Behavior Of Girders Research Articles

Flexural Behavior of Damaged Hollow RC Box Girders Repaired with Prestressed CFRP.

In recent years, numerous studies have explored the benefits of utilizing prestressed carbon fiber-reinforced polymer (CFRP) for strengthening concrete structures. However, research on the reinforcement of prestressed CFRP on full-scale hollow RC box girders, particularly damaged bridges, remains limited. In this study, both experiments and finite element analysis (FEA) were performed to investigate the flexural behavior of full-scale hollow RC box girders with varying degrees of damage, which were strengthened using CFRP with different levels of prestress. The adhesive behavior of the CFRP-concrete interface was considered in the FEA. Numerical simulations were conducted to assess the flexural behaviors of the girders, including failure modes, yield and ultimate loads, and deflections. The results revealed that the application of prestressed CFRP efficiently increased the yield and ultimate loads of the box girders. Specifically, when the degree of damage of the hollow box girder was less than 23%, the flexural bearing capacity of the repaired girder could be recovered after being strengthened with two prestressed CFRP strips measuring 50 mm in width and 3 mm in thickness. However, the risk of premature debonding at the CFRP-concrete interface increased when the prestressing level of CFRP and degree of damage of hollow RC box girders exceeded 35% and 40%, respectively. These findings suggest that the use of prestressed CFRP may be a promising method for repairing damaged hollow RC box girders, but careful consideration of the degree of damage and prestressing level would be necessary to ensure the effectiveness and safety of the repair.

Modeling and Testing of a Composite Steel-Concrete Joint for Hybrid Girder Bridges.

A hybrid girder bridge adopts a steel segment at the mid-span of the main span of a continuous concrete girder bridge. The critical point of the hybrid solution is the transition zone, connecting the steel and concrete segments of the beam. Although many girder tests revealing the structural behavior of hybrid girders have been conducted by previous studies, few specimens took the full section of a steel-concrete joint due to the large size of prototype hybrid bridges. In this study, a static load test on a composite segment to bridge the joint between the concrete and steel parts of a hybrid bridge with full section was conducted. A finite element model replicating the tested specimen results was established through Abaqus, while parametric studies were also conducted. The test and numerical results revealed that the concrete filling in the composite solution prevented the steel flange from extensive buckling, which significantly improved the load-carrying capacity of the steel-concrete joint. Meanwhile, strengthening the interaction between the steel and concrete helps to prevent the interlayer slip and simultaneously contributes to a higher flexural stiffness. These results are an important basis for establishing a rational design scheme for the steel-concrete joint of hybrid girder bridges.

Assessment of web shear stresses and shear capacity of FRP composite tub girders for highway bridges

Reinforced polymer composite tub (CT) girders are a novel solution as the main structural element of short to medium span highway bridges. These girders are lightweight and more durable than the steel and concrete bridges they are designed to replace. Although CT girders have been shown to behave well in flexure, significant questions remain as to the shear strength and buckling resistance provided by their foam-core sandwich webs, and regarding the distribution of shears under traffic live-load. Current practice is expected to provide conservative designs but could lead to inefficient material utilization, and few bridges have been placed in service to-date. In this study, CT girder sandwich web specimens were tested in near-pure shear in an attempt to assess their ultimate shear strength. The test results justify significant increases to the current web design strengths. A comprehensive suite of finite element analyses of typical girder webs was then analyzed to assess their shear buckling capacity. The analysis results were used to create design charts that provide critical web shear buckling loads for a range of web face sheet thicknesses, web foam core thicknesses, and web depths. Finally, a diagnostic field live load test of the first CT girder highway bridge placed in service is described, which focused on examining shear live load distribution. The results of this test indicate that the original design was reasonably conservative but demonstrate the need for live load distribution factors specifically tailored to the behavior of CT girders.

Experimental investigation on composite girders with CSW-CFST truss chords subjected to combined flexure and torsion

As a new type of composite girders, composite girders with corrugated steel webs and concrete-filled steel tubular (CSW-CFST) truss chords are extensively utilized in bridge engineering. To examine the structural behavior of composite girders with CSW-CFST truss chords subjected to combined flexure and torsion, model tests and finite element analysis (FEA) are employed. Using these efficient tools, the strain distribution, deformation law, failure mode, and bearing capacity of these composite girders subjected to pure torsion and combined flexure and torsion are methodically obtained. The primary objectives are to probe the applicability of existing flexure-torsion relation curves and introduce the calculation method for the bearing capacity of composite girders with CSW-CFST truss chords subjected to combined flexure and torsion. The obtained results reveal that their failure mode is influenced by the initial torsional moment. Further, their bearing capacities due to the applied initial torsional and bending moments can be maximally enhanced by about 21.6% and 6.6%, respectively. The deviation between the predicted bearing capacity by the FEA and that obtained from the tests is less than 8.6%, demonstrating the high accuracy of the FEA model. The contribution of the torsional moment to the flexural bearing capacity is either ignored or underestimated by the existing flexure-torsion relation curves, with a minimum deviation of about 22.3%. By comparing the results acquired by the extended FEA and the calculation method proposed in this paper, it is proved that the proposed calculation method for the bearing capacity of composite girders with CSW-CFST truss chords subjected to combined flexure and torsion may reduce the deviation from 22.3% to 8.3%.

Experiments on the flexural behavior of full-scale PC box girders with service damage strengthened by prestressed CFRP plates

Two full-scale PC box girders with typical damage were derived from an in-situ bridge that was in service about 20 years, to understand the strengthening effects of prestressed CFRP plates for the entire bottom slab, casting of a RC layer in composite action with the entire top slab and steel plates anchored on the webs of the shear span. The flexural tests were conducted on the two full-scale PC box girders with and without strengthening measures, and comparative analysis was conducted regarding flexural capacity, failure mechanism, rigidity, ductility and overall structural behavior. The test results showed that the strengthening measures improved the girder rigidity by 40 % before reaching cracking state and increased the yielding and ultimate capacity by 39 % and 28% respectively. The theoretical analysis was conducted to discuss failure modes for PC box girder strengthened by prestressed CFRP plates. Theoretical equations are derived to calculate the flexural capacity of strengthened PC box girder according to typical failure modes. Good agreement with tested results was obtained. The strengthening design of the prestressing CFRP plate was verified by application in a PC box girder bridge.

Effect of concrete mixture on shear behavior of prestressed concrete girders

A total of six shear-critical prestressed concrete (PC) I-girder were tested to investigate the effect of concrete mixture types on the shear behavior of PC girders. The concrete mixtures examined were conventional concrete (CC), high-performance concrete (HPC), and self-consolidating concrete (SCC) with normal (specified fc′=41.4 MPa) and high (specified fc′=68.9 MPa) compressive strengths. Test results showed that the HPC girders exhibited a shear behavior similar to the CC girders, irrespective of the concrete compressive strength. The SCC girder with normal-strength concrete (SCC-N) showed a higher ultimate shear strength ratio (Vult/Vn) and higher ultimate displacement than the corresponding CC girder (CC-N). The SCC-N mixture was designed with a similar coarse aggregate amount but a reduced maximum coarse aggregate size compared with the CC-N mixture. The better performance of SCC-N may be attributed to a better filling ability of the SCC-N mixture than the CC-N mixture. The SCC girder with high-strength concrete showed a lower Vult/Vn than the corresponding CC girder (CC-H). The lower shear strength of the SCC girder may be attributed to the lower coarse aggregate amount (19% lower) than the CC-H girder. A shear test database of PC girders was established to investigate further the effect of coarse aggregate amount on the girder shear strength. Based on the statistical analysis, the Vult/Vn and coarse aggregate amount either showed a positive or insignificant correlation. For those groups of test data that showed positive correlation, the slopes of the linear regression of the test data showed that for a 100 kg/m3 decrease of coarse aggregate amount, the Vult/Vn decreased in average by 18.5%.

The Effect of Shear Span on the Behavior of Triangularly Corrugated Web Steel Girders

Built-up steel girders have many applications in structural engineering, both in bridges and buildings. Flat web steel girders, which are the traditional choice, involve several weaknesses. Girders with corrugated webs were found to be more effective in their load-carrying capacity and deflection than girders with flat webs. In light of this, an effort is made in this work to examine how the addition of triangular corrugated webs influences the load-bearing capacity and deflection of steel girders. This study aimed to determine whether or not the strength of built-up steel with corrugated webs could be improved. A concentrated midspan load was applied to six simply supported steel beams of varying span-to-depth ratios (1.0, 1.833, and 2.5) and web corrugation amplitudes (30 and 60 mm). An increase in ultimate strength of 15.7% to 35.1% was found for webs with triangular corrugations of 30 mm and from 2% to 29.1% for webs with corrugations of 60 mm. A reduction in deflection of up to 35.3% can be attained when using triangular corrugated webs. It was also found that using webs with 30 mm corrugations was more efficient than using webs with 60 mm corrugations. The effect of corrugation was found to fade when the span-to-depth ratio increased to 2.5. This led to the conclusion that using webs of 30 mm amplitude of triangular corrugation could improve the strength and serviceability of steel girders. Doi: 10.28991/CEJ-2023-09-02-09 Full Text: PDF

Thermal Gradients and Their Effects on Bending Behavior of Composite Girders with Trapezoidal Profiled Webs

Thermal gradient may have significant effect on the bending behavior of the composite girder with trapezoidal profiled web. To quantify such an effect on the thermos-strain action, temperature elevation test and finite element modeling were carried out on the specimens with the flange sensitive to bending and the web possessed adequate buckling resistance. The cross-sectional thermal gradients for different location away from the middle of span were measured using thermocouples and correlated using Boltzmann sigmoid equations. The applicability of finite element model was validated against experiments in terms of the distribution of thermal strain, deflections and axial strains. The axial strain distributions across the flange width and along the longitudinal direction of girder were analyzed in details. The testing and finite element modeling results showed that, the deflections with applied loads near the middle of span subjected to maximum bending moment are notably influenced by the increase of thermal gradient. The maximum axial strains at the upper surface and the lower surface of the bottom flange are obviously influenced by the temperature, especially for the girders with relatively high span-depth ratios or thicker flanges. The thermal gradient at the upper surface of the bottom flange is relatively higher than that on lower surface for every 10°C rise of temperature which meant that the upper surface of the bottom flange connecting trapezoidal profiled webs is more sensitive to thermo-elastic action.

A precise internal-stress calculation algorithm for the evolution of cracking risk of the steam-curing box girder

• The refined numerical model considers the temporal-spatial evolutionary difference. • The algorithm is established to reveal the thermal behavior of box girder. • The thermal stress evolution processes are monitored by the field test. • The results of numerical simulation and field tests are compared. • Parametric analysis is performed to investigate the influence of key factors. Thermal cracking caused by the combination of heat liberation and thermal boundaries becomes a more and more serious problem during the entire steam-curing process. To understand the rules of cracking risk and find the key factors determining the distribution of thermal stress, the numerical simulation algorithm is established and the verification field tests are deployed. Firstly, based on the equivalent maturity concept, a refined mathematic model of the thermo–mechanical coupling field is established, which fully considers the temporal-spatial evolutionary difference of material properties and hydration heat release. Secondly, the numerical algorithm is further set up for the evolution law of the thermal stress and cracking risk based on the finite element method. Thirdly, triaxial temperature strains of key points are monitored using Fiber Bragg Grating (FBG) sensors in the field. Effectiveness and accuracy of the model are verified by the agreement between numerical simulation and experimental results. Finally, based on the verified numerical model, parametric analysis is performed to investigate the influence of various key factors affecting the distribution law of the thermal stress field and the evolution law of the cracking risk. The results show that the curing temperature ( T h ) and parameters of the hydration exothermic model ( θ u and m ) are crucial to influencing the thermal behavior of the steam-curing box girder. The research provides a refined numerical algorithm of the thermo-mechanical coupling field and contributes to the high quality of huge box-girder during the entire steam-curing process.

Behaviour of Plate Girders with Intermediate Transverse Stiffeners – Experimental Investigation

AbstractTransverse stiffeners are used in slender steel plate girders along the span to give web lateral support and increase plate girder shear resistance. According to several studies, transverse stiffeners are primarily engaged in out‐of‐plane bending to laterally limit the edges of the panel as it buckles, rather than axial compression to anchor the tension field. As a result, the axial loading defined in EN 1993‐1‐5 [1] for the design of transverse stiffeners, based on tension field action, is usually deemed to be substantially larger than that observed in laboratory testing and numerical simulations. The test results of six plate girders loaded to failure, with slender webs and two transverse stiffener geometries, are presented. FE‐models that accurately replicate the tests provide a thorough view of the plate girder behaviour. The stiffeners internal forces are evaluated during plate girder loading up to failure. The transverse stiffener internal forces attained by both models are compared. It is confirmed that both the axial compression and the bending moment in the intermediate transverse stiffeners are much lower than the values prescribed by the EN 1993‐1‐5 [1].

Finite element-based parametric and forensic analysis of corrosion-induced structural deterioration in prestressed concrete bridge girders

To study corrosion effects on real structures, three prestressed concrete (PC) girders salvaged from a decommissioned 27-year-old bridge in Alberta, Canada, were studied numerically and compared to experimental tests. Nonlinear finite element (FE) models were developed to simulate the degraded flexural and shear behaviour of PC girders. The FE models were used to infer the possible unknown deterioration conditions (i.e., forensic analysis) by comparing FE-predicted and experimental behaviour of the girders. Based on the developed FE models, comprehensive parametric studies considering various corrosion-induced deteriorations at a wide range of corrosion levels were also conducted. Insights gained from the parametric study assisted assessing other girders under similar conditions. It was found that corrosion defects, such as reinforcement area loss, prestress force loss, and bonding loss in the end anchorage, affect PC girder behaviour significantly and the developed FE models of corroded PC girders can assist girder condition assessment.

Review and discussion on fire behavior of bridge girders

This paper presents an overview on fire behavior of bridge girders mainly including prestressed concrete (PC) bridge girders and steel bridge girders. The typical fire accidents occurred on bridges are illustrated and, the seriousness of posing threats to bridge structures resulted from increasing traffic fires, specially intense hydrocarbon fires generated from petrol-chemicals, is highlighted. The current researches, embracing high-temperature properties of constituent materials, prestress state, measurement in fire tests, numerical methods, structural fire resistance, and so forth, taken on coping with problems existing in fire behavior and structural fire behavior in bridge girders are reviewed and discussed. Further, strategies for enhancing fire resistance of bridge girders followed with failure criterion and mode in types of bridge structures are provided. Future research area along with emerging trends in structural fire behavior of bridge girders is also recommended for mitigating fire hazards occurred on bridge girders. Herein, it can be attained a conclusion from review and discussion that prestressed concrete bridge girders with thin webs, specially T-shaped bridge girder, are prone to unstable under fire exposure conditions. High-strength concrete utilized in prestressed concrete bridge girders is vulnerable to spalling at elevated temperature. Steel-truss bridge girder present a more significant fragility to fire exposure compared than other steel bridge girders. • Fire behavior of bridge girders is reviewed and discussed. • Seriousness of bridge fires is highlighted. • Strategies for enhancing fire resistance of bridge girders are provided. • Fire resistance in types of bridge girders is investigated and presented. • Steel-truss bridge girders are significantly vulnerable to fire damage.

Finite Element Investigation of the Ultimate Capacity of Hollow-Flange Steel Girders with Web Openings

The goal of structural design is to select member sizes that are proportional to thestructural geometry in order to achieve the most cost-effective design. Steel girders weretypically made of webs, flanges and a number of internal stuffeners, the main objectiveof this research is to develop a finite element model to study the effect of the shapes andlocations of openings on the behavior of hollow flange steel plate girders. In this study,seven models were analyzed in two groups. The first group study the effect of webopenings shape openings on the behavior of hollow flange steel plate girders, while thesecond group study the effect of web openings location on the behavior of hollow flangesteel plate girders. The girders are analyzed until the final failure has occurred. Theresults obtained from finite element analysis showed that that the absence of openinghad an important effect on the ultimate load capacity. The ultimate capacity of hollowflange steel plate girder with four squares opening decreased about 5% compared tohollow flanges steel plate girder without openings.

Analytical, numerical, and experimental determination of dynamic characteristics of prestressed concrete girders

To determine the dynamic characteristics of bridges with prestressed girders, their natural frequencies and mode shapes used to construct the superstructure must be known. However, there is no agreement among scientists on how prestress force affects the dynamic characteristics of a precast prestressed girder. The purpose of this paper is to obtain the dynamic characteristics of prestressed concrete girders through analytically, numerically, and operational modal testing. For this purpose, one of a typical precast I-girder with 1.2 m height and 27.45 m effective span length is selected as a numerical application. The three-dimensional (3D) finite element model (FEM) of the girder is modeled by SAP2000. Experimental measurements of the girder were conducted at the construction site by the operational modal testing method. For experimental measurements, ten uniaxial seismic accelerometers were mounted at the top flange of the PSC girder in the x- and z-direction. The vibrations that occur from the movement of trucks and cranes at the construction site and the impact of the hammer were measured by these accelerometers as acceleration. The measured signal was collected at the data bank and then sent to the computer equipped with Operational Modal Analysis software which used Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification techniques. The dynamic behaviors of girder were derived from analysis performed by this software. At the end of the study, the dynamic characteristic was obtained by the analytical prediction, numerical and experimental were compared with each other. It is seen that natural frequencies and mode shapes obtained from theoretical prediction, numerical and operational modal testing are not too far apart.

Lateral overturning process and failure mechanism of curved steel-concrete composite box-girder bridges under specific overloading vehicles

Curved steel–concrete composite girders are regularly adopted for use in ramp bridges in urban overpasses. As such, it is important that the lateral overturning stability of girders supported by single-column piers is analyzed. In order to comprehensively evaluate the lateral overturning mechanism of girders, this paper carries out a full-range nonlinear analysis of the lateral overturning process of a three-span curved steel–concrete composite box girder based on the explicit dynamic finite element (FE) method. According to the FE analysis results and actual forces acting on the structure, a new method for analyzing overturning stability considering the corresponding limit state is proposed. The results show that the overturning process can be divided into three stages: (i) small girder rotation; (ii) large girder rotation; and (iii) lateral displacement and overturning. The mechanical behaviors, overturning processes and failure characteristics of curved steel–concrete composite girders are similar to those of typical concrete box girders. However, some distinct characteristics, including the crawling behavior of girders and buckling of bottom plates, only exist in composite girders. The proposed overturning stability checking method is found to be more appropriate for determining the bearing capacity of girders on the ultimate limit state than the current design method described in the specifications (JTG 3362-2018). Some measures – such as setting lateral movement limiting devices, setting pre-eccentricity of supports and increasing the distance between supports which can considerably improve the lateral overturning stability of steel–concrete composite girders – are highlighted.

Investigations on Interface Shear Fatigue of Semi-Precast Slabs with Lattice Girders

Due to their high cost efficiency and flexibility, semi-precast concrete slabs with lattice girders are widely used in constructions all over the world. Prefabricated concrete slabs, combined with in situ concrete topping, exhibit a quasi-monolithic structural behavior in which lattice girders serve as vertical shear reinforcement and ensure the transfer of longitudinal shear within the interface, acting in combination with concrete-to-concrete bonding mechanisms. To be applicable in industrial and bridge construction, semi-precast slabs need to have sufficient resistance against fatigue failure. To improve and expand the limits of application, theoretical and experimental investigations are conducted at the Institute of Structural Concrete (IMB), RWTH Aachen University. To investigate the fatigue behavior of lattice girders, small size tests with lattice girder diagonals were carried out. These test results have been used to derive an S–N curve (S: stress, N: number of load cycles) for lattice girders for a more refined fatigue design. Subsequently, the fatigue behavior of semi-precast slabs with lattice girders was investigated by fatigue tests on single-span slab segments. The fatigue design regulations of lattice girders according to technical approvals can generally be confirmed by this test program; however, they tend to be conservative. The use of the derived S–N curve leads to significantly improved agreement of fatigue behavior observed in tests and design expressions.

Assessment of surface crack growth of composite girders with concrete-filled tubular flanges and corrugated webs through substructure-based numerical modelling

This paper presents an analytical assessment of surface crack growth behaviour of composite girders with concrete filled tubular flanges and corrugated webs (CGCTFCWs) with the aid of substructure-based numerical modelling. Distinctive features of crack propagation on the tubular flanges with considerable stress gradient from lower to upper cracked tube surface interacted with the weld toes along the corrugated webs are replicated in the substructure modelling and discussed in details. Based on a favourable verification of stress intensity factors (SIFs) with reported model with semi-elliptical surface crack in plates and rectangular hollow section tube, an analytically derived substructure model of critical corrugated web-flange welded details coupled to the rest of the structure is developed. Such a model is distinguished itself from that based on original Newman and Raju equation by an amendatory of the stress gradient induced by the shifting of the neutral axis and the geometry as crack penetrated through the tube wall. Based on a parametric analysis, the SIFs significantly influenced by the corrugation depth ratio, the tube thickness-to-width ratio and the tube thickness-to-depth ratio in relation with the dimensionless crack length are demonstrated and taken into account in the derivation of a new geometry amendatory coefficient. An experimental investigation was also implemented to further examine and validate the modelling crack propagation response. The resultant fatigue fracture manner and the stress concentration of the hot spot are virtually in good correlation with the modelling results. Moreover, the relations between the crack growth increment and fatigue endurances from experimental measurement match well with these predicted by the NASGRO equation using amended SIFs, indicating that the proposed model is able to trace the distinct geometry effects of the corrugated web and the tubular flange on the crack propagation response of CGCTFCWs.

Nonlinear Finite Element Modelling and Parametric Study of Prestressed Steel Box Girder

Abstract The prestressing technique is easy to apply and is generally used to strengthen steel bridges and controls their gross deflection. ANSYS has been used to establish a numerical model for the mechanical behavior of a steel box girder and prestressed by external tendons. In this paper, steel plate girders with and without strengthening technique was tested to assess the effectiveness of this technology. The results showed that prestressing improves the mechanical behavior of a girder and that its effect is proportional to magnitude of the applied external load. The results of the numerical model showed good agreement with the experimental data. A full-course simulation was conducted with ANSYS for a parametric study to analyze the influence of prestressing force magnitude, span-height ratio, and tendon configurations in increasing the effectiveness of prestressed technique.

Stresses & Strains in Plate Girder with Different Bracing Systems under Combination of Loadings

Abstract: Lateral buckling is one of the most important factors in the design of steel plate girder. This buckling in the girder can be controlled by many methods. The most popular method is to add the intermediate bracing systems along the length of girder. The unsafely designed intermediate bracing systems can easily lead to serious consequences in the construction stage due to lateral buckling by torsion which happens rapidly and suddenly when the internal force in girder exceeds the ultimate value. Reversely, if the intermediate bracing systems are designed excessively, their specific stiffness will be larger than the required one then it is very costly in both material and installing process In the present study different types of torsional bracing systems are used in twin plate girder of span 8m. As the behavior of plate girders with different type of bracing system changes differently along the length and depth. Changing the layout of bracing systems could also make the design easy and more economical. Keywords: Cross-frame Bracings, Horizontal Bracings, Plate Girder, Finite Element Analysis

Flange yield and load/deflection in plate girders with different types of end stiffeners

The load/deflection behavior of plate girders was investigated both analytically and numerically. The load/deflection values in the pre-buckling and post-buckling stages were calculated by an analytical approach presented in the literature, using the finite element program ABAQUS. The analytical effects of the parameters on the load/deflection curves were compared with experimental results published in the literature. The main parameters were the imperfection, stiffener thickness, end post type (rigid, non-rigid, stiffened, zero-e or no end post), end distance, and web panel ratio. The yield of the flanges received special attention. The analytical approach well estimated the load/deflection behaviors of panels with web panel ratios < 2.2, but could not estimate the shear strength or the deflection of no end-post plate girders. Furthermore, the equation proposed in the EN 1993-1-5 standards most realistically modeled the flange-yield results, and the load/deflection behavior of shear-loaded panels.