Anchor Bolts Research Articles

Mitigating interfacial stresses in strip-bonded beams by appending end-anchored unbonded segments

Bonding strips is widely used for the strengthening of structures. This paper addresses the challenge of stress concentration in the strip-strengthened beams, where interfacial stresses at the end of the strip are usually large enough to causes premature brittle debonding failure. Lengthening bonded strips and thickening adhesive layer are effective solutions to decrease the stresses but sometimes difficult to implement. For example, obstacles under the beam may stop the strip from being lengthened with bonding. This paper proposes a feasible solution for this case that is extending the strip without bonding and then fixing it with additional anchors at the end. Analytical expressions are derived for interfacial stresses in strip-bonded beams with the end-anchored unbonded segment (EAUS). The deformation coordination relationship between EAUS and the beam is considered. The anchor bolts are analogous to elastic foundation beams to obtain their shear stiffness which will greatly influence the tension at the strip end. The theoretical results are then verified by finite element simulations. Moreover, parameter studies are performed to explore the effects of various strengthening configurations such as the length of the bonded and unbonded segments on interfacial stresses. The investigations show that the presence of the EAUS could substantially alleviate the concentration of interfacial stresses. The findings of this study provide a new approach on how to control stress concentration in the strip-strengthened beams.

Study on mechanical properties of shotcrete lattice girder in a tunnel considering the excavation effect at early-age

The lattice girder (LG) and shotcrete work together to provide support in tunnel engineering, being influenced by the hardening process of concrete and the excavation process. To elucidate the dynamic changes in the mechanical behavior of the LG during this process, the present study conducted indoor experiments using a self-developed loading system suitable for early age flow-plastic state shotcrete LG. Through the secondary development of the ABAQUS concrete hardening process constitutive model, an analysis of parameters such as curvature and load values was conducted to understand the evolution of the load patterns on the LG. Subsequently, relying on the background of the construction of an underground excavation station in Qingdao Metro, refined numerical simulations of the construction process were carried out. Combining the analysis with measured data, the following conclusions were drawn: 1. In the first three days after concrete casting, the LG specimen experiences relatively low stress, and after seven days, the LG specimen and concrete form a cohesive synergy; 2. The initial load caused the deterioration of the supporting performance of the unhardened grid concrete specimens, and the bearing capacity of the test group was reduced by 25% compared with the control group; 3. In the early stages of tunnel excavation and support, due to the low hardening process of shotcrete, the ability to transfer the surrounding rock load to the LG is limited, and the layout of the LG has no significant impact on the stability of the surrounding rock; 4. The collaborative support effect between the rebar bent frame (RBF) and concrete is greater than that of the LG, and it coordinates better with prestressed anchor bolts, presenting advantages in hard rock tunnels.

Enhancing Flexural Resistance in Pre-Damaged RC Beams with Near-Surface Mounted GFRP Bar and Bolt Anchoring System

The objective of this research was to explore the mechanical properties and failure mechanisms of reinforced concrete beams (RC beams) strengthened with near-surface mounted (NSM) glass fiber-reinforced polymer (GFRP) bars. This study focused on evaluating the effect of various factors on the load-deflection response and failure patterns of RC beams, including pre-existing damage, end anchorage, bar length, bar number, and the condition of concrete cover. The tested RC beams were divided into three groups. The first group included undamaged and damaged control beams. The second group involved the strengthening of beams after inducing damage, with variations in bar length, number, and cross-sectional area. This group also included beams strengthened by GFRP bars with and without anchors. In the third group, the effects of different cover materials, cover bonding techniques, and anchor bolts on the strengthening bars were examined. The results of the experiment indicated a notable decrease in both cracking and maximum load capacity for beams that were pre-damaged. The inclusion of anchor bolts appeared to have a noticeable effect, enhancing the load-carrying capacity and reducing mid-span deflection. Opting for two bars proved to be more effective than using three bars, leading to a higher maximum load and improved ductility. Moreover, prioritizing the bonding of the concrete cover at the end of the bars was found to be more important than bonding in the area of maximum moment.

Application research on low cost support method for surrounding rock of broken section roadway in phosphate mine area

Introduction: Taking a phosphate mine in Yunnan as the engineering research background, the fractured rock mass of the No. 1 belt roadway is selected as the research object.Methods: To reduce the cost of tunnel surrounding rock support and optimize construction technology, a combination of numerical simulation software Midas and on-site experiments was used to compare and analyze the distribution characteristics of the plastic zone of tunnel surrounding rock, deformation characteristics of tunnel surrounding rock, and stress characteristics of tunnel support anchor bolts under two support methods: double-layer spray anchor mesh and single-layer spray anchor mesh with steel bar.Results: Research findings indicate that adopting the single-layer spray anchor mesh with steel bar support method results in a more uniform distribution of the plastic zone at the top of the tunnel surrounding rock, with a smaller range. The settlement of the roof and bulging of the bottom plate in the roadway’s surrounding rock, supported by a single-layer spray anchor mesh and steel bars, measure at 75.033 mm and 82.165 mm, respectively. Additionally, the internal bulging on both sides of the roadway’s surrounding rock is recorded as 37.835 mm and 37.470 mm, respectively. On the other hand, when utilizing a double-layer spray anchor mesh for support, the settlement of the roof and bulging of the bottom plate in the roadway’s surrounding rock are measured at 84.199 mm and 85.255 mm, respectively. Correspondingly, the internal bulging on both sides of the roadway’s surrounding rock records measurements of 41.670 mm and 41.756 mm, respectively. Furthermore, adopting the single-layer spray anchor mesh with steel bar support method ensures a more even transfer of axial forces to the steel bars, thereby increasing the overall load-bearing capacity. In contrast, the anchor bolts in the double-layer spray anchor mesh support method experience higher axial forces, leading to more pronounced stress concentration.Discussion: By comparing the field monitoring data, it is evident that the single-layer spray anchor mesh with steel bar support method exhibits significantly better control over the tunnel surrounding rock than the double-layer spray anchor mesh support method. Therefore, replacing the double-layer spray anchor net support with a single-layer spray anchor net with steel bar support method is entirely feasible and can meet on-site practical production requirements. The research results hold significant value in providing guidance and reference for selecting cost-effective support schemes for tunnel surrounding rock.

Experimental and FE analysis of the behavior of steel column base connections under tension and bending moment

Most design procedures represent the steel base connection by assuming either a perfectly hinged or a fully rigid connection. However, these kinds of connections are, in fact, semi-rigid or flexible and their actual behavior is complicated. Most of the previous studies investigated these base connections experimentally under moments and axial compression only, which is completely different in the case of axial tension and moment. Therefore, experimental and numerical investigations with variable base plate thicknesses and diameters and arrangements of the anchor bolts were carried out to verify the behavior of this kind of base connection under axial tension and moment. Full-scale steel columns with hinged base plate connections were tested under the effect of two simultaneous actions, axial tension force and bending moment. Moreover, Finite Element (FE) models were developed and verified against the experimental results to conduct a parametric study. The investigated parameters were the base plate thickness and anchor bolt diameter and arrangement. The base plate connections under the effect of axial tension with moment instead of axial compression caused reductions in the rotational stiffness up to 99%. In addition, using only two bolts in this type of connection concentrated stresses on the base plate that led to big deformations. The small base plate thickness deformed easily under the effect of tension force which induced big initial gaps between the steel base plate and the Base beam and subsequently decreased the moment resistance and rotational stiffness of the base plate connection. The big elongation of the anchor bolts with small diameters increased the gap between the steel plate and the Base beam.

Comprehensive wood dwelling tests for Post‐and‐Beam and Shear‐Wall structures reflecting foundation boundaries

AbstractThis paper focuses on the ultimate state of three‐story wood dwellings with high aspect ratios, which are increasing in Japan's urban areas. Using shaking table test results from the 2019 full‐scale shaking table test, a comprehensive study is conducted on the accuracy of evaluating ultimate state through the story shear failure mode at the first story, the tension fracture mode at the wall base of the first story, and foundation sliding mode on the soil. Methods evaluating the dynamic response behaviors of the building systems are also investigated. In the test, the current Japanese seismic design guidelines were applied, and two Grade‐3 buildings were prepared. One adopted the Post‐and‐Beam structure (A‐building), and the other the Shear‐Wall structure (B‐building). A series of tests planned very different physical boundary conditions surrounding their reinforced concrete (RC) mat foundations. The sills, column bases and wall bases of the upper wood structures were anchored to the RC foundations by steel anchor bolts, according to the current Allowable Stress Design (ASD) requirements. In the first stage, A‐building equipped a Base‐Isolation system, while B‐building represented a generic foundation constructed on a 1.5 m‐height real soil ground by preparing a rigid soil box (Foundation‐Soil system). In the second stage of A‐building and B‐building, the foundation was firmly fixed (Fixed‐Foundation system), and shaking table motions were fully applied to the foundations. The entire test system was setup on the large shaking table facility at E‐Defense, and a series of tests were conducted using JMA‐Kobe motion and JR‐Takatori motion recorded in the 1995 Kobe earthquake as Maximum‐Considered‐Earthquake motions. Confirmed was the change in the structural mechanism due to the upper structural systems and the foundation boundaries. Regarding the upper wood structure performance in the Fixed‐Foundation system, a story shear failure mode was observed at the first story in A‐building, while a tension fracture mode at the base of the first story in B‐building. This difference of failure mode is difficult to determine with ASD. The maximum strength were more than four times higher than the ASD base shear force. Tension fracture capacity at the wall base was mainly enhanced by the presence of the steel anchor bolts. Regarding the foundation performance in Foundation‐Soil system of B‐building, a horizontal displacement up to 240 mm was observed between the foundation and soil when JMA‐Kobe 100% was applied. A response reduction effect was observed in the upper wood structure, similar to the Base‐Isolation system of A‐building. The initial friction and cyclic friction strength capacities between the foundation and soil were quantitatively evaluated considering the horizontal two‐directional sliding. The representative test results were converted to the corresponding SDOF systems based on the first mode response assessment. In the Fixed‐Foundation system, the dynamic response characteristics of the upper wood structures were properly represented using Ibarra‐Medina‐Krawinkler pinching model in the equivalent SDOF system.

Study on the Synergistic Effect of Primary Support and Surrounding Rock of Large Buried Depth Tunnel in Soft and Fractured Strata

The soft and fractured strata can cause significant deformation of surrounding rock during tunnel excavation. This study analyzes field monitoring test results and compares numerical simulations from the third bid project of the Dali I section construction within the water diversion project in central Yunnan to address the issue of significant deformation following tunnel excavation in soft and fractured strata. It proposes an optimized support scheme consisting of a densified steel arch and enhanced initial support strength and stiffness. In addition, the research investigates support effectiveness considering varying support strengths and steel arch ring spacing. The study findings indicated the following: (1) The tunnel traverses soft and fractured strata, causing unevenly distributed vertical convergence deformation around the cavern. The maximum settlement occurs at the crown, showing pronounced nonlinearity. (2) The maximum stress in the steel arch is concentrated at the arch crown, measuring −19.02 MPa. The arch remains compressed, with stress decreasing from the crown to the waist. (3) The axial force in the anchor bolt reduces from the crown to the arch’s waist on both sides. As the depth of the rock mass increases, the axial force in each anchor bolt decreases and the tension state is maintained. The maximum axial force reaches 46.57 kN. (4) The maximum displacement decreases from 4.21 to 0.15 cm after the optimized support structure is implemented, demonstrating the optimization scheme’s effectiveness. Future constructions can refer to this scheme and make necessary adjustments based on various terrain conditions to ensure safety.

Probabilistic model updating of steel frame structures using strain and acceleration measurements: A multitask learning framework

This paper proposes a multitask learning framework for probabilistic model updating by jointly using strain and acceleration measurements. This framework can enhance the structural damage assessment and response prediction of existing steel frame structures with quantified uncertainty. Multitask learning may be used to address multiple similar inference tasks simultaneously to achieve a more robust prediction performance by transferring useful knowledge from one task to another, even in situations of data scarcity. In the proposed model-updating procedure, a spatial frame is decomposed into multiple planar frames that are viewed as multiple tasks and jointly analyzed based on the hierarchical Bayesian model, leading to robust estimation results. The procedure uses a displacement–stress relationship in the modal space because it directly reflects the elemental stiffness and requires no prior knowledge concerning the mass, unlike most existing model-updating techniques. Validation of the proposed framework by using a full-scale vibration test on a one-story, one-bay by one-bay moment resisting steel frame, wherein structural damage to the column bases is simulated by loosening the anchor bolts, is presented. The experimental results suggest that the displacement–stress relationship has sufficient sensitivity toward localized damage, and the Bayesian multitask learning approach may result in the efficient use of measurements such that the uncertainty involved in model parameter estimation is reduced. The proposed framework facilitates more robust and informative model updating.

Anchorage failure mechanism and uplift bearing capacity of L- & J-anchor bolts in plain concrete

This paper studies the anchorage failure mechanism and bearing capacity characteristics of hooked (L- & J-) anchor bolts in plain concrete under uplift load. Static tests on L- & J- anchor bolts were carried out to study the influence of different parameters (such as bolt diameter, anchorage depth, and bolt hook length) on the failure mode of hooked anchor bolts. The test results show that the uplift bearing capacity of L- & J- anchor bolts is greatly improved compared with that of smooth bolts. Two typical failure modes, that is, concrete breakout and bolt failure. In specific, the concrete breakout occurred in the L- & J- anchor bolts with anchorage depth of 5d, and the failure mode changed from concrete breakout to bolt failure as the anchorage depth increased. The finite element model was further established to investigate the stress development of the anchorage bolt and concrete and thus reveal the anchorage failure mechanism. Furthermore, a calculation method was proposed to accurately predict the uplift bearing capacity for the hooked anchor bolts with concrete breakout, where the change rule of the breakout cone diffusion angle θi and concrete crack propagation were mainly discussed. It reveals that the anchorage depth greatly influenced the diffusion angle when the concrete breakout occurs, and the diffusion angle on both sides of L- & J- anchor bolts presented an asymmetric distribution. Compared with the code ACI318, the proposed formula considered the effect of breakout cone diffusion angle on bearing capacity, and the calculation results coincided well with the experimental and numerical results, implying that the proposed formula in this paper can be considered reliable to guide the practical engineering design.

Research on Non-destructive Testing Technology for Anchor Bolt Anchoring Quality Based on Virtual Instruments

Research on Non-destructive Testing Technology for Anchor Bolt Anchoring Quality Based on Virtual Instruments

Boltless nylon-suture technique for stereotactic electroencephalography as a safe, effective alternative when the anchor bolt is inappropriate.

The use of anchor bolts to secure electrodes to the skull can be difficult in some clinical situations. Herein, we present the boltless technique to secure electrodes to the scalp using nylon sutures to overcome the problems associated with anchor bolts. We investigated the safety, accuracy errors, and patient-related and operative factors affecting errors in the boltless technique. This single-institution retrospective series analyzed 103 electrodes placed in 12 patients. The target-point localization error (TPLE), entry-point localization error (EPLE), radial error (RE), and depth error (DE) of the electrodes were calculated. The median of the mean operative time per electrode was 9.3min. The median TPLE, EPLE, RE, and absolute DE value were 4.1mm, 1.6mm, 2.7mm, and 1.9mm, respectively. Positive correlations were observed between the preoperative scalp thickness, mean operative time per electrode, EPLE, RE, and the absolute value of DE versus TPLE (r = .228, p = .02; r = .678, p = .015; r = .228, p = .02; r = .445, p < .01; r = .630, p < .01, respectively), and electrode approach angle versus EPLE (r = .213, p = .031). Multivariate analysis revealed that the absolute value of DE had the strongest influence on the TPLE, followed by RE and preoperative scalp thickness, respectively (β = .938, .544, .060, respectively, p < .001). No complications related to SEEG insertion and monitoring were encountered. The boltless technique using our unique planning and technical method is a safe, effective, and low-cost alternative in cases where anchor bolts are contraindicated.

Experimental study and design method of embedded concrete-filled rectangular steel tube column base under cyclic load

Embedded column base has been widely used in concrete-filled steel tube (CFST) structures due to its high rigidity and good seismic performance. However, the strength analysis of the embedded CFST column base was not yet clear since there was little experimental research on it. In this paper, the experimental investigations of six embedded concrete-filled rectangular steel tube (CFRST) column bases under constant axial load and cyclic load were carried out to study the effects of embedded depth, improvement measures and axial compression ratios on the seismic performance of the column bases. The experimental results indicated that setting stiffeners, increasing the embedded depth or axial compression ratios could improve the seismic performance of the column base. In this experiment, the critical embedded depths of the columns with or without stiffeners were 0.7 and 1.5 times the column width B respectively. When the embedded depth was 0.7B, the contribution of anchor bolts to the moment resistance capacity of the column bases could reach up to 14.2%. Based on the analysis of the force transmission mechanism between the column and the concrete foundation in the embedded CFRST column base, a design method considering the contribution of different components to the moment resistance capacity of the CFRST column bases is proposed. The prediction results are in good agreement with the tested results and collected data, within ± 15% error. The parameter analysis based on the design method has revealed the influence patterns of various parameters on the moment resistance capacity of the column bases.

Seismic Performance Evaluation and Analysis of Vertical Hydrogen Storage Vessels Based on Shaking Table Testing

In this study, the structural integrity of a system installed on protrusion concrete, considering the usability of a vertical hydrogen storage vessel, was verified. To achieve this, a site survey was conducted to select the target structure, and analytical validation was performed to design specimens for shaking table tests. Subsequently, dynamic behavior characteristics were analyzed using an artificial earthquake simulated according to the procedures outlined in ICC-ES AC 156, which is the seismic design criterion. As a result, it was observed that the seismic motion was amplified by approximately 10 times compared to the original load magnitude, based on the acceleration response of the test specimen. It is inferred that the seismic motion occurring during an earthquake could cause significant damage to both the internal and external aspects of the structure, depending on the structure’s form and the composition of materials. Through analytical verification and testing, it was revealed that the main structure of the test specimen and the anchor bolts for installation met the seismic performance criteria. However, the protrusion concrete area exhibited damage, indicating a structural vulnerability when subjected to external forces such as earthquakes. Consequently, on-site measures to address this structural risk need to be explored.

Research on Rotating Machinery Fault Diagnosis Based on an Improved Eulerian Video Motion Magnification.

Rotating machinery condition monitoring and fault diagnosis are important bases for maintenance decisions, as the vibrations generated during operation are usually imperceptible to the naked eye. Eulerian video motion magnification (EVMM) can reveal subtle changes and has been widely used in various fields such as medicine, structural analysis, and fault diagnosis, etc. However, the method has a bound relationship among three parameters: spatial wavelength, amplification factor, and displacement function, so it is necessary to adjust the parameters manually in practical applications. In this paper, on the basis of the original method, an automatic solution of spatial cutoff wavelength based on brightness is proposed. First, an input video is decomposed into image sequences, their RGB color spaces are transformed into HSV color spaces, and the Value channel image representing brightness is selected to automatically calculate the spatial cutoff frequency, and then the spatial cutoff wavelength is determined, and the motion magnification video in the specified frequency band is obtained by substituting it into the original method. Then, a publicly available video is taken as an example for simulation analysis. By comparing the time-brightness curves of the three videos (original video, motion magnification video obtained by the original method and the improved method), it is apparent that the proposed method exhibits the most significant brightness variation. Finally, taking an overhung rotor-bearing test device as the object, five conditions are set, respectively: normal, rotor unbalance, loosened anchor bolt of the bearing seat, compound fault, rotor misalignment. The proposed method is adopted to magnify the motion of the characteristic frequency bands including 1X frequency and 2X frequency. The results show that no obvious displacement is found in normal working conditions, and that the rotor unbalance fault has an overall axial shaking, the bearing seat at the loose place has an obvious vertical displacement, while the compound fault combines the both fault characteristics, and the rotor misalignment fault has an obvious axial displacement of the free-end bearing seat. The method proposed in this paper can automatically obtain the space cutoff wavelength, which solves the problem of defects arising from manually adjusting the parameters in the original method, and provides a new method for rotating machinery fault diagnosis and other fields of application.

Study on damage-stress loss coupling model of rock and prestressed anchor cable in dry-wet environment

The loss of anchoring force is one of the problems to be solved urgently. The anchorage loss is a key factor causing the failure of anchoring engineering, so it is crucial to study the time-dependent variation of anchoring force. Alternating dry and wet (D-W) conditions have a significant effect on deformation of rock. The anchoring system is composed of anchoring components and rock mass, and thus rock deformation has a significant impact on the loss of anchoring force. Quantifying rock deformation under the effects of D-W cycles is a prerequisite to understanding the factors that influence loss of anchoring force in anchor bolts. In this study, we designed an anchoring device that enabled real-time monitoring of the variation in strain during D-W periods and rock testing. Nuclear magnetic resonance (NMR) measurements showed that under D-W conditions, the increment in porosity was smaller for prestressed rock than unstressed rock. The trends of prestress loss and strain variation are consistent, which can be divided into three characteristic intervals: rapid attenuation stage, slow attenuation stage and relatively stable stage. At the same stress level, the rate of stress loss and strain for the soaking specimen was the highest, while that of the dried specimen was the lowest. In the same D-W cycling conditions, the greater the prestress, the smaller the strain loss rate of the rock, especially under soaking conditions. The characteristics of pore structure and physical mechanical parameters indicated that prestress could effectively suppress damage caused by erosion related to D-W cycles. The study reveals the fluctuation behavior of rock strain and prestress loss under D-W conditions, providing a reference for effectively controlling anchoring loss and ideas for inventing new anchoring components.

Strengthening of RC beams with inadequate lap splice length using cast-in-situ and anchored precast ECC ferrocement layers mitigating construction failure risk

Design standards necessitate the use of a sufficient lap splice length when dealing with longer spans of Reinforced Concrete (RC) members. An inadequate lap splice length results in a reduction of both the flexural strength and ductility of reinforced concrete beams. The failure risk of these beams is considered a potential threat which is experimentally identified, numerically analyzed, and carefully mitigated in this research to increase building safety and sustainability to avoid risk of construction failure. The ongoing experimental and numerical research focuses on examining the structural performance of RC beams with insufficient lap splice length, which have been fortified through various applications of Engineered Cementitious Composite (ECC) ferrocement layers. A total of eleven beams, divided into four groups, were purposefully designed and tested under bending loads until they reached the point of collapse. The investigated parameters included the casting technique, installation strategy, and anchorage length (La) for such layers. Cast in situation and pre-casting scenarios were utilized in order to cast the strengthening ECC layers. The La for all layers was designed to be the main studied variable beside type of casting and installation technique. Three La values were studied: 30D, 40D, and 50D where D is the bar diameter of main reinforcement steel in tension side. It was found that, the application of chemical anchor bolts in cast in situation ECC ferrocement layers credited the higher enhancement in both cracking and ultimate stages by about 92–137% and 114–164% for cracking and ultimate levels, respectively. Then, the experimentally measured outcomes were employed for developing nonlinear Finite Element Models (FEMs) to simulate the performance of such ECC ferrocement layers that employed. The variance between numerical results and experimental counterparts ranged in between 6% and 9%, achieving an acceptable variance.

Variation characteristics of key dynamic measurement signals of anchor bolts with different anchorage qualities under pull-out loads

Pull-out load and the cement-sand ratio (CSR) can affect the non-destructive testing (NDT) results of anchor bolts. Therefore, in this article, NDT experiments were conducted on both fully and defectively grouted anchor bolts, and variation patterns of key dynamic testing signal parameters were analyzed. A longitudinal vibration model of defectively grouted anchor bolts considering dynamic and static damping was proposed, and simulated NDT of anchor bolts with varying qualities. The results indicated that grouting defects resulted in an increase in wave velocity, along with a decrease in the fundamental frequency and dynamic stiffness of anchor bolts. When grouting defects and pull-out load acted concurrently, the fundamental frequency, and dynamic stiffness of the defectively grouted anchor bolts were consistently smaller than those of fully grouted ones during the initial loading phase. With pull-out load increasing, wave velocity decreased first, then increased; fundamental frequency increased, followed by a decrease; dynamic stiffness rose. When the CSR of defectively grouted anchor bolts was reduced, wave velocity decreased, fundamental frequency increased slightly, and a substantial increase in dynamic stiffness was observed. Pull-out loads were more sensitive to anchor bolt key dynamic signals than defects and CSR. Simulated validation demonstrated the reliability of the proposed theory.

Study on instability mechanism of soft rock roadway and pressure-relief bolt-grouting support technology

Aiming at the engineering problem of roadway deformation and instability of swelling soft rock widely existed in Kailuan mining area, the mineral composition and microstructure of such soft rock were obtained by conducting scanning electron microscopy, X-ray diffraction experiments, uniaxial and conventional triaxial tests, and the law of softening and expanding of such soft rock and the failure mechanism of surrounding rock were identified. The combined support scheme of multi-level anchor bolt, bottom corner pressure relief and fractional grouting is proposed. The roadway supporting parameters are adjusted and optimized by FLAC3D numerical simulation, and three supporting methods of multi-layer anchor bolt, bottom corner pressure relief and fractional grouting are determined and their parameters are optimized. The study results show that: the total amount of clay minerals is 53–75%, pores, fissures, nanoscale and micron layer gaps are developed, providing a penetrating channel for water infiltration to soften the surrounding rock; the three-level anchor pressure-relief and grouting support technology can control the sinking amount of the roof within 170 mm, the bottom drum amount within 210 mm, the bolts of each level is evenly distributed in tension, and the maximum stress and bottom drum displacement in the pressure relief area are significantly reduced; the pressure-relief groove promotes the development of bottom corner cracks, accelerates the secondary distribution of peripheral stress, and weakens the effect of high stress on the shallow area. Using time or displacement as the index, optimizing the grouting time, filling the primary and excavation cracks, blocking the expansion and softening effect of water on the rock mass, realizing the dynamic unity of structural yielding pressure and surrounding rock modification, has guiding significance for the support control of soft rock roadway.

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

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

Investigation on guided wave characteristics of prestressed bolts based on mechanics of incremental deformations theory

The magnitude of prestress can reflect the degree of anchor bolt failure, but currently there are relatively limited theoretical research methods for the wave characteristics of prestressed bolts. For this reason, this paper establishes a viscoelastic bolt model with prestress based on the Mechanics of Incremental Deformations theory and the Kelvin-Voight viscoelastic theory, and proposes a recursive Legendre polynomial series method (RLPSM) to solve the longitudinal guided wave propagation characteristics in free bolts with prestress. The dispersion and attenuation curves of longitudinal guided waves in free bolts with various prestresses are given, and the influences of prestress on dispersion curves are analyzed. Meanwhile, the ultrasonic guided wave detection system of free bolts with prestress is established for laboratory research, and compared with the theoretical results.