Improved Longitudinal Joint Details in Decked Bulb Tees for Accelerated Bridge Construction: Concept Development

This paper focuses on an investigation of improved continuous longitudinal joint details for decked precast prestressed concrete girder bridge systems. Precast concrete girders with an integral deck that is cast and prestressed with the girder provide benefits of rapid construction along with improved structural performance and durability. Despite these advantages, use of this type of construction has been limited to isolated regions of the United States. One of the issues limiting more widespread use is a perceived problem with durability of longitudinal joints used to connect adjacent girders. This paper presents the results of a study to assess potential alternate joint details based on constructability, followed by testing of selected details. Seven reinforced concrete beam specimens connected with either lapped headed reinforcement or lapped welded wire reinforcement were tested along with a specimen reinforced by continuous bars for comparison. Test results were evaluated based on flexural capacity, curvature at failure, cracking, deflection, and steel strain. Based on the survey and the experimental program, a headed bar detail with a 152 mm (6 in.) lap length was recommended for replacing the current welded steel connector detail.     

Effect of Intermediate Diaphragms on Decked Bulb-Tee Bridge System for Accelerated Construction

One of the promising systems for accelerated bridge construction is the use of the decked precast prestressed concrete girders or decked bulb-tee girders for the bridge superstructure. Using the calibrated three-dimensional finite-element models through field tests, a parametric study was conducted to determine the effect of intermediate diaphragms on the deflections and flexural strains of girders at the midspan as well as the live load forces in the longitudinal joint. The following diaphragm details were considered: different diaphragm types (steel and concrete), different diaphragm numbers between two adjacent girders, and different cross-sectional areas for steel diaphragms. Five bridge models with different diaphragm details were developed, and the short span length effect on the bridge behavior was also studied. It was found that as long as one intermediate diaphragm was provided between two adjacent girders at midspan, changing the diaphragm details did not affect the girder deflection, the girder strain, and the live load forces in the longitudinal joint significantly. The effect of diaphragms on the midspan deflection was more prominent in the short span bridge; however, the reduction in the maximum bending moment by the diaphragms was more significant in the long span bridge than in the short span bridge. Specific design recommendation is provided in this paper.     

Experimental Determination of Resistance Characteristics of Support Details Used in Prestressed Concrete Bridge Girders

Static load tests were performed on support details used at the ends of prestressed concrete pedestrian bridge girders to determine the resistance characteristics of girder supports in the direction perpendicular to the longitudinal axis of the girders. The specimens tested represent support details that have also been widely used in prestressed concrete highway bridges in Minnesota and in other states. Two specimens, one representing the free-end detail and one representing the restrained-end detail were subjected to a combination of vertical and lateral loads. The applied loading was intended to simulate the loading conditions to which the girder ends would be subjected in the event of an over-height vehicle collision with the bridge. The tests revealed two types of lateral load resisting mechanisms depending on the type of support detail. The specimen with the free-end detail resisted the lateral loading through sliding friction between the components of the support assembly. Deformation of this specimen was a combination of shear deformation of the bearing pad and sliding of various support components. The restrained-end detail exhibited larger lateral load capacity than the free-end detail due to the resistance provided by the anchor rods that were intended to prevent the lateral movement of the girder ends. Failure of the specimen with restrained-end detail was due to the concrete breakout and bending of the anchor rods.     

Nonlinear Flexural Behavior of Prestressed Concrete Girder Bridges

This paper presents a procedure to improve the accuracy of the classical grillage method for the nonlinear analysis of concrete girder bridges. The procedure uses equivalent element plastic hinge lengths that account for the actual mesh size instead of using a mesh-independent global plastic hinge length. A thorough review of the results of tests conducted on two 1∕3-model prestressed concrete girders and a 1∕3-model prestressed concrete girder bridge is undertaken in order to model the nonlinear properties of prestressed concrete girder bridges. The purpose of this review is to study the extent of plastification and plastic hinge length development as well as the evaluation of the validity of the grillage method for the nonlinear analysis of girder bridges. An Lp transfer model is used to calculate the plastic hinge length for every beam element of the grillage based on the results from the experiments and other empirical models. The Lp transfer model allows the use of empirical data obtained from tests on individual girders to model the response of a variety of bridge configurations subjected to different loading conditions. The equivalent grillage element plastic hinge length Lgp is calculated as a function of the grillage mesh size. A number of examples are presented to demonstrate the validity of the proposed method by comparing the analytical results of grillage analysis using the Lp transfer model with those of laboratory and in situ tests on full-scale and model-scale prestressed concrete bridges. The proposed approach has a high potential for use in engineering practice because of the simple input requirement and improved accuracy.     

Behavior of Prestressed Concrete Strengthened with Various CFRP Systems Subjected to Fatigue Loading

Many prestressed concrete bridges are in need of upgrades to increase their posted capacities. The use of carbon fiber-reinforced polymer (CFRP) materials is gaining credibility as a strengthening option for reinforced concrete, yet few studies have been undertaken to determine their effectiveness for strengthening prestressed concrete. The effect of the CFRP strengthening on the induced fatigue stress ratio in the prestressing strand during service loading conditions is not well defined. This paper explores the fatigue behavior of prestressed concrete bridge girders strengthened with CFRP through examining the behavior of seven decommissioned 9.14?m (30?ft) girders strengthened with various CFRP systems including near-surface-mounted bars and strips, and externally bonded strips and sheets. Various levels of strengthening, prestressing configurations, and fatigue loading range are examined. The experimental results are used to provide recommendations on the effectiveness of each strengthening configuration. Test results show that CFRP strengthening can reduce crack widths, crack spacing, and the induced stress ratio in the prestressing strands under service loading conditions. It is recommended to keep the prestressing strand stress ratio under the increased service loading below the value of 5% for straight prestressing strands, and 3% for harped prestressing strands. A design example is presented to illustrate the proposed design guidelines in determining the level of CFRP strengthening. The design considers the behavior of the strengthened girder at various service and ultimate limit states.     

Field Test and 3D FE Modeling of Decked Bulb-Tee Bridges

This paper summarizes field-testing of eight decked bulb-tee girder bridges as well as development of three-dimensional finite-element (FE) models. Using the calibrated 3D FE models, parametric studies have been performed to study the effect of shear connectors and intermediate diaphragms on live-load distribution and connector forces. It was found that: (1) in all cases studied, the live- load distribution factor (DF) for a single-lane loaded bridge was smaller than one for a double-lane loaded bridge; (2) connector forces caused by wheel loads were not uniform along the longitudinal joint—adding intermediate diaphragms tended to reduce the difference among horizontal shear forces in connectors; (3) the maximum horizontal shear force increased with the increase of the connector spacing—intermediate diaphragms reduced the maximum horizontal shear force in connectors; (4) the maximum vertical shear force and in-plane normal tensile force in connectors do not necessarily increase with the increase of the connector spacing; and (5) the summation of connector forces in each direction along the longitudinal joint remained constant irrespective of the number of connectors in the joint.     

Seismic Performance Assessment of Simply Supported and Continuous Multispan Concrete Girder Highway Bridges

Seismic evaluations of typical concrete girder bridges are conducted for both a multispan simply supported and a multispan continuous girder bridge common to the Central and Southeastern United States. These evaluations are performed for an approximate hazard level of 2% in 50?years by performing nonlinear time history analyses on three-dimensional analytical models. The results show significant vulnerabilities in the reinforced concrete columns, the abutments, and also in unseating of the girders. In general, the longitudinal loading of the bridges results in larger demands than the transverse loading. However, the simply supported bridge sustains bearing deformations in the transverse direction which are on the same order as their longitudinal response. These results suggest that both longitudinal and transverse loading are significant and should be considered when performing seismic hazard analyses of these bridges.     

Live Load Distributions on an Impact-Damaged Prestressed Concrete Girder Bridge Repaired Using Prestressed CFRP Sheets

This paper describes detailed flexural behavior, including live load distributions, of a four-span prestressed concrete girder bridge supported by 14?m long C-shape girders (4 @ 14.05 = 56.2?m). The bridge has been damaged by frequent impact from heavy trucks, and repaired using prestressed carbon fiber-reinforced polymer sheets. A calibrated finite element analysis is conducted to investigate the flexural behavior (i.e., stress redistribution, deflection, live load distribution, and applied load effects) of the bridge in three different phases (i.e., undamaged, damaged, and repaired states) under various loading configurations. Strain localizations are noted at the damaged and repaired locations. Assessment of existing bridge codes such as the Association of State Highway and Transportation Officials Load Resistance Factor Design and Canadian Highway Bridge Design Code is conducted. The bridge codes predict well the nominal live load effect on the exterior girder, but underestimate the effect on the interior girders. A refined analysis may be recommended for this type of bridge.     

Development of Flexural Strength Rating Procedures for Adjacent Prestressed Concrete Box Girder Bridges

An investigation was conducted on noncomposite prestressed precast concrete adjacent-box-beam bridges that suffered catastrophic failures resulting from the corrosion of the prestressing steel. These failures highlight the need to improve the methods used to detect corrosion damage and, subsequently, to load rate the damaged members. Currently, the inspection of concrete box girder sections relies on visual methods that correlate longitudinal and transverse cracking, spalling, and exposed strands with the rated level of performance of the member. To improve the current inspection techniques, visual assessment methods were examined through the destructive evaluation and material characterization of seven box-beam segments. The research results indicate that the fabrication techniques used for box-beam construction in the 1950–1960 time period allowed for large variations in construction tolerance. Half-cell methods were shown not to provide an accurate or reliable method of identifying the corrosion of prestressing strands. Longitudinal cracking was shown to be an accurate and reliable indicator of the underlying corrosion of prestressing strands. The probability of corrosion on strands adjacent to longitudinal cracks was determined and quantified. On the basis of the results, a new recommendation for determining the residual flexural strength of corroded prestressed beams is provided.     

Live Load Distribution Formulas for Single-Span Prestressed Concrete Integral Abutment Bridge Girders

In this study, live load distribution formulas for the girders of single-span integral abutment bridges (IABs) are developed. For this purpose, two and three dimensional finite-element models (FEMs) of several IABs are built and analyzed. In the analyses, the effects of various superstructure properties such as span length, number of design lanes, prestressed concrete girder size, and spacing as well as slab thickness are considered. The results from the analyses of two and three dimensional FEMs are then used to calculate the live load distribution factors (LLDFs) for the girders of IABs as a function of the above mentioned parameters. The LLDFs for the girders are also calculated using the AASHTO formulas developed for simply supported bridges (SSBs). The comparison of the analyses results revealed that LLDFs for girder moments and exterior girder shear of IABs are generally smaller than those calculated for SSBs using AASHTO formulas especially for short spans. However, AASHTO LLDFs for interior girder shear are found to be in good agreement with those obtained for IABs. Consequently, direct live load distribution formulas and correction factors to the current AASHTO live load distribution equations are developed to estimate the girder live load moments and exterior girder live load shear for IABs with prestressed concrete girders. It is observed that the developed formulas yield a reasonably good estimate of live load effects in prestressed concrete IAB girders.     

Structural Testing of Prestressed Concrete Girders from the Lake View Drive Bridge

On the evening of December 27, 2005, the fascia beam supporting the east-side parapet wall of the third span of the Lake View Drive Bridge failed under the action of dead load. This paper describes the structural testing and posttest forensic examination of two girders recovered from the partially collapsed Lake View Drive Bridge. The objective of this paper is to describe the tests conducted and report the observations. An interior and an exterior prestressed concrete adjacent box girder were tested to failure in flexure. Prior to testing, an extensive visual inspection was conducted to assess the extant condition of the 42-year-old girders. Following testing, the girders were sawcut near their failure regions to permit an extensive forensic investigation. Conclusions based on the pre- and posttest inspections and test results are presented. Recommendations intended to reinforce issues that need to be considered in the bridge inspection and rating process of similar structures are presented.     

Torsional Design of Hybrid Concrete Box Girders

Hybrid concrete box-girder bridges that include prestressed slabs and corrugated steel webs provide a major improvement over traditional prestressed concrete box-girder bridges. To reduce the self-weight, high strength concrete is used for the top and bottom slabs and corrugated steel webs are employed for the webs. Because the weight of the girders has been reduced, the span length can be increased for more cost-effective design. A series of systematic tests on hybrid concrete box girders subjected to torsion has been performed. According to the test results, an analytical model was developed. Using the developed analytical model, a step-by-step procedure for torsional design of such bridges is presented in this article. Based on the design procedure proposed, a girder is designed by the analytical model and checked to satisfy structural codes.     

Experimental Study on Prefabricated Concrete Bridge Girder-to-Girder Intermittent Bolted Connections System

This paper reports on a new bridge deck slab flange-to-flange connection system for precast deck bulb tee (DBT) girders. In prefabricated bridge system made of DBT girders, the concrete deck slab is cast with the prestressed girder in a controlled environment at the fabrication facility and then shipped to the bridge site. This system requires that the individual prefabricated girders be connected through their flanges to make it continuous for live load distribution. The objectives of this study are to develop an intermittent bolted connection for DBT bridge girders and to provide experimental data on the ultimate strength of the connection system. This includes identifying the crack formation and propagation, failure mode, and ultimate load carrying capacity. In this study, three different types of intermittent bolted connection were developed. Four actual-size bridge panels were fabricated and then tested to collapse. The effects of the size and the level of the fixity of the connecting steel plates, as well as the location of the wheel load were examined. The developed joint was considered successful if the experimental wheel load satisfied the requirements specified in North American bridge codes. It was concluded that location of the wheel load at the deck slab joint affected the ultimate load carrying capacity of the connections developed. Failure of the joint was observed to be due to either excessive deformation and yielding of the connecting steel plates or debonding of the embedded studs in concrete.     

Analytical Model for CFRP-Strengthened Prestressed Concrete Girders Subject to Cyclic Loading

An analytical model is presented to simulate the behavior of prestressed concrete girders strengthened with various carbon fiber-reinforced polymer systems and subjected to static and cyclic loading. The initial concrete strains owing to prestressing and girder self weight load at the moment of the application of the strengthening system and the concrete cyclic creep as a result of the cyclic loading are considered in the model. Experimental results are used to validate the analytical model. Additionally, deflection and concrete strain increases on account of the cyclic loading are compared to the values provided by Comité Euro-International du Béton and Fédération Internationale de la Précontrainte (CEB-FIP) and Asso?i?o Brasileira de Normas Técnicas (NBR) 6118 codes. Deflection and concrete strain obtained from the analytical model were above those observed in the tested girders, especially after 100,000?cycles, owing to the logarithmic function used to express the fatigue behavior of concrete. In general, deflection provided by CEB-FIP was above experimental and analytical deflection, but otherwise concrete strain values provided by NBR 6118 were close to experimental results.     

Shear Lag Effect in Simply Supported Prestressed Concrete Box Girder

In this paper, derivation and computed formulas are provided for the shear lag coefficient in a simply supported prestressed concrete box girder under dead load. In the case of prestressed tendons having parabolic configurations, formulas to compute the shear lag effect are also developed. The magnitude of upward loading intensity caused by prestress as well as the relationship between the height of the box girder and the sag of prestressed tendons have been fully treated. Conclusions are drawn that the shear lag effect caused by dead load and prestress force is equivalent to dead load acting alone, provided that the prestressed tendon is set up with a parabolic profile. Shear lag effect caused by movable load is also analyzed according to the eccentricity of the load to the half-width ratio of the box girder. Charts were prepared to predict the shear lag coefficient for live load. Finally, having considered the shear deformation of flanges, the deflection of box girders is studied for both uniformly distributed load and concentrated load. Examples are given for illustrative purpose.     

Live-Load Distribution Factors for Prestressed Concrete, Spread Box-Girder Bridge

This study presents an evaluation of shear and moment live-load distribution factors for a new, prestressed concrete, spread box-girder bridge. The shear and moment distribution factors were measured under a live-load test using embedded fiber-optic sensors and used to verify a finite element model. The model was then loaded with the American Association of State Highway and Transportation (AASHTO) design truck. The resulting maximum girder distribution factors were compared to those calculated from both the AASHTO standard specifications and the AASHTO LRFD bridge design specifications. The LRFD specifications predictions of girder distribution factors were accurate to conservative when compared to the finite element model for all distribution factors. The standard specifications predictions of girder distribution factors ranged from highly unconservative to highly conservative when compared to the finite element model. For the study bridge, the LRFD specifications would result in a safe design, though exterior girders would be overdesigned. The standard Specifications, however, would result in an unsafe design for interior girders and overdesigned exterior girders.     

Demonstration of Use of High-Performance Lightweight Concrete in Bridge Superstructure in Virginia

The general objective of this research was the construction and evaluation of a bridge using high-performance lightweight concrete (HPLWC). The resulting bridge over the Chickahominy River near Richmond, Va., consists of 15 prestressed American Association of State Highway and Transportation Officials (AASHTO) Type IV girders made of HPLWC with a density of 1,920?kg/m3 and a minimum required 28-day compressive strength of 55?MPa. The bridge also has a lightweight concrete (LWC) deck with a density of 1,850?kg/m3 and a minimum required 28-day compressive strength of 30?MPa. This research study is chiefly concerned with investigating the effects of using lightweight concrete in prestressed girders on transfer length, development length, flexural strength, girder live-load distribution factor, and dynamic load allowance. Transfer length was determined to be 432?mm, or 33?db, for several girders at the time of prestress transfer. The development length was determined to be between 1,830 and 2,440?mm, while the flexural strength ranged from 11 to 30% higher than the AASHTO flexural capacity. The measured distribution factors and dynamic load allowance were smaller than the AASHTO standard and LRFD values.     

Combined Effect of Loading and Cold Temperature on the Stiffness of Glass Fiber Composites

Because of the short construction season and cold winters in Alaska, the prestressed concrete decked bulb-tee bridge system is very popular. However, the concrete deck is an integral part of the bridge superstructure and cannot be easily replaced when it deteriorates. Obviously, there is merit in combining durable “premanufactured” fiber-reinforced polymer (FRP) composite deck with stiffer prestressed concrete girders in cold regions. However, the effects of long-term exposure to extreme temperature variations and various moisture conditions typical of cold regions on the performance of FRP composite materials are not fully understood. This paper summarizes the combined effect of low-temperature and deformation strain levels on the longitudinal modulus of glass fiber-reinforced polymer (GFRP) samples. The modulus of elasticity of GFRP laminate coupons was tested at various temperatures down to ?31 °F (?35°C) by temporarily subjecting the samples to three strain levels of 1,000, 2,000, or 3,000 microstrains. Both biaxial and uniaxial samples subjected to a deformation of 1,000 microstrains showed an increase in stiffness when tested at increasingly colder temperatures, and no noticeable change in stiffness was seen when the samples were retested after being equilibrated to room temperature. However, samples subjected to a predetermined elevated strain level did show significant stiffness degradation after room temperature equilibration. The degree of degradation was noticeably larger for samples subjected to the low temperatures than for control samples that were subjected to the equivalent number of cycles at room temperature. It was also noted that the degradation due to load cycles or temperature coupled with load cycles was noticeably less for uniaxial samples than for biaxial samples.     

Composite Action and Adhesive Bond between Fiber-Reinforced Polymer Bridge Decks and Main Girders

This paper describes the behavior of hybrid girders consisting of fiber-reinforced polymer (FRP) bridge decks adhesively connected to steel main girders. Two large-scale girders were experimentally investigated at the serviceability and ultimate limit state as well as at failure. One of the girders was additionally fatigue loaded to 10 million cycles. Compared to the behavior of a reference steel girder, deflections of the two girders at the SLS were decreased by 30% and failure loads increased by 56% due to full composite action in the adhesive layer. A ductile failure mode occurred: Deck compression failure during yielding of the steel girder. The adhesive connections were able to prevent buckling of the yielding top steel flanges. Thus, compared to the reference steel girder, the maximum deflections at failure could be increased up to 130%. No deterioration due to fatigue loading was observed. Based on the experimental results, a conceptual design method for bonded FRP/steel girders was developed. The proposed method is based on the well-established design method for hybrid girders with concrete decks and shear stud connections. The necessary modifications are proposed.     

Tests of RC Deck Girders with 1950s Vintage Details

Large numbers of conventionally reinforced concrete (CRC) bridges in the national bridge inventory built during the 1950s are lightly reinforced for shear. Inspections revealed many of these bridges exhibit diagonal cracks resulting in load postings, monitoring, emergency shoring, repairs, and unscheduled bridge replacements. A research program was conducted to investigate the behavior and capacity of CRC bridge girders with vintage details. Laboratory tests of large-size girders representative of 1950s design and construction practice were carried out. Various steel reinforcement configurations were tested. Loading conditions were varied to reproduce girder behavior at different positions in a bridge and various loading protocols were considered. Test results provide a comprehensive data set for comparison of analysis methods and repair strategies; and indicated that anchorage of flexural steel was key to developing higher ultimate capacity, initial crack damage may not necessarily contribute to the final failure mode, and crack width alone may not indicate the level of damage to the beam.