Repeated Load Tests Research Articles

Repeated loading of soilbag-reinforced road subgrade

Soilbags are three-dimensional soil-confining units used in road foundations. This paper uses vertical repeated loading tests to investigate the performance of soilbags as reinforcement in road subgrades as well as the influence of such factors as the frequency and amplitude of loading, the number of reinforcement layers, and the buried depth of the soilbag reinforcement. The results show that soilbags as reinforcement are effective at reducing permanent and resilient deformations of the road subgrade as well as vibrations caused by traffic loads. The soilbags as reinforcement perform better when the number of soilbag-reinforced layers is increased. More than two layers of soilbags are needed to reinforce the road subgrade to make efficient use of the effect of interlayer insertion between soilbags. Furthermore, a thin surface soil cover is desirable to spread the applied pressure more effectively over the soilbags and level the subgrade.

Implication of Nondestructive Test NDT for Evaluation of Crack Healing in Asphalt Concret

Asphalt concrete practices heavy loading and environmental impacts through the service life of the pavement. Micro cracks usually initiate and accumulate to form various types of distresses. However, asphalt concrete has the ability of self-healing under rest period and environment conditioning. Asphalt concrete is a composite material consisting of aggregates, bitumen, and air voids. Its mechanical behavior is complex due to its dependency of temperature, loading frequency, and strain level. In this investigation, asphalt concrete specimens of wearing course have been prepared in the laboratory and subjected to repeated indirect tensile stresses to initiate the micro-cracks. The test was stopped after 1200 load repetitions, and the specimens were stored in an oven at 60°C for 120 minutes to allow the crack healing process by external heating to start. Specimens were returned to the testing chamber and were subjected to another round of load repetitions. Specimens were tested before and after load repetitions and crack healing with the aid of ultrasonic pulse velocity traversing the specimen using pundit instrument. The healing indicator was the change in pulse velocity before and after the repeated load test and before and after healing process. It was concluded that the velocity decreases as the loading cycles proceeds indicating the start of damage, while the ultrasonic pulse velocity increases after the micro-crack healing process.

Experimental study on fabricated shear wall structure with energy‐dissipating vertical joint

AbstractBased on the design concept of 'strong horizontal joint and weak vertical joint', an energy‐dissipating fabricated shear wall structure system with a steel damper is proposed. The wall limbs were connected using the damper to realize the rapid assembly and improve the seismic performance of the fabricated shear wall structure. Four fabricated shear wall specimens and one cast‐in‐place comparison specimen were prepared, and a low‐cycle repeated load test was carried out under an axial compression ratio of 0.1. Results show that the fabricated shear wall structure features slightly reduced bearing capacity but obviously improved ductility, and the energy dissipation of the damper improves the seismic performance of the structure. The damper can dissipate energy rapidly, reduce the damage degree of the wall limbs and work stably, suggesting its good performance as a connector.

An Experimental Study on Scale Effect in Dynamic Shear Properties of High-Damping Rubber Bearings

High-damping rubber bearing (HDRB) is one of the most popular devises which is applied for seismic isolation of structure. In order to clarify characteristics of the HDRB, various loading tests of the bearings have been conducted and the data is applied to the practical design of isolation systems. In this study, in order to investigate the scale effect on physical characteristics of HDRB, dynamic loading tests with full-scale, and scaled-model isolators, which has diameter of 1000mm, and 225mm respectively, were conducted. The test protocol covers shear strain dependency, frequency dependency tests, and repeated loading test, and the difference in shear characteristics caused by specimen scale were investigated. Repeated loading test was conducted only with scaled model, and relationship of temperature increase of the specimen and shear characteristics were evaluated. In parallel, finite element analysis (FEA) of the isolator under repeated loading was conducted. After the constitutive model of FEA was identified by the results, the FEA was extrapolated to simulate repeated loading of 1000, 1600mm diameter isolators, which can not be tested realistically by dynamic loading. dynamic loading, and change of properties along increase of number of cycles, and temperature distribution between full-scale and reduced-scale was investigated. Necessity of consideration for scale effect in evaluation of HDRB properties by dynamic testing is discussed.

Factors affecting the rutting resistance of asphalt pavement based on the field cores using multi-sequenced repeated loading test

Rutting or permanent deformation is one of the main failure modes in hot mix asphalt (HMA) pavement. Since laboratory-produced specimens could hardly reflect the actual compaction condition and material properties of asphalt mixtures in the field, it is necessary to evaluate rutting resistance in situ pavement conditions based on field cores. In this study, field cores of 30 different road sections were collected from 7 different highways in Jiangsu Province, China. A newly developed multi-sequenced repeated load (MSRL) test by Southeast University was conducted on both full-depth specimens and separated layers considering the actual load-axle spectrum and temperature gradient in the corresponding sections. A new indicator, Compound Strain Rate (εc), which indicates the deformation rate of asphalt mixtures under the actual load-axle spectrum, was proposed to evaluate the rutting-resistant of different field materials. Then, statistical evaluation including distribution analysis and Analysis of Variance (ANOVA) were conducted on the test results. According to the analysis of the correlation between εc of full-depth specimens with samples from different layers, the rutting resistance of the middle layer presents the most significant influence on the high-temperature stability of the full-depth pavement structure. In terms of material factors, binder type exhibits a significant effect on the rutting resistance of all layers while gradations only influence the results of the top layer. Considering the external factors, both road age and the accumulative number of equivalent single axle loads (ESAL) could influence the rutting resistance of different field materials, especially, the εc of materials from the middle layer. Moreover, the influence of material factors on permanent deformation performance of asphalt pavement under different traffic loads was analyzed.

Performance evaluation of warm mix asphalt using natural rubber modified bitumen and cashew nut shell liquid

Warm Mix Asphalt (WMA) is an innovative technology that aims at decreasing the mixing and compaction temperature of asphalt mixtures as compared to the conventional Hot Mix Asphalt (HMA) thereby reducing harmful emissions and fuel consumption. The rubberized asphalt mixtures are found to have better physical and strength properties, but they are compacted at a higher temperature than that of conventional mixes. In this study Cashew Nut Shell Liquid (CNSL), an organic additive, was added from 0.5% to 3 % by weight of the binder at an increment of 0.5 % to modify the bitumen. The optimum content of CNSL to reduce the viscosity was found to be 2% and the viscosity reduction was 44.4 % at 140°C The modified NRMB (Natural Rubber Modified Bitumen) was used to prepare Dense Bituminous Macadam (DBM) and a comparison of volumetric, stability and rutting characteristics of both Natural Rubber modified Hot Mix Asphalt (RHMA) and Natural Rubber modified Warm Mix Asphalt with CNSL additive (RWMA) was made. Storage stability results indicated that there was no phase separation between rubberized bitumen and additive at high temperature and will act as uniform blend at high temperatures. Dynamic Shear Rheometer test results showed that the addition of CNSL to rubberized bitumen increased the values of G*/sinδ and could improve the resistance of asphalt binder against rutting. Stability value of RWMA was 11.5 % higher than that of RHMA and rutting depth was 10.1 % less than that of RHMA. The fatigue strength results obtained from Repeated Load Testing showed that the number of cycles to failure at 20% stress level was 9.04 % more for RWMA than RHMA. All volumetric properties of both RHMA and RWMA were within the limits specified by Ministry of Road Transport and highways (MoRTH) 2013. The statistical analysis authenticates the experimental findings. ANOVA analysis for Marshall Quotient revealed that RWMA had improved compaction characteristics than RHMA and the result for rutting and fatigue strength showed that the additive CSNL and temperature had significant effect on rutting resistance and fatigue life.

Seismic behavior of corroded reinforced concrete column joints under low-cyclic repeated loading

To investigate the influence of corroded steel bars on seismic performance of reinforced concrete (RC) columns, eight full-scale RC columns were designed and fabricated, which were composed of one uncorroded RC column, three RC columns with longitudinal reinforcement corrosion and four stirrup-corroded RC columns. The electrochemical test was conducted to accelerate the corrosion of steel bars in RC columns, and the low-cyclic repeated loading tests on RC columns with corrosion-damaged steel bars were carried out. The seismic behavior indicators, including the hysteretic curves, skeleton curves, displacement ductility coefficient, stiffness degradation curves and energy dissipation capacity of corroded RC columns and uncorroded columns, were compared and discussed. The experimental results show that with the increase in steel bars corrosion degree, the pinch phenomenon of the hysteretic curve gradually increases, and the energy dissipation capacity, stiffness and plastic deformation capacity of specimen reduce significantly. The ductility and energy dissipation coefficient decreased by 20% and 36%, respectively, when the stirrups corrosion ratio of specimen reaches 15.2%, and a shear failure surface was formed in the plastic hinge zone at the foot of the columns, which leads to the change of failure mode from ductile bending failure to shear failure with poor ductility under the ultimate load for corroded columns. The influence of stirrup corrosion on the failure mode of specimens is remarkable, but the effect of longitudinal reinforcement corrosion is negligible for specimens with the corrosion ratio within 14.7%. The adverse effects caused by over 15.2% stirrup corrosion should be considered in seismic design of structures in seismic zone.

A simple method to assess replacement period of polyurethane railpad in urban railway

The service life of polyurethane railpads used in urban railways was investigated using static stiffness, thermal accelerated, fatigue, and thermal repeated loading tests. Railpads subjected to repetitive train loads and temperature changes were collected from railway sites to determine the static stiffness as a function of usage time. The stiffness of new railpads showed nonlinear behavior, unlike the linear behavior of used railpads. Thermal repeated loading tests were performed to investigate the accelerated degradation of the railpad exposed to thermal and nonthermal loading conditions. The acceleration factor and relationship between usage time and number of cyclic loads were used to predict the replacement period.

Reducing Production Temperature of Asphalt Rubber Mixtures Using Recycled Polyethylene Wax and Their Performance against Rutting

Abstract The addition of crumb rubber to asphalt binder and asphalt mixture produces desirable performance-related properties and is a step toward the pursuit of sustainable development. Nevertheless, higher mixing and compaction temperatures of asphalt rubber mixtures compared to the conventional ones may result in higher construction costs and additional environmental issues. To deal with these problems, the implementation of synthetic waxes in asphalt rubber mixtures can be used to reduce mixing and compaction temperatures. For this purpose, different contents of recycled polyethylene wax were used. The mixing and compaction temperatures of the modified mixtures were determined using the aggregate coating method and densification curves, respectively. Afterward, the effect of mixing temperatures on the rutting properties of the prepared specimens was investigated using a repeated load test. The results demonstrated that using recycled polyethylene wax not only decreased mixing temperatures considerably but also significantly improved rutting resistance.

Flexural Behaviours of Box Segmental Beams with Internal Tendons Subjected to Repeated and Static Loads

The main objective of this study is to gain a better understanding of the behaviours of different types of joints when box segmental beams are subjected to bending. Five beams with internal tendons were thus produced and tested: one beam was cast monolithically as a reference beam and four were formed as segmental beams. All beams were produced using Self Compacting-Concrete (SCC) in box sections. Each segmental beam was formed by assembling three precast concrete segments with four post tensioning tendons. The segmental beams had the same general characteristics, but with different types of joints between the segments. Four types of joints were adopted in this study;-dried, epoxied, dried strengthened with carbon fibres and multi-steel shear keyed joints. All beams were tested under two types of loadings, repeated and static. A test of repeated loading was carried out by exposing each specimen to three loading cycles. Each cycle was implemented by subjecting each specimen to up to 40% of the ultimate load then releasing the loads to return the specimen to the non-loading case. The test of static loading was carried out at the same rate of loading as the repeated load test, and all girder specimens were tested up to failure. The loads versus deflections at specified points were recorded for each 5 kN. Cracking, mode of failure and ultimate load values were recorded, along with the concrete surface strains at specified locations for both loadings. The tests results for repeated loading showed that joint type had a clear effect on behaviours in the segmental beams, which had deflection readings ranging from 16 to 61% higher than that of the monolithic (reference) beam, as well as higher tensile strain than seen in the reference beam, by 8 and 67%. Similar effects of joint type were observed under static test. At the first crack loading, the segmental beams had deflections of between 8 and 94% and tensile strains of about 5 to 18% more than the reference beam. The failure modes of the tested beams were all different. Failure of the dry joint occurred in the segment interface, while the failure of each epoxied joint and joint strengthened by carbon fibres developed in the concrete adjacent to the segment interface. The steel shear keys clearly transfer the shear resistance to the concrete parts adjacent of the joints.

Seismic Behavior and Finite Element Analysis of Reinforced Concrete Short Columns Impacted by Oblique Earthquakes

This study evaluates the seismic behavior of reinforced concrete (RC) short columns with a high axial compression ratio under oblique earthquake conditions. The studied parameters include the loading angle, axial compression ratio, the high‐strength stirrups with small spacing, and the carbon‐fiber‐reinforced polymer (CFRP) wrapped column end or outer steel plate mesh at the end of the column. Low‐cycle repeated loading tests were used to analyze the specimens’ seismic performance indices of hysteretic behavior, strength, stiffness, deformation capacity, and energy dissipation capacity. Results suggest that the OpenSees finite element program can sufficiently simulate the nonlinear response of the specimen. Oblique loading led to the increase of damage to the specimens and the deterioration of stiffness of the specimens, which was especially seen with the increase of the axial compression ratio. Accordingly, arranging high‐strength stirrups with small spacing and the column end outer steel plate mesh both transform the failure mode from shear failure to bending shear failure. Additionally, wrapping the CFRP at the end of columns improves their strength but does not improve their deformation capacity. The demonstrated success of these strategies in improving the seismic performance of RC short columns under diagonal loads with high axial compression ratios can inform practical engineering applications.

Influence of recycled concrete aggregate treatment methods on performance of sustainable warm mix asphalt

This study aimed to investigate the usability of Recycled Concrete Aggregate (RCA) in warm mix asphalt (WMA) as the implementation of sustainable construction technology. Five replacement rates (0%, 25%, 50%, 75%, and 100%) were tested for the coarse fraction of virgin aggregate (VA) with 3 types of RCA: untreated RCA, HL-treated RCA, and HCL-treated RCA. Scanning electron microscopy (SEM) analyses were performed to investigate the surface morphology for both treated and untreated RCA. The optimum asphalt cement content for every substitution rate was determined using Marshall mix design method. Thereafter, asphalt concrete specimens were prepared using the optimum asphalt cement content, followed by the evaluation of their performance properties, including the moisture damage, resilient modulus, and permanent deformation characteristics. These properties were assessed using indirect tensile strength and uniaxial repeated loading tests, respectively. It was found that, for mixes with RCA content of 100%, the untreated RCA mixes possess higher OAC than that of treated RCA mixes by 0.26%. The moisture susceptibility was improved in case of HL and HCL treated RCA by 9.09% and 10.34% as compared to untreated RCA. However, the resilient modulus and resistance to permanent deformation for the mixes with 100% RCA were lower than those prepared with VA; the decrement in Mr values are 39.17%, 28.56% and 23.09% for the untreated RCA, HL-treated RCA and HCL-treated RCA, respectively. Finally, the cost, material, and energy-saving implications of RCA were discussed.

Study of retroanalysis of asphaltic pavements resilience modules with the use of artificial neural networks

O conhecimento dos Módulos de Resiliência (MR) de pavimentos é elemento importante para a avaliação estrutural das infraestruturas existentes. Uma maneira de determiná-los é através de ensaios dinâmicos de carga repetida, em laboratório; outra forma, é utilizar a técnica de retroanálise, que consiste na obtenção dos MR a partir das espessuras das camadas e das deflexões medidas na superfície do pavimento. Nesse sentido, este artigo tem o objetivo de apresentar a retroanálise dos MR através da técnica de Redes Neurais Artificiais (RNA) como alternativa à retroanálise tradicional. Os resultados demonstraram que as RNA conseguem prever os MR com resultados de coeficientes de determinação (R2) acima de 99,9% entre os valores de referência e previstos. Desse modo, as RNA se apresentam como uma alternativa em potencial para a obtenção dessa importante propriedade mecânica dos materiais para pavimentação frente aos métodos tradicionais.

Effect of Different Aggregates on the Mechanical Damage Suffered by Geotextiles.

The installation process of geosynthetics can be, in some applications, one of the most relevant degradation mechanisms of these construction materials, affecting their performance and useful lifetime. In this work, three nonwoven geotextiles with different masses per unit area were submitted to mechanical damage under repeated loading tests with corundum and with different natural aggregates. The damage occurred in the geotextiles was evaluated by visual inspection and by monitoring changes in their short-term tensile and puncture behaviors (mechanical properties) and in their water permeability behavior normal to the plane (hydraulic property). The mechanical damage under repeated loading tests provoked relevant changes in the mechanical and hydraulic properties of the geotextiles. These changes depended on the mass per unit area of the geotextiles and on the characteristics of the aggregates. The results enabled the establishment of a correlation between the loss of mechanical strength and the variation of the water permeability normal to the plane of the geotextiles.

Effectiveness of geogrid and its position on the performance of unpaved roads under repetitive loading

Road network provides access to communities and plays a vital role in the economic development of a country. These days, the transportation sector is given the utmost importance as premature failures are very common owing to rapid industrialization and urbanization. Also, subgrade failure is a very common scenario in pavement failures. To prevent these failures, geosynthetics have been used widely. In this study, model pavement sections were built in a steel tank with black cotton soil as subgrade forming a weak subgrade layer followed by granular sub-base (GSB) and sacrificial layer at the top. Two biaxial geogrids were considered as reinforcing material, and their position was varied within the GSB layer. The pavement thickness was varied by varying the thickness of GSB. The GSB of thickness 0.25 m, 0.30 m, and 0.35 m were considered. The effectiveness of geogrid on the pavement performance was evaluated by varying the position (one-third from the top, middle, two-third from the top and interface of subgrade and GSB) of geogrid within GSB. The pavement was subjected to repeated load test to simulate traffic loading. The loading frequency was kept at 0.01 Hz. The settlement of the pavement was recorded in terms of total and plastic settlements along the surface below the load point and away from the load point. Based on the test results, the geogrid placed at a depth of two-third thickness of GSB from the top showed improved performance and is effective compared with other positions. With geogrid reinforcement at optimal position, the reduction in plastic settlement is in the order of 34% to 52% depending on the geogrid stiffness and GSB thickness thereby improving the rutting performance of the pavement. Also, with geogrid reinforcement, it is possible to reduce the pavement thickness with equivalent and/or better performance of the pavement when compared to unreinforced pavement depending on the tensile strength of the geogrid. Thus, geogrid can be used to design pavements that are durable and with low maintenance cost making sustainable pavements.

Study on shear capacity of ultra-high performance concrete squat shear walls

Ultra-high performance concrete (UHPC) is a new building material with great application prospects in the engineering field. The material’s advantages include high strength and good durability, which can reduce the cross-sectional area of members and the weight of the structure. In order to study the shear capacity of a UHPC squat shear wall, a low-cycle repeated load test was carried out on a specimen with a height-to-width ratio of 1.0. Shear failure of the specimen occurred, and the cracks were widely distributed. A large cracking load and bearing capacity were achieved, and the specimen's deformation performance met the current code’s requirements. Based on the test results, formulas for calculating the cracking load and shear bearing capacity are proposed for a UHPC shear wall with an inclined section. A comparison of the calculated and measured results indicates that the proposed formulas reflect the test results well, enabling their use in engineering applications.

Performance of the Developed Water Intake System Using Sluice Device with Differential Lift-Rig

Current water intake systems contain one sluice gate connected to one winch and an inclined conduit, and these have structural weaknesses. To address this weakness and provide a remedy, we have developed a water intake system that can connect multiple sluice gates to one winch and an inclined conduit. This new system can open and close multiple sluice gates using differential lifting devices. Mock-up tests and repeated loading tests have been conducted to confirm the correct operation and leakage status of the developed water intake system. To evaluate the performance of the developed water intake system in terms of streamline, speed, and flow rate, the numerical simulation of the computational fluid has been carried out by selecting four cases of the existing and four cases of the newly developed intake system in their upper, central, and lower parts, and the opening conditions for all of the intake openings. Simulation results show that the newly developed water intake system has better performance characteristics compared to the existing water intake system; a new maximum water speed increased by 46.2 %, new flow rate at the exit side increased by 12.5 %, and new maximum flow rate increased by 5.1 %.

Prefabricated Concrete Sandwich Wall with T-type under Cyclic Loading

In this research, a new sandwich wall system has been presented as structural elements which has unique structural configuration such as core column reinforced by spiral stirrup along the panel cross-section with spacing 650mm, foamed concrete as insulation layer, self-compacting concrete used in external layers which is significantly different from traditional sandwich wall. Seismic performance of sandwich walls with planar or 3D steel wire system is studied by low cycle repeated load test. According to the analysis of hysteresis performance and skeleton curves, this sandwich wall exhibits good seismic performance and crack resistance. Specimen with 3D steel wire shows better seismic behavior with higher strength and ductility.

Tensile creep of asphalt concrete in repeated loading tests and its effect on energy dissipation

ABSTRACT Failure of asphalt concrete in repeated loading tests could be due to fatigue or due to creep of the material. In this study, the effect of creep on the damage of asphalt concrete in these tests was investigated. Stress-controlled repeated loading tests were conducted in uniaxial tension at different frequencies. A different stress amplitude was chosen for each frequency so that the initial average stored energy in a cycle remains constant. Results indicate that the tensile creep of asphalt concrete can have a considerable effect on the damage and failure of specimens. The variations of the apparent dynamic modulus and phase angle, and the total dissipation per cycle with time, when appropriately normalised, were found to be nearly independent of the frequency of the test. In addition, the dissipation of energy in these tests that is related to the damage of the material was further evaluated. Several techniques have been suggested in the literature for the calculation of damage-related dissipation. The suitability of these techniques was analysed using the results of the study. The dissipated creep strain energy (DCSE) was found to provide the most accurate characterisation of damage-related dissipation.

Experimental study on panel zone behavior of diaphragm-through connections to concrete-filled tube columns

In order to verify the accuracy of the panel zone shear capacity calculation method of diaphragm-through connections which were proposed in previous research, the low cycle repeated load tests of six cross-shaped specimens were carried out. The seismic performance of the panel zone’s stress distribution, failure mode, hysteresis curve, and skeleton curve are comprehensively studied and analyzed. The results showed that the steel tube web and core concrete were mainly participating to bear the horizontal shear force, and the “steel frame” composed of the steel tube flange and through-diaphragm was negligible for the shear resistance; the core concrete strut calculated width and height were all one-fourth of the height and width of the panel zone. The test results are in good agreement with the results of the calculation method, which indicated that the calculation method proposed in the previous research results had good accuracy and applicability, and would use for the panel zone shear capacity calculated in the connections design.