Steel Bridge Deck Research Articles

Investigation on temperature effect of local structural stress during non-uniform cross-section steel bridge deck pavement paving

During the process of gussasphalt concrete paving on the orthotropic steel bridge deck of a non-uniform cross-section box girder bridge, the high-temperature asphalt mixture often produces temperature stresses that can affect bearings safety. In this study, a refined model of a steel box girder bridge with a 660 m scale was developed and numerical simulations were conducted using the finite element software. The temperature field was applied to the orthotropic steel bridge deck in a quasi-dynamic fashion, leading to the determination of a safe width for concrete paving. To assess the accuracy of the computational predictions, field paving was performed under the safe width condition determined from the calculations, and the temperature and local stress data were measured in the field. The results demonstrate that the finite element predictions are in good agreement with the yield strength of the bearing’s local structure, and the measurements also show a close correspondence with the structural yield strength, validating the reliability of the quasi-static simulation approach. The proposed method offers a computational tool and a reliability criterion for future finite element analyses of large-span non-uniform cross-section steel box girder bridges, as well as a safe width example for subsequent gussasphalt mixture paving on orthotropic steel bridge decks.

Correlation between high temperature performance of gussasphalt mixture for steel bridge decks and rheology of asphalt mastic

Rutting is a prevalent issue in the Gussasphalt (GA) mixture layer of steel bridge deck pavements. This study aims to investigate the correlation between the rheology of GA mastic and the high-temperature performance of the GA mixture. To achieve this objective, GA mastic underwent temperature and frequency sweep tests, along with multiple stress creep and recovery tests employing a dynamic shear rheometer. Additionally, indentation tests, uniaxial penetration tests, and Lueer fluidity tests were conducted on the GA mixture. The Grey Relational Analysis method was employed to evaluate the relationship between asphalt mastic rheology and the high-temperature deformation resistance of the GA mixture. The findings reveal that the addition of mineral filler enhances the deformation resistance of both GA mastic and the mixture. The percent difference in non-recoverable creep compliance (Jnr-diff) was minimized when the weight ratio of filler to asphalt binder (F/B) was 2.5. Furthermore, increasing the F/B ratio from 2.0 to 3.5 resulted in a more than twofold increase in the GA mixture’s shear strength. Asphalt type emerged as a significant factor affecting the indentation parameter of the GA mixture, with an F-value reaching 8.82 based on ANOVA analysis. The rheological properties of GA mastic exhibited a significant correlation with the high-temperature performance of the mixture. The highest Grey Relational Grade of 0.87 was observed between the non-recoverable creep compliance at a 3.2 kPa stress level (Jnr3.2) and indentation. In future research, greater emphasis can be placed on exploring the micromechanical properties of the GA mastic-aggregate interface.

Experimental and theoretical investigations on the static behavior of low aspect ratio shear stud connectors in ultra high performance concrete

In reinforcement project for early-built orthotropic steel bridge decks (OSDs) using ultra high performance concrete (UHPC), low aspect ratio shear stud connectors in UHPC are required. In present study, push-out tests of six static UHPC specimens with and without reinforcement bars were first conducted. The failure modes, load-slip curves and shear capacity of shear stud connectors embedded in UHPC with an aspect ratio of 1.84 were investigated. Subsequently, the experimental results of shear capacity and load-slip curves were compared with the theoretical calculation results. Finally, a new theoretical model of shear stiffness was proposed for low aspect ratio shear studs based on the energy equivalence theory. The experimental results indicated that the failure mode of all specimens was stud shank failure, while the UHPC slabs without reinforcement bars showed extensive cracks. The effect of reinforcement bars on the behavior of shear studs embedded in UHPC slabs can be negligible. The reinforcement bars mainly affected the internal force flow in the UHPC, thus limiting crack initiation and extension. The compressive strength of the UHPC and the weld collar had significant impact on the shear capacity of short studs in the UHPC. In calculating the load-slip curves of short shear stud connectors in UHPC, the theoretical results calculated using the fractional form equations were in better agreement with the experimental results. The proposed theoretical model neglecting the deformation of shear stud in elastic stage can accurately predict the shear stiffness of low aspect ratio shear stud connectors in UHPC.

Steel Structures Research Update: Innovative Steel Deck System for Highway Bridge Applications

Ongoing research on innovative steel bridge decks is highlighted. This study, currently under way at the University of Kansas, is led by Dr. William Collins, Associate Professor in the Department of Civil, Environmental, and Architectural Engineering. Dr. Collins’s research interests include fatigue and fracture of metallic structures; bridge design, fabrication, construction, and performance; and evaluation and preservation of historic structures. Among Dr. Collins’s accolades are the Robert J. Dexter Memorial Award, a Fulbright Scholar Award to conduct fracture mechanics research in Finland, and the AISC Milek Fellowship. The four-year Milek Fellowship is supporting this research on innovative steel deck systems for highway bridge applications—the first Milek Fellowship project to focus on bridges. Selected highlights from the work to date are presented, along with a preview of future research tasks.

XFEM based study on fatigue performance of rib-to-diaphragm welded joints considering initial defects

Orthotropic steel bridge decks (OSBDs) have been widely used in the field of bridges. However, their service life is significantly limited by fatigue issues. This study presents an analysis of the fatigue performance at the structural details of the rib-to-diaphragm joint, taking into account the impact of initial defects. A numerical segment model employing shell-solid coupling is established to determine the influence surface range and the most unfavorable working condition of the fatigue details, using fatigue standard vehicle loading. The accuracy of the local full-scale model is validated. A local model test of the rib-to-deck welded joint is carried out to deduce the parameter selection for the numerical simulation, based on the test results. Additionally, the crack propagation process in rib-to-diaphragm joints is simulated using XFEM. The simulation results of crack propagation demonstrate good agreement with the actual bridge crack path and shape. The crack propagation model can effectively evaluate the fatigue life, crack development stage, and shape of fatigue details. The study determines the effects of crack depth, crack length, and crack angle on fatigue performance. This study provides a basis for studying the residual fatigue life and crack propagation behavior of rib-to-diaphragm welded joints with initial defects. It is of great significance for understanding the crack propagation mechanism, formulating repair measures, and determining repair time.

Bending performance of prefabricated ultra-thin UHPC unit plate reinforced orthotropic steel bridge decks

To address the challenges related to lengthy construction period, complex maintenance requirement, and the elevated risk of shrinkage cracking associated with cast-in-place UHPC reinforcement of orthotropic steel bridge decks. This paper proposes a novel solution that prefabricated ultra-high-performance concrete (UHPC) slab with epoxy bond connection is used as a reinforcement layer for orthotropic steel bridge decks. Four sets of bending tests on composite bridge deck were carried out to compare the flexural performance of composite bridge decks under different joint forms and loading patterns. The results indicate that the precast UHPC decks delaminated from the epoxy bonding layer without failure of the epoxy layer itself in all cases. The positive bending capacity of the jointless composite bridge deck is approximately 27.67 kN, while the negative bending capacity is around 16.58 kN. For the composite bridge deckwith epoxy adhesive joints (EA-J-Ln), the negative bending capacity is 2.54 kN, and the negative bending capacity of the joint area reinforced with carbon fiber cloth (EA-JC-Ln) is increased to 4.17 kN. Therefore, the use of carbon fiber cloth can significantly improve the bending resistance of the joints. Finally, numerical model of the composite deck based on Cohesive Zone Model (CZM) was established, validating the applicability of this simulation method in the novel composite bridge deck.

Methods to Increase Fatigue Life at Rib to Deck Connection in Orthotropic Steel Bridge Decks

Orthotropic steel bridge decks (OSDs) are very popular all over the world because of the low dead load, high stiffness in the longitudinal direction, high strength ratio to weight, and can be used in various types of bridges. The life of these bridges is affected by fatigue cracks in different portions. One of major areas where the fatigue cracks appear in these bridges is rib-to-deck connection. In this research finite element analysis is carried out by using ABAQUS/CAE 2022 software to determine the ways to increase the fatigue life at rib to deck connection in OSDs. In the first part, smaller models are simulated; stress concentration is analyzed and hot spot stress (HSS) is calculated according to International Institute of Welding (IIW) and Det Norske Veritas (DNV) recommendations. In the second part, a parametric analysis is carried out to analyze the effect of weld penetration, thickness of deck, thickness of rib and rib to deck connection type. In the third part, simulation of models similar to the real field is carried out to determine whether the double welded connections are better than single welded connections. Different models are analyzed for different load cases like single wheel load, double wheel load and also the position of the wheels is changed. The boundary conditions are changed to analyze whether the boundary condition has any significant effect on the result obtained. It is found that thicker decks, thinner ribs, and low penetrated welded connections reduce the stress concentrations at rib to deck connections which ultimately increase fatigue life. Among the parameters examined, deck thickness is the most important parameter. It is found that the percentage of stress increase with percentage decrease in deck thickness follows a power relation. The overall fatigue life of double welded connection is excepted to be lower since the stress concentration is maximum at the weld toe at deck on the outer side of the closed stiffener; however, if the cracks initiate on the inner side of closed stiffener, the cracks at the weld root of single welded connection can propagate much rapidly than the cracks initiating on the inner side of the closed stiffener at the weld toe, thereby reducing the fatigue life of the single-welded specimen significantly.

Investigation into the interface bond between polyurethane concrete and steel plate

PurposePolyurethane concrete (PUC), as a new type of steel bridge deck paving material, the bond-slip pattern at the interface with the steel plate is not yet clear. In this study, the mechanical properties of the PUC and steel plate interface under the coupled action of temperature, normal force and tangential force were explored through shear tests and numerical simulations. An analytical model for bond-slip at the PUC/steel plate interface and a predictive model for the shear strength of the PUC/steel plate interface were developed.Design/methodology/approachThe new shear test device designed in this paper overcomes the defect that the traditional oblique shear test cannot test the interface shear performance under the condition of fixed normal force. The universal testing machine (UTM) test machine was used to adjust the test temperature conditions. Combined with the results of the bond-slip test, the finite element simulation of the interface is completed by using the COHENSIVE unit to analyze the local stress distribution characteristics of the interface. The use of variance-based uncertainty analysis guaranteed the validity of the simulation.FindingsThe shear strength (τf) at the PUC-plate interface was negatively correlated with temperature while it was positively correlated with normal stress. The effect of temperature on the shear properties was more significant than that of normal stress. The slip corresponding to the maximum shear (D1) positively correlates with both temperature and normal stress. The interfacial shear ductility improves with increasing temperature.Originality/valueBased on the PUC bond-slip measured curves, the relationship between bond stress and slip at different stages was analyzed, and the bond-slip analytical model at different stages was established; the model was defined by key parameters such as elastic ultimate shear stress τ0, peak stress τf and interface fracture energy Gf.

Influence of Deck Butt Weld Seams on Fatigue Life of Steel Bridge Decks Pavement: Parameter Optimization

Abstract The butt weld at the connection between orthotropic steel bridge decks (OSBDs) can potentially pose a hazard to the fatigue endurance of the steel bridge deck pavement. This study aims to optimize the parameters of the butt weld seam using finite element (FE) analysis. The optimized parameters will provide valuable guidance for the design of pavements with a focus on antifatigue properties. Initially, the dynamic modulus of the epoxy asphalt mixture (EAM) was determined through laboratory experimentation at various frequencies and temperatures. These material parameters were then used to compute the pavement’s fatigue life. Additionally, a well-established FE model was employed to analyze the deformation and fatigue life of the pavement structure. The validity of the model was verified by the theoretical calculation results. Various factors were considered, including vehicle velocities, pavement temperatures, and weld seam misalignments as well as weld seam dimensions such as height and width. The analysis was conducted using a three-dimensional steel bridge model. The results showed that decreasing pavement temperature, weld seam height, and misalignment led to an increase in pavement fatigue life. Conversely, reducing the weld seam width resulted in a decrease in fatigue life. Furthermore, the study investigated the coupling effect of different weld seam heights and widths on the fatigue life of the pavement. Contour figures were used to establish the parameter relationship formula for weld seam height and width. These findings are significant for pavement and deck designers because they enhance the understanding of the sensitivity of weld seams as design variables affecting the fatigue characteristics of pavement structures. Moreover, special attention should be given to the impact of welding parameters on the fatigue design of steel bridge deck pavement under high-temperature conditions of pavement structures.

Investigated on hot mix epoxy resin used in steel bridge deck pavement affected by collaborative toughen

The hot-mix epoxy resin commonly used in the market has insufficient toughness, resulting in cracking of steel bridge deck pavement. To obtain the excellent toughness of hot mix epoxy resin, the collaborative toughen is put forward to overcome the shortcoming. In order to character epoxy resins and epoxy asphalts affected by toughening agent, standard test method of tensile properties for plastics is used. The synergistic toughening mechanism and lyotropy of 1# rubber additive and 2# rubber additive are approved by analyzing scanning electron microscope. Synchronous thermal analyzer is applied to study reactivity of epoxy resin. The viscosity, reactivity and rheological performance of epoxy asphalt, which affected by toughen agent, are investigated by Brinell rotary viscometer and Dynamic shear rheometer respectively. According to the results, the excellent epoxy resin is obtained, when the dosage of toughen agent is 15 %. The activation energy of epoxy resin before and after toughen are 48.6 KJ/mol and 42.4 KJ/mol, respectively. Besides the toughen agent can reduce the viscosity of epoxy asphalt. Finally, R1 and R2 can enhance the elastic of epoxy asphalt and reduce the glass transition temperature of epoxy asphalt. In summary, with R1 and R2 added, the toughen of epoxy resin improved obviously. The application of toughened epoxy resin to the pavement of orthotropic steel bridge deck will has a very broad prospect.

Fatigue Reliability Assessment for Orthotropic Steel Decks: Considering Multicrack Coupling Effects

Multiple fatigue cracks are generally present in practical engineering due to the existence of welding; the size and number of cracks of orthotropic steel bridge decks are greatly uncertain. The component failure conditions caused by these cracks may have correlations. Currently, it is still a challenging issue to develop a physical model of multiple fatigue crack propagation in bridge decks and perform a fatigue reliability assessment, which is also the motivation that drives the innovation of this study. A fatigue reliability evaluation method is presented for orthotropic steel bridge decks, considering the coupling effect of multiple cracks and the randomness of vehicle loading. A numerical simulation method for multifatigue crack growth is developed by combining the ABAQUS and FRANC3D programs. The equivalent crack depth under different spacing and depths of collinear cracks is calculated by using numerical simulation and the multicrack equivalent characterization method. The critical damage accumulation function of multiple fatigue cracks is established using linear elastic fracture mechanics. Subsequently, the critical damage accumulation function of multiple fatigue cracks is established based on linear elastic fracture mechanics. In order to solve the time-consuming problem of traditional Monte Carlo method, the iHL-RF method and AK-MCS method are developed for fatigue reliability analysis. The results show that compared with the single-crack model, the fatigue reliability of orthotropic steel deck will be crucially reduced considering the coupling effect of double cracks. The MCS, iHL-RF and AK-MCS methods can effectively solve the fatigue reliability analysis problem. Compared with the MCS method, the reliability calculation time based on AK-MCS method is significantly reduced. The AK-MCS method-based method reduces the time for calculating the reliability of orthotropic steel decks by 50% compared with the iHL-RF method. The reliability analysis of orthotropic steel deck bridge based on AK-MCS method is proved to be efficient and accurate.

Analysis of Mechanical Response of Epoxy Asphalt-Repaired Pavement in Pothole Interface on Steel Bridge Deck under Coupled Temperature-Dynamic Loading

The persistence of pothole maintenance represents an enduring challenge. Past studies have largely concentrated on the materials and techniques used for remediation, with a lack of attention given to the pothole interface. This paper employed epoxy asphalt rubber (EAR-10) as the repair material, exploring the impact of coupled temperature-dynamic loading on the mechanical response of the interface. Finite element modelling (FEM), adopting the viscoelastic characteristics of EAR-10, was deployed to investigate the mechanical response of the interface under three temperature service conditions high, medium, and low when a dynamic load traversed the pothole. The stress variations in the interface at various inclinations and thicknesses of the repair blocks were also studied. In addition, the comparative analysis of high-temperature rut resistance for powdered rubber composite-modified asphalt and SBS modified asphalt was conducted via the multiple stress examination in terms of its high-temperature resilience, resistance to moisture-induced damage, and fatigue life by employing the asphalt mixture rutting test, low-temperature bending test on small beams, and the water immersion Marshall stability test, respectively. The repair efficacy of EAR-10 was appraised through post-repair water immersion rutting tests and bending tests on composite structural small beams. The results indicated that incorporating coupled temperature-dynamic loading led to a considerable increase in stress, particularly under low-temperature service conditions. An inclination angle of 30 degrees was found to be optimal for the interface. The research methodology presented here is pertinent to guiding the pothole repair in the steel bridge pavement, ensuring the strength and durability of the interface rivals that of newly constructed layers.

The impact of autonomous vehicles on the performance of steel bridge deck pavement

The widespread application of autonomous driving technology has become a prominent trend in the transportation industry. The purpose of this study was to investigate the impact of the lateral distribution pattern of autonomous vehicles (AVs) on steel bridge deck pavements (SBDP), with the aim of providing reliable theoretical support for future bridge deck pavement management and operation. A mixed traffic flow lateral distribution model was established and the Nanjing Yangtze Fourth Bridge was used as a case study. A corresponding finite-element model (FE) was constructed and Abaqus FE software was used to analyse rutting depths under different scenarios. The simulation results demonstrated that, under the zero distribution mode, a rational layout of AVs can significantly alleviate rut formation. Conversely, an unreasonable layout will reduce the service life of SBDP. Comparing the lateral distribution patterns of different vehicles, both the normal distribution and uniform distribution patterns exhibited positive effects on the SBDP. However, there was no significant difference in the magnitude of this positive impact between the two modes. This research not only fills the gap in the study of AV impact on SBDP but also proposes management methods for AVs.

Design and evaluation of semi self-compacting cold mix polyurethane mixture for steel bridge deck pavement

To enhance the environmental sustainability and pavement performance of steel bridge deck paving, a novel semi self-compacting cold mix polyurethane mixture (CMPU-10) for steel bridge deck paving was specifically designed and evaluated. Herein, this study presents the first comprehensive documentation of the research process involved in the mix design of CMPU-10. Initially, based on the theory of maximum density curve, a gradation with a Talbot index (n) of 0.40 was identified as the preliminary gradation for designing CMPU-10 by void ratio, compressive strength and slump tests. Subsequently, the aggregate grade-by-grade filling test revealed the critical influence of sieve sizes (0.075 mm, 0.6 mm, and 2.36 mm) on the mixture dense degree. From these findings, an in-depth analysis of the effects of aggregate passage under the key sieve on the degree of mixture density, compressive strengths, and flow properties led to the determination of the gradation range of CMPU-10. The optimum binder-aggregate ratio for the median gradation was determined to be 9.2%. Finally, wheel tracking, semi-circular bending (SCB) and freeze-thaw splitting tests showed that the designed CMPU-10 exhibits superior high-temperature stability performance, low-temperature cracking resistance and moisture susceptibility compared to the TAF epoxy asphalt mixture (EA-10). This paper not only provides a new potential low-carbon material for steel bridge deck paving projects, but also establishes a theoretical foundation for the optimization design and promotion polyurethane mixture.

Evaluation Method of Fatigue Life for Asphalt Pavement on the Steel Bridge Deck Based on the Inhomogeneous Poisson Stochastic Process.

The paving layer on the steel box girder bridge deck is widely used when constructing pavements for steel bridges. Owing to the orthotropic feature of steel decks, a transverse clapboard and rib can lead to a concentration of stress. Consequently, fatigue cracks are often identified in asphalt concrete pavement layers due to re-compaction caused by heavy vehicles. This study aims to derive an evaluation method of fatigue life for asphalt pavement based on the inhomogeneous Poisson stochastic process in view of the highly random and uncertain working conditions of layered composite structures. According to the inhomogeneous Poisson stochastic process, along with Miner's fatigue damage accumulation theory and the linear elastic fracture mechanics theory, the fatigue life formula could be deduced. Meanwhile, fatigue experiments for asphalt concrete are designed to investigate the correlation between the theoretical formula and the actual fatigue damage life of the material. Compared with the test, the accuracy error is within 10%, which is better than other traditional methods. Therefore, the fatigue life prediction model could better reflect the loading order effect and the interaction between loads, providing a new path for the fatigue reliability design of steel bridge deck asphalt pavement.

Acrylate composite polyurethane binder for steel bridge deck pavements: Process optimization by response surface methodology and microanalysis

AbstractTo better serve the steel bridge deck paving project, a novel room‐temperature curing acrylate composite polyurethane binder (APUB) was developed as a substitute for traditional asphalt binders. APUB was synthesized by the copolymerization of a custom‐made polyurethane prepolymer (BDO‐PU) and acrylate. Fourier transformed infrared and proton nuclear magnetic resonance spectroscopy analyses confirmed the presence of carbamate structures in prepolymer BDO‐PU. Utilizing tensile strength, breaking elongation and water absorption as optimization criteria, the response surface methodology was used to optimize synthesis process of APUB. The results showed that the optimized parameters for APUB synthesis include an isocyanate index (R) of 1.5, a mass ratio of methyl methacrylate to BDO‐PU of 1.1, and a curing agent content of 2.7%. These settings resulted in predicted values of 10.12 MPa for tensile strength, 123.85% for breaking elongation, and 0.075% for water absorption. Experimental validation demonstrated the consistency between the predicted and actual properties of APUB. Further microanalyses, including dynamic mechanical thermal analysis, differential scanning calorimetry, and scanning electron microscope, confirmed APUB exhibits excellent component compatibility and glass transition temperatures suitable for bridge engineering environments. Overall, APUB demonstrates outstanding tensile properties, water resistance, low energy consumption, and potential applications in the steel bridge deck pavement industry.

Full-temperature performance characterisation of super tough resin concrete for steel bridge deck paving

ABSTRACT The severe service environment of steel bridges put forward strict requirements for the deck pavement, especially the flexibility of paving materials. In this study, a new super tough resin-based concrete (STRC) was introduced and a comparative study of STRC and epoxy asphalt concrete (EAC) performance was conducted. Specifically, the high-temperature stability, low- and intermediate-temperature flexibility, fracture resistance, and fatigue properties were characterised by the dynamic creep test, beam bending test, semi-circular bending test, and semi-circular fatigue test, respectively. According to the results, at 70°C, the cumulative strain after 10,000 cycles of loading is about 2700μϵ and 900μϵ for STRC and EAC, respectively. At −10°C, the maximum tensile strain of EAC is only 2419 μϵ, which is significantly lower than that of STRC (17000 μϵ). For the cracking resistance, STRC exhibits larger total fracture energy, pre-peak and post-peak fracture energies, which indicates the excellent cracking resistance of STRC. Furthermore, the fatigue life and accumulated dissipated energy of STRC are higher than that of EAC. Besides, the tensile strain growth rate of EAC is significantly greater than that of STRC, which implies a lower crack propagation rate and better fatigue resistance of STRC.

Residual Stress Reduction through Thermo-mechanical Tensioning for an Orthotropic Steel Bridge Deck

Residual Stress Reduction through Thermo-mechanical Tensioning for an Orthotropic Steel Bridge Deck

Using Deep Learning-Based Defect Detection and 3D Quantitative Assessment for Steel Deck Pavement Maintenance

Efficient distress detection and identification analysis are of great significances for long-span steel bridge deck pavement maintenance. This paper proposes a pavement distress recognition method based on road quality detection equipment and deep learning. Firstly, the sub-block image is used as the processing unit, and the three-dimensional image is divided into fracture surface element and background surface element. A pavement crack recognition network (PDRNet) based on convolutional neural network is proposed, which is used for automatic recognition of pavement background element and pavement crack element. Then, considering the pixel-level neighborhood characteristics of cracks in 3D pavement images, the PDRNet model is used to detect and quantitatively evaluate pavement cracks, which combines the crack elevation detection method to extract the complete contour of cracks in the crack surface element. Finally, the distress database containing three-dimensional markers is integrated into the pavement maintenance management platform. Results show that the PDRNet proposed in this paper has high prediction accuracy on the verification set and shows good robustness to various distress, and the average accuracy is above 88%. The established spatial-temporal integration platform overcomes the communication bottleneck between different types of data, and is important to improve the maintenance management level and predict the long-term development of distress.

Experimental study on fatigue performance of double welded orthotropic steel bridge deck

Fatigue cracks which develop at multiple locations of orthotropic steel bridge decks (OSD) seriously deteriorate the safety and durability of steel bridges. U-rib fabricated using the double-sided penetration welding technique have been practically applied in bridges, but the fatigue performance of this type of U-rib has not been systematically studied. This study conducts fatigue tests on large-scale models of various fatigue details in the diaphragm area of orthotropic steel bridge decks with double-sided welds, obtaining the fatigue vulnerable locations and dominant cracking modes in the diaphragm area. The evolution law of out-of-plane deformation of diaphragm is clarified. The distribution characteristics of residual stress at the arched opening region and fatigue failure modes are acquired. Experimental results show that the interior weld toe of the U-rib-to-top-plate joint is the most fatigue-vulnerable zone, with a fatigue strength of 53.6 MPa. New fatigue cracks initiated from the weld toe of the top plate of the inner side of the U-rib or the weld toe of the U-rib perpendicularly or obliquely intersecting the longitudinal weld along 45° were found. After 10 million loading cycles, the residual stress in the arc-shaped opening area of the diaphragm reached 90–145 MPa, and the residual stress was higher where curvature of the opening was larger. The arc-shaped incision was in a circling state of tension and compression. It was also found that fatigue cracks that initiated from the weld toe of the diaphragm extended along the weld toe for some length before propagating into the diaphragm.