Bolt Failure Research Articles

A study on the failure mechanisms of layered soft rock tunnels considering the random distribution of rock mass mechanical parameters and the characteristics of anchor bolt failure

A study on the failure mechanisms of layered soft rock tunnels considering the random distribution of rock mass mechanical parameters and the characteristics of anchor bolt failure

Impact of Carbon Fiber‐Reinforced Polymer Sheets and Bolt Diameter on the Seismic Performance Enhancement of Steel Beam‐Column Joints

ABSTRACTBeam‐column joints are pivotal for ensuring the resilience of prefabricated steel structures under various loading conditions. Following the major earthquakes of the 1990s, semi‐rigid bolted connections emerged as a promising alternative to traditional welded connections. This study investigates a fully prefabricated Intermediate Beam‐Column Joint (IBCJ) with extended endplates, renowned for its excellent seismic resistance. While significant progress has been made in existing research, there is still a need to thoroughly examine the tension capacity of IBCJs concerning bolt size and explore the potential of Carbon Fiber‐Reinforced Polymer (CFRP) sheets to enhance joint performance under seismic loading. Using the finite element method, this research evaluates the performance of IBCJ under both monotonic and cyclic loading conditions. After validation with experimental data, the study examines various bolt diameters to assess their tension capacity, ductility ratio, secant stiffness, and energy dissipation capacity. The findings indicate that larger bolts exhibit higher ultimate capacities and reduced deformation at failure. Additionally, the study investigates the optimal placement and configuration of CFRP sheets, identifying the backside of the endplates as the most effective location. The application of CFRP significantly enhances bolt tension capacity by up to 1.2 to 1.3 times, demonstrating its potential in reducing bolt failure risk and improving structural reliability under seismic conditions. The superior performance of CFRP‐strengthened bolts can play a crucial role in the design and retrofitting of prefabricated steel structures, potentially contributing to the improvement of existing standards and practices of seismic enhancement of IBCJ.

Python-based numerical study on bolted joints between Fe-SMA and steel plates for structural reinforcements

In order to rehabilitate the performance of deteriorated steel structures, the active prestressed reinforcement employing new intelligent material, Iron-based shape memory alloy (Fe-SMA), has received extensive attentions. To reveal the mechanical properties of bolted joints between Fe-SMA and steel plates, a parametric method to establish finite element model via secondary development of ABAQUS based on Python scripts was proposed. It greatly reduces modelling costs and improves modeling efficiency. Besides, the proposed numerical models were verified against the experimental results by failure mode, final deformation, load-displacement characteristics, ultimate load-bearing capacity and initial stiffness. It is demonstrated that the numerical simulation results are in good agreement with the experimental results. What is more, a parametric study on thickness and geometry of steel plates, as well as the end distance, edge distance and thickness of Fe-SMA plate was conducted to verify the applicability of current leading specifications for steel structures. It is evident from the results that the thickness of Fe-SMA should be controlled to prevent failure of parent steel structures. Furthermore, similar to steel plates, the thickness of Fe-SMA plate can be considered linear and the failure of bolt can be avoided, as described in Chinese code GB 50017–2017 and Eurocode 3 Part 1–8. However, the minimum allowable edge distance in Chinese code GB 50017–2017 and the ultimate load-bearing capacity calculated by Eurocode 3 Part 1–8 is conservative for bolted joints between Fe-SMA and steel plates. Hence, it is urgent to formulate design specifications for this kind of bolted joints for the scientific and economical application of Fe-SMA in structural active reinforcements.

Disaster mechanism of large-diameter shield tunnel segments under multi-source load coupling: A case study

The deflection squeezing of the shield shell and the eccentric jack thrust significantly impact the segment dislocation and damage. Based on summarizing the derivative relationship between engineering factors and disasters, this study established a 3D numerical calculation model under the multi-source load coupling. Then, this study explored the displacement and dislocation distribution of segments, as well as their derivative relationship with bolt failure. Furthermore, this study analyzed the spatial distribution and evolution characteristics of segment damage. Further revealing the disaster mechanism and proposing the engineering treatment measures. The research results indicate that as the deflection angle increases, the vertical relative compression deformation of the segment that is detaching from the shield tail (segment-DFST) becomes more significant. The plastic strain of the internal bolts inside the two segments in direct contact with the shield shell is mainly related to the radial and longitudinal dislocation. The increase in the deflection angle will lead to a more significant increase in the adjacent dislocation on both sides and the internal dislocation. The plastic strain of the internal bolts of the segment that is completely in the shield shell (segment-CSS) is more influenced by joint opening and longitudinal dislocation under the lower eccentric compression (LEC) state. The plastic strain of the internal bolts in segment-DFST is more influenced by radial dislocation and joint opening under the LEC state. The tension damage of the segments mainly occurs on both sides of the circumferential joint and the lower part of the segment-CSS. The compression damage of the segments is mainly distributed at the top and bottom of the segment-CSS. The eccentric distribution of jack thrust has the most significant impact on the block damage of the lower part of the segment-CSS. With the increase of the deflection angle, the compression damage and distribution range of the blocks at the bottom of the segment-DFST increase sharply. The compression damage and distribution range of the segment-CSS gradually spread from the upper and lower parts to the middle of the segment. The increase in deflection angle will promote the influence of the thrust in LEC state on the compression damage of the lower block of the segment-CSS, and on the tension damage of the upper block of the segment- DFST.

Experimental study on low-cycle fatigue performance of high-strength bolted shear connections

In strong earthquakes, low-cycle fatigue fractures may occur in the bolted connections of steel braced frames. Ensuring a high low-cycle fatigue life for high-strength bolted connections is of paramount significance in enhancing the overall safety and collapse resistance of steel structures. Despite substantial research on plate fatigue failure within bolted connections, there remains a research gap regarding low-cycle fatigue failure of high-strength bolts in these connections. This study aims to address the aforementioned shortcomings by conducting 34 sets of low-cycle fatigue tests on high-strength bolted connections. The test specimens all experienced low-cycle shear fatigue fracture at the threaded or unthreaded portion of the bolt shank as the dominant failure mode. Residual deformations were observed in the holes of connection plates. Based on the test data, ultimate shear capacity of a single shear connection is around 0.61Fy (tensile yield bearing capacity of bolt) when the shear force passes through the unthreaded portion and drops to 0.54Fy for the shear force at the thread. The untreated Q355 (minimum yield strength of 355 MPa) steel surface has an average anti-slip coefficient of around 0.37, while milling reduces it to approximately 0.30. The influence patterns of loading amplitude, bolt material, minimum plate thickness, bolt diameter, shear force position and connection type on low-cycle fatigue life are given by range analysis. Among them, variance analysis shows that loading amplitude and bolt material are the primary influencing factors. The correlation coefficient between loading amplitude and low-cycle fatigue life is −0.92, indicating a strong negative correlation. The degradation amount and rate of anti-slip capacity and shear capacity of bolted connections are also investigated. To propose reliable life prediction method, three models were used to establish the relationship between dimensionless shear deformation and low-cycle fatigue life of 10.9-grade high-strength bolted connections. It is not appropriate to use the fatigue categories defined in current standards to predict the low-cycle shear fatigue life of high-strength bolted connections.

Experimental Study on the Water Absorption, Compaction Effect, and Pull-Out Bearing Characteristics of Water-Absorbing and Compaction Anchoring Bolts

In response to a series of engineering disasters encountered during the excavation and support construction of loess tunnels, considering the issues of water enrichment in surrounding rock induced by excavation disturbance and system bolt failure, drawing on the concepts of lime pile composite foundation and composite bearing arch, and based on the principle of the New Austrian Tunneling Method (NATM) that fully mobilizes and leverages the self-supporting capacity of surrounding rock, this study comprehensively considers the wetting and stress adjustment processes of the surrounding rock after excavation disturbance in loess tunnels. By adopting the technical principle of “water absorption and densification of shallow surrounding rock, suspension and anchoring of deep surrounding rock, and composite arch bearing”, a new type of water-absorbing, densifying, and anchoring bolt was developed that can reduce the water content of surrounding rock while enhancing its resistance. To further investigate the water absorption, densification effect, and pull-out bearing characteristics of this new bolt, laboratory model tests were conducted, examining the temperature, pore water pressure, densification stress of the soil around the bolt, as well as the physical properties of the soil in the consolidation zone. The test results indicate that a cylindrical heat source forms around the water-absorbing, densifying, and anchoring bolt, significantly inducing the thermal consolidation of the surrounding soil. The variations in temperature, pore water pressure, and densification stress of the soil around the bolt truly reflect the qualitative patterns of hydro-thermal–mechanical changes during the water absorption, curing, and exothermic reaction processes. The water absorption and densification segment of the bolt effectively enhances the density of the soil in the water absorption, densification, and consolidation zone, improving soil strength parameters. Compared to traditional mortar-bonded bolts, the water-absorbing, densifying, and anchoring bolt exhibits a greater pull-out bearing capacity. The research findings provide important guidance for the theoretical design and engineering application of this new type of bolt.

Structural Damage Model of Steel Structure Connections with Initial Defects: A Review

As the application of steel structures in construction continues to grow, research into their seismic performance is becoming increasingly important. This paper focuses on steel structure connections, specifically those between components with varying profiles such as H-profiles, box-profiles, and L-profiles. Additionally, it encompasses three core areas: seismic performance (bearing capacity, ductility, stiffness), initial defects (initial cracks, residual stresses, manufacturing imperfections), and damage models (weld fractures, bolt failures, plate buckling). In addition, this paper employs experimental testing and finite element, with a focus on conducting parametric analyses for the connections. Based on the primary findings, the presence of initial defects such as cracks, residual stresses, and manufacturing imperfections can lead to premature failure, concentrating damage near welds and exacerbating stress concentrations. This adversely affects factors like fatigue strength, fracture toughness, and buckling strength, ultimately reducing the seismic performance of the connections. Moreover, factors like bolt over-tensioning, geometric deviations in plate components, and corrosion can further impact bearing capacity, fatigue performance, and ductility. Crucially, these initial defects not only compromise the seismic resistance of structures but also increase the risk of structural failure. However, majority of existing research has focused on monotonic and cyclic loading studies, with limited exploration of connections under seismic conditions. Acknowledging this gap, this paper outlines a future research agenda aimed at refining the design of steel structure connections. This initiative seeks to mitigate potential adverse consequences stemming from formidable seismic events, thereby enhancing the overall resilience of these crucial connections.

An Effective Barrier Coating Technology Against Premature Bolt Failures in Underground Mines

AbstractSignificant safety and economic consequences accompany the premature failure of bolts, posing sustainability challenges for mining operations. Previous studies have indicated that hydrogen-induced stress corrosion cracking (HISCC), primarily influenced by microbial activities termed microbiologically influenced stress corrosion cracking (MISCC), stands as a major contributor to the premature failure of bolts in underground mines. Presently, an effective mechanism to mitigate these premature failures is lacking. In this study, multiple commercially available coatings undergo testing to assess their susceptibility and suitability in preventing HISCC and MISCC. Additionally, a purpose-developed coating is examined. The results reveal that the tested commercially available coatings either fail to prevent these types of corrosion or are unsuitable for the intricate conditions within underground mines. The laboratory results show the coating has a significant anti-acidic corrosion and anti-MISCC performance. Conversely, the coating formulated in this study successfully averts both MISCC and HISCC, proving its applicability within the complex geological environments prevalent in mines. This breakthrough offers a promising solution to mitigate premature bolt failures in complex underground geological environments. The developed coating presents a viable way forward for enhancing safety, reducing economic losses, and improving the overall sustainability of mining operations.

Experimental and numerical investigations of seismic performance of stepped beam-column joints with different connection forms

The seismic resilience of prefabricated steel structures significantly depends on the design and construction of beam-column joints. To address the challenges related to the installation of prefabricated wall panels and overall system assembly, this study introduces a novel stepped beam-column joint. The effectiveness of different connection configurations on the seismic behavior of the joints was investigated. A series of cyclic tests were conducted on four joint specimens with different configurations, and their failure mechanisms, hysteretic curves, skeleton curves, stiffness degradation, load-bearing capacity, and energy dissipation capacity, were revealed. The experimental results showed that the stepped joint configuration offers favourable seismic performance, with notable asymmetry observed in the response patterns under positive and negative loading directions. Reducing the height of the stepped segment or the thickness of the end plate adversely affected the seismic performance, leading to early bolt failure. Consequently, a detailed finite element model of the stepped joint was developed and the model demonstrated satisfactory agreement with the experimental results. Furthermore, a parametric analysis focusing on variations in stepped segment's height was conducted, providing insights into optimization of the load-bearing capacity of the stepped joint. The difference in the performance between the stepped joints and traditional flush end plate joints is also highlighted.

Numerical investigation study on tensile-shear failure behavior of rock bolts in inclined strata mining tunnels

In response to the problem of severe deformation and failure of the surrounding rock of the mining tunnels in inclined strata, a tensile-shear failure numerical model of rock bolts was adopted to analyze the rock bolts failure behavior and the surrounding rock mechanical response, and explore the influence of different factors on rock bolts failure. The results indicate that: (1) As angle between the rock bolt and the interface decreases, the shear force of increases, and the rock bolt is easier to fracture. The maximum displacement is 250.2 mm of fractured position. A new evaluation index of shear axis ratio was proposed. The larger the shear axis ratio, the rock bolt is easier to fracture. The shear axis ratio at the interface has increased by 95 % compared to the non interface. (2) The plastic zone and the surrounding rock deformation exhibit the same inclination trend as the strata. In final state, the maximum deformation is 297.7 mm at the bottom and top position perpendicular to the rock bolts at the interface. At the moment of rock bolts fracture, the interface displacement of surrounding rock immediately increased by about 10 mm. And the stress in the surrounding rock decreased about 1 MPa. The weakening effect of surrounding rock stress shifts with the change of rock bolt fracture position. The stress at the arch waist decreases by 44 %, the stress at the arch crown decreases by 25 %. When the fracture of the rock bolts at the arch crown and arch waist ends, the stress at the side wall begin to decrease by 40 %. (3) As the inclination angle increases, the deformation of the surrounding rock and the number of rock bolt failures increase. The range of the plastic zone in the surrounding rock gradually increases, and the degree of rock bolts asymmetric fracture more aggravated. As the diameter of the rock bolt increases, the fractured number of the rock bolts and range of plastic zone decreases.

Deformation mechanism of gob‐side entry at top coal caving mining face: A numerical study

AbstractTo investigate the significant deformation of the surrounding rock within the dynamic pressure zone of the gateroad, this study utilized the tailgate of the 1506 longwall face in Anyang Coal Mine as the engineering context. A combined approach of field measurement and numerical analysis was employed to explore the deformation and failure mechanisms of the surrounding rock under dynamic pressure. The findings indicate that before the exploitation of the 1506 longwall face, there was a notable reduction in stress across the floor and immediate roof, with minimal stress concentration observed in the coal pillar and the entity rib side. The plastic zone surrounding the tailgate was limited, suggesting a high degree of stability in the entry's surrounding rock. However, during the extraction of the 1506 longwall face, the tailgate, extending 60 m ahead of the working face, was subjected to dynamic pressure, leading to a marked increase in stress within the floor, coal pillar, and immediate roof. Stress concentration was more pronounced on the entity rib side than on the pillar rib side. This resulted in significant fissuring and severe deformation of the entry's surrounding rock. The primary failure mechanism involved damage to both the roof and floor corners, with the severity of damage escalating alongside the stress in the surrounding rock. This culminated in the failure of roof corner bolts and anchor cables, thereby compromising the stability of the entry within the dynamic pressure zone.

The Investigation of Various Flange Gaps on Wind Turbine Tower Bolt Fatigue Using Finite-Element Method

Upon careful examination, numerous wind turbine collapses can be attributed to the failure of the tower bolts. Nowadays, the Schmidt–Neuper algorithm is extensively accepted in wind turbine tower bolt design. It is not advisable to utilize the finite-element method, notwithstanding the effect of the flange gap. To quantitatively investigate the influence of flange gaps on bolt fatigue, a nonlinear finite-element model of a flange segment incorporating bolt pretension and contact elements is herein proposed. Three distinct types of flange gaps are defined intentionally. It is possible to determine the nonlinear relationship between the wall load and bolt internal force. The fatigue damage of bolts was thus computed using the obtained nonlinear curve. Comparing with the results with those of Schmidt–Neuper method revealed the bolt fatigue damage is susceptible to a specified flange gap.

Shear Performance of Demountable High-Strength Bolted Connectors: An Experimental and Numerical Study Based on Reverse Push-Out Tests

Steel–concrete composite beams, essential for large-span structures, benefit from connectors that reduce cracking at the supports. The crack resistance and alignment with sustainable building trends of high-strength bolted connectors have been extensively researched. Nevertheless, only a few studies exist on their load–slip behavior in hogging sections. In this study, the shear performance of high-strength bolted connectors subjected to tension due to hogging moments was studied based on experiments and numerical modeling according to numerous reverse push-out tests. The results revealed that tensile and splitting cracks were produced in the concrete. Their distribution was affected primarily by the concrete strength and bolt diameter; this distribution became denser at decreasing concrete strengths and increasing bolt diameters. Subsequently, an analysis of the out-of-plane displacement and load–slip response was performed to investigate the phenomenon of anchor rod sliding. A cost-effective and time-efficient finite-element (FE) model was developed to investigate the internal microstates of the specimens. It revealed a correlation between bolt cracking, specimen hardening, steel yield, and failure. A correction factor is also proposed for the shear capacity of bolts within concrete subjected to tension. The findings offer insights into the load–slip response of high-strength bolted connectors subjected to hogging moments, aiding in safer, more durable supports for steel–concrete composite beams.

Enhancing Structural Resilience: Exploring the Novel Sleeve Method for Steel T-Stub Connections

A new sleeve device has been introduced with the aim of enhancing the performance of steel structures under extreme loading conditions. Previous research has primarily focused on numerical simulations of this sleeve's application, emphasizing the need for further investigation to validate its effectiveness. This research paper presents a numerical analysis that explores how the sleeve device influences the deformation capacity and strength of a bolt up to the point of failure. The study involved the use of a T-stub connection with multiple sleeves, each featuring different geometric parameters. To assess the impact on strength and deformation capacity, a comparison was drawn between these findings and the behavior of a T-stub bolted connection without using the sleeve. In addition, Finite Element (FE) models were employed for additional parametric studies. The test outcomes demonstrated a substantial increase in the deformability of the bolted connection when utilizing the sleeve device, all the while preserving the strength and initial stiffness of the bolts. This proposed sleeve method in the study significantly enhances the connection's capacity by delaying bolt failure.

Mechanism of bolt breakage in deep mining roadway under dynamic load and advanced strengthening support technology

To reveal the problem of local instability caused by bolt breakage and failure in deep mining roadway under impact dynamic loads, and explore strengthening support technologies that can reduce bolt breakage and improve the stability of roadway support bodies. This article adopts theoretical analysis, numerical simulation, and on-site industrial experiments to conduct research, investigate and obtain the fracture failure characteristics of bolt in deep mining roadway, quantitatively characterize the deformation pressure of roadway surrounding rock and dynamic load of overburden fracture, establish the mechanical criterion of bolt fracture, and analyze the influence law of different anchoring factors on bolt force under static load and dynamic and static load combination. The results show that when the anchor angle is different, the range under dynamic load increases by 169.3 % compared with static load, when the anchor length is different, the range increases by 863.3 % relatively, and the influence is significant; while the anchor support resistance increases by 11.6 % at different times, and the range decreases by 41.5 % at different pre-tightening torque. Then, based on this criterion, the influence law of bolt failure on the stability of surrounding rock is analyzed, and the optimal support scheme is obtained by simulation research, that is, bolt cable +U steel support scheme. After adopting this scheme for support, the deformation of surrounding rock is reduced by about 60 %, and the maximum concentrated stress of surrounding rock of roadway is reduced by 15.0 %. Based on this, the support parameters of the on-site roadway were optimized and a strengthening support scheme was determined, which includes “roof bolt surface support reinforcement + anchor cable combined with U-shaped steel deep reinforcement, and two strong bolts advanced reinforcement”. The on-site strengthening support practice showed that the bolt fracture rate was reduced by 87.3 %, the deformation of the surrounding rock was effectively controlled, and the stability was significantly improved.

Optimization of inclined coal seam tunnel section angle and anchor angle based on response surface method

The mining of inclined coal seams is often accompanied by problems such as difficult to control deformation of the tunnel roof and failure of anchor bolts. Taking the transportation channel of Jinping Coal Industry 1071-1 in Shanxi Xiangkuang Mine as the background, FLAC3D numerical simulation software was used, and the method of response surface experimental design and data analysis was used to systematically study the effects of the anchor installation angle and the roof inclination angle of the tunnel section on different inclination angles. Influence of the surrounding rock stability of coal seam roadways. On this basis, a multi-index tunnel support design evaluation method based on the response surface method was proposed, and the actual support plan was optimized and industrial tests were carried out based on the actual on-site support plan. The research results show that: in terms of inclined coal seam support, the degree of influence on the tunnel stability is in the following order: anchor installation angle > tunnel section roof inclination angle > coal seam inclination angle; the optimized support design obtained through the proposed technology The method has good application effect and can improve the stability of the roadway during the mining of the working face. It also proves the effectiveness of this technology and provides new ideas for the design of anchor support of inclined coal seam roadways and the optimization of roadway sections.

Feasibility study of TSOB replacing standard high-strength bolt in T-stub connection

The feasibility study of T-head Square-neck One-side Bolt (TSOB) replacing Standard High-strength Bolt (SHB) in T-stub connections is conducted in this paper. Parametric analysis is carried out by means of finite element numerical simulation to reveal the effects of T-stub parameters and bolt parameters on the tensile performance of T-stub connections using SHBs and TSOBs. The plastic hinge theory is applied to explain the mechanism for the difference formation in tensile capacity between the two types of connections. The results show that the failure modes of TSOBs bolted T-stubs are the same as those of SHBs bolted T-stubs, including complete flange yielding, bolt failure with flange yielding, and bolt failure. For the failure of complete flange yielding, the tensile capacity of TSOBs bolted T-stubs is reduced by 7.2%∼16.4% compared with that of SHBs bolted T-stubs, whereas the modes of bolt failure with flange yielding and bolt failure do not cause a difference between the two types of connections in tensile response. Two modifications on design equation and design result by introducing hole type reduction factor and thickening flange for T-stub connections were proposed, respectively. The modified design methods can be used in the design of TSOBs bolted T-stubs and are identical to the design criteria of specifications Eurocode 3 and P398 for SHBs bolted T-stubs. Besides, the high-strength large hexagon nuts for steel structures and assembly classes of H12 and H13 recommended by GB/T 1229–2006 and GB/T 5277–1985 should be preferred for TSOBs bolted T-stubs. Moreover, horizontal slotted bolt holes are recommended for practical constructions, and the T-head aspect ratio of TSOB in the range of 1.6–2.0 does not affect T-stub tensile performance.

Mechanical Behavior of Precast Circular Semi-Continuous CFST Columns under a Uniaxial Eccentric Load

For this study, we conducted a detailed examination and comprehensive comparative analysis of the structural responses and mechanical behavior of bolted sleeve connections in precast circular semi-continuous steel tubular concrete (PCSCFST) columns. The research involved fourteen specimens, and we considered the impacts of various parameters, including eccentricity, external steel sleeve thickness, bolt diameter, and slenderness ratio. The findings revealed that the external steel sleeve significantly enhances the protection of the connection area, enabling the bolts to effectively withstand eccentric loads. However, sleeves that are too thick may lead to premature bolt failure, reducing their ultimate load-bearing capacity. Using bolts to transfer loads to the concrete significantly strengthens the restraining effect of the steel sleeve. Nonetheless, increasing the bolt diameter beyond a certain threshold may diminish this beneficial impact, potentially leading to connection failure and a decrease in ultimate load-bearing capacity. A new ‘cooperative value q’ measures component collaboration at ultimate capacity, showing that shorter columns offer less effective coordination than longer ones. Through regression analysis, we formulated a prediction for axial ultimate bearing capacity, closely aligning with the experimental data (Npre-a/Nu average value of 1.003, variance 0.00248). Three N–M curves, including the Eurocode 4 method, offered conservative predictions, with Eurocode 4 closely matching the experimental results. A refined prediction method following Eurocode 4 was developed, yielding an average Ppre-U/Pu value of 0.971 and a variance of 0.0107.

Experimental Study of the Role of Gap Size on Bolt Failure in Clevis and Lug Joints

Abstract A common standard for conservatively evaluating the required bolt strength in a clevis–lug joint is to assume that the bolt must survive under an interaction equation that combines loading caused by bending, shear, and axial preload–induced stresses. In practice, this leads to unnecessarily large bolts because the true failure mode is typically closer to simple shear with some bending stresses. In this experimental study, a clevis and lug joint with a variable gap between the clevis arms was used to determine the force necessary to break high strength bolts with various gaps between the clevis and the lug, ranging from pure shear (no gap) to a gap 2.8 times the diameter of the bolt. The testing results clearly show that failure occurs at forces that are often significantly higher than would be predicted by classic, closed-form analysis of the combined loading. In particular, the bolt failed at the force predicted by simple double shear failure theory for gap sizes up to half of the bolt diameter, and for larger gaps, the failure force was consistently higher than would be predicted by classic interaction equations. Thus, although assuming failure that is due to combined bending, shear, and axial stresses is safely conservative, the necessary bolt size is actually significantly smaller than this method predicts.

Shear performance of high-strength bolt-epoxy bonding composite connector in steel-concrete composite structure

To clarify the shear mechanism of high-strength bolt-epoxy bonding composite connectors in prefabricated steel-concrete composite structures, twenty-one direct shear specimens and six double shear specimens were carried out in this study. The pretension force, interface type, epoxy curing time and loading pattern were considered. Results revealed that the main failure mode of high-strength bolt-epoxy bonding composite connectors was that the large area of epoxy matrix was separated from the steel plate, and the bolt was sheared off. The load-slip curve of composite connector specimens included the elastic stage, epoxy failure stage, frictional slip stage, bolt force transmission stage and failure stage. Compared to the specimens with a bolt connector under recommended pretension, the average initial slip load of composite connector specimens was 437.7% higher. Additionally, the average initial slip load of specimens with 1-day epoxy curing time was 24.4% lower than 7-day curing time, but the average ultimate load and ultimate slip were 12.4% and 29.4% higher, respectively. When the pretension ratio decreased from 1.0 to 0.6, the average initial slip load of specimens with a bolt connector was significantly decreased by 33.0% and the average ultimate slip of composite connector specimens was increased by 18.1%. The average initial slip load and ultimate load of composite connector specimens were comparable under cyclic loading compared to monotonic loading. Upon the experimental results and existing formulas, some equations were proposed for predicting the initial slip load and bearing capacity of steel-concrete composite structures with composite connectors.