Bolted Specimens Research Articles

Failure modes of laminated porous panel with different connection methods

This paper discussed the problem of porous structural panel, which compared the bending and compression performance of three different layered porous structure panels with single-layer integration, multi-layer SolidWorks software coordination and multi-layer bolted connection. And through experimental and finite element simulation results, it showed that the third group of bolted specimens could prevent the occurrence of cracks and maintain the integrity of the structure effectively. The second group of software had the best bending and compression performance, and its bearing capacity, strength and deformation ability increased with the number of member layers, while the third group of bolted specimens was the opposite.

Experiments and calculation methods on the tensile capacity of a single blind bolt anchored in a circular CFST section

Composite tubular joints that connect the steel brace and circular concrete-filled steel tubular (CFST) chords are crucial for the performance of entire composite truss structures. While welding is traditionally used for these connections, bolted connections offer an alternative in challenging environments where on-site welding is not feasible. The emergence of blind bolts provides an innovative solution for bolted CFST joints by offering bolted fastening without needing access to the inner surface of a closed section. This paper focuses on the tensile performance of a single blind bolt anchored in a circular CFST section. Experiments are conducted on three different configurations of blind bolts: non-anchored blind bolt with washer, anchored blind bolt without washer, and anchored blind bolt with washer. Based on the tests, the failure mode, the ultimate capacity, and the stiffness of the CFST-blind bolt specimens are investigated. The research findings show that the stiffness and ultimate capacity of the specimen are highly influenced by the bolt diameter, concrete strength, and effective embedment length, as well as the configuration of the blind bolt. And the effective embedment length has the most significant effect on the bearing capacity of the specimen. For every 30 mm increase in bolt effective embedment length, the bearing capacity of the specimen increases by at least 25 %. Finally, practical calculation methods are proposed to determine the ultimate capacity of CFST-blind bolt joints with various configurations under tensile action. The proposed calculation methods demonstrate high accuracy, as evidenced by the good agreement between the calculated values and experimental results.

Compressive Strength of Midfoot Fusion Nail vs Midfoot Fusion Bolt and Role of Subtalar Fusion in Midfoot Charcot Fixation Model.

Operative management of midfoot Charcot arthropathy often involves an extended midfoot arthrodesis with intramedullary bolts for fixation, a method called "beaming." Recently intramedullary nails have been introduced for the same indication, presumably providing stronger fixation. This study compares midfoot fusion nails to bolts with regard to stiffness and compressive ability. Additionally, we assessed how the addition of a subtalar fusion affects the construct. Medial column fusions were performed on 10 matched cadaver foot specimens with either a midfoot fusion nail or bolt. Specimens underwent cyclical compression loading, and displacement was measured. Separately, compressive forces produced were compared between the 2 fixation constructs using a synthetic bone block model. Lastly, another 10 matched specimens with midfoot fusion nails were evaluated with or without subtalar fusions. No differences in stiffness were found in comparing matched specimens between nail vs bolt or comparing nail only without subtalar fusion (STF) vs nail with STF. The compressive force produced by the nail specimens was significantly and substantially greater than the bolted specimens (751.7 vs 139.0 N, P = .01). The accumulated height drop at the midfoot after cycling was 0.5 mm more in the nail group than in the bolt group (1.72 vs 1.22 mm, P = .008). The nail with STF group had greater initial height drop at the midfoot than the nail-only group (0.68 vs 0.34 mm, P = .035) with similar initial height drop at the ankle. However, there were no differences in strength among the matched pairs of midfoot nail-only vs midfoot nail with STF as measured by displacement after fatigue or maximum force at load to failure. The overall cadaveric comparisons between matched pairs of nails vs bolts, and nail-only vs nail with STF, did not provide noteworthy differences between the groups with regard to strength or stiffness. However, the compressive force of the midfoot fusion nail was far superior to the bolt in a synthetic bone model. These data provide valuable insight comparing implants used in Charcot midfoot arthrodesis.

A new method for visually and real-timely measuring stress and load distributions in bolt with photoelastic technology

After analyzing the stress characteristics of the bolt, we determined that it can be regarded as experiencing a planar stress state due to the absence of circumferential stress. Consequently, a photoelastic bolt specimen was fabricated by taking a slice across its diameter. Using a photoelastic bench, we collected interference fringe images of the photoelastic specimen under different loads. This method enabled us to visually and continuously measure the stress distributions within the specimen in real-time. Additionally, the load distribution ratio of each tooth was derived. By comparing these results with those obtained through numerical simulation, we were able to validate the reasonability of the theoretical assumption regarding the load distribution of each tooth in the bolt. Our method establishes a solid foundation and can be effectively utilized for precise thread connection design.

Effect analysis of uneven thickness of resin annulus on anchorage failure of cable bolt and uniformity guarantee device

Resin grouted cable bolts are widely used in the control of surrounding rock in underground engineering such as roadways and tunnels. This study conducted theoretical analysis and laboratory experiments to investigate the influence mechanism and characteristics of the uneven thickness of the resin annulus on the anchorage performance of the cable bolt, and developed an effective method for controlling the uneven thickness. The theoretical analysis of the shear stress distribution in the resin annulus under tension revealed that, when the thickness of the resin annulus is uniform, the shear stress in the resin annulus and interface around the cable bolt has balanced distribution overall. When the resin annulus thickness is uneven, the shear stress level is higher in the thinner area compared with the thicker area of the resin annulus. The pullout test results for cable bolt specimens anchored with different resin annulus thicknesses reveal that, as the thickness uniformity of the resin annulus decreases, the pullout load of the anchored specimen decreases to different degrees. According to the structure of the cable bolt and the resin anchoring construction characteristics, the resin annulus thickness uniformity guarantee device (RATUGD) was designed. The results obtained by a device working effect experiment reveal that the RATUGD can significantly improve the thickness uniformity of the resin annulus, and the pullout resistance of the anchored specimen is also ensured when the device is used. This study elucidated the influence mechanism of an uneven resin annulus on the anchoring performance of a cable bolt to a certain extent. Additionally, technology that ensures the resin annulus uniformity is proposed to further ensure and enhance the support effect of a resin grouted cable bolt on the surrounding rock of underground engineering such as roadways and tunnels.

Influence of Lateral Pressure on the Mechanical Performance of Bolted Specimens under Biaxial Compression

The influence of lateral pressure (σ2) on the stability of the surrounding rock of roadway increases after excavation. The rock bolt is usually used to improve the stability of the surrounding rock. Therefore, it is important to understand the biaxial compressive behaviors of the bolted samples influenced by lateral pressure. In this study, biaxial compression experiments are carried out to investigate the biaxial compressive properties of bolted rock samples influenced by lateral pressure. The results show that bolting can improve the peak strength, inhibit the post-peak strength attenuation and reduce the pre-peak brittleness of the bolted rock mass. With the increase of lateral pressure, the strength and elastic modulus of the bolted samples increases approximately parabolic and linearly, respectively. The failure modes of the bolted samples influenced by lateral pressure can be divided into splitting failure and compression-shear failure. A reinforcement mechanism of bolt is observed, namely axial action, axial and transverse action at the pre- and post-peak stages of the bolted samples. Based on a modified true triaxial Mohr-Coulomb strength criterion and this bolt reinforcement mechanism, a new method for calculating the equivalent cohesion and equivalent internal friction angle of the bolted specimens under biaxial compression is proposed. The research results of this paper have certain reference value for the stability control of roadway

Effect of surface retaining elements on rock stability: laboratory investigation with sand powder 3D printing

This study aims to investigate the beneficial effects of surface retaining elements (SREs) on the mechanical behaviors of bolted rock and roadway stability. 3D printing (3DP) technology is utilized to create rock analogue prismatic specimens for conducting this investigation. Uniaxial compression tests with acoustic emission (AE) and digital image correlation techniques have been conducted on 3DP specimens bolted with different SREs. The results demonstrate that the strength and modulus of elasticity of the bolted specimens show a positive correlation with the area of the SRE; the AE characteristics of the bolted specimens are higher than those of the unbolted specimen, but they decrease with an increase in SRE area, thus further improving the integrity of the bolted specimens. The reinforcement effect of SREs on the surrounding rock of roadways is further analyzed using numerical modelling and field test. The results provide a better understanding of the role of SREs in rock bolting and the optimization of rock bolting design. Furthermore, they verify the feasibility of 3DP for rock analogues in rock mechanics tests.

Push-out behavior of GFRP bolts shear connectors in FRP-concrete hybrid beam

GFRP bolt has emerged as a promising shear connector in FRP-concrete hybrid beams due to flexible arrangement and ease of installation. Shear connectors are critical to maintaining the composite action and are key to the design of hybrid beams. 30 push-out tests were conducted to investigate failure mode, ultimate strength, and shear load-slip (P-S) relationship of GFRP bolts. Test parameters included bolt types, layout of bolts, longitudinal row spacing of bolts (Sl), bolt diameter (d), and bolt embedment depth (he). Results revealed that specimens with GFRP bolts exhibited bolt shank shear failure, pry-out failure of bolts, and splitting failure of concrete. In contrast, specimens with stainless-steel bolts suffered bearing failure of bolt holes in the FRP flange. Typical P-S curves of GFRP bolt specimens consisted of micro-slipping and significant-slipping phases, showing non-linear response, while P-S curves of stainless-steel bolts exhibited a linear response till failure. The effect of layout of bolts was found negligible if the longitudinal row spacing and horizontal spacing was not less than 6d and 4d, respectively. Specimens with a larger d and he demonstrated greater shear capacity. Based on the test results, prediction equations associated with failure modes were introduced to predict the capacity of GFRP bolt, which yielded results in accordance with experiments. Additionally, a refined description of P-S relationship was proposed by curving fitting, and the results correlated well with the experiments.

Investigation of the effect of pre-tightening forces on bolted connection for FRP-steel joints

This paper experimentally and numerically investigates the effect of pre-tightening forces on bolted connection for double-lap FRP-steel joints, considering varied levels of pre-tightening forces. In the experimental phase of this study, six bolted double-lap pull-pull specimens with varying pre-tightening degrees (preloaded of 0, 3, 6, 7, 8, and 9 N·m, respectively) were examined. Test results indicated that all specimens exhibited bearing failure of FRP plates and the load capacity was significantly influenced by the pre-tightening forces applied through bolts. The highest loading capacity (27.1 kN) was recorded for the specimen with a preloaded of 6 N·m. In order to study the stress distribution of FRP plate for the bolted specimens, three-dimensional finite element (FE) models were conducted. Based on the FE analyzing results, the pre-tightening coefficient Pc (the coefficient of the preload increment per pre-tightening torque of bolts) of 750 m−1 was concluded and further proved by the analysis of the stress in contact zones for specimens preloaded by 0, 3, and 6 N·m.

Seismic behavior and simplified hysteretic model of precast concrete wall panels with bolted connections under cyclic loading

Bolted prefabricated concrete wall panel structures are considered to be of great advantage in the current construction industry as they allow efficient recycling or direct replacement of aging components for structural renewal and repair. However, the parts of bolted connectors still have many problems such as complex construction and high positioning accuracy requirements. Furthermore, comparative studies on different bolted connections have been limited to date. This paper proposes a simplified tensile-bolt connection and a shear bolt-steel plate connection for low-rise wall-based structures in earthquake-prone zones, which can adapt to the fast-easy and reliable installation manners on construction sites. Three tension-bolted specimens and three shear-bolted specimens were tested under quasi-static cyclic loading. The seismic performances studied include failure modes, hysteretic behaviors, deformation, energy dissipation capacity, stiffness degradation, and steel strain distributions. The results indicated that both types of bolted specimens meet the seismic safety of low-rise buildings. By analyzing the typical skeleton curve and hysteretic loop of the specimens, based on a linear regression fitting analysis, the characteristic points of the proposed skeleton model curves were proposed which could evaluate the restoring characteristics of the curves well. A simplified restoring force model was proposed which has a high evaluation accuracy. The research results can give references to the further application of bolt-connected fabricated wall panel structures.

A RESIN TYPE ADDITIVE USE TO IMPROVE LOAD BEARING CAPACITIES OF GROUTED ROCK BOLTS EXPOSED TO THERMAL CYCLES

A thermoset PMS (Polyvinyl modified silicone) type polymer additive effect on load bearing capacities of cement grouted rock bolt specimens exposed to thermal cycles was investigated with a series of experimental studies. The additive used in this study was in liquid phase while adding into the fresh cement mix and started to solidify by polymerization after being mixed well in the cement grout. The silicone based thermoset product was selected to use because of its ability of polymerization in contact with water. According to the results of this study, the load bearing capacity loss due to thermal cycles was found to be notably limited as a result of using the thermoset additive. Therefore, the additive tested in this study was assessed to improve resistivities of the cement grouted rock bolts against the thermal changes.

Investigation into durability degradation and fracture of cable bolts through laboratorial tests and hydrogeochemical modelling in underground conditions

Premature failures of cable bolts caused by durability degradation in underground reinforcement systems have been more and more often observed. To identify various factors affecting the corrosion process, the corrosion processes were examined through laboratorial testing programs as well as hydrogeochemical modelling. Experiments were carried out in simulated underground conditions in “corrosion cells” containing stressed cable bolt specimens as well as groundwater, clay, coal or a combination of the materials. Water chemistry and corrosion pattern analysis of specimens in different testing conditions were conducted. Hydrogeochemical models were established and the formation of corrosion products, the change of ion concentration and factors related to corrosion rates were studied. The results showed the corrosion degree of specimens could be classified into three categories. The dissolved oxygen was the main factor affecting the general corrosion and stress level, pH and electrical conductivity were secondary factors. Erosive ions were main factors affecting localised corrosion which was mainly observed to form at high stress areas. A ‘staple’ like crack initiated at localised corrosion were observed which was identified as a potential site for stress corrosion cracking. The modelling results showed sulphide iron generated in presence of microorganisms which would also accelerate stress corrosion of specimens. The obtained results and proposed methodologies would establish quantifiable data to compare variable mine conditions and help understand the corrosion mechanisms in underground conditions.

Experimental study on post-fire mechanical properties of Grade 12.9 high-strength bolts

This paper aims to experimentally investigate the post-fire mechanical properties of Grade 12.9 high-strength bolts. To evaluate the effects of elevated temperatures and the bolt diameter on the post-fire mechanical properties, seven different diameters of the Grade 12.9 bolts were heated based on a standard temperature–time diagram with the ranges of 20 to 900 °C. Upon air-cooling and reaching room temperature (a heating and cooling cycle), 105 bolt specimens were subjected to the standard tensile test. The experimental results, including the post-fire stress–strain curve, yield strength, tensile strength, modulus of elasticity, and ductility, were presented. The results indicated that changes in mechanical properties were noticeable for temperatures higher than 400 °C. Although the post-fire modulus of elasticity did not significantly change, the post-fire yield and tensile strengths decreased substantially if the maximum temperature exceeded 400 °C. After heating up to 900 °C and then cooling down and reaching ambient temperature, Grade 12.9 steel bolts showed a 60% reduction in strength. The comparison of the results showed that the effect of diameter on the post-fire yield and tensile strengths of Grade 12.9 bolts was insignificant and could be neglected, but on elastic modulus and ductility, the diameter effect needs to be considered. In addition, the scanning electron microscope (SEM) images indicated that the elevated temperatures remarkably changed the microstructural characteristics of the Grade 12.9 bolts. Finally, based on the test results, the prediction equations of the post-fire mechanical properties of the Grade 12.9 high-strength bolts were proposed.

Microstructural evolution and hot-compressive behavior of Waspaloy forged bolts: experimental and finite element simulation

This study aims to present the optimum technological parameters of the hot forging process of aerospace bolts. Deformation-related parameters were determined according to the relevant conditions for commercial production of bolts. Deformation behavior and evolution of the microstructure of Waspaloy were systematically studied at temperature in the range of 1000–1120 °C and strain rate in the range of 0.01–10 s−1. The obtained results revealed the sensitivity of the flow stresses to the deformation parameters and stresses increased when deformed at lower temperatures or higher strain rates. At the high strain rates of 5–10 s−1, the flow curves exhibited a pronounced flow softening. The curves demonstrated a dynamic equilibrium at the low strain rates of 0.01–0.1 s−1. A constituent model of Waspaloy was established to describe the flow characteristic of Waspaloy. The microstructures showed that the grain refinement of DRX at low temperature (1000–1040 °C) was the main mechanism for microstructural evolution, while the grain growth kinetic was the dominant mechanism at high temperature (1080–1120 °C). The DRX kinetic model of this superalloy was established. Also, the constitutive and dynamic recrystallization models were used in the Deform-3D software for validation. The obtained results revealed that the simulation results matched well with the experimental results of grain sizes at different regions of the bolt specimens. The study can provide guidance to optimize technological parameters and predict the microstructure for commercial bolt forging.

Insights into the characteristics of corrosion products formed on the contact and exposed regions of C1045 steel bolt and nut fasteners exposed to aqueous chloride environments

• Corrosion products on different regions of C1045 bolt are characterized for the first time. • Differential aeration/concentration effects induced heterogeneity in the corrosion products. • Reactive phases, γ-FeOOH and β-FeOOH dominated at the exposed and contact region, respectively. • Magnetite, Fe 3 O 4 was detected in both regions under low oxygen conditions. • Due to the low amount of α-FeOOH, the rusts in both regions lack stability and protectiveness. This study investigated the characteristics of corrosion products formed on the contact and exposed regions of C1045 steel bolt and nut fasteners used in structures exposed to aqueous chloride environments. The corroded surface morphology, rust compositions, and corrosion kinetics of the bolt specimen were studied by visual observation, optical microscopy (OM), scanning electron microscopy (SEM), X-Ray diffractometry (XRD), micro-Raman, electron probe micro-analyzer (EPMA), and potentiodynamic polarization techniques. Results obtained showed a variation in corrosion kinetics, morphology, and composition of the rust layer which were driven by differential aeration and concentration effects. Due to the availability of sufficient dissolved oxygen, the oxyhydroxide compound, lepidocrocite (γ-FeOOH) was detected in the outer rust layer in the exposed region, whereas the inner rust layer was composed of magnetite (Fe 3 O 4 ). However, the oxygen-deficient contact surface revealed the presence of akaganeite (β-FeOOH) and magnetite (Fe 3 O 4 ) as dominant oxide phases. The most stable phase, goethite (α-FeOOH) was also detected in the rust formed in both regions, though in significantly low amounts. Furthermore, owing to variation in environmental conditions, the amount and density of the rust layer varied in the different regions. The estimated corrosion stability values for the different regions revealed that the corrosion products formed on the steel surfaces were non-protective, suggesting the need for specific surface treatment as a protective measure.

Mechanical Behavior of High-Strength Bolted Joints Fabricated from Fire-Resistant Steel at Elevated Temperatures

The use of fire-resistant steel is an effective way to alleviate fire safety issues in steel structures. Considering the limited research on bolted joints fabricated from fire-resistant steel, this study presents the results of the experimental investigation on the mechanical behavior of 40 specimens of bolted joints at room temperature and elevated temperatures (20°C∼700°C). These specimens are assembled with fire-resistant steel plates and fire-resistant high-strength bolts (or ordinary high-strength bolts). The mechanical behavior of these specimens was investigated, which included the failure mode, deformation performance, and degradation of bearing capacity. The experimental results show that the treatment of the friction surface (specifically, impeller blasting and sprayed hard quartz sand) has a negligible effect on the ultimate strength of specimens and a relatively significant effect on the slip strength. In addition, reduction factors of the tensile strength (KN) and slip strength (KS) for both fire-resistant bolt specimens and ordinary high-strength bolt specimens decrease with the increase in temperature, especially in the case of elevated temperatures ranging from 400°C to 700°C. Prediction models with different reliability degrees are proposed to calculate the degradation of tensile strength under elevated temperatures, which has the potential to be used for the fire-resistant design of steel connections and structures.

Experimental Study of Constant-Amplitude Fatigue Performance of M39 High-Strength Bolts in Grid Structures with Bolt-Sphere Joints

Grid structures with bolt-sphere joints are widely used in industrial plants. With the installation of suspension cranes, high-strength bolts are subjected to repeated alternating loads and cause fatigue problems. Due to their dispersive nature, the degree of difficulty and cost of fatigue tests are extremely high. Due to the lack of a recognized fatigue design method, engineering designers have encountered great difficulties, and the promotion and application of such methods are severely restricted. In this paper, we successfully implemented a constant-amplitude fatigue test of M39 high-strength bolt specimens on an American MTS Landmark 370.50 fatigue testing machine and obtained the corresponding S-N curve from the statistical analysis of the test data. Using the nominal stress amplitude Δσ and the hot point stress amplitude Δσk as the design parameters, we established a corresponding constant-amplitude fatigue design method. We performed a microscopic analysis of the fracture surface using a TESCAN Mira3 LMH scanning electron microscope and revealed the fatigue failure mechanism of the high-strength bolts.

A new energy-absorbing bolt used for large deformation control of tunnel surrounding rock

In order to control the large deformation of tunnel surrounding rock, a new energy-absorbing bolt is developed. This bolt can be transformed into a rigid support when the deformation of the surrounding rock reaches the length of the sleeve tube, thus preventing the surrounding rock from continuing to deform. Moreover, this bolt has a simple structure and is easy to manufacture and assemble. Then the static tensile test is conducted on the bolt specimen to test its working performance. The test results show that when the cone angle of the cone block is small, the load–displacement curve of the bolt contains three stages; when the cone angle is large, the load–displacement curve contains only two stages. Meanwhile, both the average constant resistance and the maximum absorbed energy increase linearly with the increase of cone angle. On this basis, ignoring the influence of shear stress, and it is supposed that the thickness of the sleeve tube is constant, then the theoretical calculation formula of constant resistance for the new bolt is derived, and the rationality of the formula is verified using the static tensile test results. It is found that the error of the calculated result is less than 15% when the cone angle does not exceed 15°. At last, the numerical simulation method is used to analyze the performance of the new bolt. The simulation results indicate that the generation of shear stress and the change of tube thickness during the movement of the cone block are two important factors that cause theoretical errors.

Fatigue life predictions of carbon fiber reinforced plastic in specimens of double-shear bolted joint

It is noted that in modern aircraft composite structures there is a significant number of composite and metal-composite shear bolted joints, the fatigue life of which is an important factor to ensure the operating safety of such constructions. Thus, special attention is given to the evaluation of the layered composites fatigue life in such joints during tests and calculations of the similar structures components. Despite a considerable number of publications and studies on this subject, it can be observed that many important methodological issues have not been solved yet in this field. These problems can deal with the choice of the main mode of layered composites fatigue damage in shear bolted joints; the uncertainty of the basic fatigue curve; the practical absence of some models, representing diagrams of constant life fatigue for the layered composites in the joints under consideration; the uncertainty of fatigue damage summation rule in the layered composites in the investigated joints. Based on the review results and the data analysis of domestic and foreign publications including the results of specially conducted studies, the solutions to these problems are proposed. The proposed solutions were verified by analyzing the calculated and experimental data on the fatigue life of carbon fiber reinforced plastic laminates НТА7/6376 [45/-45/0/90]3S in the double-shear bolted joints specimens.

Preventing failure of the anchoring system in underground coal mines

Cable bolts are commonly used as anchoring element in many underground mines. Reports on the premature failure of cable bolts in underground coal mines due to stress corrosion cracking (SCC) have been increasing in the past two decades. The previous studies found that the diffusion of atomic hydrogen into steel causes the SCC in cable bolts, which is known as hydrogen-induced stress corrosion cracking (HISCC). While the research on the mechanism of the HISCC in underground mines needs to be continued, it is essential to develop prevention measures to avoid such a failure. In this study, a variety of prevention measures that claim to prevent corrosion of steel were examined. Specifically, barrier coating, i.e., polymer, epoxy coating, as well as the sacrificial coating, i.e., hot-dip galvanising, methods were tested. Testing specimens were made by inserting loading pins between locked cable bolt king wires (coated) to simulate the in-situ stress condition. Cable bolt specimens were then fully immersed into a hydrogen sulphide solution to determine their resistance against HISCC. The test results showed that all the coatings had delayed the failure in varying degrees, but very few have significantly extended the time to fracturing. The polymer and epoxy coatings have become breached during the testing, and the failure occurred shortly after. The galvanised coating was dissolved in the testing solution and again allowed access of the solution to the steel surface, and subsequently resulted in failure. This indicates that these coatings can be potentially applied to prevent SCC failure; however, their impacts on the performance of bolts, such as their bonding with grout and bolt, still need to be considered.