Reinforcing Transverse Glulam Deck Panels with Through-bolted Glulam Stiffener Beams: Theoretical Analysis

Two design criteria, allowable stress design (ASD) and load and resistance factor design (LRFD), are presented for calculating glued-laminated (glulam) stiffener beam depth and number of dome head through bolts used in deck-to-deck connections for longitudinal stringer, transverse deck glulam bridges. Design examples for six deck panel spans (762–3,658 mm) and an applied 89 kN wheel load are also presented. The connection configurations (stiffener beam depth and number of dome head bolts) for both ASD and LRFD differ only in the stiffener beam depth (maximum 15% difference). Both ASD and LRFD criteria performed very well when compared to experimental observation and results of loaded stiffener beam connected deck panels.     

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.     

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.     

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.     

Reliability-Based Optimum Design of Glulam Cable-Stayed Footbridges

This work presents a procedure for finding the reliability-based optimum design of cable-stayed bridges. The minimization problem is stated as the minimization of stresses, displacements, reliability, and bridge cost. A finite-element approach is used for structural analysis. It includes a direct analytic sensitivity analysis module, which provides the structural behavior responses to changes in the design variables. An equivalent multicriteria approach is used to solve the nondifferential, nonlinear optimization problem, turning the original problem into sequential minimization of unconstrained convex scalar functions, from which a Pareto optimum is obtained. Examples are given illustrating the procedure.     

Fatigue Behavior of Composite-Reinforced Glulam Bridge Girders

While composite-reinforced glulam beams have been used in several bridge demonstration projects, knowledge of their fatigue behavior is quite limited. In this study, the response of full- and partial-length fiberglass composite-reinforced glulam beams under fatigue cycling followed by quasi-static bending to failure is examined. To mimic anticipated in-service conditions, a hygrothermal cycling regime was developed that replicates the effective stress history of a 50-year service life with a 55-day period in a moisture-controlled kiln. In addition, some of the beams had initial delaminations introduced between the reinforcing and the wood similar to those observed in field investigations of reinforced glulam bridge girders. For the partial-length reinforced beams, reinforcing with both confined and unconfined ends was considered. The results of the postfatigue tests to failure were compared with the expected strength. In addition, the stiffness of the beams was monitored during the fatigue cycling. It was found that, with the exception of the unconfined, partial-length reinforced beams, all specimens had a residual strength that compared favorably with the expected strength. Further, neither the preconditioning nor the fatigue cycling had an appreciable impact on the stiffness of the reinforced beams. The unconfined, partial-length reinforced beams did not perform well under fatigue loading and do not seem to be a viable alternative for use as reinforced glulam bridge girders.     

Reliability Analysis of Plank Decks

The objective of this study is to summarize the load and resistance criteria for highway bridge plank decks, and to estimate the reliability of plank decks designed by the AASHTO Code. Both transverse and longitudinal planks for a variety of typical stringer spacings and plank sizes are considered. Truck traffic load data are based on the model used to calibrate the 1994 AASHTO LRFD Code. However, for plank decks, wheel load rather than whole vehicle weight is most important, and these statistics are developed for this study. For wood planks, dead load and dynamic load are not significant. The limit state considered is flexural strength, and resistance statistics are presented for wood planks in terms of modulus of rupture. Special flat-wise use data are presented to account for section aspect ratio as well as edge of load application. The reliability analysis is carried out using the procedure developed for calibration of AASHTO LRFD. Reliability indices for both the AASHTO Standard and AASHTO LRFD Code are presented for plank decks. The results indicate that there are considerable differences in plank reliability indices. Causes of inconsistencies in safety are identified.     

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.     

Probability of Drift Blockage at Bridge Decks

Drift seriously increases the destructive power of a flood event. Drift accumulations and blockages at river bridges are a widespread problem, possibly leading to their total destruction. Although drift is a major threat, limited knowledge is currently available on the likelihood of drift blocking. Drift either accumulates at a single pier, or it spans between two or more piers, or it gets blocked at the bridge deck. The main purpose of this experimental study is to analyze the drift-blocking probability at bridge decks depending on: (1)?drift dimensions, (2)?freeboard, (3)?flow characteristics, and (4)?bridge characteristics. Systematic model tests include the accumulation of both single logs and rootstocks. The test flow conditions represent a major flood event, where the freeboard tends to zero and the drift is able to touch the bridge deck. The results indicate significant effects of the freeboard, the approach flow Froude number, and the bridge characteristics on drift accumulation. They allow for an estimation of the blocking probability and therefore can be used as a risk assessment tool to identify endangered bridges prior to a flood event. The model tests demonstrate further the randomness of the blocking process, resulting occasionally in a wide scatter of data.     

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.     

Distribution of Compressive Stresses in Transversely Posttensioned Concrete Bridge Decks

A parametric study was carried out in order to understand the salient aspects affecting the distribution of compressive stresses in transversely posttensioned concrete bridge decks. Alternative finite element modeling techniques and alternative software were considered and the corresponding analytical results were compared with the experimental results from previous investigations. It was found that the distribution of compressive stresses is mainly affected by the support conditions of the girders and the axial stiffness of the diaphragms.     

Investigation of Cracking in Concrete Bridge Decks at Early Ages

The loads, construction procedures, and material behavior influence the performance of the bridge deck as well as its structural integrity. This paper includes a thorough investigation to identify the probable causes of cracking in reinforced concrete bridge decks, particularly at early ages. The objectives of the study were addressed through a literature review process and a comprehensive nationwide survey. Experiments were performed to establish the magnitude of the modulus of elasticity of concrete at early ages as well as the curvature it can withstand without cracking. A computer program was developed to take into account the loads due to sequence of pours. A compendium was developed to categorize the various causes of cracking to identify appropriate procedures that may control this cracking. The parameters considered in the investigation were age of concrete, stage and sequence of pours, curing procedures, heat of hydration, strength gain, thermal changes, and construction type. Results of the literature review and survey indicated that in most cases, cracking of concrete may be attributed to the high evaporation rate and high magnitude of shrinkage. Other factors include the use of high slump concrete, excessive water in the concrete, insufficient top reinforcement cover, insufficient vibration of the concrete, inadequate reinforcing details of the joint between the new and old deck, sequence of pour, and weight and deflection of the forms. The calculated curvatures for the selected bridges were smaller than the curvatures needed to crack dynamically loaded fresh concrete in a laboratory environment.     

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.     

Analysis of Life-Cycle Maintenance Strategies for Concrete Bridge Decks

This paper presents the development of a project-level decision support tool for ranking maintenance scenarios for concrete bridge decks deteriorated as a result of chloride-induced corrosion. The approach is based on a mechanistic deterioration model and a probabilistic life-cycle cost analysis. The analysis includes agency and user costs of alternative maintenance scenarios and considers uncertainties in the agency cost and the corrosion rate in the deterioration model. The tool presented in this paper can be used to find the optimal condition index of a given bridge deck that minimizes life-cycle cost. Based on the results obtained on three existing bridge decks, it is shown that the total life-cycle cost (user cost plus agency cost) is a nonlinear function of the maximum tolerable condition of the deck, Sm, and that for a practical range of Sm, the relationship between total life-cycle cost and Sm is convex.     

Behavior of Composite Bridge Decks with Alternative Shear Connectors

An experimental study of composite bridge decks with alternative shear connectors has been performed. The alternative shear connector consists of concrete filled holes located in the webs of grid main bars and friction along the web embedded in the slab, which enables shear transfer between the concrete slab and steel grid. Results of static and fatigue tests on full-scale prototype decks indicated that composite action between the concrete slab and steel grid is maintained well above the service load range even after fatigue loading, the eventual loss of composite action at overload is gradual, failure was controlled by punching shear of the concrete slab and was unaffected by the shear connectors, and no significant change in behavior was observed due to fatigue loading. Further, the measured stress range at the shear connection location would not control the fatigue behavior of the deck in positive bending, and no fatigue cracking of the steel grid was observed in negative bending.     

Orthotropic Plate Model for Estimating Deflections in Filled Grid Decks

Concrete filled grid bridge decks exhibit orthogonal elastic properties and significant two-way bending action enabling orthotropic plate theory to determine structural response for these elements. Current American Association of State Highway and Transportation Officials load and resistance factor design (LRFD) specifications employ an orthotropic plate model to predict live load moment in concrete filled grid bridge decks but provide no guidance for computing displacement, a potentially important serviceability consideration. This paper presents equations to approximate the maximum deflection in concrete filled grid bridge decks based on orthotropic plate theory, multiple patch loads, LRFD design truck and tandem load cases, the influence of multiple spans, and the two most common deck orientations.     

Note on Chloride-Induced Corrosion of Reinforced Concrete Bridge Decks

This technical note presents numerical results to predict the corrosion initiation time of reinforced concrete bridge decks using measured surface chloride accumulation. Based on actual core measurements, the surface chloride, which is mainly derived from the deicing salts used during winter maintenance operations, is assumed to increase linearly over a period of time and then remains constant afterward. The chloride ions penetrate the concrete by diffusion and corrosion is initiated when the concentration of the ions around the reinforcement steel reaches a critical value needed to break the passive film surrounding the steel. The corrosion initiation time is computed for different values of the diffusion coefficient and the concrete cover. Such results are useful for scheduling bridge deck maintenance and rehabilitation programs.