Steel Bolts Research Articles

Load transfer distribution in bolted-sealed joints

ABSTRACT Rubber-like materials such as sealant with recent developments in formulation are widely used in various structural components, especially in aerospace industry with many applications such as the sealing of bolted joints on aircraft. The objective of this paper is to assess the load transfer distribution in bolted-sealed joints through an approach coupling both experimental and numerical tests. Quasi-static and relaxation tests under uniaxial and pure shear loading were carried out to determine the parameters of phenomenological hyperelastic laws and of the generalized Maxwell model for the sealant PR 1782 C2. The fastener is an alloy steel bolt with a protruding head when the substrates are made from aluminum 2024-T3. Experimental and numerical quasi-static tests were then performed on double-lap bonded and bolted-sealed joints under in-plane loading. The numerical tests are done using 2D and 3D Finite Element (FE) models; they involve the visco-hyperelastic behavior previously assessed for the sealant. Accounting for visco-hyperelasticity makes it possible to better estimate the load transfer between bolt and sealant layer. Typically, the bolt load transfer rate is derived from numerical output for different sealant thicknesses. In the considered geometrical joint configuration, the sealant load contribution is between 7% and 13% according to the sealant thickness. Methodology and results provide a solid basis for the fatigue strength prediction of bolted-sealed joints.

Seismic behavior of a novel liftable connection for modular steel buildings: Experimental and numerical studies

Modular steel buildings (MSBs) have achieved considerable popularity in multi-to-high rise constructions due to the favorable mechanical characteristic, eco-friendliness, cost-effectiveness, and enhanced construction efficiency. As the critical part of MSBs, the inter-module connection has an important influence on determining the seismic performance of MSBs. This study presented an experimental-numerical investigation on an innovative fully prefabricated liftable connection (FPLC) for MSBs. To study the seismic performance of the FPLC, quasi-static tests were conducted on four full-scale specimens. The seismic behavior of the specimens, including failure mode, hysteretic response, strength and stiffness degradation, deformation characteristic, etc. was evaluated and compared in detail. The effect of the section of the twin-beams, the dog-bone weakening of the beam and the connecting method between the corner fitting and twin-beams on the seismic behavior of the FPLC was revealed. Moreover, the feasibility for seismic application of the FPLC was evaluated according to Chinese code GB 50,011–2010 and Eurocode 3 Part 1–8. The results indicated that the proposed FPLC met the limit of elastic and elastic-plastic inter-story drift ratios required by GB 50,011–2010. According to Eurocode 3 Part 1–8, the FPLC with welded beams should be classified as “semi-rigid” connections, while the FPLC, whose beams were connected to the column walls by the steel angles and bolts, was classified as a “pinned” connection. Then, a refined finite element model (FEM) was developed and verified by the test results. Furthermore, the verified FEM was utilized to analyze the distribution of the equivalent plastic strain, the stress variation path, and the yielding area of the twin-beams to further reveal the energy dissipation and damage mechanism of the FPLC. Finally, a simplified FEM was established and the comparison with the test results proved its reliability and efficiency. The present study will contribute to provide a comprehensive understanding on seismic performance and design of the inter-module connection for MSBs.

Analysis of the Behaviour of Composite Connections in Multi-Storey Buildings Under Earthquake Loading

In the past years, number of beams and slabs in steel structures that are executed as composite steel – concrete elements has significantly increased. In moment-resisting frames with composite steel – concrete slabs, slab reinforcement in tensile zone needs to be considered in design of composite steel – concrete beam – to – column connections with steel plates and bolts in tensile zone. However, the number of reinforcement bars that should be taken into account in connection design significantly depends on the effective width of the concrete slab. Moreover, directions for calculation of the effective width of the concrete slab are still not unambiguous as they can be calculated either according to recommendations from Eurocode 4 or Eurocode 8. In this paper, composite connections are briefly explained and main differences between composite steel – concrete beam – to – column connections and corresponding steel connections are summarized. Furthermore, behaviour of a composite steel – concrete beam – to – column connection under bending moment and shear force induced by earthquake loading is investigated using finite element analysis in software package Abaqus. Finally, a parametric study is carried out in order to examine the suitability of two code recommendations for determination of the effective width of concrete slab in case of seismic loading.

Influence of the temperature changes on stresses in carbon composite fastening bolts

High joint strength of composite structures can be achieved by using mechanical fasteners. The materials used for rivets and bolts have lower coefficients of thermal expansion than composites in the direction perpendicular to the reinforcement fibers. It is suspected, therefore, that temperature changes can cause stress changes in mechanical fasteners. The purpose of this study was to experimentally determine and analytically substantiate the values of stress changes resulting from a change in temperature in the range from -20 to 60°C in M8 steel bolts fastening carbon composite. The value of stress changes was estimated to be around 100 MPa, which can consequently lead to joint unsealing or plastic deformation of the mechanical fastener.

Constitutive model of austenitic high-strength A4L-80 bolts at elevated temperatures

In recent years, the use of austenitic bolts in building structures increased rapidly. It is important to conduct the fire-resistant design of austenitic bolts because their mechanical properties may deteriorate faster than normal high-strength steel bolts in a fire. Therefore, the mechanical properties of the austenitic bolts at elevated temperatures should be clarified to provide a basis for structural fire design. In this paper, an experimental study was conducted to investigate the mechanical properties of A4L-80 stainless steel bolts at elevated temperatures ranging from 20 to 900 °C. Stress-strain curves and mechanical property index were obtained by the tensile tests. The test results were compared with other types of austenitic bolts and base materials at elevated temperatures, and a constitutive model of A4L-80 stainless steel bolts was proposed. It was seen that the proposed reduction factors can effectively predict the mechanical property of A4L-80 at elevated temperatures; the constitutive model was consistent with stress-strain curves obtained from tests.

Study on the analytical model of bending deformation for spliced glass beams with stainless steel bolts

To deal with the problems of high cost in super long glass manufacturing, which restricts their applications and development in glass structures, spliced glass beams (SGB) with stainless steel bolts connections was developed. The bending deformation of the SGB with stainless steel bolts have not been elucidated because it is difficult to achieve full beam equal stiffness in the splicing part. In view of this, the conjugate beam method was utilized to calculate the bending deformation of the SGB with stainless steel bolts. The bending deformation of the SGB with stainless steel bolts was investigated by the bending performance test, while the location of abrupt stiffness change and the actual correction coefficient were determined. It is verified by finite element analysis, on the basis of which the influence law of the height-to-span ratio and the height-to-thickness ratio of glass and stainless steel plate on the ultimate load and maximum deflection of SGB with stainless steel bolts were studied. The results confirmed that SGB composed of as few stainless steel bolts as possible can fully utilize the bending capacity of glass. This study provides a simplified calculation method for the engineering design of SGB, and opens up an idea for the design of glass structures.

Numerical and experimental study of the conical connection of the blade of a rotary machine

The paper presents an experimental and numerical study of the tapered socket of the aluminum blade root of the mine main ventilation fan, which is based on the tests of a simplified full-scale model with a discarded airfoil and its subsequent finite element analysis. The calculation model takes into account elastoplastic properties of materials and non-linear contacts with friction. The proposed joint consists of an aluminum tapered blade root, two steel retainers with similar tapered surfaces, and two steel bolts that join the retainers around the root. Pre-tightening the bolts allows fixing the blade in an unloaded state in the socket and prevents its unwanted turns. Such a tightening is taken into account in the finite element analysis by means of determining, in compliance with special rules, the axial force of the pretension of the bolts. With the help of a hydraulic press acting on the lower surface of the airfoil root, the effect of the centrifugal load on the conical joint from the side of the blade airfoil is simulated. Nonlinear static analysis of the elastoplastic behavior of the structure allows determining the destructive loads that cause the bolts to break with the subsequent disconnection of the fasteners and the blade to fly out of the seat. The graphs of the equivalent von Mises stresses indicate that the maximum stresses are reached in the working part of the bolts, which fully corresponds to the nature of the destruction of the structure upon reaching the maximum equivalent load on it. The experimental study confirms the correctness of the determination of contact stresses at the tapered socket location. Correspondence of the results of the static analysis with the results of the full-scale experiment makes it possible to draw a conclusion about the correctness of the conducted finite element modelling. This allows using the developed formulation of the problem to determine the strength of rotor structures with conical connections of blades without performing preliminary experimental studies. In addition, the developed technique can be extended to a larger range of conical and cylindrical joints due to the simplicity of the approach and the versatility of the formulation of the nonlinear finite-element problem which models structures with preloaded or tensioned elements.

Study on the elastic stiffness calculation method of single-bolted steel-bamboo scrimber-steel shear connections

Bolted steel-bamboo scrimber-steel (SBSS) connections are commonly employed in composite bamboo structures, but their equivalent stiffness in the elastic phase is difficult to determine. This study develops a novel theoretical formula for estimating the equivalent stiffness in the elastic phase of single-bolted SBSS shear connections considering various failure modes. Specifically, the method focuses on calculating the contact stiffness between the bolt and the pre-drilled hole wall, as well as the shear load applied to the bolt end by the steel plate. The method uses the double-shear yield mode, which is included by European Yield Modes (EYM), and the beam on elastic foundation theory (BEFT), and considers the bamboo scrimber embedment stiffness, bolt diameter and steel plate strength class. The method is tested by conducting experiments on single-bolted SBSS connections with varying load and fiber direction (LFD) angles, bolt diameters, steel plate thicknesses and strength grades. The results show that the connection stiffness increases with bolt diameter and steel plate strength grade, decreases with LFD angle, and is not affected by steel plate thickness. The parameter μ, which is important in the theoretical equations, is also calibrated based on the experimental data. The proposed method is validated by comparing it with existing test results of single-bolted SBSS connections. This paper provides a simple and reliable model for predicting the equivalent stiffness in the elastic phase of bolted SBSS connections in bamboo scrimber structures and offers useful insights for their design.

Seismic behavior of a novel slotted steel plate shear wall under monotonic, cyclic, and time history analysis

Steel plate shear walls (SPSWs) are lateral load-resistant systems used as energy dissipation members in new or existing structures due to their stable hysteretic behavior. However, structures equipped with conventional SPSWs may have a higher initial stiffness, which causes them to be subjected to too much force during moderate earthquakes. In the present study, a novel slotted SPSW is developed to minimize the lateral forces of traditional SPSWs. The slotted SPSW consists of horizontal boundary elements (HBEs), vertical boundary elements (VBEs), and two layers of incline-slotted infill plates (ISIPs) connected by high-strength steel bolts. The proposed system's seismic behavior and damaged mode were compared with those of conventional SPSW using monotonic and cyclic analysis. The research results show that the slotted SPSW exhibits stable hysteretic behavior with a significant energy dissipation capacity. Furthermore, the slotted SPSW was applied to a three-story frame structure. Nonlinear time history analysis was conducted under far-field and near-field ground motion records to determine how a slotted SPSW system affects structure response. According to numerical results, the base force of the structure equipped with a slotted SPSW system was minimized to 37.0% and 49.6% under near-field and far-field earthquakes, respectively.

Development of a Cr-Ni-Mo alloyed stress corrosion-resistant anchor bolt steel

PurposeThe purpose of this paper is to develop new types of anchor bolt materials by adding corrosion-resistant elements for alloying and microstructure regulation.Design/methodology/approachThree new anchor bolt materials were designed around the 1Ni system. The stress corrosion cracking resistance of the new materials was characterized by microstructure observation, electrochemical testing and slow strain rate tensile testing.FindingsThe strength of the new anchor bolt materials has been improved, and the stress corrosion sensitivity has been reduced. The addition of Nb makes the material exhibit excellent stress corrosion resistance under –1,200 mV conditions, but the expected results were not achieved when Nb and Sb were coupled.Originality/valueThe new anchor bolt materials designed around 1Ni have excellent stress corrosion resistance, which is the development direction of future materials. Nb allows the material to retain its ability to extend in hydrogen-evolution environments.

Simulation and Experimental Validation of Bimetallic Corrosion Between Galvanized Bolt and Mild Steel Plate: Effect of the Bolt Configuration

Simulation and Experimental Validation of Bimetallic Corrosion Between Galvanized Bolt and Mild Steel Plate: Effect of the Bolt Configuration

Evolution of corrosion degradation in galvanised steel bolts exposed to a tropical marine environment

The time-dependent degradation of galvanised steel bolts subjected to marine atmospheric exposure for a maximum period of 2 years in the Wenchang marine environment of Hainan province, South China, was investigated. The results showed that the zinc coating used as a protective surface finish deteriorated quickly due to the harsh environmental conditions. The deterioration of the zinc coating resulted in premature corrosion of the underlying steel substrate as early as 6 months. The main Zn corrosion products found at the initial exposure time were simonkollite (Zn5(OH)8Cl2·H2O), hydrozincite (Zn5(OH)6(CO3)2), and zincite (ZnO). At subsequent exposure times, major steel corrosion products such as lepidocrocite (γ-FeOOH), akaganeite (β-FeOOH), goethite (α-FeOOH), magnetite (Fe3O4), and maghemite (γ-Fe2O3) were detected. Fe3O4/γ-Fe2O3 was consistently found in the rust formed at both the exposed and crevice thread regions between 6 and 24 months of exposure. Based on the geometry of the bolt fastener, the corrosion rate and phase composition distribution varied between the two regions. Differences in oxygen exposure levels, corrosion kinetics, and electrochemical stability of the corrosion products were primary factors in these distinctive corrosion behaviours.

On the failure and replacement of weathered rock climbing bolts

In several major outdoor rock climbing areas in the United States, it has become standard practice to remove plated steel bolts used as fixed anchors and replace them with stainless steel equivalents. To examine the need and efficacy of this practice, test results are reported for the failure strengths of plated steel bolts collected from a variety of climbing areas in Colorado, Wyoming, and California that had been exposed to full environmental conditions for periods varying between 16 and 40 years. The bolts were extracted from their original positions and tested in two fixtures designed specifically for this research corresponding to simple shear and bolt/nut thread strength that both closely simulated possible types of loading that could exist in typical usage. Strength distribution curves are provided for a number of bolts, varying in size and type. In addition, a special study was completed using a simplified numerical model of a failed bolt that resulted in a fatality to analyze the stresses and better understand the possible failure mechanism. The results of the experimental testing and the benefits of the replacement strategy are contrasted with well-documented cases of the loosening of the newer stainless steel bolts. This replacement practice needs more investigation and most likely significant revision.

Failure mode and capacity prediction for bolted T-stub connections using ensemble learning

The present study utilizes machine learning (ML) algorithms, namely decision trees, and ensemble learning methods including bagging, random forests, gradient boosting, and extreme gradient boosting to identify the failure mode and predict the corresponding capacity of preloaded bolted T-stub steel connections subjected to tension. A nonlinear finite element model (FEM) was first developed and validated against experimental results from literature. Subsequently, a matrix of 3447 FEMs, covering a wide range of design parameters, were generated to train and test the ML models. In addition, to evaluate the significance of each input parameter in predicting the connections' capacity, different embedded feature selection techniques were employed. Furthermore, different interpretability methods were utilized to uncover the interrelationships between the input features and the modeled outputs to further interpret the developed Blackbox models. The results highlight the effectiveness of ML techniques in predicting the failure modes and corresponding capacity of bolted T-stub connections, supporting their potential as robust and rapid design tools which ensure adequate designs for new connections or effective assessments for existing ones.

Performance indices and fragility assessment of steel frame structure with bolted low-yield-point steel connection components

A resilient steel frame structure equipped with replaceable ductile and energy-dissipative connection components was developed in this study. Connective components, such as splice plates and T-stubs are made of low-yield-point steels (LYPs), which have superior ductility and energy dissipation capacity. The plastic hinge can be separated from the column surface by local weakening, thus concentrating local damage within low-yield-point steel connection components (LYP-Cs) to effectively enhance ductility of the structure. Five-story and ten-story bolted steel frame structures with four configuration parameters were designed to investigate the seismic performance and damage development of steel frame structures with LYP-Cs (SF-LYP-Cs). Corresponding numerical models were established. Welded steel frame structures with traditional reduced beam sections (SF-RBS) were also established for comparison. Pushover analyses were conducted to explore the effect of structural fuses and to obtain multi-stage performance indices of the resilient steel frame structure based on energy dissipation proportion (EDP) and damage behavior. Incremental dynamic analysis was performed to verify proposed performance indices, and seismic performance of SF-LYP-Cs was evaluated via fragility analysis. The results showed that LYP-Cs were not only effective structural fuses but also effectively delayed the damage development in the primary members, thus reducing the failure probability of the structures. The multi-stage performance indices were conductive to describe the multiple lines of resistance and effects of structural fuses. A larger weakening degree and smaller beam height mitigated plastic damage development in primary members. When LYP-Cs dominate the system’s energy dissipation, the section sizes of columns and the number of structural stories exert only slight influence on the structural performance indices.

Seismic behaviour of precast concrete beam-column connections with bolted end plates

This paper presents the seismic behaviour of a dry beam-column connection with bolted end plates for precast concrete structures. Experimental tests were carried out on one cast-in-situ connection and three precast concrete connections with bolted end plates to study the behaviour under reversed cyclic loading. The load resistance, failure mode, ductility and energy dissipation capacity were determined from experimental results. Comparisons were made among different connections to show the influence of end plates and stiffeners on the connection behaviour. Test results showed that precast concrete connections with bolted end plates mainly dissipated energy through bending of the end plate and deformation of steel bolts. The final failure of connection resulted from the yielding of the end plate or crushing of concrete in the compression zone of beams, depending on the thickness of the end plate and the presence of stiffeners. The connection with bolted end plates could achieve good ductility and energy dissipation. Moreover, failure of columns and the joint core was prevented through the use of end plates. An analytical method was also proposed to evaluate the moment-rotation relationship of connections. The contributions of joint core, steel bolts and the end plate to rotational stiffness and moment resistance were quantified in the analytical method. Comparisons with test results showed that the analytical method can estimate the moment-rotation curve of connections with bolted end plates with good accuracy when failure of connection was dominated by steel bolts or the end plate. Design recommendations were also proposed for connections with bolted end plates.

New design approaches for tension, shear and interaction resistance of carbon steel bolts

More economical and statistically verified design approaches for carbon steel bolts are presented based on an extensive literature review and own systematical experimental investigations into the tension, shear and interaction resistance of carbon steel bolts conducted at the Institute for Metal and Lightweight Structures of the University of Duisburg-Essen, Germany. Herein, reliability analyses according to EN 1990, Annex D were carried out and confirmed that an increase of the reduction factor to k2 = 1.0 for the tension resistance Ft,Rd is in principle possible. Regarding the shear resistance of carbon steel bolts, simplified but more economical shear coefficients a independent of the position of the shear plane are proposed. Finally, newly design equations for the interaction resistance of carbon steel bolts are proposed, which are in line with the new interaction formulations developed by Stranghöner/Abraham and implemented in prEN 1993–1-4 and abZ/abG Z-30.3-6 for stainless steel bolts. The new interaction concept provides a more economical design compared to EN 1993–1-8/prEN 1993–1-8 and serves to harmonise the European design rules between carbon and stainless steel.

Numerical Study on Seismic Behavior of Demountable Joints Consisting of Reinforced Concrete Columns and Steel Beams

In this study, three new types of demountable connections, consisting of reinforced concrete columns and steel beams, are proposed, and their seismic performance is investigated through the use of cyclic loading tests. The test results reveal that these three demountable RCS joints show good seismic performance, in which the ductility coefficients of specimens RCS-1 and RCS-2 are improved by 69% and 109%, respectively, compared with the reference group of RCS-0 specimens. Various parameters, such as the beam flange thickness, bolt strength, and connecting steel strength, were analyzed using the finite element software ABAQUS 2021 to determine the effect of these parameters on the seismic performance and behavior of the connections. The results also show that the three demountable RCS joints are very sensitive to the variation in beam flange steel thickness, while the connector steel strength and bolt type have very little effect on the joint load-carrying capacity. In addition, different current theoretical approaches for calculating the shear bearing capacity in the panel zone of joints are discussed.

Seismic performance of precast lightweight aggregate concrete shear walls with supplementary V-ties

This study examined the flexural behavior of a precast lightweight aggregate concrete shear wall (PLCSW). To minimize crosstie arrangement congestion in the boundary elements and improve ductility, the conventional reinforcing crosstie was replaced with the supplementary V-tie developed by Yang et al. Additionally, a bolting technique, which combines steel plates, bolts, and nuts, was applied to the PLCSW wall-to-base connection. The behavior of these specimens was compared with the flexural behavior of conventional precast concrete shear walls (PCSW) connected via the spliced sleeve technique. Eight PCSW specimens with different crossties (supplementary V-ties or conventional reinforcing crossties) were prepared and wall-to-base connection techniques (bolting or spliced sleeve connections) applied. All specimens were tested under constant axial load and cyclic lateral loads. The ductility performance of PCSW was verified through a comparative analysis of the displacement ductility ratio and work damage index between the PCSW with supplementary V-ties and those with conventional reinforcing crossties. The ductility performance of PCSW utilizing supplementary V-ties and the bolting technique exhibited superior ductile performance resulting in a high work damage index, which was 1.22 times higher than that of the PCSW with conventional reinforcing crossties. Meanwhile, even though the shear wall specimens connected via the spliced sleeve technique were produced with normal-weight aggregate concrete, their work damage indices were slightly lower than those of the specimens utilizing conventional reinforcing crossties and the bolting technique. Consequently, the PCSWs with the spliced sleeve did not satisfy the seismic connection performance requirements specified in NEHRP, whereas the precast sand-lightweight aggregate concrete shear walls with supplementary V-ties utilizing the bolting technique satisfied the requirements. Therefore, the ductility and seismic connection performances of PCSWs with a complex detail arrangement of the boundary element can be effectively improved by using a supplementary V-tie and applying bolting techniques.

Research on mechanical property of glued timber truss connected by steel plates and bolts

In order to deeply understand the mechanical performance of glued-laminated timber trusses connected by steel-plates and bolts, two groups of truss specimens were designed and fabricated by changing the connection forms of the nodes, while maintaining the height and span of the trusses unchanged. Each group of truss specimens was subjected to the mid-span load. At the same time, finite element numerical analysis was conducted on the tested trusses. Based on the agreement between the experimental and numerical simulation results, the influence of the parameters of thickness-to-diameter ratio and height-to-span ratio on the mechanical performance of these trusses was explored. The research results show that both types of node connections in the glued-laminated timber trusses have good bearing capacity. The main failure modes are the splitting of the diagonal web members at the mid-span node and the crushing failure of the bolt holes. The HJ-C type truss, which has the upper and lower chord members connected, exhibits better ductility, greater stiffness, and better structural synergy in load-bearing capacity. As the thickness-to-diameter ratio increases, the form of the bolts at the truss failure gradually changes from being straight to yielding. The optimal thickness-to-diameter ratio is 8.3. As the height-to-span ratio decreases, the initial stiffness and ultimate load-bearing capacity of the truss show a decreasing trend. The truss exhibits better mechanical performance when the height-to-span ratio is 1/4.