Joints In Steel Structures Research Articles

Thermal cycles, structure and properties of welded joints in structural steels during welding in extreme cold conditions

The article summarizes research on the thermal cycles, structure, and properties of welded joints made from low-alloy and low-carbon steels during arc welding in sub-zero temperatures. This review aims to analyze previous research to create solid recommendations for welding steel bridge structures during winter conditions. The results of a comparison of experimental measurements of thermal cycles of welding samples with different sizes made at room and subzero ambient air temperatures (down to minus 50 °C) are considered. It is shown that in small plates with dimensions of 200 × 250 × 10 mm, due to more intense heat reflection from the edges of the specimen, the thermal cycles of welding at different temperatures do not differ significantly. In more massive samples (sized 450 × 250 × 10 mm), an increase in the cooling rate of the overheated welded joint area is observed compared to room temperature welding. The impact of hydrogen on the development of cold cracks in low-alloy steels during welding at temperatures below freezing is examined. Metallographic analysis has revealed that the structural changes that occur during the welding of various steel grades are notably different and are influenced by the steel’s chemical composition as well as the thermal cycle parameters of the welding process. Dilatometric studies indicate that variations in the levels of alloying elements within different grades significantly influence the kinetics of austenite transformation. Therefore, to identify the best welding techniques for subzero temperatures, it is essential to consider not just how heat disperses in these conditions, but also the kinetics of phase changes and their effects on the structure and properties of the products resulting from austenite decomposition.

Failure mechanisms in pre-tensioned bonded hybrid joints

ABSTRACT This study investigated the failure mode of pre-tensioned bonded hybrid joints in steel structures using Digital Image Correlation (DIC) alongside Finite Element Analysis (FEA) and compared the results with those of adhesive bonded joints of identical geometry. While all joint types initially exhibited ideal adhesive joint behaviour at low loading levels, with linear elastic response, differences emerged as loading increased. In particular, hybrid joints exhibited out-of-plane deformations near the ends of the splice plates, a feature not observed in bonded joints. Shear deformations consistently peaked at the ends of the overlap for all joint types and increased with increasing load levels. In contrast to bonded joints, hybrid joints demonstrated resilience under escalating loads, maintaining resistance due to the presence of bolts despite the increased deformations. This study contributes to the understanding of the observed failure mode: while hybrid joints initially resembled ideal bonded joints at lower loads, increasing loads caused critical cracks to initiate at the overlap ends in the adhesive layer, culminating in bonded joint failure. In conclusion, this study has elucidated the failure mode of hybrid joints, providing insights for modelling and dimensioning in steel structures.

Experimental study of self-tightening high-strength single-side bolted joints under low cyclic loading

Single-side bolts can be installed on one operating surface and are very suitable for closed cross-section connections. Based on the forming mechanism of materials, a new type of self-tightening high-strength single-side bolt, named SHSB-PRO (Progressed version), was developed herein. The SHSB-PRO was successfully applied to the assembled steel structure joints, with a range of low cyclic loading tests executed. In this test, three assembled steel structure joints were designed. Two of them were connected using SHSB-PRO, while the third was connected using traditional torsional shear high-strength bolt. Different bolt types and axial compression ratios of the steel column were examined to explore their impact on the seismic behavior of the joints. Through the low cyclic loading test, data such as hysteresis curves, skeleton curves, and strain in key parts of the joints were obtained. The mechanical properties, energy dissipation characteristics, failure mechanisms, and seismic performance of these assembled joints were elucidated. The test results indicate that the forming quality of the SHSB-PRO is stable within the joint, and a fine stress condition is maintained. The joints connected by the SHSB-PRO exhibit seismic performance comparable to those with torshear high-strength bolted connection. All joints failed due to the formation of the plastic hinge of the steel beam above the stiffener, and the joints connected by SHSB-PRO belong to the rigid joint. The influence of the axial compression ratio on the load-bearing capacity, ductility, and stiffness of the joints connected using SHSB-PRO is virtually minimal when the ratio is no more than 0.2. The finite element model was rigorously validated against the experimental results, demonstrating its accuracy and reliability in capturing the behavior of SHSB-PRO joints. The research herein lays a foundation for the design and improvement of SHSB-PRO, and promotes its wide application in civil engineering.

Influence of corrosion on ultra-low cycle fatigue performance of steel butt-welded joints with various welding methods

Preferential corrosion of welded joints in steel structures has been observed in a wide range of scenarios and should receive enough attention. The current work focuses on the corrosion and ultra-low cycle fatigue (ULCF) behavior of low-alloy steel weld joints. Firstly, 1600 h neutral salt spray (NSS) tests were conducted on welded joints made by different welding methods, and then topography scanning of corrosion pits was carried out. It was found that the welded region is more susceptible to corrosion. Dynamic polarization curves of the welded joints were measured, and the results show that the self-corrosion potential of the welded region is lower than that of the base metal (BM) region, while the corrosion current density is higher than that of the BM region. Subsequently, cyclic tests were carried out on the corroded weld joints. The results show that corrosion can cause a maximum reduction of 11.79% in yield load and 20.87% in ultimate load of the welded joints. Corrosion has slight influence on the energy dissipation capacity of welded joints, but the maximum reductions in ULCF life could reach 77.31% due to corrosion. Fractography analysis further shows that secondary cracks, map cracks, and intergranular brittle fracture, apart from more common fatigue fracture, ductile fracture, and quasi-cleavage fracture, appear on the fracture surfaces. Supplementary numerical simulation was conducted to enable a better understanding of the failure processes. In the simulation, a geometric modeling method using topography scanning data of corrosion surface was proposed. By using the proposed modeling approach, together with Chaboche cyclic plasticity constitutive model and cyclic void growth model (CVGM) for capturing fracture behavior, the predicted results show an acceptable agreement with the experimental ones.

Fatigue experiment and assessment of butt-welded joints in steel structures considering misalignment and weld geometry effects

This study investigates the fatigue behavior of butt-welded joints considering the effects of misalignments and weld geometries. Fourteen specimens were fabricated with varied assembly root gaps and axial eccentricities, and they were subjected to cyclic tensile loading with constant amplitude. Misalignments (both axial and angular) and weld geometries (including weld toe radius, flank angle, weld reinforcement height, and width) were measured using a 3D optical scanning system and subsequently used for fatigue evaluation in terms of fatigue crack locations and fatigue strength. The fatigue test results indicate a noticeable decrease in nominal stress fatigue strength as the assembled axial eccentricities increase, regardless of the assembled root gaps. However, the correlation between assembled root gaps and fatigue strength is not clear, as a larger assembled root gap corresponds to a flatter weld reinforcement on one hand and an increase in angular misalignment on the other hand. Several stress magnification factor (SMF) and stress concentration factor (SCF) formulae available in the literature are employed to characterize the combined effects of misalignment and weld geometries. The investigation results indicate that misalignments and weld geometries both play critical roles in the fatigue behavior of butt-welded joints. The combination of Remes and Varsta's SCF formula with Luo et al.'s SMF formula is the most recommended method due to its accuracy and robustness regarding the evaluation of both the fatigue crack locations and fatigue life in the investigated butt-welded joints.

Effect of Beam-Column Connection Types on the Response Modification Factors of Steel Frames

A key component of steel structural design is the careful selection of structural modeling joints in steel structures, as the behavior of the joints affects the structure's strength and displacement characteristics. According to the capacity for transferring moment, connections in the analysis of frames are categorized as rigid, semi-rigid, or pinned. Also, the response modification factor (R-factor) is an effective parameter used in the seismic design of structures. However, the influence of the beam-column connection's stiffness factor on the response modification factor did not seem to have been considered in seismic design codes. Consequently, the R-factor under static pushover and dynamic loading is being studied for moment-resisting steel frames (MRSFs) with 3-, 6-, and 12-story using three different forms of beam-column connections depending on the connections' stiffness (m). The rigidities of the connections are taken 20, 10, and 5 for rigid, stiff semi-rigid, and flexible semi-rigid connections, respectively. The MRSFs are subjected to ten records with varying frequency contents and ground motion durations. The ductility reduction factor (Rμ), the over-strength reduction factor (Ro), and the R-factor were determined. The results indicated that the beam-column connection rigidity factors affected the R0, Rμ, and R-factors. Also, the R-factors were more affected by the rigidity factors for the beam-column connections and the number of story frames.

Fracture, deformation route, and mechanical performance of welded cold-formed ultra-high strength steel S1100

This study investigates the influence of cold-forming on the weldability and fracture behavior of ultra-high strength steel S1100. The mechanical performance and fracture of such steels while simultaneously subjected to cold-forming and welding still require further research, although cold-forming and welding have crucial roles in fabricating economical structures with relatively acceptable strength-to-weight ratios. Hence, S1100, as a thermomechanically processed ultra-high strength carbon steel, was subjected to bending with different radii (representing various levels of cold-forming) and welded with gas-metal arc welding. Next, the strength, ductility, and toughness of the welded samples were evaluated using tensile tests. In addition, digital image correlation was used with the tensile tests to study the plasticity and final failure. Further, macrographs by optical microscopy and fractography by scanning electron microscopy were utilized to investigate the fracture locations and mechanisms of the welded joints. The results confirmed the reliability of the welded joints in steel structures, and the fracture of the welded material was identified as ductile, regardless of its cold-forming degree. Heat-affected zone softening, as a common drawback associated with welded ultra-high strength steel, did not adversely affect the fracture mechanism of welded S1100, even in its cold-formed state.

Damage and failure of semi-rigid steel joints during progressive collapse

Ductile metal materials during a ductile failure will suffer from micro-void damage, simulation of which can contribute to the prediction of the macro fracture of steel structure. In this paper, the Gurson-Tvergaard-Needleman (GTN) constitutive model which describes the aggregate failure of metal voids is selected as the constitutive relation to investigating the damage evolution and fracture of semi-rigid joints in steel structures during a progressive collapse. During the process, specific parameters of the GTN model of steel are confirmed based on the combined results of the test and numerical simulation. The progressive collapse of two kinds of semi-rigid joints of steel pipe-to-H shaped steel were simulated by a nonlinear finite element method. A comparison between the simulation and test results verified that the GTN constitutive model can accurately simulate the fracture failure of the steel semi-rigid joints. Besides, a simplified joint failure model based on concentrated plastic hinge theory is proposed. Considering the damage and fracture of semi-rigid joints and the collision contact among different components, the progressive collapse of the semi-rigid steel frame structure is simulated by explicit dynamic analysis based on a finite particle method. Afterwards, the dynamic response of the structural progressive collapse can be predicted more accurately.

Mechanical properties of MAG butt welded dissimilar structural steel joints with varying strength from grade S355 up to S960

AbstractMixed connections made of normal-strength and high-strength structural steels allow for optimized material usage and production effort in applications where, as a result of different mechanical effects on materials of the same type, it would otherwise be necessary to adjust the plate thickness. Reduced material consumption and smaller weld geometries can thus generate ecological and economic advantages. When welding high-strength structural steels, however, significant softening can occur in the heat-affected zone, which can influence the load-carrying behavior of the overall joint. Since there are currently no appropriate standards for butt welds made of steels with different strengths up to S960, a separate design concept is required. In this paper, the weldability and load-carrying capacity of multilayer MAG welded butt joints designed as mixed connections of a normal-strength structural steel S355 and a high-strength structural steel in the range S690 to S960 are investigated. Extensive experimental investigations are carried out, in which other influencing variables such as the filler metal used, the heat input, the plate thickness, and the weld geometry are varied in order to identify their effects on the load-carrying capacity of the welded joints. Among other things, the results form the basis for an empirically based design model for mixed connections.

Implementation of a digital image correlation system in the research of steel structure joints

Implementation of a digital image correlation system in the research of steel structure joints

Experimental investigation on a novel curved steel damper for the beam-column joints of steel structures

Researchers have developed many passive damping devices to dissipate seismic energy using steel’s yielding property. Some proposed thick curved steel plates, while others proposed complex-shaped steel dampers. For instance, some have developed Shear Yielding Panel Devices (SYPD) and Triangular-plate Added Damping and Stiffness (TADAS) dampers for moment-resisting frames. However, these devices require additional steel bracings to be fitted into the structure. The present work reports an experimental study on a new energy dissipation device. The proposed damper is made of a steel plate cut into a curved shape (diaphragm), welded to flanges, and stiffened to create sub-panels. The damper can be fitted to the beam-column joints of steel structures using a bolted connection and does not need bracings; hence, it can be easily replaced after a seismic event. Eight devices were fabricated and tested under quasi-static cyclic loading protocol as per ATC 24. The results showed that all specimens exhibited hysteresis behavior, dissipated between 10 and 20 kJ of input energy, and provided a damping ratio of up to 40 %, depending on the damper’s geometry. Thus making it an effective seismic-resistant design system for new constructions and an alternative retrofitting tool for existing structures.

Numerical study on behaviour of T‐stubs with bolts in tapped holes

AbstractBolts in tapped holes (BTH) use threads on the bolt hole wall as an anchorage instead of nuts used in standard bolt assemblies. Requirements for BTH application are given in the draft version of new Eurocode prEN 1993‐1‐8, including the definition of minimum thread engagement lengths. BTH connected T‐stubs under tension were investigated in analytical parametric study to determine the influence of thread engagement length requirements on general applicability of BTH. FE models of BTH connected T‐stubs in tension were created and validated with experimental results. Analytical and FEM parametric studies were conducted in order to clearly investigate the difference between thread engagement length requirements, with the aim of possibly alleviating the minimum thread engagement requirements and enabling better applicability of BTH in structural steel joints.

Impact of joint geometries in bonded-bolted hybrid joints for steel construction

This paper summarises findings of a study that investigated the effect of joint geometry on the load capacity of hybrid joints, which are a promising method for increasing the load capacity of joints in steel structures. The results showed that all geometries resulted in higher joint capacity for hybrid joints than for bonded joints, with an impressive increase of 43% to 142%. Furthermore, the study identified the specific effects of joint width, overlap length and distance of the bolts to the end of the overlap on joint capacity. Widening the joint led to an almost linear increase in load capacity for both hybrid and untightened bonded joints. Increasing overlap length also contributed to increasing load capacities, but not as efficiently as joint width. Despite numerical simulation and observations of fracture surfaces indicating that shortening the edge distance would increase joint capacity by applying higher compression to the overlap end, edge distance did not have a significant effect on the load capacity of hybrid joints. These findings are a significant step towards establishing a comprehensive design procedure for hybrid joints and provide important insights into their underlying principles. However, further investigation is necessary to fully understand the mechanisms responsible for the observed effects. Ultimately, developing accurate predictive models for joint strength will greatly benefit the field of structural engineering.

Dynamic Characteristics of a Novel Right-Angle Viscoelastic Damper (RVD) Using Polyurethane Damping Materials

Excessive plastic deformation may occur at the beam-column joints under seismic action and lead to connection failure, increasing the possibility of collapse of the entire frame structure. In order to improve the seismic performance of assembled steel structure joints, a right-angle viscoelastic joint damper with polyurethane as the core energy dissipation material is proposed in this paper. First, the temperature scanning tests of polyurethane materials were carried out based on the dynamic mechanical analysis method. Second, the dynamic mechanical test and numerical simulation analysis of the designed right-angle viscoelastic damper were performed to reveal the dynamic energy dissipation characteristics of the right-angle damper. Finally, the dynamic time-history damping analysis was performed on the steel frame structure equipped with RVDs. The results show that the TA value of polyurethane material reached its peak at 2.0 Hz, which is the ideal frequency for the material’s damping ability. The right-angle damper made of polyurethane material has a softening nonlinear characteristic, and the peak value of the loss factor was obtained at 2.0 Hz, which is consistent with the results of the dynamic performance of the polyurethane material. The numerical simulation results demonstrate that stress on the steel plates and viscoelastic layers is reasonable. When the excitation level did not exceed 9 mm displacement amplitude, the energy input to the damper was dissipated by polyurethane, and the steel plates never showed plastic deformation. The time-history analysis of the steel structure shows that the dampers designed in this paper have a good control effect on the interstory displacement, acceleration, and interstory shear force of the structure. The research results lay the necessary foundation for the engineering application of polyurethane materials in the field of beam-column joints vibration damping.

Effect of Filler Wire Composition on Hot-Dip Galvanizing Performance of S355JR Structural Steel Joints

Effect of Filler Wire Composition on Hot-Dip Galvanizing Performance of S355JR Structural Steel Joints

Structural features of buildings from metal structures

The article is devoted to the issue of preserving the architectural heritage of the outstanding Russian engineer V.G. Shukhov. Three objects are considered: the Moscow Radio Tower on Shabolovka, the “Shukhov Prolet” of the Sheet Rolling Shop and the Water Tower, located in the city of Vyksa, Nizhny Novgorod Region. The main design parameters of these structures and the results of their technical examination, the emergency response measures taken to ensure the safety of the Radio Tower in Moscow, and recommendations for the restoration of all three structures with the transfer of the Sheet Rolling Shop and the Water Tower to the central part of Vyksa are presented. It is planned to reconstruct the historical appearance of the buildings, as well as to improve the surrounding area. It is supposed to restore the geometric shape of the section by laser deposition of powder metal, and only if it is impossible to restore the element, its replacement is provided. To preserve the historical appearance, the joints of steel structures will be bolted, imitating rivets. In the course of excavation, archaeological research is planned, since within the boundaries of the construction site (the city of Vyksa) there may be areas of preserved cultural strata of the cultural heritage site “Estate-industrial complex, XVIII-XIX centuries”.

РЕСТАВРАЦИЯ АРХИТЕКТУРНОГО НАСЛЕДИЯ В.Г. ШУХОВА

The article is devoted to the issue of preserving the architectural heritage of the outstanding Russian engineer V.G. Shukhov. Three objects are considered: the Moscow Radio Tower on Shabolovka, the "Shukhov Span" of the Sheet-rolling Shop and the Water Tower located in Vyksa, Nizhny Novgorod region. The main technical parameters of these structures and the results of their technical inspection are presented, emergency measures taken to ensure the safety of the Radio Tower in Moscow and recommendations for the restoration of all three structures with the transfer of the Sheet Rolling Shop and the Water Tower to the central part of the city Vyksa. It is planned to recreate the historical appearance of the buildings, as well as the improvement of the adjacent territory. It is supposed to restore the geometric shape of the cross-section by laser spraying of powdered metal, and only if it is impossible to restore the element, its replacement is provided. In order to preserve the historical appearance, the joints of steel structures will be on bolts imitating rivets. Archaeological investigations are planned during the excavation, as areas of preserved cultural strata of the cultural heritage object "Manor-industrial complex, XVIII-XIX centuries" may lie within the boundaries of the construction territory (Vyksa).

Analysis of the functional state of flanged joints

This article discusses related aspects of the formation and provision of the functional quality of the load-bearing elements of frame systems. The subject of the study is the analysis of the state of steel structures with the possible manifestation of violations of the shape of structural elements in flanged joints. The formation and provision of the functional qualities of metal structures and their connections is carried out at all main stages of the life cycle. The scientific hypothesis consists in the assumption that the analysis of the parameters of the stress-strain state in metal structures, characterized by the presence of deviations from the established indicators of functional quality, contributes to an accurate assessment of the parameters of the state and service life. The conditions and circumstances characterizing the possibility of loss of functional qualities of flanged joints of steel structures are determined. A block diagram of the analysis of risks associated with manifestations of the shrinkage distortion of flanges, which reduce the operational reliability of steel structures, has been developed. It is advisable to supplement the methodological basis for the development of design solutions for steel structure units with a forecast (modeling) of the state and operational suitability of a flange connection in the presence of shrinkage distortion of flanges. The results of the analysis of possible states of loss of bearing capacity using a predictive model will contribute to the development of rational parameters of labor intensity and material consumption of manufacturing flanges of steel structures.

HEAT INPUT EFFECT OF THE FCAW PROCESS ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF STRUCTURAL STEEL JOINTS

Flux-cored wires are commonly used in structural and pipeline welding, shipbuilding, offshore constructions, and petrochemical and power generation industries. The higher heat inputs in the multi-pass welding result in shorter production time while considerably changing the properties of the welded joint. In this study, robotic flux cored arc welding with varying heat inputs (between 0.56-2.52 kJ/mm) was performed to determine the effect of heat input on weld microstructure, hardness, tensile properties, and impact toughness in the structural steel joints. Results exhibited that decrease in heat input from 2.52 to 0.56 kJ/mm changed the majority of the microstructure from polygonal ferrite to acicular ferrite. Furthermore, this increased by 56%, 37%, and 47% in yield strength, tensile strength, and hardness values, respectively, while decreasing by 30% and 15% in elongation and Charpy impact test results, respectively. Moreover, all welded joints displayed a satisfying toughness value higher than the requested value of 47 J, even at the test temperature of -50 °C. Finally, it can be concluded that the optimum results were obtained with a heat input of 1.26 kJ/mm, considering the minimum requirements of the AWS A5.20 standard and the expectations in applications.

An innovative mechanical model for structural steel joints

An innovative mechanical model for the characterisation of structural steel joints is presented in this paper. The model relies on the so-called “component method” to simulate the joints through an assembly of extensional springs and rigid elements. The proposed approach solves the inconsistencies met in the existing spring models and allows bypassing the analytical assembly procedure prescribed by the current version of Eurocode 3 for the prediction of joints’ behaviour. Key features systematically disregarded in classical spring models, i.e., the group effects and the variation of shear forces on the height of the column web panel, are incorporated in the proposed mechanical model. The latter allows predicting the behaviour of steel joints respecting the European normative provisions yet based on mechanical criteria only. Comparisons with experimental and analytical results show the model’s code compliance and prove its accuracy in characterising the actual behaviour of structural joints.