I-girder Bridges Research Articles

Analysis of non-uniform torsion in curved incrementally launched bridges

Incremental launching is a common and convenient methodology to build continuous girder bridges on several piers. Although it has mainly been applied to straight bridges with box sections, today it is also used for construction of horizontally curved bridges with concrete and composite steel–concrete closed or open sections like I-girders. In these cases the contribution of torsion to the stress state becomes of primary importance when the construction stages of these bridges are analysed. Moreover, the presence of thin-walled cross-sections, makes the analysis of non-uniform torsion fundamental when the angle of twist per unit length is not constant or warping is prevented in those sections where rigid internal diaphragms occur. Consequently the stress state in the launching phases can be strongly influenced by non-uniform torsion, especially for the evaluation of axial stresses in I-girder bridges, where non-uniform torsion presents its maximum influence. In this paper a methodology for the repetitive analysis of launching steps is proposed, based on the Hamiltonian Structural Analysis method, which takes into account the internal characteristics of non-uniform torsion (warping and bimoment) in order to evaluate the influence of prevented warping on the stress state at each stage of launching. The methodology is convenient because it can be considered a sort of generalised beam theory and presents a reduced computational burden with respect to finite element or boundary element procedures, with fast solution of many bridge launching static schemes. A validation of the method is given through a comparison with finite element procedures and literature data. An application is presented on a bridge with different typologies of cross-section in order to compare the different behaviours of thin-walled sections and the different degree of influence of non-uniform torsion on the stress state. The results are given in the form of envelope graphs of internal forces and stresses for the entire launching sequence and for the different cases examined.

Probabilistic Performance Assessment of Retrofitted Skewed Multi Span Continuous Concrete I-girder Bridges

The unique dynamic response of skewed bridges causes them to experience more noticeable damage compared to straight bridges during seismic events. The effectiveness of different retrofit strategies on the fragility of skewed bridges can change with the skew angle. This article assesses the impact of skew angle and various retrofit strategies on the fragility of multi span continuous concrete I-girder bridges. The results indicate that the level of effectiveness of a retrofit strategy is highly dependent on the skew angle and damage state of interest and an appropriate retrofit strategy should be chosen based on the vulnerability of the components.

Curvature Limitations for Slab-on-I-Girder Bridges

In recent years, horizontally curved bridges have been widely used in congested urban areas, where multilevel interchange structures are necessary for modern highways. In bridges with light curvature, the curvature effects on bending, shear, and torsional stresses may be ignored if they are within an acceptable range. Treating horizontally curved bridges as straight bridges with certain limitations is one of the methods to simplify the design procedure. Bridge design specifications and codes have specified certain limitations to treat horizontally curved bridges as straight bridges. However, these limitations do not differentiate between bridge cross section configurations, in addition to being inaccurate in estimating the structural response. Moreover, these specifications were developed primarily for the calculation of girder bending moments. To investigate the accuracy of these limitations, a series of horizontally curved, braced concrete slab-over steel I-girder and slab-on-concrete I-girder bridges were analyzed, using three-dimensional finite-element modeling, to investigate their behavior under dead loading. The major internal forces developed in the members were determined, namely, girder longitudinal bending stresses, vertical deflections, vertical support reactions, and bridge fundamental flexural frequencies for different degrees of curvature, span length, bridge width, and span continuity. Empirical equations for these straining actions were developed as a function of those for straight bridges. The stipulations made in bridge codes for treating a curved bridge as a straight bridge were then correlated with the obtained values from the finite-element modeling. Results proved that such code limitations were unsafe. Based on the data generated from this parametric study, sets of empirical expressions were developed to determine such limitations more accurately and reliably.

Optimizing Horizontally Curved, Steel Bridge, Cross-Frame Arrangements to Enhance Construction Performance

AbstractUnlike straight bridges where cross frames and diaphragms are considered secondary members that predominantly stabilize the compression zones of noncomposite girders during construction, the interaction of bending and torsion in horizontally curved, steel, I-girder bridges renders these components primary load-carrying members. The effect of curvature on horizontally curved bridge behavior has been shown to be more critical during construction owing to a lack of a large, hardened, concrete deck that helps to stiffen and stabilize the entire system. Therefore, cross frames play important roles with respect to stabilizing the girders and distributing loads in curved bridges during construction. This work examined the effects of a bracing system that involved skewing cross frames relative to a normal to the girder’s web, termed skewed cross frames, on the construction behavior of horizontally curved, I-girder bridges having radially oriented substructure units (abutments and piers). The performance o...

Numerical study on post-fracture redundancy of the two-girder steel-concrete composite highway bridges

As the Japan bridge inventory ages and traffic volumes increase, the government is spending more on maintaining their existing structures to extend the service life of the current bridge inventory. This includes two-girder bridges that are classified as fracture critical and non-redundant. Owing to the increased inspection costs associated with these fracture-critical bridges, there is a need to evaluate alternate load paths and to implement retrofit methods on existing bridge structures to avoid bridge replacement. In this paper, fracture redundancy of the two-girder bridge is investigated through a case study for a three-span continuous twin I-girder bridge. The finite element analysis is carried out to evaluate the load-carrying capacity after fracture of a girder of the two-girder bridge. Damage of studs near the moment contra-flexure regions are also considered in this study. Spacing between the transverse beams is discussed as possible techniques to improve redundancy and reduce the fracture potential of two-girder bridge structures. The concrete slab is indicated to be a significant member for guarantying the redundancy of the two-girder steel-concrete composite bridges.

Evaluation of common design policies for precast, prestressed concrete I-girder bridges

Evaluation of common design policies for precast, prestressed concrete I-girder bridges

A parametric study and rating of steel I-girder bridges subjected to military load classification trucks

This paper presents the flexural behavior and corresponding load rating of simply-supported steel I-girder bridges subjected to military truck loads. The military trucks are categorized by the Military Load Classification (MLC) system according to the North Atlantic Treaty Organization (NATO). A total of 144 load cases are studied for 6 different bridge models based on validated 3-dimensional finite element analysis (FEA) models to examine the deflection, lateral load distribution, and load rating of the bridges. The parameters examined include bridge characteristics (span length, girder spacing, and girder stiffness) and vehicular properties (wheel-line spacing, number of axles, and weight). The response of the bridges under the MLC trucks is compared with that under the standard HS20 trucks of the American Association of State Highway and Transportation Officials Load and Resistance Factor Design (AASHTO LRFD) specifications. Existing predictive models for load distribution factors are evaluated, including the applicability of bridge code provisions for the MLC trucks. The load rating methods based on the Load Factor Rating (LFR) and the Load and Resistance Factor Rating (LRFR) are studied.

Analisis Perhitungan Jembatan Gelagar I pada Jembatan Jalan Raya dan Jembatan Kereta Api

The bridge is a means of connecting roads which is disconnected by barriers of the river, valley, sea, road or railway. Classified by functionality, bridges can be divided into highway bridge and railroad bridge. This study discusses whether the use of I-girder with 210 m height can be used on highway bridges and railway bridges. A comparison is done on the analysis of bridge structure calculation of 50 m spans and loads used in both the function of the bridge. For highway bridge, loads are grouped into three, which are self weight girder, additional dead load and live load. The additional dead loads for highway bridge are plate, deck slab, asphalt, and the diaphragm, while for the live load is load D which consists of a Uniform Distributed Load (UDL) and Knife Edge Load (KEL) based on "Pembebanan Untuk Jembatan RSNI T-02-2005". The load grouping for railway bridge equals to highway bridge. The analysis on the railway bridges does not use asphalt, and is replaced with a load of ballast on the track and the additional dead load. Live load on the structure of the railway bridge is the load based on Rencana Muatan 1921 (RM.1921). From the calculation of the I-girder bridge spans 50 m and girder height 210 cm for railway bridge, the stress on the lower beam is over the limit stress allowed. These results identified that the I-girder height 210 cm at the railway bridge has not been able to resist the loads on the railway bridge.

Improvement effects of bottom lateral bracings on dynamic performance of curved steel twin I-girder bridges under running vehicles

The torsional stiffness of curved twin I-girder bridges is very low, which may lead to a vulnerability to eccentric dynamic loads. This study is intended to investigate the improvement effect of bottom lateral bracings on dynamic performance of curved twin I-girder bridges under running vehicles, using a developed numerical approach. In this approach, to conduct the running vehicle-bridge interaction analysis, finite element method is used to create the detailed models of both the curved bridge and the running vehicle. Parametric studies are carried out using these numerical models to investigate the effect of bottom lateral bracings on the dynamic performance of the curved bridge under running vehicles. The numerical results indicate that the proposed bottom lateral bracing systems can increase the torsional stiffness of the bridge, whose increasing rate depends on the type of bracing configuration. The bottom lateral bracings can also distribute dynamic loads smoothly between the two main girders, which leads to a more stable structure.

Statistical determination of significant curved I-girder bridge seismic response parameters

Curved steel bridges are commonly used at interchanges in transportation networks and more of these structures continue to be designed and built in the United States. Though the use of these bridges continues to increase in locations that experience high seismicity, the effects of curvature and other parameters on their seismic behaviors have been neglected in current risk assessment tools. These tools can evaluate the seismic vulnerability of a transportation network using fragility curves. One critical component of fragility curve development for curved steel bridges is the completion of sensitivity analyses that help identify influential parameters related to their seismic response. In this study, an accessible inventory of existing curved steel girder bridges located primarily in the Mid-Atlantic United States (MAUS) was used to establish statistical characteristics used as inputs for a seismic sensitivity study. Critical seismic response quantities were captured using 3D nonlinear finite element models. Influential parameters from these quantities were identified using statistical tools that incorporate experimental Plackett-Burman Design (PBD), which included Pareto optimal plots and prediction profiler techniques. The findings revealed that the potential variation in the influential parameters included number of spans, radius of curvature, maximum span length, girder spacing, and cross-frame spacing. These parameters showed varying levels of influence on the critical bridge response.

Use of response surface metamodels to generate system level fragilities for existing curved steel bridges

Fragility curves that have been developed for curved steel bridges have not extensively addressed horizontal curvature and do not sufficiently account for major contributing curved bridge components that influence their seismic response (e.g., radius of curvature, cross-frame spacing, etc.). This study considers a group of horizontally curved steel I-girder bridges located in Pennsylvania, New York and Maryland to examine the influence of important parameters on their seismic response and develop system level fragility curves for the bridge group. The developed methodology is then applied to specific bridges. This paper provides description of the procedure used to generate representative curved bridge fragility curves using input from select component fragilities. The curves were generated for representative bridge systems, and utilized fragilities from important bridge seismic components created using Response Surface Metamodels (RSMs). The critical components included items at the bearings and the supporting pier columns. A statistical screening approach, using design of experiments and incorporating seismic response information obtained from nonlinear time history analyses, was used to determine critical curved bridge component seismic response ranges. Monte Carlo simulation was then implemented to assist with fragility generation for both the group of bridges and sample bridges. Using the generated fragility, case studies were performed to investigate the effects of the certain bridge parameters on seismic vulnerability. Findings indicated that parameters that significantly influenced seismic fragilities were the number of spans, radius of curvature, and maximum span length.

Verification of shear live-load distribution factor equations for I-girder bridges

The “S-over” Load Distribution Factor (LDF) has been used for many years for determining the distributed moments and shear forces of a girder. Only until recently after the adaptation of the AASHTO LRFD Bridge Design Specification, new LDF equations are proposed using power functions. Although these new equations can more accurately predict the distributed moments and shear forces similar to both field and finite element analysis results, they are complex and they do not represent the fundamental background of LDF but rather based on regression analysis. Therefore, a more fundamental equation such as the S-over LDF is needed for the engineer to have a better understanding of the relationship between the girder sizes and spacing. The primary objective of this study is to develop a simplified S-over LDF for shear for steel and prestressed concrete I-girder bridges. Actual field testing of seven I-girder bridges were evaluated and validated to the developed Finite Element Analysis (FEA) model. A parametric study of bridges with various girder spacing and length were performed to develop the proposed equations. Results show that the proposed equations have excellent correlation with the more exact FEA model as well as the computer-based analysis.

Finite element model updating of a simply supported skewed PSC I-girder bridge using Hybrid Genetic Algorithm

Hybrid Genetic Algorithm (HGA) which combines the genetic algorithm as a global optimization and the simplex method as a local optimization is proposed for a finite element model updating of a real prestressed concrete bridge structure. In order to minimize the updating error between the measurement and the finite element model updating result, objective functions which are combinations of fitness functions based on the natural frequency, the mode shape and the static displacement are introduced. And an interface tool is also developed in order to utilize various element library and numerical analysis tools which are provided by commercial finite element and numerical analysis programs. A simply supported skewed PSC girder bridge which has 30 m span length is selected for the verification of the proposed FE model updating algorithm. Static vehicle loading test and forced vibration test by traveling vehicle as well as ambient vibration test were carried out to obtain the reference measurement data for numerical updating. A grillage model is used for the finite element analysis. Effect of the spring element to simulate the realistic support condition which is not perfectly free or restrained in real situation as well as that of the objective function on the updating accuracy are studied. From the result of parametric study, it is investigated that the use of spring element for support condition is effective to minimize the updating error for natural frequency and mode shape. Furthermore, including the static displacement fitness function together with those of dynamic properties may improve the global behavior of updated finite element model. It is concluded that the hybrid genetic algorithm proposed in this study is a very effective finite element model updating method to find an accurate result in updating real bridge structure based on measured data.

Three-Dimensional Parametric Data Exchange for Curved Steel Bridges

Improved software interoperability is key to realizing more fully the potential benefits of integrated and accelerated project delivery in a way that also somehow ensures product quality. The increasing appeal of three-dimensional (3-D) building information modeling (BIM) notions applied to bridges [known as bridge information modeling (BrIM)] motivates the need for principled prescriptions of associated electronic data exchanges between various project stakeholders and the various software applications that they use. Such data exchanges must be sufficiently precise to facilitate detailing for fabrication and construction while being sufficiently concise to facilitate parametric modeling and thereby avoid needless data duplication. The highway geometry to which bridges must conform distinguishes BrIM from the building column grid orientation of BIM at the outset of the bridge life cycle. In contrast to the over defined highway geometry in the LandXML data exchange standard, a 3-D control curve is defined, presented, illustrated, and recommended as the basis for parametric data exchange suitable through the life cycle of steel I-girder bridges on (straight and) curved alignments. This 3-D control curve combines in a single curve the traditional horizontal control line and profile grade line that bridge structural engineers receive from highway designers to define bridge geometry. Data exchanges associated with three distinct stages in the life cycle of a steel bridge are defined and illustrated: analysis and design, detailing for fabrication, and erection and construction. The data exchange based on a 3-D control curve provides the data integrity required through the life cycle of a steel bridge.

Numerical Simulation Study of Tsunami Wave Force for I-girder bridge

Numerical Simulation Study of Tsunami Wave Force for I-girder bridge

Calibration of Turkish LRFD bridge design code for slab on steel plate girders

In Turkish design practice, slab on steel composite I-girder bridges have been designed to span between 50 and 80 meters. To date, modified versions of the AASHTO LFD (Load Factor Design) or ASD (Allowable Stress Design) requirements are adapted in Turkey. The recent switch of the U.S. bridge codes to Load Resistance Factor Design (LRFD) method also necessitates the calibration of the Turkish LRFD design code that is under development. In this on-going research, it has been determined that the current Turkish design truck is not very appropriate to be used in design of bridges with span lengths in excess of 50 meters. The main aim of this study is to define a new type of live (truck) load to be used in the basic gravity load combination, as well as to develop the corresponding load factors to be implemented in the design of slab on steel composite I-girder bridges. In this scope, usually a target reliability index is selected to reflect the safety level of current design practice based on the uncertainties associated with the design parameters. For the basic gravity load combination, which includes the dead and live loads, a minimum target reliability of 4.00 is selected, instead of 3.50 that have been used in the U.S. In the statistical computations of the reliability index, the quantification of uncertainties is made based on local data supplemented by information compiled from relevant international literature.

Bridge rating protocol using ambient trucks through structural health monitoring system

A protocol for the development of a set of load rating distributions for a steel I-girder bridge will be presented. The critical regions of the bridge were instrumented using strain sensors to measure the real-time strain time history resulting from ambient trucks. This study focused on five-axle trucks traveling the south-lane of the bridge. Strain time history data was used to calibrate finite element models according to two scenarios: known and unknown truck characteristic selections. These truck characteristics identified from Weight-In-Motion (WIM) data obtained from Iowa state highways were used in the model calibration. The calibrated models, along with standard HS-20 trucks following AASHTO Load Factor Rating (LFR) method, were used to calculate a set of load ratings for each strain set as per the scenarios. Multiple load rating distributions created for strain sets were combined into a single holistic distribution. For the proposed protocol verification, the distribution was compared to that obtained from a rating package currently used by the Iowa Department of Transportation (Iowa DOT). The resulting distribution sets had means of 1.36 and 1.41 for known and unknown truck selections, respectively and subsequently were 24% and 27% greater than those values obtained from the Iowa DOT rating package. The distribution can be used not only to statistically evaluate structural capacity of such bridges, but also provide essential information for assigning retrofit prioritization of such bridges.

Application of evolutionary operation to the minimum cost design of continuous prestressed concrete bridge structure

This paper implements an evolutionary operations based global optimization algorithm for the minimum cost design of a two span continuous prestressed concrete (PC) I-girder bridge structure. Continuity is achieved by applying additional deck slab reinforcement in negative flexure zone. The minimum cost design problem of the bridge is characterized by having a nonlinear constrained objective function, and a combination of continuous, discrete and integer design variables. A global optimization algorithm called EVolutionary OPeration (EVOP), is used which can efficiently solve the presented constrained minimization problem. Minimum cost design is achieved by determining the optimum values of 13 numbers of design variables. All the design constraints for optimization belong to AASHTO Standard Specifications. The paper concludes that the robust search capability of EVOP algorithm has efficiently solved the presented structural optimization problem with relatively small number of objective function evaluation. Minimum design achieved by application of this optimization approach to a practical design example leads to around 36% savings in cost.

Effects of bottom bracings on torsional dynamic characteristics of horizontally curved twin I-girder bridges with different curvatures

Curved twin I-girder bridges (CTIGBs) have low torsional stiffness that makes them vulnerable to dynamic loads. This study investigates the effects of bottom bracings on the torsional dynamic characteristics of CTIGBs. Five types of bottom bracings are designed to investigate their effects on the dynamic characteristics of CTIGBs with different curvatures under free and forced vibrations. To perform numerical investigations, three-dimensional (3-D) finite element (FE) bridge and vehicle models are established using commercial ANSYS code, and then a vehicle-bridge interaction analysis approach is proposed. Road roughness profiles generated from power spectral density and cross spectral functions are also taken into account in the analyses. The numerical results show that torsional frequencies increase significantly after providing bottom bracings, and the increasing rate depends on the type of bottom bracings and their locations of installation. Bottom bracings can act as load transmitting members from one main girder to the others. Large negative bearing forces that have occurred in bridges with small radii of curvatures can be remarkably reduced by providing bottom bracing systems. It is found that the performances of several bottom bracing systems are effective in improving the torsional dynamic characteristics of the bridges in this study.

Bending Strength of a Horizontally Curved Composite I-Girder Bridge

AbstractHorizontally curved I-girders are subjected to combined vertical bending and torsion under gravity loads alone. The torsional behavior of open I-shaped girders is commonly and conveniently transformed to self-equilibrating lateral bending of flanges. The interaction of vertical bending and lateral flange bending reduces the vertical moment–carrying capacity of the section. The interaction equations for predicting the nominal bending strength of horizontally curved I-girders of compact-flange sections subjected to vertical moment and torsion have been derived. Singly symmetric composite and noncomposite I-shaped cross sections in the positive and negative moment zones, respectively, are considered. These strength criteria are based purely on the static equilibrium of the cross section with no secondary amplification considered. The limitations and applicability of the derived equations toward the design use are demonstrated and analyzed.