Fatigue Details Research Articles

Simulation study on fatigue behavior of wrap-around weld at rib-to-floorbeam joint in a steel-UHPC composite orthotropic bridge deck

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.

Reassessment of fatigue detail categories of bolts and rods according to EC 3-1-9

The paper deals with the reassessment of fatigue detail categories of bolts and rods in EC 3-1-9 based on published fatigue test data and further conducted investigations. An elaborate database structure has been set up to evaluate the available fatigue test data in a differentiated way. Detail categories of bolts and rods in tension and shear have been investigated and re-evaluated based on the developed data base. Moreover, fatigue tests and numerical investigations on prestressed bolts in T-joints, L-joints and different types of end plate connections have been performed. Several influences on the fatigue strength (e.g. material influence, size effect, fabrication differences) have been analysed and design recommendations are given. The conducted fatigue tests on bolts in tension fit into the spreading band of 573 tests results conducted in the past, confirming fatigue class 50. However, bolts with rolled threads show a higher fatigue strength than those with cut threads, which has been included into the recommendations for fatigue details of bolts. Fatigue class 100 for bolts in shear has also been confirmed, however based on few data. Numerical investigations show, that bolts should be placed as close as possible to the tension flanges, while end plates should be dimensioned thick enough with an overhang including an additional bolt row.

Fatigue analysis of wire arc additive manufactured (3D printed) components with unmilled surface

First investigations have been carried out on the characterisation of the as-welded surface roughness of unmilled wire arc additive manufactured (WAAM) components, followed by an experimental determination of the fatigue strength. Subsequently, randomly based finite-element (FE) simulations are carried out to expand the findings. The statistical characteristics of the surface provide the input values for the Monte-Carlo (MC) simulation. Here, the fatigue strengths of single-wire and multiple-wire welded components have been compared applying the effective notch stress concept performing over 2200 simulations. Finally, a fatigue detail classification for surfaces of WAAM components is given following the principles of EN 1993-1-9 [1].

Improvement of Stop-Hole Method on Fatigue-Cracked Steel Plates by Using High-Strength Bolts and CFRP Strips

Steel bridges are extremely damaged by fatigue subjected to cycling load. Therefore, it is often necessary to put forward effective reinforcement to strengthen steel structures during the daily maintenance. In this study, two repairing methods of high-strength bolts and high-modulus CFRP strips on the basis of stop-hole repair method were introduced, respectively, to investigate fatigue improvement of cracked steel plates. First of all, numerical analysis was conducted to predict the repair efficiency and investigate the optimal parameters of each method. Variables studied were stop-hole diameter, pretightening force of bolt, and size of CFRP patch. Subsequently, a total of 12 specimens were tested to study the repairing efficiency of cracked steel plates with various strengthening methods through cyclic loading. At the same time, the failure mode and fatigue life were analyzed to present the improvement of fatigue performance. In addition, the experimental results were compared against the S-N curves of this strengthened fatigue detail. The outcomes of this study revealed that an improvement in the influence of fatigue-crack repair with the adoption of these two strengthening methods was evident. Numerical results showed that the addition of these materials could significantly diminish stress concentration factor around hole edge and improve their fatigue performance in comparison with only stop-hole method. Fatigue test results indicated that the crack initiation life of specimens repaired by stop-hole method was more than 20 times that of the unrepaired specimens. The high-strength bolt reinforced stop hole and CFRP patched stop hole can extend the crack initiation life by 9 and 8 times, respectively, in contrast to control specimens with sole stop-hole method. Finally, it was demonstrated that repairing damaged steel plates with stop-hole method alone was not enough to satisfy the fatigue strength requirements of various countries. But the fatigue strength category of damaged steel plates after further repairing with high-strength bolts and high-elastic-modulus CFRP, respectively, was higher than category A of AASHTO.

Revision of fatigue detail categories of plain members and mechanically fastened joints according to EC3-1-9

The present paper deals with the reassessment of fatigue detail categories of plain members and mechanically fastened joints (Table 8.1 in EC3-1-9) based on published fatigue test data. For a differentiated re-evaluation of details an elaborate database structure has been set up. Detail categories of different types of plain members and mechanically fastened joints have been investigated and revised by evaluating the collected fatigue data. Finally, several influences on the fatigue strength of the revised details have been analysed and design recommendations are given. For shear or gas cut plates, higher fatigue classes have been determined. In case of sheared or gas cut plates with subsequent dressing and double covered preloaded joints, higher inverse slopes of the S-N curves as currently incorporated in EC3-1-9 prove to be more realistic. A dependence of fatigue strength on stress ratio and yield strength as well as fabrication properties have been shown. For double covered preloaded joints, a dependence of fatigue strength on yield strength is significant and it is therefore recommended to include a higher fatigue class for higher strengths into the detail catalogue.

Fatigue performance prediction of S235 base steel plates in the riveted connections

Although several old riveted bridges served more than 100–150 years in the world, some of them are still in the application, generally limited by the economic budget or cultural relic protection reason. Hence, the status of those bridges needed to be evaluated to support the bridge management and rehabilitation, especially with the increasing traffic flow along with their service life. Nowadays, fatigue detail class 71 in the EN 1993-1-9 is generally recommended to evaluate the fatigue behaviour of the riveted joints. But the predicted fatigue behaviour of riveted connection using the recommended S-N curves is excessive conservative because the differences of connection geometries and materials are not fully considered using the global nominal stress methods. Therefore, in this paper, a two-phase fatigue performance approach based on local strain and Paris law, respectively, fatigue crack initiation and propagation phases, combined with numerical simulation, is an effective surrogate method to predict the fatigue performance of riveted connections, considering the material and geometry effects. A good agreement is observed when compared to numerical simulation with experimental observations.

Optimization Analysis Method of New Orthotropic Steel Deck Based on Backpropagation Neural Network‐Simulated Annealing Algorithm

To study the effects of the fatigue performance due to the major design parameter of the orthotropic steel deck and to obtain a better design parameter, a construction parameter optimization method based on a backpropagation neural network (BPNN) and simulated annealing (SA) algorithm was proposed. First, the finite element (FE) model was established, and the numerical results were validated against available full‐scale fatigue experimental data. Then, by calculating the influence surface of each fatigue detail, the most unfavorable loading position of each fatigue detail was obtained. After that, combined with the data from actual engineering applications, the weight coefficient of each fatigue detail was calculated by an analytic hierarchy process (AHP). Finally, to minimize the comprehensive stress amplitude, a BPNN and SA algorithm were used to optimize the construction parameters, and the optimization results for the conventional weight coefficients were compared with the construction parameters. It can be concluded that compared with the FE method through single‐parameter optimization, the BPNN and SA method can synthetically optimize multiple parameters. In addition, compared with the common weighting coefficients, the weighting coefficients proposed in this paper can be better optimized for vulnerable parts. The optimized fatigue detail stress amplitude is minimized, and the optimization results are reliable. For these reasons, the parameter optimization method presented in this paper can be used for other similar applications.

Low-frequency sinusoids for enhanced shear buckling performance of thin plates

Thin plates subject to shear are ubiquitous in structures, used in webs of flexural members, shear walls, curved aircraft fuselages, ship hulls, etc. Given shear buckling concerns, these slender elements must be designed to balance plate depth and thickness. As slenderness limits capacity, strategies such as stiffeners or corrugations can enhance efficiency but are not without costs. In plate girder fabrication, the use of transverse and/or longitudinal stiffeners introduce poor fatigue details, while corrugation requires web forming and complex flange-to-web welding. The authors propose an alternative strategy, forming low-frequency sinusoidal (LFS) patterns along the plate's longitudinal axis as a novel, less fabrication-intensive approach to enhancing shear capacity of thin plates. The frequencies studied here are much lower than those used in commercial corrugated products and previous research, resulting in lower forming stresses, prospective fabrication using conventional semi-automatic welding techniques, and potentially improved fatigue behavior. Experimentally validated finite element models are used to evaluate sinusoidal frequency, amplitude, initial geometric imperfection, plate depth, and plate slenderness. Elastic shear buckling load, ultimate shear load, and shear yielding are used to evaluate effects of the parameters. Significant increases in shear strength and material efficiency can be achieved using an LFS approach. A standardized low-curvature LFS shape with 1.2 m wavelength is applicable to a wide range of plate depths and thicknesses without the need for specialized equipment to form the plate or weld the web-to-flange interface. LFS plates combine durability, material efficiency and ease of fabrication in a strategy that can benefit the industry.

Analysis of fatigue test data to reassess EN 1993‐1‐9 detail categories

AbstractThis paper addresses the assessment of fatigue details according to EN 1993‐1‐9, which form the basis of the most important fatigue verification, the nominal stress approach. First of all, a suitable statistical methodology had to be defined for consistent detail classification. A structured database on the MySQL platform serves as a basis for the evaluation of the detail categories. In addition to fatigue test data documented in the background document to EN 1993‐1‐9, this database also includes new test data provided by the authors. After selecting the most meaningful test data, important details, such as longitudinal welds, were reassessed. In addition, the authors carried out fatigue tests in connection with numerical simulations in order to be able to evaluate the fatigue strength with better accuracy. The results so far show that the details analysed often prove to have a higher fatigue strength than currently documented in EN 1993‐1‐9.

Uneven spatial distribution of fatigue cracks on steel box-girder bridges: a data-driven approach based on Bayesian networks

Orthotropic steel decks (OSD) of bridges are subjected to cyclic vehicle loads, leading to the growth of fatigue cracks. Fatigue strengths are dependent on fatigue details and the load effects vary from position to position; consequently, the spatial distribution of fatigue cracks on the bridge deck is not uniform. Previous studies on fatigue effects of OSD are mainly limited to a single fatigue detail. This article presents a Bayesian network (BN)-based method to investigate the uneven distribution of fatigue cracks on a cable-stayed bridge deck. The bridge deck is divided into girder-elements, and types of fatigue cracks are considered. Critical variables controlling the uneven distribution of fatigue cracks are represented by root nodes, while the fatigue states of girder-elements are represented by leaf nodes; the causal relationships are described by directed edges between nodes. The proposed approach is validated using field inspection results. A sensitivity analysis is conducted to reveal the importance of each node in the BN. Compared to previous researches involving fatigue cracks, the proposed approach is superior in calculating the occurrence probabilities of types of fatigue cracks given critical variables as well as quantitatively analysing the main causes for types of fatigue cracks.

Procedures of Fatigue Analysis by Supporting Direct Load Application on Midship Sections

Fatigue evaluation of ship structures using direct calculation methods to calculate fatigue loads are standard practice today. There are several numerical codes available for use in analyses of these fatigue loads. In addition to the varying degrees of computational complexity associated with fatigue prediction methods, the inherent uncertainties of these procedures are also large. This paper introduces the procedure for stochastic fatigue analysis of typical midship models with direct load transfer applied, where an oil tanker is considered. It also covers a comparison of the results with the component-based approach included in the DNVGL Class Note 30.7: “Fatigue Assessment of Ship Structures”. The "real" case analysis includes both internal pressure loads from tank fluids as well as external pressure adjusted for wet and dry surfaces in the waterline area, according to DNVGL Class Note 30.7. Local fine mesh models of fatigue details have been analysed using the sub-modelling technique. The procedure performs well on a typical midship model apart from the file sizes of the generated load transfer files. With 25 wave periods and 12 different headings, the analysed 3-cargo-hold model (1/2 + 1 + 1/2) in the midship area had to be split into four super elements in order to get the analysis through finite element analyses. The procedure is suitable for vessels where warping (torsion) is of less importance. The described procedures are supported by a developed tool to be used in the analysis procedures. Three details of local fine mesh models such as deck erection butt weld, longitudinal stiffener through web-frame, and bottom erection butt weld have been analysed. The results have been compared with the component-based approach. For some of the details there are comparable results, but for others the results vary significantly. The typical trend is that the details heavily influenced by the external pressure (side longitudinal) give less comparable results than e.g. a detail in the main deck mainly influenced by global loads. A comparison of the effect of reducing versus not reducing the pressure amplitude in the waterline on the fatigue life has also been performed and discussed.

Fatigue performance of U-rib butt welds in orthotropic steel decks

This study focuses on the orthotropic steel deck (OSD) of a cable-stayed bridge with a plate-truss composite structure. Fatigue tests and numerical simulations were conducted to investigate fatigue features in an OSD with a broad U-rib and embedded sections, considering the assembly tolerance. For the purpose of this study, the pre-stressing force method was adopted to simulate the initial axial pressure in the deck. Fatigue tests were done on three full-scale segment specimens (a total of 6.5 million variable amplitude fatigue cycles). Initial long macro cracks are observed in the arc segment of butt welds. The length of these initial cracks is proportional to the stress amplitude. Fatigue crack propagation stages in the broad U-rib can be divided into four parts with clear demarcation points. The crack growth rate is proportional to the crack length; this increases as a result of the axial force. The initial axial pressure accelerated the crack propagation rate of fatigue details of butt welds. It is recommended that the butt welds of the broad U-rib embedded section can be designed using the fatigue strength of category FAT112 in Eurocode 3. In addition, empirical correction formulas for fatigue strength correction for assembly tolerance of the embedded section are proposed.

Current tendencies in welding of steel bridges; choice of material and use of thick plates

The emergence of new efficient materials, the high demands on the quality of the welded joints, while ensuring their safety in operation, outstanding aesthetic forms, the complexity of the new European welding standards, the pressure of the short execution times, had as result the adoption of modern solutions for steel and composite bridges. Durability is also one of the demands of the European Standards. The use of thick heavy plates can lead to reduction of the constructive depth, possibility for improved fatigue details, short execution time and easy maintenance. In this direction the fabrication efficiency is important, the need of a correct technology is vital. The role of the welding specialist is determinant. The paper presents some examples in the realization of modern steel and composite bridges with thick plates for the Romanian highways network.

Nonlinear Optimization of Orthotropic Steel Deck System Based on Response Surface Methodology.

The steel bridge deck system, directly subjected to the vehicle load, is an important component to be considered in the optimization design of the bridges. Due to its complex structure, the design parameters are coupled with each other, and many fatigue details in the system result in time-consuming calculation during structure optimization. In view of this, a nonlinear optimization method based on the response surface methodology (RSM) is proposed in this study to simplify the design process and to reduce the amount of calculations during optimization. The optimization design of the steel bridge deck system with two-layer pavement on the top of the steel deck plate is taken as an example, the influence of eight structural parameters is considered. The Box-Behnken design is used to construct a sample space in which the eight structural parameters can be distributed evenly to reduce the calculation workload. The finite element method is used to model the mechanical responses of the steel bridge deck system. From the regression analysis by the RSM, the explicit relationships between the fatigue details and the design parameters can be obtained, based on which the nonlinear optimization design of the bridge deck system is conducted. The influence of constraint functions, objective functions, and optimization algorithms is also analyzed. The method proposed in this study is capable of considering the influence of different structural parameters and different optimization objectives according to the actual needs, which will effectively simplify the optimization design of the steel bridge deck system.

Material and Structure Performance of RPC Pavements for Steel Bridge Decks

To solve the fatigue cracking problem in orthotropic steel decks (OSD) and to prevent the early damage of bridge pavements resulting from the low stiffness of the bridge deck system, epoxy-resin-perfused concrete (RPC) pavements were developed for improving the modulus and road performance of paving materials. The mechanical and road performance of RPC and the bonding performance of the waterproofing adhesive layer were studied via laboratory experiments. The mechanical property of RPC pavements and their protective function on OSD were analyzed by using a finite element model. Composite beam fatigue life and acceleration loading tests were performed on a scaled model to verify the performance of these pavements. Results show that RPC has excellent high-and low-temperature stability and water stability that can meet the requirements and has a relatively long fatigue life. The bonding strength of RPC pavements and steel plate is better than that of epoxy asphalt concrete and Gussasphalt concrete pavements. RPC pavements have a relatively low tensile stress on the surface and a relatively high shear stress below the surface, but these stresses are far lower than the material strength. When paved with RPC, the stress in the fatigue details of OSD is reduced by more than 20%. The maximum relative deflection between ribs, the minimum curvature radius, and the relative deflection to span ratio of RPC are also favorable, thereby providing additional protection for the bridge deck system. The fatigue life tested with a five-point bending composite beam is more than 1 million times, which meets the requirements. In the acceleration loading test, RPC pavements do not show any rut, whereas the OSD shows no cracking when loaded for 12 thousands times. The engineering application results demonstrate the feasibility of using RPC pavements and show that these pavements and OSD endure no damage.

Cracking reasons and features of fatigue details in the diaphragm of curved steel box girder

The cracking reasons and features of fatigue details in the diaphragm of curved steel box girder were studied based on a real curved steel bridge with three spans located in Nagoya, Japan. The cracking conditions of certain fatigue details were summarized according to in situ monitoring data. The in-plane and out-of-plane deformation was analyzed considering structural features and loading conditions of the bridge as a whole. The influence of the curve on fatigue characteristics was investigated and reasons for cracking were concluded. Moreover, the fatigue test was carried out on cracking details to verify cracking behaviours in the real bridge, based on which the cracking laws were summarized. The results indicated that the unevenly distributed loadings caused by the curvature resulted in a greater stress on outside details than on inside details in the curved steel box girder, which was the major difference in the fatigue characteristics between curved and straight steel box girders. The eccentricity of vehicle loadings and structural characteristics were the major reasons behind the antisymmetric propagation of the cracks in the diaphragm-web rib weld. Apparent interference could be observed in the fatigue cracks of the diaphragm-U rib weld on both sides of an identical U rib.

Fatigue Failure of runway beams due to wheel loads

ABSTRACTThe introduction of the Eurocode 3 led to a significantly stricter fatigue classification, especially for flange to web connections of runway beams of heavy duty cranes compared to former national design rules like DIN 4132. At present, this leads to a doubling of the cross‐sectional thicknesses, which e.g. can result into web plates with extreme thicknesses of 80 mm. Execution as well as monitoring of such flange to web connections using full penetration tee‐butt welds are quite critical and thus no longer to be realized reasonably.On this account new fatigue strengths for the runway beam specific fatigue detail “Top flange to web junction of runway beams” in EC3‐1‐9 Table 8.10 have been established within the FOSTA‐research project “Fatigue failure of runway beams due to wheel loads in heavy smeltery cranes” as recommendations for an eventually modification or even extension of the current codes. In Particular, the detail executed using full penetration tee‐butt welds has been investigated in the framework of this research project.The essential core of the methodical approach is that real existing crane runway girders have been examined, documented and evaluated in regard of fatigue failure of the flange to web connection. In this way, a direct quantitative assessment of safety against fatigue failure for the investigated detail could be derived. In addition, synthetic notch cases have been investigated numerically. The results of both methodologies have been prepared for a proposal of amendment of the current codes. This paper provides an insight into the methodological approaches and the main results achieved.

Effect of low temperatures on constant amplitude fatigue properties of Q345qD steel butt-welded joints

The development of transportation infrastructures stimulates increasingly more welded steel bridges in cold and severe cold regions in China. The low temperature there imposes additional challenges for the welded fatigue details. This study firstly examines experimentally the fatigue properties of the butt-welded joints made of Q345qD bridge steel under high-cycle constant-amplitude tensile action at the room and low temperature of −60 °C. The experimental results reveal the occurrence of multiple fatigue crack initiation and illustrate that the low temperature increases slightly the fatigue strength of the butt-welded details. The numerical simulation examines the fatigue crack propagation behavior of butt-welded joints with initial pre-existing single and multiple cracks under the room and low temperature, which achieves a good agreement with the experimental results. Based on the experimental and numerical validation, this study finally discusses the effect of the low temperature on the fatigue life of butt-welded joints and demonstrates that the lower fracture toughness under the low ambient temperatures influences marginally on the fatigue crack propagation life of the butt-welded details. The enhanced resistance to the fatigue crack propagation of structural steels at low temperatures contributes to the improved fatigue strengths of the butt-welded joints.

Fatigue testing and analysis of I-girders with trapezoidal corrugated webs

Composite box girders with corrugated steel webs excel conventional concrete box girders in multiple ways in bridge industry, such as deadweight reduction, construction speed and quality. However, girders with trapezoidal corrugated webs are susceptible to fatigue under inevitable repeated heavy traffic loads. This paper conducted a large-scale fatigue test of an inclined I-girder with corrugated web under four-point bending, given the scant fatigue test data for this kind of girder and the inadequate validation of relevant fatigue detail category (FAT). Test results show that the critical crack initiated in combined bending-shear region, though multi-cracks initiated at weld toe of the web-to-flange welded detail in constant moment region. The test girder failed almost simultaneously as the critical crack propagated through the flange plate thickness and extended to one side of the flange plate edge. The other two less critical cracks in the constant moment region approximate to be fatal in the final stage of crack propagation. The fatigue failure criterion of the test girder, therefore, is conservatively recommended as the worst case of two conditions, namely the critical crack reaches 1.6 times of flange plate thickness in length or propagates through flange plate thickness. The parametric finite element analysis (FEA) was also conducted to investigate the influence of the corrugation parameters on the stress conditions at fatigue sensitive spot. The FEA results indicate that the shear force prompted the transfer of the location of critical crack from the constant moment region to the combined bending-shear region, and shortened the fatigue life of test girder by 11.3%. In general, the evaluation results indicate that FAT of the web-to-flange welded detail under four-point bending can be recommended as FAT 90 for nominal stress approach, FAT 120 for structural hot spot stress approach and FAT 225 for effective notch stress approach.

Experimental study on fatigue performance of UHPC-orthotropic steel composite deck

UHPC-orthotropic steel composite deck is an innovative and efficient bridge deck system, however the failure mode of this composite bridge deck under fatigue load is still not well understood, particularly when the deck is in hogging bending. To investigate the fatigue behavior of the UHPC-orthotropic steel composite deck, two multi-span full scale composite bridge decks in hogging bending were experimentally studied. To simulate the bridge deck under negative bending, the specimens were designed with the mid-span deck simply supported and two overhanging decks each side. Each specimen was tested twice. In the first test phase, the specimen was loaded with a vertical force acting on one side span, while in the second test phase, the specimen was vertically loaded on another side span. Tests revealed that among the all fatigue-prone details of an orthotropic steel deck, only the longitudinal cracks were observed occurring in the low portion of rib web which was near the weld toe of the rib to the transverse diaphragm. The fatigue strength of these specific cracks longitudinally orientated can be evaluated in a term of the vertical stress range of the rib below the weld toe under the fatigue details category C of AASHTO or category 71 MPa of Eurocode3. Shear connection failure of the composite deck was also found featuring with delamination between UHPC and steel bridge deck. Fatigue damage of the short headed studs was further inspected and evaluated by means of drilling test. It is found that the fatigue life of the shear connection is governed by the fatigue shear strength of the short headed studs, which is much longer than the fatigue life codified in the specifications for studs of conventional composite beams. The fatigue shear connection strength of the composite bridge deck can be assessed conservatively in a term of the fatigue shear strength of the headed studs.