Finite difference method for dynamic response analysis of anchorage system

Based on some assumptions, the dynamic analysis model of anchorage system is established. The dynamic governing equation is expressed as finite difference format and programmed by using MATLAB language. Compared with theoretical method, the finite difference method has been verified to be feasible by a case study. It is found that under seismic loading, the dynamic response of anchorage system is synchronously fluctuated with the seismic vibration. The change of displacement amplitude of material points is slight, and comparatively speaking, the displacement amplitude of the outside point is a little larger than that of the inside point, which shows amplification effect of surface. While the axial force amplitude transforms considerably from the inside to the outside. It increases first and reaches the peak value in the intersection between the anchoring section and free section, then decreases slowly in the free section. When considering damping effect of anchorage system, the finite difference method can reflect the time attenuation characteristic better, and the calculating result would be safer and more reasonable than the dynamic steady-state theoretical method. What is more, the finite difference method can be applied to the dynamic response analysis of harmonic and seismic random vibration for all kinds of anchor, and hence has a broad application prospect.

Numerical experimental study on optimum design of anchorage system for Xiashu loess slope

In FLAC ^(3D),cable element or modified pile element can be used to build slope anchoring model.However,the difference between the two structural elements and their influence on the calculation results have not been studied in depth.In order to solve this problem,the Xiashu loess slope anchoring models based on cable element and modified pile element were constructed respectively.A variety of anchoring schemes were designed by orthogonal experiment method,and then they were brought into the model for calculation and the calculation results were analyzed by range analysis and variance analysis.The results show that the modified pile element can bear the bending moment and reflect the strain softening property of the grout.From the perspective of slope safety factor,the anchorage length and anchor bolt spacing are the main factors affecting the stability of the slope,and the anchorage angle is the secondary factor.The grout in cable element is assumed to be an elastic-perfectly plastic material,so the safety factor of the slope can be significantly increased by increasing the length of the anchor bolts.This will bring potential risks to the slope treatment project.Therefore,in the calculation of the slope anchoring model,the modified pile element is more suitable for simulating the anchor bolt.

Basic dynamic characteristics and seismic design of anchorage system

Based on some assumptions,the dynamic governing equation of anchorage system is established.The calculation formula of natural frequency and the corresponding vibration mode are deduced.Besides,the feasibility of the theoretical method is verified by using a specific example combined with other methods.It is found that the low-order natural frequency corresponds to the first mode of vibration,and the high-order natural frequency corresponds to the second mode of vibration,while the third mode happens only when the physical and mechanical parameters of anchorage system meet certain conditions.With the increasing of the order of natural frequency,the influence on the dynamic mechanical response of anchorage system decreases gradually.Additionally,a calculating method,which can find the dangerous area of anchorage engineering in different construction sites and avoid the unreasonable design of anchor that may cause resonance,is proposed to meet the seismic precautionary requirements.This method is verified to be feasible and effective by being applied to an actual project.The study of basic dynamic features of anchorage system can provide a theoretical guidance for anchor seismic design and fast evaluation of anchor design scheme.

Three-dimensional Finite Element Analysis of a Newly Designed Onplant Miniplate Anchorage System

The purpose of this research was to evaluate the structural stress and deformation of a newly designed onplant miniplate anchorage system compared to a standard anchorage system. A bone block integrated with a novel miniplate and fixation screw system was simulated in a three-dimensional model and subjected to force at different directions. The stress distribution and deformation of the miniplate system and cortical bone were evaluated using the three-dimensional finite element method. The results showed that the stress on the plate system and bone was linearly proportional to the force magnitude and was higher when the force was in a vertical direction（Y-axis）. Stress and deformation values of the two screws（screw 1 and 2） were asymmetric when the force was added along Y-axis and was greater in screw 1. The highest deformation value of the screws was 7.5148 μm, much smaller than the limit value. The load was decreased for each single miniscrew, and the ability of the new anchorage system to bear the load was also enhanced to some degree. It was suggested that the newly designed onplant miniplate anchorage system is effective, easily implanted and minimally invasive.

A genetic algorithm for dynamic parameters reverse deduction of integrated anchorage system

In the analysis of the system of anchoring bar and wall rock in small strain and longitudinal vibration dynamic response, the influence of the cement grouting as well as the rock layer on the anchor bar can be evaluated as the two kinds of parameters: the dynamic stiffness and the damp, which are the vital reference of the anchorage quality. Based on the analytic solution to the dynamic equation of the integrated anchor bar, the new approach which combines genetic algorithm and the toolbox of Matlab is applied to solve the problem of multi-parameters reverse deduction for integrated anchorage system in dynamic testing. Using the traits of the self-organizing, self-adapting and the fast convergence speed of the genetic algorithm, the optimum of all possible solutions to dynamic parameters is obtained by calculating the project instances. Examples show that the method presented in this paper is effective and reliable.

Safety analysis of temporary anchorage system for immersed tube in Shenzhen-Zhongshan Link

In the construction of the Shenzhen-Zhongshan Link,a temporary anchorage system,distributed uniformly along the pipe wall,has been employed.To assess the safety and reliability of this system,a combined method utilizing numerical analysis and model experiments was applied to study the safety of the temporary anchorage system and the reliability of the tension rods.Firstly,an overall model of the caisson segment based on GINA rebound force was established to analyze the stress state of the entire system.Secondly,a comprehensive numerical analysis and model experiment verification were conducted for the single tensioning system,revealing its failure mode and safety margin.The results indicate that the tension rod systems are uniformly stressed at an average of 444 k N during underwater jointing,with a safety factor of 1.94.At this point,the maximum von Mises stresses appearing at the front plate corners and the lower edge of the U-groove,with stress values of 181.8 MPa and 172.4 MPa,and safety factors of 1.54 and 1.71,respectively.When the tension rod force reaches 940 k N,the tensioning system reaches its bearing limit,with initial yielding occurring at the front plate corners.Model experiments were conducted to verify the theoretical analysis results,under a test load of 444 k N,the stresses at the front plate corners and the lower edge of the U-groove were 159.6 and 195.9 MPa,respectively.As the test load increased to 940 k N,these stresses reached 390 and 389 MPa,exhibiting good agreement with the numerical analysis.Considering the uncertainty of loads and materials,a reliability analysis of the tension rods was conducted,yielding a reliability index of 4.34,meeting the secondary safety standard.Based on the comprehensive analysis,it can be concluded that the temporary anchorage system in the caisson segments of the Shenzhen-Zhongshan Link exhibits excellent safety margins.

Development of multi-functional anchorage support dynamic-static coupling performance test system and its application

In underground engineering with complex conditions,the bolt(cable)anchorage support system is in an environment where static and dynamic stresses coexist,under the action of geological conditions such as high stresses and strong disturbances and construction conditions such as the application of high prestress.It is essential to study the support components performance under dynamic-static coupling conditions.Based on this,a multi-functional anchorage support dynamic-static coupling performance test system(MAC system)is developed,which can achieve 7 types of testing functions,including single component performance,anchored net performance,anchored rock performance and so on.The bolt and cable mechanical tests are conducted by MAC system under different prestress levels.The results showed that compared to the non-prestress condition,the impact resistance performance of prestressed bolts(cables)is significantly reduced.In the prestress range of 50–160 k N,the maximum reduction rate of impact energy resisted by different types of bolts is 53.9%–61.5%compared to non-prestress condition.In the prestress range of 150–300 k N,the impact energy resisted by high-strength cable is reduced by76.8%–84.6%compared to non-prestress condition.The MAC system achieves dynamic-static coupling performance test,which provide an effective means for the design of anchorage support system.

Optimization of anchorage support parameters for soft rock tunnel based on displacement control theory

In the construction of a soft rock tunnel,it is critical to accurately estimate the pre-stressed anchor support parameters for surrounding rock reinforcement;otherwise,engineering disasters may occur.This paper presents a support parameter selection method that aims to allow deformation as a control objective,which was applied to the tunnel located in Muzailing Highway,Min County,Dingxi City,Gansu Province,China.Through theoretical analysis,we have identified five factors that influence pre-stressing anchorages.The selection of mechanical parameters for the rock mass was carried out using an inverse analysis method.Compared with the measured data,the maximum displacement error of the numerical simulation results was only 0.07 m.The length of anchor cable,circumferential spacing of anchor cable,longitudinal spacing,and pre-stress index are adopted as the input parameters for the support vector machine neural network model based on particle swarm optimization(PSO-LSSVM).Besides,the vault subsidence and the maximum deformation of surrounding rock are considered as output values(performance indices).The goodness of fit between the predicted values and the simulated values exceeds 0.9.Finally,all support parameters within the acceptable deformation range are calculated.The optimal support variables are derived by considering the construction cost and duration.The field application results show that it is feasible to construct the sample database utilizing the numerical simulation approach by taking the displacement as the control target and using the neural network to specify the appropriate support parameters.

Numerical simulation study on shear resistance of anchorage joints considering tensile-shear fracture criterion of 2G-NPR bolt

2G-NPR bolt (the 2nd generation Negative Poisson’s Ratio bolt) is a new type of bolt with high strength, high toughness and no yield platform. It has signifcant efects on improving the shear strength of jointed rock mass and controlling the stability of surrounding rock. To achieve an accurate simulation of bolted joint shear tests, we have studied a numerical simulation method that takes into account the 2G-NPR bolt's tensile–shear fracture criterion. Firstly, the indoor experimental study on the tensile–shear mechanical properties of 2G-NPR bolt is carried out to explore its mechanical properties under diferent tensile–shear angles, and the fracture criterion of 2G-NPR bolt considering the tensile–shear angle is established. Then, a three-dimensional numerical simulation method considering the tensile–shear mechanical constitutive and fracture criterion of 2G-NPR bolt, the elastoplastic mechanical behavior of surrounding rock and the damage and deterioration of grouting body is proposed. The feasibility and accuracy of the method are verifed by comparing with the indoor shear test results of 2G-NPR bolt anchorage joints. Finally, based on the numerical simulation results, the deformation and stress of the bolt, the distribution of the plastic zone of the rock mass, the stress distribution and the damage of the grouting body are analyzed in detail. The research results can provide a good reference value for the practical engineering application and shear mechanical performance analysis of 2G-NPR bolt.

Effects of anti-pull ties on the bearing behaviors of shallow tunnel-type anchorages in soft rock

Tunnel-type anchorages(TTAs)installed in human gathering areas are characterized by a shallow burial depth,and in many instances,they utilize soft rock as the bearing stratum.However,the stability control measures and the principle of shallow TTAs in soft rock have not been fully studied.Hence,a structure suitable for improving the stability of shallow TTAs in soft rock strata,named the anti-pull tie(APT),was added to the floor of the back face.Physical tests and numerical models were established to study the influence of the APT on the load transfer of TTAs,the mechanical response of the surrounding rock,the stress distribution of the interface,and the failure model.The mechanical characteristics of APTs were also studied.The results show that the ultimate bearing capacity of TTAs with an APT is increased by approximately 11.8%,as compared to the TTAs without an APT.Also,the bearing capacity of TTAs increases approximately linearly with increasing height,width,length,and quantity of APTs,and decreases approximately linearly with increasing distance from the back face and slope angle of the tie slope.The normal squeezing between the tie slope and the surrounding rock increases the shear resistance of the interface and expands the range of the surrounding rock participating in bearing sharing.Both tension and compression zones exist in the APT during loading.The tension zone extends from the tie toe to the tie bottom along the tie slope.The range of the tie body tension zone constantly expands to the deep part of the APT with an increasing load.The peak tensile stress value is located at the tie toe.The distribution of compressive stress in the tie body is the largest at the tie top,followed by the tie slope,and then the tie bottom.

A Study of the system control model of caisson dewatering of the north anchorage of Taizhou Bridge

A caisson foundation is applied to the north anchorage of Taizhou Yangtze River Highway Bridge of which the initial caisson sinking requires dewatering. Since the caisson foundation is quite close to nearby buildings, a system control model is established with source (sink) distribution and intensity being the object function, minimum requirements of settlement and deformation of surroundings caused by dewatering and dynamic water levels during different working procedures being constraints, and the design parameter of pumping wells being the variable,so as to lower the jeopardizing of surrounding buildings, which provides a new method for active control over settlement during dewatering. Such a method of dewatering based on system control model should be of significance for similar projects involving dewatering.

Is it possible to anchor a tooth with photobiomodulation?

During orthodontic treatment,we can achieve differential movements by using photobiomodulation(PBM)as an adjuvant before applying force.We can expect a greater bone density that initially resists movement while applying PBM to the other teeth to achieve an accelerating effect.The proposed protocol is to use an 810 nm laser at 0.1W power,applying between 4 and 6J per tooth for 22 s on the vestibular and lingual root surfaces,following the axial axis of the tooth.The energy density depends on the tip selected in the instrument.Normal bone remodeling cannot be avoided by applying high doses of PBM.PBM should be applied before orthodontic force to reduce tooth movement.In addition,PBM can be used during force application to teeth that require acceleration to achieve differential movement in orthodontic treatments.The protocol is the same in both scenarios.

Reliability analysis for anchorage of reinforced concrete beams with longitudinal cracks due to corrosion at anchorage zone

An anchorage reliability analysis approach for simply supported reinforced concrete beams under corrosion attack in the anchorage zone is developed.The first-order second-moment method is employed to analyze the effects of various factors on the anchorage reliability.These factors include both the length and width of cover cracking due to reinforcement corrosion,the cover thickness,the anchorage length,and the stirrup ratio.The results show that the effect of corrosion-induced crack length on the reliability index for anchorage,β0,is negligible when the crack on the concrete surface is just appearing,but with the crack widening,the β0 value is reduced significantly;the considerable changes in β0 result from a variation in cover depth and anchorage length;the effect of changes in the diameter or space of stirrups on the anchorage resistance is very limited,and the variation in β0 is also very low.

Deformation and failure characteristics of anchorage structure of surrounding rock in deep roadway

This paper investigated the stress evolution,displacement field,local deformation and its overall distribution,and failure characteristics of the anchorage structure of surrounding rock with different rockbolt spacing through the model experiments.The influences of the pre-tightening force and spacing of rockbolt on the support strength of the anchorage structure of surrounding rock were analyzed by the simulation using FLAC3D numerical software.The support scheme of the excavated roadway was then designed,and the effectiveness of this support scheme was further verified by the displacement measurement of the roadway.The results showed that the maximum displacement between the roof and floor of the west wing track roadway in Kouzidong coal mine,China is about 42 mm,and the maximum displacement between its both sides is about 72 mm,indicating that the support scheme proposed in this study can ensure the stability and safety of the excavated roadway.

Bearing mechanism of a tunnel-type anchorage in a railway suspension bridge

A tunnel-type anchorage(TTA)is one of the main components in suspension bridges:the bearing mechanism is a key problem.Investigating the deformation characteristics,development law,and failure phenomenon of a TTA under load can provide the theoretical basis for a robust design.Utilizing the TTA of the Jinsha River suspension bridge at Lijiang Shangri-La railway as a prototype,a laboratory model test of the TTA was carried out for three different contact conditions between the anchorage body and the surrounding rock.The stress and deformation distribution law of the anchorage body and its surrounding rock were studied,and the ultimate bearing capacity and failure mode of the TTA were analyzed.The test results show that the compressive stress level is highest at the rear part of the anchorage body.Moving away from the rear portion of the body,the stress decays in a negative exponential function.Based on the load transfer curve,the calculation formula for the shear stress on the contact surface between the anchorage body and the surrounding rock was derived,which shows that the distribution of the shear stress along the axial direction of the anchorage body is not uniform.The distance from the maximum value to the loading surface is approximately 1/3 of the length of the anchorage body,and the stress decreases as the distance from the loading surface increases.Furthermore,the contact condition between the anchorage body and surrounding rock has a great influence on the bearing capacity of the TTA.The increase in the anti-skid tooth ridge and radial anchor bolt can improve the cooperative working capacity of the anchorage body and the surrounding rock,which is approximately 50%higher than that of the flat contact condition.The main function of the anchor bolt is to increase the overall rigidity of the TTA.The contact condition between the anchorage body and the surrounding rock will lead to a change in the failure mode of the TTA.With an increase in the degree of contact,the failure mode will change from shear sliding along the interface to trumpet-shaped inverted cone-shaped failure extending into the surrounding rock.

Intrusion of Overerupted Maxillary Molars with Miniscrew Implant Anchorage: A Radiographic Evaluation

The aim of this retrospective study was to quantitatively evaluate the treatment effects of in- trusion of overerupted maxillary molars using miniscrew implant anchorage and to investigate the apical root resorption after molar intrusion. The subjects included 30 patients whose average ages were 35.5±9.0 years. All patients had received intrusion treatments for overerupted maxillary molars with miniscrew anchorage. There were 38 maxillary first molars and 26 maxillary second molars to be in- truded. Two miniscrews were inserted in the buccal and palatal alveolar bone mesial to the overerupted molar. Force of 100-150 g was applied by the elastic chains between screw head and attachment on each side. Lateral cephalograms and panoramic radiographs taken before and after intrusion were used to evaluate dental changes and root resorption of molars. Only 6 of the 128 miniscrews failed. The first and second molars were significantly intruded by averages of 3.4 mm and 3.1 mm respectively （P〈0.001）. The average intrusion time was more than 6 months. The crown of the molars mesially tilted by averages of 3.1 degrees and 3.3 degrees （P〈0.001） for first and second molars. The amounts of root resorption were 0.2-0.4 mm on average. The intrusion treatment of overerupted molars with miniscrew anchorages could be used as an efficient and reliable method to recover lost restoration space for pros- thesis. Radiographically speaking, root resorption of molars was not clinically significant after applica- tion of intrusive forces of 200 to 300 g.

Influence of anchorage length and pretension on the working resistance of rock bolt based on its tensile characteristics

In coal mining roadway support design,the working resistance of the rock bolt is the key factor affecting its maximum support load.Effective improvement of the working resistance is of great significance to roadway support.Based on the rock bolt’s tensile characteristics and the mining roadway surrounding rock deformation,a mechanical model for calculating the working resistance of the rock bolt was established and solved.Taking the mining roadway of the 17102(3)working face at the Panji No.3 Coal Mine of China as a research site,with a quadrilateral section roadway,the influence of pretension and anchorage length on the working resistance of high-strength and ordinary rock bolts in the middle and corner of the roadway is studied.The results show that when the bolt is in the elastic stage,increasing the pretension and anchorage length can effectively improve the working resistance.When the bolt is in the yield and strain-strengthening stages,increasing the pretension and anchorage length cannot effectively improve the working resistance.The influence of pretension and anchorage length on the ordinary and high-strength bolts is similar.The ordinary bolt’s working resistance is approximately 25 kN less than that of the high-strength bolt.When pretension and anchorage length are considered separately,the best pretensions of the high-strength bolt in the middle of the roadway side and the roadway corner are 41.55 and 104.26 kN,respectively,and the best anchorage lengths are 1.54 and 2.12 m,respectively.The best anchorage length of the ordinary bolt is the same as that of the high-strength bolt,and the best pretension for the ordinary bolt in the middle of the roadway side and at the roadway corner is 33.51 and 85.12 kN,respectively.The research results can provide a theoretical basis for supporting the design of quadrilateral mining roadways.

Model test of the stability degradation of a prestressed anchored rock slope system in a corrosive environment

The long-term stability of a prestressed anchored slope might be influenced by the durability of the anchorage structure.To understand long-term stability of anchored rock slopes,the research presented herein evaluated the performance evolution of a prestressed anchored bedding slope system in a corrosive environment by model test.The corrosion process in a prestressed anchor bar was monitored in terms of its open-circuit potential(OCP),corrosion current density(CCD),and electrochemical impedance spectroscopy(EIS).The stability of the prestressed anchored slope was evaluated by monitoring changes in anchorage force and displacements.The experimental results show that prestress and oxygen could reduce the corrosion resistance of the anchor bar,and anchor bars in a chloride-rich environment are very susceptible to corrosion.Prestressed tendons in a corrosive environment suffer a loss of anchorage force,the prestress decreases rapidly after locking,and the rate thereof decreases until stabilising;in the later stage,corrosion leads to the reduction of the cross-sectional area of the steel bar which may cause the reduction in anchorage force again.Anchorage force controls the deformation and stability of the anchored slope,the prestress loss caused by later corrosion may lead to an increased rate of displacement and stability degradation of the prestressed anchored rock slope.

Systematic review of mini-implant displacement under orthodontic loading

A growing number of studies have reported that mini-implants do not remain in exactly the same position during treatment, although they remain stable. The aim of this review was to collect data regarding primary displacement immediately straight after loading and secondary displacement over time. A systematic review was performed to investigate primary and secondary displacement. The amount and type of displacement were recorded. A total of 27 studies were included. Sixteen in vitro studies or studies using finite element analysis addressed primary displacement, and nine clinical studies and two animal studies addressed secondary displacement. Significant primary displacement was detected （6.4-24.4 μm） for relevant orthodontic forces （0.5-2.5 N）. The mean secondary displacement ranged from 0 to 2.7 mm for entire mini-implants, The maximum values for each clinical study ranged from 1.0 to 4.1 mm for the head, 1.0 to 1.5 for the body and 1,0 to 1.92 mm for the tail part. The most frequent type of movement was controlled tipping or bodily movement. Primary displacement did not reach a clinically significant level. However, clinicians can expect relevant secondary displacement in the direction of force. Consequently, decentralized insertion within the inter-radicular space, away from force direction, might be favourable. More evidence is needed to provide quantitative recommendations.

Long-term Hardening Characteristics of Prestressed Anchorage Grout

Grout plays an important role in the transmission and maintenance of anchoring force,and in the protection of anchorage materials against corrosion.Thus,the hardening characteristics of grout directly affect the anchoring effectivity and long-term reliability.We have excavated a prestressed anchorage which has been in service for 20 years,and have tested the grout which has worked for that long period under complicated geological conditions through strength tests and have analyzed its mineral composition using scanning electron microscopy(SEM) and X-ray diffraction(XRD).The results show that the mineral composition of the 12.5 m segment differs from other segments,and corresponds with poor coagulation characteristics of the 12.5 m segment grout.Analysis shows that unhydrated tricalcium silicate may be the reason for the localized poor coagulation.