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Fatigue assessment of longitudinal rib-to-crossbeam welded joints in orthotropic steel bridge decks
Abstract
Fatigue cracks at rib-to-crossbeam welded joints in orthotropic steel decks (OSDs) accelerate degradation of steel bridges. This research aims to investigate fatigue cracking characteristics of rib-to-crossbeam welded joints, and assess the fatigue strength of the welded joints through fatigue testing and finite element analysis. Nine large- scale specimens were tested under static and fatigue loading to explore the failure mode, fatigue life, and failure process. The fatigue test results were compared with the fatigue strength values recommended in different de- sign specifications. Based on the hot spot stress and notch stress approaches, S\N curves for rib-to-crossbeam welded joints were derived and compared with the existing fatigue test data. The results indicate that fatigue cracks that initiate from the weld end at the weld toe controls the fatigue resistance of the rib-to- crossbeam welded joints. A statistical analysis was performed to study the probability distribution of the fatigue strength.
... Detail C3a has been studied by researchers using experiments and Finite Element (FE) simulations [1,[10][11][12][13][14][15]. A relatively slow crack propagation rate for this detail is attributed to the cracks growing away from the crossbeam weld with its stress-raising effect. ...
... This is because the magnetic particle method, instead of visual control (the naked eye inspection), was used for crack detection in [12]. In [14], progressively increased load levels with an interval of 0.5 million cycles were applied and the visibility of crack at the initiation stage was not reported. The data in these two references are excluded from the statistical analysis. ...
... Patterns of crack propagation (grey hatched area represents the weld leg).Journal of Constructional SteelResearch 222 (2024) Statistical analysis of detail C3a using the authors' own experiments and data in the literature[1,[11][12][13][14][15] (results with mark ''*'' are excluded from the statistical analysis). ...
... Generally, there were several commonly-used methods for evaluating the fatigue performance of weld details, such as the nominal stress method [14], hot spot stress method [15,16], critical distance theory [17,18], and the equivalent structural stress method [19][20][21]. The hot spot stress method takes into account the effects of structural stress concentration caused by the geometrical discontinuity of the weld joint and adopts fewer hot spot S-N curves to characterize the fatigue life [22][23][24]. The equivalent structural stress could be employed to effectively unify different joint forms, thicknesses, and loading forms, and it was suitable for the unified evaluation of various fatigue modes [12]. ...
... where y is the distance between the neutral surface and the nodal. The relationship between the nodal forces and the line forces can obtained from [23]. Similarly, the line moments can be solved by employing a matrix equation. ...
... Similarly, the line moments can be solved by employing a matrix equation. The equivalent structural stress ΔS s can be used for correlating fatigue test results among different connections and loading conditions, regardless of plate thickness t and bending ratio r [22,23]. Note: the number in ( ) indicates that no fatigue cracks were observed at this fatigue cycle during test. ...
The fatigue cracking at transverse diaphragm cutouts and rib-to-diaphragm connections is one of the primary ways in which orthotropic steel decks (OSDs) are damaged. In this study, the fatigue damage mechanism of the cutouts and rib-to-diaphragm connections was investigated through a full-scale model experiment and numerical simulations. The applicability and accuracy of different fatigue evaluation methods for the cutouts and rib-to- diaphragm connections were compared. Furthermore, the fatigue behavior of the novel rib-to-diaphragm connection was evaluated, and its optimized structure was suggested based on parametric analysis. The results show that a complex stress distribution dominated by in-plane stresses was observed at the rib-to-diaphragm connection under wheel loading. The cracking of the weld toe at the transverse diaphragm side was found to be the dominant failure mode. The hot spot stress method has a higher prediction accuracy than the critical distance theory for predicting the fatigue life of the cutouts. For the longitudinal rib-to-transverse diaphragm connection, the hot spot stress method could be used to predict the fatigue life of U-rib side weld toes based on fatigue grade FAT 90, and the equivalent structural stress method provided a reasonable prediction of the fatigue life for all fatigue failure modes. Last but not least, a novel rib-to-diaphragm connection structure that can effectively improve fatigue performance was suggested, and its fatigue life was evidenced to be greater than 50 million cycles after geometrical parameter optimization.
... If the additional deformation caused by temperature is constrained by boundary conditions, additional stresses will be generated [3][4][5], which can reach 20% to 30% of the allowable stress in serious cases [6]. The latter will lead to serious problems such as concrete cracking, support disengagement, steel structure buckling, fatigue damage, and even bridge failure [7][8][9][10][11]. To control the structural deformation and stress caused by temperature in the construction, control, and structural health monitoring (SHM) of steel-concrete composite beam bridges, temperature measuring points are often arranged in the key section to collect temperature data [12]. ...
... The middle span is a steel box composite beam. Figure 6 shows the main geometric parameters of the section, location of temperature measuring points C1-C5-SL1-SL7-SR1-SR7, paths, and surface types (1)- (9). A single-span stiffened steel truss suspension bridge is located at 119.610° E, 28.334° N, at 571.100 m above sea level. ...
... For large bridge structures, it is difficult to accurately test the temperature on each boundary. Therefore, the second type of boundary condition was adopted in this paper, and it requires the known heat flux on the boundary which can be calculated by Equations (7)- (9). q(t) is used to represent the heat flux of the known object boundary, namely, the second boundary condition: ...
An optimization method of temperature measurement point layout for steel-concrete composite bridges based on the total least squares improved piecewise Douglas–Peucker (TLS-IPDP) algorithm was proposed to solve the problem that the traditional temperature measurement data cannot reflect the actual temperature gradient (TG) due to the position of measurement points on different paths is not reasonable. The characteristic curves of TG for the most unfavorable period and annual period are extracted from the finite element model. The rationality of the proposed method is illustrated by two typical steel-concrete composite beams with steel plates and steel boxes. By improving the classical Douglas–Peucker (DP) algorithm, the TLS-IPDP algorithm proposed in this paper has a better approximation effect on the original data. Compared with the traditional temperature measuring point arrangement method, the TLS-IPDP algorithm optimized arrangement in this paper realized the measuring point arrangement with different variable spacing under different paths; the temperature gradient curve obtained was closer to the real temperature distribution, and had higher accuracy in the region with a large gradient. In addition, the proposed method has the function of manually specifying the location of feature points and reserving the required number. The optimized arrangement of measuring points can meet the requirements of measuring points number and measurement accuracy. The method presented in this paper can provide a useful reference for temperature data acquisition and sensor layout for health monitoring of steel-composite bridges.
... However, due to stress concentration caused by structural discontinuities, weld bead notched, etc., fatigue failure problems are regarded as the main obstacle to the application of such structures. The U-rib to diaphragm welded joints in OSDs are prone to fatigue cracks under the combined action of in-plane tension and out-ofplane distortion [1]. It has also been reported that the number of fatigue cracks at such details is the highest, accounting for 38.2% of the total [2]. ...
... This rubber plate was positioned at the center of the specimen deck, where the external load was numerically verified to produce unfavorable tensile stresses at the welds of interest simultaneously. By referring to the load level defined in [1], where fatigue of the U-rib to diaphragm weld was studied based on similar OSD specimens, a fatigue load featured with a maximum load of − 20 kN, a minimum load of − 260 kN, and the loading frequency of 4 Hz was used in this paper. ...
... The fatigue cracks were initiated at the weld toe and propagated towards both sides of the diaphragm, as illustrated in Fig. 4(a). The crack features revealed by dye penetration are consistent with those reported by Huang et al. [1], demonstrating the validity of the designed fatigue specimen as well as the load configuration. Fig. 4(b) shows the steel substrate after grit blasting. ...
This paper investigated fatigue strengthening of U-rib to diaphragm welds in orthotropic steel bridge decks (OSDs) using the carbon fiber-reinforced polymer (CFRP). Fatigue testing and CFRP strengthening were performed on a full-scale OSD specimen with several U-rib to diaphragm welds. A strengthening configuration was proposed during the experiment. The testing results show that the attachment of CFRP plates on the cracked U-rib wall performed well in reducing both the local fatigue stresses and the average crack growth rate. Then, a multi-objective optimization and decision-making framework was proposed to realize the optimum design of the strengthening configuration. Considered the critical factors to the strengthening efficiency and cost, the material elastic moduli, CFRP size, and strengthening timing were chosen as design variables while maximizing the strengthened fatigue performance and minimizing the total cost were together regarded as the optimization targets. Considering the uncertainty of macrocrack propagation, Monte Carlo Simulation was used to predict the lifecycle fatigue life distribution. Then, a probabilistic assessment criterion for the strengthed fatigue performance was derived by theoretical derivation. Repeated numerical simulations were conducted to obtain the strengthened stress intensity factors using a multi-scale OSD model. Based on these simulated data, a surrogate model of the optimization objective was developed by Response Surface Methodology, which successfully considered the interaction effects between multiple design variables. Finally, the optimum CFRP strengthening configurations were derived by genetic algorithm and multi-attribute decision-making. This study is convinced to not only advance our understanding of CFRP strengthening of U-rib to diaphragm welded joints but also facilitate the optimum application of CFRP material in maintaining deteriorating steel structures.
... Steel bridge has been widely employed in highway and railway engineering because of its advantages such as light-weight, high bearing capacity and easy of assembly and construction [1][2][3][4]. However, fatigue cracks often appear at the welded joints of steel bridge resulting from weld defects, welding residual stress, and cyclic stresses subjected to traffic loads [5][6][7][8][9]. ...
... (2) Step 2: The equilibrium evolution equation for the number density balance of micro-cracks is proposed, and the equilibrium evolution equation is solved to obtain the solution for the number density of microcracks. (3) Step 3: A fatigue damage evolution model based on the number density of micro-cracks is established. Then, the model parameters by using the regression analysis of fatigue test data are determined. ...
... The fatigue cracks are often observed in OSDs of steel bridge [3], which seriously affect the safety and durability of OSDs. Especially, fatigue cracking from the rib-to-diaphragm welded joints is a common failure mode in OSDs. ...
Welding is a rapid and flexible connection that facilitates the use of a broad range of steel bridge. However, fatigue cracks initiating from various welded connection details are common problems in steel bridges. Therefore, it is vital to accurately evaluate the fatigue damage evolution and fatigue life of welded joints in steel bridge. In this study, a fatigue damage evolution model based on the meso-damage mechanics was proposed to evaluate the fatigue damage of welded joints in steel bridge. The number density of micro-cracks was adopted as the damage variable in the fatigue evolution model. Finite element modelling and user material subroutine (UMAT) in ABAQUS were combined to simulate fatigue damage evolution of welded joints in steel bridge. The fatigue damage evolution model was embedded in UMAT while the UMAT was coupled with the finite element model of the welded joints under cyclic loading. Then, the proposed model was validated by fatigue tests. The fatigue damage evolution model was also used to investigate the fatigue damage evolution process, and fatigue life prediction of the typical welded joints specimens in orthotropic steel decks (OSDs) of steel bridge. The results indicate that the fatigue strengths of nominal stress method were estimated to be 63.8 MPa for typical welded joints. The fatigue cracks mainly initiating at the weld toe and propagating along the weld toe line. The simulation results indicate that the fatigue damage evolution model provides superior ability in evaluating fatigue damage process and fatigue life of welded joints in steel bridge.
... Soliman et al. (2016) considered the optimum crack size for applying maintenance in LCM of a mode-I-dominated ship fatigue detail, and the result supports that higher expected service life is associated with a smaller repair crack size. In fact, this is not always the case, particularly for fatigue cracking of U-rib to diaphragm welded joint in an orthotropic steel bridge deck (OSD) (Huang, Zhang, Bao, & Bu, 2019), in which SIF ranges meet a sharp decrease when the crack moves away from the stress concentration zone, implying later maintenance may provide a better result. Besides, it is important to acknowledge that fatigue is a dynamic issue. ...
... A rubber sheet measuring 400 Â 400 Â 54 mm is employed to distribute fatigue loads, aiming to mimic a single tire of the vehicle model proposed in (CEN., 2003). According to the fatigue load defined in (Huang et al., 2019), the fatigue load is characterized by the maximum value of À20 kN, the minimum value of -260kN, and the loading frequency of 4 Hz. ...
... The typical crack of the critical fatigue detail generally initiates at the weld toe of the diaphragm to U-rib weld and propagates to both sides of the diaphragm along the longitudinal direction ( Figure 5) (Huang et al., 2019). Due to a lack of appropriate equipment, a fixed electronic magnifier is employed to approximate a monitoring system to deliver damage-related data for updating the macrocrack growth parameters. ...
This paper presents a Digital Twin-driven framework for fatigue lifecycle management of steel bridges. A probabilistic multi-scale fatigue deterioration model is proposed to predict the entire fatigue process of steel bridges. Bayesian inference of the deterioration parameters realizes the real-time updating of the predicted lifecycle fatigue evolution process, which provides a good basis for lifecycle optimization. To avoid an empirically predefined repair crack size for maintenance, an optimization process for maintenance strategies is included. The relationship of the extended lifetime and the design repair crack size is constructed by numerical experimental design and surrogate modeling. The solution for optimum repair crack size is obtained while maximizing the extended fatigue life and minimizing the maintenance costs. Based on the occurrence time distribution of the optimum repair crack size, the inspection/monitoring planning is determined from a probabilistic optimization process based on the minimization of the expected damage detection delay and the lifecycle costs. The uncertainties associated with the damage occurrence and detection ability are considered during the formulation of the expected damage detection delay by decision tree analysis. Based on Digital Twin concept, the predicted deterioration process, derived maintenance, and inspection/monitoring planning are timely updated until a defined stopping rule is met.
... Orthotropic Steel Deck (OSD) systems have become a fundamental element in modern bridge construction. OSDs are generally made from a flat and thin steel plate strengthened by a series of longitudinal stiffeners (ribs) that are supported by orthogonal transverse floor beams [20,54]. Crossbeams are used to transfer the loads transversely to longitudinal girders which are the main load carrying system. ...
... Welding is used to connect different components and to form an integrated OSD. This indicates that in many elements of OSDs working under fluctuating loading, fatigue can be considered as the main limit state [20,31,53,22]. Fig. 1 depicts the typical fatigue cracks observed near the welding area in OSDs. ...
... This, however, does not include a rib-to-deck fatigue detail since they are not currently pre-qualified within design standards [47]. With this respect, several studies have been performed to investigate the fatigue crack growth within the weld toe region of ribto-deck fatigue details [46,10,20,11]. However, the fatigue test data for the crack propagation in the root of the fillet weld is limited [31]. ...
Rib-to-deck connections are one of the most critical fatigue-prone locations in orthotropic steel decks. Initiated cracks in the root of a fillet weld in this location can propagate towards the deck plate due to the existence of transversal tension within the deck plate near the cracking area. Such cracks can put the structure in a very critical situation since they can reach their critical length without being inspected. The main goal of this paper, therefore, is to investigate the influence of the transversal tension on the crack propagation direction in this region. For that, one translates the loading and boundary conditions from a 3D model to a 2D model to avoid computational issues with 3D modelling. Then, a 2D crack propagation analysis is performed using XFEM method, enabling the comparison of several repair solutions. To illustrate the proposed concepts, this paper investigates the fatigue problem on a real bridge case study and characterizes the effectiveness of two possible repair solutions to cope with such fatigue issues.
... Orthotropic steel decks (OSD) are composed of orthotopically deck plates stiffened by longitudinal ribs and transverse diaphragms, which are widely used in various types of large-and medium-sized long-span steel bridges due to the benefits of a high bearing capacity, light weight, and short construction period [1][2][3][4][5][6]. In the past decades, this type of steel deck has been improved in terms of design, fabrication, and maintenance, and the structural behavior has been enhanced. ...
... The strain gauge arrangement is shown in Figure 7. The strain was converted, and the comparisons between tests and the FE model are shown in Figure 8. (1) (2) ...
The orthotropic steel deck is sensitive to fatigue, and a number of cracks have been found in existing bridges. Based on the long-span Guangzhou Mingzhu Bay steel arched bridge, this paper focus on the cracking process, fatigue mechanism, and fatigue performance evaluation of an orthotropic steel bridge deck under traffic load. A finite element model of a three-U-rib and three-span bridge deck was first established to investigate the stress state and the most unfavorable wheel loading position under the longitudinal wheel load. Then, four full-scale single-U-rib specimens were fabricated with high-strength lower alloy structural steel Q370qD in compliance with construction standards. High-cycle loading was subsequently implemented according to the Specification for Design of Highway steel bridge (JTG D64-2015), and the crack initiation, propagation process, and fatigue failure modes were studied. The results showed the stress at structural concern points is larger than in other locations, which was located around 35 mm from the welding seam of the U-rib and the lower end of the diaphragm plate. The Mingzhu Bay steel bridge deck meets the fatigue design requirements. However, the bottom of the welding seam between the U-rib and diaphragm plate is a dangerous fatigue position, and attention should be paid to the welding quality at this position during construction.
... August Wöhler put forward the concept of stress amplitude-fatigue frequency curve [3]. In the subsequent fatigue design, the nominal stress amplitude of the structure is controlled in a reasonable range [4][5][6][7], and the different fatigue strengths of welded joints were classified by the standard [8]. The essence of limiting the stress amplitude is to make the stress amplitude less than the threshold of microcrack propagation. ...
... SWT parameter and normal stress amplitude ∆σ were obtained according to the above calculation, the initiation life (N stage I ) and the stable propagation life (N stage II ) of crack can be calculated by Equations (4) and (8). As shown in Table 2, the fatigue test results (N e ) and calculation results (N f ) of specimens N1~N5 are summarized, the relationship between stress amplitude and fatigue life of stud is usually expressed by logarithmic relation. ...
To investigate the fatigue performance of the stud connectors of steel-concrete structures, fatigue crack propagation analysis and fatigue life calculation were carried out. Firstly, the finite element model with the initial crack based on linear elastic fracture mechanics (LEFM) was established, and the parameter analysis of the stress intensity factors (SIFs) of the studs and cracks with different geometric sizes was performed. Then, the propagation with mixed-type fatigue crack and I-type fatigue crack of the stud were calculated, and the variation of effective SIFs with the fatigue crack depth was analyzed. Finally, the flow chart of stud fatigue life evaluation which considers crack initiation and stable propagation was presented, and the short stud of steel-UHPC composite structures was taken as an example and verified. The calculation results show that the fatigue crack propagation type and the initial crack have an obvious influence on the fatigue life of the stud. It has acceptable accuracy that the fatigue life of short stud in UHPC simulated by considering the crack initiation. The critical damage parameters are greatly affected by the fatigue stress amplitude, and the initiation life of fatigue crack can account for more than 90% of the total fatigue life. This paper can provide a reference for evaluating the fatigue performance of studs in steel-concrete composite structures. Accurate evaluation of the fatigue life of stud connectors conforms to the concept of sustainable development.
... It is urgent to conduct experimental and numerical studies on full-scale deck-U rib joints in the OBD and develop specific S-N curves.(See Fig. 1) In addition, researchers have conducted theoretical studies and fatigue tests on U rib-to-deck connections, including single-sided welded joints [14][15][16][17][18][19][20], retrofitted bridge connections [21], butt joints [2223], and double-sided welded joints [9][10][11]. To investigate the fatigue property of deck-U rib connections, researchers conducted experimental and numerical studies with specimens with various length scales [24][25][26][27][28][29][30]. ...
... The traction structural stress can be corrected considering positive and negative stress ratios using Eqs. (15) and (16) [75]. ...
In this study, the fatigue resistance properties of single- and double-sided welded joints in OBD are investigated using the traction structural stress method by conducting experimental and numerical investigations. Full-scale fatigue specimen tests are conducted to analyze the fatigue property validations and failure modes, considering the effects of length scale, residual stress relaxation, angular misalignment corrections, and stress ratio. Double-sided welded joints have been found to fail at the interior weld toe with the propagation direction of deck thickness, and the prediction results will be more accurate considering the effect factors of angular misalignments and stress ratio. The specific united master S-N curve for the fatigue performance prediction of single- and double-sided welded joints in OBDs is recommended with the combination of fatigue test data.
... However, the welded joints in such structures are susceptible to fatigue cracking under the combined effect of cyclic loads, material heterogenous, and welding residual stresses [19,20]. The U-rib to diaphragm welded joint with irregular geometric form is one of the prominent fatigue-prone details in OSDs, enduring the combination effect of in-plane loading and out-of-plane distortion [21]. A review on fatigue of steel bridge decks by Zhang et al [22] showed that the number of fatigue cracks at the U-rib to diaphragm welds is the largest, accounting for 38.2% of the total. ...
... Alternatively, fatigue experiment on a segmental OSD specimen was conducted to achieve the fatigue data of the welded joints of interest. By referring to the specimen proposed by Huang et al. [21], the designed specimen with a global dimension of 2,900 × 1,200 × 594 mm consisted of an 18 mm thick deck, two U-ribs spaced 600 mm with a thickness of 8 mm, two diaphragms spaced 2,300 mm with a thickness of 14 mm, and several stiffened plates. All the components were made of steel Q345 and connected by employing MIG welding with carbon dioxide as the shielding gas. ...
Accurate fatigue life prediction facilitates the fatigue maintenance of steel bridges. Since Digital Twin can simulate the lifecycle for physical objects at various scales, this study aims to provide a Digital Twin-driven framework for non-deterministic fatigue life prediction of steel bridges. A probabilistic multiscale model was developed to depict the fatigue evolution throughout the bridge lifecycle. The small crack initiation period was well described by the modified Fine and Bhat model considering microstructure uncertainties. After obtaining the critical model parameter via crystal plastic finite element simulation, the modified model was further calibrated using the assumed historical fatigue data in Digital Twin database. Based on the initiated half-penny-shaped small crack, the small crack initiation period was connected to the macrocrack extension period. Given the uncertainties of macrocrack propagation, the Paris’ law with random growth parameters was adopted. The Bayesian inference of the growth parameters realized the real-time calibration of the macrocrack growth model using Markov chain Monte Carlo simulation. The feasibility of the proposed framework was demonstrated through fatigue tests on a segmental steel deck specimen with mixed-mode deformed U-rib to diaphragm welded joints. The results show that the predicted fatigue initiation life and residual fatigue life are in good agreement with the experimentally observed life results. In summary, the proposed framework enhances our understanding of the fatigue evolution mechanism throughout the bridge lifecycle and provides an entirely new approach to accurately predict the fatigue life of steel bridges under various sources of uncertainties.
... Multiple fatigue cracks were identified in different welded details of steel box girders. Notably, welded joints of U-rib to deck (Fu et al., 2018;Villoria et al., 2021;Yun et al., 2019) and rib-diaphragms (Guo et al., 2015) were reported to have serious cracks based on inspection data. Hence, U-rib to deck welded joints and longitudinal diaphragm welded joints are two critical fatigue details discussed in this study. ...
... The accuracy of these methods is insufficient to meet the requirements of fatigue assessment for existing bridges. Additionally, some researchers have analyzed the fatigue performance of bridges using normal stress, hot spot stress, and notch stress methods [12,13]. The vehicle-bridge coupled dynamic analysis technology effectively addresses these issues [14][15][16]. ...
This study proposes a fatigue life analysis method for long-span CFST arch bridges based on a vehicle–bridge coupled vibration analysis model, which can analyze the structural dynamic effects and the excessive fatigue damage caused by the passage of vehicles. In situ test analysis of bridge dynamic characteristics is carried out, and a numerical model considering the vehicle–bridge coupled system is validated according to the measured vibration modes, frequency, and displacement time history. The results indicate that the proposed vehicle–bridge coupled vibration numerical model can be used to simulate the dynamic response of the bridge under various conditions. The factors of vehicle speed, vehicle weight, and road surface condition are further selected to analyze the vehicle–bridge coupled vibration effect, and it is found that the response time history is more sensitive to the vehicle weight factor. In addition, the fatigue life of suspenders at different positions is compared, which is found to decrease significantly with a reduction in suspender length. Due to damage to the suspender caused by environmental erosion, the cross-sectional area decreases and the stress amplitude changes, resulting in a decrease in the fatigue reliability of the suspender under different conditions.
... Cheng et al. [14] investigated the crack propagation behavior of rib-to-floor, beam-welded connections in ultra-high performance, concrete-reinforced OSDs, which were subjected to longitudinal flexural loads. Huang et al. [15] investigated the propagation characteristics and fatigue life of rib-to-diaphragm welded joints under a constant amplitude load. Fang et al. [16] investigated the fatigue failure mechanism and optimization of double-sided welds in OSDs. ...
The fatigue cracking of orthotropic steel bridge decks (OSDs) is a difficult problem that hinders the development of steel structures. The most important reasons for the occurrence of fatigue cracking are steadily growing traffic loads and unavoidable truck overloading. Stochastic traffic loading leads to the random propagation behavior of fatigue cracks, which increases the difficulty of the fatigue life evaluations of OSDs. This study developed a computational framework for the fatigue crack propagation of OSDs under stochastic traffic loads based on traffic data and finite element methods. Stochastic traffic load models were established based on site-specific, weigh-in-motion measurements to simulate fatigue stress spectra of welded joints. The influence of the transverse loading positions of the wheel tracks on the stress intensity factor of the crack tip was investigated. The random propagation paths of the crack under stochastic traffic loads were evaluated. Both ascending and descending load spectra were considered in the traffic loading pattern. The numerical results indicated that the maximum value of KI was 568.18 (MPa·mm1/2) under the most critical transversal condition of the wheel load. However, the maximum value decreased by 66.4% under the condition of transversal moving by 450 mm. In addition, the propagation angle of the crack tip increased from 0.24° to 0.34°—an increase ratio of 42%. Under the three stochastic load spectra and the simulated wheel loading distributions, the crack propagation range was almost limited to within 10 mm. The migration effect was the most obvious under the descending load spectrum. The research results of this study can provide theoretical and technical support for the fatigue and fatigue reliability evaluation of existing steel bridge decks.
... Another critical point in OSDs is represented by the fatigue cracks at the rib-to-floor beam welded joints, which can accelerate the damage to this kind of bridge. To this aim, Huang et al. [14] performed fatigue tests on nine rib-to-crossbeam welded specimens in order to investigate their fatigue cracking features and their fatigue resistance. It was found that fatigue cracks had initiated from the weld toe of the rib-to-floor beam and subsequently propagated at the rib wall in the longitudinal direction. ...
Orthotropic steel deck (OSD) bridges are lightweight constructions which are convenient, especially for the achievement of long spans. Conversely, due to the stress concentration in correspondence to the numerous and unavoidable welded construction details, this bridge typology is prone to fatigue cracking under the effect of cyclic loading with high-stress amplitudes. Existing OSD bridges are particularly vulnerable to fatigue damage accumulation because of the dated standards adopted at the time of their design and the fact that heavy lorries have increased in travel frequency and weight. In the present paper, a case study of a northern Italian existing highway viaduct, built in the 1990s, is presented and analyzed. The fatigue damage accumulation was carried out according to the fatigue load models for road bridges reported in Eurocode EN 1991-2 and the assessment criteria indicated in EN 1993-1-9. The stress amplitude, in correspondence to the critical details of the bridge, is assessed by means of detailed finite-element calculations carried out with the software MIDAS GEN®. The amplitude and frequency of the travelling weights are assessed based on real traffic monitoring from the highway. Moreover, an automatic “rain-flow” algorithm is implemented, which is able to detect each nominal stress variation above the fatigue limit. In general, the bridge is not fully compliant with today’s standards when considering the entire duration of the prescribed life of the design. Countermeasures, like lane number reductions and lane reshaping, are critically analyzed since their effectiveness is questionable as far as the reduction in heavy traffic is concerned. Other interventions, like the replacement of the pavement in order to improve the stress redistribution upon the connection details below the wheel footprint, and continuous bridge inspections or monitoring, look more promising.
... It is generally believed that the fatigue crack grow at the welding toe between diaphragm and U-rib belongs to tensile-shear mixed mode crack (Choi et al., 2008;Sim et al., 2009). Compared with the single tensile mode crack, the propagation behaviors of the mixed mode crack will change significantly under complicated load, thus the fatigue life of this type of crack is difficult to predict, hence the maintenance is more difficult (Gao et al., 2017;Huang et al., 2019;Patel et al., 2010). ...
Steel box girders are easily subjected to fatigue cracking under the vehicle loading, and the crack initiating from arc notch of diaphragm is one of the typical fatigue details. The stress characteristics of diaphragm and U-rib in real bridge under the vehicle loading were analysed, as well as the deformation characteristics. Experimental work on fatigue crack propagation and bearing capacity was conducted. Simulations using the finite-element method were undertaken, and the crack propagation behaviours were studied. It is found that the out-of-plane deformation is the main cause of crack propagation at arc notch of diaphragm in real bridge. Fatigue testing data of 9 diaphragm-rib specimens carried out by the vibration fatigue test system and results of FEM simulations show that the rate and path of fatigue crack propagation changed significantly during the fatigue crack propagation. The fatigue crack initiates as a tensile-shear mixed mode crack and turns to single tensile mode with the increase of crack length.
... It implied that high residual stress existed at the Cutout detail and could highly contribute to cracking at this detail. Numbers of large-scale specimens were tested by Huang [21] to explore the failure process of RF details. It was found that the fatigue failure process of RF joints can be divided into four stages that fatigue cracks initiate from the weld end at the weld toe, then extended beyond the thickness of the floor beam, deflected upward and propagate through the rib wall, and finally propagate at an accelerated rate until failure. ...
The rib-to-floorbeam (RF) connection is the most complicated joint in orthotropic steel decks (OSDs), where four fatigue-prone details are created, i.e., the RF at the rib side (RF-R), RF at the floor beam side (RF-F), RF at the rib wall (RF-W), as well as the floor beam cutout detail. In order to clarify the behavior of those details under the passage of trucks, a controlled truck loading test and finite element analysis (FEA) are performed at various typical transverse loading locations on a newly built long-span cable-stayed bridge. The research finds that, in the bridge transverse direction, stresses at the four details presented significant local effects. Only when these details are underneath the deck plate covered by the wheel patch a notable stress can be produced at these details. In the bridge longitudinal direction, the wheel loading effect at the four details can be discerned only when the wheels load on the deck supported by their adjacent floor beams. The results find that, under wheel loading, the stress ranges at the RF-R, RF-F and Cutout details are compressive, while the stress at the RF-W detail is in tension. The riding-rib-wall loading is the most critical transverse loading location for the RF and Cutout details, and the RF-W is the most critical fatigue detail in the RF connection. The FEA indicates that, due to offset of wheel loads, floor beams may suffer from severe out-of-plane bending, while ribs may experience notable warping and distortion. Under the passage of the tandem axles, the individual axle cannot be identified, and only one stress cycle is produced at the four details.
... Nowadays, in order to meet the increasing traffic demand, the steel box girders with larger width would be designed, in which more traffic lanes could be set. Many super-wide steel box girders have been used in the real bridge, such as Qingshan Yangtze River Bridge (girder width: 48 m) [13], Yunlongwan Bridge (girder width: 48.5 m) [14], Linggang Bridge (girder width: 63.9 m) [15], New San Francisco-Oakland Bay Bridge (girder width: 78.74 m) [16], etc. However, the spatial effects (e.g., shear-lag effect, complex deformation effect) of the super-wide steel box girders are quite obvious [17,18], and the effects of wheel loads on the welded details are different in each lane [19], which means the influence of vehicle transverse location should be analyzed carefully. ...
This study presents an investigation on the fatigue analysis of four types of details on orthotropic steel decks (OSDs) for a cable-stayed super-wide steel box girder bridge based on finite-element analysis (FEA) with vehicle transverse distribution model (VTDM). A high-fidelity 3D FE model verified by the static load test is established to satisfy the fatigue analysis accuracy. The stress behavior of super-wide steel box girders under the vehicle load at different lane locations is investigated. Then, considering the effect of VTDM, the fatigue life analysis of four typical details is performed using the Miner cumulative damage rule. The results show that the vehicle transverse location has a great influence on the stress behavior of details with sharp influence surface, and the stress ranges in the outermost lane are larger than those in other lanes, indicating that the details of OSD in the outermost lane are prone to fatigue. The fatigue life analysis indicates that the diaphragm cutout is more prone to fatigue than other details, which should be carefully treated in bridge maintenance.
... Taking the example of the commonly-used closed rib with trapezoidal cross-section, the torsional rigidity of the ribs is reduced due to the distortion of ribs if the tire load is eccentric from the axis of the rib. At the intersection of rib and crossbeam, the deformation is impeded by the heavy crossbeam which causes high stress concentrations at the web of rib and finally makes this detail prone to fatigue [6][7][8][9]. On the other hand, the cost that is spent on welding the rib-to-crossbeam joint with cope holes is rather expensive. ...
In orthotropic steel decks (OSDs), the rib-to-crossbeam joint is the most complex joint. When dealing with the intersection of the rib to the crossbeam, the prevailing approach is to design a cope hole in the crossbeam web. Nevertheless, the stress concentration induced by rib distortion makes this joint a fatigue-prone detail. Furthermore, the weld connecting the rib and the crossbeam heavily relies on the manual welding, which leads to high fabrication costs. In this paper, the possibility of canceling the cope hole is discussed. Calculation results of different modeling methods using solid elements and shell elements are first compared with experimental results. Then, several design parameters of an OSD without cope holes are investigated adopting the hot spot stress method. Based on the results of the parametric analyzes, optimized dimensions of the rib-to-crossbeam joint without cope holes are selected. The comparison of the models with and without cope holes is performed. Fatigue life assessments are conducted based on the influence surfaces of reference points predefined around the rib-to-crossbeam joint. Research results reveal that the most critical position for the rib-to-crossbeam joint without cope holes is at the curvature on the rib side. The radius of rib has a local influence on the points at the curvature. A larger radius could effectively lower the maximum stress range. The fatigue performance of the rib-to-crossbeam joint depends on the distribution of the tire load. Considering less fatigue-prone locations and reduced fabrication costs, the overall performance of the optimized rib-to-crossbeam joint without cope holes is better.
... The results indicate that the FAT90 fatigue class is the most suitable for estimating the fatigue resistance of rib-to-crossbeam welded connections in a railway OSD. Huang et al. (2019a) tested nine large-scale specimens using static and fatigue loading to explore the failure mode, fatigue life, and failure process. The hot spot stress was computed by linear extrapolation. ...
... By conducting fatigue testing of full-scale OSD and FEA for wrap-around weld, Zhang et al [12] concludes that the S-N curves of FAT90 and FAT225 in Eurocode 3 [13] can be employed to perform the fatigue evaluation of the fatigue detail for hot-spot stress method and notch stress method, respectively. Those conclusions were further conformed by Huang et al [14]. By utilizing the full-scale OSD specimen and submodel FEA technique, Zhu et al [15] deems that internal bulkheads are available to enhance the fatigue performance of the wrap-around weld at RF joint and the bulkhead shape will greatly affect the hot-spot stress. ...
As an innovative cement-based material, the ultra-high performance concrete (UHPC) has been recently utilized to reinforce the orthotropic steel bridges. Based on an in-situ steel-UHPC composite orthotropic deck bridge, both the field testing and multi-scale finite element analysis modelling were conducted to investigate the fatigue behavior of wrap-around weld at rib-to-floorbeam (RF) joint, and factors influencing stress were further studied to achieve an infinite fatigue life. It is found that a primary tensile stress cycle is jointly produced by the axle group of truck, while a small reversal compressive cycle will be generated when the axle is directly located on the floorbeam. The stress behavior of fatigue detail is extremely sensitive to the localized effect of axle loading instead of entire truck configuration. Since significant stress concentration and high stress gradient exist in the wrap-around weld, it is essential to utilize the hot-spot stress approach rather than nominal stress approach. The wrap-around weld presents an obvious out-of-plane bending deformation, which results from the torsion effect and Poisson’s effect. The Dong’s structural stress reveals that the surface stress is dominated by bending stress. The application of bulkhead can greatly improve the fatigue performance of wrap-around weld. Both the large-scale rib and U-shaped rib are preferable, which are available to achieve an infinite fatigue life without extra fabrication procedure.
Fatigue cracking of rib-to-deck conventional single-sided welded joints is a prevalent issue in orthotropic steel decks (OSDs), significantly impacting their structural integrity and durability. Rib-to-deck innovative double-sided welded joints have the potential to enhance the fatigue resistance of OSD. However, Welding Residual Stresses (WRS) significantly influence the fatigue life of these joints, mandating its consideration in fatigue assessments. This study introduces a novel approach for assessing the fatigue reliability of rib-to-deck double-sided welded joints in OSDs, accounting for the effects of traffic vehicle loading and WRS. Initially, a comprehensive fatigue damage equation for welded joints of OSDs was formulated, integrating WRS and dynamic vehicle loads, utilizing fracture mechanics theory. Subsequently, a measurement-based random traffic model was utilized to derive the vehicle-induced stress spectra at the welded joints. The effects of deck thickness, fatigue crack depth and fatigue crack aspect ratio on the stress intensity factor (SIF) of the crack at the weld toe were analyzed. These three variables were considered as feature vectors for the construction of a polynomial model of the shape functions, which was utilized to calculate the SIF. Finally, the fatigue reliability of the rib-to-deck double-sided welded joints in OSDs subject to traffic vehicle loading considering the WRS was estimated using Monte Carlo simulation. The influence of traffic volume growth on fatigue reliability was discussed. This research underscores the critical role of WRS in the fatigue performance of welded joints in OSDs and offers an innovative framework for assessing the fatigue reliability of steel bridge welds.
U-rib to diaphragm welds in orthotropic steel decks (OSDs) experience mixed-mode fatigue cracks and exhibit a more intricate stress state compared to the well-studied deck to U-rib welds. To mitigate the failure risks associated with such cracks, an investigation was conducted into a strengthening method using externally bonded carbon fiber-reinforced polymer (CFRP) plates through extensive fatigue experiments and numerical simulations. Three large segmental OSD specimens were tested to evaluate fatigue behavior, as well as stress indicators and crack growth rates before and after strengthening. Complementing the experimental results, validated multi-scale numerical models were established to provide further insight into stress intensity factors. This study demonstrated the effectiveness of the strengthening method and thoroughly investigated the influences of various strengthening parameters. A three-step method for determining the optimal strengthening configuration was also proposed, aiming to maximize both structural safety and the probability of crack arrest. The findings presented in this study contribute to our understanding of fatigue behavior in OSDs and provide valuable guidance for the design and application of CFRPs in bridge maintenance.
The prediction of fatigue cracks on orthotropic steel decks is of great significance to the maintenance of bridges. However, fatigue cracks are affected by various uncertainties in reality, which encourages a data‐driven study for the sake of reliability and accuracy of predictions. Based on the crack inspection data from orthotropic steel decks on actual bridges in China, the feature engineering is conducted considering fatigue crack behaviors, and the machine learning models are trained and tested for predicting cracks, including XGBoost, random forest, and multiple decision trees. According to the receiver operating characteristic curves of the three models, the XGBoost model has the best performance, whereas the average AUC is about 0.75, limited by the insufficient data volume of positive samples. With the SHAP values of all features, the interpretation of the machine learning model is presented, indicating that the global effects, that is, the longitudinal position, the loading condition, and the bridge age, are always influential factors for fatigue cracks. The local features concerning the interactions between cracks have an effect on crack behaviors to a certain extent, but less important. Accordingly, the interpretable machine learning model can provide conservative predictions in a rather transparent way on this issue, which can benefit decision‐making in bridge designs, maintenance, and management.
The design of orthotropic bridge decks (OBD) is driven by fatigue. The Eurocode on fatigue of steel structures – prEN 1993‐1‐9:2023 – provides fatigue resistance (S‐N) curves for relevant details in OBD. These curves are to be used with the far field (nominal) stress. However, due to the complex geometry and loading of OBD, the nominal stress is not well defined for many details. In addition, cracks have been found in practice in OBD at locations for which S‐N curves are not provided. In order to overcome these issues, experimental and numerical studies are carried out on the use of local stresses (hot‐spot stresses where possible) for the fatigue design of OBD. The different stress extraction method also implies the use of different S‐N curves. A large number of fatigue tests carried out in the past have been re‐evaluated to determine the hot‐spot stress S‐N curves. Additional fatigue tests have been carried out for details lacking data. The study has resulted in a guideline to design OBD for fatigue with the hot‐spot stress method. This guideline, TS 1993‐1‐901:2023, will be published as a Technical Specification (TS) to the standard prEN 1993‐1‐9:2023.
This paper provides a short background to the newly created TS. It demonstrates the derivation of S‐N curves based on available tests for a number of details. It highlights fatigue relevant details that are missing in prEN 1993‐1‐9:2023 and that are added to TS 1993‐1‐901. It explains how to evaluate cracks starting from the root of the weld, for which the hot‐spot stress method is traditionally not applicable. Finally, the paper demonstrates how the method can be applied in the fatigue design, including the application of the load in finite element models.
In this work, a bionic structure was redesigned for a specific type of crossbeam and the corresponding modification strategies were formulated. Three modification schemes were put forward and the corresponding parameterized analysis models established. Sensitivity analysis results guided the variable parameter selection and the total design of an orthogonal test. Data obtained were utilized to establish a neural network model that reflects the dynamic nonlinear mapping relation. Then, a collaborative optimization design method was proposed that was based on the neural network and the genetic algorithm for secondary design of the rib thickness. Through optimizing the neural network model by NSGA-II, Pareto optimal results were obtained. The results showed that the mass of the newly designed crossbeam had been reduced by 3.74%, while the first three orders of natural frequency had been increased by 6.67%, 3.47% and 14.20%, respectively. The bionic modification structure and the collaborative optimization design method were proved to be valuable for redesign in the remanufacturing field.
Fatigue performance of orthotropic steel decks (OSDs) is one of the concerns that should be carefully considered, since OSD is reported as one of the most structures experiencing fatigue defects. In this study, the fatigue crack propagation behavior of welded connections in OSDs was investigated using 3D crack simulation based on the linear elastic fracture mechanics (LEFM). Fatigue testing results of rib-to-deck and rib-to-floorbeam welded specimens were considered to validate the applicability and efficiency of the crack propagation analysis. Stress intensity factors (SIFs) of the test specimens were computed using the M−integral approach, where Mode I (opening mode) and mixed-mode (i.e., combining Mode I, II, and III) of failure were considered. Additionally, the effect of the applied stress range amplitude, initial crack size, and UHPC layer thickness on the crack propagation behavior of welded joints under consideration were explored. The results indicated that the crack simulation analysis is acceptable and applicable for the evaluation of fatigue crack propagation of welded connections in OSDs. The computed SIFs demonstrated that the governing propagation mode of rib-to-deck and rib-to-floorbeam welded joints is Mode I (opening mode) and the effect of shear and tearing is limited. For both details (i.e., RD and RF welded joints) the decrease of the stress range amplitude and the increase of the UHPC layer thickness considerably slowed the crack propagation, while the increase of the initial crack size significantly accelerated the crack propagation. Comparison of the test and numerical results with the Ssingle bondN curves showed that FAT100 curve of the IIW specification is recommended to predict the fatigue strength of RD and RF welded joints in OSDs reinforced by UHPC layer.
This study investigated the fatigue behavior of fillet weld steel joints (including cruciform and T-welded joints) in marine structures based on experimental tests and finite element analysis (FEA). In cyclic tensile loading, fatigue failure of full-scale specimens consistent with in-plane failure mode of marine structures was validated with ultrasonic phased array testing (UPAT). The effect of incomplete penetration and weld profile on fatigue performance were analyzed based on traction structural stress method. The results showed that the failure mode of load-carrying cruciform joints would change when the incomplete penetration ratio p’/tr reached 0.91. And the concave weld profile is better choice for welded structures anti-fatigue design. In view of the complexity of fatigue performance evaluation of fillet weld joints in IIW and BS7608 standards, a unified master S–N curve covering different plate thicknesses, materials, and weld profiles was proposed.
To investigate the fatigue performance and fatigue damage process of the Orthotropic Steel Deck (OSD) - Ultra-High Performance Concrete (UHPC) composite bridge deck, a two-span continuous full-scale specimen was designed and tested under cyclic loading. Test results showed that the fatigue cracks firstly initiated near the lower part of the weld toe of the rib-to-cross beam welded joint, and then cracks along the weld length of the U-rib butt-welded joint developed. These observations followed by the OSD-UHPC interface debonding. The U-rib bolted joint exhibited better fatigue resistance than the U-rib butt-welded joint. The S-N curves of the rib-to-cross beam welded joint, the U-rib butt-welded joint and the U-rib bolted joint were established based on existing fatigue test data, and were compared with provisions in design codes. The S-N curves from the beam test for the short-headed stud connectors were compared with that from the push-out test. And the established S-N curves with 95% survival probability from the push-out test could be used to assess the global fatigue performance of the composite deck. Considering the durability-based critical crack width of UHPC, the established tensile S-N curve regarding critical UHPC crack width of 0.05 mm could be used to evaluate the anti-fatigue cracking ability of the UHPC layer in the composite deck system.
The orthotropic steel deck is widely used in long-span steel bridges due to its simplicity and efficiency. The welded joint of the U-rib to e deck panel area is extremely sensitive to fatigue cracks. In this study, an orthotropic steel deck with an arc-shape stiffener was proposed that aimed to alleviate the fatigue cracks and enhance the fatigue resistance in long-span steel bridges. Based on the Mingzhu Bay steel bridge, the proposed steel deck FE model was first established. Then, the moving vehicle load was applied to investigate the impact of the arc-shape stiffener on the fatigue stress amplitude and distribution. The Miner fatigue cumulative damage theory was employed to evaluate the fatigue life of the orthotropic steel deck with arc-shaped stiffener, and comparative analyses were carried out. Finally, the results show the maximum stress of the orthotropic steel deck with an arc-shaped stiffener is reduced by 15%, and the fatigue life is improved by 40% compared with the OSD.
In this study, the distribution of residual stress of the substructure model and small coupon specimens in orthotropic steel bridge structures is experimentally and numerically investigated to validate adequate specimen sizes. Blind‐hole drilling and X‐ray diffraction methods are used to capture longitudinal and transverse residual stresses and evaluate the effects of the cutting process. The maximum LRS and TRS were reduced by 16.6% and 15.6% from those that existed before cutting, verifying the proper size of small voucher specimens. The width‐to‐thickness ratio of 6–6.25 of small coupon specimens has proven sufficient to capture the effects of stress triaxiality induced by the residual stress. In the spirit of master S‐N curves in ASME standard, the role of residual stress was represented in the fatigue process and does not be additionally taken into account when predicting the fatigue performances of welded structures using prediction methods based on the S‐N curves. Residual stress is experimentally studied for validating adequate specimen sizes. Width‐to‐thickness ratio of 6–6.25 of small coupon specimens was proven sufficient. Residual stress was included in test data and need not be additionally considered.
Cutouts are usually used in orthotropic steel decks (OSDs) of bridges and subject to complex stresses under loads. This research performed experimental and theoretical investigations to evaluate the effect of a thin UHPC layer on the fatigue performance of upper cutouts in OSDs. A full-scale specimen was fabricated and tested under static and fatigue loads before and after the specimen was strengthened with the UHPC layer. The results show that a fatigue crack initiated from the weld toe at the upper cutout after 1.15 million cycles of fatigue load with a load range of 216 kN. The use of the UHPC layer generated a steel-UHPC composite specimen subject to an extra fatigue loading for 2 million cycles with the same load range. The propagation length of the fatigue crack was only 1.2 mm, and the propagation rate was reduced from 0.61 × 10⁻⁴ mm/cycle to 0.0095 × 10⁻⁴ mm/cycle, with a reduction of 98.4%. The peak stress at the crack tip decreased from 139.0 MPa to 51.6 MPa, by 62.9%. A series of finite element analyses was performed to evaluate the fatigue damage. It was found that the use of the UHPC layer significantly reduced fatigue damage in the fatigue-prone detail around the upper cutouts and extended the fatigue life accordingly.
Resin asphalt is one of the best choices for steel deck pavements owing to its excellent performance characteristics, such as high rigidity, excellent high-temperature stability, and convenient construction. Recently, resin asphalt has been increasingly used in orthotropic steel decks (OSDs), significantly influencing their stress levels. To determine the effect of a resin asphalt pavement on the stress behaviors and fatigue performance of double-side welded rib-to-deck (RTD) joints, experimental and numerical approaches were combined. A full-scale OSD specimen with a steel deck pavement was fabricated and tested under different temperature conditions. The experimental results indicated that the transverse bending rigidity of the deck could be improved by laying the resin asphalt pavement, and the stress ranges of the double-side welded RTD joints were significantly reduced. The stress behaviors of double-side welded RTD joints are sensitive to the pavement temperature. Thus, the stress ranges of the double-side welded RTD joints increased significantly with the temperature of the resin asphalt pavement. Furthermore, the numerical results showed that the maximum equivalent stress range of the double-side welded RTD joints occurred at crack type T2, under the transverse loading location of e = −150 mm. The equivalent stress range of the four crack types in the double-side welded RTD joints decreased significantly as the thickness of the resin asphalt pavement increased. The findings of this study suggest that the influence of resin asphalt pavements and their temperature effect must be considered to accurately evaluate the fatigue performance of RTD joints.
Various fatigue failure modes (i.e., cracking position and orientation with respect to a weld) can develop in welded rib to deck connections in orthotropic bridge deck structures. After demonstrating its effectiveness in correlating fatigue test data covering different failure modes, the master S‐N curve method was then adopted in this study for determining the critical failure mode in welded U‐rib to deck connections. These include considerations of additional failure modes potentially present in double‐sided welds between U‐rib and deck versus the traditional single‐sided weld design. The effects of weld penetrations and test loading conditions on failure mode development have been quantitatively established by means of the master S‐N curve method. The master S‐N curve method is employed for capturing typical failure modes of OBD. Anti‐fatigue performance variations between double‐ and single‐sided joints are studied. A parameterized analysis of weld penetration and fillet size effects is conducted.
In this study, the fatigue failure mechanism and fatigue resistance properties of U ribs in orthotropic bridge decks (OBD) with welded single- and double-sided joints are investigated by experimental and numerical investigations. The traction structural stress method is validated to be applicable for evaluating the toe-U rib failure mode by designing and conducting full-scale three-point bending fatigue tests. Fatigue cracks initiated at the external toe-U rib and propagated along U rib thickness. Toe-U rib failure mode was not affected by the weld penetration and setting internal weld. Bending traction structural stress played a significant role with a constraint distance of 75mm, clarifying the failure mechanism of fatigue cracks observed in toe-U ribs.
In recent years, ultra-high-performance concrete (UHPC) has been extensively used in orthotropic steel decks (OSDs) to improve their structural characteristics and extend their fatigue lives. In the present study, an experimental investigation was conducted on three full-scale rib-to-floorbeam welded connections to study the influence of utilizing UHPC overlay on fatigue behavior of such welded connection in OSDs. Two rear axle loads of HL-93 fatigue truck codified in the AASHTO specification were applied in the tests and the effect of longitudinal flexural were considered. Fatigue tests were conducted with full fatigue performance including the failure modes, crack initiation and propagation paths, fatigue lives, and vertical rigidity degradations fully reported. The obtained fatigue test results demonstrated that the application of UHPC overlay remarkably extended the fatigue life of the studied rib-to-floorbeam connections; the fatigue lives at the test end (Nf) were extended by 74.6% under the effect of the same hot spot stress range. The vertical rigidity of the two UHPC reinforced specimens were degraded by 12.3% and 7.3% compared to 15.1% for the unreinforced specimen, indicating that the UHPC reinforced specimens still have considerable load-carrying capacities until the fatigue failure. Moreover, it is demonstrated that the FAT100 fatigue curve provided in IIW fatigue design recommendations could be employed to predict the fatigue resistance of rib-to-floorbeam welded joints in OSDs.
Orthotropic steel-UHPC composite deck consists of orthotropic steel deck and ultra-high performance concrete (UHPC) layer. The shear force transferred by shear studs at the interface between steel deck and the UHPC layer is a key in fatigue design. Based on the finite element (FE) whole model analysis of composite deck, the detailed submodels of composite deck segments with single stud and single row studs were established respectively. It aimed to investigate the interface stress distribution and slip behavior of steel-UHPC composite deck under negative bending moment, and explore the failure mechanism of short headed stud. In term of shear force relationship, considering likely influences such as location and pattern of loading, flexural stiffness of the composite deck and stud arrangement, the whole model analysis results were compared with the submodel analysis results, and a fitting formula of shear relationship between the two models was proposed. A formula for fatigue design of short headed stud in orthotropic steel-UHPC composite deck was also proposed. In respect to the longitudinal and transverse shear force distribution of studs, composite deck stiffness, hot spot stress of fatigue-prone details of steel bridge deck and the maximum stress level of UHPC layer, the evaluation method of stud arrangement was proposed. The calculation results were assessed and compared with the stud layout schemes of three actual steel-UHPC composite decks, and the effectiveness of the design formula was validated.
Ultrahigh-performance concrete-orthotropic steel composite bridge deck is composed of the orthotropic steel deck and a thin ultrahigh-performance concrete (UHPC) overlayer. In the previous fatigue tests, two typical fatigue failure modes were found and identified. As a supplementary test after fatigue tests, air penetration method is capable of providing a reference to the quantitative and non-destructive damage detection of fatigue damage of UHPC. To further the previous study, a detailed numerical investigation is accomplished through complimentary finite element (FE) analysis. Compared with the solid element model, the refined shell-solid element model can better reflect the mechanical behavior. It is illustrated that the vertical stress can be adopted in assessing the fatigue strength of rib-to-diaphragm welded connection in the field test by means of nominal stress method. The combination of various factors would lead to fatigue shear failure of the short headed-studs. The fatigue strength of rib-to-diaphragm welded connection predicted by the hot spot stress method and the consistent nominal stress (CNS) method can basically meet the requirements of FAT90. The consistent nominal stress method can be used as the optimization method of nominal stress of fatigue detail. It is demonstrated that the fatigue life of UHPC can be estimated by S-N curves of ordinary concrete conservatively. The allowable equivalent maximum stress level can be taken as 0.55 for two million cycles of fatigue loading, and 0.52 for five million cycles of fatigue loading.
This study investigates the fatigue performance of rib-to-floorbeam welded connection in orthotropic steel decks (OSDs) reinforced by using ultra-high-performance concrete (UHPC) overlay. Three full-scale rib-to-floorbeam welded connections were fabricated and tested, one specimen represents the conventional OSD type, and the other two specimens represent the UHPC reinforced OSD type, so that the effect of employing UHPC layer can be explored. One rear axle load of HL-93 fatigue truck provided in AASHTO specifications was considered in the fatigue tests. The behaviors including fatigue crack initiation and propagation process, fatigue failure mode, characteristic fatigue life, and vertical rigidity degradation were all observed in the fatigue tests. Experimental results indicated that, under the effect of the same load amplitude, three cracks were observed for the unreinforced specimen, while only one crack for UHPC reinforced specimen was detected. It was observed that using UHPC overlay significantly extended the fatigue life of the rib-to-floorbeam welded connections, where the crack initiation life (N0) and through U-rib thickness fatigue life (N1) were increased by 236 % and 268 %, respectively, under the same load range. Moreover, vertical rigidity was significantly enhanced by employing UHPC layer, which could be due to the fact that the maximum rigidity degradation of the unreinforced and UHPC reinforced specimens were 25% and 14% under the effect of 0.64 and 1.64 million load cycles, respectively.
Civil engineering structures play an important role in any country for improving the economy together with the social and environmental welfare. An unwanted failure might cause significant impacts at different levels for the structure owner and for users. Fatigue is one of the main degradation processes on steel structures that causes structural failure before the end of the designed service life. To avoid unexpected failures due to fatigue, a comprehensive structural Life Cycle Management (LCM) is required to minimize the life-cycle cost and maximize the structural service life. One of the main objectives within the LCM can be related to optimizing the structural maintenance planning. Achieving this goal is a challenging task which requires to address some challenges such as predicting the structural performance under uncertainty, employing Structural Health Monitoring (SHM) data to reduce uncertainties, taking into account crack propagation behavior for given components, reliability and cost-informed decision making, and effect of maintenance actions among others. Accordingly, following contributions are considered in this research to improve the capabilities of structural LCM which are explained shortly in the sequel.Developing a new time-dependent reliability method for fatigue reliability analysis.Investigating the effectiveness of advanced crack propagation tools to study unwanted fatigue cracking problems and characterizing some possible repair actions on a real case study.Introducing the assumptions and simplification steps required to integrate the proposed time-dependent reliability method with crack propagation models to approximate the time-dependent fatigue reliability.As the first contribution of this thesis, a new time-dependent reliability method called AK-SYS-t is proposed. This method provides an efficient and accurate tool to evaluate time-dependent reliability of a component compared to other available methods. AK-SYS-t relates the time-dependent reliability to system reliability problems and tries to exploit the efficient system reliability methods such as AK-SYS towards time-dependent reliability analysis. It is worth mentioning that time-dependent reliability analysis is necessary in this context since the performance deterioration (such as fatigue) is a time-dependent process associated with time-dependent parameters such as fatigue loading.Another related topic is the study of crack propagation phenomenon with advanced modeling tools such as Finite Element Method (FEM) and eXtended Finite Element Method (XFEM). For illustration purposes, the crack in the root of a fillet weld is considered (common fatigue detail in bridges with orthotropic deck plates). One important issue investigated herein is the influence of the transversal tension in the deck plate on the direction of the crack propagation. It is shown how increasing the transversal tension in the deck plate may change the crack propagation towards the deck plate. Such cracks are considered dangerous since they are hard to inspect and detect. In the end, XFEM is used to investigate the effectiveness of two possible repair solutions.A supplementary contribution is related to introducing the required steps in order to integrate the newly developed time-depend reliability method with crack propagation problems through some applicational examples. This is a challenging task since performing the time-dependent reliability analysis for such problems requires a cycle-by-cycle calculation of stress intensity factors which requires huge computational resources. Therefore, the aim here is to introduce the assumptions and simplification steps in order to adopt the AK-SYS-t for fatigue reliability analysis. Accordingly, two examples are considered. (...)
Stress distributions along the critical section of the floorbeam cutout detail of two different cutout geometries were studied based on bridge field tests. Stress concentration at cutout detail was significant and highly dependent on cutout geometry, hence nominal stress could not be applied. The existing HSS models failed to exclude significantly nonlinear stress at original cutout detail due to their first reference points too close to free edge of cutout, and hence they significantly underestimated fatigue life. A new HSS model, with two reference points located respectively 1.0 t and 1.5 t away from the free edge of cutout, was suggested and validated for the two types of cutout geometry. Because the retrofit cutout geometry increases stress at the area 0.5 t away from the free edge, the fatigue life using various HSS models is significantly low compared to the bridge design life. It is concluded that the suggested HSS model and FAT100 may be applicable to fatigue evaluation of cutout detail with different cutout geometry.
Welded residual stress and stochastic traffic at the deck-to-rib welded joints in the orthotropic steel deck (OSD) of bridges highly affects the fatigue life of bridges. This study presents a strain energy-based method to evaluate the service life of welded joints in the OSD considering the combined effects of traffic load and welded residual stress. Thermomechanical analysis is performed for the welding process of the welded joints using a finite-element model to analyze the distribution of welded residual stress at critical locations of the welded joints. An analysis model is developed to simplify the nonlinear superposition of vehicle-induced stress and welded residual stress. A modified strain energy-based fatigue evaluation approach is presented based on the superposition of stresses. Based on the presented model, a new Wa-Nf curve is proposed to take the effects of welded residual stress into consideration. The presented method is validated against experimental results, and then it is applied to investigate the fatigue life of welded joints in an in-service cable-stayed bridge. The theoretical and inspection results are compared and analyzed. The results show that there is a better coincidence between the predicted fatigue life using the presented approach and the inspected fatigue life in contrast with the conventional approach of neglecting the effects of welded residual stress.
Fatigue is among the most critical forms of damage potentially occurring in steel bridges, while accurate assessment or prediction of the fatigue damage status as well as the remaining fatigue life of steel bridges is still a challenging and unsolved issue. There have been numerous investigations on the fatigue damage evaluation and life prediction of steel bridges by use of deterministic or probabilistic methods. The purpose of this review is devoted to presenting a summary on the development history and current status of fatigue condition assessment of steel bridges, containing basic aspects of fatigue, classical fatigue analysis methods, data-driven fatigue life assessment, and reliability-based fatigue condition assessment.
The effective notch stress approach to fatigue assessment of existing large-size specimens for diaphragm-to-rib welded connection in orthotropic steel deck is investigated. Two kinds of specimens are designed. Specimen 1 has the form of circular arc transition; specimen 2 has the form of vertical transition. The first principal stress distribution at weld toe and weld root is calculated by the sub-model method of ANSYS software. By means of the maximum first principal stress analysis, it is possible to distinguish whether fatigue cracks will initiate at the weld toe or the weld root, which is agreed with the fatigue test results. Furthermore, the fatigue strength of specimen 1 and specimen 2 are evaluated by the effective notch stress approach according to fatigue tests. Finally, the factors affecting the stress intensity at the weld toe are studied.
In the original version of the book, the belated corrections from author to modify the sentence in Sect. 3.7.3 of Chapter 3 and to update the equations in Tables 6.3 and 6.4 of Chapter 6 have been incorporated.
The welding residual stress has a prominent contribution to the fatigue damage in deck-to-rib joints of orthotropic steel decks. To estimate the fatigue reliability of deck-to-rib joints with the combined effect of welding residual stress and stochastic traffic flow, a simplified mechanical model is employed to analyze the combined effect of welding residual stress and vehicle-induced stress. The fatigue reliability assessment is conducted by considering the increases of both the traffic flow and the gross vehicle weight with the strain energy density based method. The results demonstrate that the obtained stochastic traffic flow model agrees well with that measured from the weigh-in-motion system, validating the accuracy of the established stochastic traffic flow model for the fatigue reliability analysis. From the calculated fatigue reliability indices with or without the effect of welding residual stress, it can be concluded that the welding residual stress has a prominent negative influence on the fatigue resistance. The effect of the increase of the gross vehicle weight is more significant than that with the increase of the traffic flow on the fatigue reliability, demonstrating that the growth of the gross vehicle weight has a more detrimental impact on the fatigue service life.
This book provides background and guidance on the use of the structural hot-spot stress approach to fatigue analysis. It also offers Design S-N curves for use with the structural hot-spot stress for a range of weld details, and presents parametric formulas for calculating stress increases due to misalignment and structural discontinuities.
Highlighting the extension to structures fabricated from plates and non-tubular sections. The structural hot-spot stress approach focuses on cases of potential fatigue cracking from the weld toe and it has been in use for many years in tubular joints.
Following an explanation of the structural hot-spot stress, its definition and its relevance to fatigue, the book describes methods for its determination. It considers stress determination from both finite element analysis and strain gauge measurements, and emphasizes the use of finite element stress analysis, providing guidance on the choice of element type and size for use with either solid or shell elements. Lastly, it illustrates the use of the recommendations in four case studies involving the fatigue assessment of welded structures using the structural hot-spot stress
This research presented the fatigue tests of longitudinal stringer-to-deck (SD) welded connections, which have been identified as the locations most sensitive to fatigue damage in the orthotropic steel decks (OSDs) of railway bridges. Four full-scale SD connections were fabricated, and two loading patches were considered. Static loading was first carried out to obtain the structural hot spot stresses at weld toes as well as stress concentration factors (SCFs), by which the hot spots providing the highest stresses were identified. Cyclic loading was then implemented next to the static loading, and the behaviors including fatigue crack initiation and propagation process, fatigue failure mode, characteristic fatigue life, as well as degradation of vertical rigidity, were all obtained from the test. The crack growing process can be totally divided into four stages, and the fatigue lives after the crack arrived at the deck edge were very short. Variations of crack dimensions were also obtained, and the simplified formulae of crack growth rate were numerically fitted so that the crack propagation lives can be predicted by using the crack dimensions. Comparisons also show that the FAT 100 curve in IIW fatigue design recommendation could overestimate the fatigue resistance of such connections where double-sided fillet welds were used to connect the stringer web and the deck plate, and therefore double-sided groove welds with partial or full penetrations are recommended for the stringer-to-deck connections in railway bridge decks.
In this study, the fatigue performances of longitudinal-to-transverse rib connections in orthotropic steel decks were assessed by finite element analysis and the hot spot stress approach. Orthotropic steel decks have the following features: (1) stress conditions around welded connections vary depending on the longitudinal and transverse positions of the tire loads, (2) both bending and membrane stresses act on the complex formed connections, and (3) the structures contain comparatively thin steel plates of 6–16 mm thickness. To assess the fatigue performances of the connections in orthotropic steel decks, the effects of traveling load, bending stress, and plate thickness were considered. As a result of the assessments, the connection with a non-slit transverse rib was evaluated to have high fatigue strength in either open or closed longitudinal rib. Finally, the fatigue performances of the connections were confirmed by fatigue tests.
To study the fatigue failure behavior and fatigue strength of the orthotropic deck of highway steel bridge, the Zhongdu Changjiang River Bridge in Jiangjin, Chongqing was cited as an example, the main girder segments of the main span of the bridge were selected to establish the full-scale model of the orthotropic deck and the fatigue test for the model was carried out. In the test, the stress data of the fatigue vulnerable details were collected, the cracks in the details were observed and the fatigue strength of the details was evaluated, using the hot spot stress method. The results show that the fatigue cracks appear at the weldment of the notch between the stiffening rib web and diaphragm, the longitudinal fatigue cracks appear at the weldment of the top plate and stiffening rib web while no fatigue cracks appear at the notch of the diaphragm, however, great tensile stress does exist there. The fatigue strength at the weldment of the notch between the stiffening rib web and diaphragm is greater than that of the category 90 in the Eurocode and is also greater than that of the category C of the AASHTO. The fatigue strength of the weldment of the top plate and the stiffening rib web is greater than that of the category 112 in the Eurocode and is also greater than that of the category C in the AASHTO. © 2016, Journal Press, China Railway Bridge Science. All right reserved.
Based on an orthotropic steel deck of a long-span cable-stayed bridge, a full-scale fatigue test was carried out for researching the fatigue behavior of critical details in steel bridge decks. The load cycle had reached 10.2 million when the fatigue test was completed. The results show that fatigue cracks are found at the rib-to-deck details and also at weld toe of rib-to-diaphragm which expand along rib web; due to the welding residual stress, cracks are found in the compressive zone of rib-to-diaphragm; however, none is found in the cutout of diaphragm; based on the stress change criterion, the fatigue detail of rib-to-diaphragm satisfies the category D of AASHTO Specification and the category 63 of Eurocode while the fatigue detail of rib-to-deck is more than the category D of AASHTO Specification and the category 71 of Eurocode; if fatigue crack observation rule is adopted, the fatigue detail of rib-to-diaphragm is higher than the category D of AASHTO Specification and the category 80 of Eurocode.
To study if the fatigue strength of the structural details of U-rib and diaphragm welding joints of the orthotropic steel bridge deck plates can meet the fatigue design requirements under the action of repeated vehicle load, the steel box girder structure of Jiujiang Changjiang River Highway Bridge was taken the research object, the fatigue samples were designed, the fatigue tests were carried out and the stress amplitude~numbers of cycling curves with the failure probability respectively being 50% and 2.3% for assessment of the fatigue life of the structural details were obtained. With reference to the Eurcode 3, the obtained fatigue curves were extended to the life zone and the fatigue design curves and equations that were suitable for the structural details were proposed. Based on the measured vehicle load spectrum and the simplified finite element model, the proper loading ways and load impacting coefficients were selected, the stress~time history curves of the concerned points were calculated and the fatigue life of the structural details were assessed. The results of the calculation and assessment show that under the action of the measured vehicle load spectrum, the maximum stress amplitude value of the structural details is 24.49 MPa, the value is less than the fatigue cut-off limit and therefore the fatigue strength of the structural details can meet the fatigue design requirements.
Orthotropic steel decks have serious fatigue problems especially on the connections between longitudinal and transverse ribs. In this paper, experimental and analytical works were conducted to evaluate the fatigue performance of connections between longitudinal U-ribs and transverse ribs with and without the slit on the transverse rib web. Finite element analyses of the specimen for all possible loading cases clarified the influence surfaces for structural hot spot stress (SHSS) working on weld toes of the connections. Fatigue tests with the loading case that generates the maximum and minimum SHSS on the connections were conducted. Fatigue test results for the slit connections evaluated by SHSS show agreement with previous fatigue data of similar connection details. No fatigue crack was initiated on the connection without the slit after 4.6 million cycles compared to fatigue failure of the slit connection at 0.7 million cycles.
The cutout hole locating at the place of rib-to-diaphragm welded connection is adopted to minimize the restraint, which is caused by the floor-beam web to rib rotation at the support due to the unsymmetrical loads in orthotropic deck. In practice, an inevitable problem is that there is a large number of welding joint's cracks formed at the edge of cutout hole. In this study, a comparative experiment is carried out with two types of cutout hole, the circular arc transition and the vertical transition. The fatigue life estimation of specimens is investigated with the application of the structural hot spot stress approach by finite element analyses. The results are compared with the ones of the fatigue tests which are carried out on these full-scale specimens. Factors affecting the stress range are also studied.
The notch stress approach for fatigue assessment of welded joints is based on the highest elastic stress at the weld toe or root. In order to avoid arbitrary or infinite stress results, a rounded shape with a reference radius instead of the actual sharp toe or root is usually assumed. Different proposals for reference radii exist, e.g. by Radaj who proposed a fictitious radius of 1 mm to consider micro-structural support effects for steel. The present guideline reviews different proposals for reference radii together with associated S-N curves. Detailed recommendations are given for the numerical analysis of the notch stress by the finite or boundary element method. Several aspects are discussed, such as the structural weakening by keyhole-shaped notches and the consideration of multiaxial stress states. Regarding the fatigue strength, appropriate S-N curves are presented for different materials. Finally, four examples illustrate the application of the approach as well as the variety of structures which can the analysed and the scatter of results obtained from different models.
Orthotropic steel decks are used in beams and cable-supported bridges. Fatigue cracks of the vertical rib–deck welded joint have been found in some of the bridges. In this paper, the structural hot spot stress (SHSS) approach is applied to evaluate the rib–deck fatigue. Refined solid models are built using a multi-sub-model technique. Stress around the weld tip is analyzed and effects of the weld profile, the weld toe radius and mesh size are discussed. The SHSS is analyzed using the surface stress extrapolation method, the stress linearization method and the 1 mm stress method. Fatigue strength of the joint based on the SHSS is proposed. Results of this study show that the refined multi-sub-model considering the weld detail can reflect the mechanical behavior of the rib–deck joint. Variation of the SHSS by the three methods decreases to less than 10% and a convergent SHSS is achieved using the refined models. The derived fatigue strength for the rib–deck joint using the SHSS of the refined models is close to FAT100. A more precise fatigue strength prediction can be achieved using the refined model while the coarse models result in a conservative design.
Local approaches to fatigue assessment are used to predict the structural durability of welded joints, to optimise their design and to evaluate unforeseen joint failures. This standard work provides a systematic survey of the principles and practical applications of the various methods. It covers the hot spot structural stress approach to fatigue in general, the notch stress and notch strain approach to crack initiation and the fracture mechanics approach to crack propagation. Seam-welded and spot-welded joints in structural steels and aluminium alloys are also considered.
This completely reworked second edition takes into account the tremendous progress in understanding and applying local approaches which has been achieved in the last decade. It is a standard reference for designers, structural analysts and testing engineers who are responsible for the fatigue-resistant in-service behaviour of welded structures.
Fatigue design rules for welded structures have not kept pace with computing developments in design, notably the increasing use of finite element stress analysis (FEA). In this respect, a design approach based on the hot-spot stress is expected to be the most suitable for treating welded joints in which weld toe cracking is the likely mode of failure. As part of a recent JIP addressing the fatigue design of FPSOs, available hot-spot S-N data obtained from structural weld details, including results obtained as part of the JIP, were evaluated as the basis for hot-spot stress design S-N curves.
As part of the Joint Industry Project ‘FPSO Fatigue and Fracture Capacity’, a Special Task Group with nine participants performed investigations regarding finite element (FE) modelling and analysis of typical structural details in FPSO’s (Floating Production, Storage and Offloading Units) as well as in ships. The purpose of this special effort was to develop recommendations on appropriate hot spot stress methods and S N data for fatigue strength design. In total, five details with different characteristics, from both geometry and fatigue loading perspectives, were selected for which stress measurements and fatigue tests are available. Various finite element models were developed by participants, using different types and sizes of elements, modelling and stress evaluation techniques as well as FE programs. Comparisons between the analysis results and measured stresses near the weld toes allow conclusions to be drawn. Three different stress extrapolation techniques for predicting hot spot stresses at the weld toes were investigated. The resulting hot spot stresses, together with the estimated fatigue lives, are compared against the existing design S-N curves published by the International Institute of Welding (IIW). It was concluded that the hot spot stresses predicted using the three stress extrapolation techniques, where the element sizes and stress evaluation points are determined by the plate thickness in most cases, can be used with the current design S-N curves. One of the recommended methods requires no stress extrapolation, which is considered an attractive and practical alternative to the existing practices developed by class societies.
The welded joints between longitudinal rib and crossbeam of an orthotropic steel bridge deck are potentially critical to fatigue failure due to stress concentration at the end of the weld toe, caused by in-plane and out-of-plane deformations due to negative bending moments produced by live loads on the deck. The objective of this study is to evaluate the stress characteristics and fatigue crack behaviour of the longitudinal rib-to-crossbeam joints in an orthotropic steel bridge deck and to investigate the effectiveness of crack repair using a stop-hole. Static and fatigue test on full scale specimens were performed to observe the fatigue strength and crack propagation at the longitudinal rib-to-crossbeam joints. The measured stress distributions were compared with the F.E. analysis results. The test results show that fatigue cracks are initiated at the weld toe of the longitudinal rib-to-crossbeam joint with an inclined angle and rib-to-deckplate joint. Fatigue crack growth of the joint was analyzed by the mixed-mode analysis using the strain energy density factor. The stop-hole method was applied to delay fatigue crack growth of the longitudinal rib-to-crossbeam joint.
Finite element analysis is being used by designers for fatigue assessment of structures. It is therefore important that a proper link between calculated hot spot stress and fatigue capacity is established. The fatigue capacity is expressed as a hot spot stress S-N curve. This paper presents a derivation of a hot spot stress S-N curve to be used when the hot spot stress is derived from finite element analysis of plated structures. The hot spot S-N curve is linked to the methodology used for finite element analysis of plated structures that is being included in design recommendations for fatigue assessment of welded structures.
The current (2004) fatigue design provisions in the 3rd Ed. of the AASHTO LRFD Bridge Design Specifications identify and classify the rib-to-web (rib-to-diaphragm) connections commonly utilized in steel orthotropic bridge decks where cutouts are used. The fatigue resistance of these details has been established through full-scale laboratory testing. This paper examines how the fatigue stress range was defined and determined during the testing which established the fatigue resistance of the details. A procedure to calculate or measure stresses at the rib-to-diaphragm connection, which is consistent with the fatigue resistance published in the AASHTO LRFD Bridge Design Specifications, is presented.
Final design of the replacement orthotropic deck panels for the rehabilitation of the Williamsburg Bridge in New York City was based on laboratory fatigue tests of a full-scale prototype and an as-built orthotropic deck panel carried out at Lehigh University in the latter 1990s. The tests focused on determining and comparing the fatigue resistance of two different welded rib-to-diaphragm connection details that were recommended in the 1994 AASHTO LRFD Bridge Design Specifications and an alternative proposed by Steinman. The test on the prototype panel demonstrated that the fatigue resistance of the alternative detail was superior and influenced additional design changes that were incorporated into the replacement panels installed on the southern inner and outer roadways. Subsequent tests on the as-built panel further confirmed that the fatigue resistance of the alternative detail was superior and demonstrated that the additional design changes were also beneficial. Static and dynamic tests revealed the complex behavior of the orthotropic deck panels and demonstrated the effectiveness of retrofit and repair options at cracked connections. An assessment of fatigue resistance based on fracture mechanics models provided theoretical correlation. This research has led to the revision of design specifications for steel orthotropic decks first provided in the 2000 Interim AASHTO LRFD Specifications.
Weld cracks in orthotropic decks with closed ribs on the Haseltal and Sinntal bridges in West Germany and on the Severn Crossing in the United Kingdom occurred at the intersections of the discontinuous ribs with the floor beams and at the rib-to-deck welds, and were caused by inappropriate details and welds not suitable for transmitting stresses between the deck components at these junctions. Good practice requires continuity of the ribs through the floor beams, the use of welds with good penetration into the rib webs at their junction with the deck plate, and avoidance of welded attachments to the ribs or to the deck plate. No weld failures or cracks are known in orthotropic bridge decks with correct details and general performance record of such decks is satisfactory. Careful design, detailing and fabrication of orthotropic decks is essential, especially in cases with long rib spans. Insufficient attention to details can result in costly failures; there is no reason, however, to question the reliability of orthotropic decks where the rules of good design and fabrication practice have been observed.
The structural stress approach, which considers the stress increase due to the structural configuration, allows the fatigue strength assessment of welded ship structures with various geometries on the basis of an S–N curve depending only on the type of weld. However, a unique definition and the numerical calculation of the structural stresses are problematic, which has resulted in the development of different variants of the approach. These are discussed and compared with each other in the present paper. The application to three examples shows the variation and differences in the analysed stresses and predicted fatigue lives, which are compared with those derived from fatigue tests.
This study concerns the behaviour of the closed stiffener (trough) to crossbeam connection in orthotropic steel bridge decks and in particular, the connection where a continuous closed stiffener passes through the crossbeam. For this connection, the crossbeam in-plane and out-of-plane behaviour is analysed. The nominal stresses for unit loads on the crossbeam, unit rotations of the connection and the deck bending are determined for locations that are relevant for fatigue. For these locations, the geometrical stress concentration factors are also determined. Traffic loads for fatigue from ENV 1991-3 (EN 1991-2) are simulated by maximum crossbeam load, connection rotation and deck bending moment intervals with equivalent numbers of cycles. By applying geometrical stress concentration factors to the nominal stresses the geometrical stresses are obtained. By scaling these geometrical stresses of the unit loads, rotations and deck bending moments, the resulting geometrical stress intervals are used for a fatigue assessment of an example crossbeam with three different types of connections: - Closed stiffener through a cut-out with a cope hole, - Closed stiffener through a close fitting cut-out, - Closed stiffener fitted between the crossbeams. The restraints generated by local bending in the deck and torsion in the closed stiffeners are analysed separately. The results of the calculations obtained by analytical models and FE models, are compared with measurements. Conclusions are drawn about the analytical models and the sensitivity of the analysed locations to fatigue cracks.
This dissertation presents the research into renovation techniques for orthotropic steel bridge decks. These techniques are needed to solve fatigue problems in the decks of these bridges, as several fatigue cracks have been detected in the deck structure of these bridges the last decade. A well-known example of fatigue cracks are those observed in the deck plate of the Van Brienenoord bascule bridge in 1997, at that time a 7 year old bridge. The renovation techniques are part of a proposed maintenance philosophy for steel bridge decks. Lifetime calculations, inspections and renovation techniques are the three essential parts of this philosophy. A reliable lifetime calculation model for fatigue damage in the deck plate is described, including the influence of the asphalt surfacing. Accurate calculation results are obtained, both for movable and fixed bridges. Inspection programs can be based on the lifetime calculation results. Several innovative inspection techniques are presented briefly. For fixed bridges the replacement of the asphalt surfacing with a reinforced high performance concrete surfacing is an effective renovation method. For movable bridge decks three solutions that extend the lifetime of the orthotropic deck structure were researched in this thesis.
This dissertation presents the research into fatigue classifications of welded joints in orthotropic steel bridge decks. These classifications are needed to calculate the fatigue life of these joints and should be included in the design codes. For years bridge design was mainly based on static loading. Due to the development of modern light weight steel structures and extremely increasing traffic loading fatigue design becomes more and more important. A review of all available data on orthotropic decks and related fatigue test results is included. The majority of the full scale fatigue testing on orthotropic decks has been carried out by members of a European Working Group. The statistical analysis procedure used to derive the weld classes for Eurocode 3 is used to place all of the main joints in the appropriate class, and to rank different designs of each joint. In addition, recommendations are made for both good joint design and those to be avoided. The composite action between the steel deck plate and the surfacing on orthotropic decks is an important aspect of the performance, in particular because the stifness of the combined unit helps to reduce strains in the welded structure as well as in the surfacing, which results in a longer lifetime. Numerical as well as experimental analysis of the stress reduction is reported. Furthermore this dissertation highlights site measurements on existing bridges and shows the development of different wearing course systems.
A Study of Manufacturable Rib-To-Floor Beam Connections in Steel Orthotropic Bridge Decks
- K Kitner
K. Kitner, A Study of Manufacturable Rib-To-Floor Beam Connections in Steel
Orthotropic Bridge Decks, Master's thesis Lehigh University, Bethlehem, 2016.
Design of Steel Structures. Part 2: Steel Bridges
European Committee for Standardization. EN 1993-2:2006, Eurocode 3: Design of
Steel Structures. Part 2: Steel Bridges. Brussels (Belgium), 2006.
British standards BS 5400, Steel, Concrete and Composite Bridges. Part 10: Code of Practice for Fatigue
B.S.I. British standards BS 5400, Steel, Concrete and Composite Bridges. Part 10:
Code of Practice for Fatigue, British Standards Institution, London, 1980.
American Association of State Highway and Transportation Officials
American Association of State Highway and Transportation Officials, AASHTO LRFD
Bridge Design Specifications, (Washington D.C) 2012.
Fatigue Design Recommendations for Steel Structures
JSSC, Fatigue Design Recommendations for Steel Structures, Japanese Society of
Steel Construction, 2012 (in Japanese).
Fatigue Analysis of Steel Bridge Details: Hot Spot Stress Approach
- A Bhargava
A. Bhargava, Fatigue Analysis of Steel Bridge Details: Hot Spot Stress Approach, PhD
dissertation The George Washington University, Washington D.C, 2010.
Fatigue Life Assessment of Welded Bridge Details Using Structural Hot Spot Stress Method, Master's thesis
- Zamiri Akhlaghi
F. Zamiri Akhlaghi, Fatigue Life Assessment of Welded Bridge Details Using Structural Hot Spot Stress Method, Master's thesis Chalmers University of Technology,
Göteborg, Sweden, 2009.