Load Test Apparatus Research Articles

Development of a new loading test apparatus for microfocus X-ray CT and its application to the investigation of soil behavior surrounding driven open-section piles

In recent years, X-ray CT scanners with task-specific modifications, such as microfocus and/or a synchrotron, have been widely implemented in a variety of fields, including medical and industrial fields. Since microfocus X-ray CT systems enable the visualization of whole samples, and also yield a relatively high resolution of the region of interest in the sample, they are commonly utilized in the fields of soil mechanics and geotechnical engineering. This paper describes a novel loading test apparatus that is specifically designed for microfocus X-ray CT systems capable of performing loading tests to investigate soil behavior during the installation of driven open-section piles. The loading tests were designed to take the micro-level spatial resolution of microfocus X-ray CT systems into account. Digital image correlation (DIC) is subsequently implemented to analyze the obtained CT images, making it possible for measurements to be taken of the displacement fields in the ground following installation of the model pile. Finally, the versatility of this novel test apparatus is proof of its high potential for application in different types of loading tests.

Fatigue life prediction of the modified asphalt mixtures with ANFIS modeling

In this study, the effect of Styrene-Butadiene-Styrene (SBS) modification on physical and mechanical properties of hot mix asphalt, in terms of fatigue characteristics, are evaluated.As such, 87 samples were prepared using 15 different mixtures, and the repeated load-fatigue indirect tensile test was applied to these samples using a Suleyman Demirel University (SDU) asphalt tester apparatus. In addition, it is also used to analyze the effects of gradation, bitumen percentage, loading, and polymer type on fatigue behavior. 18 control samples were prepared to analyze the effect of SBS modification on fatigue performance. The other objective of the study is to present the reliability of the computer controlled repeated loading test apparatus. Linear regression and Adaptive Neuro Fuzzy Inference System (ANFIS) was used to analyze the results of the test, and models were developed and analyzed in terms of modeling. At the end of the study, the variables that are effective in improving the fatigue performance are addressed in detail, as well as the ANFIS environment likely to be used in non-linear modeling of such studies.

Evaluation of Reinforced Sub-Base Layer on Expansive Sub-Grade Soil

Reinforcedpavementlayershavebeengainingpopularityinthefield ofcivil engineeringdue totheir highlyversatileandflexible nature.Withthe adventofgeosynthetics in civil engineering, reinforced earth technique has taken a new turn in its era. The practice of reinforced earth technique became easy and simple with geosynthetics. The research requirements are providing the materials and manufacturing of the loading machine (loading test apparatus). Materials include soil (bentonite), granularsub base, sand, and geogrid. The testing program consists of preparing of 6 models that represent layers beneath flexible pavement layers (subgrade and sub base layers). The model dimensions are 800*800*800 mm, subgrade layer is 400 mm thick and sub base layer 300 mm thick. The model tests include using geogrid reinforcement at the interface of the subgrade and sub base layer and in the center of sub base layer. It was concluded that a geo-grid reinforced soil is stronger and stiffer and gives more strength than the equivalent soil without geo-grid reinforcement. Geo-grids provide improved aggregate interlock in stabilizing road infrastructure through sub base restraint and base reinforcement applications, Geo-grid reinforcement provided between the sub base course and subgrade soil carries the shear stress induced by vehicular loads and thus it reduces the load transferred to the subgrade and the volume changes induced by swelling of the subgrade soil. The load carrying capacity of the pavement system is significantly increased for geogrid reinforced sub base stretch compared to unreinforced sub base layer on expansive soil subgrade. Comparison of the results of the model without geogrid reinforcement with other models reveals that there is an increase in the bearing capacity of model that includes geogrid reinforcement at the interface of subgrade by about 40%; and 20% for the model that consists of geogrid reinforcement in the center of sub base layer.

Impact of reinforcement layer material and thickness on deflections measured in the static and dynamic plate load tests

The bearing capacity and compaction values obtained in the plate load tests (the latter determined indirectly) often depend on the used test method: static - using static load test apparatus (VSS) or dynamic - using light weight deflectometer (LWD). Despite extensive comparative studies the correlation between two test methods still remains an issue. With the values obtained in the field tests and with the use of numerical calculations allowing for the impact of viscoplastic phenomena, the authors managed to demonstrate how big is the effect of not only the type of material, but also of the thicknesses of the reinforced subgrade layers on the discrepancy between the displacement values obtained with the two test methods in consideration. The behaviour of the subgrade material during the tests was verified using the finite element method. The share of elastic, plastic and creep strains in the total strain was determined for different layered systems and thicknesses.

A study on the deformation characteristics of ballasted track at structural transition zone by multi-actuator moving loading test apparatus

At a structural transition zone between concrete structure and embankment, settlements of ballasted tracks generally become larger than those in a general section. To investigate the deformation characteristics of ballasted track at the transition zone, scale model tests using multi-actuator moving loading test apparatus were carried out. This test apparatus is equipped with sixteen electric–hydraulic actuators to simulate a moving train load traveling on the rails. In the test case without any buffering structure at the transition zone, large local settlement appeared even under the condition of constant moving load without any dynamic wheel load change. Conversely, by installing an approach block (wedge-shaped backfill with well graded and well compacted crushed stone) at the transition zone, local large settlement did not appear. Similarly by installing an approach slab (reinforced concrete slab) or a resilient mat (resilient polyurethane mat installed on the concrete structure), settlement at the transition zone became less than that in the case without any buffering structure.

Edge load strength test for indirect estimation of unconfined compressive strength

In this paper a new test called “Edge Load Strength” (ELS) for indirect estimation of unconfined compressive strength (UCS) of rock samples is introduced. The test apparatus is almost the same as point load test apparatus except that a flat seating replaces the lower conical platen of the point load apparatus. A cubic rock sample is placed on this seating and the point load is applied by the upper conical platen at a certain point close to the edge of the sample. The applied loads and the vertical displacements are continuously recorded during loading. The failure surface passes through the point of application of the point load by the upper conical platen and the front face of the specimen. ELS is carried out on 10 rock types and the results are correlated with the results obtained from UCS tests. It is shown that rather good correlations exist between ELS and UCS tests for the estimation of rock strength and elastic modulus.

Relative brittleness characterization of some selected granitic building stones: Influence of mineral grain size

Being crystalline materials, brittleness may be an important issue for granitic rocks, especially when they are subject to certain loading conditions. Therefore, in practice, more specifically in their usage as a natural building stone, there is a need for their brittleness characterization. This paper reports a study carried out on some selected granitic rock types in order to determine their relative brittleness index values and relate it to their mineral grain size. For this purpose, three different types of granitic rocks similar in mineral composition, but diverse in grain sizes were selected for the execution of the study. The relative brittleness index values of the studied rock types were determined from the size effect method by using the point load test apparatus. Based on the results of this investigation it is was concluded that, rather than the proportions of the rock forming minerals such as quartz and feldspars, the grain size of feldspars could be the dominant parameter affecting relative brittleness values of the tested rocks.

Restoring Force Characteristics of Laminated Rubber Bearings Under Various Restraining Conditions

We conducted the measurement of restoring force characteristics of laminated rubber bearings under various restraining conditions. In the experiment, we provided three laminated rubber bearings with various second shape factors S2=3,4,4.94. The restoring force is obtained by using a newly designed combined loading test apparatus. By using this apparatus, the laminated rubber bearing could be subjected to shear, compressive and rotational deformations independently. In this experiment, we defined the degree of restraint as the ratio of the bending moment to the restricting bending moment which was measured when the rotation angle of the laminated rubber bearing was zero radian. This means that the flanges on both sides of the laminated rubber bearings were kept parallel during horizontal deformations. From the experiment, it was confirmed that restoring force characteristics were affected by the degree of restraint. Some reduction in restoring forces was observed when the degree of restraint was small. In particular the laminated rubber bearing with a small second shape factor, namely the rubber bearing, had a slender shape, easily buckling under small horizontal displacement. It was also confirmed that bending stiffness of the laminated rubber bearing had shear strain dependency and vertical load i.e., surface pressure dependency. The results of this experiment reveal that we should consider the reduction of the restoring force if the upper or lower structure of the laminated rubber bearing is not sufficiently rigid.

Pseudo-dynamic buckling experiments on thin cylindrical shells under biaxial seismic loads

A buckling design research program has been carried out to establish seismic design guidelines for a fast breeder reactor. In doing so, the buckling strength of the cylindrical part of the reactor vessel of a fast breeder reactor under horizontal and vertical seismic loads has been clarified. The effects of axial loads on the horizontal seismic responses in pre- and post-buckling states of thin cylindrical shells are investigated. Pseudo-dynamic buckling experiments are performed to study the dynamic buckling characteristics of thin cylindrical structures when subjected to seismic loads. The buckling tests use model cylinders made of an aluminum plate and a biaxial loading test apparatus. The axial seismic loads reduce the lateral load-carrying capacity of the shells in the pre- and post-buckling regions so that they amplify the horizontal response displacement. An amplification factor that accounts for the effects of the vertical loads is presented and its validity is verified experimentally.

RELATION OF CRUSHING STRENGTH OF SILICA BRICK AT VARIOUS TEMPERATURES TO OTHER PHYSICAL PROPERTIES*

The failure at elevated temperatures under constant load for silica brick is reported using the Iupuy load test apparatus. The crushing strength at 1500°F, 1800°F. 2100°F, and 2400°F is recorded, as well as the crushing strength at room temperature. The size of test piece utilized normally was 1 by 1 by 2′/2 inches. A definite relationship is shown to exist between the strength at room temperature and that at elevated temperatures. The effect of variation in lime content, bats content, and fluxes is also reported. Data were obtained on brick made from three different quartzites. Additional physical data are reported to give information concerning the properties of the brick tested.

THE TESTING OF SILICA BRICK

The Steger Load Test Apparatus. —Pressure was applied, in a granular-carbon resistance furnace, to the small test cylinders by means of a hollow carborundum rod. The temperature was read with an optical pyrometer sighted through this hollow pressure red. The volume changes were indicated by a pointer and scale and recorded by means of a rotating drum. (See Fig. 1.) Estimation of Quartz and Cristobalite in the Finished Br —The areas occupied by each type of crystal on the photomicrograph were determined with the aid of a transparent cross-section grating. Suggested Specifications for A1 Silica Brick. —Trust specific gravity not greater than 2.38; not more than 2% permanent Linear expansion after heating to 1600°C in one and one-half hours, and holding at that temperature for one-half hour; the amount of quartz land silicates) as determined by the grating method applied to photomicrograph should not exceed 15%.