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.

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.

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.

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.

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.

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.

Evaluation of Long-term Stability of Vertical Control in Hyperdivergent Patients Treated with Temporary Anchorage Devices

This study aims to evaluate,the long-term stability of vertical control in hyperdivergent patients treated with temporary anchorage devices.The sample included 20 hyperdivergent patients without anterior open bite.The temporary anchorage devices were used to intrude the upper incisor and molars for vertical control.Lateral cephalograms were established prior to treatment,immediately after treatment,and during retention. The upper molars and incisors were intruded by 1.33 mm and 1.41 mm after treatment (P<0.05).U6-PP increased by 0.11 mm and 0.23 mm during the first and second stages of retention (P>0.05).U1-PP was found to possess a significant extrusion of 1.2 mm during the first stage (P<0.05),which increased by 0.68 mm during the second stage (P>0.05). The mandibular plane angle (MP-SN)decreased by 2.58 degrees following treatment, and underwent a relapse of 0.51 degree and 0.42 degree during the first and second stages of retention respectively (P>0.05).No significant soft tissue changes occurred,with the exception of increased upper lip length during the second stage (P<0.05).Maxillary anterior and posterior intrusions,counter clockwise rotation,of the mandibular plane,and improved profiles can be successfully achieved following treatment with vertical control. During the first stage of retention (less than three years),intruded molars and incisors both exhibited some extrusion,and molars had better long-term stability than incisors. During the second stage of retention (three to six years),the therapeutic effects appeared stable,with the exception of some increase in upper lip length.Rotated mandibular plane remained stable during the entire retention period.

Load Transfer Test of Post-Tensioned Anchorage Zone in Ultra High Performance Concrete

Researches on ultra-high performance concrete (UHPC) have been conducted worldwide owing to its outstanding durability and strength performances. The exploitation of the mechanical properties of UHPC will render it possible to achieve economic design through substantial reduction in the cross sectional dimensions and simplification in the reinforcement arrangement. This paper investigates experimentally the load transfer in the prestressed concrete anchorage zone. To provide distinctive features of UHPC compared to ordinary concrete, the cross sectional dimensions of the member were reduced and the stress distribution, deformation and cracking pattern of the PS anchorage zone were examined experimentally according to the degree of reinforcement of the members chosen. The distributions of the bursting stress, spalling stress and longitudinal edge stress in the specimens were observed according to the various types of reinforcement. All the specimens satisfied the load-bearing capacity criterion specified by the European ETAG-013 guidelines and their stress distributions were similar to those in the PS anchorages of post-tensioned members applying ordinary concrete. The cracks propagated longitudinally with lengths up to twice the cross sectional dimensions and their width was smaller than when applying ordinary concrete owing to the bridging effect of the steel fibers in UHPC. Accordingly, the exploitation of the high strength of UHPC enabled us to secure the resistance of the anchorage with no need for particular reinforcing devices.

Behavior Characteristics of Bonded Type Anchorage for CFRP Tendon

This paper examines the shear stress and displacement occurring in CFRP tendons through finite element analysis on the parameters influencing the anchoring performance to evaluate the behavioral characteristics of the bonded type anchorage for CFRP tendon. The selected parameters are the inner angle of the anchorage barrel, the friction between the barrel and filling material, and the elastic modulus of the filling material. The difference in the behavioral characteristics is examined for each parameter. In view of the analytic results, the shear stress developed in the CFRP tendon reduces with larger inner angle of the barrel and lower elastic modulus of the filling material. However, such combination provokes also the increase of the relative displacement of the CFRP tendon. Especially, slip failure may occur due to the lack of the confining force necessary for the anchorage due to the sudden loss of vertical force brought by the wedge force. The experimental results relative to barrel inner angles of 2° and 4° showed that the specimen with an angle of 2° preserved its anchoring performance up to tensile failure whereas the specimen with an angle of 4°?failed in developing its maximum anchoring performance due to slip failure.

Experimental and Numerical Study on Anchorage Strength and Deformation Properties of Blocky Rock Mass

This study experimentally and numerically investigated the anchorage properties,bolt force evolution,deformation and stress fields of blocky rock mass with various dip angles of joint surfaces under an applied axial load.The results show that due to bolt reinforcement,the axial stress-strain curves of anchorage blocky rock mass show typical strain-hardening characteristics,and comparedwithmodels without anchorage,the peak strength and elastic modulus increase by 21.56%and 20.0%,respectively.With an increase in axial stress,the lateral strain continuously increases,and restriction effects of bolts reduce the overall deformation of model surfaces.The axial stressstrain curves of anchorage blocky rock mass in the simulations present a“double peak strength”phenomenon due to bolt reinforcement,and the peak strength,second peak strength,residual strength,surface displacement field,as well as the principal stress fields all depend on the dip angles of joint surfaces.As a result of the bolt reinforcement effects,cone-shaped compression zones are produced in the models,and compression zones of adjacent bolts superimpose with each other to form anchorage belts,improving the overall bearing capacity of anchorage models.Obvious stress concentration can be observed at both bolt end and anchorage section.Not only the role of bolt support transfers the blocky rock mass to be a three-dimensional stress state through compression effects,but also it improves both tensile strength and shear resistance of both joint surfaces and the overall blocky rock mass.

Microbiological Advances in Orthodontics:An Overview and Detailed Analysis of Temporary Anchorage Devices

Dental biofilm is the initiating factor of oral diseases,such as periodontitis and caries.Orthodontic treatment could alter the microbiome structure balance,and increase the risk of such diseases.Furthermore,fixed appliances can induce temporary changes in the microbiome community,and the changes that clear aligners bring are smaller by comparison.Temporary anchorage devices(TADs)are skeletal anchorages that are widely used in orthodontic treatment.Microorganisms affect the occurrence and development of inflammation surrounding TADs.At present,existing researches have verified the existence of plaque biofilm on the surface of TADs,but the formation of plaque biofilm and plaque composition under different stable conditions have not been fully understood.The development of high-throughput sequencing,molecular biology experiments,and metabonomics have provided new research ideas to solve this problem.They can become an effective means to explore the microbiome surrounding TADs.

Focal mechanism inversion of the 2018 M_(W)7.1 Anchorage earthquake based on high-rate GPS observation

The M_(W)7.1 Anchorage earthquake is the most destructive earthquake since the 1964 M_(W)9.2 great Alaska earthquake in the United States.In this study,high-rate GPS data and near-field broadband seismograms are used in separate and joint inversions by the generalized Cut-and-Paste(gCAP)method to estimate the focal mechanism.In order to investigate the influence of crustal velocity structure on the focal mechanism inversion results,two velocity models(Crustl.0 and Alaska Earthquake Center(AEC))are used for detailed comparison and analysis.The results show that:(1)The two nodal planes of the optimal double-couple solution are nearly north-south striking,with dip angles of about 30°and 60°respectively,and the centroid focal depth is 54-55 km,which is an intraplate normal fault event.(2)The inversion results for the two types of data and the two velocity models are consistent with some previous studies,which indicates that the results are stable and reliable.The more accurate velocity structure model is helpful for focal mechanism inversion of the complex earthquake.(3)The inclusion of high-rate GPS data in joint inversion provides a more effective constraint on centroid depth.

Analysis on Bearing Capacity of Tunnel-Type Anchorage of a Long-Span Suspension Bridge

Due to complicated rock structure and environment, a prototype test for a tunnel-type anchorage is infeasible. Based on the rock mass parameters from tests, a three-dimensional （3D） elastoplastic analysis was performed to simulate the influence of the construction procedure of Siduhe bridge with tunnel-type anchorage （TTA） in Hubei Province, China. The surrounding rock and concrete anchorage body were simulated by 8 nodes 3D brick elements. The geostatic state of the complex geometric structure was established with initial data. The in-situ concrete casting of the anchorage body and excavation of the rock mass were simulated by tetrahedral shell elements. The results show that the surrounding rock is in an elastic state under the designed cable force. The numerical overloading analysis indicates that the capacity of the surrounding anchorage is 7 times that of the designed cable force. The failure pattern shows that two anchorage bodies would be pulled out in the end. The maximum shear stress appears 10 m before the back anchorage face. The maximum range influenced by the TTA under ultimate loads is about 16 m.

A New Thionine Modified Electrode by Anchorage to Bi-(2-aminoethyl)-aminodithiocarboxyl Acid Self-assembled Monolayers through Coordination with Cu^(2+#)

A new method for preparing chemically modified gold electrode by anchoring thionine to self-assembled bi - (2 -aminoethyl) -aminodithiocarboxyl acid(BANTC) monolayers through coordination with Cu2+ is described. This thionine modified electrode exhibits two-new redox couples.Two protons were involved in the electrochemical process undergone by the couple I in the pH range of 5.0-10.0. The apparent surface electron transfer rate constant is about 0.050s-1.

Study on Fatigue Behavior of Anchorage of Cable and Girder of Long Span Cable-Stayed Bridge

A full scale model test is done and a FEM model is established to investigate the fatigue behavior of the Nancha cable stayed bridge of the Nanjing Second Yangtz River Bridge, a long span steel bridge with a main span of 628 m. The results of test and FEM are analyzed and compared. It is shown that they are in good agreement. It is verified that the fatigue characteristic of the anchorage structure of cable and girder of the bridge satisfies the requirements specified by Chinese, British and American codes.

Orthodontic Intrusion of over Erupted Permanent Maxillary Molars Using Temporary Anchorage Devices

In most cases, damaged mandibular molars result in over eruption of the opposing maxillary molars. This by itself constitutes a complicated clinical scenario;since the rehabilitation of the edentulous mandibular space usually requires a pre-prosthetic intervention. Multiple treatment options are valid and the choice depends primarily on the severity of the problem. Orthodontic molar intrusion is one of these options. This case report shows how the supra erupted maxillary permanent molars were intruded with the help of temporary anchorage devices placed interradicularly between the maxillary posterior teeth. A total of nine months was enough to complete the treatment. Following the orthodontic molar intrusion, the lower edentulous spaces were restored with dental implant supported prosthesis in order to establish a stable functional occlusion.

Stress Analysis of New Type Pre-Stressed Anchor Bearing Plate Combining Stamping with Welding Forming and Its Anchorage Zone

An anchor bearing plate transfers the anchoring force from anchor plate to the concrete and the pre-stress is formed in the concrete structure. Currently, the main type of anchor bearing plate is cast iron. It is brittle during transportation and tension process. This paper presents a new type of anchor bearing plate combined stamping with welding forming. The structure of the new type anchor bearing plate is introduced. The stress states of the anchor bearing plate and anchorage zone under work are studied. Various specifications of anchor bearing plate are studied by ANSYS finite element analysis software following the AASHTO specification. The analysis results are compared with the results of the same type of OVM round-shaped anchor plate. The study results show that the new pre-stressed anchor plates combined stamping with welding forming are feasible and more sturdy which can meet the engineering demand.

Strut-and-Tie Method as a Basis for Optimization of Hoop Prestressed Tendons in Abnormally Shaped Anchorage Zone of Cable-Stayed Bridge Pylon

Based on full-scale segment model tests of the abnormally shaped anchorage zone of the Maling River cable-stayed bridge pylon and FEM analysis, its mechanical and deformation properties were obtained, and the validity of FEM analysis was verified. An optimal layout of prestressed tendons in the anchorage zone was obtained by using the strut-and-tie method （STM）. The comparison FEM analysis between the full-scale segment model and the optimal prestressed tendons model show that： the optimal model not only saves prestressed tendons, but also achieves the same cracking resistance; STM method is reliable and accurate in the analysis of the abnormally shaped anchorage zone of cable-stayed bridge pylon.