Joints In Orthotropic Steel Decks Research Articles

GPR-assisted evaluation of probabilistic fatigue crack growth in rib-to-deck joints in orthotropic steel decks considering mixed failure models

Rib-to-deck (RD) welded joints in orthotropic steel decks (OSDs) of bridges demonstrates two major fatigue failure models, including the toe-to-deck (TTD) cracking and root-to-deck (RTD) cracking. Generally, the sole failure model is employed in the fatigue assessment of RD joints, causing a hot dispute on the dominant failure model. In this paper, the fatigue crack growth (FCG) in RD joints has been evaluated considering uncertainties and mixed failure models. A probabilistic fatigue crack growth (PFCG) model is at first established for the RD joint, in which two crack-like initial flaws are assumed at the weld toe and root of the RD joint. After that, the gaussian process regression is used to assist and boost the PFCG simulation. Then, the PFCG model is implemented on a typical OSD with the random traffic model. Finally, the result of the PFCG model is discussed in detail, including the failure model, fatigue reliability and life prediction, and crack size evolution. It is revealed that both the TTD and RTD cracking models have a notable contribution to fatigue failure and could not be ignored. More crucial, a remarkable reduction can be observed in the fatigue reliability of RD joints when considering mixed failure models. This study not only highlights the influence of mixed failure models on the fatigue performance of welded joints, but also provide an insight into the application of novel machine learning tools in solving the traditional structural issue.

Review on fatigue life assessment methods for welded joints in orthotropic steel decks of long-span bridges

Orthotropic Steel Decks have been used in long-span bridges for several decades because of their high capacity to weight ratio. However, many fatigue related issues have been reported. This paper provides an overview of the main existing fatigue prediction models and discusses their relevance for the fatigue life assessment of Orthotropic Steel Bridge Decks (OSBDs). Several case studies have proven the importance of considering the combined effect of wind and traffic loadings to estimate the fatigue life of long-span bridges. The importance of incorporating welding residual stresses is also well documented while it is often disregarded in design practices. Reliability-based fatigue assessment methods make it possible to quantify how the sources of uncertainty related to loading conditions, welding residual stresses or fabrication defects can affect the fatigue reliability of OSBDs. Monte Carlo simulations are often used to perform probabilistic analyses, but machine-learning algorithms are very promising and computationally efficient. The shortcomings of the Palmgren-Miner rule are discussed and the need for alternative damage accumulation indexes is clear. A number of conclusions are drawn from the analysis of fatigue tests conducted on OSBDs.

Experimental investigation and numerical simulation on welding residual stress of innovative double-side welded rib-to-deck joints of orthotropic steel decks

An innovative double-side welded rib-to-deck (RTD) joint has been developed recently to enhance fatigue performance of orthotropic steel decks (OSDs) in steel bridges. The welding residual stresses (WRS) will lead to reduction in fatigue resistance of RTD joints in steel bridges. It is essential to study WRS and its distribution to estimate the fatigue resistance of innovative double-side welded RTD joints accurately. To investigate WRS caused by the double-side welding process, the experimental tests on four specimens of double-side welded RTD joints were carried out by means of longitudinal critical refraction (LCR) wave method. A sequentially coupled three-dimensional thermo-mechanical finite element (FE) analysis model was established to simulate the double-side welding process, and it was validated by the WRS results of experimental investigation. Then, the effects of welding parameters and geometric configuration of RTD joints on WRS and its distribution are analyzed by the validated numerical simulation. The results show a reasonable agreement between WRS simulation and the experimental data. WRS at the surface of weld seam and plate components is strongly affected by the welding speed, but comparatively weakly depends on the weld penetration rate, the assembly gap and the deck thickness.

FATIGUE EVALUATION FOR ROOT CRACKS IN U-RIB TO DECK WELDED JOINTS OF ORTHOTROPIC STEEL DECKS

本論文は，鋼床版のUリブとデッキプレートの溶接部のルートき裂であるデッキ進展型き裂，ビード進展型き裂の双方を対象に，疲労評価方法について検討したものである．具体的には，疲労試験および有限要素解析により，ルートき裂のき裂発生寿命を評価することができる応力を明らかにするとともに，それを溶接部周辺の参照応力から推定する方法を提案した．また，き裂進展解析によりデッキ進展型き裂，ビード進展型き裂の進展挙動を再現し，いずれのき裂が発生するかを判別する手法を提案した．

Fatigue crack growth behavior of rib-to-deck double-sided welded joints of orthotropic steel decks

Innovative double-sided welding is expected to improve the fatigue resistance of rib-to-deck welded joints of orthotropic steel decks (OSDs). Welding crack-like defects are the crucial issue affecting the fatigue performance of rib-to-deck double-sided welded joints. This study presents a numerical simulation of three-dimensional (3D) mixed mode fatigue crack growth behavior of rib-to-deck double-sided welded joints of OSDs. Maximum tensile stress theory and equivalent stress intensity factor (SIF) were used to simulate mixed mode fatigue cracks growth. The Paris law model was employed to predict the fatigue life. Fatigue cracks of rib-to-deck double-sided welded joints were characterized by the presence of mixed mode cracks of modes I (open), mode II (shear), and mode III (tear), which was dominated by mode I. The equivalent SIF was found to be complex at the growth stage with the maximum value at the two ends of the crack front and the minimum value at the midpoint of the crack front. The crack shape became flatter in the later phase of the crack growth. The fatigue crack surface underwent deflections during crack growth, making the final crack shape exhibiting the characteristic of a spatial curved surface. The initial crack geometry showed a significant impact on the fatigue life.

The Evolution of Residual Stress in Rib-Diaphragm Joints of Orthotropic Steel Decks Subjected to Thermal Cutting and Welding.

Residual stresses change the stress ratio of fluctuating stresses, hence seriously affect the fatigue life of orthotropic steel decks (OSDs) under traffic loading. Residual stress distributions near the U rib-diaphragm joints are very complicated and need to be investigated further. In this paper, a systematic method has been proposed for calculating the residual stress field in the joint of U rib and diaphragm due to thermal cutting and welding. Firstly, a mathematical model of cutting heat sources was established to predict the temperature field. Then, a numerical elastoplastic thermomechanical model was built to predict the residual stress evolutions in a diaphragm-rib joint through the whole fabrication process involving flame cutting and welding. Moreover, the simulated temperature contours at the fusion zone and the residual stress distributions in the rib-diaphragm joint were compared and verified against the experimental ones. The numerical results showed a great agreement with the experimental ones, indicating that the heat source model can be used to accurately predict the temperature field during flame cutting. Finally, the validated numerical model was utilized to conduct parametrical analyses on the effects of thermal processing rates, e.g., the cutting and welding speeds and on the residual stress distribution in the rib-diaphragm joint. The results indicate that a faster cutting speed and a slower welding speed can decrease the residual stress magnitude at the rib-diaphragm joints and reduce the high-stress zone near the diaphragm cutouts.

Fatigue Reliability Analysis of Rib-To-Deck Joints Using Test Data and In-Situ Measurements

In this paper, the fatigue performance of rib-to-deck joints in orthotropic steel decks (OSDs) using thickened edge U-ribs (TEUs) and the OSD using conventional U-ribs (CUs) are investigated based on the fatigue test result and in-situ monitoring data. Firstly, comparative fatigue tests were carried out with full-scale rib-to-deck specimens. Probability–stress–life (P–S–N) curves were derived through the test data measured from a total of 18 specimens, including 7 CU specimens and 11 TEU specimens. According to the results, the TEU can lead to a notable enhancement in the fatigue strength of rib-to-deck joints, i.e., 21.4% in terms of nominal stress and 21.1% in terms of hot spot stress. After that, a typical OSD steel bridge was selected as the prototype to investigate the fatigue performance of rib-to-decks in the OSD using TEUs under actual applications. In the analysis, the uncertainty in both fatigue strength, and vehicle loads were considered. A multi-scale finite element model of the prototype bridge was established, and numerical analysis conducted to derive the vehicle-induced stress spectra of the rib-to-deck joints in critical positions. In the derivation, a stochastic traffic model was employed, through which the in-situ measurement was incorporated. Finally, fatigue reliability analysis was carried out for the prototype bridge based on the above works. The result showed that a notably higher fatigue reliability can be expected in the rib-to-deck joint in OSDs using TEUs when compared with the joints in OSDs using CUs, which in turn can lead to notable improvement in fatigue life. For instance, under the target reliability of 2.3, the fatigue life of the two critical rib-to-deck joints were, respectively, increased by 153% and 155% when using TEUs.

Fatigue performance of rib-to-deck double-side welded joints in orthotropic steel decks

Fatigue cracking of rib-to-deck welded joints is the major fatigue problem of the orthotropic steel deck (OSD). It is important to evaluate the fatigue performance improvement of rib-to-deck double-side welded joints in an OSD when compared with single-side welded joints. In this study, the software ABAQUS and FRANC3D were used to set up a multiscale finite element model for segments of an OSD. Under vehicle load, the mode I stress intensity factor (SIF) of a fatigue crack at the rib-to-deck single-side and double-side welded details without or with the effect of welding residual stress was computed. The relationship between the mode I SIF of the fatigue crack and the key parameters was analyzed, including welded penetration, thickness of deck plate and the initial crack surface length and depth. The results showed that the welding residual stress can significantly influence the SIF values of the rib-to-deck welded joints in the OSD. The maximum SIF of the crack in the rib-to-deck double-side welded joints was 29.6% less than that of the single-side welded joints, which can effectively improve the fatigue performance of the rib-to-deck welded joints. The effect of the welded penetration rate on the fatigue performance of rib-to-deck double-side welded joints was only slight. By increasing the thickness of the deck, reducing the initial crack surface length and depth, the SIF of cracks in the rib-to-deck double-side welded joints can be significantly decreased, and this approach improves fatigue performance.

Dynamic Bayesian network-based system-level evaluation on fatigue reliability of orthotropic steel decks

Fatigue fractures can be frequently observed in welded joints in orthotropic steel decks (OSDs) after just a few decades of operation, which become the major deterioration mechanism deterring the serviceability of OSDs. In this paper, a novel dynamic Bayesian network (DBN) model has been established for the fatigue reliability analysis of OSDs at system-level. The exact inference algorithm is applied in the DBN model with discrete variables. Special modifications have been made on the existing algorithm to improve the computational efficiency in dealing with the deck system consisting of a considerable number of joints. Using the DBN model, the fatigue reliability of welded joints can be predicted and updated with the inspection and monitoring results at system-level. At the same time, a framework is established for the system-level reliability considering the fatigue fracture of rib-to-deck (RD) joints, the dominant cracking pattern affecting the serviceability of OSDs. For illustration, a typical OSD bridge in China has been selected to carry out a case study. To derive the stress spectrum required by the DBN model, the stochastic traffic model is employed, and the influence-based Monte Carlo simulations have been carried out. As a result, the fatigue reliability can be predicted at both component- and system-levels. Meanwhile, the observation of the traffic and the inspection result has been fused into the DBN model to update the deteriorating state of the deck system. Besides, the effect of enhancement and maintenance has been highlighted, including the enhancement in fatigue strength at the construction stage, and the repair and traffic control during the operation stage.

Stochastic Traffic-Based Fatigue Life Assessment of Rib-to-Deck Welding Joints in Orthotropic Steel Decks with Thickened Edge U-Ribs

Rib-to-deck (RD) joints in orthotropic steel decks (OSDs) are highly prone to fatigue cracking under heavy traffic. An innovative longitudinal rib, named the thickened edge U-rib (TEU), has been proposed to enhance the fatigue strength of RD joints and validated through model tests. However, more studies are still required on the effect of TEUs in real engineering applications. To this end, a typical OSD bridge in China has been investigated, based on the experimental results. In the analysis, a stochastic traffic model is employed to simulate the vehicle-induced fatigue actions comprehensively. The framework of the stochastic model is proposed by considering the randomness in both the vehicles and their lateral distribution. Then the traffic model is instantiated using standard truck models in conjunction with the codes of practice as well as the observed data. A multi-scale finite element model is later established to determine the stochastic stress responses, whereas the influence surface method is used to improve computational efficiency. In this study, Monte Carlo simulations have been carried out to derive the stress spectra for the RD joints at different critical locations. Based on the test data and the derived spectra, an engineering assessment has been performed to obtain the fatigue life of RD joints in OSDs with and without TEUs, respectively. The new findings show that the position of joints has a remarkable influence on the stress spectra of RD joints, which results in the notable difference in fatigue life of the joints. Further, the fatigue life of RD joints can be significantly prolonged by using TEUs, and the prolongation rates are varied from 141% to 161% depending on the calculation methods and traffic models used.

An equivalent structural stress-based fatigue evaluation framework for rib-to-deck welded joints in orthotropic steel deck

Rib-to-deck welded joints in orthotropic steel decks have demonstrated different fatigue failure modes that have different fatigue resistance. Among the different failure modes, the mode corresponding to the lowest fatigue resistance governs the fatigue resistance of the welded joint. The ability of determining the governing failure mode is essential for predicting the fatigue resistance of the welded joints. This research establishes a fatigue evaluation framework for determining the dominant failure mode of rib-to-deck welded joints. The framework is established based on the equivalent structural stress method and validated using model test data. The results indicate that the proposed framework provides accurate prediction of the dominant fatigue failure mode of rib-to-deck welded joints. Based on the presented framework, the fatigue resistance of the welded joints is reasonably predicted, and the effect of weld penetration ratio on the fatigue failure mode is investigated.

Fatigue Performance of Orthotropic Steel Decks with FRP Angles: Field Measurement and Numerical Analysis

AbstractRib-to-deck joints in orthotropic steel decks (OSDs) are among the most fatigue-prone details of steel bridges. To improve the fatigue performance of existing bridges with OSDs, a strengthe...

Fatigue assessment of longitudinal rib-to-crossbeam welded joints in orthotropic steel bridge decks

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 design specifications. Based on the hot spot stress and notch stress approaches, SN 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.

Fatigue process of rib-to-deck welded joints of orthotropic steel decks

The numerous welded joints in orthotropic steel decks (OSDs) lead to a high probability of fatigue damage. One of the most detrimental problems is the severe reduction of the serviceability due to cracks in rib-to-deck welded joints, which require in-depth studies on the entire fatigue process. The linear elastic fracture mechanics has been proven to be effective in this aspect. When put into practice on actual projects, however, its accuracy and feasibility are largely dependent on features in various scales. This paper presents an investigation on the fatigue behavior of orthotropic steel decks with respect to multiscale concerns. By performing fatigue tests on OSD specimens welded by 15-mm-thick deck plates and 6-mm-thick stiffeners of S355 steel, the rib-to-deck weld toe crack that penetrates the deck plate is produced and the crack growth path is addressed using beach mark method. Afterwards, a two-dimensional local model of the rib-to-deck weld toe crack is built using the extended finite element method by which the stress intensity factors for early-stage cracks can be obtained. Based on the similar concept of nominal stresses, it can easily be linked to the macroscopic model and forms a non-concurrent method that enables to simulate the crack growth at rib-to-deck weld toe. As a result, a crack growth rate curve for the test specimen is given and different stages are analyzed with respect to the Paris law, indicating a clear influence of the early-stage fatigue cracks. The material constants of crack growth are obtained and validated, which may further be introduced to the fatigue assessment and life estimation for the maintenance work of OSDs.

Residual stress relaxation at innovative both-side welded rib-to-deck joints under cyclic loading

Innovative both-side welded rib-to-deck joints of orthotropic steel decks (OSDs) was developed to enhance the fatigue resistance and extend the service life of bridges. Compared with the conventional welded joints, the both-side welded joints are subjected to different weld residual stresses (WRS) and WRS relaxation (WRSR) due to the different welding processes. Properly assessing the WRS and WRSR is a prerequisite for predicting fatigue damage and service life of OSDs. This study presents a new method to analyze the WRSR in rib-to-deck welded joints under cyclic loading. The initial WRS at a both-side welded rib-to-deck joint was measured using an ultrasonic method and simulated using a sequentially-coupled thermo-mechanical finite element model. The model is validated against the test data, and then used to analyze the WRSR. The influence of cyclic stress amplitude and stress ratio on the WRSR is investigated. The WRS rapidly drops in the first cycle and then gradually deceases until stabilized after about 5 cycles. The magnitude of the WRSR increases with the stress amplitude and the stress ratio. Finally, a formula is derived to predict the WRSR based on the stress amplitude and stress ratio.

Fatigue Behavior Investigation and Stress Analysis for Rib-to-Deck Welded Joints in Orthotropic Steel Decks

The fatigue problems in orthotropic steel decks have raised widely concerns in recent years. This study focused on the root crack mechanism at rib-to-deck welded joints, based on the previous test results of sectional specimens and the matching FE analysis, the fatigue behaviors of structure detail were investigated by considering the effect of root gap shapes, weld penetrations, and plate thicknesses on crack initiation. Besides, various root crack depths were simulated in models to clarify the stress variations occurring during the propagation stage under cyclic loading. The results showed that the root gap shape and penetration rate have an impact on the root cracking direction and fatigue life at the initiation stage, but seem not directly related to the crack propagation mechanism; the higher penetration rate is advantageous for the prevention of root crack initiation. However, although the stiffness increased with the increase in plate thickness, the fatigue life of crack initiation might be reduced owing to the low fatigue strength of the thick deck plate, whereas the U-rib thickness has limited effect on the stress response of the root tip. Moreover, the significant difference between the 8 mm-crack model and other crack models is the high stress concentration around the crack tip. The stress conditions of root tip would be changed under loading cycles when a root crack propagated into half of deck plate thickness. Finally, the effect of structural dimensions on fatigue strength were also compared according to test results and FEA.

Fatigue reliability evaluation of deck-to-rib welded joints in OSD considering stochastic traffic load and welding residual stress

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.

Fatigue Performance of Rib-to-Deck Joints in Orthotropic Steel Decks with Thickened Edge U-Ribs

Fatigue Performance of Rib-to-Deck Joints in Orthotropic Steel Decks with Thickened Edge U-Ribs

Experimental investigation for structural parameter effects on fatigue behavior of rib-to-deck welded joints in orthotropic steel decks

Abstract Various fatigue cracks occurred in orthotropic steel decks have been reported in the last decade. The fatigue cracks initiated at the weld root of the fillet weld of rib-to-deck plate were investigated in this study. The fatigue behaviors were investigated by performing 19 full-scale fatigue tests, which conducted on six types of orthotropic steel decks with different structural parameters. The fatigue cracking patterns and their influence factors were discussed by comparing the crack propagation angles, crack lengths and depths of the cracked section. Meanwhile, the cracking mechanism and stress responses around root tip were analyzed by establishing elastic finite element models, and verify with fatigue tests results. The results of the experimental analysis demonstrated that fatigue cracks did not occur where the stress ranges were purely compressive, it was considered the welded joint might under the low tensile residual stress so that the effective stress range was reduced. Similarly, the magnitude of tensile stress range would play a decisive role during the root crack propagation. It was found that increasing the penetration rate had the beneficial effect of preventing root cracking. There was also a significant improvement in the fatigue durability when the deck plate thickness was increased from 12 mm to 16 mm. Finally, some special treatments in welded joint such as: the grinding at weld toe could avoid crack at toe but might lead to a deeper root crack, and the press straighten could be an effective treatment for preventing root cracks propagating in depth.

Fatigue Behavior of Stiffener to Cross Beam Joints in Orthotropic Steel Decks

In the paper the possibility to evaluate the fatigue strength of stiffener to cross beam joints in orthotropic steel decks is discussed. The proposed methodology, based on Paris-Erdogan law, allows to derive a sound estimate of the stress intensity factor K combining the indirect approach, based on the Rice J-integral, with the direct one, based on the extrapolation of experimental or numerical data. The practical implementation of the proposed methodology allowed to predict correctly the actual fatigue life of a previously tested real scale specimen, so validating its potentialities.