Pretensioned Bridge Girders Research Articles

Numerical investigation into the effects of corrosion on the shear performance of pretensioned bridge girders with cast-in-place slabs

Corrosion and shear cracking are frequently observed near supports of pretensioned bridge girders in coastal climates, so non-linear finite element analysis was used to study the effect of corrosion on shear performance in a real case study. Varying degrees of corrosion and various locations (top strands, bottom strands, vertical stirrups and girder-slab interface) were considered. The analyses included construction phases, concrete creep and shrinkage, and the effects of corrosion on the properties of prestressing and reinforcing steel, concrete, and the bond between concrete and reinforcement. The study shows that high (20%) corrosion in the bottom layer of strands can modify the failure mode from concrete crushing in the web to strand slippage or crushing of concrete in the support zone with limited cracking. Although severe strand corrosion significantly compromises girder capacity and ductility, failure occurs only when there is overloading. The predicted failure mode was also sensitive to material parameters, in particular the corrosion-induced crack widths used for modelling the reduced concrete strength. Nevertheless, some similarities were noticed between observed and predicted cracking occurrence. For moderate corrosion (10%), girder capacity was limited by strand fracture, but extensive flexure and shear cracking would appear before failure. 20% corrosion in the vertical stirrups in the web seems to have potentially smaller effect on the shear capacity than 20% corrosion in the strands in support, while corrosion in the top strands or stirrups in the girder-slab interface did not affect the girder capacity.

Shear Behavior of Ultrahigh-Performance Concrete Pretensioned Bridge Girders

Shear Behavior of Ultrahigh-Performance Concrete Pretensioned Bridge Girders

Inspection and Assessment of Corrosion in Pretensioned Concrete Bridge Girders Exposed to Coastal Climate

The most common methods for detecting chloride-induced corrosion in concrete bridges are half-cell potential (HCP) mapping, electrical resistivity (ER) measurements, and chloride concentration testing, combined with visual inspection and cover measurements. However, studies on corrosion detection in pretensioned structures are rare. To investigate the applicability and accuracy of the above methods for corrosion detection in pretensioned bridge girders, we measured pretensioned I-shaped girders exposed to the Norwegian coastal climate for 33 years. We found that, even combined, the above methods can only reliably identify general areas with various probabilities of corrosion. Despite severe concrete cracking and high chloride content, only small corrosion spots were found in strands. Because HCP cannot distinguish corrosion probability in the closely spaced strands from other electrically connected bars, the actual condition of individual strands can be found only when concrete cover is locally removed. Wet concrete with high chloride content and accordingly low HCP and low ER was found only in or near the girder support zones, which can therefore be considered the areas most susceptible to chloride-induced corrosion. We conclude by proposing a procedure for the inspection and assessment of pretensioned girders in a marine environment.

Gradient-based fibre detection method on 3D micro-CT tomographic image for defining fibre orientation bias in ultra-high-performance concrete

Ultra-high-performance fibre reinforced concrete (UHPC) is a class of advanced cementitious composites characterized by its high compressive and flexural strengths, toughness and enhanced durability. The mechanical properties of the UHPC are to a great extent dependent on fibre volume fraction, orientation and distribution within the cementitious matrix. However, determination of the true three-dimensional fibre orientation and distribution is challenging. In this paper micro-computed tomography (micro-CT) is used to determine these parameters. Cylindrical samples of UHPC were extracted from a dogbone tension test specimen and from a pretensioned bridge girder, and high-resolution micro-CT images were then acquired. Using the scanned data, and following three-dimensional image reconstruction and image processing, quantitative fibre information was obtained via a novel image post-processing technique based on local-intensity gradient significantly improving cross-fibre detection compared to existing techniques. The estimated fibre volume fraction is close to design and experimentally measured values. Straight and hooked end fibres in UHPC sample were successfully identified and segmented using this novel technique. The test results show the fibre arrangement to be highly anisotropic with fibres aligned predominantly in one direction, which is attributed to the casting processes and flow.

Influence of excessive end slippage on transfer length of prestressing strands in PC members

The precise estimation of transfer length in prestressed concrete (PC) members is essential to accurately estimate their shear and moment capacities. At present, most of the design guidelines over-simplify transfer length predictions neglecting various factors which significantly affects the transfer length. The goal of the present study is to examine the effects of excessive strand slippage on transfer length, developed stress and the moment envelope of pre-tensioned bridge girders. A 3-D nonlinear finite element modelling technique has been developed to model the bond-slip behaviour between the prestressing strand and the surrounding concrete to appropriately simulate the transfer of prestressing force. The developed modelling technique has been validated using a prismatic mono-strand beam commonly used in laboratories. The validated technique has been then utilized to develop a finite element model for a TxDOT Type A pre-tensioned bridge girder with twelve strands. Additionally, time dependent effects due to shrinkage and creep have been incorporated in the model to analyze the effects of these parameters on transfer length and end slip.The modelling technique developed in the present study was able to adequately capture the linear as well as non-linear response of prestressed members. Finite element studies on the bridge girder showed that the transfer length in the girder increases substantially due to the end slip of the strands. Time dependent analysis showed an average increase of 4% in the transfer length over a period of 94 days. Investigation of the flexural behaviour of the bridge girder with varying strand surface conditions showed that the moment capacity of the girder with significant end slips is reduced in the development region. It can thus be concluded that, strand end slip measurement should be added to the quality control procedures for pre-tensioned members.

Comparative Analysis of Pretensioned Bridge Girder By Using Fem

Comparative Analysis of Pretensioned Bridge Girder By Using Fem

Finite Element and Experimental Investigation on the Flexural Response of Pre-tensioned T-Girders

A number of analytical and numerical approaches exist for modeling concrete structural members. Finite-element analysis (FEA) is a numerical method that is widely applied to concrete structures based on the use of the nonlinear behavior of materials. The challenge of modeling prestressed concrete structures lies in the treatment of the interface between concrete and prestressing tendons. The FEA-modeling technique discussed in this study is based on general-purpose finite-element packages. This study describes FEA of full-scale high-strength self-compacting concrete, HSSCC pre-tensioned T-girders and its comparison with experimental results. Three 9 m length fully pre-tensioned bridge girders, PHSSCC were designed and cast using HSSCC. The girders were instrumented to monitor deflection, pre-tensioned losses, tendon, steel bar, and concrete strains. The girders were then load tested (until failure), predominantly under flexure, and their service and ultimate results including cracking, flexural stiffness, flexural strength, and different ductility indexes were investigated and compared with FEA results. The software package ABAQUS was used to simulate girders and their bonding conditions to verify the accuracy of FEA. A very good agreement was achieved for numerical and experimental crack patterns. The comparison of finite-element modeling (FEM) and experimental results of load-upward and downward deflections indicated satisfactory agreement throughout the load history of the beams until failure. Comparing FEM and experimental results, reasonable agreement was observed for the two methods of ductility indexes. Finite-element modeling tends to overestimate stress in prestressed tendons at the ultimate state of specimens.

Experimental Investigation of Prestress Losses in Full-Scale Bridge Girders

An experimental study was conducted in which 30 full-scale, precast, pretensioned bridge girders were constructed and instrumented with the intention of investigating prestress loss. Several different precast beam fabrication plants were used to investigate the influence of different concrete materials and construction techniques. The constructed girders were conditioned in several different climates for up to 3 years. During this period, prestress loss was measured by using vibrating wire gauges (VWG) embedded in test specimens. Following the conditioning period, the girders were flexural service load-tested to quantify the prestress loss at the time of testing and in turn verify the losses measured using VWGs. Prestress losses were found to be heavily influenced by concrete stiffness, which was dependent on coarse aggregate type and quantity. The measured short- And long-term prestress losses were compared to those determined using several different estimation procedures, suggested by ACI Committee 423.

Implementation of 0.7 in. diameter strands at 2.0 × 2.0 in. spacing in pretensioned bridge girders

Implementation of 0.7 in. diameter strands at 2.0 × 2.0 in. spacing in pretensioned bridge girders

Flexural Behavior of High-Early-Strength Self-Consolidating Concrete Pretensioned Bridge Girders: Experimental Evaluation

A research program investigated the application of high-early-strength self-consolidating concrete (SCC) for precast, prestressed bridge girders. The SCC and conventional concrete (CC) in mixtures had a target 16-h release strength of 34 MPa (5,000 psi). Testing was performed to evaluate the flexural response and bond performance of the girders. This included assessing and comparing camber and deflection, moment-curvature, cracking moment, nominal moment, and crack development of prestressed bridge girders containing SCC and CC. In addition, river gravel and limestone aggregate were used to evaluate the impact of aggregate type on the mechanical properties and bond performance in the full-scale testing of both SCC and CC girders. Early-age characteristics, material properties, and field observations are also documented. Test results indicate that the flexural capacity and bond performance of the SCC girders are similar to those of the companion CC girders. Also, AASHTO equations for the nominal moment were found to be appropriate for SCC girder-deck systems similar to those tested in this study. The AASHTO expressions used were found to be appropriate for estimating the cracking moment for the river gravel SCC girder-deck system, but they slightly overestimated the cracking moment for the limestone SCC girder-deck system.

Strand Debonding for Pretensioned Bridge Girders to Control End Cracks

Characteristic cracks occur at prestressed bridge girder ends during prestress release due to the transfer of the prestress force to the concrete. This research investigated the quantitative and qualitative impact of strand debonding on cracking through nonlinear finite element analysis (FEA) and plant observations. The analysis included plastic behavior of concrete and stress redistribution after tension induced cracking. Prestressed bulb tee girders, 54, 72, and 82 in. (1372, 1829, 2083 mm) deep, were analyzed with 25, 35, and 50% of the strands debonded at the girder end. The tensile strains were used to judge cracking, and were compared with cases that had no debonding. The results showed that 25% debonding can completely eliminate the excessive concrete tension strains associated with cracks in critical locations. For cracks in other locations, related strains were considerably reduced with 25 to 35% debonding, and eliminated with 50% debonding. The selection of the strands to be debonded significantly impacts cracking. Recommendations on debonding strands and desirable bonded strand patterns are presented.

Experimental Study on Full-Scale Pretensioned Bridge Girder Damaged by Vehicle Impact and Repaired with Fiber-Reinforced Polymer Technology

AbstractA bridge was damaged when a dump truck violated the height clearance limitation on Highway 401 in Ontario, Canada. The collision caused extensive damage to the AASHTO Type-III precast/prestressed bridge girders, which led to the closure of the two-lane bridge. Crack mapping showed extensive torsion-shear cracks between the girder quarter points, horizontal crack at the flange-web junctions, and spalled concrete at point of impact. Preliminary elastic testing on the girder established that the flexural capacity of the girder had not been significantly affected. As such, flexural strengthening was not necessary. Crack patterns and severity, followed by analysis, have shown that the girder is deficient in shear capacity. Therefore, the girder was strengthened for shear throughout its entire length using carbon fiber–reinforced polymer (CFRP) sheets. This paper presents a summary of the design and detailing of the elastic behavior test conducted before repair, the girder repair methodology, and result...

Nonlinear finite element modeling of cracking at ends of pretensioned bridge girders

Recent bridge designs have created efficient prestressed concrete girder sections with thin webs, and high levels of prestress. The transfer of the large stresses from strands to concrete causes these slender sections to undergo cracking at the ends of the girders. Due to the large amount of cracking, a nonlinear analysis is necessary to reveal and understand the behavior of the concrete and reinforcement bars at prestress release. Finite element modeling is an excellent tool to perform this task. The accuracy of the analyses, however, depends on the input parameters, some of which are challenging to define for a nonlinear problem. This paper identifies the input parameters and modeling features that have significant impact on the results of nonlinear finite element analyses for pretressed concrete girder ends. The sensitivity of the results to the tensile properties of concrete, the bond properties between concrete and steel rebars and the form of prestress transfer to the concrete were evaluated. The impact of modeling related properties such as the order of elements on the predicted results was also investigated. Available test data was used to verify the modeling techniques. Once verified, the finite element modeling was extended to girders where significant cracking is observed. The full field tensile strain patterns obtained through the verified finite element models are used to explain observed cracking. The effectiveness of the end reinforcement bars, intended to control cracking, was examined.

Bond Performance in Self-Consolidating Concrete Pretensioned Bridge Girders

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Use of 0.7-in.- diameter strands in pretensioned bridge girders

For several years, 0.7-in.-diameter (18 mm) prestressing strands have been successfully used in cable bridges. Using these large-diameter strands in pretensioned concrete girders at 2 in. spacing increases prestressing force, allowing for longer spans, shallower structural depth, and wider girder spacing that the more commonly used 0.6-in.-diameter strands. This paper discusses the design and production issues associated with using 0.7-in.-diameter strands in pretensioned concrete bridge girders. Two full-scale I-girders pretensioned using 0.7-in.-diameter strands were fabricated and tested to address production concerns and evaluate transfer length, development length, and end-zone cracking associated with the 0.7-in.-diameter strands. The results indicate that 0.7-in.-diameter strands can be used with no major changes to the current production practices or AASHTO bridge design specifications. The design and construction of the first pretensioned concrete bridge to use 0.7-in.-diameter (18 mm) strands is highlighted.

Full-Scale Testing of Pretensioned High-Strength Concrete Girders with Debonded Strands

The flexural and shear behavior of three full-scale pretensioned high-strength concrete (HSC) bridge girders, which were designed to a modified bulb tee (BT) section according to AASHTO specifications, were investigated experimentally to evaluate the applicability of high-strength concrete and a higher percentage of debonding ratio to pretensioned bridge girders. The test results indicated that performance in terms of load-carrying capacities, ductility, and crack patterns was improved by using high-strength concrete compared to predictions of AASHTO specifications. In addition, the prestressed concrete (PSC) specimen, in which higher percentages of debonded strands were used, showed superior load-carrying capacities, stiffness, and ductility compared to the specimen in which the number of partially debonded strands did not exceed 25% of the total number of strands. A parametric study on the relationship between concrete strength, debonding ratio, and maximum girder length was conducted. Cracking angle analysis was carried out and compared with the AASHTO specifications and RESPONSE 2000 program.

Bond Strength and Transfer Length of Pretensioned Bridge Girders Cast With Self-Consolidating Concrete

While self-consolidating concrete (SCC) is becoming popular in the United States, there are concerns regarding the bond strength, transfer length, and development length of prestressing strands and mild steel reinforcement with SCC. In this study, a literature survey on the bond strength of SCC was conducted. Pullout tests were performed to determine the bond strength of pretensioning strands and mild steel reinforcing bars. Results show that while the bond strength of SCC with deformed reinforcing bars is adequate, there may be adverse reactions with the use of viscosity-modifying admixtures in SCC.

Prestress Losses in High Performance Lightweight Concrete Pretensioned Bridge Girders

This research investigated prestress losses, creep and shrinkage of pretensioned girders made with expanded slate high performance lightweight concrete. The purpose of the investigation was to determine how long term behavior affects the prestress losses in high strength precast, prestressed concrete bridge girders. The two high performance lightweight concretes (HPLC) developed for this study had strengths of 8000 and 10,000 psi, and air dry unit weights of 116 and 118 lb/ft. Prestress losses were estimated using the American Association of State Highway and Transportation Officials (AASHTO) refined, AASHTO lump sum, Precast/Prestressed Concrete Institute (PCI), and American Concrete Institute (ACI) 209 methods. All these methods overestimated the time dependent losses. This result means that these methods are conservative for estimating time dependent losses of expanded slate HPLC girders.

End Zone Reinforcement for Pretensioned Concrete Girders

In this study, a literature review was conducted to establish the background of current specifications and to evaluate the applicability of various theories and methods for design of end zone reinforcement. Analytical methods reviewed in this paper include finite element analysis, strut- and-tie modeling, and the Gergely-Sozen equivalent beam method. Previous experimental work combined with work conducted as part of this study were used to correlate between various theoretical and experimental results. This paper illustrates that no single theoretical method adequately represents the complex behavior at the end of a pretensioned concrete member. A general semi-empirical design procedure is proposed here. It is based on theoretical behavior and experimental observation. Standard reinforcement details are given. The proposed procedure could result in reduction in the congestion of reinforcement while maintaining acceptable crack control at the member end. Application of the proposed procedure to highly pretensioned bridge girders is demonstrated.

Estimating Post-Tensioning Grout Bleed Resistance Using a Pressure-Filter Test

Grouted tendons are found in the precast, prestressed concrete industry in a number of applications, including post-tensioned tendons added for live load and continuity requirements in pretensioned bridge girders. A key property for a high quality grout is proper bleed resistance. Bleed water trapped in the grouted duct collects at high points and forms voids, leaving steel more vulnerable to attack by aggressive agents. This paper summarizes available pressure-filter test data of grouts along with actual pumping tests over the last 34 years. The data are combined with a calculated pressure approach for determining the required bleed resistance suitable for a particular elevation change. A procedure for carrying out a pressure filter test is given and three numerical design examples for various post-tensioning applications are included. Recommendations are provided for structural elements with high, medium, and low elevation changes. The use of these recommendations should result in grouts that produce a reasonably small amount of bleed water.