Capacity Evaluation of Exterior Sacrificial Shear Keys of Bridge Abutments

Shear keys are used in bridge abutments to provide transverse support for the superstructure. The damage observed on bridge abutments in the aftermath of the 1994 Northridge Earthquake prompted the revision of the design of shear keys. As part of this revision, experimental and analytical work was conducted to investigate the seismic behavior of exterior shear keys in bridge abutments designed in accordance with current guidelines and to investigate shear keys designed for damage control. The latter work was aimed at providing guidance for seismic design of shear keys to act as structural fuses that would limit the input force in the abutment piles. Ten shear keys were designed and built at 1:2.5 scale of a prototype abutment design provided by Caltrans. The study concluded that a smooth construction joint should be considered at the interface of the shear key–abutment stem wall to allow sliding shear failure. A mechanism model was developed for capacity evaluation of shear keys with sliding shear failure. The results of the experimental program and development of the simple analytical model for capacity evaluation of exterior shear keys are presented in this paper.     

Assessment of Shear Forces on Bridge Abutments: Simplified Method

The conventional application of reduction factors to response spectrum analysis results is inappropriate for the abutment shear forces, which are based on elastic action. On the other hand, adopting the unreduced values from the elastic dynamic analysis does not achieve equilibrium among the abutment shear forces, deck inertia forces, and reduced pier forces. A simplified method is here proposed for the assessment of the shear on the abutments, documented by comparison with response spectrum and time history nonlinear analyses for several bridge configurations. For the analyzed configuration of the bridge with an internal movement joint, the response spectrum analysis underestimates the shear on the abutment for low values of the abutment flexibility and overestimates it when the stiffness of the abutments becomes higher than that of the piers. In all the case studies analyzed, the proposed method approximates the time history results better than the response spectrum.     

Effects of Pier and Deck Flexibility on the Seismic Response of Isolated Bridges

The seismic response of bridges isolated by elastomeric bearings and the sliding system is investigated under two horizontal components of real earthquake ground motions. The selected bridges consist of multispan continuous deck supported on the piers and abutments. Three different mathematical models of the isolated bridge are considered for the analytical seismic response by considering and ignoring the flexibility of the deck and piers. The mathematical formulation for seismic response analysis of various mathematical models of the bridges isolated by different isolation systems is presented. The accuracy and computational efficiency of various mathematical models of isolated bridges is investigated by comparing their responses under different system parameters and earthquake ground motions. The important parameters selected are the flexibility of deck, piers, and isolation systems. There was significant difference in the computational time required for different models, but it was observed that the seismic response of the bridges obtained from different equivalent mathematical models is quite comparable even for an unsymmetrical bridge. Thus, the earthquake response of a seismically isolated bridge can be effectively obtained by modeling it as a single-degree-of-freedom system (i.e., considering the piers and deck as rigid) supported on an isolation system in two horizontal directions.     

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.     

Simulating the Behavior of GRS Bridge Abutments

Geosynthetic-reinforced soil (GRS) bridge-supporting abutments are similar in principle to GRS retaining walls, except that GRS abutments are typically subjected to a much higher area load, and that the loads are close to the wall face. The GRS abutment technology is relatively new, but it has great potential, and it has been gaining some popularity in recent years. This paper describes the finite element analyses of two full-scale loading tests of GRS bridge abutments referred to as the “National Cooperative Highway Research Program (NCHRP) experiment.” The analysis was carried out using the computer program Dyna3d, developed at the Lawrence Livermore National Laboratory. The finite element analysis of the NCHRP experiment will help with the understanding of the complex behavior of GRS structures in general, and the behavior of GRS bridge abutments with modular block facing in particular. The analysis of the two full-scale loading tests allows the loading conditions that are of greatest concern in the design of the bridge abutments to be examined rationally. The analysis shows that the performance of a GRS abutment, resulting from the complex interaction among the various components, while subject to a service load or a limiting failure load can be simulated in a reasonably accurate manner. In addition, a parametric study was conducted to investigate the performance of the modular block facing GRS bridge abutments subjected to live and dead loads from a bridge superstructure. This study investigated the performance of the GRS bridge abutments as they are affected by backfill properties, reinforcement stiffness properties, and reinforcement vertical spacing.     

Integral Abutment-Backfill Behavior on Sand Soil—Pushover Analysis Approach

This paper presents a study on the behavior of the abutment-backfill system under positive thermal variation in integral bridges built on sand. A structural model of a typical integral bridge is built, considering the nonlinear behavior of the piles and soil-bridge interaction effects. Static pushover analyses of the bridge are conducted to study the effect of various geometric, structural, and geotechnical parameters on the performance of the abutment-backfill system under positive thermal variations. The shape and intensity of the backfill pressure are found to be affected by the height of the abutment. Furthermore, the internal forces in the abutments are found to be functions of the thermal-induced longitudinal movement of the abutment, the properties of the pile, and the density of the sand around the piles. Using the pushover analysis results, design equations are formulated to determine the maximum forces in the abutments and the maximum length of integral bridges based on the strength of the abutments. Integral bridges with piles encased in loose sand and oriented to bend about their weak axis, abutment heights less than 4?m, and noncompacted backfill are recommended to limit the magnitude of the forces in the abutments.     

Allowable Bearing Pressures of Bridge Sills on GRS Abutments with Flexible Facing

Compared to geosynthetic-reinforced soil (GRS) retaining walls, GRS abutment walls are generally subjected to much greater intensity surface loads that are fairly close to the wall face. A major issue with the design of GRS abutments is the allowable bearing pressure of the bridge sill on the abutments. The allowable bearing pressure of a bridge sill over reinforced soil retaining walls has been limited to 200?kPa in the current NHI and Demo 82 design guidelines. A study was undertaken to investigate the allowable bearing pressures of bridge sills over GRS abutments with flexible facing. The study was conducted by the finite element method of analysis. The capability of the finite element computer code for analyzing the performance of GRS bridge abutments with modular block facing has been evaluated extensively prior to this study. A series of finite element analyses were carried out to examine the effect of sill type, sill width, soil stiffness/strength, reinforcement spacing, and foundation stiffness on the load-carrying capacity of GRS abutment sills. Based on the results of the analytical study, allowable bearing pressures of GRS abutments were determined based on two performance criteria: A limiting displacement criterion and a limiting shear strain criterion, as well as the writers’ experiences with GRS walls and abutments. In addition, a recommended design procedure for determining the allowable bearing pressure is provided.     

Designing and Testing of Concrete Bridge Decks Reinforced with Glass FRP Bars

In addition to their high strength and light weight, fiber-reinforced polymer (FRP) composite reinforcing bars offer corrosion resistance, making them a promising alternative to traditional steel reinforcing bars in concrete bridge decks. FRP reinforcement has been used in several bridge decks recently constructed in North America. The Morristown Bridge, which is located in Vermont, United States, is a single span steel girder bridge with integral abutments spanning 43.90 m. The deck is a 230 mm thick concrete continuous slab over girders spaced at 2.36 m. The entire concrete deck slab was reinforced with glass FRP (GFRP) bars in two identical layers at the top and the bottom. The bridge is well instrumented at critical locations for internal temperature and strain data collection with fiber-optic sensors. The bridge was tested for service performance using standard truck loads. The construction procedure and field test results under actual service conditions revealed that GFRP rebar provides very good and promising performance.     

Construction and Testing of an Innovative Concrete Bridge Deck Totally Reinforced with Glass FRP Bars: Val-Alain Bridge on Highway 20 East

The Val-Alain Bridge, located in the Municipality of Val-Alain on Highway 20 East, crosses over Henri River in Québec, Canada. The bridge is a slab-on-girder type with a skew angle of 20° over a single span of 49.89?m and a total width of 12.57?m. The bridge has four simply supported steel girders spaced at 3,145?mm. The deck slab is a 225-mm-thick concrete slab, with semi-integral abutments, continuous over the steel girders with an overhang of 1,570?mm on each side. The concrete deck slab and the bridge barriers were reinforced with glass fiber reinforced polymer (GFRP) reinforcing bars utilizing high-performance concrete. The Val-Alain Bridge is the Canada’s first concrete bridge deck totally reinforced with GFRP reinforcing bars. Using such nonmetallic reinforcement in combination with high-performance concrete leads to an expected service life of more than 75?years. The bridge is well instrumented with electrical resistance strain gauges and fiber-optic sensors at critical locations to record internal strain data. Also, the bridge was tested for service performance using calibrated truckloads. Design concepts, construction details, and results of the first series of live load field tests are presented.     

Analytical Solutions to General Orthotropic Plates under Patch Loading

Orthotropic plates are widely used in bridge deck systems. However, these are not commonly treated as such within design specifications, and semianalytical solutions are not presently available for all deck types. This paper develops deflection equations for infinitely wide and simply supported thin plates considering each of the three cases of orthotropy: (1)?relatively torsionally stiff, flexurally soft; (2)?uniformly thick plate; and (3)?torsionally soft, flexurally stiff; subjected to arbitrary patch loading. These are common boundary and loading conditions encountered for bridge deck applications. The reported analytical solutions enable rapid evaluation of multiple moving patch loads to determine maximum design load effects and permit validation of numerical and finite-element methods. Application of the solutions will produce guidelines that can prescribe design demands and establish practical design simplifications for treatment of different bridge deck and slab systems in a uniform and consistent manner.     

Flexural Lateral Load Distribution Characteristics of Sandwich Plate System Bridges: Parametric Investigation

The sandwich plate system (SPS) is a relatively new bridge deck system that consists of steel face plates bonded to a rigid polyurethane core. The decks are thin, lightweight, and modular in design and can be tailored to numerous applications. This system provides an excellent alternative for the rapid construction and rehabilitation of bridge decks. With any new system, there exists some uncertainty in the design procedures as a result of the limited population for comparison. This paper presents the results of a finite-element parametric investigation of the lateral load distribution characteristics of SPS bridges. The parametric study primarily focuses on the influence of deck thickness on distribution behavior as compared to conventional reinforced concrete decks. Results from the study demonstrate that the inherent flexibility of a thin SPS deck yields larger distribution factors (up to 20%) than a typical reinforced concrete deck, but these distribution factors can still be conservatively estimated with current AASHTO LRFD methods. Additional comparisons indicate that the distribution behavior of SPS bridges can also be estimated with the equations proposed by the NCHRP 12-62 project.     

Nonlinear Finite-Element Analysis for Highway Bridge Superstructures

The most popular type of bridge in service today is the concrete deck on steel-girder composite bridge. A finite-element model is built to analyze the superstructure of this type of bridge under working load conditions. The deflections along a test bridge are computed by using this method; the results obtained are close to the experimental data. The concrete deck of the bridge is analyzed using nonlinear finite elements, of which the analytical procedure is described in detail. A comparison is also made between this method and the traditional transformed area method.     

Sustained-Load and Fatigue Performance of a Hybrid FRP-Concrete Bridge Deck System

The design and construction of bridge systems with long-term durability and low maintenance requirements is a significant challenge for bridge engineers. One possible solution to this challenge could be through the use of new materials, e.g., fiber-reinforced polymer (FRP) composites, with traditional materials that are arranged as an innovative hybrid structural system where the FRP serves as a load-carrying constituent and a protective cover for the concrete. This paper presents the results of an experimental investigation designed to evaluate the performance of a 3/4 scale hybrid FRP-concrete (HFRPC) bridge deck and composite connection under sustained and repeated (fatigue) loading. In addition, following the sustained-load and fatigue portions of the experimental study, destructive testing was performed to determine the first strength-based limit state of the hybrid deck. Results from the sustained-load and fatigue testing suggest that the HFRPC deck system might be a viable alternative to traditional cast-in-place reinforced concrete decks showing no global creep behavior and no degradation in stiffness or composite action between the deck and steel girders after 2 million cycles of dynamic loading with a peak load of 1.26 times the scaled tandem load (TL). Furthermore, the ultimate strength test showed that the deck failed prior to the global superstructure at a load approximately six times the scaled TL.     

Design and Construction of a Bridge in Very High Performance Fiber-Reinforced Concrete

The design, technology, and construction of a small road bridge made of very high performance fiber-reinforced concrete is described in this paper. The bridge consists of precast prestressed concrete beams with a cast-in-place ordinary concrete deck. A preliminary experimental investigation was conducted to define the mix design, to establish the properties of the material and its durability, and to study the flexural behavior of the prestressed concrete beams with and without the concrete deck. The effect of steel fibers at the structural level, where there is an influence of constitutive behavior and size effects, was analyzed by testing a prestressed beam using very high performance fiber-reinforced concrete without fibers. The establishment of the structural properties of the material then allowed the design of the final section of the bridge beams and the definition of a model to justify the design rules adopted. This project represents an attempt to demonstrate the industrial feasibility of very high performance concrete structural elements manufactured with conventional raw materials and usual production techniques and to evaluate the production technology when utilizing steel fibers.     

Evaluation of Effective Width and Distribution Factors for GFRP Bridge Decks Supported on Steel Girders

Glass fiber-reinforced polymer (GFRP) bridge deck systems offer an attractive alternative to concrete decks, particularly for bridge rehabilitation projects. Current design practice treats GFRP deck systems in a manner similar to concrete decks, but the results of this study indicate that this approach may lead to nonconservative bridge girder designs. Results from a number of in situ load tests of three steel girder bridges having the same GFRP deck system are used to determine the degree of composite action that may be developed and the transverse distribution of wheel loads that may be assumed for such structures. Results from this work indicate that appropriately conservative design values may be found by assuming no composite action between a GFRP deck and steel girder and using the lever rule to determine transverse load distribution. Additionally, when used to replace an existing concrete deck, the lighter GFRP deck will likely result in lower total stresses in the supporting girders, although, due to the decreased effective width and increased distribution factors, the live-load-induced stress range is likely to be increased. Thus, existing fatigue-prone details may become a concern and require additional attention in design.     

Lateral-Torsional Buckling of Stepped Beams with Continuous Bracing

Continuous span multibeam steel bridges are common along the state and interstate highways. The top flange of the beams is typically braced against lateral movement by the deck slab, and in many bridges the cross section is stepped at discrete points along the span. Design equations for lateral–torsional buckling (LTB) resistance in the American Association of State Highway and Transportation Officials “Load and resistance factor design bridge design specifications” are for prismatic beams and ignore the lateral restraint provided by the bridge deck. A new design equation is proposed that can be applied to I-shaped stepped beams with continuous top flange lateral bracing. By including the effects of the change in cross section size and the continuous top flange bracing, the calculated LTB resistance is significantly increased. Critical bending moment values from the proposed equation are compared to values from finite element method buckling analyses. The new equation is sufficiently accurate for use in design and in the evaluation of existing bridges.     

Experimental Characterization and Optimization of Hybrid FRP/RC Bridge Superstructure System

An experimental investigation was performed to assess the performance of a hybrid fiber-reinforced polymer/reinforced concrete bridge system. The full-scale laboratory specimen was representative of an 813?mm (32?in.) wide strip of a completed bridge in San Patricio County, Tex. The specimen was first subjected to static loading prior to casting the reinforced concrete deck. Displacement, strain, and acoustic emission were recorded. After completion of the nondestructive static loading a reinforced concrete deck was cast in the laboratory to represent one unit of the completed bridge. Load was statically applied with several increased load cycles until failure occurred at a load level exceeding 18 times the calculated design load. The results of the static testing indicated that the original design of the hybrid bridge was very conservative. An optimized design of the hybrid bridge was then derived. The static load testing program and the resulting optimized design are described.     

Field Performance of the Fiber-Reinforced Polymer Deck of a Truss Bridge

The MD 24 Bridge over Deer Creek in Harford County, Md., was one of the projects chosen by the Federal Highway Administration’s Innovative Bridge Research and Construction Program for bridge deck replacement by fiber-reinforced polymer (FRP) composites. A thorough discussion is presented on Maryland State Highway Administration’s first bridge rehabilitation project utilizing a FRP deck. The discussion includes design details, installation procedure, construction methods and in situ load testing with a wireless monitoring system. The research team installed a monitoring system to record the effects of live loads on the bridge system, including truss members, steel stringers, and plate action of the FRP deck. Finite-element models were also used in this phase. Dynamic effects of the FRP system, composite action between steel stringers and the FRP deck as well as the effective width and distribution factors of stringers were obtained and compared with the AASHTO specifications. Recommendations are also offered on improving the design details based on this experience.     

Filament-Wound Glass Fiber Reinforced Polymer Bridge Deck Modules

The demand for the development of efficient and durable bridge decks is a priority for most of the highway authorities worldwide. This paper summarizes the results of an experimental program designed to study the behavior of an innovative glass fiber reinforced polymer (GFRP) bridge deck recently patented in Canada. The deck consisted of a number of triangular filament wound tubes bonded with epoxy resin. GFRP plates were adhered to the top and bottom of the tubes to create one modular unit. The experimental program, described in this paper, discusses the evolution of two generations of the bridge deck. In the first generation, three prototype specimens were tested to failure, and their performance was analyzed. Based on the behavior observed, a second generation of bridge decks was fabricated and tested. The performance was evaluated based on load capacity, mode of failure, deflection at service load level, and strain behavior. All decks tested exceeded the requirements to support HS30 design truck loads specified by AASHTO with a margin of safety. This paper also presents an analytical model, based on Classical Laminate Theory to predict the load-deflection behavior of the FRP decks up to service load level. In all cases the model predicted the deck behavior very well.     

Frequency of Discharge Causing Abutment Scour in South Carolina

The purpose of this study is to evaluate the adequacy of the 100-year discharge along with the Froehlich bridge abutment scour equation adopted by the U.S. Federal Highway Administration (FHwA) in predicting abutment scour for bridge design purposes in South Carolina streams. The analysis utilized bridge properties, stream cross-sectional and hydraulic data, local flood frequency equations, a one-dimensional steady river flow computer model (WSPRO), and procedures recommended by the FHwA for predicting abutment scour. A method was developed to identify the single stream-discharge at each bridge that can cause the abutment scour that was observed at 73 bridge abutments. Analysis of the results revealed that for one-third of the abutments in the sandy soil region of South Carolina, the flow rates required to produce the observed scour depths had return periods greater than 100?years. Although for bridges in the region dominated by clay soil, the return periods were significantly smaller than 100?years.