Forensic Examination of a Noncomposite Adjacent Precast Prestressed Concrete Box Beam 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. To gain insight into the potential causes of the failure a series of forensic analyses were conducted on the beams decommissioned from the bridge. The study correlates external observations of surface condition with internal chloride profile, depth of carbonation, and existing corrosion. The forensic investigation indicated that strand cover was reduced due to the construction methods of the time. The chloride level in the concrete at the lower layer of strands was high enough that corrosion would be expected. Chloride attack was identified to have come from the leakage of water between beams from the bridge deck surface above. Based on the research findings recommendations are made for visual inspection, and guidelines are provided for condition rating of noncomposite prestressed concrete box beam bridges.     

Inspecting the Lightweight Precast Concrete Panels in the Woodrow Wilson Bridge Deck of 1982

This paper presents the results of a detailed inspection of the deck panels of the Woodrow Wilson Bridge installed in 1982. The original cast-in-place concrete deck, constructed in 1962, was replaced with full-depth lightweight precast concrete deck panels that enabled rapid construction with minimal traffic disruption. The inspection of the Woodrow Wilson deck provides valuable information about the performance of the precast concrete panels, joints, and connections after 20 years of very harsh traffic loads and environmental stressors. The deck panels performed well overall, with the only serious problems at expansion and contraction joints. All of these joints exhibited cracking and rusting. The most prevalent type of cracking appeared to be due to restrained shrinkage between the new polymer concrete, the older precast panels, and the rigid steel joints. This location is more vulnerable to cracking and leaking because there is no prestress across the joint. The multilayered corrosion protection methods used for the transverse and longitudinal post-tensioning tendons were very successful.     

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.     

The risk of hydrogen embrittlement in high-strength prestressing steels under cathodic protection

High strength prestressing steels in prestressed concrete structures are protected against corrosion due to passivation resulting from the high alkalinity of the concrete. If depassivation of the prestressing steel occurs due to the ingress of chlorides the corrosion risk can be minimized by application of cathodic protection with impressed current. The risk of hydrogen embrittlement of the prestressing steel is especially pronounced if overprotection is applied due to hydrogen evolution in the cathodic reaction. The present work considers this risk by hydrogen activity measurements under practical conditions and application of different levels of cathodic protection potentials. Information on threshold potentials in prestressed concrete structures is provided, too.     

Modified Skew Bending Model for Segmental Bridge with Unbonded Tendons

Segmental bridges with unbonded prestressed tendons have some advantages over conventional concrete bridges, such as weather-independent construction and the corrosion protection of the prestressing tendons. This paper analyzes the behavior of a prestressed segmental bridge with unbonded tendons under combined loading of torsion, bending, and shear. According to experimental research, a modified skew bending model was developed to calculate the load-carrying capacity of segmental bridges subjected to combined bending, shear, and torsion. A finite element method (FEM) was used to investigate the deflection behavior of such a structure and to check the theoretical model. The theoretical and FEM research results compared favorably with test results. Finally, suggestions for the design and construction of segmental bridges with external prestressing were made.     

Deflection Control of Concrete Beams Pretensioned by CFRP Reinforcements

Use of carbon fiber reinforced polymers (CFRP) reinforcement for prestressing concrete structures introduces a promising solution for deterioration of concrete structures due to corrosion of steel reinforcements. Due to the low elastic modulus and limited strain at failure of CFRP reinforcement, partial prestressing could be the most appropriate approach to enhance deformability and reduce the cost in comparison to fully prestressed concrete structures. For members reinforced or prestressed with fiber reinforced polymers reinforcements, serviceability requirements may be the governing criteria for the design; therefore, deflection under service loading conditions should be well defined. This paper introduces simplified methods to calculate the deflection of beams prestressed by CFRP reinforcement under short-term and repeated loading. It also examines the applicability of current approaches available to calculate the deflection. Based on an experimental program undertaken at the University of Manitoba, bond factors are introduced to account for tension stiffening of concrete beams prestressed by CFRP. A procedure to determine the location of the centroidal axis of cracked prestressed sections is also proposed. The proposed methods for deflection calculation are calibrated using the results obtained from different experimental programs. Design guidelines are proposed to predict the deflection of beams partially prestressed by CFRP reinforcement.     

Strength-Fatigue Behavior of Fiber Reinforced Polymer Strengthened Prestressed Concrete T-Beams

Strengthening concrete girders with fiber-reinforced polymers (FRP) is becoming an increasingly common practice as more research investigations are favorably qualifying the technique. However, important behavioral aspects, such as fatigue in prestressed concrete beams, are yet to be adequately evaluated. An experimental program was conducted to test five pretensioned, prestressed concrete T beams designed for specific prestressing strand stress ranges under live-load conditions. The experimental testing consisted of precracking the beams, strengthening them with carbon FRP, and mechanically loading them to study the effect of increasing the live load on strand fatigue. The beams were either loaded monotonically to ultimate capacity or cyclically fatigued and then loaded monotonically to failure. All the beams were monotonically loaded past their cracking moment at midspan prior to strengthening, to simulate girders in the field. Beam 1 was tested as a control specimen under static loading up to failure. Beams 2 and 3 were strengthened with carbon FRP to have a design stress range of 124 MPa (18 ksi) under service load condition. Beams 4 and 5 were strengthened to have a higher stress range of 248 MPa (36 ksi). For all the strengthened beams, the failure mode observed was FRP rupture. The results favorably qualify the application of FRP strengthening to increase the live load of concrete beams prestressed with straight strands.     

Longitudinal Cracking Distress on Continuously Reinforced Concrete Pavements in Illinois

The Illinois Department of Transportation (IDOT) initiated a failure investigation to determine the distress mechanisms causing premature longitudinal cracking on continuously reinforced concrete pavements (CRCP) on several Illinois interstates. The longitudinal cracking approximately followed the embedded reinforcement steel and occurred in both the driving and passing lanes. In this paper, the results from field visual surveys, coring, and petrographic analyses are reported along with a review of archival construction and material records of the distressed CRCP sections. A laboratory forensic study was also performed on several field extracted slabs. The results of the field and laboratory investigation show the cracking was not initiated by steel corrosion, deleterious reactions in the concrete materials, or an inadequate structural design. Rather, the cracking is related to settlement of the steel bars in the concrete. Settlement cracking is conventionally thought to occur only in concrete slabs and decks with plastic (high slump) concrete and small values of bar cover depth, while the studied CRCP sections have large values of cover depth and were cast with stiff (low slump) concrete. The settlement was likely caused by the relative settlement of heavy steel bars (22?mm diameter) within the lower density concrete during the original CRCP construction. The technique of placing the steel bars in the fresh concrete (called tube-feeding) further contributed to the development of this distress, and this practice is no longer employed by IDOT.     

Flexural Behavior of an Ultrahigh-Performance Concrete I-Girder

The flexural behavior of an ultrahigh-performance concrete (UHPC) was investigated through the testing and related analysis of a full-scale prestressed I-girder. A 28?ksi (193?MPa) compressive strength steel fiber reinforced concrete was used to fabricate an 80?ft (24.4?m) long AASHTO Type II girder containing 26 prestressing strands and no mild steel reinforcement. Intermediate and final behaviors, including cracking, flexural stiffness, and moment capacity, were investigated. Test results are compared to predictions based on standard analytical procedures. A relationship between tensile strain and crack spacing is developed. The uniaxial stress-strain response of UHPC when subjected to flexural stresses in an I-girder is determined and is verified to be representative of both the stress and flexural stiffness behaviors of the girder. A flexural design philosophy for this type of girder is proposed.     

Theoretical Study on Short-Term and Long-Term Deflections of Fiber Reinforced Polymer Prestressed Concrete Beams

This paper presents the methods for predicting the short-term and time-dependent deflections of fully or partially prestressed concrete beams with fiber reinforced polymer (FRP) tendons under sustained bending moment and axial force. The age-adjusted effective modulus method is used to model the creep behavior in the concrete and the relaxation in the FRP prestressing tendons. A tension-stiffening model is proposed to evaluate the stiffness of the section after cracking. The analytical values are compared to the test results and it is found that the analytical values are in good agreement with the experimental results.     

Theoretical Analysis of Transfer Lengths in Pretensioned Prestressed Concrete Members

The realistic design of pretensioned prestressed concrete members requires adequate determination of transfer length for prestress forces. The purpose of the present paper is to propose a rational theory, which can evaluate the transfer lengths realistically for arbitrary designed pretensioned members. The theory considers the prestressing steel as a solid cylinder and the surrounding concrete as a hollow cylinder. The compatibility condition is then imposed at the steel–concrete interface with an appropriate equilibrium equation. The possible cracking of surrounding concrete in a radial direction due to expansive pressure after prestress transfer has been considered by employing an appropriate tensile stress–crack width relation. The equilibrium equations are solved for each successive segment in longitudinal direction and the strain buildup curves from the end of pretensioned members are obtained, which provides the basis for the determination of transfer length. Comprehensive tests were conducted to measure the transfer lengths for various design variables, including the concrete strength, strand diameter, cover thickness, and strand spacing. The measured values of transfer lengths were compared with the calculated ones and the comparison indicates that the theoretical prediction exhibits good correlation with test data. The proposed theory allows more realistic prediction of transfer lengths for rational design of actual pretensioned prestressed concrete members.     

Comparison of Prestress Losses for a Prestress Concrete Bridge Made with High-Performance Concrete

Five prestressed concrete girders made with high-performance concrete were instrumented using vibrating-wire strain gages. Their behavior was monitored for three years from the time of casting. The measured change in concrete strain at the centroid of the prestressing strands was used to evaluate changes in prestress. The total measured prestress loss was as large as 28% of the total jacking stress. Due to the higher stresses, this loss is larger than would be expected for a girder made with conventional-strength concrete. The observed values of prestress losses were compared with values calculated using the recommended AASHTO LRFD and NCHRP 18-07 procedures. The AASHTO LRFD method overpredicted the average prestress losses for the highly stressed Span 2 girders by 20% while the NCHRP method underpredicted the average losses by 16%. The NCHRP method was found to be more inclusive and adaptable to regional construction. The calculated NCHRP Span 2 losses were found to be within 10% of the average measured losses when the elastic shortening losses were calculated based on measured data and differential shrinkage was calculated based on continuous beams.     

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.     

Performance of Segmental and Posttensioned Bridges in Europe

With a history a decade or two longer than in the United States, the October 1999 Scanning Tour by the Federal Highway Administration was to examine European performance, durability and maintenance of prestressed concrete, segmental, and cable-stayed bridges to help identify possible concerns and to estimate future needs for maintenance, repair, retrofit or replacement in the United States. All countries reported corrosion of prestressing tendons, concrete, or reinforcing steel—but generally in a minority (2% or so) of structures—from poor quality grouting of tendons or honeycombed concrete allowing ingress of water and chlorides. For new construction, improved grouts and stringent practices have been introduced. Both external and internal tendons are used in European segmental construction. More “robust” ducts of durable polyethylene are being introduced (Switzerland) and new “greased and sheathed” monostrands find favor for repair or retrofit. Where appropriate, new fiber composite materials are used for rehabilitation as in the United States. Widespread European policy is to apply waterproof membranes, drainage, and protective overlays to bridge decks of all types of construction. Less aggressive deicing is being introduced. Structures have been replaced mostly for functional obsolescence rather than deterioration. Maintenance inspection is similar to that in the United States but with a greater commitment to upkeep. Available nondestructive investigation techniques for tendons and cable-stays include X-ray, ultrasonic, electrical resistance, magnetic perturbation, georadar, etc., but their use requires engineering expertise and interpretation. Instrumentation with remote monitoring is occasionally installed on major structures. European cable-stay structures are performing well. Current trends are to greased and sheathed monostrands in high-density polyethylene pipes. Wind-rain vibrations are suppressed by ribbed stay-pipes and∕or various types of damping installed during or after construction. Segmental and cable-stay developments in Europe and the United States are moving in parallel directions and improved technology. With appropriate attention to improved grouting, these types of structures continue to be built and will serve well into the foreseeable future.     

CFRP Prestressed High-Strength Concrete Prisms Subjected to Direct Tension

This paper describes the behavior of carbon fiber-reinforced polymer (CFRP) prestressed high-strength concrete prisms under direct tension. Seven prestressed concrete prisms with different levels of prestressing were cast and tested. Prisms were 50×50?mm in cross section and their lengths varied between 1,400 and 2,000?mm. Concrete compressive strength was as high as 147?MPa. Tension stiffening, crack width, and crack spacing in prisms were investigated. Concrete properties, such as the stress–strain relationship under direct tension and bond strength, were also determined. Test results revealed that tension stiffening in CFRP prestressed high-strength concrete is significant when higher concrete strength and higher prestressing level are applied. Tension stiffening factors are proposed based on the postcracking behavior of concrete. Experimental results also showed that increasing the prestressing level increases the amount of tension stiffening and reduces the number of cracks, which delays their appearance. However, cracks widened at a faster rate in the prisms with higher prestressing levels. Experimental results were compared with Comite Euro-International du Beton and American Concrete Institute proposed equations. Modifications were suggested for the above-mentioned equations to account for use of CFRP bars in prestressed sections.     

Effects of Temperature Variations on Precast, Prestressed Concrete Bridge Girders

The monitoring of a precast, prestressed girder bridge during fabrication and service provided the opportunity to observe temperature variations and to evaluate the accuracy of calculated strains and cambers. The use of high curing temperatures during fabrication affects the level of prestress because the strand length is fixed during the heating, the coefficients of thermal expansion of steel and concrete differ, and the concrete temperature distribution may not be uniform. For the girders discussed here, these effects combined to reduce the calculated prestressing stress from the original design values at release by 3 to 7%, to reduce the initial camber by 26 to 40%, and to increase the bottom tension stress in service by 12 to 27%. The main effect of applying the standard service temperature profiles to the bridge was to increase the bottom stress by 60% of the allowable tension stress. These effects can be compensated for by increasing the amount of prestressing steel, but in highly stressed girders, such an increase leads to increased prestress losses (requiring yet more strands) and higher concrete strength requirements at release.     

Improved Longitudinal Joint Details in Decked Bulb Tees for Accelerated Bridge Construction: Fatigue Evaluation

This companion 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, which are cast and prestressed with the girder, provide benefits of rapid construction along with improved structural performance and durability. Despite these advantages, the 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 the perceived problem with durability of longitudinal joints used to connect adjacent girders. Four full-scale slabs connected by No. 16 (#5) headed reinforcement detail using a 152 mm (6 in.) lap length were fabricated and tested. An analytical parametric study was conducted to provide a database of maximum forces in the longitudinal joint. These maximum forces are then used to determine the loading demand necessary in the slab testing due to the service live load. Static and fatigue tests under four-point pure-flexural loading, as well as three-point flexural-shear loading, were conducted. Test results were evaluated based on flexural capacity, curvature behavior, cracking, deflection, and steel strain. Based on these test results, the improved longitudinal joint detail is a viable connection system that transfers the forces between the adjacent decked bulb tee girders.     

Prestressing Schemes for Incrementally Launched Bridges

Incremental launching is a competitive construction method for medium-span prestressed concrete bridges. Compared with other techniques for in situ casting, in short bridges it is an alternative to the use of falseworks and reduces the cost of labor with the same investment. In longer bridges it is an alternative to movable shuttering systems and reduces both investment and labor cost. Compared with segmental precasting, it may reduce both investment and the cost of prestressing, which may be partial instead of total, with the same advantages in terms of industrial production. Due to its competitiveness and overall quality, this construction method is widely used in Europe. During launch, the superstructure is moved over fixed bearings. The superstructure dead load produces temporary flexural and shear stresses within the cross section that are quite different from those produced by the service loads and, consequently, require special prestressing schemes, thoroughly illustrated in this paper.     

50-Year-Old Prestressed Segmental Concrete Bridges

The first prestressed segmental concrete bridge in the United States opened to traffic was a small bridge in Madison County, Tennessee. The bridge was constructed using prestressed concrete segments and was opened to traffic in October 1950. Prestressed concrete beams were placed side by side to form the superstructure of the bridge. The construction of this bridge and several other similar prestressed concrete bridges are described herein. The existing condition of eleven prestressed concrete bridges remaining in Tennessee is given. Only minor spalling, leaching, and horizontal cracking are present in the superstructure after fifty years of service. Many of the design features introduced in this design can be found in today’s modern precast segmental concrete bridges.