Higher Level Evaluation of a Reinforced Concrete Slab Bridge

In New Mexico, many reinforced concrete slab (RCS) bridges provide service on interstates I-10, I-25, and I-40. The load rating for this type of bridge largely depends on the live-load moment in the slab. Consequently, the objective of this study was to determine a more accurate value for the equivalent strip width using higher level evaluation techniques. A continuous RCS bridge was evaluated starting with an AASHTO load and resistance factor rating analysis. A diagnostic test was then conducted to measure live-load strains which showed that the slab stiffness fit within cracked and gross section behavior. Furthermore, slab moments from finite element analysis agreed reasonably well with experimental moments derived using the average of the cracked and gross section modulus. From refined analysis, the equivalent strip widths for positive moment were 26.1 and 22.1% greater than those calculated by the AASHTO approximate method for the exterior and interior spans, respectively. The refined widths for negative moment were greater than AASHTO by 13.1 and 11.1%. This increase in the equivalent strip width reduced the live-load effects, which proportionally increased the rating factors.     

Live-Load Analysis of a Curved I-Girder Bridge

Horizontally curved, steel girder bridges are often used in our modern infrastructural system. The curve in the bridge allows for a smother transition for traffic, which creates better road travel. However, some of the disadvantages of horizontally curved bridges are that they are more difficult to analyze, design, and sometimes construct in comparison to conventional straight bridges. This study focuses on a three-span, curved steel I-girder bridge which was tested under three boundary condition states to determine it’s response to live load. The measured live-load strains were used to calibrate a finite-element model. The finite-element design moments and distribution factors for the three condition states were then compared with the results based on the V-load method. These different boundary conditions provided the researchers a unique opportunity to evaluate the impact that these changes had on the bridges behavior. It was found that while the V-load method produced positive bending moments that were close to the finite-element moments for some of the girders, this was a result of the V-load moment being unconservative and the distribution factor being conservative.     

Influence of Skew Angle on Reinforced Concrete Slab Bridges

The effect of a skew angle on simple-span reinforced concrete bridges is presented in this paper using the finite-element method. The parameters investigated in this analytical study were the span length, slab width, and skew angle. The finite-element analysis (FEA) results for skewed bridges were compared to the reference straight bridges as well as the American Association for State Highway and Transportation Officials (AASHTO) Standard Specifications and LRFD procedures. A total of 96 case study bridges were analyzed and subjected to AASHTO HS-20 design trucks positioned close to one edge on each bridge to produce maximum bending in the slab. The AASHTO Standard Specifications procedure gave similar results to the FEA maximum longitudinal bending moment for a skew angle less than or equal to 20°. As the skew angle increased, AASHTO Standard Specifications overestimated the maximum moment by 20% for 30°, 50% for 40°, and 100% for 50°. The AASHTO LRFD Design Specifications procedure overestimated the FEA maximum longitudinal bending moment. This overestimate increased with the increase in the skew angle, and decreased when the number of lanes increased; AASHTO LRFD overestimated the longitudinal bending moment by up to 40% for skew angles less than 30° and reaching 50% for 50°. The ratio between the three-dimensional FEA longitudinal moments for skewed and straight bridges was almost one for bridges with skew angle less than 20°. This ratio decreased to 0.75 for bridges with skew angles between 30 and 40°, and further decreased to 0.5 as the skew angle of the bridge increased to 50°. This decrease in the longitudinal moment ratio is offset by an increase of up to 75% in the maximum transverse moment ratio as the skew angle increases from 0 to 50°. The ratio between the FEA maximum live-load deflection for skewed bridges and straight bridges decreases in a pattern consistent with that of the longitudinal moment. This ratio decreased from one for skew angles less than 10° to 0.6 for skew angles between 40 and 50°.     

Response of Slab Bridges Before, During, and After Repair

Continuous reinforced concrete slab bridges rely on reinforcing steel bars near the top of the deck over the piers to carry negative moment. Transfer of forces in these bars may be jeopardized by deterioration and repair procedures that involve variable depth removal of deteriorated concrete around the bars. Partial or full loss of continuity could overstress the bottom reinforcement. Truckload testing of three bridges with various levels of damage was conducted before, during, and after repair in an attempt to quantify the level of loss of continuity and to examine the effectiveness of repair in terms of increasing the load transfer and enhancing the overall stiffness. Test results show loss of stiffness during repair but increased stiffness after completion of repair. The continuity was found to be lost during repair, and the slab dead load positive moments may be increased by as much as 50%. After repair, the continuity was restored, and the live-load distribution was essentially unaltered. For the test bridges, the redistribution of dead-load moment to the positive-moment zones did not appreciably affect the overall bridge rating factor. The amount of moment redistribution may be controlled through planning of repair steps.     

Stay-in-Place Fiber Reinforced Polymer Forms for Precast Modular Bridge Pier System

This paper presents an innovative modular construction of bridge pier system with stay-in-place fiber reinforced polymer (FRP) forms filled with concrete. Two 1/6 scale precast modular frames were prepared of a prototype bridge pier system. Three different types of connections were considered: male-female, dowel reinforced with or without tube embedment, and posttensioned. The frames were load tested in negative and positive bending. Subsequently, the cap beams were cut from the frames and tested to failure in four-point bending. Posttensioned joints exhibited the most robust and ductile behavior and proved to be the preferred method of joining stay-in-place forms. Even with dowel bars, the male-female joints lacked the necessary structural integrity in the pier frames. Better surface preparation for FRP units and higher quality grouting may improve the response. Embedment of the columns into the footing provided additional stiffness for the connection. The study indicated that internal reinforcement is not necessary for the stay-in-place forms outside the connection zone. The experiments also showed the importance of maintaining appropriate tolerances and match casting for male-female and embedment connections. Overall, however, feasibility of the precast modular FRP system was demonstrated in this study.     

Secondary Prestressing Moments in Rehabilitated Posttensioned Bridges

Typical rehabilitation procedures for posttensioned slab bridges involve removing concrete from the top surface of the bridge, replacing corroded reinforcement, and resurfacing with new concrete. These permanently change primary and thus secondary prestressing moments. Continuous posttensioned bridges often rely on secondary prestressing moments to counteract dead and live load moments over interior supports and thus changes caused by rehabilitation impact serviceability and, particularly, ultimate limit states. An analysis procedure is derived for computing the changes in prestressing moments caused by rehabilitation. The impact of rehabilitation on a two-span continuous voided-slab bridge is evaluated considering rehabilitation schemes where both spans are rehabilitated simultaneously,?or where one span is completely rehabilitated before work commences on the other. Rehabilitation creates concentrated primary prestressing moments at the exterior supports and at interfaces between solid and voided regions that reduce or even reverse the secondary moment at the interior support. The two-span scheme virtually eliminates secondary prestressing moments and, contrary to intuition, the span-by-span scheme has a markedly greater impact.     

Wheel Load Distribution in Simply Supported Concrete Slab Bridges

This paper presents the results of a parametric study related to the wheel load distribution in one-span, simply supported, multilane, reinforced concrete slab bridges. The finite-element method was used to investigate the effect of span length, slab width with and without shoulders, and wheel load conditions on typical bridges. A total of 112 highway bridge case studies were analyzed. It was assumed that the bridges were stand-alone structures carrying one-way traffic. The finite-element analysis (FEA) results of one-, two-, three-, and four-lane bridges are presented in combination with four typical span lengths. Bridges were loaded with highway design truck HS20 placed at critical locations in the longitudinal direction of each lane. Two possible transverse truck positions were considered: (1) Centered loading condition where design trucks are assumed to be traveling in the center of each lane; and (2) edge loading condition where the design trucks are placed close to one edge of the slab with the absolute minimum spacing between adjacent trucks. FEA results for bridges subjected to edge loading showed that the AASHTO standard specifications procedure overestimates the bending moment by 30% for one lane and a span length less than 7.5 m (25 ft) but agrees with FEA bending moments for longer spans. The AASHTO bending moment gave results similar to those of the FEA when considering two or more lanes and a span length less than 10.5 m (35 ft). However, as the span length increases, AASHTO underestimates the FEA bending moment by 15 to 30%. It was shown that the presence of shoulders on both sides of the bridge increases the load-carrying capacity of the bridge due to the increase in slab width. An extreme loading scenario was created by introducing a disabled truck near the edge in addition to design trucks in other lanes placed as close as possible to the disabled truck. For this extreme loading condition, AASHTO procedure gave similar results to the FEA longitudinal bending moments for spans up to 7.5 m (25 ft) and underestimated the FEA (20 to 40%) for spans between 9 and 16.5 m (30 and 55 ft), regardless of the number of lanes. The new AASHTO load and resistance factor design (LRFD) bridge design specifications overestimate the bending moments for normal traffic on bridges. However, LRFD procedure gives results similar to those of the FEA edge+truck loading condition. Furthermore, the FEA results showed that edge beams must be considered in multilane slab bridges with a span length ranging between 6 and 16.5 m (20 and 55 ft). This paper will assist bridge engineers in performing realistic designs of simply supported, multilane, reinforced concrete slab bridges as well as evaluating the load-carrying capacity of existing highway bridges.     

Influence of Haunches on Performance of Precast-Concrete, Short-Span, Skewed Bridges with Integral Abutment Walls

Precast-concrete, skewed bridges with integral abutment walls are, typically, designed as simplified plane rigid portal frames, neglecting the degrading effects of the skew angle, the influence of haunches between the abutment walls and the deck, and laterally unsymmetrical vertical loading. This practice produces underdesigned bridges for certain aspect ratios. It is well known that the higher shear and torsional moments near the obtuse corners cause cracking and local deterioration. To evaluate the limitations of this practice, an experimental and analytical study was carried out for the live load response at the linear service level. It has been observed that for certain bridge configurations, both the positive and negative moment stresses are higher than the stresses given by plane frame analysis. The presented qualitative results enable comparison of performance characteristics.     

Experimental Testing of Pile-to-Cap Connections for Embedded Pipe Piles

For bridges supported by piles, acceptable system performance under seismic loading depends on effective pile-to-cap connections. A fixed pile-to-cap connection is often desirable to help control deflections during lateral loading when soft soils are present. While reinforcement bar cages that extend from the pile into the cap are effective in providing a fixed pile-to-cap connection, it is more economical to rely on pile embedment to provide fixity and moment resistance. This study investigated embedded pile-to-cap connections for concrete-filled pipe piles. Four full-scale specimens, each consisting of a cap with two piles, were investigated in the field under cyclic loading. The specimens had minimal reinforcement and varying amounts of pile embedment. Results show that the moment resistance of pile-to-cap connections can be significantly greater than what is typically calculated based on the flexural reinforcement and embedment bearing. Excess moment capacity may be explained by friction between the pile and the cap at the connection. This friction mechanism is described and discussed in the context of experimental results from other studies.     

Parametric Study of Concrete Integral Abutment Bridges

A parametric study was conducted to extend the results of an experimental program on a concrete integral abutment (IA) bridge in Rochester, MN to other integral abutment bridges with different design variables including pile type, size, orientation, depth of fixity, and type of surrounding soil, fixity of the connection between the abutment pile cap and abutment diaphragm, bridge span and length, and size and orientation of the wingwalls. The numerical results indicated that bridge length and soil types surrounding the piles had a significant impact on the behavior of IA bridges. To select pile type and orientation, there is a need to balance the stresses in the piles with the stresses in the superstructure for long IA bridges or IA bridges in stiff soils. Plastic hinge formation is possible at the pile section near the pile head for combined critical variables, such as long span, compliant piles in weak axis bending, deep girders, and stiff soils. Because large pile curvatures or stresses may be caused due to the rotation of the pile cap during temperature increases, hinged connections between the abutment pile cap and diaphragm are not recommended for the practice of IA bridges. Cast-in-place piles are recommended only for short-span IA bridges because their relatively large bending stiffness can cause large superstructure concrete stresses during temperature changes.     

Evaluation of Rotational Stiffness of Elastomeric Bearing Pad-Anchor Bolt Connections on Deep Foundation Bents

Experimental tests are performed on a bearing pad-anchor bolt connection to study rotational stiffness and moment transfer capabilities of a typical bridge configuration. The experimental program is divided in two phases. The first phase consisted of shear and compression properties of two types of bearing pads. The second phase consisted of a total of 42 full-scale tests of a bearing pad-anchor bolt connection. The tested bridge-bent configuration includes two AASHTO Type II girders made continuous with a slab and diaphragm, bearing pads, pile caps, and piles. Variables included axial loads applied to the piles and bearing pads, two different sets of bearing pads, and three different pile types. The bridge connection is subjected to lateral cyclic reversed loading in one-cycle displacement increments. Test results show the potential for this type of connection to sustain lateral loads and flexural moments, and to develop the full strength of the pile elements. Shear and compression modulus are also obtained for the bearing pad types used in this study. Rotational stiffness values for the connection are determined as a function of varying axial loads.     

Parapet Strength and Contribution to Live-Load Response for Superload Passages

The main objective of this study is to evaluate the effects of parapets on the live-load response of slab-on-girder steel bridges subjected to superload vehicles and the effects of these loads on the parapets. A superload is a special permit truck that exceeds the predefined weight limitation. The presence of parapets can result in reduced girder distribution factors (GDFs) for critical girders, and this reserve strength can be considered for passage of a superload truck. This reduction is investigated, as well as the effects of discontinuous parapets and the capacity of parapets. Two steel bridges with significantly different geometric proportions were analyzed to evaluate the sensitivity of the structure to the effects of parapets. It was found that the GDFs can be decreased by as much as 30%, depending on the stiffness of the girders and the transverse truck position if the parapets are included in the analysis. The axial forces and bending moments resisted by the parapets were compared with the capacity of the parapets. The parapets and their connection with the deck were found to have adequate strength to accommodate the demand imposed by the superload trucks included in the study. For the discontinuous parapets, the open joint was determined to be acting like a notch, which increases the bottom flange stresses in the positive moment region and the tensile deck stresses in the negative moment region.     

Endurance of Deck-to-Deck Connections in Transverse Hardwood Glulam Decks

Dowel and stiffener beam deck-to-deck connections transfer shear and moment between hardwood glued-laminated (glulam) transverse deck panels in longitudinal timber bridges. The connections resist relative deflections between the deck panels and aid in the prevention of reflexive cracking of the bituminous wearing surface at panel joints. Cyclic loading can reduce the stiffness of some types of deck-to-deck connections resulting in shortened service life. The performance of dowel and stiffener beam deck-to-deck connections for hardwood glulam transverse panel bridge decks was evaluated during cyclic laoding. Five tests were conducted with steel dowel connected deck panels, and five tests were conducted with glulam stiffener beam connected deck panels. Each connection was subjected to 1,000,000 load cycles. Degradation of connector stiffness with increasing number of load cycles was determined. Stiffener beam connections had better cyclic load response than the steel dowel connections. Steel dowel connections experienced approximately 20% degradation of stiffness after 1,000,000 load cycles. Most stiffener beam connections experienced little to no stiffness degradation after 1,000,000 load cycles; the smaller stiffener beam experienced 14% degradation after 1,000,000 load cycles. All connections remained within the limits of deflection criteria established in the 1994 AASHTO LRFD Bridge Design Specifications.     

Fatigue Performance of Stringer-to-Floor-Beam Connections in Riveted Railway Bridges

The behavior of double-angle stringer-to-floor-beam connections in riveted railway bridges is examined experimentally. A series of static and fatigue tests were performed on three full-scale bridge parts taken from an old riveted railway bridge. The results of the static tests reveal that the amount of end moment developed in these connections as a result of their rotational stiffness could be considerable. As a result of the cyclic variation in this moment, fatigue damage might develop in these connections. This damage was, however, observed to have a fairly low propagation rate and did not immediately reduce the load-carrying function of the connections.     

Statistical Modeling of Coupled Shear-Moment Resistance for RC Bridge Girders

Many reinforced concrete bridges are posted or restricted to traffic, and repair or replacement decisions for these bridges involves both economical and safety considerations. To avoid the high costs of unnecessary replacement or repair, safety evaluation should be done with the most accurate methods available. Due to variability in material properties, geometrical properties, and methods of analysis, load carrying capacity evaluation may lead to uncertain outcomes. This paper presents a statistical model for combined shear-moment resistance of conventionally reinforced concrete bridge girders with common vintage design details and properties. New statistical data on stirrup spacing variability were developed from field measurements on in-service deck-girder bridges and these were combined with available data in the literature to model resistance uncertainty. The model offers bias factor and coefficient of variation for combined moment and shear carrying capacity per modified compression field theory. AASHTO-LRFD and ACI-318 were utilized to calculate capacity of the selected sections and strength reduction factors in AASHTO-LRFD and ACI-318 were compared using the obtained statistical parameters.     

Rapid Ranking Procedures for Gusset Plate Connections in Existing Steel Truss Bridges

Evaluation and rating of steel truss bridge connections has become imperative for many transportation agencies after the recent collapse of the I-35W Bridge in Minneapolis. Detailed engineering capacity calculations of gusset plate connections are time consuming and thus expensive. Large numbers of connections are in the national inventory and must be evaluated. A screening process and a simplified rapid screening process are proposed for ranking gusset plate connections in steel truss bridges to help bridge engineers identify possible vulnerable connections and aid field inspections. The procedures consider member demands relative to the connection geometric proportions for four different parameters: fasteners, plate tension, plate compression, and overall horizontal shear. The methods are demonstrated for two bridges, including the collapsed I35W Bridge, and clearly identify connections U10 and L11 as vulnerable for three of the four parameter types (fasteners were not identified as vulnerable for these connections). The ranking approach is not proposed as a substitute for thorough, detailed, and expert assessment of the connections, but rather allows rating engineers to more quickly prioritize detailed evaluations in an ordered systematic way from the most likely vulnerable connections to the least likely vulnerable connections. This technique may be considered analogous to performing screening tests on a new patient to indicate the likely medical condition prior to conducting more sophisticated and costly investigations.     

Flexural Behavior of Continuous FRP-Reinforced Concrete Beams

Continuous concrete beams are commonly used elements in structures such as parking garages and overpasses, which might be exposed to extreme weather conditions and the application of deicing salts. The use of the fiber-reinforced polymers (FRP) bars having no expansive corrosion product in these types of structures has become a viable alternative to steel bars to overcome the steel-corrosion problems. However, the ability of FRP materials to redistribute loads and moments in continuous beams is questionable due to the linear-elastic behavior of such materials up to failure. This paper presents the experimental results of four reinforced concrete beams with rectangular cross section of 200×300?mm continuous over two spans of 2,800 mm each. The material and the amount of longitudinal reinforcement were the main investigated parameters in this study. Two beams were reinforced with glass FRP (GFRP) bars in to different configurations while one beam was reinforced with carbon FRP bars. A steel-reinforced continuous concrete beam was also tested to compare the results. The experimental results showed that moment redistribution in FRP-reinforced continuous concrete beams is possible if the reinforcement configuration is chosen properly. Increasing the GFRP reinforcement at the midspan section compared to middle support section had positive effects on reducing midspan deflections and improving load capacity. The test results were compared to the available design models and FRP codes. It was concluded that the Canadian Standards Association Code (CSA/S806-02) could reasonably predict the failure load of the tested beams; however, it fails to predict the failure location.     

Finite-Element Analysis of Steel Bridge Distortion-Induced Fatigue

Welded plate girder bridges built before the mid-1980s are often susceptible to fatigue cracking driven by out-of-plane distortion. However, methods for prediction of secondary stresses are not specifically addressed by bridge design specifications. This paper presents a finite-element study of a two-girder bridge that developed web gap cracks at floortruss-girder connections. The modeling procedures performed in this research provide useful strategies that can be applied to determine the magnitude of distortion-induced stresses, to describe the behavior of crack development, and to assess the effectiveness of repair alternatives. The results indicate severe stress concentration at the crack initiation sites. The current repair method used at the positive moment region connections is found acceptable, but that used at the negative moment region connections is not satisfactory, and additional floortruss member removal is required. Stress ranges can be lowered below half of the constant amplitude fatigue threshold, and fatigue cracking is not expected to recur if the proposed retrofit approach is carried out.     

Design and Evaluation of Experimental Bridges in Tennessee

This paper describes the design and evaluates the adequacy of the moment connection of an experimental two-span highway bridge designed by the Tennessee Department of Transportation. The Massman Drive Bridge is an experimental design that unifies the construction economy of simple span bridges and the structural economy of continuous span bridges. The experimental connection, consisting of cover plates and kicker wedge plates, is used to connect the two adjoining girders over the center pier. As a result, the bridge is designed to function as a continuous bridge during the deck pour and behave compositely with the reinforced concrete deck under the live load. After completing a moment comparison analysis, it is concluded that the Massman Drive Bridge indeed acts as continuous over the pier as it was designed.     

Finite-Element Modeling of Bridge Deck Connection Details

Many steel bridges built prior to 1960 have bridge deck connections that are subject to high cycle fatigue. These connections may be nearing their fatigue limit and will require increased inspection and repair over the next 10–20 years. The Winchester Bridge on Interstate 5 in Roseburg, Ore., required the extensive replacement of connection details because of fatigue crack growth. This report describes the results of a study to assess the loading conditions for the connection details on the Winchester Bridge. Finite-element modeling methods were used to characterize the structure, on both a global and local level. The global model provided the boundary conditions for the local model of the connection details. The local model included the effects of rivet preload and friction. Finite-element analysis results were validated by hand calculation. The analysis showed significant variation in connection detail stress range, depending on the detail’s longitudinal and lateral location.