No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Falling weight impact acceleration-time signals analysis for road modulus detection: Theoretical and experimental investigations
... The approach also has limitations, including high computational costs, complex parameter calibration, and challenges in handling large-scale problems. Despite these limitations, it remains a valuable tool for geotechnical modeling, particularly for problems involving both discrete and continuous behavior, which has been widely applied in landslide modeling, rock fracture mechanics, and reinforced soil analysis (Tan et al. 2020;Xu et al. 2024). ...
The destabilization of glacial valley deposits in high position poses a substantial risk to both the valleys themselves and the infrastructure located downstream. However, the inherently challenging accessibility of these high-altitude regions complicates the task of conducting thorough stability assessments. This study introduces a comprehensive identification methodology that integrates remote sensing technology with air-ground surveys to investigate the stability of high-position glacial valleys, thereby laying the groundwork for subsequent stability evaluations in areas prone to deformation. To exemplify the effectiveness of this approach, three glacial valleys situated at an average altitude exceeding 4500 m in Basu County, Southeast Tibet, China, were selected for case study analysis. The findings reveal that significant landslide events within these high-position glacial valleys can be discerned by comparing reference points in optical satellite imagery. In the 2# glacial valley, substantial deformation is concentrated along the central axis, whereas in the 1# and 3# glacial valleys, deformation is predominantly observed in the scarp regions, as determined by Interferometric Synthetic Aperture Radar (InSAR) analysis. The principal sliding zone is identified within the altitudinal transition zone between 4400 and 4700 m. The maximum deformations recorded under a 24-h, 200-year return period rainfall event and a 15-s seismic event with an acceleration of 0.41 g (g = 9.8 m/s²) were 1.66 m and 6.7 m, respectively. This integrated approach provides a practical framework for the investigation of high-position glacial valleys, thereby facilitating the assessment and mitigation of geological hazards in these otherwise inaccessible environments.
This article presents the case study of our research in the field of innovative methods of pavement subgrade quality control using the CIST (Clegg Impact Soil Tester) device. The CIST device developed by Dr Clegg from the University of Western Australia measures soil compaction indirectly using the CBR value. The value is evaluated based on the deceleration rate of a falling 4.5 kg weight moving in a vertical guide roller. In Europe, for the assessment of the mechanical efficiency (bearing capacity) of cohesive soils in the pavement subgrade, priority is given to indirect assessment methods especially using the laboratory determination of CBR (Californian Bearing Ratio) and directly through the implementation of a static plate load test (SPLT). This article reports the long-term results of our research in the field of verification and validation of an innovative CIST device, which minimizes the time, space, and economic disadvantages of SPLT. This article presents the results of determining the field of applicability of the CIST device for cohesive soils, the correlation dependencies (CD) of the CBR values determined by the CIST device, and, according to STN 72 1016, the CD of the impact dynamic deformation modulus Evd from the CIV (Clegg Impact Value). We consider the most important results of our long-term research to be a recognition of the ability of CIST to assess the quality of cohesive soils up to a compression value of 40 mm, corresponding to a CBR of 2.2% and a modulus of subgrade deformation of 20 MPa. A very strong correlation dependence of CBRClegg [%] on the moisture content of clayey soils in the interval from 5 to 19% was also observed. The presented knowledge led to the creation of relevant documents for the credible implementation of the CIST device in the system approach for assessing the quality of the pavement subgrade.
The Delamination Threshold Load (DTL) is a key parameter representing damage resistance of a laminate and is normally identified by locating a sudden drop in the impact force-time history for the laminate made of unidirectional layers. For the woven composite, however, their failure mechanisms appear different and the current literature is not providing any clear procedure regarding the identification of the delamination initiation, as well as the evolution of the failure mechanisms associated with it. In this paper, experimental data have been collected using woven glass and carbon fiber composites. The results are analyzed in terms of force-time and force-displacement curves. While delamination and other damages were clearly observed using ultrasonic scans, the analysis of the results does not reveal any trend changes of the curves that can be associated with the incipient nucleation of delamination. A preliminary discussion regarding the nature of the mechanisms through which the delamination propagates in woven composite and a justification for the absence of a sudden change of the stiffness have been presented. It raises a question on the existence of DTL for woven composites under low velocity impact.
In this paper, the moduli of elasticity of compacted loess and lateritic-loess soils on-site were estimated from the laboratory test. These were coarse grain soils used for the construction of base course and embankment of the railway line. The knowledge of the soil properties on-site such as the compacted elastic moduli is essential for the design and selection of materials. A total of 108 samples consisting of 36 samples of compacted soils on-site and 72 samples of compacted soils in laboratory were tested using plate bearing tests. The water contents of the compacted soil on-site were controlled to be within ±2% of optimum water content. The water content and density of compacted soil on-site were determined and used for the compaction of soils in the laboratory. For the testing in laboratory, two loading types viz., point load and uniform load were performed using the compacted 15-cm diameter mold (California Bearing Ratio). The results showed that the point load test gave a slightly better estimation of elastic modulus with R² of 0.977 than the uniform load test with R² of 0.970. The experiment showed that the on-site elastic moduli of loess and lateritic-loess soils could be accurately estimated from the laboratory load tests.
Falling Weight Deflectometry (FWD) tests are performed around the centres of two rectangular concrete plates, with geophones measuring vertical deflections in eight directions. Experimental results allow for quantifying asymmetries regarding the structural behaviour. Significant asymmetries are found for a 22-year-old plate scheduled for replacement. A new plate, tested a few weeks after production, is found to behave in a virtually double-symmetric fashion. Structural analysis of the new plate is based on Kirchhoff–Love plate theory, using free-edge boundary conditions. The support of the plate is provided by a Winkler foundation. Performing a static analysis, the uniform modulus of subgrade reaction is optimised to reproduce the measured deflections. The result is not convincing. The model is extended towards consideration of a second optimisation variable: a uniform auxiliary surface load. This allows for reproducing the measured deflections. The auxiliary load is superimposed with the pressure resulting from the Winkler foundation. This yields a realistic distribution of subgrade pressure. Dividing it by the deflections results in the distribution of the effective modulus of subgrade reaction. Finally, the analysis is extended towards the consideration of inertia forces. They increase the effective moduli of subgrade reaction determined by means of static analysis by less than 3.5%.
The detection of the deformation characteristics of geotechnical materials is very important for improving the safety of highways. With the improvement of the detection technology, the falling ball test (FBT) method has been gradually applied to measure mechanical properties of the geomaterials. In order to determine the reliability and the stability of the FBT method, the results of using the FBT method to detect the deflection value of the cement stabilizing layer are compared in this paper with the results of using a falling weight deflectometer (FWD), which is recognized worldwide as an ideal non-destructive detection equipment for the road mechanical performance. It is found that FBT method has high stability and reliability during the test.
Through the experiment, the deflection detection methods of the falling-ball instrument and the falling weight deflect meter (FWD) were compared, and their correlations were analyzed. The results show that the test depth and range of FWD are larger than the falling-ball instrument, and there is a good linear relationship between the road surface deflection values measured by the falling-ball instrument and FWD.
In this paper the study of the dependence of the dynamic interaction force of solids on the impact of local compression obtained according to the extended theory of impact is carried out.The results of the theoretical study are compared with the results of an experiment conducted earlier by other authors. We can conclude that the results obtained in the extended theory, qualitatively better conform with the data of the experiment than the results obtained in the classical theory of G. Hertz.
To improve the accuracy of back-calculation of soil modulus using the portable falling weight deflectometer (PFWD), a viscoelastic method (VEM) overcoming the limitations of the conventional linear elastic method (LEM) was proposed. A quasi-static dynamic analysis technique of Laplace transformation and a modified Gauss–Newton optimization algorithm were adopted in the proposed method. The back-calculation program was compiled with MATLAB. The effectiveness of the proposed method was verified with the in situ plate load test (PLT) conducted on a highway embankment. In situ test results showed that a time lag existed between the peaks of deflection and load, and load-deflection curves were nonlinear, which indicated the viscoelastic nature of the soil. The back-calculated modulus using the LEM and VEM was higher than that using the PLT. In the case of low stiffness soil, the average error of back-calculation using the LEM and VEM was 53.1% and 14.8%, respectively. However, for stiffer soil, the average error of back-calculation using the LEM and VEM method was 12.4% and 4.3%, respectively. Moduli of back-calculation using LEM and VEM methods were used to perform flexible pavement analysis, which showed that with an 8% reduction of modulus, the pavement service life reduced by 25%. More accurate estimation of modulus can save maintenance cost in the future.
The appropriate modeling of the soil-pile interaction (SPI) is critical to get the reasonable dynamic responses of bridge structure under impact loading. Of various SPI modeling approaches, utilizing p-y and t-z curves is a common method to represent the nonlinear lateral resistance and skin friction of pile-surrounding soil. This paper accomplished SPI modeling for the bridge pylon impact analysis with compression-only nonlinear springs and linear dashpots. The kinematic interaction and pile group effect were incorporated into the SPI. A variety of pylon impact analyses were conducted under energy-variation impact loads. The structure dynamic responses were compared and discussed considering the influences of pile group effect, soil damping, and axial t-z spring. An approximate approach was proposed to derive the linearized stiffness of soil for the purpose of engineering calculation. It was concluded from the extensive simulations that the impact load generated from higher initial energy induced more significant structural responses and larger soil inelastic deformation than smaller initial energy. The piles in the leading row possessed larger bending moments, whereas they exhibited smaller pile deformation than the responses of trailing row piles. Soil damping applied in SPI played positive roles on the reduction of structural responses. Replacing the t-z spring by fixing the degree-of-freedom (DOF) in the vertical direction was capable to yield satisfactory results of structural responses. The proposed linear soil stiffness was demonstrated to be applicable in the SPI modeling of structure impact analysis.
The degree of deterioration in the structural capacity of a pavement is an important indicator of its performance. Conventional falling weight deflectometer, which assesses pavement capacity based on the deflection bowl data under impact loads and is the prevalent method in practice, only characterize the overall bearing capacity of pavement. It does not possess sufficient accuracy in measuring the modulus of pavement structural layer. In this paper, a smart pavement schema was proposed where built-in sensors are incorporated to monitor pavement stress and strain responses under aircraft loads. Theoretical relationship between pavement mechanical responses of a two-layered elastic system subjected to service load is established, which is used for back calculating the modulus of asphalt layer. To demonstrate the concept, sensors are deployed along a taxiway in Beijing Capital International Airport, Beijing, China. The measured mechanical responses by the sensors were incorporated to back-calculate the modulus of asphalt layer, which are then verified through dynamic modulus experiments. The results show that back-calculated modulus by incorporating sensor data is repeatable and can be applied for real-time evaluation of pavement performance without affecting the traffic. Extension of the model and analysis to multi-layered elastic system are discussed.
The subgrade resilient modulus (Mr) is an essential parameter in pavement analysis. However, available Non-Destructive Testing devices (NDT) such as the Falling Weight Deflectometer (FWD) have limitations that prevent their widespread use at the network-level. This study describes the development of a model that utilizes the Rolling Wheel Deflectometer (RWD) measurements to predict the Mr for flexible pavements. RWD and FWD measurements obtained from a testing program conducted in Louisiana were used to train an Artificial Neural Network (ANN) based model. The ANN model was 19 validated using data from a testing program independently conducted in Minnesota. The ANN model showed acceptable accuracy in both the development and validation phases with coefficients of determination of 0.73 and 0.72, respectively. Furthermore, the limits of agreement methodology showed that 95% of the differences between the Mr calculated based on FWD and RWD measurements will not exceed the range of ±21 MPa (±3 ksi).
The importance of understanding the response of structural composites to impact cannot be overstated. This understanding includes both the impact phenomena themselves and the influence of materials properties on the impact response. This paper presents the need for instrumented testing to optimize our understanding of the impact event, especially the response of the impacted material. The conclusion is drawn that the impact force history is a more relevant measure of a materials characteristics than is the total kinetic energy of the impactor. Static and dynamic impact phenomena are assessed to lay the foundation for the eventual development of a standardized test method focused on the lower velocity range impact response behavior of composites. In addition, a relatively inexpensive but very versatile low-velocity, instrumented pendulum impact tester is described and actual test data for both graphite fiber/thermoset matrix and graphite fiber/thermoplastic matrix are compared. Actual energy absorption curves are shown. A simple method is described to allow direct measurement of the total energy exchanged during the impact event, and the use of these data to permit the vital dynamic calibration of the load cell for every different impact event is illustrated. The different stages in the damage process are characterized, for the first time, for the two materials systems studied.
A general and comprehensive analysis on the continuous contact force models for soft materials in multibody dynamics is presented throughout this work. The force models are developed based on the foundation of the Hertz law together with a hysteresis damping parameter that accounts for the energy dissipation during the contact process. In a simple way, these contact force models are based on the analysis and development of three main issues: (i)the dissipated energy associated with the coefficient of restitution that includes the balance of kinetic energy and the conservation of the linear momentum between the initial and final instant of contact; (ii)the stored elastic energy, representing part of initial kinetic energy, which is evaluated as the work done by the contact force developed during the contact process; (iii)the dissipated energy due to internal damping, which is evaluated by modeling the contact process as a single degree-of- freedom system to obtain a hysteresis damping factor. This factor takes into account the geometrical and material properties, as well as the kinematic characteristics of the contacting bodies. This approach has the great merit that can be used for contact problems involving materials with low or moderate values of coefficient of restitution and, therefore, accommodate high amount of energy dissipation. In addition, the resulting contact force model is suitable to be included into the equations of motion of a multibody system and contributes to their stable numerical resolution. Ademonstrative example of application is used to provide the results that support the analysis and discussion of procedures and methodologies described in this work.
KeywordsContact force–Continuous analysis–Soft materials–Coefficient of restitution–Elastic energy–Internal damping–Multibody dynamics
Reinforced concrete rock sheds are usually covered by a layer of soil as a shock-absorbing cushion. To better understand the damping abilities of this cushion in order to estimate the impact action, an experimental study has been carried out. Blocks stimulating falling rock blocks were dropped from various heights on a reinforced concrete slab covered by different fill materials. After describing the test and measuring devices, the experimental results are analysed and mathematical expressions for some of the problem variables are presented.
Clamped circular composite plates made of quasi-isotropic graphite/epoxy laminate were analyzed for static equivalent impact loads. The analysis was based on the minimum total potential energy method and used the von Karman strain-displacement equations. A step-by-step incremental transverse displacement procedure was used to calculate plate load and ply stresses. The ply failure region and modes (splitting and fiber break) were calculated using the Tsai-Wu and the maximum stress criteria, respectively. Reduced moduli were then used in the failed region in subsequent increments of analyses. The analysis predicted that the failure would initiate as splitting in the bottom-most ply and then progress to other plies.
When an impact load is sufficiently small, its influence on the pavement structure is mainly from the surface layer material. To explore the influence depth of an impact load and back‐calculation of the pavement surface modulus, both numerical calculation and experimental testing were conducted, and the results are presented in this paper. The numerical calculation was performed through a DEM‐FDM‐coupled model. After a new modulus back‐calculation algorithm is formed by analyzing the numerical modeling results, experimental tests were also conducted for verification, and the results were analyzed. The max value of the falling weight impact force was closely related to the elastic modulus of the material, and the influence depth was controllable. Finally, it is proved that the method can be used to calculate the surface layer modulus and estimate the surface layer thickness.
As a key input parameter of asphalt pavement design, the modulus parameters directly affect the results of pavement stress analysis. During the mechanical evaluation analysis, researchers usually use material modulus instead of structural modulus as input parameter, so the possible deviations between the field measured mechanical responses and the calculated responses are ignored in this case. Therefore, the field mechanical response and the calculations mechanical response of finite element method (FEM) with different moduli input were evaluated in this research. The field strains of each pavement layer under dynamic and static load conditions were determined by embedding the fiber Bragg grating (FBG) sensors, and the field deflection test was carried out by Beckman beam. A total of 11 types of material moduli were obtained through various modulus tests, and which were implemented in the FEM model for the strain and deflection calculation of pavement structure, and then the calculated mechanical responses were compared with the field measured mechanical responses. The results indicated that a specific modulus should be selected to ensure the calculated value effectively reflect the measured mechanical response. For the FEM calculation of dynamic strain, it is recommended to use static flexural modulus for asphalt layer and use dynamic flexural modulus for CSG layer as modulus input with average errors of 16.9% and 7.5% respectively. For the FEM calculation of static strain, it is recommended to use dynamic compressive resilience modulus for asphalt layer and use static flexural modulus for CSG layer as modulus input with average errors of 18.7% and 11.5% respectively. Besides, it is recommended to select dynamic flexural modulus or compressive modulus in static four-point bending test as the modulus input for pavement deflection analysis with the error of about 4.8%.
Modulus is a critical parameter for evaluating the bearing capacity and remaining life of pavements. The prevalent modulus back-calculation method by using the pavement surface deflections captured from falling weight deflectometer (FWD) could characterize the overall bearing capacity of pavements. However, a non-uniqueness issue may occur when identifying the modulus of each layer from the perspective of mathematics. Alternatively, this paper presents a novel application to real-time modulus evaluation based on asphalt pavement health monitoring with built-in sensors. First, the sensor layout is optimized on the basis of the theoretical relationship between modulus and mechanical response inside the pavement. The proposed sensor layout, including input (random loads), output (mechanical responses), and environmental sensing modules, is illustrated in detail. Then, the procedure for real-time modulus evaluation is proposed, and the convergence and uniqueness of modulus evaluation results are investigated. Lastly, a case study of the realistic asphalt pavement health-monitoring system is conducted to demonstrate the effectiveness of the application to real-time modulus evaluation. The results indicate that the proposed modulus evaluation method has a potential to identify the modulus of each pavement structural layer in real time with a convergent and unique solution under a realistic traffic load. The evaluation process has the advantage of not interfering with traffic compared with the prevalent FWD-based modulus evaluation method. The pavement health monitoring with built-in sensors is recommended for newly built roads to facilitate long-term real-time performance assessment and maintenance decision making.
The early damage of the semi-rigid base asphalt pavement is related to the pavement structure modulus's unreasonable matching. In this study, three typical pavement structures were selected to analyze the pavement structures' influence on the pavement service life. A three-dimensional finite element pavement structure model was established. The independent variables are subgrade modulus, base course modulus, and subbase modulus. The deflection, the bottom tensile stress, and maximum shear stress were chosen as the evaluation indexes. The effect of the modulus on the mechanical response of the pavement structure was analyzed. The optimal modulus combination of the pavement structure was determined through multi-factor range analysis. The mechanical response and fatigue life before and after the optimization pavement structure were compared. The results showed that the field measured modulus of Structure 1 and 2 was higher than the design modulus. Moreover, while the modulus of base course and subbase course was increased, the deflection gradually reduced. The base course's bottom tensile stress and the subbase were increased, and the maximum shear stress was basically unchanged. After the modulus combination optimized pavement structure, the mechanical response was significantly reduced. The fatigue life based on the deflection and bottom tensile stress, and the laboratory normalized fatigue equation were significantly increased. By the combination of fatigue performance of pavement materials and pavement structure, it was possible to provide an effective optimization method for the design of semi-rigid base asphalt pavement in this research work.
Traffic Speed Deflectometer (TSD) is primarily capable of evaluating the pavement conditions at the network level with regard to the structural capacities. This paper mainly reviews the utilization of TSD for the pavement structural evaluations. With the Doppler lasers configured in a specific truck, TSD can measure the deflection velocity (slope) at a traffic speed. The measured deflection can be calculated by either area under the curve (AUTC) method or Euler–Bernoulli beam (EB) method. Moreover, the pavement moduli backcalculated by either 3D Move simulation or the Artificial Neural Networks (ANNs) from TSD measurements tend to well correlate those backcalculated from FWD measurements. It is noted that structural capacities derived from TSD measurement were reliable in assessing the pavement conditions. Additionally, the pavement roughness has a significant effect on TSD measurements. Therefore, Traffic Speed Deflectometer has a promising applied prospect in pavement structural evaluations.
The main purpose of this paper is to explore the change rules of hammer acceleration during the impact process. The impact force in the real impact process is difficult to measure directly, so we need to measure acceleration to obtain it indirectly. It is difficult to do research through experiments. Numerical simulation is an effective means to research on pavement structure dynamic damage and destruction. A continuous-discrete coupling model is established to explore the change rules of acceleration and impact force under the influence of various factors by changing the hammer weight, hammer height and plate material. The results show that the drop height is the most important factor affecting the acceleration of the hammer; and the larger peak impact force can be obtained by reducing the weight of the hammer but increasing the drop height. The acceleration increases with the increase of the plate modulus.
Semi-flexible pavement (SFP) material has been promoted to apply in pavement engineering mainly for its excellent performance in rutting resistance. But its mechanical behavior is complicated due to its heterogeneity and interlocking structure. According to the present study, the damage process of SFP (with and without fiber), as well as its porous asphalt (PA) matrix, under uniaxial compression test was detected employing acoustic emission (AE) technique. The heterogeneity and the interlocking effect were varied by changing the matrix porosity and the gradation, respectively. The stress-strain curves reveal that cement grouting could decrease the material's failure strain distinctly, while the addition of fiber made no effect on the results. Nevertheless, both the cement grouting and the addition of fiber caused medium and high amplitude (50-65 dB) AE signals during the AE detection. Besides, the Rise Angle (RA) value and energy distribution both illustrate that there was increasing trend in the amounts of shear cracking in SFP during compression, which was different from asphalt mixtures. And the addition of fiber could restrain the shear cracking to improve the crack resistance. Quantificationally, heterogeneity was characterized by standard deviation of compositions' modulus and an interlocking index was extracted from a modulus micromechanical model to characterize the interlocking effect. The Weibull distribution was adopted to characterize the damage evolution, where the cumulative AE energy was chosen as the damage variable. The result shows the two Weibull parameters m, n had obviously positive correlation with the matrix porosity and the interlocking index, respectively.
To accurately and effectively simulate the cracking and crushing process of concrete pavement under multi-head impact loading, a large-scale road 3D model that considers concrete pavement, subgrade and soil foundation is established. Then, the discontinuum element method is applied in the concrete pavement's potential fracture area, and the continuum element method is applied in the hammer body and the non-fracture area of concrete pavement. A cohesive model is applied to the element interface of the concrete fracture area, and a contact element is used to deal with the interaction between the hammer body and the pavement. Mesoscopic simulations on the impact cracking process of concrete pavement are conducted by considering the element shapes, three-dimensional aggregates, impact locations and impact velocities. Finally, impact testing and core drilling are conducted in the field to evaluate the simulation results. The results demonstrate that the cracking and crushing process of concrete pavement can be quickly simulated via the continuum-discontinuum element method (CDEM), and the simulation results agree with the results of the in-site tests. The concrete pavement model that is meshed by tetrahedral elements and includes aggregates can result in a higher calculation efficiency and superior impact cracking performance. Concrete pavement is severely crushed in the impact contact area, closed quadrangle crack surfaces form along the inside of four hammerheads, and tension crack surfaces mainly propagate along the long axis of the rectangular hammerheads. The impact locations mainly affect the crack distribution of the concrete pavement, and the impact velocities determine the fracture degree. As the impact velocity increases, the impact force linearly changes, whereas the fracture degree varies according to a power function. Overall, the influence of the impact velocities on concrete cracking is greater than the impact locations.
Ballasted tracks at transition locations such as approaches to bridges and road crossings experience increasing degradation and deformation due to dynamic and high impact forces, a key factor that decreases the stability and longevity of railroads. One solution to minimise ballast degradation at the transition zones is using rubber energy absorbing drainage sheets (READS)manufactured from recycled tyres. When placed beneath the ballast layer, READS distributes the load over wider area and attenuate of the load over a longer duration thus decreasing maximum stress, apart from reducing the energy transferred to the ballast and other substructure components. Subsequently, the track substructure experiences less plastic deformation and degradation. These mats also provide an environmentally friendly and cost-effective alternative. In this study, a series of large-scale drop hammer impact tests was carried out to investigate how effectively the READS could attenuate impact loads and help mitigate ballast deformation and degradation. Soft and stiff subgrade were used to investigate the load-deformation response of ballast (with and without READS), subjected to impact loads from a hammer dropped from various heights (h d = 100–250 mm). Laboratory test results show that the inclusion of READS helps to reduce the dynamic impact load transferred to the ballast layer resulting in significantly less permanent deformation and degradation of ballast, apart from significant attenuation of load magnitude and vibration to the underlying subgrade layers.
Since the determination of resilient modulus (Mr) from the repeated load triaxial test is rather complicated, due to the expensive procedure and time-consuming nature, attempts have been made to estimate it using other properties, such as the unconfined compressive strength and California bearing capacity based on empirical models. However, because of the dynamic nature of the Mr, it should be estimated by other simple-procedure dynamic properties. The Clegg hammer test has been considered as an alternative since it is not only dynamic in nature but also simple and quick. There has been no report of any previous study on correlating between CIV and Mr of construction and demolition (C&D) aggregates containing crumb rubber. In this research, a series of experiments were conducted to measure the Mr and CIV of the waste crushed rock (WCR) and recycled crushed concrete (RCC) mixed with the rubber of two different sizes and different contents (0, 0.5, 1, and 2%) for making a green pavement. The experimental results show that the CIV and Mr of both aggregates increased with the fine crumb rubber components but decreased with the coarse rubber content. The increase of CIV and Mr due to the increase of fine rubber percentage can be attributed to the filler effect of fine rubber particles that provides better interfacial bonding condition. The analytical results show that a strong correlation exists between the Mr, confining stress, deviator stress and the CIV with the R2 value ranging from 0.74 to 0.99.
This study focused on evaluating airfield flexible pavement responses from surface deflec-tions measured under Heavy Weight Deflectometer (HWD) testing. Finite Element (FE) models were developed to predict pavement responses and develop the synthetic database. Field testing data at the National Airport Pavement Test Facility (NAPTF) were used to validate the FE model results and the proposed deflection-response relationship. The results indicate that good correlations were obtained between tensile strains and Area Under Pavement Profile (AUPP) and between shear strains and Surface Curvature Index (SCI). respectively. Further study will be conducted to enhance the database and improve prediction accuracy.
The maximum impact force caused by a rockfall is a very important factor for the design of protection measures for houses, roads, and bridges. To establish an impact force model, the kinetic energy of the rock block, the impact angle between the movement direction of the block and the surface of the object hit by the block, and the modulus of elasticity of rock and object were analyzed with the Buckingham theorem and simplified to two dimensionless parameters. Physical tests were conducted with different kinetic energies, moduli of elasticity of the rock, and the object. Balls of iron, granite, marble, sandstone, and wood were used to simulate rock blocks in the tests. The objects hit by the balls are composed of steel, concrete, and wood. The relationships between the maximum impact force and the kinetic energy, and modulus of elasticity determined by dimensional analysis were confirmed by these experiments. Experiments were carried out with different impact angles to determine the influence of the impact angle on the impact force. A maximum impact force model is obtained from these relationships and by experiments with impact forces ranging from 225 to 15,583 N. A comparison with results reported from other studies shows that the maximum impact force model gives reasonable results over a very large range of impact forces from 21.4 to 8.16 MN. We assume that the model can be used to calculate the impact force at the full field scale.
This paper focused attention to the falling weight deflectometer (FWD) load-time history. For a commonly used device, it studied the pulse generation mechanism and the influence of different load histories on backcalculation results. In this connection, a semi-analytic impact theory was first introduced for realistically simulating FWD pulse generation. Then a newly developed finite-element code was presented for FWD interpretation; the code is capable of addressing dynamics, time-dependent layer properties, and quasi-nonlinear behaviour. Both new developments were demonstrated for an experimental dataset that resulted from operating an FWD with different loading configurations. It was found that backcalculated parameters are sensitive to the FWD pulse features. Consequently, it is recommended that, whenever advanced pavement characterisation is sought, experimental attention should be placed on generating diverse FWD pulse histories. Collectively, the resulting deflection histories will contain pertinent constitutive information for supporting the calibration of more complex pavement models.
Dynamic modulus has been recognized as an objective and sensitive material property for designing and evaluating pavement systems. To accurately measure the in situ elastic modulus (E = 2(1 + ν)ρVs2) for nondestructive quality assessment of asphalt pavements, field measurements of density (ρ) via an electromagnetic gauge and shear-wave velocity (Vs) via surface-wave testing were examined for four paving projects covering a range of mixes and traffic loads. A quality control/quality assurance (QC/QA) procedure was developed to correct the in situ moduli at different field temperatures to a common reference temperature using a fitting function from experimental data for QC and using master curves from laboratory dynamic modulus tests for QA. The corrected in situ moduli can then be compared against the maximum moduli for an assessment of the actual pavement performance.
Purpose
– The purpose of this paper is to develop a method to model entire structures on a large scale, at the same time taking into account localized non-linear phenomena of the discrete microstructure of cohesive-frictional materials.
Design/methodology/approach
– Finite element (FEM) based continuum methods are generally considered appropriate as long as solutions are smooth. However, when discontinuities like cracks and fragmentation appear and evolve, application of models that take into account (evolving) microstructures may be advantageous. One popular model to simulate behavior of cohesive-frictional materials is the discrete element method (DEM). However, even if the microscale is close to the macroscale, DEMs are computationally expensive and can only be applied to relatively small specimen sizes and time intervals. Hence, a method is desirable that combines efficiency of FEM with accuracy of DEM by adaptively switching from the continuous to the discrete model where necessary.
Findings
– An existing method which allows smooth transition between discrete and continuous models is the quasicontinuum method, developed in the field of atomistic simulations. It is taken as a starting point and its concepts are extended to applications in structural mechanics in this paper. The kinematics in the method presented herein is obtained from FEM whereas DEM yields the constitutive behavior. With respect to the constitutive law, three levels of resolution – continuous, intermediate and discrete – are introduced.
Originality/value
– The overall concept combines model adaptation with adaptive mesh refinement with the aim to obtain a most efficient and accurate solution.
This book presents a compilation of information and analytical methods on the subject of the impact strength of materials. It contains ten chapters dealing with: 1, elementary one-dimensional elastic stress waves in long uniform bars due to impact; 2, applications of elementary one-dimensional stress wave theory; 3, elastic stress waves: more general considerations; 4, plasticity theory and some quasi-static analyses; 5, one dimensional elastic-plastic stress waves in bars; 6, impulsive loading of beams; 7, dynamic loading of rings and frames; 8, dynamic plastic deformation of plates; 9, plastic deformation in a semi-infinite medium due to impact; and 10, plastic deformation in plates due to impact. Two appendices contain: 1, useful conversion factors; and 2, text tables in SI units. (TRRL)
During impact the relative motion of two bodies is often taken to be simply represented as half of a damped sine wave, according to the Kelvin-Voigt model. This is shown to be logically untenable, for it indicates that the bodies must exert tension on one another just before separating. Furthermore, it denotes that the damping energy loss is proportional to the square of the impacting velocity, instead of to its cube, as can be deduced from Goldsmith's work. A damping term is here introduced; for a sphere impacting a plate Hertz gives . The Kelvin-Voigt model is shown to be approximated as a special case deducible from this law, and applicable when impacts are absent. Physical experiments have confirmed this postulate.
In this paper, the contact force between two colliding bodies is modeled by using Hertz’s force-displacement law and nonlinear
damping function In order to verify the appropriateness of the proposed contact force model, the drop type impact test is
carried out for different impact velocities and different materials of the impacting body, such as rubber, plastic and steel
In the drop type impact experiment, six photo interrupters in series close to the collision location are installed to measure
the velocity before impact more accurately The characteristics of contact force model are investigated through experiments
The parameters of the contact force model are estimated using the optimization technique Finally the estimated parameters
are used to predict the impact force between two colliding bodies in opening action of the magnetic contactor, a kind of switch
mechanism for switching electric circuits
Remaining service life (RSL) has been defined as the anticipated number of years that a pavement will be functionally and structurally acceptable with only routine maintenance. Usually RSL is computed from pavement condition survey results. This paper presents a methodology whether RSL was estimated from pavement surface deflections. Deflection data were collected with a Dynatest 8000 falling weight deflectometer (FWD) from 1998 to 2006. Nonlinear regression procedure in the Statistical Analysis Software and Solver in Microsoft Excel were used in model development. The results showed that a sigmoidal relationship exists between RSL and center (FWD first sensor) deflection. Sigmoidal RSL models have very good fits and can be used to predict RSL at the network level based on the center deflection from FWD.
Collision - a blind spot in theoretical mechanics
- Yu
Coupled discrete-continuous simulation and analysis of dynamic interactions between hammer and pavement
- Liu
Road and Bridge Technology Co., Specifications for design of highway asphalt pavement, Ministry of Transport of the People's Republic of China
- L Cccc