Search Results (12)

As the rock fracture in the roof anchorage blind zone of coal roadway develops, it not only brings about serious deformation, but also results in barrier effect on anchorage stress, restricting the efficiency of the bolt support. In this paper, the existence and formation mechanism of the anchorage blind zone in the roadway roof supported by prestress bolt are found. Through field research, theoretical analysis, and numerical simulation, the main control influencing factors of the anchorage blind zone are studied. Results show that stress of rock mass in the anchorage blind zone increases with stronger bolt prestress and decreases with longer bolts (free-segment length); the length of the free segment is the main control factor that affects the range of the anchorage blind zone. Moreover, the corresponding control countermeasures are put forward that properly increasing the bolt prestress and shortening the free segment can effectively increase the stress value of the rock mass in the anchorage blind zone and reduce the scope of the zone. Under the condition of high prestress of the anchor bolt, how to reasonably select the thickness of the anchor layer so as to control rock mass deformation not only in the anchorage blind zone but also in the whole anchorage area at the same time is the key. Based on the surrounding mining conditions of the test roadway, the working method is proposed that uses a high-prestress cable to construct the roof thick anchor layer as well as a short bolt to strengthen the shallow rock mass of the roof so as to improve the bearing performance of the rock mass in the free segment, especially in the anchorage blind zone. Field validation demonstrated that the proposed strategy not only suppresses the “net pocket” phenomenon but also enhances resource efficiency by optimizing material usage (e.g., reduced bolt length and targeted prestress allocation). This approach contributes to sustainable mining practices by extending roadway service life and minimizing frequent maintenance, thereby reducing long-term environmental impacts associated with roof failures. Full article

In this paper, the quasi-static reciprocating loading test was carried out for the T-stub steel middle column joints with blind-bolt connections. As the thickness of the T-stub steel increased, the damage failure modes were different. The load–displacement curve, cumulative energy dissipation, equivalent viscous damping coefficient, damage index and other characteristics of the joints were analysed. When T-stub steel was used as a connector, its thickness affected the damage development mode. As the thickness of T-stub steel increased, the bearing capacity and plastic displacement were improved, the energy dissipation capacity was significantly increased, and the rotational stiffness retention ability of the joint was improved, but the damage index value was not significantly increased. Finally, the damage index and the rotational stiffness degradation coefficient under each loading level were numerically fitted, and the polynomial and exponential rotational stiffness models were established, taking into account the damage index. These two models took into account the reduction in rotational stiffness caused by damage under each level of load, and the rotational stiffness under each loading level could be obtained from the damage index and the initial rotational stiffness. Full article

The quantitative calculation and evaluation of seismic damage play a crucial role in ensuring structural safety, conducting performance-based structural analysis, and implementing seismic strengthening measures. However, there is limited research on the damage performance of blind-bolted T-stub steel connections used extensively in prefabricated buildings. In this study, the tensile sub model of a blind-bolted T-stub steel connection in a beam–column joint is investigated. The influence of the flange and web thickness of the T-stub connector, as well as the shear-loaded connecting bolts on the web of the T-stub, on the tensile performance of the sub model are considered. Four tensile destructive tests are conducted on a T-stub connector connected to a hollow section column using blind bolts. The experimental results, including failure modes, force–displacement curves, and strain development in the hollow section column and T-stub, are discussed and analyzed in this study. The test results reveal three main failure modes for this tensile substructure: the plastic deformation of the hollow section column, the bending fracture of the T-stub flange, and the fracture of the T-stub web bolt holes due to compression. Furthermore, a ductile damage finite element analysis method is employed to simulate the fracture damage process of the substructure, and the corresponding damage index is calculated using the typical Park–Ang damage model for evaluation, showing good agreement with the damage classification levels specified in FEMA. Full article

To study the deformation and failure mechanisms of soft rock mining roadways, the 1506 return airway of Anyang Coal Mine is taken as the engineering background. Based on limit analysis theory, a failure model based on a rigid slider system is constructed to assess the failure of the soft rock surrounding a roadway. The formulas for calculating the self-weight power of the slider in the velocity discontinuity line of the rock surrounding the roadway, the work power of the surrounding rock pressure, and the energy dissipation rate of the velocity discontinuity line are derived, and the upper limit objective function of the velocity discontinuity line height is obtained. The failure characteristics and fracture evolution process of the surrounding rock under different mining stresses are analyzed by means of physical similarity simulations. The simulation results show that shear failure occurs first on the roadway side due to stress concentration. The fissures expand along the bottom angle of the roadway to the blind support area and the low-intensity support area. The cracks weaken the support strength of the angled anchor cable and bolt in the roadway shoulder. Under the action of roof pressure, the status of the rock mass inside and outside the shear slip zone changes from static to dynamic. This causes deformation and failure of the roadway roof, side, and floor. Full article

Due to their high bending stiffness, high torsional stiffness, and high local stability, rectangular section members of Al alloy space structures are frequently utilized as load-bearing elements. However, the joint construction is more complex because of the closed cross-section. To join rectangular section members without drilling holes in them, a variety of blind bolts that can be placed and fastened on one side have been devised. The blind bolts researched in this paper is known as BOM bolt. The shear resistance of BOM-bolted Al alloy connections is investigated using shear testing and finite element calculations of individual bolts and bolt groups. According to the test and numerical simulation results, the formulas for the compressive strength of the aluminum plate and the shear capacity reduction factor of BOM-bolted long connections are derived. Full article

With the development of blind bolts that can be installed from the outer side of a section, the application of steel pipe hollow sections in prefabricated structures has become possible. The novel one-side bolt with a flip-top collapsible washer (FTW-OSB) is proposed, which can fold the washer at the end of the bolt to achieve a simple and efficient installation. Firstly, the components and installation process of the FTW-OSB are introduced. Additionally, axial tensile tests were carried out on three types of new bolts, and the failure mode, load–displacement curve, and ultimate capacity were analyzed. Based on this, the finite element model was verified, and through a series of finite element parameter analyses, the influence of washer size and construction, the friction coefficient, and the contact surface size on the new bolt were analyzed and optimized. The results show that the L-shaped washer can prevent washer rotation and has better anchoring performance than the I-shaped washer. The washer thickness, height, and upper contact surface size are the key factors affecting the anchoring performance of the FTW-OSB bolt. Among these factors, when the washer thickness increases from 0.1 d₀ to 0.3 d₀, the ultimate capacity and initial stiffness of the FTW-OSB bolt increase by 136.5% and 100.3%, respectively. The lower contact surface size and friction coefficient can be ignored. The failure model of the FTW-OSB is mainly washer shear failure and bolt tension failure. By effectively adjusting the washer thickness, side wall height, and upper contact surface size, shear failure of the washer can be avoided and an anchoring performance can be achieved that is the same as that of the same type of 10.9-grade ordinary high-strength bolt. Full article

When carbon-fiber-reinforced plastic (CFRP) and steel are joined using blind riveting and bolting, fastener inclination occurs due to the clearance between the fastener and hole. To this end, this study investigated the unavoidable occurrence of clearance when joining metal and composite materials using mechanical fastening. The effect of inclination on the lap shear strength (LSS) was quantitatively investigated under various conditions. In riveting, breakage occurred mainly in the rivet; the LSS between the CFRP and steel improved by approximately 33% when the clearance was filled with structural adhesive compared to that in the unfilled state. In bolting, a washer was essential since it not only reduced the force exerted on the bolt but also reduced the bending deformation of the steel plate where breakage occurred. The clearance-filling effect showed the same effect as using a washer even without using it. In addition, the LSS was improved by approximately 10% by filling the clearance with a structural adhesive in the case of bolting with washers. Additionally, the force distribution for the fastening segment was calculated under the application of an external force, and the results demonstrated that hybrid-bonded fastening using a clearance-filling during mechanical bonding is essential for strong fastening. Full article

A detailed nonlinear finite element model was established based on completed experiments to investigate the behavior of a blind-bolted T-stub composite joint that connects a composite beam to a concrete-filled square tube column. This was accomplished by comparing the experimental results and the finite element simulation results using the hysteresis curve, failure mode, plastic deformation and strain development of the T-stub to ensure the reliability and accuracy of the finite element model. A parametric study was carried out on the base model to expand the library of test data. It was observed from the comparison that the proposed nonlinear FE model predicted the behavior of the composite joint. The wall thickness of the column and reinforcement ratio had a significant influence on the ultimate bending moment of the composite joint and the performance of the composite joint was mainly controlled by the reinforcement ratio when the concrete slab was under a positive bending moment. The flange of the T-stub, the web of the T-stub and the axial compression ratio had little effect on the performance of the composite joint. Full article

The paper presents failure scenarios for various types of connections between a thin-walled beam and a sandwich panel. In addition to standard connections used in civil engineering applications, that is, self-drilling fasteners for sandwich panels, the study examined the use of bolts, blind rivets, and double-sided acrylic tape applied linearly and pointwise. The connections were subjected to the horizontal load applied with constant eccentricity with respect to the plane of the connection surface. This load arrangement simulates the behaviour of a free flange of the thin-walled beam in bending while lateral-torsional buckling occurs. In this way, the research covers the determination of the lateral stiffness of the thin-walled beam-free flange, while the other flange is connected to the sandwich panel using various connection systems. Full article

Modified blind bolts (Hollo-Bolt) and a locally strengthened steel tube column in the panel zone were created to overcome the moment-resisting problem for the bolted connections between concrete-filled hollow section columns and open section beams and to enhance the performance of connections. The cyclic loading was conducted on a total of six modified anchored blind bolted flush end-plate connections to concrete-filled steel tube (CFST) columns. The key parameters investigated were the tube wall thickness, end-plate thickness, blind bolt anchorage method, and beam section. The failure mode, hysteretic behavior, strength, stiffness, ductility, and energy dissipation capacity of the connections were analyzed and evaluated with all details. The results indicated that connections with modified anchored blind bolts and locally strengthened steel tubes could avoid the premature failure of CFST column and exhibit an improved behavior with a favorable strength, stiffness, and stiffness degradation. The test observations reveal two representative failure modes, and the tube wall thickness and blind bolt anchorage method have a significant effect on the resultant failure mode. Moreover, the use of thin endplate and weak beam can effectively enhance the hysteretic behavior of joints, ductility, and energy dissipation capacity; and the change in anchoring method has little effect on the stiffness. Finite element (FE) analysis models were established for the aforementioned connections. The numerical models were validated against the experimental results and exhibited good agreement. Finally, based on the component method, an initial stiffness calculation method was established for the connections. Full article

As the square steel tube in the tension zone is always the weakest part of moment-resisting joints, modified blind bolts (Hollo-Bolts) and a locally strengthened steel tube in the panel zone were adopted to enhance the joint performance. Cyclic loading tests were carried out on eight anchored blind-bolted extended end-plate joints between square concrete-filled steel tube (CFST) columns and steel beams. The test parameters included the end-plate thickness, steel tube wall thickness, beam section size, local strengthening connection method, blind bolt anchorage method, and stiffeners. The failure mode, hysteretic behavior, stiffness, strength, ductility, strength degradation, stiffness degradation, and energy dissipation capacity of the joints were studied and analyzed. The test results showed that the application of anchored blind bolts and a locally strengthened steel tube can fully utilize the bolt strength and significantly improve the joint performance, especially in terms of strength and strength degradation. The test observations revealed three typical failure modes for the joints, and the failure mode depended on the weakest component. In addition, the local reinforcement of C-channel and change in the anchorage method had a limited effect on the initial stiffness. Greater end-plate thickness and the use of stiffeners significantly increased the joint stiffness and decreased the rate of stiffness degradation. The use of stiffeners also significantly enhanced the ductility and energy dissipation by moving plastic hinge outward from the joints. Finally, finite element analysis (FEA) models were developed and validated against the experimental results, and the stress distribution and force transfer pattern were investigated. Full article

This study proposes an effective steel frame modular system and evaluates the structural performance of its beam-column connection through experimental and analytical work. The new steel frame modular system utilizes the blind bolts, which allow free access to the structural members of the closed cross-section. In addition, the new modular system is designed such that the strength of its beam members is considerably lower than that of its column members to implement the strong column-weak beam concept. In order to investigate the effectiveness of the proposed modular beam-column connection, two types of specimens were designed and tested. One of the two specimens has four knee brace members to increase the bending stiffness of the connection, while the other does not have these components. The applied load versus displacement curves are plotted for the two specimens, and their failure modes are identified. Finally, a simplified analytical model for the modular beam-column connection is proposed, and its effectiveness is validated by performing its push-over analysis and comparing its results with the test results. Full article