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Influence of hot-dip galvanization on the fatigue performance of high-strength bolted connections
... When constant tensile stresses σm > 0 are superimposed onto fluctuating actions (i.e., typical conditions for bridge details due to permanent loads [31][32][33]), the mean stress effect can be explicitly accounted for by means of a non-dimensional prestress coefficient cw To this end, it is worth highlighting that the usual values of R 0 for mild steels (10 −1 -10 0 mm [20]) often result in Ω SED being included in the HDP-affected zone of drilled plates. Therefore, the selected value of R 0 should be properly reduced to account for localized material damage. ...
... When constant tensile stresses σ m > 0 are superimposed onto fluctuating actions (i.e., typical conditions for bridge details due to permanent loads [31][32][33]), the mean stress effect can be explicitly accounted for by means of a non-dimensional prestress coefficient c w depending on the stress ratio R = σ min /σ max as follows (Equations (3) and (4)): ...
Riveted railway bridges with already long structural lives can still be commonly found in service in Europe. In light of their peculiarities, they are often prone to fatigue damage; nevertheless, very few prescriptions regarding fatigue assessment of these structures can be found in current European provisions. Within this framework, the present paper illustrates the advanced fatigue assessment of an Italian riveted railway bridge selected as a case study. For this purpose, multi-scale finite element modelling of the bridge was developed, and the most critical details were assessed through application of the advanced strain energy density (SED) method. The obtained outcomes were compared both with other studies in the literature and prescriptions from the current and upcoming versions of EN1993-1-9.
... Bolt connections are extensively utilized in bridges, large industrial facilities, and prefabricated concrete frame structures within civil engineering due to their structural stability, adaptability, and ease of construction [1][2][3][4]. When subjected to vibrational loads, fatigue failure and loosening can occur in bolt structures, with fatigue failure often emanating from localized loosening [5]. ...
The complexity of the thread surface makes it challenging to analyze the mechanism of bolt loosening from a mechanical perspective. To analyze the mechanism of bolt loosening, this paper proposes a mathematical model. Initially, the characteristics of the threaded surface are precisely represented using cylindrical and Cartesian coordinate systems, and the contact relationship of the thread contact surface is derived through normal and tangential vectors. Subsequently, the integral expressions for friction force and torque under transverse load are derived. The results indicate that as the frictional force between the contact surfaces increases, the torque caused by the friction force gradually decreases. Complete slip occurs when the frictional force reaches the critical value, at which point the torque is essentially at its minimum. Furthermore, the comparison between theoretical and finite element results demonstrates that the derived formulas can qualitatively express the loosening mechanism of the bolt under transverse load. Parametric analysis shows that the greater the transverse amplitude, the more likely the contact surfaces will slip. Slip reduces the resistance torque between the contact surfaces, leading to bolt loosening. Increasing the friction coefficient of the thread contact surface and ensuring that the friction coefficient of the bolt head contact surface is sufficiently different from that of the thread contact surface can effectively prevent bolt loosening. This strategy ensures that at least one contact surface maintains adhesion during vibrations, sustaining an adequate resisting torque to counteract loosening.
... This parametrical study aimed at capturing differences in seismic performance of medium-and high-ductile steel EBFs deigned according to EN1998-1:2004 and prEN1998-1-2:2023. For this purpose, the following assumptions were made: -Both I-shaped short-link and long-link EBFs were considered; -Connections design was not addressed, i.e., in spite of the influence of the cyclic behavior of details on the global structural performance [12][13][14][15][16]. Therefore, pinned releases were adopted among bracings, beams and columns; -Two different levels of seismic action were selected, i.e. S δ = 6.5 m/s 2 (threshold value among DC2 and DC3 [3]) and 7.5 m/s 2 ; -For each seismic index value, all allowed design prescriptions were assumed, i.e., DCM/DC2 and DCH/DC3 for S δ = 6.5 m/s 2 and DCH/DC3 for S δ = 7.5 m/s 2 . ...
... The uniaxial stress-strain relationship assigned to the fibres is the Steel02 [16] material, which is based on the Menegotto-Pinto model [17], assuming a value of the yield strength equal to 444 MPa, i.e., the expected yield strength of the steel in line with the code provisions, an elastic modulus equal to 210000 MPa and a post-yield strain hardening ratio equal to 0.5%. The degradation of the brace response due to fatigue, which can occur in either high-cycle [18,19] or low-cycle [11] conditions, is not modelled. The nonlinear out-of-plane rotational behaviour of the gusset plates is simulated using zero-length rotational springs, following the methodology outlined in [20], while rigid links are used to account for their geometrical dimensions. ...
Offshore wind turbine support structures, which connect the wind turbine transition piece and/or tower to the seabed, are located below the sea level and are in direct contact with seawater during the entire lifespan; therefore, they are highly susceptible to corrosion damage and cracking. In particular, the pitting corrosion is very crucial in these support structures, as it leads to local stress concentrations and thus affects the fatigue life. Although corrosion protection mechanisms are commonly implemented in offshore wind turbines, they have a finite life and therefore corrosion damage cannot be completely avoided during the entire life cycle, and this can lead to pitting corrosion on the steel surface. This paper aims to investigate the impact of pitting corrosion on fatigue durability of steel structures by performing tests on lab-scale coupons, made of S355 structural steel which is widely employed in fabrication of offshore wind support structures. For this purpose, cross-weld uniaxial samples were initially exposed to seawater for different time durations and then tested under cyclic loading condition. Furthermore, the durability analysis of corroded samples was carried out using a modified NASGRO equation. The results show that the pitting corrosion significantly reduces the fatigue life, and its level of life reduction is strongly dependent on the seawater exposure time. Moreover, the results show that employment of a linear trend for lower stress ranges would result in significant underprediction of the fatigue life, hence over-conservatism in the design life, at longer seawater exposure times.
Support structures for offshore wind turbines and the corresponding transformer platforms are highly susceptible to corrosion. In particular, the phenomenon of pitting is crucial, as it leads to local stress concentrations and thus affects the fatigue life of structures. Despite corrosion protection systems, corrosion cannot be completely avoided, which can lead to pitting corrosion on the steel surface. This leads to fatigue life reduction, since the structures are exposed to high dynamic loads. Local stress concentrations can be considered in local concepts but so far, corrosion effects in local concepts are insufficiently defined. Hence, this paper aims to investigate the impact of pitting corrosion and the corresponding stress concentration on the fatigue life endurance of structural steel, used for offshore wind support structures. For this purpose, a total of 36 pre-corroded specimens with pitting were tested against fatigue failure and monitored with Digital Image Correlation. In addition, the specimens were scanned with a high-resolution 3D scanner and converted to numerical models by reverse engineering, to determine the stress concentrations on the surface. In most cases the hotspots from the numerical model coincide with the crack location detected with Digital Image Correlation. The notch effect has a significant impact on the crack location and crack path.
Fatigue performance is often a key aspect when dealing with existing steel structures such as steel bridges or offshore constructions. This issue proves to be more critical as these structures are usually located in aggressive environments and are thus exposed to progressive degradation. Indeed, disruptive phenomena such as corrosion can severely worsen the fatigue performance of the steel components. Currently, the normative standards do not provide a codified procedure for the fatigue checks of steel structures subjected to ongoing corrosion. Within this framework, in this paper a simplified approach for the life-cycle assessment of corroded steel structures is proposed. For this purpose, the concept of “critical corrosion degree” is introduced, allowing the expression of corrosion fatigue checks in a more direct “demand vs. capacity” form with respect to the currently available methods. A first validation of such methodology is reported for the corrosion fatigue tests drawn from the literature. The predicted levels of critical corrosion are in good agreement with the values of artificially induced corrosion (i.e., 4, 8, and 12% of mass loss, respectively), with a maximum relative error of ≈9.3% for the most corroded specimen. Finally, parametrical analyses are performed, highlighting the influence of the model parameters on the corrosion fatigue performance of the steel elements.
Bolts and bolted connections are frequently used in civil engineering steel structures. This paper presents a meta study where a few thousand fatigue tests on these elements are evaluated. The evaluation reveals that current specifications in design standards need updating to account for the relevant stress parameter and production methods. This substantially reduces the scatter of the fatigue resistance. The shape and position of the fatigue resistance (S-N) curves also require updating. The results of this study have been implemented in the new revision of European standard EN 1993-1-9. This paper provides the background for the modifications.
The aim of the present work was to evaluate high-strength bolt corrosion fatigue based on metallographic examinations. The conducted tests were focused on the analysis of damaged martensitic bolts. It was found that the combined presence of cyclic loads and a corrosive environment was the cause of the accelerated fatigue of the fastening bolts. The tests carried out indicate that the actual operating conditions were different than expected. The corrosion contributed to the loosening of the bolts and initiation of fatigue cracks in the bolt threads. Further damage of the galvanized bolts was caused by fatigue crack growth in their threaded part that propagated towards the centre of the material. Cracks in the zinc coating were transferred to the steel substrate. The corrosion was favored by the oxygen concentration cell and numerous radial cracks appear in the zinc coating. The vibrations accompanying the operation of the wind tower led to their further propagation and the formation of the fatigue fracture in one of the bolts.
Evaluation of hydrogen effect on the fatigue crack growth behavior of medium-Mn steels via in-situ hydrogen plasma charging in an environmental scanning electron microscope, Abstract Fatigue crack growth (FCG) tests were conducted on a medium-Mn steel annealed at two intercritical annealing temperatures, resulting in different austenite (γ) to ferrite (α) phase fractions and different γ (meta-)stabilities. Novel in-situ hydrogen plasma charging was combined with in-situ cyclic loading in an environmental scanning electron microscope (ESEM). The in-situ hydrogen plasma charging increased the fatigue crack growth rate (FCGR) by up to two times in comparison with the reference tests in vacuum. Fractographic investigations showed a brittle-like crack growth or boundary cracking manner in the hydrogen environment while a ductile transgranular manner in vacuum. For both materials, the plastic deformation zone showed a reduced size along the hydrogen-influenced fracture path in comparison with that in vacuum. The difference in the hydrogen-assisted FCG of the medium-Mn steel with different microstructures was explained in terms of phase fraction, phase stability, yielding strength and hydrogen distribution. This refined study can help to understand the FCG mechanism without or with hydrogen under in-situ hydrogen charging conditions and can provide some insights from the applications point of view.
A formula is proposed to predict fatigue strength of corroded members and joints of steel structures. The concept of the formula is first studied from recently identified mechanism of corrosion fatigue. Hence, the corresponding fatigue strength curve (i.e. S‐N curve) of corroded steel is presented. It is further improved to derive linear, bilinear or trilinear S‐N curve for corroded constructional details of steel structures. The parameters of the corroded steel S‐N curve are determined based on the corrosion fatigue testing results of different types of steel specimens in air, fresh water and seawater. Hence, the parameters for the derived S‐N curve of corroded constructional details are predicted based on the above parameters and tabulated for the detail categories given in the Eurocode and DNVGL code. The proposed S‐N curve formula is compared with full‐scale fatigue test results of several constructional details, and the validity of the formula is confirmed.
It is well known that ferrous materials can be damaged by absorption of hydrogen. If a sufficient quantity of hydrogen penetrates into the material, static fracture and the material's fatigue performances can be affected negatively, in particular causing an increase in the material crack growth rates. The latter is often referred as Hydrogen Affected-Fatigue Crack Growth Rate (HA-FCGR). It is therefore of paramount importance to quantify the impact, in terms of hydrogen induce fatigue crack growth acceleration in order to determine the life of components exposed to hydrogen and avoid unexpected catastrophic failures. In this study, in-situ fatigue crack growth rate testing on Compact Tension (CT) specimens were carried out to determine the fatigue crack growth behaviour for a Fe-3 wt%Si alloy and X70 pipeline steel. Tests were carried out in two environmental conditions, i.e. laboratory air and in-situ electrochemically charged hydrogen, and different mechanical conditions in terms of load ratio (R = 0.1 and R = 0.5, for the Fe-3 wt% Si, R = 0.1 for the X70 steel) and test frequency (f = 0.1 Hz, 1 Hz and 10 Hz) were adopted under electrochemically charged hydrogen conditions. The results show a clear detrimental effect of H for the specimens tested in hydrogen when compared to the specimens tested in air for both materials and that the impact of hydrogen is test frequency-dependent: the hydrogen induced acceleration is more prominent as the frequency is decreased. Post-mortem surface investigations consistently relate the global crack growth acceleration to a shift from transgranular to Quasi-cleavage fracture mechanism. Despite such consistency, the acceleration factor strongly depends on the material: Fe-3wt%Si features acceleration up to 1000 times while X70 accelerates up to 76 times when compare to the material fatigue crack growth rate recorded in air. Observation of the deformation activities in the crack wake in relation to the transition into hydrogen accelerated regime in fatigue crack growth show a tendency toward restricted plastic activity in presence of hydrogen.
Press-hardened steel (PHS), used for automotive safety-related structure parts, is sensitive to hydrogen embrittlement due to its martensitic microstructure. Hydrogen is introduced in PHS during the hot press forming (HPF) process, by an atmospheric corrosion process. In this study, the hydrogen embrittlement behavior of uncoated, aluminized, and galvanized PHSs was investigated. The Al-10%Si coating promoted the absorption of diffusible hydrogen at elevated temperature during the HPF while the reacted coating layer prevented the absorbed hydrogen from out-diffusing through the reacted coating surface layer at room temperature. Therefore, the aluminized PHS showed a greater sensitivity to both the hydrogen uptake and the resultant embrittlement, as compared to the uncoated and galvanized PHSs. Use of galvanized PHS for HPF application reduces the risk of hydrogen embrittlement, since the Zn coating effectively prevents the hydrogen uptake. The greater embrittlement resistance of the galvanized PHS is possibly due to the inhibition of the hydrogen generation reaction by the surface ZnO oxide layer and the low rate of hydrogen transport through the liquid Zn phase.
This note summarizes some recent investigation results on the behavior of corroded steel bolted joints under uniaxial fatigue loading. Fatigue test specimens, were made up using S355 structural steel plates joined together with preloaded M12 bolts of class 10.9 with a geometry that corresponds to the Δσ = 112 MPa EC3 detail category. The accelerated corrosion process was accomplished using an electrolyte consisting of an aqueous 5% NaCl solution whereby the specimens were treated. In particular, during the corrosion process specimens were repeatedly immersed for 2 minutes in the electrolyte and then removed keeping them 60 minutes long in free air at 35 °C. An atmospheric corrosion in marine-industrial environment is wellrepresented through corrosion test. Fatigue loading tests and surface morphology measurement of uncorroded and corroded specimens were performed and the results were compared.
Structures exposed to aggressive environmental conditions are often subjected to time-dependent loss of coating and loss of material due to corrosion; this causes reduction in the cross-sectional properties of the members, increased surface roughness, surface irregularities and corrosion pits, and degradation of material strengths. These effects have been identified and simulated in different research studies. However, time and corrosive media dependent fatigue strength curves for materials have not been discussed in the design or assessment guidelines for structures. This paper attempts to review the corrosion degradation process and available approaches/models used to determine the fatigue strength of corroded materials and to interpolate corrosion deterioration data. High cycle fatigue and full range fatigue life formulae for fatigue strength of corroded materials are proposed. The above formulae depend on the endurance limit of corroded material, in addition to the stress-life fatigue curve parameters of the uncorroded material. The endurance limit of corroded material can either be determined by a limited number of tests in the very high-cycle fatigue region or predicted by an analytical approach. Comparison with experimentally measured corrosion fatigue behavior of several materials is provided and discussed.
Protection against metallic materials corrosion is one of the most important means to reduce both aintenance costs and environmental impact. In the last years new studies on chemical baths compositions and fluxes have been performed in order to improve processes, corrosion resistance and mechanical behavior of Zn based coatings. Chemical bath composition is often improved by the Sn addition which increases the fluidity of
the melt. Ti addition makes the coatings to change color under appropriate heat treatment. In this work a comparative microstructural analysis, in Zn-Sn and Zn-Ti coatings, is performed to evaluate intermetallic phases formation kinetics and the influence of intermetallic microstructure on coating damage under constant bending deformation.
In this paper, the corrosion effects on the fatigue performance of the friction connections are experimentally and numerically investigated. Fatigue test was conducted on the connections with four corrosion levels, and the failure mode and fracture surfaces were analyzed. Based on the finite element modeling of the connection, the crack initiation life caused by the fretting fatigue was calculated based on several multiaxial fatigue criteria, and the crack propagation life in the complex stress field was predicted using the AFGROW software. The results show that the fatigue life of the friction connections could be significantly reduced by corrosion, and the fatigue failure occurred near the minimum cross-section plane of the inner plates. It was also observed that the fatigue cracks initiated at the fretting wear scar and the corrosion pits at the hole edge for the uncorroded and corroded connections, respectively. The predictions show that the fatigue life prediction method in which the crack initiation and propagation lives are both considered can accurately predict the fatigue behavior of the uncorroded connections under different stress ranges. The fatigue life of the corroded friction connections with a mass loss ratio greater than 7.8% can be estimated by assuming an initial crack at the hole edge in the minimum cross-section plane and ignoring the crack initiation life induced by fretting damage.
Metallic pipelines carrying water and/or oil/gas are exposed to deterioration, leaks/bursts, and failures due to corrosion. A suitable corrosion protection technique can prevent corrosion of these metallic pipelines, particularly in hostile environments, and corrosive soils. It can also reduce pipe deterioration, leaks/breaks, and failure, prolong service life, and improve the transportation process. Based on prior studies, this comprehensive review is regarded as an early attempt to cover both external and internal corrosion protection techniques for metallic pipelines in depth. The external corrosion protection techniques are classified into passive, active and hybrid corrosion protection techniques. The passive techniques include coatings, linings, barriers, material design, electrical isolation, inhibitors, and multi-passive techniques. Whereas active corrosion protection techniques include sacrificial anode and impressed current cathodic protections. Active and passive techniques are frequently combined to provide a more comprehensive corrosion protection system against newly discovered corrosion causes or coating degradations. On the other hand, internal corrosion protection techniques include internal coatings/linings/barriers, corrosion allowance, inhibitors/chemical treatments, dehydration, pigging, pipe material selection and flow control. The functions, merits, demerits, limitations/shortcomings, and requirements of corrosion protection techniques, as well as the various considerations that control their use have been covered and discussed. This comprehensive review will assist researchers, practitioners, and the industrial sector in prioritizing their policies in order not only to select the appropriate external and internal corrosion protection technique but also to fill current research gaps and focus on the future directions.
High strength steel (HSS) wire ropes are widely used in civil engineering to act as hangers or bridge cables. These kinds of structural members are particularly prone to both corrosion and fatigue damage owing to typical exposition and load conditions. Within this framework, in the present paper a comprehensive state of the art review dealing with literature and normative models for fatigue checks of corroded wire ropes is presented. Most peculiar aspects related to correct fatigue demand and strength evaluation in wire ropes are discussed on the basis of over 40 research works.
In this paper, the combined effect of corrosion and fatigue on the fatigue strength of steel connection plates is thoroughly investigated through a comprehensive experimental program. A model for fatigue strength degradation as a function of corrosion rate is developed. The mechanism of fatigue strength degradation is also examined to gain a insightful understanding of fatigue strength degradation under simultaneous corrosion and fatigue environments. It is found in the paper that the simultaneous corrosion and fatigue environment can lead to higher degradation in fatigue strength of connection plates than those subjected to pre-corrosion and fatigue test afterward. It is also found that the reduction in grain size of steel plates is one of main mechanisms for the degradation in fatigue strength of the connection plate. The significance of the paper lies in developing a testing methodology to create a simultaneous corrosion and fatigue environment for connections and study its effect on fatigue strength. The knowledge of degradation mechanism of fatigue strength of steel connections under simultaneous corrosion and fatigue environment contributes to corrosion science of steel structures.
The bolts and their arrangement strongly influence stiffness, strength and ductility of T-Stub connections. Preloaded bolts are typically adopted to improve the stiffness and limit the opening of the connection under serviceability conditions. EN1993-1-8 allows using two types of high resistance preloaded bolts, namely the German HV (acronym of Hochfeste Bolzen mit Vorspannung, which is the German for High Resistance bolts for pretension and the British/French HR (acronym of High Resistance) without making any distinction. However, the tensile failure modes of these bolts are different (i.e. nut stripping for HV and shank necking for HR) and may affect the ultimate tensile response of the T-Stub connections with weak bolts (e.g. failure mode type 2 and 3). Furthermore, despite the effects of geometrical non-linearities at large deformations are not specifically addressed in current codes, the membrane action developing in the flange and the shear force and bending moment in the bolt may influence the reserve of ductility of the T-Stub that plays an important role in case of seismic and robustness scenarios. In addition, the presence of initial imperfections (e.g. the misalignment of the web as respect to the bolts and the flange bowing) can influence the non-linear behaviour of the connection. The influence of all these aspects on resistance and ductility of T-Stub connections are investigated by means of both experimental monotonic tests and parametric finite element analyses. On the basis of the obtained results, design rules are discussed with the aim to guarantee extra ductility of T-Stub connections.
Today, the industrial and scientific community is devoting increasing attention to the effect of hot dip galvanizing on the fatigue strength of structural steel details. In structures such as bridges, hot dip galvanized (HDG) steel is quite often used. Along their lifetime, such structures are repeatedly submitted to stresses of varying amplitudes, leading to fatigue usually being the design criterion. In Germany, recent experimental work on a range of HDG details was carried out, which led to the publication of a guideline recognized as relatively conservative towards HDG components in steel bridge constructions. While, also quite recently, in Norway, recent studies on the behaviour of bolted HDG joints submitted to fatigue concluded that quite similar behaviour compared to uncoated steel equivalents can be expected. The present paper re-investigates, in a uniform and transparent way, the available data for similar uncoated and HDG details. In total, the data for 8 details are presented and discussed. One tries to respond to the question if hot dip galvanizing has such a detrimental effect that, the rules of current version of EN 1993-1-9 should be amended. Finally, the authors give guidance on how the current design rules concerning HDG details should be amended. These guidelines take into account the most recent draft revision of EN 1993-1-9, under preparation by the CEN/TC 250/SC 3 technical group responsible by Eurocode 3.
Fatigue crack growth (FCG) test was done on a pre-cracked single-edge notched tensile (SENT) specimen with oligocrystalline ferritic structure. Innovative in-situ hydrogen (H)- charging by plasma inside an environmental scanning electron microscope (ESEM) was adopted to directly observe the H influence on the FCG behavior of this material. Diverse in-situ and post-mortem characterization methods including secondary electron imaging, backscatter electron imaging, electron backscatter diffraction (EBSD) and scanning probe microscopy (SPM) were used to investigate the material's behavior. It was observed that the crack growth rate was enhanced by about one magnitude when H was charged, in comparison with the reference test in vacuum (Vac). The FCG procedure was concluded as strongly associated with the plasticity evolution in the vicinity of the crack-tip. A simple model based on the restricted plasticity was proposed for the H-enhanced FCG behavior. A peculiar frequency dependency of the H-enhanced FCG behavior was observed at low loading frequencies (0.015Hz–0.15Hz): under the same in-situ H-charging condition, a lower frequency gave a slower crack growth rate and vice versa. This behavior was explained by the thermally activated dislocation motion correlated with the plasticity shielding effect during crack growth.
The effect of hydrogen (H) on the fatigue behavior is of significant importance for metallic structures. In this study, the hydrogen-enhanced fatigue crack growth rate (FCGR) tests on in-situ electrochemically H-charged ferritic Fe-3wt%Si steel with coarse grain size were conducted. Results showed strong difference between the H-charged and the non-charged conditions (reference test in laboratory air) and were in good agreement with the results from literature. With H-charging, the fracture morphology changed from transgranular (TG) type to “quasi-cleavage” (“QC”), with a different fraction depending on the loading frequency. With the help of electron channeling contrast imaging (ECCI) inside a scanning electron microscope (SEM), a relatively large area in the failed bulk specimen could be easily observed with high-resolution down to dislocation level. In this work, the dislocation sub-structure immediately under the fracture surfaces were investigated by ECCI to depict the difference in the plasticity evolution during fatigue crack growth (FCG). Based on the analysis, the H-enhanced FCG mechanisms were discussed.
Hydrogen-Affected Fatigue Crack Growth (HAFCG) in commercially pure iron has been characterized in terms of hydrogen gas pressure, loading frequency and stress intensity factor range ΔK. A higher hydrogen gas pressure decreases the critical value of ΔK triggering the HAFCG enhancement, and a lower loading frequency increases the HAFCG enhancement. Intergranular FCG in the non-accelerated regime is likely caused by the hydrogen-induced microvoid coalescence along the grain boundary, while a brittle cyclic cleavage fracture in the accelerated regime can be explained in terms of crack tip sharpening and hydrogen-enhanced decohesion process.
This new edition encompasses current design methods used for steel railway bridges in both SI and Imperial (US Customary) units. It discusses the planning of railway bridges and the appropriate types of bridges based on planning considerations. Modern steel material properties and the loads applied to steel railway bridge superstructures are followed by methods of structural analysis used for modern steel railway bridge design. It also presents the design of axial force members used in truss construction, flexural members used for beam and girder bridges, and the connections used in all bridges are outlined, as well as bridge loads and moving load analysis. It also includes information concerning the fabrication and erection of steel railway superstructures.
This paper presents an experimental research on the fatigue performance of corroded high-strength steel wires used in bridges. Three dimensional (3D) profile measurements and fatigue tests were conducted on the steel wires on six corrosion levels. It is found that the experimental pitting depth followed a normal distribution and both the location and scale parameters increased with the corrosion degree. The fatigue test results indicated that corrosion could cause a significant decrease in the fatigue life of corroded steel wires. The S-N curves were bilinear in the log-log scale and the logarithmized fatigue life decreased linearly with the corrosion degree. An empirical formula for fatigue life calculation was established considering the corrosion effect. A method based on 3D measurements and AFGROW software was proposed to predict the remaining fatigue life of corroded steel wires. The predicted fatigue lives agreed well with the test results.
This book is primarily a textbook. It is written for engineers, students and teachers, and it should also be useful for people working on various topics related to fatigue of structures and materials. The book can be used for graduate and undergraduate courses and for short courses for people already working in the industry, laboratories, or research institutes. Furthermore, the book offers various comments which can be useful to research-workers in order to consider the practical relevance of laboratory investigations and to plan future research. An important theme of the book is the understanding of what happens in the material of a structure in service if the structure is subjected to a spectrum of cyclic loads. Knowledge of the fatigue mechanism in the material and how it can be affected by a large variety of practical conditions is essential for dealing with fatigue problems. The designer of a dynamically loaded structure must “design against fatigue”. This includes not only the overall concept of the structure with related safety and economic aspects, but also questions on detail design, joints, production and material surface quality. At the same time, the designer must try to predict the fatigue performance of the structure. This requires a knowledge of the various influencing factors, also because predictions on fatigue have their limitations and shortcomings. Similar considerations arise if fatigue problems occur after a long period in service when decisions must be made on remedial actions.
This paper investigates the effect of a galvanizing coating on the fatigue strength of S355 structural steel. While in the literature some results from fatigue tests made on unnotched specimens can be found, very few results are available dealing with notched components and, at the best of authors’ knowledge, no results are available dealing with welded joints. The aim of the present paper is to partially fill this lack of knowledge. A comparison is carried out, between hot dip galvanized fillet welded cruciform joints made by S355 structural steel and not treated welded joints characterized by the same geometry, subjected to a load cycle new experimental data are summarized in the present contribution, in terms of stress range and averaged stress energy density range in a control volume of radius .
This short technical note summarizes some recent data from hot dip galvanized steel bolted connections under fatigue loading. In particular the effect of a galvanizing coating on the fatigue strength of S355 structural steel is analyzed in detail showing that the decrease of the fatigue life is very limited if compared with that of uncoated joints and the results are in good agreement with Eurocode detail category, without substantial reductions. The procedure for the preparation of the specimens is systematically described in this note providing a useful tool for engineers involved in similar practical applications. The results are compared with previous data from notched galvanized specimens weakened by a central hole and not treated specimens characterized by the same geometry.
A coating consisting of iron-zinc alloy phases, which are formed during a metallurgical reaction between the two metals, is being applied on the hot-dip galvanized steel components. The piece galvanizing, industrially carried out, is a wet or dry process. The continuous galvanization equipment is intended for bands or wires. Small parts are galvanized in devices with centrifugation.
The aim of this investigation was to elucidate the influence of galvanizing on fatigue properties. Hot rolled steels of different strength levels (yield strength 290-690 MPa) were fatigue-tested (load control R = 0) in the hot-dip galvanized condition. In addition, an electrolytically galvanized high strength cold rolled steel was included. There was no influence of hot-dip galvanizing on the fatigue properties for low and medium strength steels (yield strength 290-535 MPa). However, for the steel of the highest strength level (yield strength 690 MPa) a significant reduction in endurance limit was observed (35%). In the case of grit blasting instead of pickling as pretreatment to galvanizing, the effect was less pronounced (12% reduction). No influence of electrolytic galvanizing on the fatigue properties for the cold rolled steel was noticed. The Sandelin peak is discussed and a plausible explanation is given. The phenomenon is related to discontinuous (or eutectic) growth influenced by the absolute and relative stabilities of the ζ and δ phases. The influence of silicon follows with this approach.
We investigate the effect of a galvanizing coating on the fatigue strength of S355 structural steel. Although some results on fatigue tests of unnotched specimens are available, those on notched components are scarce. A comparison is carried out between hot-dip galvanized specimens weakened by a central hole and untreated specimens of the same geometry for two nominal load ratios R = 0 and R = −1. In total, over 60 new experimental data are summarized and analyzed in the present contribution.
The corrosion protection of steel and composite bridges in Germany and Europe is generally secured by organic coating systems with a theoretical duration of protection of up to 25 years. In the prevailing expected service life of approximately 100 years for road bridges, therefore, several maintenance cycles of the organic corrosion protection system cannot be avoided. In contrast, the predominantly statically loaded structures encountered in steel structural engineering allow for significantly longer maintenance intervals of 80 years and greater through the use of hot-dip galvanized steel components. Under the aspects of sustainability and cost-effectiveness, hot-dip galvanizing thus offers an ad-vantage as a corrosion protection system. Bridges, however, are subject to cyclic loading and require disproving material fatigue in accordance with EN 1993-1-9 (EC 3-1-9). Notwithstanding, the com-pulsory computational fatigue analysis of hot-dip galvanized steel parts cannot be obtained using the applicable design regulations because the effects of hot-dip galvanizing on the fatigue strength of steel subject to cyclic loading has not been sufficiently scientifically investigated to date, and as a consequence it is not part of the currently valid design standards.
The objective of the finished research project was to develop and provide the required basic scientific and technical expertise for the application of hot-dip galvanizing as corrosion protection for steel and composite bridges of short and medium span-widths subject to cyclic loading. In the accomplishment of this objective, it was important to consider economic and sustainability factors.
The basis for the accomplishment of this objective consisted of fatigue strength testing on hot-dip galvanized and non-galvanized specimens with construction details typical for bridge construction in accordance with EC 3-1-9. Furthermore, it was necessary to provide evidence of the corrosion pro-tection of hot-dip galvanizing spanning a service life of 100 years for the structure. This was based on exposure tests to determine the current corrosivity of road bridges under moderate climatic condi-tions. In addition, a repair technology of equivalent duration of protection was developed for e.g. assembly joint welds using thermal sprayed zinc coatings, which was tested for its performance both under simulated loading in the laboratory as well as in outdoor exposure.
In dem hier vorgestellten Forschungsprojekt wurden durch die TU Dortmund, die MPA Darmstadt und das Institut für Korrosionsschutz Dresden GmbH der wissenschaftliche und technische Nachweis eines sicheren Einsatzes der Feuerverzinkung im Stahl‐ und Verbundbrückenbau erbracht (Teil 1 s. Stahlbau, H. 1/2015). Durch Laborbelastungen und Freibewitterung konnte die Korrosionsschutzwirkung der Feuerverzinkung für bis zu 100 Jahre, d. h. über die gesamte rechnerische Lebensdauer einer Brücke hinweg, nachgewiesen werden. Durch zusätzliche Entwicklung einer Ausführungsanweisung für Montagestöße können damit die ökologischen und ökonomischen Vorteile gegenüber den aktuell eingesetzten Korrosionsschutzsystemen genutzt werden.
Hot‐dip galvanizing in bridge construction – Part 2: Using hot‐dip galvanizing as a lifetime corrosion protection for bridge constructions. In the here presented research project the scientific and technical evidence for the safe use of hot‐dip galvanizing for steel and composite bridges were provided by TU Dortmund, MPA Darmstadt and Institut für Korrosionsschutz Dresden GmbH. By laboratory tests and natural weathering the evidence of the corrosion protection of hot dip galvanizing for up to 100 years, i. e. over the entire calculated life of a bridge, could be provided. With the additional developed design guide for mounting joints the environmental and economic advantages over the currently applied corrosion protection systems can be used.
Corrosion behaviour of the high-strength galvanized steel wires under tensile stress was researched by electrochemical polarization and salt spray test (SST) using simulated acid rain as electrolyte. Electrochemical polarization and SST results showed corrosion rate rose significantly with increasing tensile stress; white grains were observed by SEM after polarization, while cellular and dendritic crystals appeared on the rust layer after SST. XRD and TG-DTA results revealed (Zn(OH)2)3 · ZnSO4 · 5H2O was the main corrosion product, and traces of Fe2(SO4)2O · 7H2O, Fe2(SO4)3, Fe2O3 · H2O were also detected. A three-stage corrosion process for the galvanized steel wires during SST was proposed.
Brittle failure of components weakened by cracks or sharp and blunt V-notches is a topic of active and continuous research. It is attractive for all researchers who face the problem of fracture of materials under different loading conditions and deals with a large number of applications in different engineering fields, not only with the mechanical one. This topic is significant in all the cases where intrinsic defects of the material or geometrical discontinuities give rise to localized stress concentration which, in brittle materials, may generate a crack leading to catastrophic failure or to a shortening of the assessed structural life. Whereas cracks are viewed as unpleasant entities in most engineering materials, U- and V-notches of different acuities are sometimes deliberately introduced in design and manufacturing of structural components.
Dealing with brittle failure of notched components and summarizing some recent experimental results reported in the literature, the main aim of the present contribution is to present a review of some local approaches applicable near stress raisers both sharp and blunt. The reviewed criteria allowed the present authors to develop a new approach based on the volume strain energy density (SED), which has been recently applied to assess the brittle failure of a large number of materials. The main features of the SED approach are outlined in the paper and its peculiarities and advantages accurately underlined. Some examples of applications are reported, as well. The present review is based on the authors’ experience over more than 15 years and the contents of their personal library. It is not a dispassionate literature survey.
The critical conditions for hydrogen embrittlement (HE) risk of high strength galvanized steel (HSGS) wires and tendons exposed to alkaline concrete pore solutions have been evaluated by means of electrochemical and mechanical testing.There is a relationship between the hydrogen embrittlement risk in HSGS and the length of hydrogen evolution process in alkaline media. The galvanized steel suffers anodic dissolution simultaneously to the hydrogen evolution which does not stop until the passivation process is completed. HSGS wires exposed to a very high alkaline media have showed HE risk with loss in mechanical properties only if long periods with hydrogen evolution process take place with a simultaneous intensive galvanized coating reduction.
This paper summarizes the results of 400 fatigue tests of high-strength bolted joints that were reported in eight domestic and six foreign studies. The following variables were investigated: type of bolt and washer, bolt pattern, bolts-to-member strength ratio, initial bolt tension, yield strength, skew, joint length, and partial connection of member elements. The analysis of the data showed that within the limits on maximum stress imposed by the American Association of State Highway and Transportation Officials (AASHTO) specifications on edge distance, bolt spacing, etc., both friction-type and bearing-type joints can be designed to Category B on the basis of the gross area stress range. The fatigue of long bolted joints with more than four bolt rows in a line of stress must be lowered from Category B to C. The stress range in members that transfer load through some, but not all, cross-sectional elements must be calculated using a reduced effective gross area.
The high-cycle fatigue behaviour of a hot-dip galvanised ferritic–pearlitic steel and of a hot-dip galvanised Ti-alloyed high-strength interstitial-free steel was investigated. The testing mode was constant displacement, fully reversed plane bending. Both test materials were tested unstrained and 10% uniaxially pre-strained. Pre-straining improves the high-cycle fatigue behaviour of both steels, probably due to strain-hardening of the matrix. Some relations that have been put forward in attempts to mathematically describe the high-cycle fatigue range of the S–N curve (by Stromeyer, Weibull, Heywood, Basquin) were compared to the experimental data. The Basquin relation was found to agree best.
This paper reviews and discusses the phenomenon of LMAC in galvanised steel and outlines important factors in the design of galvanised steel structures. It considers causative factors in LMAC and highlights the importance of good weld design and fabrication procedures in avoiding cracking. It illustrates some of the concepts via examples of cracking observed in large and small steel structures.
The corrosion fatigue behaviour of a hot-dip galvanised ferritic pearlitic steel and of a hot-dip galvanised Ti-alloyed high-strength interstitial free steel was investigated. The testing mode was constant displacement, fully reversed plane bending. Both materials were tested as received and 10% uniaxially pre-strained. The effect of pre-straining on the zinc coating was investigated using polarisation resistance measurements and the scanning reference electrode technique (SRET). It was found that pre-straining is detrimental to the corrosion fatigue behaviour of both steels, due to damage to the zinc coating, leading to increased localised corrosion and in general higher corrosion rates.
The first parametric investigation about corrosion fatigue (CF) behaviour of pre-split high-strength galvanized steel wires was conducted for perfecting the design and maintenance of modern bridge cable structures. Counting the cycle number to failure presents that lower fatigue endurance always correlates with higher stress amplitude, while decrease in load ratio and/or increase in cyclic load frequency significantly prolongs the CF life. Electron fractography indicates that the fatigue crack growth rate of the steel wires is lower in air with the presence of tyre tracks on the fracture surface, and faster in aggressive media resulting from anodic dissolution and crack opening displacement at the crack tips. Longer CF endurance of bridge cable steel wires can be expected through ideal thermo-mechanical treatment after the successive cold drawing, for a significant benefit on corrosion resistance and microstructure improvement.
Mean stress effects in finite-life fatigue are studied for a number of sets of experimental data for steels, aluminium alloys and one titanium alloy. Specifically, the agreement with these data is examined for the Goodman, Morrow, Smith–Watson–Topper and Walker equations. The Goodman relationship is found to be highly inaccurate. Reasonable accuracy is provided by the Morrow and by the Smith–Watson–Topper equations. But the Morrow method should not be used for aluminium alloys unless the true fracture strength is employed, instead of the more usual use of the stress-life intercept constant. The Walker equation with its adjustable fitting parameter γ gives superior results. For steels, γ is found to correlate with the ultimate tensile strength, and a linear relationship permits γ to be estimated for cases where non-zero mean stress data are not available. Relatively high-strength aluminium alloys have γ≈ 0.5, which corresponds with the SWT method, but higher values of γ apply for relatively low-strength aluminium alloys. For both steels and aluminium alloys, there is a trend of decreasing γ with increasing strength, indicating an increasing sensitivity to mean stress.
The paper clarifies the effect of a galvanizing coating on the fatigue strength of a ferritic steel. Depending on experimental conditions and on the microstructure of the coating, a reduction in fatigue strength is observed especially when the coating is thick. Cracks in the galvanizing coating rapidly form under cyclic loading and then propagate into the steel substrate. This completely modifies the distribution of crack lengths. Very short cracks are not observed in the steel when galvanized. It is shown that the propagation of a crack in the substrate from the coating is only possible when the crack completely crosses the coating. By assimilating the coating thickness to a crack in the steel substrate, the fatigue resistance of hot-dip galvanized steel can be predicted using the Kitagawa–Takahashi diagram.
The mechanisms behind the reduction of the fatigue strength of high-strength steel owing to hot-dip galvanizing have been studied. Three coating thicknesses were considered, ranging from 80 to 220 μm. The steel has a proof stress of 680 MPa. Fatigue loading was performed at an amplitude below the fatigue limit of the uncoated steel. The coated steels gave lives of between 5×104 and 8×104 cycles. The thickest coating gave the shortest life.Metallographic observation of material not exposed to fatigue loading showed there was a crack network in the δ- and ζ- layers of the coatings. Some initial cracks penetrated through half or more of the coating depending on the coating thickness. Short cracks were found in the steel at the interface to the coating.The crack pattern after fatigue loading followed the original pattern in the coating. Additional cracks were created in the thickest coating. A higher frequency of cracks inside the steel was observed for the steels with thicker coatings. These cracks started at cracks in the coating.Finite-element calculations for the driving forces of the original cracks showed that the material with the thinnest coating was fatigue loaded close to the threshold for crack propagation. The two materials with thicker coatings had driving forces for their original cracks that exceeded the threshold. These results were in good agreement with the lives observed experimentally.
Thesis (M.S. in Engineering)--University of Texas at Austin, 2006. Includes bibliographical references. Vita.
Corrosion Protection - Chapter 6 of Offshore Structures - 2nd Edition
- M A El-Reedy
El-Reedy MA. Corrosion Protection -Chapter 6 of Offshore Structures -2 nd
Edition. Gulf Professional Publishing 2020, Oxford, UK, 359-417.
Bolted Connections with Hot Dip Galvanized Steel Members with Punched Holes
- Valtinat
Valtinat G, Huhn H. Bolted Connections with Hot Dip Galvanized Steel Members
with Punched Holes. Connections in Steel Structures 2004;5:297-310.