Cyclic Traffic Loading Research Articles

Road surface permanent deformations with a shallowly buried steel-reinforced high-density polyethylene pipe under cyclic loading

Steel-reinforced high-density polyethylene (SRHDPE) pipe is a new type of pipe used in roadways for drainage due to its obvious advantages, such as good corrosion resistance and light weight. In some projects, they are shallowly buried. To investigate the effects of the shallowly-buried pipe on the permanent deformation of road surface under cyclic traffic loading, two laboratory tests of an unpaved road with a buried SRHDPE pipe under cyclic loading were conducted. A 610 mm diameter SRHDPE pipe was buried in a compacted sand trench covered by aggregate or sand base courses in Tests 1 and 2, respectively. A Mechanistic-Empirical (M-E) model was calibrated with the laboratory test data and then adopted to conduct a parametric study on the road surface rutting. It was found that the SRHDPE pipe has very small deflection under the cyclic traffic loadings. The M-E model could predict the permanent road surface deformations well under cyclic loading before the road failed. Parametric studies showed that the road surface permanent deformation was intensified as the stiffness of buried pipe increased. The road surface deformation decreased as the pipe embedment depth increased and an optimum pipe buried depth existed to get the same road surface deformation between the road sections with and without a drainage pipe.

Real-Time Output-Only Identification of Time-Varying Cable Tension from Accelerations via Complexity Pursuit

AbstractIn-service cables of structures, such as those in cable-supported buildings and cable bridges (e.g., stay cables and suspenders), suffer from cumulative fatigue damage caused by dynamic loads (e.g., the cyclic traffic loads on cable bridges) and wind excitation (on the cable-supported buildings and bridges). Monitoring the time history of time-varying cable tension for assessing their fatigue damage is thus essential to diagnose their health condition and predict their future performance. Currently, embedded measurement devices such as anchor load cells, elastomagnetic (EM) sensors, and optical fiber Bragg grating (OFBG) sensors are able to directly record the time-varying cable tension time history; however, poor durability, high costs, and intensive labor of installation significantly hinder their applicability in practice. On the other hand, a vibration-based technique manifests itself as a convenient, cost-effective, and reliable approach to determine the cable tension, and is widely used; it ...

Determination of traffic-load-influenced depths in clayey subsoil based on the shakedown concept

The determination of the depth of traffic load influence is significant for pavement and embankment design on soft soil. In this study, a method based on strain-controlled criteria is presented to estimate the depths within which the behavior of a saturated clayey subsoil is affected by cyclic traffic loads. Based on the shakedown concept, the following depths of influence can be defined: (1) the threshold depth, beyond which the dynamic effect of the traffic loads is insignificant; (2) the plastic shakedown limit depth, within which the subsoil experiences noticeable and continuous deformation; and (3) the critical failure depth, within which the soil fails due to the accumulation of strain. This method for determining the depths of influence is advantageous because it is applicable to various soil types. The data required for this method consist of vertical stress responses along the soil profile and three cyclic stress limits of the soil. Based on the development of pore pressure and the dynamic strain behaviors during undrained cyclic triaxial tests, the following cyclic stress limits of the soft clay subsoil are determined: a threshold cyclic stress ratio CSRt of 0.03, a plastic shakedown limit stress ratio CSRp of 0.33 and a critical cyclic stress ratio CSRc of 0.44. These cyclic stress limits are used to determine the corresponding depths of influence, which are then used to implement ground improvements and strengthen the dynamic carrying capacity of the road structures.

Cyclic behaviour of an unsaturated silt at various suctions and temperatures

Subgrade soils are constantly subjected to daily variations of temperature and suction in the field. Their deformation under cyclic traffic loads can greatly affect the performance of a pavement. Yet, the behaviour of unsaturated subgrade soils under cyclic loads at various temperatures and suctions is not fully understood. In this study, a new suction- and temperature-controlled cyclic triaxial apparatus was developed. Using temperature-compensated Hall effect transducers, the accumulated plastic axial and volumetric strains and resilient modulus of an unsaturated silt under cyclic loads were measured at suctions ranging from 0 to 60 kPa and temperatures ranging from 20 to 60°C. Experimental results show that yield stress increases with increasing suction (suction-induced hardening), but decreases with increasing temperature (thermal-induced softening). Consequently, axial plastic strain accumulated during cyclic loading–unloading is larger at lower suctions and higher temperatures. At a given temperature, measured resilient modulus significantly increases when suction increases. On the other hand, the influence of temperature on resilient modulus depends on suction level. At zero suction, resilient modulus is slightly affected by temperature. At suction larger than zero, an increase in temperature induces an obvious decrease in resilient modulus. It is evident that thermal effects on resilient modulus are more significant at unsaturated than saturated states.

Protocol for Testing Fouled Railway Ballast in Large-Scale Cyclic Triaxial Equipment

Abstract A testing protocol was developed to measure accumulation of vertical plastic deformation in fouled railway ballast under cyclic traffic loading. Large-scale cyclic triaxial (LSCT) test equipment was constructed to test fouled ballast under various stress conditions. A method of introducing fouling material and moisture to ballast specimens was critical to the resulting deformational behavior. Specimens for LSCT testing should be prepared by mixing ballast with relatively dry fouling material (moisture <5 % for granular fouling and <15 % for clay-based fouling) prior to compaction to prevent a heterogeneous distribution of fouling within the specimen. A full-scale track model experiment (FSTME) was built to determine a representative state of stress (RSS) for railway ballast for use in the LSCT testing. The RSS allows for testing of ballast under consistent stresses to compare the effect of material characteristics of fouling such as fouling content and moisture content. A RSS of 90 kPa (confining) and 300 kPa (deviator) for a train axle load of 264 kN was suggested based on the FSTME results. Measured deformation of fouled ballast using the proposed testing protocol was compared with a published vertical deformation of railway track in a track test section. Results of this study indicate that the proposed testing protocol can simulate the vertical plastic deformation of railway ballast at a specified stress level.

Tension bar systems under cyclic loading

The aim of the research presented in the paper is to clarify the behaviour of tension bar systems under cyclic loading. These components may be subjected to climatic conditions, especially to dynamic wind load, which may cause their vibrations. If the wind load were significantly influencing behaviour of the structure, the non negligible combination of normal force and bending moment would occur in the bar. Members used on bridges are additionally subjected to effects of cyclic traffic loads. Both dynamic wind load and traffic loading are major actions causing high-cycle fatigue of civil engineering structures and bridges.

Prediction of Permanent Deformation of Pavement’s Unbounded Layers Based on Cyclic Triaxial Tests

This research presents an analytical model for determining permanent deformation of pavement's sub-grade and unbound granular base and sub-base material due to cyclic traffic loading. The model is given for interpreting results of repeated load triaxial tests. It considers long term elastoplastic behavior and resilient behavior of sub-grade and unbound granular material. Permanent deformations are expressed as a function of the number of loading cycles and the spherical component and the deviatoric component of the repeated loading. The permanent axial deformation is given as a function of the resilient modulus and the secant modulus for different states of spherical and distortional stresses, and number of loading cycles. By analytical derivation it is presented that the normalized permanent axial strain can be expressed with the modulus values and the parameter D. The moduli are expressed as the functions of the spherical stress component and the distortional stress component. The magnitude of normalized permanent axial strain depends on the limit value of the resilient modulus and ratios between resilient and secant modulus. The parameter D gives the shape of the change of the normalized permanent axial strain with the number of cycles, and is a function of the change of modules with the number of cycles. The applicability of the presented model is demonstrated on the practical example of a repeated load triaxial test of sub-base granular material.

Experimental Study for Evaluating Crack Retardation of Asphalt Concrete Overlays

This paper presents the development of Asphalt Concrete Slab Fatigue Testing Equipment and its use in evaluating crack retardation of AC overlay under opening and mixed modes of displacement. The dense bituminous macadam (DBM) and the unreinforced and geotextile reinforced open graded asphalt concrete (OGAC) overlays are investigated under cyclic simulated thermal and traffic loads having 5 mm differential deflection with zero load efficiency factor. Variation of tensile force and deformation in AC overlay with a number of simulated thermal load cycles are observed and cumulative decay of parameters, viz. tensile force, stiffness, and shear modulus, are computed. Overlay life, decay parameters, base isolation, and fabric effectiveness factors (FEF) are also evaluated. It is found that the unreinforced OGAC overlay performed better than that of DBM as a crack relief layer. In purely opening mode of displacement the best performance shown by the geotextile reinforced OGAC overlay becomes worse under mixed mode of displacement.

SUBSIDENCE PREDICTION OF KANTO LOAM SOIL BASED SUBGRADE USING CYCLIC LOADING EXPERIMENT

In a road excavation to lay a gas distribution pipeline, the re-use of the excavated soil for the subgrade backfill greatly reduces the environmental impact. However, when Kanto loam soil, which is widely distributed in the Kanto region, is employed for the backfill material, the relationship between the amount of the subsidence of the subgrade soil and the cyclic traffic loading is needed. In this study, cyclic loading tests on Kanto loam soil were conducted to investigate the subsidence characteristics. The subsidence prediction method of Kanto loam soil based subgrade under cyclic traffic loading was proposed using the cyclic loading test results. A full scale traffic loading experiments against road beds backfilled with Kanto loam soil were carried out. Consequently, a good correlation was shown to exist between the amount of the predicted subsidence and the measurement results.

Composite deck construction for the rehabilitation of motorway bridges

Traffic decks of steel or composite motorway bridges sometimes provide the opportunity of using the composite action between an existing steel deck and a reinforced concrete plate (RC plate) in the process of rehabilitation, i.e., to increase the load-carrying capacity of the deck for concentrated traffic loads. The steel decks may be orthotropic decks or also unstiffened steel plates, which during the rehabilitation are connected with the RC plate by shear studs, such developing an improved local load distribution by the joint behaviour of the two plate elements. Investigations carried out, both experimentally and numerically, were performed in order to quantitatively assess the combined static behaviour and to qualitatively verify the usability of the structure for dynamic loading. The paper reports on the testing, the numerical simulation as well as the comparison of the results. Conclusions drawn for practical design indicated that the static behaviour of these structures may be very efficient and can also be analysed numerically. Further, the results gave evidence of a highly robust behaviour under fatigue equivalent cyclic traffic loading.