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.     

Dynamic Behavior of Deck Slabs of Concrete Road Bridges

This paper treats the dynamic effect of traffic actions on the deck slabs of concrete road bridges using the finite-element method. All the important parameters that influence bridge-vehicle interaction are studied with a systematic approach. An advanced numerical model is described and the results of a parametric study are presented. The results suggest that vehicle speed is less important than vehicle mass and that road roughness is the most important parameter affecting the dynamic behavior of deck slabs. The type of bridge cross section was not found to have a significant influence on deck slab behavior. The dynamic amplification factor varied between 1.0 and 1.55 for the bridges and vehicles studied. These results should be validated by further work.     

Effect of Bearing Pads on Precast Prestressed Concrete Bridges

Precast AASHTO concrete bridge I-beams are often supported at the ends by elastomeric bearing pads. The bearing pad-bridge beam interface defines support boundary conditions that may affect the performance of the bridge. In this study, finite-element modeling was used to validate AASHTO bearing stiffness specifications. Stiffness characteristics of the Florida DOT bearing pads were theoretically determined under varying elastomer shear modulus values. Finite-element models of AASHTO Types III and V beams were subjected to simulated static truckloads. Vertical and horizontal spring elements simulating new bearing pads were incorporated at the ends of the beam models. A full section of a bridge on U.S. Route 27 was also modeled, and the results were compared with field tests. In general, the restraint effects of the bearing pads are beneficial to the performance of the beams and the bridge. The beneficial effect, however, is small for new bearing pads and more pronounced under a drastic increase in bearing stiffness due to aging and colder temperatures. Such a dramatic increase in bearing stiffness must be justified if the beneficial elements are to be utilized. Current Florida DOT bearing pads are serving the main purpose of their application, which is to provide minimum horizontal restraint force to the beams while allowing horizontal movement.     

Cracking and Reinforcement Corrosion in Short-Span Precast Concrete Bridges

A nationwide survey revealed 14 states having bridges comprised of precast, nonprestressed, concrete channel beams. Currently, the Arkansas State Highway and Transportation Department (AHTD) bridge inventory includes approximately 389 in-service bridges using 5.79?m precast channel beams that were constructed using 1952 AHTD bridge details. Results from a statewide inspection of these bridges conducted by the writers revealed bridges with extensive concrete longitudinal cracking at the flexural reinforcing steel level and exposed reinforcing steel. Approximately 2,000 beams in 95 precast concrete channel beam bridges were inspected during a statewide investigation; longitudinal cracking at the reinforcing steel level was observed in 60.4% of the beams and exposed flexural reinforcement in 21.2%. A combination of flexure cracking from the live-load overloads and the presence of moisture has led to this high level of beam deterioration. The source of this moisture is humidity and water seepage at joints between adjacent beams. This paper examines the causes of longitudinal cracking deterioration by examining the influences of water permeation and humidity on the corrosion of flexural reinforcement in precast concrete channel beams.     

Application of Suspension Bridges Stiffened by Prestressed Concrete Slabs in China

Four suspension bridges stiffened by prestressed concrete slabs were designed and constructed on highways in southwestern mountainous areas of China. These bridges are the first applications of its kind in China. This paper discusses the site condition, adaptability, and design and construction features of these bridges. These bridges have single suspension spans between 278 and 388?m and deck width between 14.4 and 15.0?m. The longitudinal distance between hangers is only 5?m, which is relatively small for this bridge type, and there are only two lanes. The dual direction prestressed concrete slabs are 0.6?m deep, and its wind blocking area is relatively small. Dynamic analysis and wind tunnel tests verify that the wind resistance requirements are easily satisfied.     

Structural Behavior of Single Key Joints in Precast Concrete Segmental Bridges

A group of five full-depth male–female shear key specimens were match cast and tested to examine the shear capacity of epoxy-jointed single keys. Another group of four specimens were match cast using full-scale dimensions of a segmental construction bridge deck system for testing the fatigue and water tightness at a segment joint. Both cold-weather and hot-weather epoxy types were used to join the specimens. In addition to the experimental testing, finite-element analysis was also used to model the static response of the joint specimens. The observed failure mode of all shear-key specimens was fracture of concrete along the joint with shearing of the key. Good agreement was observed between the experimental test results and the finite-element analysis in terms of the failure mode of unreinforced specimen and the load of crack initiation of the specimens. Fatigue loading had a minor effect on the behavior of the posttensioning bars. The contribution of either the cold-weather or hot-weather epoxies to the joint shear strength was significant knowing that for similar concrete properties, the hot-weather epoxy specimens showed an increase of about 28% in the shear capacity, in comparison to the cold-weather epoxy specimens. The excellent performance of the epoxy-jointed shear keys was verified by field application on a prototype model simulating a portion of the Wacker Drive Bridge system. It was concluded that implementing AASHTO procedures result in conservative estimates of the shear strength of the single keyed joint since it neglects the contribution of the epoxy and underestimates the strength of the key itself.     

Delamination Effects in Reinforced Concrete Slabs Strengthened with Circular Composite Patches

The behavior of reinforced concrete slabs strengthened with fully or partially bonded (delaminated) circular patches is analytically investigated. The model derived follows the concepts of the high-order theory, and uses variational principles, equilibrium, and compatibility requirements, the constitutive equations of reinforced concrete (RC) members and composite laminates, and the fracture-mechanics concept of energy release rate. A substructuring approach, in which the localized response of the strengthened area is modeled assuming circular axis-symmetric behavior, is adopted. The investigated substructure consists of fully bonded and delaminated regions, where the delaminated faces can slip horizontally one with respect to another. A distinction is made between delaminations with contact, in which the delaminated faces accommodate vertical normal compressive stresses, and delaminations without vertical contact, in which the cracked interface is free of stresses on any kind. The field and governing equations of the fully bonded, delaminated (with or without contact), and unstrengthened regions, as well as the boundary/continuity conditions that combine these regions together, are derived. The influence of the existence of a delaminated area at the center of the slab and the effect of its size on the localized and overall behavior are investigated numerically. The elastic energy release rates associated with the growth of the delaminated area and their influence on the failure mode of the strengthened structure are also studied. The investigation reveals that the formation of a delaminated region reduces the composite action of the RC slab and the bonded patch, is involved with stress concentrations near the edge of the region, and may trigger an unstable delamination failure of the strengthened slab.     

Realistic Assessment for Safety and Service Life of Reinforced Concrete Decks in Girder Bridges

The lack of safety of deck slabs in bridges generally causes frequent repair and strengthening. The repair induces great loss of economy, not only due to direct cost by repair, but also due to stopping the public use of such structures during repair. The major reason for this frequent repair is mainly due to the lack of a realistic and accurate assessment system for bridge decks. The purpose of the present paper is therefore to develop a realistic assessment system which can estimate reasonably the safety, as well as the service life of concrete bridge decks, based on the deterioration models that are derived from both the traffic loads and environmental effect. A deterioration model due to chloride ingress is first established. The damage models due to repetitive traffic loads considering the dry and wet conditions of deck slabs are proposed. These models are used to calculate the remaining life of a bridge deck slab. A prediction method for service life of deck slab due to loading and environmental effects is developed based on material, as well as structural evaluation. The proposed method includes the assessment of corrosion in material level, and the analyses of flexure, shear, and fatigue in structural level. Finally, an assessment system for prediction of safety and remaining service life is developed based on the theories established in this study. The developed assessment system will allow the correct diagnosis of damage state and the realistic prediction of service life of concrete decks in girder bridges.     

Concrete Cracking in Tension Members and Application to Deck Slabs of Bridges

Currently, estimations of the crack width in the deck slab of bridges given by codes of practice are based on either theoretical or empirical approaches considering mainly the monotonic loading behavior. However, cracking in reinforced tensile members is highly influenced by the loading history (including both the loading and unloading processes) because of the irreversible nonlinear behavior of bond and of tensile response of concrete, resulting into residual cracks of non-negligible width. This paper investigates the influence of this phenomenon and presents a physical model describing it. An analytical model is developed and its results are compared to various tests with good agreement. Finally, a simple design formula is derived and recommendations for its application to practical cases are proposed.     

Strengthening of Reinforced Concrete Bridge Decks Using Carbon Fiber-Reinforced Polymer Composite Materials

This paper presents the results of an investigation of the monotonic and fatigue behavior of one-way and two-way reinforced concrete slabs strengthened with carbon fiber-reinforced polymer (CFRP) materials. The five one-way slab specimens were removed from a decommissioned bridge in South Carolina. Three of the slabs were retrofitted with CFRP strips bonded to their soffits and the other two served as unretrofit, control specimens. Of the five one-way slab specimens, one unretrofit and two retrofit slabs were tested monotonically until failure. The remaining two specimens, one unretrofit and one retrofit, were tested under cyclic (fatigue) loading until failure. In addition, six half-scale, two-way slab specimens were constructed to represent a full-scale prototype of a highway bridge deck designed using the empirical requirements of the AASHTO LRFD Bridge Design Manual. Of the six square slabs, two were unretrofitted and served as the control specimens, two were retrofitted using CFRP strips bonded to their soffits making a grid pattern, and two were retrofitted with a preformed CFRP grid material bonded to their soffit. Three slabs, one unretrofit, one CFRP strip, and one CFRP grid retrofitted, were tested monotonically until failure and the remaining three slabs were tested under cyclic (fatigue) loading until failure.     

Composite T-Beams Using Reduced-Scale Rectangular FRP Tubes and Concrete Slabs

A composite system consisting of rectangular glass fiber reinforced polymer (GFRP) tubes connected to concrete slabs, using GFRP dowels has been developed. Seven beam specimens have been tested, including hollow and concrete-filled GFRP tubes with and without concrete slabs. Beam–slab specimens had two different shear span-to-depth ratios and one specimen had carbon–fiber reinforced polymer (CFRP)-laminated tension flange for enhanced flexural performance. Additionally, three double-shear GFRP tube-slab assemblies have been tested to assess the shear behavior of GFRP dowels, in both hollow and concrete-filled tubes. Three compression stubs of concrete-filled tubes were also tested by loading them parallel to the cross-section plane, to study GFRP web buckling behavior. The study showed that GFRP dowels performed well in shear and that composite action is quite feasible. While hollow tubes can act compositely with concrete slabs, more slip between the tube and slab would occur, compared to a concrete-filled tube-slab system. Simplified models are proposed to predict critical web buckling load of fiber reinforced polymer (FRP) tubes. Based on the models, a critical shear span-to-depth ratio of 4 was determined, below which web buckling may occur before flexural failure.     

Simulation of Construction of Cable-Stayed Bridges

Construction of cable-stayed bridges involves major changes in configuration of the structure with the addition and removal of structural components to the partially constructed structure. At every stage of construction, it is necessary to have sufficient information about the existing partial structure as-built, to verify the requirements called for in the construction guidelines and to investigate the effects of possible modifications in the construction procedures. The final stresses and deformations in the completed structure are strongly dependent on the sequence of events during the construction and the erection procedure used. Therefore, analysis of the actual construction sequence is an important first step in any analysis of the performance of the bridge under external loads. In this paper a general methodology for construction sequence simulation of cable-stayed bridges is presented, and stage-by-stage construction of an actual bridge is simulated. The objective of the simulation is to evaluate short-term and long-term influences of the construction sequence on the structural integrity of the cable-stayed bridge. Comparisons are presented between results from the present analysis, conventional procedures, and the actual field measurements.     

Stability Analysis of Box-Girder Cable-Stayed Bridges

The objective of this study is to investigate the stability characteristics of box-girder cable-stayed bridges by three-dimensional finite-element methods. Cable-stayed bridges have many design parameters, because they have a lot of redundancies, especially for long-span bridges. Cable-stayed bridges exhibit several nonlinear behaviors concurrently under normal design loads because of large displacements; the interaction among the pylons, the stayed cables, and the bridge deck; the strong axial and lateral forces acting on the bridge deck and pylons; and cable nonlinearity. A typical two-lane, three-span, steel box-girder cable-stayed bridge superstructure was selected for this paper. The numerical results indicate that, if the ratio of the main span length with respect to the total span length, L1∕L, is small, the structure usually has a higher critical load. If the ratio Ip∕Ib increases, the critical load of the bridge decreases, in which Ip is the moment of inertia of the pylon and Ib is the moment of inertia of the bridge deck. When the ratio Ip∕Ib is greater than 10.0, the decrement becomes insignificant. For cable arrangements, bridges supported by a harp-type cable arrangement are the better design than bridges supported by a fan-type cable arrangement on buckling analysis. The numerical results also indicate that use of either A-type or H-type pylons does not significantly affect the critical load of this type of structure. In order to make the numerical results useful, the buckling loads have been nondimensionalized and presented in both tabular and graphical forms.     

Fatigue Life Evaluation of Concrete Bridge Deck Slabs Reinforced with Glass FRP Composite Bars

Since bridge deck slabs directly sustain repeated moving wheel loads, they are one of the most bridge elements susceptible to fatigue failure. Recently, glass fiber-reinforced polymer (FRP) composites have been widely used as internal reinforcement for concrete bridge deck slabs as they are less expensive compared to the other kinds of FRPs (carbon and aramid). However, there is still a lack of information on the performance of FRP–reinforced concrete elements subjected to cyclic fatigue loading. This research is designed to investigate the fatigue behavior and fatigue life of concrete bridge deck slabs reinforced with glass FRP bars. A total of five full-scale deck slabs were constructed and tested under concentrated cyclic loading until failure. Different reinforcement types (steel and glass FRP), ratios, and configurations were used. Different schemes of cyclic loading (accelerated variable amplitude fatigue loading) were applied. Results are presented in terms of deflections, strains in concrete and FRP bars, and crack widths at different levels of cyclic loading. The results showed the superior fatigue performance and longer fatigue life of concrete bridge deck slabs reinforced with glass FRP composite bars.     

Seismic Performance of Multisimple-Span Bridges Retrofitted with Link Slabs

During earthquakes multisimple-span bridges are vulnerable to span separation at their expansion joints. A common way of preventing unseating of spans is to have cable or rod restrainers that provide connections between adjacent spans. Alternatively, dislocation of the girders can be controlled with a link slab that is the continuous portion of the bridge deck between simple spans. Seismic retrofit with link slab should be more cost-effective than the existing methods when it is performed during redecking or removal of expansion joints. Maintenance cost associated with expansion joints could also be reduced. This paper discusses the use of link slabs for retrofit of seismically deficient multisimple-span bridges with precast, prestressed concrete girders. The concept is equally applicable to bridges with steel girders. Analytical studies for typical overpasses were performed to investigate the effectiveness of the proposed link slab application. A simple preliminary design procedure was also developed.     

High-Order Analysis of Reinforced Concrete Slabs Strengthened with Circular Composite Laminated Patches of General Layup

A high-order model for the analysis of reinforced concrete (RC) slabs strengthened with externally bonded composite laminated patches of a general layup is presented. The model follows the concepts of the high-order theory and it is based on variational principles, equilibrium, and compatibility requirements. The classical lamination theory is adopted for the composite patch and it yields a set of coordinate dependent constitutive relations. The governing equations form a set of partial differential equations with variable coefficients. The solution procedure adopts the Galerkin and the multiple-shooting methods in the circumferential and radial directions, respectively. The proposed model is used for the numerical study of a square RC slab strengthened with a circular cross-ply laminated patch. The results focus on the overall behavior of the slab and the localized shear and vertical normal stresses near the edge of the bonded patch. Comparison with results obtained using a simplified axisymmetric model is also presented and discussed. The study reveals that the anisotropy of the bonded patch affects the overall and the localized response of the strengthened slab. It also shows that the simplified axisymmetric analysis tends to underestimate the stresses and stress resultants, and thus may be considered unsafe.     

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.     

Optimization of Cable Tensioning in Cable-Stayed Bridges

During the structural analysis of cable-stayed bridges, some specific problems arise that are not common in other types of bridges. One of these problem is the derivation of an optimal sequence for the tensioning of the stay cables. This paper describes a novel solution to this problem, the unit force method. The method takes into account all relevant effects for the design of cable-stayed bridges, including construction sequence, second-order theory, large displacements, cable sag and time-dependent effects, such as creep and shrinkage or relaxation of prestressing tendons. Information about the implementation of this method into a computer program is given, and an example of a practical application of this method concludes this paper. The method is not restricted to the design of cable-stayed bridges and may well be used for other structural applications in the future.     

Long-Term Behavior of Precast Segmental Cantilever Bridges

An investigation is conducted to quantify long-term effects on a family of four precast segmental bridges. Segments are prefabricated, transported, and set into place with an appropriate lifting device and a launching gantry. Attention has been paid to the effects of long-term deformations of concrete, to avoid noticeable geometrical variations in its shape but also to account for redistribution of stresses, which creates a difficult analytical problem to solve. An attempt is made to provide a practical treatment of serviceability analyses of this type of concrete structure, having an evolutive process of erection, presenting: (1) an “exact” incremental step-by-step time approach; (2) a simplified approach for the inclusion of time dependent effects of creep and shrinkage; and (3) a comparison of both approaches, in order to treat these kinds of problems by means of a simplified approach.     

Evaluation of Composite Sandwich Bridge Decks with Hybrid FRP-Steel Core

A hybrid concept of composite sandwich panel with hybrid fiber-reinforced polymer (FRP)—steel core was proposed for bridge decks in order to not only improve stiffness and buckling response but also be cost efficient compared to all glass fiber-reinforced polymer (GFRP) decks. The composite sandwich bridge deck system is comprised of wrapped hybrid core of GFRP grid and multiple steel box cells with upper and lower GFRP facings. Its structural performance under static loading was evaluated and compared with the ANSYS finite element predictions. It was found that the presented composite sandwich panel with hybrid FRP-steel core was very efficient for use in bridges. The thickness of the hybrid deck may be decreased by 19% when compared with the all GFRP deck. The failure mode of the proposed hybrid deck was more favorable because of the yielding of the steel tube when compared with that of all GFRP decks.