Effects of Fabrication Procedures on Fatigue Resistance of Welded Joints in Steel Orthotropic Decks

A common practice for the fabrication of steel orthotropic bridge decks in the United States is to use 80% partial joint penetration (PJP) groove welds between the closed ribs and deck plate. However, it is difficult to eliminate weld melt-through with the thin rib plates. Heat straightening after welding, sometimes combined with precambering, is used to meet the deck plate flatness requirement. To study the effects of both weld melt-through and distortion control measures on the fatigue resistance of the rib-to-deck plate welded joint, six full-scale two-span orthotropic deck specimens were subjected to laboratory testing. Specimens, 10 m long and 3 m wide with four closed ribs, were fabricated with and without weld melt-through and were heat straightened; three specimens were also precambered. To simulate the effect of repetitive truck traffic, each specimen was tested up to 8 million cycles. Test results showed that six cracks initiated from the weld toe outside the rib. Only one crack developed at the weld root inside the rib; this crack initiated from a location transitioning from the 80% PJP to 100% penetration weld. None of the cracks propagated through the deck plate thickness. Precambering was beneficial in fatigue resistance as two effectively precambered specimens did not experience cracking in the PJP welds.     

Consistent Approach to Calculating Stresses for Fatigue Design of Welded Rib-to-Web Connections in Steel Orthotropic Bridge Decks

The current (2004) fatigue design provisions in the 3rd Ed. of the AASHTO LRFD Bridge Design Specifications identify and classify the rib-to-web (rib-to-diaphragm) connections commonly utilized in steel orthotropic bridge decks where cutouts are used. The fatigue resistance of these details has been established through full-scale laboratory testing. This paper examines how the fatigue stress range was defined and determined during the testing which established the fatigue resistance of the details. A procedure to calculate or measure stresses at the rib-to-diaphragm connection, which is consistent with the fatigue resistance published in the AASHTO LRFD Bridge Design Specifications, is presented.     

Moving-Wheel Fatigue for Bridge Decks Strengthened with CFRP Strips Subject to Negative Bending

This paper presents the negative bending of reinforced concrete slabs strengthened with near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) strips. Six slab specimens, three of which are strengthened with CFRP strips, are tested in static and fatigue loads. A wheel-running fatigue test machine is used to simulate vehicular loads on a bridge deck. The effectiveness of CFRP strengthening for bridge decks in cantilever and pseudonegative bending is examined based on moment-carrying capacity and cyclic behavior under the wheel-running fatigue loads, including crack patterns and damage accumulation. The moment-carrying capacity (static) of the cantilever slab strengthened with the NSM CFRP strips is improved by 68.4% when compared to that of an unstrengthened slab. The damage accumulation rate of the strengthened cantilever slab owing to the fatigue load is significantly lower than that of the unstrengthened slab. The damage accumulation of the strengthened slab gradually increases and is irreversible when the fatigue cycles increase. The fatigue-induced flexural cracks of the slabs develop along the wheel-running direction. A simple predictive model is presented to estimate the fatigue life of the test slabs.     

Fatigue Evaluation of Rib-to-Deck Welded Joints of Orthotropic Steel Bridge Deck

This study reported fatigue test results of 300-mm-wide specimens with three details: 80% partial joint penetration (80%PJP), weld melt-through (WMT), and both. The specimens were cut out from full-scale orthotropic deck specimens of 16-mm-thick deck plate. In the fatigue test, the deck plate was subjected to cyclic bending loading and the rib was free from loading. The fatigue fracture surfaces showed that the presence of WMT may affect the initiation of fatigue cracks. A propensity to root cracking rather than toe cracking was observed. Plotting fatigue test results in an S-N diagram showed that the specimens with WMT seemed to have slightly lower fatigue strengths than the 80%PJP specimens, but the difference is more likely to be within a usual scatter of test data, which means that both details have comparable fatigue strength. The present test results satisfied the S-N curves of JSSC-E (80?MPa at 2×106 cycles) or AASHTO-C (89?MPa at 2×106 cycles).     

Application of Orthotropic Thin Plate Theory to Filled Steel Grid Decks for Bridges

Although AASHTO LRFD specifications provide moment capacity equations as an approximate design method and recommend an orthotropic plate model as the refined method for the analysis of filled grid decks, no guidelines are provided for the determination of the flexural rigidities associated with the plate analysis. This technical note briefly reviews orthotropic thin plate theory, discusses the determination of the flexural rigidities using Huber’s assumption, and applies the theory to concrete-filled steel grid decks. The accuracy of the orthotropic plate analysis is assessed by comparing it to results of an earlier finite-element analysis.     

LRFD Orthotropic Plate Model for Live Load Moment in Filled Grid Decks

Due to the orthogonal elastic properties and significant two-way bending action, orthotropic plate theory may best be used to describe the behavior of concrete filled grid bridge decks. The current AASHTO LRFD specification employs an orthotropic plate model with a single patch load to predict live load moment in concrete filled grid bridge decks, which may not be conservative. This paper presents alternative equations to predict maximum moments, based on classical orthotropic plate theory, which include multiple patch loads, both the LRFD design truck and tandem load cases, and the two most common deck orientations. The predicted moments are verified through finite-element analyses.     

High-Cycle Fatigue of Diagonally Cracked Reinforced Concrete Bridge Girders: Field Tests

Large numbers of conventionally reinforced concrete deck–girder (RCDG) bridges remain in-service in the national highway system. Diagonal cracks have been identified in many of these bridges, which are exposed to millions of load cycles during service life. The anticipated life of these bridges in the cracked condition under repeated service loads is uncertain. RCDG bridges with diagonal cracks were inspected and instrumented. Strain and crack displacement data were collected under ambient traffic conditions and controlled test trucks. Results indicated relatively small stirrup stresses and diagonal cracks exhibited opening and closing under truck loading.     

Fatigue and Strength Evaluation of Two Glass Fiber-Reinforced Polymer Bridge Decks

The use of glass fiber-reinforced polymer (GFRP) bridge decks is appealing for applications where minimizing dead load is critical. This paper describes fatigue and strength testing of two types of GFRP decks being considered for use in the retrofit of an aging steel arch bridge in Snohomish County, Washington, where a roadway expansion is necessary and it is desirable to minimize the improvements to the arch superstructure. Each test used a setup designed to be as close as practicable to what will be the in situ conditions for the deck, which included a 2% cross slope for drainage. The fatigue testing consisted of a single 116 kN (26 kip) load applied for 2 million cycles, which corresponds to an AASHTO HS-25 truck with a 30% impact factor, and the strength testing consisted of multiple runs of a monotonically applied minimum load of 347 kN (78 kips). Results from the fatigue testing indicated a degradation of the stiffness of both deck types; however, the degradation was limited to less than 12% over the duration of loading. Further, the results showed both deck types accumulated permanent deck displacement during fatigue loading and one deck type used a detail with poor fatigue performance. That detail detrimentally impacted the overall deck performance and caused large permanent deck deformations. It was also found that degradation of composite behavior between the deck and girders occurs during fatigue loading and should be included in design.     

Transverse Cracking of Concrete Bridge Decks: State-of-the-Art

This state-of-the-art paper presents the results of a comprehensive literature review of the cause of transverse deck cracking. It includes compilation of experimental and analytical research results as well as survey studies on the effects of different factors on concrete deck cracking. Consistent with the past work on the subject, causes of transverse deck cracking are classified under three categories, namely: (1) material and mix design, (2) construction practices and ambient condition factors, and (3) structural design factors. The literature review revealed that the first two items have been studied extensively over the past several decades, while literature is limited on the effect of structural design factors on deck cracking. This paper evaluates the existing work in depth and presents recommendations on mix design and construction procedures to reduce the potential for transverse deck cracking. Furthermore, areas for additional research are identified.     

Stiffness and Strength Evaluations of a Shear Connection System for FRP Bridge Decks to Steel Girders

This paper reports on research investigating a nongrouted sleeve-type connection used to attach fiber-reinforced polymer (FRP) decks to steel girders. The connection system was investigated for stiffness, strength, fatigue resistance, and degree of composite action. Static and fatigue tests were conducted first at the component level on push-out specimens to obtain P-Δ (load-displacement) and S-N (stress range–fatigue life) relationships, from which design formulas were developed. Then tests were conducted at the system level on a 1∶3 scaled-bridge model by using this sleeve-type connection, and the results showed this shear connection can satisfy requirements from AASHTO specifications for fatigue, strength, and function. Further, three-point bending tests were conducted on a T-section model cut from the scaled bridge, and approximately 25% composite action was achieved for two different connection spacings. The structural efficiency of this shear connection is shown, and this connection design is applied in practice.     

Performance of Coated Reinforcing Bars in Cracked Bridge Decks

The presence of cracks in bridge decks that are reinforced with epoxy-coated reinforcing (ECR) bars has raised some concerns among bridge and maintenance engineers in the state of Iowa. To study the effects of deck cracking on the performance of ECR bars, several concrete cores that contained reinforcing bars were collected from 80 bridges that are located in different counties throughout the state of Iowa. These samples were collected from cracked and uncracked areas of the bridge decks. Concrete powder samples were collected from these cores and were analyzed in the laboratory to determine the diffusion of the chloride in the bridge decks. This study revealed that no sign of corrosion was detected for the ECR rebars that were taken at the uncracked bridge deck locations. In addition, no delamination or spalling was observed for the bridge decks where bars in the core samples, which were taken at the cracked bridge deck locations, exhibited signs of corrosion. The collected ECR rebars samples were rated according to the degree of the corrosion that was observed on each bar. These ratings were used to develop condition/age relationships that were utilized to estimate the functional service life of bridge decks that are reinforced with ECR bars.     

Transverse Cracking of Concrete Bridge Decks: Effects of Design Factors

Early transverse cracking is one of the dominant forms of bridge deck defects experienced by a large number of transportation agencies. These cracks often initiate soon after the bridge deck is constructed, and they are caused by restrained shrinkage of concrete. Transverse cracks increase the maintenance cost of a bridge structure and reduce its life span. Most of the past efforts addressing transverse bridge deck cracking have focused on changes over the years in concrete material properties and construction practices. However, recent studies have shown the importance of design factors on transverse bridge deck cracking. This paper presents results of a comprehensive finite-element (FE) study of deck and girder bridge systems to understand and evaluate crack patterns, stress histories, as well as the relative effect of different design factors such as structural stiffness on transverse deck cracking. The results of this study demonstrate the development of transverse deck cracking and emphasize the importance of these design factors. They also recommend preventive measures that can be adopted during the design stage in order to minimize the probability of transverse deck cracking.     

Fatigue Behavior and Nondestructive Evaluation of Full-Scale FRP Honeycomb Bridge Specimen

An experimental investigation was performed to assess the projected fatigue performance of a fiber-reinforced polymer honeycomb bridge that has recently been completed in Troupsburg, N.Y. The laboratory specimen was representative of a 305-mm-wide strip of the completed bridge. The specimen was first subjected to fatigue loading. Load, displacement, and strain were measured every 25,000 cycles. The data indicated minimum signs of degradation after 2 million cycles of fatigue loading, as reflected in slightly increased values of vertical deflection and strain at midspan. After completion of the fatigue loading, the specimen was evaluated with acoustic emission. Load was statically applied and increased incrementally until failure occurred at a load level exceeding 16 times the fatigue level loading. The results of the static testing also indicated that only minor damage occurred due to fatigue. Field load testing of the actual bridge has been completed by the New York State Department of Transportation, and the results are discussed as they pertain to the fatigue and static load testing programs described.     

Control of Creep and Shrinkage Effects in Steel Concrete Composite Bridges with Precast Decks

Creep and shrinkage in concrete deck of steel-concrete composite bridges can result in significant redistribution and consequent increase in bending moments at continuity supports and also increase in deflections. Studies are presented for the control of creep and shrinkage effects in steel-concrete composite bridges with precast concrete decks. A hybrid procedure recently developed by the authors has been used for carrying out the studies. The procedure accounts for creep, shrinkage and progressive cracking in concrete decks. Single span, three span and five span bridges have been analyzed for different thicknesses of concrete decks and grades of concrete. Both the shored and unshored constructions have been considered. It is shown that, for both constructions, the increase in bending moments and midspan deflections can be controlled to a significant degree, without putting constraints on design parameters, by simply delaying the time of mobilization of composite action between the precast concrete deck panels and the steel section. It is also observed that though the percentage change in bending moments due to creep and shrinkage is similar for shored and unshored constructions, the percentage change in midspan deflection is significantly higher for shored construction.     

Fatigue and Strength Performance of Concrete-Filled Steel-Grid Bridge Deck

The present paper reports on the results from a series of full-scale experimental tests carried out on concrete-filled steel-grid bridge deck assemblies. The testing focused on assessing the fatigue performance and ultimate strength response of a full-depth-overfilled concrete-filled steel-grid deck configuration. The results from the experimental testing program described herein are compared with the predicted deck responses as per the current AASHTO provisions contained in the LRFD and 16th edition specifications.     

Nondestructive Assessment of Damage in Concrete Bridge Decks

Impact-echo tests were performed on a precast, reinforced concrete bridge slab that was removed from a maintenance bridge built in 1953 in South Carolina. Impact-echo tests were first performed to nondestructively assess the initial condition and the distribution of damage throughout the slab by analyzing the variation in propagation wave velocity. It was found that the velocity varied by as much as 900?m/s throughout the slab. After the in-service condition was assessed, the slab was subjected to a full-scale static load test in the laboratory and impact-echo tests were again performed, this time to evaluate the initiation and progression of damage (stiffness loss and crack development) within the slab. After structural failure of the slab, a reduction in propagation wave velocity up to 6% was observed correlating to a reduction in slab stiffness. Cracks were detected within the concrete slab that were not visible from the surface. Areas with preexisting damage experienced more crack growth when subjected to the load test than those that were initially intact. Locations exhibiting stiffness loss, crack propagation, and localized damage can be differentiated such that the method can be used to make decisions between rehabilitating and replacing concrete bridge decks depending upon the severity of damage.     

Critical Evaluation of Strain Measurements in Glass Fiber-Reinforced Polymer Bridge Decks

An experimental study of principal strains and deflections of glass fiber-reinforced polymer (GFRP) composite bridge deck systems is presented. The experimental results are shown to correlate well with those of an analytical model. While transverse strains and vertical deflections are observed to be consistent, repeatable, and predictable, longitudinal strains exhibit exceptional sensitivity to both strain sensor and applied load location. Large, reversing strain gradients are observed in the longitudinal direction of the bridge deck. GFRP deck system geometry, connectivity, material properties, and manufacturing imperfections coupled with the observed strains suggest that the performance of these structures should be assessed under fatigue loading conditions. Recommendations for accurately assessing longitudinal strain in GFRP bridge decks are made, and a review of existing data is suggested.     

Full-Scale Tests of Bridge Steel Pedestals

Overheight vehicle collisions can cause major damage to bridges. To address the issue of limited vertical clearance heights and reduce the likelihood of impact damage, the Georgia Department of Transportation has implemented a program to elevate major highway bridges using very short columns referred to as steel pedestals. The process to elevate the bridges and install the steel pedestals is cost effective and efficient, resulting in minimum disruption to highway traffic. However, in practice, these pedestals are not detailed to provide end fixity, so they add considerable flexibility to the superstructure supports and potentially make the bridge more susceptible to instability and damage from seismic loads. Therefore, there is a need to evaluate how these steel pedestals will perform under the low-to-moderate earthquakes expected in this region. A full-scale 12.2?m (40?ft) dual steel girder simply supported bridge elevated with 500?mm (19?in.) and 850?mm (33?1/2?in.) steel pedestals is constructed based on typical field procedures. The full-scale bridge specimen is subjected to quasistatic unidirectional reversed cyclic loads to determine the strength and deformation capacity of the steel pedestals and overall system performance. The kinematics, mechanisms, and load–displacement hysteretic relationships of the bridge steel pedestals and its components are presented. Results show that the steel pedestals undergo kinematic rigid body motion, dissipate energy, and demonstrate reasonable deformation and strength capacities when subjected to quasistatic, reversed cyclic loads.     

Evaluation of Load Distribution Factor by Series Solution for Orthotropic Bridge Decks

In bridge engineering, the three-dimensional behavior of a bridge system is usually reduced to the analysis of a T-beam section, loaded by an equivalent fraction of the applied live load, which is called the live load distribution factor (LDF). The LDF is defined in the both the AASHTO Standard Specifications and the LRFD Specifications primarily for concrete slabs and has inherent applicable limitations. This paper provides explicit formulas using series solutions for LDF of orthotropic bridge decks, applicable to various materials but intended for fiber-reinforced polymer (FRP) decks. The present formulation considers important parameters that represent the response characteristics of the structure that are often omitted or limited in the AASHTO Specifications. A one-term series solution is proposed based on the macroflexibility approach, in which the bridge system is simplified into two major components, deck and stringers. The governing equations for the two components are obtained separately, and the deflections and interaction forces are solved by ensuring displacement compatibility at stringer lines. The LDF is calculated as the ratio of the single stringer interaction force to the summation of total stringer interaction forces. To verify this solution, a finite-element (FE) parametric study is conducted on 66 simply supported concrete slab-on-steel girder bridges. The results from the series solution correlates well with the FE results. It is also illustrated that the series solution can be applied to predict LDF for FRP deck-on-steel girder bridges, by favorable comparisons among the analytical, FE, and testing results for a one-third-scale bridge model. The scale test specimen consists of an FRP sandwich deck attached to steel stringers by a mechanical connector. The series solution is further used to obtain multiple regression functions for the LDF in terms of nondimensional variables, which can be used for simplified design purposes.     

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.