High-strength Bolts Research Articles

Experimental and parametric study on friction-type high-strength bolted connections between steel frames and cross-laminated timber infill walls

Timber-steel hybrid structural systems provide a prospective solution for utilizing timber in multi-storey and high-rise buildings. The system of steel frame with infilled cross-laminated timber (CLT) shear walls is an effective hybrid timber-steel one. In the design of this kind of hybrid system, the connections between CLT walls and steel frame beams are key issues, because they have great impacts on the distribution of lateral forces in structures. In this paper, a friction-type high-strength bolted connection (FHBC) between CLT walls and steel frame beams is proposed. To investigate the performance of the proposed FHBC, experiments were conducted on the FHBCs fabricated with three- and five-ply CLT. The mechanical behaviors of the connections were evaluated. The pretension loss in the tested FHBCs with three-layer CLT is less than 15 % within a displacement of 10 mm. Besides, enhancement of axial force in the high-strength bolt was observed in the five-layer connections during the loading procedure. Theoretical analysis was performed to provide recommendations on the initial pretension force of FHBCs. Furthermore, a solid element-based numerical model was developed and validated by the experimental results. The parametric analysis was conducted to investigate the effect of friction coefficient and initial pretension force on the mechanical behaviors of FHBC. The numerical simulation results show that the greater the initial pretension force is, the bigger the slip activation force and ultimate load-carrying capacity of the FHBC are. When the friction coefficient between CLT wall and steel beam is greater than 0.4, the ultimate load-carrying capacity does not increase much. The experimental and numerical results demonstrate that such connections can provide sufficient stiffness, strength, and ductility to transfer the shear force between the CLT shear walls and the steel frame beams.

Effect of direct-quenching and tempering on hydrogen-induced delayed fracture resistance of high-strength bolt steel

This investigation attempts to explore the potential significance of controlled forging, i.e., direct-quenching at two different finish-forging temperatures of ∼930 °C (B8H sample) and ∼780 °C (B8L sample), and tempering at 600 °C in improving the hydrogen-induced delayed fracture (HIDF) resistance of a 1300-MPa-grade high-strength bolt steel by constant load tensile testing using circumferentially notched round bar specimens and hydrogen thermal analysis. The microstructural characteristics of the tested samples were analyzed and their influences on HIDF were discussed. The results showed that the B8L sample demonstrated a considerably increased HIDF resistance expressed by critical notch delayed fracture stress of 1825 MPa and a decreased hydrogen embrittled index of as low as 21% compared with those of 1675 MPa and 27% for the B8H sample, although the former exhibited slightly higher strength and absorbed hydrogen content. Scanning electron microscopy observation of the fracture surface demonstrated that the B8L sample prevented the brittle intergranular fracture with smaller quasi-cleavage facet and decreased area fraction of the brittle crack initiation zone compared with the B8H sample. The increased resistance to HIDF of the B8L sample is primarily because of its fine microstructure with increased number of finely distributed V-rich nanoscale MC precipitates and decreased dislocation density. It is proposed that controlled forging coupled with V-microalloying is a feasible and economical way to further increase the HIDF resistance of high-strength bolt steel.

Damage analysis and mechanical performance evaluation of frame structures in recycling

Research on the recycling of space frame structures is beneficial to reduce the waste of resources and has important engineering application prospects. Repeated disassembly tests were carried out on a full size space frame structure with bolt-ball joints. The maximum number of cycles was 3. The test results showed that with the increase of the number of cycles, the damage of joints and tubes gradually increased, the phenomenon of false tightening increased, and the construction efficiency decreased. After three cycles, the damage of high-strength bolts accounted for 16.56 % and the damage of steel tubes accounted for 5 %. Due to the component damage and construction deviation, the deformation and stress of the structure after unloading could not be restored to that before loading. However, within three cycles, the overall displacement and stress of the frame structure under general roof loads were almost not affected by component damage and construction deviation. Furthermore, the distribution pattern of displacement and stress was independent of the number of cycles. The maximum mid-span displacement of the structure was about 80 mm and the maximum difference of the overall stress level was within 10 MPa. Finally, according to the test results, the relevant engineering suggestions for the recycling of space frame structures were put forward.

Experimental and numerical investigations of the shear performance of reinforced concrete deep beams strengthened with hybrid SHCC-mesh

This paper investigates the shear strengthening of simply supported deep beams using welded wire mesh and glass fiber mesh filled with strain-hardening cementitious composites (SHCC) concrete. Nine reinforced concrete (RC) deep beams were tested in this study to investigate different shear-strengthening techniques including the type of mesh (glass fiber mesh and welded steel wire mesh), number of layers (single and double), and the effects of additional anchor using high-strength bolts on the shear performance of RC deep beams. The results showed the SHCC-mesh jackets increased the ultimate load of the deep beams by up to 82 %, cracking load by up to 73 %, elastic stiffness by up to 457 %, and energy absorption by up to 380 % compared to the unstrengthen control beam. Furthermore, the welded wire mesh provided greater enhancements of strength, stiffness, and energy absorption than the glass fiber mesh. In addition, anchoring the jackets further improved the strengthening efficiency. Advanced nonlinear three-dimensional finite element models were also simulated to capture the structural responses of the RC deep beams strengthened using welded wire mesh and glass fiber mesh. It was found that the numerical models accurately predicted the behavior of the beams upon validation against the experimental results.

A novel slit damper configuration to enhance ductility and seismic behavior of concentrically braced frames

Steel slit dampers are the specific type of metallic yielding dampers used for the structural passive control. They are constructed by introducing a series of openings or slits in a steel plate to control the seismic behavior of structures. These dampers absorb energy through shear yielding, flexural yielding, or a combination of both. In this paper, a new form of steel slit damper is introduced and examined. The novel damper, called the Zipper-shaped Slit Damper (ZSD), is composed of two nested boxes connected through high-strength bolts. There are several steel strips in an external box and L-shaped profiles to prevent out-of-plane buckling, maximize flexural capacity, and ensure optimal lateral force distribution. Additionally, L-shaped profiles are welded to the ends of the steel strips. To assess the structural capacity and seismic behavior, ZSD is modeled in three dimensions using ABAQUS finite element software. The model is first validated against experimental results and then subjected to cyclic nonlinear static analysis, comprising 15 models with different width-to-thickness and height-to-width ratios of steel strips. The failure index (FI), based on equivalent plastic strain, is employed to predict the moment of failure. The results obtained from the FI were analyzed, and the analysis was limited until the moment of the first failure. On average, the novel damper demonstrated improved durability with an increase in the height-to-width ratio, resulting in enhanced ductility up to 8.75. Additionally, within each width -to-thickness ratio group, a 0.5 unit increase in this ratio corresponded to a reduction of approximately 10 % in energy dissipation efficiency. The equivalent viscous damping in the models averaged 42 %. The analysis indicated that all models exhibited stable hysteresis cycles and had high ductility and energy dissipation. Also, considering the obtained results, it can be concluded that the ZSD, due to its replaceable components, ease of construction, and easy installation, can be utilized in concentrically braced frames. Mechanical models, as well as stiffness and force relationships for design and implementation in braced frames, are presented. The findings provide valuable insights for the utilization of this innovative damper in seismic-resistant structural systems.

Research on the anti-slip performance of arc groove cable clamps

Cable clamps are crucial for connecting component and transmitting prestress in cable structures. The anti-slip performance of the cable clamp is an important factor affecting the stability and safety of the structure. This paper introduces a novel test device to evaluate the anti-slip performance of arc groove cable clamps, and anti-slip performance experiments are performed on four arc groove cable clamps and four straight groove cable clamps. Long-term high strength bolt preload loss tests are conducted to investigate the loss pattern. Furthermore, seventeen parametric finite element models are developed to analyze the effects of groove bending angle, bolt length, cable force, and pressure plate stiffness on the anti-slip performance of arc groove cable clamps. It is found that the arc groove cable clamp exhibits a higher anti-slip bearing capacity, with a friction coefficient equivalent to that of the straight groove cable clamp, both exceeding 0.2. The bolt preload stabilizes at a certain value after 96 h of screwing the bolt, while it stabilizes after 24 h of tensioning the cable. The increase in the bolt length and angel of arc groove, as well as the reduction in the stiffness of the pressure plate, have a positive impact on the anti-slip bearing capacity of the arc groove cable clamp. There is a critical cable force that results in the lowest anti-slip bearing capacity of the arc groove cable clamp. These research results provide valuable insights for the design and engineering application of arc groove cable clamps.

Discussion on ultimate resistance formulas of high-strength bolts under tensile-shear coupling loading

Bolted connections are one of the key connection configurations in steel structures. The ductile fracture prediction is one of the challenges in the structural integrity evaluating of steel structures. To guarantee the safety of steel bridge in connections, an accurate assessment of the ultimate resistance of high-strength bolts under combined tensile-shear loads is necessary. However, the impacts of various parameters on high-strength bolts under combined tensile-shear loads are not sufficiently analysed in the existing references. Hence, in this paper, the validated mesoscale critical equivalent plastic strain (MCEPS) method is used to evaluate the ultimate resistance of high-strength bolts with different bolt grades, bolt diameters, bolt types, hole clearance, and preload force when the bolts are exposed to combined tensile-shear loading. The simulation results are compared to existing design specifications. Finally, the formula modifications in the existing design standards are proposed based on statistical analysis on numerical parametric results.

Novel steel connection for modular houses in indigenous communities: An experimental study

Remote Indigenous communities across Canada are facing housing shortages and the need for major repairs, which resulted from engineering challenges that obstructed the construction phases. Prefabricated steel moment-resisting frame modular houses are currently utilized as alternatives to typical conventical houses because of their technical advantages, such as better-quality control, lightweight structures, and ease of transportation to remote and rural regions. To explore the potential use of hollow structural sections (HSS) in panelized steel modular structures, this study presents a novel steel-bolted connection for connecting HSS beams to HSS columns using high-strength long bolts, indicating that the connections can be easily installed without requiring skilled workers and heavy machinery. Six specimens were fabricated and tested under monotonic load with a Digital Image correlation (DIC) camera to capture full-field 3D displacement and deformation until failure accurately. The impact of different geometric parameters such as bolt arrangement, extended plate thickness, number of bolts, and the existence of stiffener on the mechanical performance of the joint, stiffness, inelastic rotation, ductility, and failure modes were analyzed. Bolt arrangement with an aspect ratio of 1:1 was found to increase the connection capacity, initial stiffness, and ductility by 7%, 216%, and 26%, respectively. The yielding and rotation of the extended plate were eliminated using a stiffener. Increasing the number of bolts triggered the connection's ability to gain more capacity at earlier stages and reduced joint rotation by 60%.

Multi-scale experimental study on the failure mechanism of high-strength bolts under highly mineralized environment

High-strength bolts have become indispensable support materials in geotechnical engineering, but the incidence of safety accidents caused by bolt fractures under complex geological conditions is increasing. To address this challenge, this study focuses on a typical roadway in the Xinjulong coal mine, employing a combination of mechanical performance testing, microscopic and macroscopic analyses to investigate the failure mechanism of bolt breakage. The research indicates that the cracks in the failed bolts underground exhibit subcritical patterns, with the presence of oxides and Cl elements, and multiple intergranular fractures internally, consistent with the characteristics of stress corrosion failure. Additionally, inherent defects in the bolts are also a primary cause of failure. For instance, for type A bolts, the levels of P and S elements significantly exceed the normative requirements, forming inclusions, while the low content of elements like Si and V leads to reduced plasticity, toughness, and corrosion resistance. Furthermore, the excessive pitch in type A bolts leads to stress concentration and cracking under complex loads. The study concludes that the synergistic effect of stress corrosion cracking and inherent flaws in bolts are the main causes of failure. Therefore, it is recommended to enhance the reliability and safety of bolt support by optimizing the bolt shape and developing anti-corrosion bolts, thereby achieving long-term stability in underground engineering.

Numerical investigation of the behavior of combination connections with pretensioned high-strength bolts and longitudinal fillet welds

Numerical analysis is conducted to investigate the behavior of double shear combination connections made with pretensioned high-strength bolts and longitudinal fillet welds. The finite element (FE) models were validated using the results of an experimental investigation and utilized to develop a better understanding of the influence of critical input parameters on the connection behavior. Slip-dependent surface frictional and weld ductile fracture models were incorporated into the numerical models to simulate the nonlinear behavior of the connections. The numerical simulations confirm that at low slip displacements, the force carried by the combination connection can be estimated as the summation of the friction resistance introduced by the pretensioned bolts and the shear force carried by the fillet welds. The results also indicate that the behavior and capacity of the combination connection are not sensitive with respect to the weld location compared to the center of gravity of the bolts as long as no eccentricity is introduced within the force transfer mechanism. The paper also investigates the stress distribution within the connection plates and studies the effect of fillet weld size on the behavior of combination connections.

Behavior of high-strength U-shaped bolt shear connector in prefabricated composite beams

This paper presents a novel high-strength U-shaped bolt (HUB) shear connector, which can enhance the integrity, disassembly ease, construction quality, and efficiency of prefabricated steel–concrete composite beams. Seventeen push-out tests were conducted to investigate the effect of the bolt diameter, reserved aperture ratio of concrete slab, bolt width–diameter ratio, bolt length–diameter ratio, and concrete slab thickness on the shear performance of the HUB shear connector. Specimens with a short length–diameter ratio (h/d ≤ 3) exhibit damage characterized by bolt pull-out and bolt bending, while those with a long length–diameter ratio (h/d ≥ 4) experienced bolt shear damage. Subsequently, a finite element model was developed for the push-out tests, enabling a comprehensive study of the shear transfer mechanism, failure mechanism, and stress distribution of the HUB shear connector. Finally, the shear resistance models from different codes were verified. The total slip and simplified load–slip models were proposed.

Tensile behavior of novel column-to-column connection for modular steel construction using high-strength bolts

As an important aspect of the city upgrade plan, installing the elevators for existing multi-story residential buildings means a lot to the residents of the higher floors, especially for old people. To minimize the site disruption and overcome the space limitation of installation, the modular elevator shafts have been widely adopted. The external wall decoration panels are normally pre-installed on the elevator shaft frame elements in the workshop, which makes it difficult for the connection between upper and lower segments using the high-strength bolts due to very limited space for applying the pre-tension. A novel column-to-column connection is presented in this study, consisting of an end plate, web opening of column web and strengthening plate at each of the column end. The tensile behavior of the proposed connection is first investigated through an experiment. Subsequently, a detailed finite element model is built and verified using the test results, with which a parametric study is conducted with the main parameters considered. Finally, a simple analytical solution for predicting the design load of the proposed connection is developed employing the yield line theory. Comparisons with the finite element results indicate the high accuracy of the proposed solution. The presented connection is believed to be a good solution for the on-site connection between H-columns of highly assembled modular structures, not limited to the elevator shafts.

Shear-bearing capacity prediction of concrete-infilled double steel corrugated-plate shear walls

The concrete-infilled double steel corrugated-plate shear wall (CDSCW), consisting of two corrugated plates, infilled concrete, and two boundary elements, is a highly efficient force-resistant structural component under axial compression, in-plane bending, and shear loading. Previous research has primarily focused on the structural performance of CDSCWs under axial compression and bending loads. However, there is still a lack of a sufficiently accurate design method for predicting the shear-carrying capacity of CDSCWs. This paper presents numerical investigations into the shear buckling behavior of corrugated plates and proposes the shear strength design method of CDSCWs. Firstly, the shear elastic bilateral buckling behavior of corrugated plates subjected to lateral constraints of high-strength bolts is explored, considering influences of the bolt arrangement, the bolt spacing, and the dimensions of the plates. The formulas involving various buckling modes are established as a foundation for the further elastoplastic buckling capacity prediction. Then, by applying the normalized slenderness ratio, this study suggests the shear-carrying capacity design of the corrugated plates considering the bolt constraints and unilateral concrete constraint on the plates. Moreover, the shear-carrying mechanism of the CDSCWs is revealed: when CDSCWs experiences shear failure, the corrugated plates are primarily subjected to the shear load, with the boundary elements acting as constraints on the corrugated plates. Finally, a design method is proposed for the CDSCWs’ shear-carrying capacity prediction, which shows good accuracy and offers foundations for the stability design of corrugated plates under shear loads.

Prefabricated bolted PEC beam-to-CFST column joints: Development and its seismic behavior

This paper developed a novel bolted connection of prefabricated partially encased composite (PEC) beam to concrete-filled steel tubular (CFST) column by end-plates or π-connectors, and two joints with varying design details were tested subjected to cyclic loading. The seismic performance of the developed connections was investigated by experimental and finite element (FE) analysis. It was observed that both the two type connections exhibited concrete crushing within the PEC beam, accompanied by localized buckling and eventual fracture of the flanges in the main steel component of the beam. At the same time, other components were essentially in the elastic phase, such as end-plates, π-connectors, high-strength bolts, and column steel tubes. The bolted end-plate connections demonstrated excellent hysteretic performance, exhibiting high ductility factors. The stiffness, ductility, and energy dissipation capacity of the bolted π-connector connections were significantly diminished due to the influence of relative slippage between the π-connectors and the beams, in stark contrast to the bolted end-plate connection. According to Eurocode 3, the suggested connection configurations exhibited semi-rigid behavior and full-strength characteristics for non-sway frames.

Local buckling of the bottom flange in steel-concrete composite beams with trapezoidal corrugated webs subjected to end restraint at high temperatures

Steel-concrete composite beams with trapezoidal corrugated webs (SCBCW) are prone to rapid failure at high temperatures due to local instability of the bottom flange. The failure mechanism of SCBCW, which is an integral part of the holistic structure and subject to axial and rotational restraints from adjacent members at elevated temperatures, differs from conventionally simply supported steel-concrete composite beams with straight webs. To investigate the evolution of local buckling in the compressed flange of SCBCW under high temperature conditions, a composite beam model with frame restraints was developed using ABAQUS finite element software. In this model, the composite beam is connected to restraint frame columns through high-strength bolts. The changes in axial stress, bending moment, and deflection of the compressed flange of SCBCW were analyzed as temperature increased. Results indicate that at elevated temperatures, additional bending moments occur in the flange plane due to axial restraints, section temperature gradients, section negative bending moments and accordion effect caused by corrugated web on compressed bottom flange of SCBCW. This leads to a gradual increase in axial compressive stress before local buckling occurs followed by a decrease due to internal force redistribution upon onset of buckling. Studies show that initial buckling of bottom flange occurs on one side of flat section of web where axial compressive stress is relatively high while restraint effect on web is low; Subsequent local buckling of the beam then appears on opposite side adjacent flat section of web after initial buckle occure on one side. After local buckling appears on both sides of web tension bands appear on both sides where bottom flange experiences localized bucking. The setting of longitudinal stiffeners (LS) can effectively improve the local stability of the bottom flange of the composite beam, while the setting of transverse stiffeners (TS) has no significant impact.

Seismic performance of an assembled monolithic concrete column

A prefabricated concrete column-to-column structure connected by high-strength bolts is proposed. To explore the seismic performance and failure form of the structure, the finite element analysis software is used to simulate the low-cycle repeated load test. The hysteretic curve and skeleton curve of the structure are obtained, and the stiffness degradation law, ductility and energy dissipation capacity of the structure are quantitatively analyzed to evaluate the seismic performance of the structure. The results show that the ductility coefficient of the structure is basically between 2.19 and 4.97, and the ductility coefficient of most specimens is greater than 3.0, indicating that the structure has good ductility and deformation capacity. The equivalent viscous damping coefficients of the specimens are in the range of 0.21–0.29, indicating that the structure has good energy dissipation capacity. In a certain range, increasing the thickness of the end plate has no significant impact on the energy consumption capacity of the structure. The compressive strength of the concrete in the core area is greatly improved under the constraint of the end plate bolts, and end plate bolt connection can well realize the transmission of force and give full play to the performance of materials.

Constitutive Model and Mechanical Properties of Grade 8.8 and 10.9 High-Strength Bolts at Elevated Temperatures

Constitutive Model and Mechanical Properties of Grade 8.8 and 10.9 High-Strength Bolts at Elevated Temperatures

Hybrid FRP-concrete-steel prestressed double-skin wind turbine towers: Concept, design considerations and research needs

The past decade has seen rapid development of offshore wind energy around the world. Furthermore, to improve the efficiency of power generation, wind turbine development has been trending towards increasingly large and tall turbines. These developments call for innovations in the form of wind turbine towers to address the challenges faced by existing tower forms (e.g., steel tubular towers and prestressed concrete towers) in structural adequacy, construction efficiency and/or maintenance. This paper presents a new form of hybrid wind turbine towers which possesses many important advantages over the existing tower forms and are particularly suitable for large offshore wind turbines. The new hybrid towers, termed herein hybrid FRP-concrete-steel prestressed double-skin wind turbine towers or PDSWTs, are prefabricated in segments and then assembled on site. The PDSWT segments are a variation of hybrid FRP-concrete-steel double-skin tubular members (DSTMs), and they consist of an outer confining tube made of fibre-reinforced polymer (FRP), a thin steel inner tube with welded shear studs, prestressed concrete between the two tubes, and flanges welded at the ends of the steel tube. The onsite assembly of the tower involves mainly connecting the steel flanges of two adjacent segments using high-strength bolts, and installing prestressed tendons through the whole tower. In this paper, the rationale behind the development of PDSWTs is first explained, followed by a discussion of the design considerations and future research needs to facilitate the practical applications of the new tower form.

Experimental and numerical study on extended endplate beam-column joints after high temperature to resist progressive collapse

This paper presents experimental and numerical investigations on the collapse-resisting behavior of extended endplate beam-column joints after high temperatures. The failure patterns and structural responses of extended endplate (EP) joints after high temperature to resist progressive collapse were first described, and then the effects of fire temperature and temperature duration on their collapse resistance mechanisms were also analyzed in detail. The test results demonstrate that all specimens withdrew from work owing to the serious deformation of endplate bolt holes or the brittle fracture of high-strength bolts, resulting in the catenary mechanisms of EP joints not being adequately developed. Compared with previous studies, it is shown that the fire temperature exerts the most significant effects on the carrying capacities and deformability of EP joints, and the collapse resistance of corresponding assemblies is most sensitive to the fire temperature. However, the temperature durations have an insignificant influence on the development of flexural mechanism resistance, especially for those after 600 °C and 800 °C. Moreover, the corresponding refined FE models in consideration of the damage and fracture of ductile metals have been established to reproduce the structural response of specimens after high temperature. To improve the post-fire collapse-resisting performance of assemblies, both the lateral plate reinforcement and welding reinforcement methods were proposed and compared with the assistance of validated FE models. From a practical viewpoint, the reinforcement with lateral plates is determined as a superior technique for post-fire EP joints against progressive collapse.

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.