Joints In Orthotropic Steel Decks Research Articles

Digital fatigue cracking test and fatigue life assessment of rib-deck joints in orthotropic steel decks

The orthotropic steel decks (OSDs) are vulnerable to fatigue fractures, which will inevitably impair the normal service of the steel bridge panels. To determine the impact of the initial cracks on the fatigue life, this study constructed an evaluation model of the OSD rib-to-deck joints crack based on the fracture mechanics principle. And combined it with the multi-scale finite element analysis model, the digital fatigue test model of the whole bridge was established. Research shows: A typical I-II-III composite crack with the supremacy of type I crack can be seen in the OSD rib-to-deck joints. Fatigue cracks developed at the deck weld toe dominate the fatigue failure mode. Further research revealed that as the depth of cracks increased, the stress on the cross-section was redistributed. The intensity factor then displayed a trend of growing and then gradually flattening or even dropping. Based on the relationship between cracks of different depths and the remaining life of the OSDs, recommendations are given for bridge maintenance. The multi-scale digital fatigue test can provide analysis and simulation methods for the fatigue crack propagation in the steel bridge deck of the bridge in operation.

Residual stresses effects on fatigue crack growth behavior of rib-to-deck double-sided welded joints in orthotropic steel decks

Rib-to-deck (RTD) innovative double-sided welded joints have the potential to enhance the fatigue resistance of orthotropic steel decks (OSDs). However, welding residual stress (WRS) has been reported to be a contributing factor to fatigue cracking of steel bridges. This paper performed fatigue crack growth of the RTD innovative double-sided welded joints of OSD considering WRS. Firstly, a thermal-mechanical sequential coupling finite element model (FEM) of the RTD double-sided welded joints was established. The WRS distribution along the direction of deck thickness was analyzed. Secondly, the FEM of the OSD segment with crack was established. The fatigue crack behavior of RTD double-sided welded joints under the combined action of vehicle load and WRS was studied. Finally, the influences of initial crack on fatigue life was analyzed. Results indicate the distribution of the transverse WRS along the direction of deck thickness is tension-compression-tension stress, which has the characteristics of the sinusoidal function. The ∆ Keff value increases significantly considering WRS than without considering WRS during crack growth. WRS has a significant effect on fatigue life, and the fatigue life of the weld toe without considering WRS is about twice that of considering WRS. The crack depth and aspect ratio ( a0/ c0) of the initial crack affect the fatigue life of RTD double-sided welded joints.

Fatigue improvement of rib‐to‐deck welded joints using adhesively bonded steel patches ‐ LEFM‐based parametric study

AbstractRib‐to‐deck welded joints in orthotropic steel decks of bridges are prone to develop fatigue cracks. Repairing such cracks allows for prolonging the life of the infrastructure, provided that structural safety is guaranteed. Among others, the repair technique of adhesively bonded steel patches is relatively simple and inexpensive. Moreover, it has the advantage that the original structure is not altered, e.g. as in the case of crack stop holes. This technique has been used in other details like the diaphragm of steel bridges. However, limited information is available when applied to rib‐to‐deck joints, which are the most common joint type in orthotropic steel decks. This study proposes two repair schemes using adhesively bonded steel patches for the rib‐to‐deck joints. A 3‐D finite element model which takes account of the crack size is established. Based on linear elastic fracture mechanics (LEFM), a parametric study is performed to investigate the effect of patch geometry and adhesive thickness on the performance of repair schemes.

Effect of ultrasonic impact treatment on welding residual stress and fatigue resistance of doubly-welded rib-to-deck joints in OSD

Innovative doubly-welded rib-to-deck joints (DRJ) have been developed to enhance the fatigue life of orthotropic steel decks (OSD) used in steel bridges. However, the welding process and welding residual stress (WRS) distribution of DRJ are more complicated than those of conventional single-side welded rib-to-deck joints. To release WRS and improve the fatigue resistance of DRJ, ultrasonic impact treatment (UIT) and fatigue tests were performed in this study. The effect of the UIT process on the WRS distribution and fatigue resistance of the DRJ was investigated. Furthermore, the welding processes of the DRJ and UIT were simulated using the finite element method and validated against the relevant measurements. Subsequently, they were used to investigate the effect of the UIT process on the WRS distribution and represent the mechanism of fatigue failure of the DRJ. Compared with the as-welded specimens without UIT, the fatigue strength of the DRJ increased by more than 60%, and the UIT process altered the dominant fatigue failure mode of the DRJ. The fatigue crack, caused by a UIT-induced fold defect, tends to initiate at the bottom of the impact pit. Owing to the UIT process, the adverse tensile WRS in the weld toe is eliminated, and beneficial compressive residual stress is introduced, leading to an improvement in the fatigue strength of the DRJ.

Fatigue strength evaluation by measurable stresses for root cracks in U-rib to deck welded joints of orthotropic steel decks

Fatigue strength evaluation by measurable stresses for root cracks in U-rib to deck welded joints of orthotropic steel decks

Monitoring fatigue cracks in rib-to-deck joints of orthotropic steel deck using ultrasonic Lamb waves

Fatigue cracks in rib-to-deck joints of orthotropic steel decks (OSDs) endanger the safety of bridges and are difficult to detect. This paper proposes to monitor fatigue cracks using ultrasonic Lamb waves. An OSD specimen instrumented with ultrasonic sensors was fabricated and tested to crack under fatigue loads. Ultrasonic Lamb waves were measured to detect, locate, visualize, and evaluate fatigue cracks using a probabilistic inspection of damage method. A finite element model was developed to understand wave propagation and crack growth process, and utilized to perform parametric studies on the type, position, and severity of cracks. The results indicated that fatigue cracks were effectively monitored by ultrasonic Lamb waves. Errors of crack positions were less than 5 mm. The damage probability distribution increased with the crack depth and crack length. The ultrasonic Lamb waves are more sensitive to toe-deck and root-deck cracks than other modes of cracks in rib-to-deck joints.

A unified fatigue life evaluation method for different failure modes of the repaired rib-to-deck joints in orthotropic steel decks

The rib-to-deck welded joints in orthotropic steel decks (OSDs) are prone to fatigue damage with different fatigue failure modes. The damage accumulation of the corresponding failure modes should be estimated in repair design. This study proposed a unified fatigue life evaluation method for different failure modes of rib-to-deck welded joints based on the structural stress method and linear damage accumulation theory. The method considers the effect of crack depth and crack propagation on life evaluation, validated by the tests of repaired rib-to-deck joints with interior repair welds. Damage accumulation before and after repairing corresponding to different failure modes was assessed. The dominant failure modes before and after repairing were analyzed. Finally, the damage accumulation law of welded joints after repair under standard traffic load was investigated based on the existing damage status of each failure mode of the rib-to-deck welded joint. The results indicate that the failure mode will transfer from root-deck to exterior toe-deck at the rib-to-deck joint after the interior repair welding. The dominant failure mode of the repaired joint is governed by the existing damage status and the repair method.

An investigation on fatigue crack propagation behavior of welded connections in UHPC reinforced OSDs using 3D crack simulation

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 SN 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.

Fatigue test and failure mechanism of new rib-to-floorbeam welded joints in OSDs

To improve the fatigue performance of rib-to-floorbeam (RTF) welded joints in orthotropic steel decks (OSDs), a new RTF welded joint was proposed in this study. The full-scale segment fatigue tests including the traditional and new RTF welded joints were carried out, and the fatigue performance of new RTF welded joints was evaluated. The fatigue failure mechanism was analyzed by using numerical simulation. The results show that the fatigue crack initiation appears at the weld toe of the bottom rib of the new RTF welded joint, while the fatigue crack of the traditional RTF welded joint initiates at the end of the weld toe. Besides, the fatigue crack propagation rate of the new RTF welded joint is remarkably lower than that of the traditional RTF welded joint. The new RTF welded joint is about twice fatigue life of the traditional RTF welded joint. The weld residual tensile stress (WRS) is the main factor in the fatigue crack initiation of RTF welded joints subjected to compression-compression cyclic loading.

Experimental study on fatigue behavior of trapezoidal rib-to-deck welded joints in orthotropic steel decks strengthened with CFRP sheets

Due to the unavoidable stress concentrations and welding defects, the trapezoidal rib-to-deck welded joints of Orthotropic Steel Bridge Decks (OSBD) are prone to fatigue cracking. It is a new exploration to apply Carbon Fiber Reinforced Polymer (CFRP) sheets to strengthen the complex welded joints to improve the fatigue strength. In this paper, the comparative tests of un-strengthened and CFRP strengthened welded joints were carried out. The hot spot stress distribution under static load and fatigue behavior under cyclic load were studied, considering the influence of the number of CFRP sheet layers. The experimental results indicate that CFRP reinforcement can effectively reduce the stress concentrations at weld toe of the deck, and three-layers reinforcement has a greater effect than one-layer reinforcement. There was no significant difference in failure modes between the un-strengthened and CFRP strengthened welded joints. The fatigue cracks of all joints originated from weld toe of the deck, and then expanded along the width and thickness of the deck which caused the deck to break. CFRP reinforcement can significantly improve the fatigue life of trapezoidal rib-to-deck welded joints under the same nominal stress range and three-layers reinforcement presented a longer fatigue life. The S-N curve [Formula: see text] based on the hot spot stress range at weld toe of the deck was established, which can be applied to the fatigue strength design of un-strengthened and CFRP strengthened rib-to-deck welded joints. The mechanism that CFRP reinforcement can significantly improve the fatigue performance of welded joints can be concluded to less stress concentrations and slower growth rate of the crack.

A simplified method for fatigue life evaluation of welded joints in OSD considering welding residual stress relaxation

The welding residual stress at the welded joints of orthotropic steel decks (OSD) has a significant influence on the fatigue life, and welding residual stress relaxation (WRSR) occurs under vehicle loading. The existing fatigue evaluation method for steel bridges does not consider the WRSR on fatigue life and may cause a large deviation between the fatigue life prediction results and the fatigue cracking in the field. This paper proposes a simplified fatigue life evaluation method that can consider WRSR quantitatively. First, the initial welding residual stress (IWRS) distribution model is established based on residual stress tests and numerical simulation. Second, the simplified mechanical model of the coupled effect of IWRS and vehicle-induced structural stress as well as the law of WRSR are established via stress analysis at the weld toe section of DRWJs under external loading. Furthermore, the peak/valley value of the coupled effect of IWRS and vehicle-induced structural stress are determined, and a stress time-history simplification method considering WRSR is proposed. On this basis, a simplified fatigue life evaluation method considering the WRSR of DRWJs on OSDs is finally proposed and combined with the Q345 steel full-range SN curve model. The Jiangyin Yangtze River Highway Bridge is used as an example to demonstrate the fatigue life evaluation procedure of this proposed model in detail. Based on the multiscale finite element model (FEM) considering the coupling effect of the WRS and vehicle loading stress, the real stress time-history curves of DRWJs under vehicle loading cases are extracted and compared to those of the simplified method. Based on the full-range SN curve model considering IWRS and WRSR, the fatigue life of the welding joints of Jiangyin Bridge is finally calculated, and the results are more accurate and closer in value to the field observations of fatigue cracking when compared with the Eruocode3 standard. This provides a theoretical basis for fatigue analysis and lifetime assessment technology of large span highway steel box girder bridges.

Influence of resin asphalt pavement on stress behaviors of double-side welded rib-to-deck joints in orthotropic steel decks

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.

Fatigue strength and crack growth of double-side welded rib-to-deck joint in orthotropic steel decks

Fatigue failure in orthotropic steel decks (OSDs) leading to the reduction in service life of bridge structures has been paid much attention. The innovative double-side welded rib-to-deck (DWRTD) joint was proposed to enhance the fatigue resistance of OSDs. In this study, fatigue tests of several specimens of DWRTD joints were conducted by an innovative test setup to reveal the real stress state of DWRTD joints in OSDs. The fatigue resistance of DWRTD joints was estimated by hot spot stress method associated with S-N curve. Beach marks were introduced to record the process of fatigue crack propagation. Furthermore, single-crack and multi-crack propagation simulations were executed based on fracture mechanics to analyze the effect of multi-crack propagation and coalescence on the fatigue life of DWRTD joints. The fatigue test results indicate that the fatigue strength of DWRTD joints satisfies the design category FAT100 (100 MPa at 2 × 106 cycles) in IIW, and the fatigue crack initiation from the interior deck weld toe dominates the fatigue failure of DWRTD joints. The multi-crack propagation and coalescence significantly accelerate the fatigue failure of DWRTD joints, and the fatigue life will be overestimated neglecting the multi-crack propagation.

Fatigue performance of rib-to-deck joints in orthotropic steel deck with PWHT

Post-weld heat treatment (PWHT) displays potential for enhancing the fatigue strength of rib-to-deck (RD) welded joints in orthotropic steel decks (OSDs) by mitigating welding residual stress. In this study, residual stress measurements, fatigue tests, and fracture analyses were performed to investigate the influence of PWHT on the welding residual stress and fatigue strength of RD joints. Eighteen full-scale specimens were fabricated, i.e. ten PWHT-processed specimens and eight as-welded specimens without additional treatment. Hole drill (HD) and X-ray diffraction (XRD) were used to measure the residual stress in four PWHT specimens and four as-welded specimens. The PWHT specimen showed a reduction in the peak residual stress by 76% and 78% in the HD and XRD results, respectively. Fatigue tests were carried out on the six PWHT specimens and four as-welded specimens. The comparison was made between the two specimen types using the mean value of equivalent fatigue strength derived at 2 million cycles. The results indicated that PWHT improved the mean equivalent fatigue strength of RD joints by 23% and 33% under nominal stress and hot-spot stress, respectively. Parametric investigations were carried out using finite element-based fracture analysis to elucidate the influence of residual stress mitigation on fatigue crack growth in RD joints. The result indicated a significant decrease in the crack growth rate owing to residual stress mitigation. Such a decrease enhances the fatigue strength of RD joints.

Time-variant fatigue reliability assessment of rib-to-deck welded joints using ANN-based methods

Environmental corrosion and vehicle load significantly influence the fatigue damage of steel bridges. To efficiently investigate the combined effect of stochastic vehicle load and environmental corrosion on the fatigue damage of welded joints of orthotropic steel decks (OSDs), an artificial neural network (ANN) assisted assessment framework is proposed. A stochastic fatigue vehicle load model and an atmospheric corrosion model are first adopted for probabilistic modeling of stress response of rib-to-deck (RD) welded joints. To reduce the calculation cost of large-scale finite element analyses (FEA) runs in probabilistic simulation, the relation is generated between the equivalent stress range and variables (i.e., vehicle loads and corrosion depth) using ANNs. The time-variant fatigue reliability, therefore, can be calculated using Monte Carlo (MC) simulations by considering the uncertainties of variables in limit-state functions. The efficiency and feasibility of the proposed framework are demonstrated with a steel bridge. Finally, parametric studies investigate the influence of traffic volume and corrosion on the time-variant fatigue reliability of RD welded joints.

Machine Learning-Assisted probabilistic fatigue evaluation of Rib-to-Deck joints in orthotropic steel decks

This study integrates the fatigue test and numerical prediction to derive a comprehensive probability-stress-life (P-S-N) curve for rib-to-deck (RD) welded joints in orthotropic steel decks. Fatigue tests of RD joints are conducted to measure fatigue strength and crack growth data. Based on the test, a probabilistic fatigue crack growth (PFCG) model is established to predict the distribution of fatigue life under various stress ranges. Two machine learning tools are adopted to assist the PFCG model-based prediction, i.e., the Gaussian process regression (GPR) and dynamic Bayesian network (DBN). The GPR is used to train a surrogate model solving stress intensity factors for the PFCG prediction, using 2,000 samples generated from finite element (FE) analyses. The trained model is then validated by a new dataset of 100 FE samples. An adapted DBN model is proposed to update the PFCG model with the fatigue crack growth data measured from ten specimens. According to the result, the application of GPR can reduce the solution cost of the PFCG prediction by approximately 1,875 times. Compared with the prior PFCG model, the updated posterior model shows an improved agreement with the test data, i.e., the maximum difference in fatigue strength between model prediction and test data decreases from 12% to 3%. Based on the posterior PFCG model, the P-S-N curve of RD joints is statistically derived using sufficient numerical samples.

Fatigue behavior of rib-to-floorbeam welded connections in UHPC reinforced OSDs subjected to longitudinal flexural

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.

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.