Bending Behavior of Steel Pipe Girders Filled with Ultralight Mortar

Bending behavior of steel pipes filled with ultralight mortar was studied by bending tests using a steel pipe, steel pipes filled with ultralight mortar, and steel pipes filled with light aggregate concrete and normal concrete. The steel pipe model filled with normal concrete had 1.8 times higher bending strength than the steel pipe model. The bending behavior of the steel pipe filled model with ultralight mortar was not improved when the compressive strength of the ultralight mortar was less than 1 MPa. However, ductility was much improved when the compressive strength was over 5 MPa, and the ultimate steel strain was more than double of the steel pipe model. The strains of steel and concrete in all the models were proportional to the distance from the neutral axis until the steel plate yielded. A simple analytical method was proposed to calculate the bending moments of the ultralight mortar filled steel pipes. The calculated values agreed very well with the test results.     

Flexural Capacity of Compact Composite I-Girders in Positive Bending

Current American Association of State Highway and Transportation Officials (AASHTO) bridge specifications for compact composite steel girders in positive bending with adjacent compact pier sections limit the allowable maximum strength to a value between the full plastic moment and the hypothetical yield moment of the cross section as a function of the depth of web in compression. The strength prediction equations derived using these methods provide conservative values when compared to the results of the parametric studies used to develop the equations. Recent experimental tests coupled with finite-element analysis and mechanistic evaluations of the cross-section flexural capacity suggest that larger capacities may be achieved than those determined from AASHTO’s prediction equations. This paper presents an assessment of the behavior of composite positive bending specimens. A summary of a comprehensive literature review is provided coupled with results of the analytical and experimental evaluation of the nominal moment capacity of composite girders. Lastly, a less conservative design moment capacity expression developed from this assessment is provided.     

Large Shear Studs for Composite Action in Steel Bridge Girders

Shear studs used in composite steel bridge construction are typically 19.1 mm (? in.) or 22.2 mm (? in.) in diameter. This paper presents the development and implementation of the 31.8 mm (1??in.) stud diameter. Because the 31.8 mm (1??in.) stud has about twice the strength and a higher fatigue capacity than the 22.2 mm (? in.) stud, fewer studs are required along the length of the steel girder. This would increase bridge construction speed and future deck replacement, and reduce the possibility of damage to the studs and girder top flange during deck removal. Studs also can be placed in one row only, over the web centerline, freeing up most of the top flange width and improving safety conditions for field workers. This paper provides information on the development, welding, quality control, and testing of the 31.8 mm (1??in.) stud. Information on the first bridge built in the state of Nebraska with the 31.8 mm (1??in.) studs is provided.     

Optimum Design of Welded Steel Plate Girder Bridges Using a Genetic Algorithm with Elitism

The genetic algorithm (GA) is a general optimization technique that has some unique features that are especially suitable for structural engineering problems. This work uses a simple GA with elitism to find the optimum design of welded steel plate girder bridges. The objectives are to minimize the weight and the cost of the girders. Two types of plate-girder bridges are studied: a single-span bridge and a two-equal-span continuous bridge. Bridges with various span lengths, in increments of 20?ft, are investigated; results are tabulated, parametric studies are made, and meaningful conclusions are drawn.     

Proposed Effective Width Criteria for Composite Bridge Girders

In a composite section, in-plane shear strain in the slab (acting as a flange in the composite girder) under the applied bending causes the longitudinal displacements in the parts of the slab remote from the webs to lag behind those near the webs. This phenomenon, termed shear-lag, can result in an incorrect calculation of the displacement and extreme fiber stresses when using only the elementary theory of beam bending. The effective width concept has been introduced, widely recognized, and implemented into different codes of practice around the world as a simplified practical method for design and evaluation of structural strength and stiffness while accounting for shear-lag effects indirectly. Each code implements different ideas and approaches for specifying effective width. This paper proposes simpler and more versatile design criteria for computing the effective width (beff) in steel-concrete composite bridges. A parametric study was conducted based on finite-element analysis of bridges selected by a statistical method—namely, design of experiment concepts. Both simple-span and multiple-span continuous bridges were considered in the parametric study. The finite-element methodology was validated with companion experiments on 1/4- and 1/2-scale specimens. Effective width values at the critical sections were computed from stresses extracted from FEM models and used in developing candidate design equations. The final design criteria were selected based on assessment of impact of candidate equations. Use of full width—the most versatile, simplest, and sufficiently accurate effective width design criteria, is proposed for both positive and negative moment regions.     

Effective Slab Width Definition for Negative Moment Regions of Composite Bridges

Currently, the AASHTO-LRFD design code specifies the same effective slab width design criteria for both positive moment sections and negative moment sections. The only difference in computing effective slab width between the positive and negative moment regions is the value of effective span length (Le), the definition of which is problematic. The effective slab width concept for the positive moment regions has been investigated by many researchers. However, the classical effective slab width definition does not take into account both the strain variation through the slab thickness and the mechanism that redistributes load from concrete to steel reinforcement after cracking. In this paper, a more robust effective slab width definition for the negative moment section is introduced to account for these factors. The proposed definition is developed for negative moment regions and explored by using the finite-element method (FEM). The finite-element modeling scheme is briefly discussed, and the model is successfully verified with experimental results. Numerical results show the simplicity, accuracy, and robustness of the proposed definition in extracting effective slab width values from FEM results. Numerical results also indicate that the effective slab width criteria in the current AASHTO-LRFD Specifications is typically conservative for larger girder spacings. Detailed calculations of effective slab width for the negative moment regions using the proposed definition are summarized at the end of this paper.     

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.     

Fatigue and Fracture of Steel Girders

This paper presents an overview of materials selection, design, and detailing of steel girders for fatigue and fracture limit states. The historical context of the fracture control plan for bridges is presented. A discussion of fracture toughness of structural steel and weld metal is presented along with typical Charpy and fracture-toughness test data, including the new high-performance steel A709 HPS 485W. Fatigue of cover plate details and distortion-induced cracking are discussed. Methods of dealing with variable-amplitude loading are then compared to test data.     

Correction of Errors in Simplified Transverse Bending Analysis of Concrete Box-Girder Bridges

In design practice, the transverse bending analysis of box-girder bridges is commonly done by modeling the cross section as a frame of unit width with imaginary supports at the web locations. The transverse bending moments obtained from simple frame analysis (SFA) is sometimes increased by a small percentage to accommodate the errors in modeling. In this paper, a large number of simply supported box-girder bridges have been analyzed by both SFA and three-dimensional finite element analysis for different load conditions and wheel contact areas, and the errors in SFA have been studied and quantified. The error is found to vary widely at the web-top flange junction as well as under the load (maximum sagging moment), depending on the eccentricity of loading, the wheel contact dimensions and the web-flange thickness ratio. Accordingly, a set of correction factors to the results of SFA have been proposed, which is expected to be of significant use in design practice. The use of the correction factors is demonstrated by means of two illustrative examples. The scope of the study is limited to the simplest case of a single-cell concrete box-girder bridge (simply supported with end diaphragms) without overhanging flanges.     

Seismic Behavior of Steel Girder Bridge Superstructures

Recent earthquakes exposed the vulnerabilities of steel plate girder bridges when subjected to ground shaking. This paper discusses the behavior of steel plate girder bridges during recent earthquakes such as Petrolia, Northridge, and Kobe. The paper also discusses the recent experimental and analytical investigations that were conducted on steel plate girder bridges and their components. Results of these investigations showed the importance of shear connectors in distributing and transferring the lateral forces to the end and intermediate cross frames. Also, these investigations showed the potential of using end cross frames as ductile elements that can be used to dissipate the earthquake input energy. The paper also gives an update on specifications and guidelines for the seismic design of steel plate girder bridges in the United States.     

Shear Capacity of Hybrid Plate Girders

The AASHTO LRFD Bridge Design Specifications, in versions up to and including the 2003 interim, limit the shear resistance of hybrid steel I-girders to the shear buckling or shear yield load and prevent consideration of the additional capacity due to tension field action, which homogeneous girders are allowed to include. This limitation severely affected the economy of girders utilizing high-performance steel, whose optimum configuration is often hybrid. Therefore, an experimental investigation was initiated by the National Bridge Research Organization at the University of Nebraska-Lincoln to address the limitation on the consideration of tension field action in hybrid girders. This paper presents the findings of that research. Eight simply supported steel I-girders were designed, constructed, and loaded to failure to investigate their failure mechanisms and shear capacities. All girders tested were capable of supporting loads greater than those predicted, considering full contribution from tension field action. Further, despite the coincidence of high levels of both shear and moment, relative to their respective capacities, the specimens were all capable of supporting loads greater than those predicted if shear and moment interaction were ignored. Due in part to the results of the research being presented, modifications appeared in the 2004 version of the AASHTO LRFD bridge design specifications such that the shear strength provisions apply equally to both hybrid and homogeneous girders.     

Stability Bracing Requirements for Steel Bridge Girders with Skewed Supports

Cross frames and diaphragms are critical elements for the stability of I-shaped steel bridge girders during construction. The AASHTO specifications are relatively vague with regards to the stability design requirements of the braces. Spacing limits that have been used in past AASHTO specifications have been removed from the Load and Resistance Factor Design Specification, which instead requires the bracing to be designed by a rational analysis. Whereas the AASHTO specification does not define what constitutes a rational analysis, stability bracing systems must possess adequate stiffness and strength. The commercially available software packages that are typically used in bridge design generally do not have the capabilities to determine the adequacy of the bracing from a stability perspective. This paper outlines the stability bracing requirements for bridges with normal and skewed supports. The effects of support skew on the stiffness and strength requirements for stability bracing are addressed. Solutions that are available for systems with normal supports were modified to account for the effects of the support skew angle. Two orientations of the intermediate bracing were considered: parallel to the skew angles and perpendicular to the longitudinal girder axis. The solutions are presented and compared with finite-element results. The design solutions have good agreement with the finite-element solutions.     

Development and Implementation of a Continuous Strain Monitoring System on a Multi-Girder Composite Steel Bridge

This paper describes the implementation and evaluation of a long-term strain monitoring system on a three-span, multisteel girder composite bridge located on the interstate system. The bridge is part of a network of bridges that are currently being monitored in Connecticut. The three steel girders are simply supported, whereas the concrete slab is continuous over the interior supports. The bridge has been analyzed using the standard AASHTO Specifications and the analytical predictions have been compared with the field monitoring results. The study has included determination of the location of the neutral axes and the evaluation of the load distributions to the different girders when large trucks cross the bridge. A finite-element analysis of the bridge has been carried out to further study the distribution of live load stresses in the steel girders and to study how continuity of the slabs at the interior joints would influence the overall behavior. The results of the continuous data collection are being used to evaluate the influence of truck traffic on the bridge and to establish a baseline for long-term monitoring.     

Design for Shear in Curved Composite Multiple Steel Box Girder Bridges

Modern highway bridges are often subject to tight geometric restrictions and, in many cases, must be built in curved alignment. These bridges may have a cross section in the form of a multiple steel box girder composite with a concrete deck slab. This type of cross section is one of the most suitable for resisting the torsional, distortional, and warping effects induced by the bridge’s curvature. Current design practice in North America does not specifically deal with shear distribution in horizontally curved composite multiple steel box girder bridges. In this paper an extensive parametric study, using an experimentally calibrated finite-element model, is presented, in which simply supported straight and curved prototype bridges are analyzed to determine their shear distribution characteristics under dead load and under AASHTO live loadings. The parameters considered in this study are span length, number of steel boxes, number of traffic lanes, bridge aspect ratio, degree of curvature, and number and stiffness of cross bracings and of top-chord systems. Results from tests on five box girder bridge models verify the finite-element model. Based on the results from the parametric study simple empirical formulas for maximum shears (reactions) are developed that are suitable for the design office. A comparison is made with AASHTO and CHBDC formulas for straight bridges. An illustrative example of the design is presented.     

Rotation Compatibility Approach to Moment Redistribution for Design and Rating of Steel I-Girder Bridges

Recent research has culminated in the development of moment redistribution design and rating procedures based on a “rotation compatibility” procedure. The key aspects of the rotation compatibility method are presented herein along with the resulting series of simple equations that may be used for both design and rating of straight continuous-span steel I-girders. This procedure has several advantages over the previous moment redistribution procedures. Most significantly, the rotation compatibility method provides a rational basis for removing the current restrictions on girder geometries permissible for use with moment redistribution provisions. Thus, sections that are more slender and/or have greater unbraced lengths, compared to previous inelastic procedures, may be considered. This is particularly beneficial for incorporating inelastic methods into rating specifications because many existing bridges have geometries such that they have previously been outside the scope of applicability of inelastic procedures. A second key advantage of the rotation compatibility procedure is that maximum allowable redistribution moments are specifically computed, which justifies the use of higher levels of moment redistribution and consequently greater design economy in some cases.     

State of Practice for Positive Moment Connections in Prestressed Concrete Girders Made Continuous

Precast bridges are often constructed as single span for dead load, but continuous for live load. A diaphragm connection is provided for negative moment continuity. However, the connection may also be subjected to positive moments due to time-dependent effects. Because these moments may be large enough to damage the diaphragm or even the girders, a positive moment connection is often provided. This paper reports on a study to determine the types of positive moment connections used across the country and to identify potential problems with these types of connections. A questionnaire survey was conducted to assess the state of practice for precast prestressed concrete bridges made continuous. The survey provides valuable information on this type of bridge and updates a previous survey on this subject.     

Repair of Cracked Steel Girders Connected to Concrete Slabs Using Carbon-Fiber-Reinforced Polymer Sheets

This paper presents the results of an experimental study on the repair of artificially damaged steel–concrete composite beams repaired using adhesively bonded carbon-fiber-reinforced polymer (CFRP) sheets. Eleven, 2 m long, beams composed of W150×22 steel sections with 465×75?mm concrete slabs were tested in four-point bending. Severe damage was first introduced in ten beams by saw cutting the tension flange completely at mid span, to simulate a fatigue crack or a localized severe corrosion. Standard modulus (SM) and high modulus (HM) CFRP sheets were then used to repair nine damaged beams. The length and number of CFRP layers applied to the cracked flange on the underside, or on both sides, were varied. Results showed that the damage had reduced flexural strength and stiffness by 60 and 54%, respectively. Nevertheless, CFRP-repaired beams achieved various levels of recovery, and in some cases, exceeded the original capacities. The strength of beams repaired with sheets, ranging in length from 8 to 97% of the span, varied from 46–116% of the original undamaged strength, whereas the stiffness range was 86–126% of original stiffness. SM-CFRP failed by debonding whereas HM-CFRP was ruptured. Bonding the sheets to both sides of the flange was not very advantageous over bonding to the underside only.     

Impact Factors for Curved Continuous Composite Multiple-Box Girder Bridges

The results from a parametric study on the impact factors for 180 curved continuous composite multiple-box girder bridges are presented. Expressions for the impact factors for tangential flexural stresses, deflection, shear forces and reactions are deduced for AASHTO truck loading. The finite-element method was utilized to model the bridges as three-dimensional structures. The vehicle axle used in the analysis was simulated as a pair of concentrated forces moving along the concrete deck in a circumferential path with a constant speed. The effects of bridge configurations, loading positions, and vehicle speed on the impact factors were examined. Bridge configurations included span length, span-to-radius of curvature ratio, number of lanes, and number of boxes. The effect of the mass of the vehicle on the dynamic response of the bridges is also investigated. The data generated from the parametric study and the deduced expressions for the impact factors would enable bridge engineers to design curved continuous composite multiple-box girder bridges more reliably and economically.     

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

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