Steel Orthotropic Bridge Decks (OBDs) are widely used in long-span and movable bridges. Fatigue resistance analysis plays an important role in the design or assessment of OBDs. One possible fatigue failure is the crack initiating from the weld root of stiffener-to-deck plate connections at crossbeams. A full-scale experimental investigation in this study using a 20 mm thick deck plate with a dimension of 9.4 m × 5.1 m, including three crossbeams, represents the modern designed OBDs. The experiments show an arrest of crack propagation with a final crack depth of approximately 75% of the deck plate thickness. On the contrary, through thickness cracks develop in deck plates of 10 or 12 mm. Hot spot stress based fatigue detail categories (DC) using various failure criteria derived from the tests. Analysis with the effective notch stress shows that the DC has low sensitivity to the amount of weld penetration. The results of analyses with the eXtended Finite Element Method (XFEM), employed to analyse the fatigue crack propagation path and crack arrest, are in line with the experimental study.

@en

Steel Orthotropic Bridge Decks (OBDs) are widely used in the superstructures of movable and long-span bridges. There is a high concentration of stress at many welded connections, which are governing the fatigue performance of OBDs. The fatigue behaviour of the lower end of weld in crossbeam-to-stiffener connection with cut-outs is studied from multiple experimental results obtained from a 48m2 full-scale specimen, as well as finite element simulations. The fatigue resistance of the detail is recommended based on 8 experiments reported in the current study and experiments in the literature using the hot spot stress method. The influence of the load location on the hot spot stress is analysed. The effective notch stress method is used to evaluate the fatigue resistance with different weld profiles.@en

Fatigue cracks in the stiffener-to-deck plate connections of orthotropic bridge decks, initiating from the weld toe or root and propagating into the stiffener or weld throat, are experimentally and numerically studied. A statistical analysis of the structural stress is carried out using the experimental data. Automatic welded specimens show a significantly higher fatigue resistance than manual welded ones for both details of the study. Including results in the literature, the characteristic fatigue resistances appear larger than the values in current standards and range between 100 and 160 MPa. A proposal for the fatigue resistance values is given for design purposes. The effective notch stress, averaged strain energy density factor, and fracture mechanics methods are employed to study the sensitivity of the weld toe and root cracks for different (geometrical) variations, such as the lack of weld penetration. Among them, the fracture mechanics method agrees best with the experimental data. With the increase of weld penetration ratios from 75% to 100%, the fracture mechanics predicted fatigue resistances remain approximately equal for the weld toe cracks and increase for the weld root cracks.

@en

This study derives the fatigue resistance of welded details in orthotropic decks using structural stress (hot-spot stress where possible) based on tests described in literature and tests by the authors. The data are supported with linear elastic fracture mechanics simulations. Details covered are the rib to deck weld, the crossbeam to deck weld and the deck butt weld. High fatigue resistances are found, caused by favourable loading modes (bending and compression) and reduced driving force with the growth of cracks. The technical specification TS 1993-1-901, part of the new generation of Eurocodes, is based on the results of this study.

@en

Pultruded FRP composite material was increasingly used in the applications of civil infrastructures, especially for bridge decks. Thus, the long-term life of these materials in hostile environments is critical. In this paper, experimental studies have been undertaken to characterise the moisture diffusion of pultruded FRP composite materials and adhesives. Gravimetric experiments were carried out for the rectangular FRP composite specimens, which were exposed to the vapour environmental condition and also immersed in water. Moisture uptake curves as a function of time were obtained. Correspondingly, based on the moisture diffusion theory, the diffusion coefficients of FRP composite material parallel to the pultrusion direction were identified. All the FRP specimens reached the moisture saturation level within two days. Comparing with the moisture diffusion process in different aging conditions, the conclusion can be drawn that the rates of moisture uptake are more sensitive to temperature and the moisture saturation levels of FRP material are only dominated by relative humidity and immersed water. For the gravimetric experiments of adhesive specimens，after 37 day environmental ageing, only polyurethane adhesive material reached the moisture equilibrium as 2.667% of the initial self-weight within 6 days. This value is much higher than that of FRP material in the same ageing condition of 40℃, 96% RH. But the moisture diffusion process into adhesives is quite slower.@en

The orthotropic steel decks (OSDs) are widely used in bridge engineering to support traffic loads. A possible crack, initiating from the weld toe of rib-to-deck welded joint and growing into the deck plate, is studied using linear elastic fracture mechanics. A detailed FE model is created and the results are compared with the fatigue tests published. Good agreement is found between beach marks from experiments and calculated crack fronts in FE. An engineering approach with the crack shape simplified as a semi-ellipse is applied. Geometric correction factors for a hand calculation method is proposed based on the parametric analysis. Using the proposed correction factors, Monte Carlo simulation is carried out with failure criteria defined with respect of the crack depth reaching “50%” of the deck thickness, “75%” of the deck thickness, and the failure criterion “2A FAD” according to BS7910. Predicted results using the failure criterion “75%” show good agreement with experimental data, for 5%, 50%, and 95% survival probabilities. Effects of initial crack shapes and sizes are discussed using the improved hand calculation model. Lower fatigue resistance is found when the initial crack is shallow or large. In addition to the standard weld geometry in which the weld profile is represented by a straight line, concave and convex arc shape weld profiles are studied. Fatigue resistance is improved in the case with assumption of concave arc weld profile. The difference of fatigue resistance between the cases with a straight line and convex arc weld profiles is small.

@en

The orthotropic steel decks are one of the most widely used bridge decks, especially in moveable and long span bridges. Numerous cracks have been detected in existing bridges, mainly in the welded connections. Fatigue performance of the bridge decks governs the design. The crack at the rib-to-deck joint is one of the most representative types. Strict requirements of the configuration of this joint are given in design codes resulting in classification categories based on experimental findings. Fatigue life of the crack initiation and changes of the stress conditions are usually experimentally investigated. However, prediction of the crack propagation and the effect of the cracks on the local stress fields are not possible to be fully understood based on experiments only. In this paper, finite element models are refined around the crack tip using software programs Abaqus and FRANC3D to study the crack propagation of rib-to-deck joint between crossbeams. The results is compared with beach marking tests in literature. Good agreement is found between predicted results and test data for both the crack shapes and loading cycles. The largest SIF range is predicted in the middle of the developed crack. It is then moved to the position 0.19 (relative distance, normalized by the width of the specimen) away from the crack priori to the fracture. During propagation period, structural integrity is affected by the crack and stress redistribution phenomenon is observed.@en

SIROCO investigated the slip-resistant behaviour of carbon and stainless steel preloaded connections as well as the preloading behaviour of stainless steel bolting assemblies in principle. The slip factor test procedure according to Annex G of EN 1090-2 was investigated regarding the influence of the test speed, preload level, tightening method, criteria for the slip load and load level for extended creep tests, different bolting assemblies and surface conditions (grit blasted, hot-dip galvanized, alkali/ethyl zinc silicate coating, thermally sprayed with aluminium/zinc and combinations). Improvements regarding the slip factor test procedure have been formulated which have already partly been implemented in the revision of EN 1090-2. Enhanced slip factors allow more economic slip-resistant connections. The use of stainless steel bolting assemblies in preloaded bolted slip-resistant connections joining stainless steel plates was studied through investigations into the creep/relaxation behaviour with regard to potential preload losses, the tightening and slip resistance behaviour for austenitic, duplex, lean duplex and super duplex stainless steels. Preload losses due to the viscoplastic deformation behaviour in preloaded stainless steel bolting assemblies lie in the same range as those for carbon steel. Stainless steel bolting assemblies are in principle preloadable and galling can be avoided using suitable lubricants and tightening methods. Slip factors for stainless steel slip-resistant connections show high values for grit blasted surfaces whereas even 1D and shot blasted surfaces demonstrated slip factors for practical use. Recommendations for design and execution of slip-resistant connections and amendments to EN 1993 1-4, EN 1993-1-8 and EN 1090-2 are formulated.@en

To investigate the mechanical degradation of the shear properties of glass fiber-reinforced polymer (GFRP) laminates in bridge decks under hygrothermal aging effects, short-beam shear tests were performed following the ASTM test standard (ASTM D790-10A). Based on the coupled hygro-mechanical finite element (FE) analysis method, an inverse parameter identification approach based on short-beam shear tests was developed and then employed to determine the environment-dependent interlaminar shear modulus of GFRP laminates. Subsequently, the shear strength and modulus of dry (0% M_t/M∞), moisture unsaturated (30% M_t/M∞ and 50% M_t/M∞), and moisture saturated (100% M_t/M∞) specimens at test temperatures of both 20 °C and 40 °C were compared. One cycle of the moisture absorption-desorption process was also investigated to address how the moisture-induced residual damage degrades the shear properties of GFRP laminates. The results revealed that the shear strength and modulus of moisture-saturated GFRP laminates decreased significantly, and the elevated testing temperature (40 °C) aggravated moisture-induced mechanical degradation. Moreover, an unrecoverable loss of shear properties for the GFRP laminates enduring one cycle of the moisture absorption-desorption process was evident.

@en

Modern steel manufacturing techniques make it possible to produce steel with the nominal yield strength up to 1300 MPa for structural purposes. However, the application of very high strength steels is still limited in the civil engineering structures due to lack of knowledge about the effects of the manufacturing process and experimental results regarding the structural behaviour of the material. Moreover, in a fatigue loaded very high strength steel structure absolute and relative stress variations will be higher compared to stresses in structures made of lower steel grades. Accordingly, the fatigue issue will be one of the most important design criteria for very high strength steel structures. In this current study, V-shape welded specimens were manufactured from S690 and S890 rolled steels and cast steels with similar yield strengths. Fatigue cracks were created in the weld toe of the specimen under a fluctuated loading and subsequently the fatigue damaged specimens were repaired by the removal of the cracks with subsequent welding. The fatigue strength curves of repaired specimens are compared with the detail categories of EN 1993-1-9 [8] and the fatigue strength curves of the test results in the as-welded condition from literature. The fatigue strength of the fatigue damaged connections was completely recovered by the established repair procedure.@en

The orthotropic steel decks (OSDs) are one of the most widely used bridge components, especially in moveable and long span bridges. Numerous cracks have been detected in this type of deck in existing bridges, mainly in the welded joints. The fatigue performance of the bridge deck dominates its design. Among them, the crack at the rib-to-deck joint is one of the most representative types. At the crossbeam conjunction, high stress concentration makes the joint more sensitive to fatigue loading. In this paper, finite element models are built using software program Abaqus integrated with FRANC3D. The calculated stress at uncracked stage is validated with measured data obtained from laboratory tests. Afterwards, cracks are inserted at the weld root and the stress intensity factor ranges in mode I (ΔK _I ) are calculated. Parametric analysis with various cracks is carried out. General correction factors are calculated from the finite element calcualtion with the power fit values.

@en

Full-scale fatigue tests were performed on two retrofitted orthotropic bridge decks (OBDs). The retrofitting systems consist of adding a second steel plate on the top of the existing deck. The aim is to reduce the stresses at the fatigue-sensitive details and therefore extend the fatigue life of the OBD by stiffening the existing deck plate. Two retrofitting systems were studied. The bonded system consists of bonding a second steel plate to the existing deck by vacuum infusing a thin adhesive layer (2 mm) between the two steel plates. The sandwich system consists of bonding the second steel plate through a thick polyurethane core (15 mm). The aim of the study was to assess the fatigue performance of both retrofittings. No fatigue damage was detected in the retrofitting layers during fatigue tests after three million cycles of wheel load. The stresses close to the deck-plate-to-stiffener welds decreased by at least 55% when using the bonded steel plates system and 45% when using the sandwich steel plates system. Both systems proved to have sufficient fatigue life to withstand traffic wheel loads running on orthotropic bridge decks and help extend the fatigue life of the existing OBD.

@en

Fatigue crack formation is an inevitable issue for welded steel structures subjected to cyclic loading. Accordingly, repair of the fatigue crack in welded steel structures is unavoidable to prolong fatigue life. However, there is limited knowledge available about the procedure to be adopted for the repair and the life extension to be expected after the repair. The current paper is focused on the effects of the repaired an artificial crack in the base material of S690 and S890 high strength rolled steels on the fatigue strength of the material. An artificial crack was created in the middle of the plate test specimens by spark machining and subsequently, the crack was repaired by using the FCAW (flux-cored arc welding) process. The repaired specimens were tested in a four point bending test rig with a constant amplitude loading for creating a uniform bending moment at the weld region such that the weld cap to be exposed to tensile stresses. The test results show that most of the fatigue cracks initiated at the start-stop points of the weld cap and the fatigue crack initiation life of the specimens occupy approximately 45% of the total fatigue life. The statistical analysis of the test results revealed that the characteristic fatigue strength of the repaired specimens is very close to the detail category 160 of EN 1993-1-9 [5].@en

The RFCS project SIROCO (2014–17) included research on the further development and optimization of double shear connections with injection bolts to achieve slip- and creep-resistant bolted connections considering various influencing parameters. The type of resin, the curing condition of the resin, the geometrical and mechanical characteristics of the connection and the type of loading were studied. Results showed, for example, that of the five epoxy resins investigated, only RenGel SW404 + HY2404 (Araldite) fulfils the requirements given in Eurocode 3. A bearing stress of 175 MPa is safely allowable in the long-term without exceeding imposed deformation limits.

@en

Purpose – This study aims to reveal more information and understanding on performance and failure mechanisms of high strength steel endplate connections after fire. Design/methodology/approach – An experimental and numerical study on seven endplate connections after cooling down from fire temperature of 550°C has been carried out and reported herein. Moreover, the provisions of European design standard for steel structures, Eurocode 3, were validated with test results of high strength steel endplate connections. Findings – In endplate connections, a proper design using a thinner high strength steel endplate can achieve the same failure mode, similar residual load bearing capacity and comparable or even higher rotation capacity after cooling down from fire. It is found that high strength steel endplate connection can regain more than 90 per cent of its original load bearing capacity after cooling down from fire temperature of 550°C. Originality/value – The post-fire performance of high strength steel endplate connection has been reported. The accuracy of Eurocode 3 for endplate connections is validated against test results. Keywords Numerical study, Experimental study, High strength steel, After fire, Endplate connection

@en

The FRP-steel girder composite bridge system is increasingly used in new constructions of bridges as well as rehabilitation of old bridges. However, the understanding of composite action between FRP decks and steel girders is limited and needs to be systematically investigated. In this paper, depending on the experimental investigations of FRP to steel girder system, the Finite Element (FE) models on experiments were developed and analyzed. Comparison between experiments and FE results indicated that the FE models were much stiffer for in-plane shear stiffness of the FRP deck panel. To modify the FE models, rotational spring elements were added between webs and flanges of FRP decks, to simulate the semirigid connections. Numerical analyses were also conducted on four-point bending experiments of FRP-steel composite girders. Good agreement between experimental results and FE analysis was achieved by comparing the load-deflection curves at midspan and contribution of composite action from FRP decks. With the validated FE models, the parametric studies were conducted on adhesively bonded connection between FRP decks and steel girders, which indicated that the loading transfer capacity of adhesive connection was not simply dependent on the shear modulus or thickness of adhesive layer but dominated by the in-plane shear stiffness K.

@en

Influence of moisture absorption/desorption on the flexural properties of Glass-fibre-reinforced polymer (GFRP) laminates was experimentally investigated under hot/wet aging environments. To characterize mechanical degradation, three-point bending tests were performed following the ASTM test standard (ASTM D790-10A). The flexural properties of dry (0% M_t/M_∞), moisture unsaturated (30% M_t/M_∞ and 50% M_t/M_∞) and moisture saturated (100% M_t/M_∞) specimens at both 20 and 40 °C test temperatures were compared. One cycle of moisture absorption-desorption process was considered in this study to investigate the mechanical degradation scale and the permanent damage of GFRP laminates induced by moisture diffusion. Experimental results confirm that the combination of moisture and temperature effects sincerely deteriorates the flexural properties of GFRP laminates, on both strength and stiffness. Furthermore, the reducing percentage of flexural strength is found much larger than that of E-modulus. Unrecoverable losses of E-modulus (15.0%) and flexural strength (16.4%) for the GFRP laminates experiencing one cycle of moisture absorption/desorption process are evident at the test temperature of 40 °C, but not for the case of 20 °C test temperature. Moreover, a coupled hygro-mechanical Finite Element (FE) model was developed to characterize the mechanical behaviors of GFRP laminates at different moisture absorption/desorption stages, and the modeling method was subsequently validated with flexural test results.

@en

Purpose-This paper aims to investigate and assess a perspective of combining high-strength-steel endplate with mild-steel beam and column in endplate connections. Design/methodology/approach-First, experimental tests on high strength steel endplate connections were conducted at fre temperature 550°C and at an ambient temperature for reference. Findings-The moment-rotation characteristic, rotation capacity and failure mode of highstrength-steel endplate connections in fre and at an ambient temperature were obtained through tests and compared with those of mild-steel endplate connections. Further, the provisions of Eurocode 3 were validated with test results. Moreover, the numerical study was carried out via ABAQUS and verifed against the experimental results. Originality/value-It is found that a thinner high-strength-steel endplate can enhance the connection's rotation capacity both at an ambient temperature and in fre (which guarantees the safety of an entire structure) and simultaneously achieve almost the same moment resistance with a mild steel endplate connection.

@en