Web Gap Research Articles

Digital simulation of distortion-induced fatigue in steel bridges with different geometrical configurations

Distortion-induced fatigue cracks at web gaps often occur in multi-girder steel bridges under vehicle loads. This paper presents full size digital simulations of steel girder bridges with different geometrical configurations, to explore the distortion-induced fatigue cracking performance. In the digital simulations, four geometrics are considered, in addition to two web gap details, namely the vertical stiffener web gap and the horizontal gusset plate web gap. Introducing multi-layer and multi-pass welds residual welding stress fields, digital fatigue simulation results show that the distortion-induced fatigue cracks at both web gaps are Mode I-II-III combined cracks dominated by Mode I. The coupling of the three modes is more prominent at the vertical stiffener web gap compared to the horizontal gusset plate web gap. In the skewed bridge, curved bridge, and skewed-curved bridge, the significant bending-torsional coupling effect, the structural asymmetry, and the stress deformation asymmetry cause an increment in distortion ranges, fatigue crack growth rates, and the proportions of Mode II and III cracks. The fatigue strength categories for vertical stiffener web gap and horizontal gusset plate web gap in straight, skewed, curved and skewed-curved bridges are category 125, 112, 110 and 110, and category 160, 140, 100 and 100 of the Chinese specification and Eurocode, respectively. Therefore, the geometrical configuration is an important factor affecting the distortion-induced fatigue behavior, which should be considered in the fatigue design and maintenance of steel girder bridges.

Stress Concentration Factor-Based Hot-Spot Stress Prediction Model for the Web-Gap Weld of Main Girder in Steel Truss Bridge

Fatigue cracking is one of the main diseases of steel bridges in operation stage. Scientific evaluation is of great significance to improve structural durability. However, obtaining the hot-spot stress (σHSS) extrapolation point is challenging due to limited space around certain structural details in steel bridges. To overcome this limitation, a HSS prediction method incorporating the stress concentration factor (SCF) was proposed. Additionally, a structural mechanics model based on the mechanical characteristics of the web gap in the main girder of a steel truss bridge was established to calculate its nominal stress. Experimental and numerical simulations have been conducted to investigate the effects of various geometric parameters of the web gap on the SCFs. On this basis, a formula for predicting the SCF in web-gap weld was developed using multiple linear stepwise regression analysis. A fatigue evaluation framework considering the SCF for the web-gap weld were proposed. The result shows the web gap is affected by the joint actions of rotation and displacement, with the web gap of the end floor beam being more prone to fatigue damage. Moreover, the structural mechanics model considering the joint actions of rotation and displacement aligns better with the actual stress characteristics. The proposed SCF prediction formula for the web-gap weld demonstrates an error of less than 5% compared to the FE results. The fatigue damage obtained by the proposed HSS prediction method is consistent with the traditional extrapolation method, hence validating the feasibility and reliability of the proposed approach.

Effect of liquid bridge on the thickness deviation between wafers sawn by diamond wire

Diamond wire web will be rearranged due to the reduction of structural stiffness and the enhancement of capillary force in the system for sawing ultra-thin wafers with fine-diameter diamond wire, which can cause uneven thickness between the as-cut wafers and affect the subsequent processing. A model for analyzing the transverse sawing behavior of the diamond wire caused by the liquid bridge after sawing into a workpiece was developed in this study by extending the dynamical model for a double-wire system with liquid bridge action to a multi-wire system. The stable transverse sawing state of the wire was obtained by analyzing the variation of the transverse sawing force with the as-cut wafer thickness thinning. Accordingly, the wafers thickness deviation rate affected by the wire groove wear and the liquid bridge action was calculated. The effects of the wire groove wear, the initial wire web gap, and the wire length between the guide wheel and the workpiece on the thickness deviation between the wafers sawn by the diamond wire were explored. The results show that the wafers thickness deviation increases with the increased wear of the wire grooves when the initial wire web gap is smaller than the minimum gap at which spontaneous wires adhesion can occur. The increase of wire groove wear makes the double-wire sawing more likely to occur. In addition, the wafers thickness deviation increases with decreases in the initial wire web gap and increases in the wire length between the guide wheel and the workpiece. Reducing the ratio of the initial wire span to the workpiece width helps to suppress the liquid bridge action during slicing and avoid the double-wire sawing. Since the minimum gap at which spontaneous wires adhesion can occur is large for the thick-diameter diamond wire, the fine-diameter diamond wire can be a better option for sawing the ultra-thin wafer to avoid the effect of liquid bridge on the wafers thickness deviation to the greatest extent.

Influence of distortion ratio on distortion-induced fatigue behavior of steel girder bridges

The physical fatigue test and a new proposed research methodology called the digital fatigue test are used to investigate distortion-induced fatigue performance at web gap regions in steel girder bridges. Digital fatigue test based on the extended finite element method can combine factors such as residual welding stress, initial defects, and fatigue action, to simulate the propagation of mixed-mode cracks. Physical and digital fatigue test results show fatigue strength decreases significantly with increasing distortion ratio, which is the ratio of the minimum and maximum distortion at web gaps. When distortion ratio and nominal stress ratio increased from 0.2 to 0.5, the fatigue strength of 60 mm horizontal gusset plate–vertical​ stiffener web gap and 40 mm vertical stiffener web gap decreases by 43% and 50%, respectively.

Effect of a liquid bridge on the dynamic behavior of diamond wires during slicing

Diamond wire sawing with narrower kerf losses and thinner as-cut wafers is a critical technology to further reduce wafering costs in the semiconductor industry. Nevertheless, as the scale of the wire web decreases, the effect of the liquid bridge formed by the capillary condensation of the cutting fluid between the diamond wires becomes significant. Moreover, the transverse wire vibration reduces the wire web gap at certain moments, which makes it easier for the wires to adhere to each other after wetting, thus hindering the slicing process. Therefore, a dynamical model for a double-wire system with liquid bridge action was developed in this study based on the transverse vibration theory of a diamond wire under support excitations to reveal the action mechanism of the liquid bridge between diamond wires. The dynamic adhesion process between the diamond wires moving with the supports is discussed. The effects of the guide wheel manufacturing error and the sawing parameters on the critical gap for spontaneous adhesion between the diamond wires are analyzed. The results show that the static double-wire system does not generate spontaneous adhesion when the surface gap of the wires is between the critical gap for spontaneous adhesion and the maximum adhesion gap. The support excitation causes the transverse wire displacement, which increases the critical gap for spontaneous adhesion to increase the risk of wires adhesion. The critical gap for spontaneous adhesion increases with increases in the guide wheel manufacturing error and the wire span as well as the wire speed and decreases with increases in the wire groove diameter and the wire tension. When the manufacturing error is doubled, the critical gap for spontaneous adhesion will increase more than twice this error increment. Strict control of the guide wheel manufacturing error is the most effective way of reducing the risk of wires adhesion during processing. Increases in the guide wheel diameter and decreases in the wire span and the wire speed within a reasonable range, or enhancing the mechanical properties of the wire to improve its breaking force, also help to reduce the critical gap for spontaneous adhesion.

Field Investigation of Causes of Fatigue Damage in Web Gap Plate Based on Strain and Displacement Measurements in In-Service Steel Girder Bridge

Field Investigation of Causes of Fatigue Damage in Web Gap Plate Based on Strain and Displacement Measurements in In-Service Steel Girder Bridge

Transverse forced vibration of a diamond wire under support excitations

Diamond wire sawing is a key technology for wafer processing in the semiconductor industry. Transverse wire vibration decreases the wire web gap to below the critical adhesion spacing between the wires, which is an important factor that limits the development of diamond wire slicing technology toward narrower kerf losses and thinner as-cut wafers. In fact, the external excitation source that causes the diamond wire vibration comes primarily from the supports at both ends of the wire. Therefore, an analytic model for transverse forced vibration of a diamond wire under support excitations was developed in this study based on the transverse vibration theory of an axially-moving string fixed at both ends. This partial differential equation with non-homogeneous boundary conditions was solved using the superposition principle and the finite element method. To verify the theoretical model, experimental equipment to text the transverse vibration of a diamond wire with support excitations was developed. The support excitation signal and the wire vibration response were obtained using accelerometer measurements and machine vision detection, respectively. The theoretical results agree well with the experimental results, indicating the correctness of this proposed model. The effects of the vibration source and the installation parameters on the transverse vibration displacement of a diamond wire are discussed. The results show that hysteresis in the movement of the center of the wire causes a certain additional high-frequency vibration, which can make this maximum transverse displacement to be greater than the excitation amplitude, thus making the wire transverse vibration change non-linearly with some parameters. The maximum transverse vibration displacement at the center of the diamond wire increases with increases in the guide wheel machining error amplitude and the wire diameter as well as the wire span, while it decreases with increases in the wire groove diameter and the wire tension. This maximum transverse vibration displacement decreases by approximately 100.22 % and 6.17 % when the guide wheel manufacturing error amplitude and the wire groove diameter are reduced by half and doubled, respectively. Improving the manufacturing accuracy of the guide wheel is still the most effective way of reducing the transverse vibration displacement of the wire. In addition, appropriate increases in the groove diameter and the wire tension and decreases in the wire span are also beneficial for suppressing the wire vibration.

Distortion – Induced Fatigue Failure at Main Girders of a Railway Bridge – Strain Measurements in Service and Analyses Based on Fracture Mechanics

AbstractAt the main girders of a three span continuous plate girder railway bridge, built in the 1970s, through‐thickness cracks were detected in the web, at the location of the transverse stiffener to main girder connections. Based on former Austrian standards for steelwork, the transverse stiffeners are not welded to the main girder flanges in order to increase their fatigue resistance. Instead, fitting pieces between the stiffeners and the bottom flanges were used.Within the paper the geometry and the location of the cracks are presented. For the global stresses, due to moments and shear forces, numerical simulations of the train passages were done. Based on these global stresses only, the fatigue damage for the main girders was evaluated at each position of a transverse stiffener connection. Since there was no significant agreement between the distribution of the global fatigue damage along the main girder and the crack positions, the out‐of‐plane distortion in the web gap region was expected as the obvious cause for the cracks.To verify the complex local stress field in the web gap region (interaction of global and local stresses), comprehensive strain measurements were done during service. The relevant results, including passages of slow and fast individual locomotives, passenger and freight trains, are presented and compared.Finally, based on the measured stress range spectra the further crack growth behavior was analyzed and the residual fatigue life was predicted using a linear elastic fracture mechanics (LEFM) approach where also the mixed‐mode conditions at the crack tips were considered.

Distortion-induced fatigue behavior of vertical stiffener web gaps in steel girder bridges

This paper reports full-scale fatigue tests, conducted to explore the distortion-induced fatigue behavior of vertical stiffener web gaps in steel girder bridges, considering parameters such as web gap size, nominal stress ratio and distortion ratio (a newly proposed physical parameter). The results show that the fatigue strength of weathering steel web gaps improves with the increase of the web gap size, but worsens with the increase of the stress ratio and the distortion ratio. It was found that the fatigue strength for 20 mm, 40 mm and 60 mm weathering steel web gaps corresponds to categories 36, 71 and 100 in Eurocode 3, when the nominal stress ratio and the distortion ratio are less than 0.3. However, when the nominal stress ratio and distortion ratio are between 0.3 and 0.5, the fatigue strength for 20 mm is below category 36, while for 40 mm and 60 mm, it corresponds to categories 45 and 80, proving the stress and distortion ratio dependency.

Impact of reinforcement and geometry of deep beam – Research perspective

Present construction industry is moving towards high rise and multi-storeyed building which requires the deep beam element to dissipate the load to adjacent element. Loads are transferred from slab to column by beams, and in the case of longer spans, deep beams are used. In deep beams, the theory of simple bending principles does not apply and does not follow the conventional beam theory, and is designed in accordance with non-linear stress distribution in depth of the structural member. A complete literature review focusing on shear strength of deep beams was conducted. Design criteria such as web reinforcement, shear length to depth ratio, vertical reinforcement, beam size, beam depth, side face reinforcement, percentage of reinforcement, crack width criteria, and shear span deflection is varied by the researchers to analyze the shear behaviour of deep beams. Since shear failure is a key concern, of deep beam, many researchers have researched the shear strength behaviour of deep beams in the previous years. Possibility to shear failure is high in deep beam, so structural reinforcements must be revamped as soon as possible. Web gaps in deep concrete beams interrupt the transfer of loads to the supports, reducing the member's shear strength. While such gaps can have a substantial impact on the structure's life, most study on deep beams has concentrated on the shear behaviour of concrete members. Present research lays the groundwork for presenting a new shear strengthening technique during member design.

Action mechanism of liquid bridge between electroplated diamond wires for ultrathin wafer slicing

Ultrathin wafer slicing with low kerf loss for electroplated diamond wire sawing is the primary means to improve the productivity in wafering and reduce the manufacturing costs in the photovoltaic industry. Nevertheless, the reduction of the diameter and spacing of the diamond wires makes the liquid bridge action between them significant, which will affect the slicing process. Therefore, based on the principle of minimum potential energy, an analytic model of adhesion caused by the liquid bridge between the diamond wires with protruding abrasives is established in this paper. The variation of the adhesion length with initial wire web gap, wire span, and wire tension as well as wire diameter is analyzed. The results show that the adhesion length was increased with the increase of the wire diameter. The reduction of the initial wire web gap would increase the adhesion length, that was, the limitation of the liquid bridge on the thinner wafers sawing was more obvious. The adhesion length was decreased with the decrease of the wire span or the increase of the wire tension. So it is effective to weaken the limitation of the liquid bridge on the wafers slicing by reducing the wire span or enhancing the wire strength. Then, an experiment on the action of the liquid bridge between the diamond wires was carried out. The theoretical results were in accord with the experimental ones well, and the maximum error was 8.27%. The research work is of great significance to further reduce kerf loss and wafer slicing thickness.

Bonding and bolting angle reinforcement for distortion-induced fatigue in steel girder bridges

Physical fatigue tests and numerical simulation were conducted to verify the effectiveness of cold reinforcement methods of distortion-induced fatigue cracks at web gaps in steel girder bridges. Test results indicate that stop-holes could temporarily arrest crack growth. However, bolting and bonding angle could effectively arrest further cracking, and reduce distortions and fatigue stresses. Numerical simulation analysis results show that the equivalent stress intensity factor decreased dramatically below the corresponding threshold after bolting or bonding reinforcement. The innovative bonding angle reinforcement strategy is more recommended for better reinforcement effectiveness, no damage to the original structure, and avoiding traffic disruption.

Evaluation of novel combined CFRP-steel retrofit for repairing distortion-induced fatigue

Distortion-induced fatigue damage at crossframe-to girder connections affects many steel bridges built before the mid-1980s. This type of damage is associated with a prevalent detailing practice at the time which avoided welding connection plates to girder flanges to avoid fatigue cracks. The lack of connectivity and out-of-plane motion of the crossframe produce a flexible gap region in the girder web where fatigue cracks often develop, requiring frequent inspections, costly maintenance, and repairs.This paper presents a study evaluating the use of CFRP in conjunction with steel sections to repair complex patterns of distortion-induced fatigue cracks in steel bridge web gaps, without the need for bolting to the flange or concrete deck removal. A steel girder-to-crossframe subassembly was tested in distortion-induced fatigue to evaluate the performance of the retrofit measure. Realistic crack patterns were introduced by applying fatigue loading, and the efficacy of the repair method was evaluated by monitoring crack growth with the repair in place. Twelve test trials were performed: five in the unretrofitted condition to propagate the cracks, and seven in the retrofitted condition to evaluate performance of the repair. The study evaluated multiple crack patterns, different configurations of the retrofit, presence or absence of mechanical anchorage to the flange, footprint of the CFRP relative to the steel retrofit elements, and different surfaces connected by the CFRP.The results showed that the combined CFRP-steel retrofit measure was effective in preventing distortion-induced fatigue crack initiation and propagation.

Finite Element Analysis of Cold Formed Steel Channel Columns with Complex Edge Stiffeners and Web Holes using Abaqus

The present theory work means to think about the numerical examination on models of channel segment with middle and complex edge stiffeners and web gaps under pivotal pressure. A wide scope of parameters, for example, slimness proportion, spine width and thickness have been considered in the investigation. An aggregate of 12 channel models with various parameters, for example, length, thickness and rib width are reenacted. The limited component non-direct examination program ABAQUS V6.14-2 is utilized to reproduce the models. The material properties are acquired from Coupon test. Component type utilized in this non-straight examination is SHELL. A Static, Riks step is utilized to complete examination. The Failure modes, extreme burden and the pressure conveyance around web gaps are inquired about. The relocation parts in every augmentation of burden along X, Y and Z bearings and Rotation segment about X course are gathered. The Von-Mises pressure forms, Deformed shapes and disappointment modes including nearby, horizontal distortional and parallel torsional clasping modes are acquired. The pivotal burden limits of pressure individuals with various parameters are looked at.

Numerical simulation of distortion-induced fatigue crack growth using extended finite element method

Aiming to investigate the propagation behaviour of distortion-induced fatigue cracks in steel bridge web gaps, multi-scale numerical analysis models were built based on fracture mechanics theory and extended finite element method (XFEM), combining with the full-scale fatigue tests data. Propagation behaviours of representative fatigue cracks in vertical stiffener web gaps and horizontal gusset plate web gaps were analysed. Finite element models of welds connecting web, vertical stiffener and horizontal gusset plate were built, and the welding residual stresses of such details were analysed. Significant transverse welding residual tensile stresses exist at stiffener web weld toes for web gap details. Residual stress measurements were conducted, and the crack shape and the propagation direction path were basically the same with that in the numerical simulation, indicating that the numerical simulation results were relatively reliable. Furthermore, the welding residual stress fields were considered in the crack propagation analysis models. Representative fatigue cracks at web gaps are Mode I leading mixed-mode cracks of Modes I, II and III. Crack propagation considering welding residual stress has faster propagation rate and is more consistent with fatigue test results. The welding residual stress cannot be ignored for analysis and assessment of distortion-induced fatigue cracks in steel bridges.

Experimental study on retrofitting method against fatigue cracking at the upper end of web gap plates on load distribution cross beam ends

Experimental study on retrofitting method against fatigue cracking at the upper end of web gap plates on load distribution cross beam ends

Effectiveness of fatigue retrofits to transverse beam and sway bracing connections in steel bridges

A great number of fatigue cracks have been found in the welded joints at the top end of web gap plates in the transverse beam connection, at the top end of vertical stiffeners in the sway bracing connection, and at the web penetrations with the transverse beam bottom flange. The present paper is a report on the verification of the effectiveness of 3 new types of retrofit methods proposed against those fatigue crackings. Stress measurements were carried out before and after retrofit works in a 45 years old bridge located in one of the heaviest traffic routes in Japan. As a result, fatigue life was considerably improved after the retrofit works, except for the case of vertical stiffener upper end retrofitted by the jack-up method. Fatigue life was improved to more than a several times by the TRS method for the vertical stiffener upper end and web gap, and to more than tens of times at the girder web slot area after retrofitting.

Detection of fatigue cracking in steel bridge girders: A support vector machine approach

This study presents an artificial intelligence approach for the detection of distortion-induced fatigue cracking of steel bridge girders based on the data provided by self-powered wireless sensors. The sensors have a series of memory gates that can cumulatively record the duration of the applied strain. The gates are activated as soon as the electrical charge generated by piezoelectric strain transducer exceeds pre-defined thresholds. In the present study, the distribution of the sensor output has been characterized by a Gaussian cumulative density function. For the analysis, extensive finite element simulations were carried out to obtain the structural response of an existing highway steel bridge girder (I-96/M-52) in Webberville, Michigan. Different damage states were defined by extending the lengths of the crack at the web gaps from 10mm to 100mm. Damage indicator features were extracted for different data acquisition nodes based on the sensor output distribution. Subsequently, support vector machine (SVM) classifiers were developed to fuse the clustered features and identify multiple damage states. The results indicate that the models have acceptable detection performance, specifically for cracks larger than 10mm. The best classification performance was obtained using the information from a group of sensors located near the damage zone.

Distortion-Induced Fatigue Cracking in a Seismically Retrofitted Steel Bridge

This study examines the effect of a seismic retrofit on distortion-induced fatigue cracking in a steel girder bridge in the Midwestern United States. The seismic retrofit of the bridge was deemed necessary following a structural review initiated by the Federal Highway Administration (FHWA) in response to the 1989 Loma Prieta Earthquake. Following the review, the bridge was modified using a conventional seismic retrofit strategy to meet the 1995 FHWA standards for survivability and seismic performance. Upon completion of the retrofit, subsequent inspections identified new cracks (at the location of the retrofit) in the webs of longitudinal girders at transverse stiffener locations in an area known as the web gap. This study investigates the influence of the seismic retrofit strategy on crack formation by comparing principal stresses in the web-gap region of the original and retrofitted bridge under dead, live and thermal loading. A three-dimensional linear-elastic finite element analysis of the bridge before and after the retrofit is presented with results obtained from a commercial finite element software package. Comparisons of stresses before and after the retrofit indicate a measurable increase in stress near the web-gap region attributable to thermal and live loads following the retrofit. In addition, several viable repair strategies to limit these web-gap stresses and subsequent distortion-induced fatigue are presented. The results to date clearly demonstrate the importance of considering fatigue-sensitive details in seismic-retrofit strategies.

Distortion-Induced Fatigue Crack Growth

Out-of-plane distortion of transverse cross-bracing systems in bridge superstructures has been known to cause localized fatigue cracking. The cracking is a result of the differential displacement of adjacent bridge girders, which causes high stress concentrations in unstiffened web-gap regions at the interface of girder and stiffener connection plates. Fatigue cracking within the web gap can occur because of cyclical loading scenarios. Rehabilitation efforts have shown to be unpredictable in preventing crack propagation once through-thickness crack profiles have developed. Therefore, understanding the mechanisms causing fatigue crack propagation in such detail is essential in developing effective repair methods. In this study, numerical analyses of typical web-gap connections are conducted using the extended FEM to characterize crack directionality and growth rate. Simulations varying the web-gap length, stress range, loading ratio, and initial crack length were used to determine the primary variables effecting crack growth in the web-gap region. Increasing the web-gap length was noted to stabilize crack propagation rates, resulting in stable growth, which can be correlated to the Paris Law. Elongation of horizontal initial crack lengths resulted in reorientation of crack growth. In stiffer web gaps, a combined high stress ratio and long initial crack length resulted in crack profiles propagating into the flange-web interface with eventual crack arrestment. The study suggests that horizontal extension of initial cracks has the potential to cause the crack to arrest, after stable propagation, without adversely compromising local structural integrity of bridge superstructures.