010-014-PSU 014,
31 May 2010, 116p.)
Assuring Bridge Safety and Serviceability in Europe
U.S. engineers need advanced tools and protocols to better assess and assure safety and serviceability of bridges. The Federal Highway Administration, American Association of State Highway and Transportation Officials, and National Cooperative Highway Research Program sponsored a scanning study of Europe to identify best practices and processes to assure bridge safety and serviceability. The scan team found that the European highway agencies expect their bridge programs to not only ensure user safety, but also to meet serviceability expectations and enhance capital investment decisions. The team gathered information on safety and serviceability practices and technologies related to design, construction, and operations.
(US Federal Highway Administration International Scanning Program report FHWA-PL-10-014,
August 2010, 60p.)
Vessel Crushing and Structural Collapse Relationships for Bridge Design
Accounting for waterway vessel collision is an integral component of structural design for any bridge spanning a navigable waterway. Each time a vessel traverses a given waterway, there is an inherent risk that the vessel may become aberrant from the intended transit path, and once aberrant, may strike a nearby bridge structural component. The research presented in this report focuses on the development of improved probability of collapse expressions for bridge piers subject to barge impact loading, where such relationships are integral to current bridge design methodologies.
(University of Florida Structures Research Report 2010/72908/74039,
August 2010, 231p.)
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