Flexible pavement longitudinal joint quality evaluation using non-destructive testing

Longitudinal joint construction quality is critical to the life of flexible pavements.Maintaining deteriorated longitudinal joints has become a challenge for many highway agencies.Improving the joint's quality through better compaction during construction can help achieve flexible pavements with longer service lives and less maintenance.Current quality control(QC)and quality assurance(QA)plans provide limited coverage.Consequently,the risk of missing areas with poor joint compaction is significant.A density profiling system(DPS)is a non-destructive alternative to conventional destructive evaluation methods.It can provide quick and continuous real-time coverage of the compaction during construction in dielectrics.The paper presents several case studies comparing various types of longitudinal joints and demonstrating the use of DPS to evaluate the joint's compaction quality.The paper shows that dielectric measurements can provide valuable insight into the ability of various construction techniques to achieve adequate levels of compaction at the longitudinal joint.The paper proposes a dielectric-based longitudinal joint quality index(LJQI)to evaluate the relative compaction of the joint during construction.It also shows that adopting DPS for assessing the compaction of longitudinal joints can minimize the risk of agencies accepting poorly constructed joints,identify locations of poor quality during construction,and achieve better-performing flexible pavements.

Seismic performance of double- skin steel- concrete composite box piers: Part Ⅰ——Bidirectional quasi-static testing

To study the seismic performance of double-skin steelconcrete composite box（ DSCB） piers, a total of 11 DSCB pier specimens were tested under bidirectional cyclic loading. The effects of the loading pattern, the steel plate thickness, the axial load ratio, the slenderness ratio and the aspect ratio were taken into consideration. The damage evolution process and failure modes of the tested specimens are presented in detail. Test results are also discussed in terms of the hysteretic curve, skeleton curve, ductility and energy dissipation capacity of DSCB pier specimens. It can be concluded that the hysteretic performance of DSCB piers in one direction is affected and weakened by the cyclic loading in the other direction. DSCB piers under bidirectional cyclic loading exhibit good performance in terms of load carrying capacity, ductility, and energy dissipation capacity. Overall, DSCB piers can meet the basic aseismic requirements. The research results can be taken as a reference for using DSCB piers as high piers in bridges in strong earthquakeprone areas.

Seismic performance evaluation of an infilled rocking wall frame structure through quasi-static cyclic testing

Earthquake investigations have illustrated that even code-compliant reinforced concrete frames may suffer from soft-story mechanism.This damage mode results in poor ductility and limited energy dissipation.Continuous components offer alternatives that may avoid such failures.A novel infilled rocking wall frame system is proposed that takes advantage of continuous component and rocking characteristics.Previous studies have investigated similar systems that combine a reinforced concrete frame and a wall with rocking behavior used.However,a large-scale experimental study of a reinforced concrete frame combined with a rocking wall has not been reported.In this study,a seismic performance evaluation of the newly proposed infilled rocking wall frame structure was conducted through quasi-static cyclic testing.Critical joints were designed and verified.Numerical models were established and calibrated to estimate frame shear forces.The results evaluation demonstrate that an infilled rocking wall frame can effectively avoid soft-story mechanisms.Capacity and initial stiffness are greatly improved and self-centering behavior is achieved with the help of the infilled rocking wall.Drift distribution becomes more uniform with height.Concrete cracks and damage occurs in desired areas.The infilled rocking wall frame offers a promising approach to achieving seismic resilience.

Cyclic shear behavior of en-echelon joints under constant normal stiffness conditions

To reveal the mechanism of shear failure of en-echelon joints under cyclic loading,such as during earthquakes,we conducted a series of cyclic shear tests of en-echelon joints under constant normal stiffness(CNS)conditions.We analyzed the evolution of shear stress,normal stress,stress path,dilatancy characteristics,and friction coefficient and revealed the failure mechanisms of en-echelon joints at different angles.The results show that the cyclic shear behavior of the en-echelon joints is closely related to the joint angle,with the shear strength at a positive angle exceeding that at a negative angle during shear cycles.As the number of cycles increases,the shear strength decreases rapidly,and the difference between the varying angles gradually decreases.Dilation occurs in the early shear cycles(1 and 2),while contraction is the main feature in later cycles(310).The friction coefficient decreases with the number of cycles and exhibits a more significant sensitivity to joint angles than shear cycles.The joint angle determines the asperities on the rupture surfaces and the block size,and thus determines the subsequent shear failure mode(block crushing and asperity degradation).At positive angles,block size is more greater and asperities on the rupture surface are smaller than at nonpositive angles.Therefore,the cyclic shear behavior is controlled by block crushing at positive angles and asperity degradation at negative angles.

Assessment of cyclic deformation and critical stress amplitude of jointed rocks via cyclic triaxial testing

Jointed rock specimens with a natural replicated joint surface oriented at a mean dip angle of 60were prepared,and a series of cyclic triaxial tests was performed at different confining pressures and cyclic deviatoric stress amplitudes.The samples were subjected to 10,000 loading-unloading cycles with a frequency of 8 Hz.At each level of confining pressure,the applied cyclic deviatoric stress amplitude was increased incrementally until excessive deformation of the jointed rock specimen was observed.Analysis of the test results indicated that there existed a critical cyclic deviatoric stress amplitude(i.e.critical dynamic deviatoric stress)beyond which the jointed rock specimens yielded.The measured critical dynamic deviatoric stress was less than the corresponding static deviatoric stress.At cyclic deviatoric stress amplitudes less than the critical dynamic deviatoric stress,minor cumulative residual axial strains were observed,resulting in hysteretic damping.However,for cyclic deviatoric stresses beyond the critical dynamic deviatoric stress,the plastic strains increased promptly,and the resilient moduli degraded rapidly during the initial loading cycles.Cyclic triaxial test results showed that at higher confining pressures,the ultimate residual axial strain attained by the jointed rock specimen decreased,the steadystate dissipated energy density and steady-state damping ratio per load cycle decreased,while steadystate resilient moduli increased.

A novel method for geometric quality assurance of rock joint replicas in direct shear testing-Part 2:Validation and mechanical replicability

Each rock joint is unique by nature which means that utilization of replicas in direct shear tests is required in experimental parameter studies.However,a method to acquire knowledge about the ability of the replicas to imitate the shear mechanical behavior of the rock joint and their dispersion in direct shear testing is lacking.In this study,a novel method is presented for geometric quality assurance of replicas.The aim is to facilitate generation of high-quality direct shear testing data as a prerequisite for reliable subsequent analyses of the results.In Part 1 of this study,two quality assurance parameters,smf and V_(Hp100),are derived and their usefulness for evaluation of geometric deviations,i.e.geometric reproducibility,is shown.In Part 2,the parameters are validated by showing a correlation between the parameters and the shear mechanical behavior,which qualifies the parameters for usage in the quality assurance method.Unique results from direct shear tests presenting comparisons between replicas and the rock joint show that replicas fulfilling proposed threshold values of σ_(mf)<0.06 mm and
|V_(Hp100)|
<0.2 mm have a narrow dispersion and imitate the shear mechanical behavior of the rock joint in all aspects apart from having a slightly lower peak shear strength.The wear in these replicas,which have similar morphology as the rock joint,is in the same areas as in the rock joint.The wear is slightly larger in the rock joint and therefore the discrepancy in peak shear strength derives from differences in material properties,possibly from differences in toughness.It is shown by application of the suggested method that the quality assured replicas manufactured following the process employed in this study phenomenologically capture the shear strength characteristics,which makes them useful in parameter studies.

A statistical damage-based constitutive model for shearing of rock joints in brittle drop mode

Some rock joints exhibit significant brittleness,characterized by a sharp decrease in shear stress upon reaching the peak strength.However,existing models often fail to accurately represent this behavior and are encumbered by numerous parameters lacking clear mechanical significance.This study presents a new statistical damage constitutive model rooted in both damage mechanics and statistics,containing only three model parameters.The proposed model encompasses all stages of joint shearing,including the compaction stage,linear stage,plastic yielding stage,drop stage,strain softening stage,and residual strength stage.To derive the analytical expression of the constitutive model,three boundary conditions are introduced.Experimental data from both natural and artificial rock joints is utilized to validate the model,resulting in average absolute relative errors ranging from 3%to 8%.Moreover,a comparative analysis with established models illustrates that the proposed model captures stress drop and post-peak strain softening more effectively,with model parameters possessing clearer mechanical interpretations.Furthermore,parameter analysis is conducted to investigate the impacts of model parameters on the curves and unveil the relationship between these parameters and the mechanical properties of rock joints.Importantly,the proposed model is straightforward in form,and all model parameters can be obtained from direct shear tests,thus facilitating the utilization in numerical simulations.

Unstable evolution of railway slope under the rainfall-vibration joint action

Understanding the unstable evolution of railway slopes is the premise for preventing slope failure and ensuring the safe operation of trains.However,as two major factors affecting the stability of railway slopes,few scholars have explored the unstable evolution of railway slopes under the joint action of rainfall-vibration.Based on the model test of sandy soil slope,the unstable evolution process of slope under locomotive vibration,rainfall,and rainfall-vibration joint action conditions was simulated in this paper.By comparing and analyzing the variation trends of soil pressure and water content of slope under these conditions,the change laws of pore pressure under the influence of vibration and rainfall were explored.The main control factors affecting the stability of slope structure under the joint action conditions were further defined.Combined with the slope failure phenomena under these three conditions,the causes of slope instability resulting from each leading factor were clarified.Finally,according to the above conclusions,the unstable evolution of the slope under the rainfall-vibration joint action was determined.The test results show that the unstable evolution process of sandy soil slope,under the rainfall-vibration joint action,can be divided into:rainfall erosion cracking,vibration promotion penetrating,and slope instability sliding three stages.In the process of slope unstable evolution,rainfall and vibration play the roles of inducing and promoting slide respectively.In addition,the deep cracks,which are the premise for the formation of the sliding surface,and the violent irregular fluctuation of soil pressure,which reflects the near penetration of the sliding surface,constitute the instability characteristics of the railway slope together.This paper reveals the unstable evolution of sandy soil slopes under the joint action of rainfall-vibration,hoping to provide the theoretical basis for the early warning and prevention technology of railway slopes.

Research on safety control technology of high-speed railway combined test based on threatening event analysis

Purpose–Safety management is a key point and poses a challenge in joint testing.To detect and address potential accidents’hidden dangers early,this paper conducts research on the safety control technology for high-speed railway joint tests by incorporating the concept of hazardous events.Design/methodology/approach–Aiming at ensuring the safety of high-speed railway combined inspections and trials,this paper starts from the dual prevention mechanism.It introduces the concept of threatening events,defines them and analyzes the differences between threatening events and railway accidents.The paper also proposes a cause model for threatening events in high-speed railway combined inspections and trials,based on three types of hazard sources.Furthermore,it conducts research on the control strategies for these threatening events.Findings–The research on safety control technology for high-speed railway combined operation and testing,based on the analysis of threatened events,offers a new perspective for safety management in these operations.It also provides theoretical and practical support for the transition from passive prevention to active risk pre-control,which holds significant theoretical and practical value.Originality/value–The innovation mainly includes the following three aspects:(1)Building on the traditional dual prevention mechanism,which includes risk hierarchical management and control as well as hidden danger investigation and management,a triple prevention mechanism is proposed.This new mechanism adds the management of threatening events as the third line of defense.The aim is to more comprehensively identify and address potential security risks,thereby enhancing the efficiency and effectiveness of security management.(2)In this paper,the definition of a railway threatening event is clarified,and the causative model of a high-speed railway threatening event based on three kinds of danger sources is proposed.(3)This paper puts forward the control strategy of the high-speed railway combined operation and trial,which includes five key links:identification,reporting,analysis,rectification and feedback,which provides a new perspective for the safety management of the high-speed railway combined operation and trial and has important theoretical and application value.

Dental Treatment Using Quantum Mechanics for Knee Joint Pain

In clinical practice, dentists sometimes encounter phenomena that cannot be explained by modern western medical concepts;for example, the patient’s medical symptoms improve by bringing medicines or dentures close to the body. Although it seems difficult to completely elucidate the mechanism through modern western medicine, it can be explained using quantum mechanics. The quantum, the smallest unit of matter composition, exhibits wave-particle duality. The fact that symptoms can be improved simply by bringing dentures or medicines closer to the body indicates that the waves emitted by dentures or medicines interfere with the pathological waves emitted by the pathological site. Thus, the pathological waves are deformed and lead to a change in symptoms. In this way, quantum theory can explain phenomena that are difficult to elucidate in conventional medicine, which are encountered in clinical practice. So far, the author has presented a case of difficulty in raising the upper limb where the symptoms improved without the need for dentures in the mouth by adjusting the dentures outside the mouth. This time, the author would like to introduce a case which the patient’s knee pain improved by adjusting the dentures outside the mouth.

Particle flow study on strength and meso-mechanism of Brazilian splitting test for jointed rock mass

A discrete element method （DEM） called particle flow code （PFC2D） was used to construct a model for Brazilian disc splitting test in the present study. Based on the experimental results of intact Brazilian disc of rock-like material, a set of micro-parameters in PFC2D that reflected the macro-mechanical behavior of rock-like materials were obtained. And then PFC2D was used to simulate Brazilian splitting test for jointed rock mass specimens and specimen containing a central straight notch. The effect of joint angle and notch angle on the tensile strength and failure mode of jointed rock specimens was detailed analyzed. In order to reveal the meso-mechanical mechanism of crack coalescence, displacement trend lines were applied to analyze the displacement evolution during the crack initiation and propagation. The investigated conclusions can be described as follows. （1） The tensile strength of jointed rock mass disc specimen is dependent to the joint angle. As the joint angle increases, the tensile strength of jointed rock specimen takes on a nonlinear variance. （2） The tensile strength of jointed rock mass disc specimen containing a central straight notch distributes as a function of both joint angle and notch angle. （3） Three major failure modes, i.e., pure tensile failure, shear failure and mixed tension and shear failure mode are observed in jointed rock mass disc specimens under Brazilian test. （4） The notch angle roles on crack initiation and and joint angle play important propagation characteristics of jointed rock mass disc specimen containing a central straight notch under Brazilian test.

Seismic performance of precast bridge columns connected with grouted corrugated-metal duct through biaxial quasi-static experiment and modeling

In this paper,the seismic behaviors of precast bridge columns connected with grouted corrugated-metal duct(GCMD)were investigated through the biaxial quasi-static experiment and numerical simulation.With a geometric scale ratio of 1:5,five specimens were fabricated,including four precast bridge columns connected with GCMD and one cast-in-place(CIP)bridge column.A finite element analysis model was also established by using OpenSees and was then calibrated by using the experimental results for parameter analysis.The results show the biaxial seismic performance of the precast bridge columns connected with GCMD was similar to the CIP bridge columns regarding ultimate bearing capacity and hysteresis energy,and further,that it could meet the design goal of equivalent performance.The seismic performance of the precast bridge columns connected with GCMD deteriorated more significantly under bi-directional load than under uni-directional load.A proper slenderness ratio(e.g.,7.0-10.0)and longitudinal reinforcement ratio could significantly improve the energy dissipation capacity and deformation capacity of the precast bridge columns,while the axial load ratio and concrete strength had little influence on the above properties.The research results could bring insights to the development of the seismic design of precast bridge columns connected with GCMD.

Nonlinear Modeling and Identification of Structural Joint by Response Control Vibration Test

Components of mechanical product are assembled by structural joints,such as bolting,riveting,welding,etc.Structural joints introduce nonlinearity to some engineering structures,and the nonlinearity need to be modeled precisely.To meet serious quality requirements,it is necessary to detect and identify nonlinearity of mechanical products for structural optimization.Modal test to acquire a dynamic response has been applied for decades,which provides reliable results for finite element(FE)model updating.Here response control vibration test for identification of nonlinearity is presented.A nonlinear system can be regarded as linearity for particular steady state response,and classical linear analysis tool is applicable to extract modal data for particular response.First,its applicability is illustrated by some numerical simulations.Subsequently,it is implemented on experimental setup with structural joints by shaking table.The stiffness and damping function dependent of relative displacement are fitted to describe its inherent nonlinearity.The spring and damping forces are identified by harmonic balance method(HBM)to predict output response.Based on the identified results,the procedure is recommended that it allows a reliable measurement of nonlinearity with a certain accuracy.

Experimental study on the shear performance of quasi-NPR steel bolted rock joints

Quasi-NPR(negative Poisson’s ratio)steel is a new type of super bolt material with high strength,high ductility,and a micro-negative Poisson’s effect.This material overcomes the contrasting characteristics of the high strength and high ductility of steel and it has significant energy-absorbing characteristics,which is of high value in deep rock and soil support engineering.However,research on the shear resistance of quasi-NPR steel has not been carried out.To study the shear performance of quasi-NPR steel bolted rock joints,indoor shear tests of bolted rock joints under different normal stress conditions were carried out.Q235 steel and#45 steel,two representative ordinary bolt steels,were set up as a control group for comparative tests to compare and analyze the shear strength,deformation and instability mode,shear energy absorption characteristics,and bolting contribution of different types of bolts.The results show that the jointed rock masses without bolt reinforcement undergo brittle failure under shear load,while the bolted jointed rock masses show obvious ductile failure characteristics.The shear deformation ca-pacity of quasi-NPR steel is more than 3.5 times that of Q235 steel and#45 steel.No fracture occurs in the quasi-NPR steel during large shear deformation and it can provide stable shear resistance.However,the other two types of control bolts become fractured under the same conditions.Quasi-NPR steel has significant energy-absorbing characteristics under shear load and has obvious advantages in terms of absorbing the energy released by shear deformation of jointed rock masses as compared with ordinary steel.In particular,the shear force plays a major role in resisting the shear deformation of Q235 steel and#45 steel,therefore,fracture failure occurs under small bolt deformation.However,the axial force of quasi-NPR steel can be fully exerted when resisting joint shear deformation;the steel itself does not break when large shear deformation occurs,and the supporting effect of the jointed rock mass is effectively guaranteed.

Strength and deformation characteristics of irregular columnar jointed rock mass: A combined experimental and theoretical study

The irregularity of jointed network poses a challenge to the determination of field mechanical param-eters of columnar jointed rock mass(CJRM),and a reasonable prediction of deformation and strength characteristics of CJRM is important for engineering construction.The Voronoi diagram and three-dimensional printing technology were used to make an irregular columnar jointed mold,and the irregular CJRM(ICJRM)specimens with different dip directions and dip angles were prepared.Uniaxial compression tests were performed,and the anisotropic strength and deformation characteristics of ICJRM were described.The failure modes and mechanisms were revealed in accordance with the final appearances of the ICJRM specimens.Based on the model test results,the empirical correlations for determining the field deformation and strength parameters of CJRM were derived using the dip angle and modified joint factor.The proposed empirical equations were used in the Baihetan Project,and the calculated mechanical parameters were compared with the field test results and those obtained from the tunneling quality index method.Results showed that the deformation parameters determined by the two proposed methods are all consistent with the field test results,and these two methods can also estimate the strength parameters effectively.

Quality Evaluation of Diffusion Bonded Joints by Electrical Resistance Measuring and Microscopic Fatigue Testing

Micro-structure related behavior of diffusion bonding joints is a crucial issue in device and reactor fabrication of Micro Chemo Mechanical Systems.However,the previous studies have been focused on the macro mechanical performance of diffusion bonded joint,especially diffusion bonding conditions effects on tensile strength,shearing strength and fatigue strength.The research of interfacial micro-voids and microstructures evolution for failure mechanism has not been carried out for diffusion-bonded joints.An interfacial electrical resistance measuring method is proposed to evaluate the quality of bonded joints and verified by using two-dimensional finite-element simulation.The influences of micro void geometry on increments of resistance are analyzed and the relationship between bonded area fraction and resistance increment is established by theoretical analysis combined with simulated results.Metallographic inspections and micro-hardness testing are conducted near the interface of diffusion bonded joints.For the purpose of identifying the failure mechanisms of the joints,both microscopic tensile and fatigue tests are conducted on the self-developed in-situ microscopic fatigue testing system.Based on the microscopic observations,the mechanism of interfacial failure is addressed.The observation result shows that for 316LSS diffusion-bonded joints,microstructure evolution and effect of micro-voids play a key role in interfacial failure mechanism.Finally,a new life prediction model in terms of the increment of electrical resistance is developed and confirmed by the experimental results.The proposed study is initiated that constituted a primary interfacial failure mechanism on micron scale and provide the life prediction for reliability of components sealed by diffusion bonding.

Microstructural Evolution on the T91 Dissimilar Metal Joints during Creep Rupture Tests

T91 steel is one of the new materials presently employed in power plant pipe components. The creep rupture strength and microstructure of the T91+10CrMo910 and T91+13CrMo44 welded joints were analyzed during creep rupture tests. Creep transgranular ductile rupture occurred at the 10CrMo910 matrix in the T91+10CrMo910 welded joints and creep intergranular brittle rupture occurred at the 13CrMo44 HAZ in the T91+13CrMo44 joints. Microhardness measurements showed high hardness at the heat affected zone (HAZ) of T91 and a sharply drop at the 13CrMo44 HAZ during creep rupture. The metallographic tests showed that no obvious microstructure degradation was observed in the 10CrMo910 HAZ and matrix, while creep cracks appeared at the 13CrMo44 HAZ. T91 steel had relatively high creep resistant strength in the welded joints tested. Recovery occurred in the T91 HAZ with the growth of subgrain size and the decrease of dislocation density during creep. It was concluded that the dissimilar joints of T91 and low alloy heat-resistant steel should have close creep strength matching to increase the service life of the overall joints at elevated temperature.

Assessment of mechanical properties of aluminium alloy welded joint using small punch test

The small punch test technique （SPT） was used to evaluate the mechanical properties of various materials and the basic method to test material tensile mechanics peqeormance from an inverse finite element （ FE） arithmetic with SPT was put forward. The research shows that specific tensile mechanical behavior and strain-stress distribution of each district of weld seam can be accurately determined by small punch test. Therefore, mechanical behavior of the inhomogeneous joint can be predicted by a numerical model. The simulation comes to good agreement with experimental data.

Cyclic Shear Tests on Key Connection Joints of Modularized Constructions

Modularized construction is a new type of prefabricated building system with green environmental protection and excellent performance. There are few studies on the seismic performance of its key connection joint. This paper presents a new type of assembled connection joint for the high-rise modularized construction. Cyclic shear tests of full-scale joints were carried out, and the key indexes of their seismic performances including the hysteretic performance, ductility, and energy dissipation capacity were analyzed and obtained. The results show that the hysteresis loops of longitudinal and lateral cyclic shear tests were both plump in shapes. The ductility coefficients were 4.54 and 4.98, and the energy dissipation coefficients were 1.83 and 1.43, respectively. The test joint had good ductility and energy dissipation capacity. The positions of yield failure of specimens were mainly concentrated in the connection areas between the column and short beam or end-plate. The research can provide the technical reference for the seismic design and engineering application of related modularized constructions.

Investigation of long-wavelength elastic wave propagation through wet bentonite-filled rock joints

The saturation of the compacted bentonite buffer in the deep geological repository can cause bentonite swelling,intrusion into rock fractures,and erosion.Inevitably,erosion and subsequent bentonite mass loss due to groundwater inflow can aggravate the overall integrity of the engineered barrier system.Therefore,the coupled hydro-mechanical interaction between the buffer and rock during groundwater inflow and bentonite intrusion should be evaluated to guarantee the long-term safety of deep geological disposal.This study investigated the effect of bentonite erosion and intrusion on the elastic wave propagation characteristics in jointed rocks using a quasi-static resonant column test.Jointed rock specimens with different joint conditions(i.e.joint surface saturation and bentonite filling)were prepared using granite rock discs sampled from the Korea Underground Research Tunnel(KURT)and Gyeongju bentonite.The long-wavelength longitudinal and shear wave velocities were measured under different normal stress levels.A Hertzian-type power model was used to fit the wave velocities,and the relationship between the two fitted parameters provided the trend of joint conditions.Numerical simulations using three-dimensional distinct element code(3DEC)were conducted to better understand how the long-wavelength wave propagates through wet bentonite-filled rock joints.