Large Test Specimens Research Articles

Probability distribution on cleavage fracture in function of Jc for reactor ferritic steel in transition temperature region

This paper presents the results and methods used for determining of probability of cleavage fracture toughness of ferritic reactor steel in transition temperature area. The steel tested in this study is steel know as 20MnMoNi 55 by DIN standard, typically used for structures working at low temperatures. In addition, the effect of test specimen geometry, temperature and fatigue crack initiation rate on fracture toughness was investigated in order to predict the fracture behaviour and probability of cleavage fracture. Two main studies joined in on one are presented in this paper. Testing in both studies were performed according to ASTM 1820 standard and the Weibull distribution with regression analysis, which includes fitting the experimental results in a logarithmic coordinate system, was used to predict the Jc values. Cleavage fracture probabilities in the function of Jc for large test specimen, C(T)100 and C(T)200 were determined based on the results obtained by testing of small C(T)50 specimens, for the purpose of direct savings and decreased costs of specimen testing. Cleavage fracture probability, represented by using Weibull distribution of experimental data will provide a clear insight into material behaviour at different temperatures. The influence of ΔK values during fatigue pre-cracking procedure on the fracture toughness scatter was also presented and discussed.

Weibull probability distribution for reactor steel 20MnMoNi55 cleavage fracture in transition temperature

This paper presents the results and methods used for determining of fracture toughness of reactor steel, denoted as 20MnMoNi55, typically used for structures working at low temperatures, in transition temperature area. In addition, the effect of test specimen geometry and temperature on fracture toughness was investigated in order to predict the fracture behavior and probability of failure. Failure probabilities (i.e. cleavage fracture) in the function of Jc for large test specimens, CT100 and CT200 were determined based on the results obtained by testing of small CT50 specimens, for the purpose of direct savings and decreased costs of specimen testing. Failure probability, represented using Weibull distribution of experimental data, will provide a clear insight into material behavior at different temperatures. Other factors affecting the obtained test results will also be discussed.

Characterizing damage and fracture of sheet metal materials using large scale test specimen

Several approaches to characterizing damage evolution and fracture behaviour of sheet metal materials are currently in existence. These are based on different testing methodologies and test specimen designs, some of which, when combined with higher sheet thicknesses used for aluminium alloys in the automotive field, can reach and exceed geometrical limits required for the plane stress assumption commonly applied to numerical modelling of sheet metal materials. Furthermore, if shell elements are to be used in modelling of such structures, the characteristic length of the element should be larger than the thickness of the modelled sheet material. In order to allow for element sizes accounting for the two considerations outlined above, new test specimen geometries covering a range of stress triaxialities have been developed with a deformation region significantly larger than that of other commonly used test specimen designs. The geometries have been manufactured and tested on an automotive grade AA6xxx series aluminium alloy with DIC strain measurement to determine failure strains. The results were then applied to finite element models using various element sizes and the behaviour of the numerical models compared to the test results.

Three-dimensional periodic materials as seismic base isolator for nuclear infrastructure

Recent advance of periodic materials from the field of solid-state physics into that of earthquake engineering has resulted in a novel seismic isolation technique. In this study, we developed a new configuration of structural foundation using a three-dimensional (3D) periodic material for seismic isolation of critical infrastructure, particularly nuclear infrastructure. To this aim, we first performed analytical and finite element studies to compare two different types of 3D unit cells, i.e., Bragg Scattering and Locally resonant unit cells, to investigate their characteristics and applicability as a seismic isolator. We then designed a large scale test specimen based on the Bragg-scattering type unit cell using common construction materials: reinforced concrete blocks and polyurethane sheets. The designed test specimen was constructed and tested using a shake table subjected to different types of excitations in the horizontal and vertical directions as well as the torsional mode. The dynamic response of a small modular reactor (SMR) building model protected by the 3D periodic foundation demonstrates that 90% response reduction was achieved within the frequency band gaps. The response attenuation was achieved in all three tested directions. Moreover, the periodic foundation-isolated SMR building exhibited a stable response with negligible rocking on the structural system.

Effects of High Temperature on the Burst Process of Carbon Fiber/PVA Fiber High-Strength Concretes.

This paper carried out burst tests on the carbon and polyvinyl alcohol (PVA) fiber high-strength concrete specimens to investigate the effects of fiber type, fiber content, water content, heating rate and test specimen size on the burst, and the whole burst process of fiber-high concrete was photographed and recorded. The results indicated that fiber addition will improve the high temperature burst behavior of the high-strength concrete, and the performance of PVA is greatly different from that of carbon fiber. The water content and heating rate have little influence on the burst of the PVA test specimen, but they will greatly affect the carbon fiber test specimen. The size of the test specimen has a great influence on the burst. For the PVA concrete test specimen, the large size test specimen bursts on the surface; as for the carbon fiber test specimen, the large size test specimen delays the initial burst time, but the burst becomes fiercer.

An Automated Large-Scale Apparatus for 3-D Cyclic Testing of Soil-Structure Interfaces

Soil-structure interfaces exist widely in many geotechnical applications and play an important role in soil-structure interaction. Few data have been found on the three-dimensional (3-D) interface behaviors because of the limitation of test devices. A new large-scale test apparatus—the 80-ton 3-D Multifunction Apparatus for Soil-structure interface (3DMAS)—has been professionally designed and developed to investigate the cyclic behaviors of soil-structure interfaces subjected to 2-D and 3-D complex loading conditions. New features of the 3DMAS apparatus include: (1) accurate 3-D loading and control system to allow 3-D interface tests; (2) high loading capability and installation of large test specimens; (3) new measurement method to enable the direct measurement of the structure’s displacement relative to the soil; (4) accurate application of three typical boundary conditions normal to the interface; (5) accurate application of various shear paths in tangential direction; (6) computerized and automated control and measurement systems, allowing forces and displacements to be easily and accurately controlled and measured. The effectiveness and reliability of this apparatus has been verified by a series of 3-D displacement-controlled and stress-controlled direct shear tests conducted on the interface between gravelly soils and structures under the three normal conditions of constant stress, constant stiffness, and constant volume. Typical test results indicate that the 3-D mechanical behavior of soil-structure interfaces is significantly different from the 2-D behavior and that it is necessary to systematically investigate the 3-D shearing behavior of the interface.

Class A and C predictions for Ballina trial embankment with vertical drains using standard test data from industry and large diameter test specimens

Consolidation using prefabricated vertical drains has been one of the most popular ground improvement methods in the past few decades. In this paper, a benchmarking exercise is performed to compare the accuracy of the available methods through both Class A and Class C predictions for a trial embankment stabilised by prefabricated vertical drains (PVD) at the site of the National Field Testing Facility (NFTF). In this paper, the main difference between Class A and Class C is that additional soil properties specially required to represent the visco-plastic behaviour or creep have been included, which were absent in the authors’ original Class A predictions made before the availability of field data. Naturally, the inclusion of visco-plastic behaviour improves the settlement and excess pore water pressure predictions significantly, especially after about 1–1.5years. The site is located in Ballina, NSW and is owned by the Roads and Maritime Services (RMS) of NSW. A trial embankment was constructed over this soft Holocene clay under the auspices of the ARC Centre of Excellence in Geotechnical Science and Engineering (ARC-CGSE). Prefabricated vertical drains were installed with an array of field instrumentation including inclinometers, piezometers, settlement plates and total pressure cells. Large scale consolidometer testing was also carried out on undisturbed soil specimens (350mm in diameter) retrieved from the site to obtain additional consolidation parameters needed for radial consolidation analysis. Class A and Class C predictions were performed via numerical and analytical approaches. The results show, that for this case history, the suggested approaches can match the observed field performance well, with the exception of long term excess pore water pressures (say beyond 1.5years) and the lateral displacement approaching the ground surface.

Imperfection analysis on the patch loading resistance of girders with open section longitudinal stiffeners

Previous studies proved that the patch loading resistance model of the EN1993-1-5 can lead to significant underestimation of the patch loading resistance in case of longitudinally stiffened girders. Recently there are several research activities to improve the design method. In the current study experimental research program is executed on 8 large scale test specimens having different longitudinal stiffener configurations and loading lengths to extend the available background and to verify advanced numerical model. In parallel to the experiments a finite element model is developed considering the geometrical and material nonlinearities and geometric imperfections. The current paper presents the experimental tests and focuses on the modelling technique of the geometric imperfections, which can have large importance in case of coupled instabilities. Based on the experiments and numerical investigations design recommendations are given for equivalent geometric imperfection shapes and magnitudes for girders with longitudinally stiffened web. The measured resistances are compared to different resistance models found in the international literature and their accuracies are evaluated.

FIRE RESISTANCE OF ALUMINIUM GLAZED CURTAIN WALLS, Test results comparison depending on the side of fire exposure

This paper discusses the main issues related to the fire resistance of aluminium glazed curtain walls including the tests methodology and way of classification of this type of building elements. Moreover, the paper presents the comparison of fire resistance test results of large test specimens of curtain walls in full configuration depending on the side of fire exposure. Temperature rises have been compared on unexposed surface of the curtain walls tested for standard and external fire exposure. To made the comparison four test specimens of glazed aluminium curtain walls in full configuration, were tested. Curtain walls had the same transom – mullion structure. Two test specimens were tested for external fire exposure, and two for standard fire exposure. Dimensions of exposed surfaces were 5000 x 4500 mm (width x height) for external fire exposure and 5000 x 4800 mm (width x height) for internal fire exposure.

Assessment of Fatigue Behaviour of Orthotropic Steel Bridge Decks using Monitoring System

During the last decades orthotropic steel decks have become a widely used component of steel bridges, however high numbers of fatigue cracks have been recently detected in these structure types. It is well known, that the orthotropic decks are sensitive to fatigue damage, therefore safe fatigue design is important for the safety assessment of bridge structures. The fatigue damage assessment and life prediction of steel bridges can be carried out by using online structural health monitoring systems (SHM). By using the SHM system, it is possible to detect deterioration, determine anomalies and assess the safety level which will allow optimum maintenance strategies. On-structure long-term monitoring systems have been already successfully implemented on bridges all around the world in order to detect cracks just like on the orthotropic steel deck structure of M0 Háros Danube highway Bridge in Hungary. The purpose of the current research program is the investigation and analysis of the fatigue behaviour of this orthotropic steel bridge deck and the evaluation process improvement of the data rows collected by the monitoring system. Additional laboratory tests are carried out at 6 large scale test specimens at the Budapest University of Technology and Economics, Department of Structural Engineering to determine the fatigue resistance of closed section longitudinal stiffeners. In parallel finite element model is developed to simulate the fatigue behaviour of the analyzed components and to investigate its fatigue behaviour by numerical analysis. The aim of the current study is to analyze and verify the structural behaviour of the orthotropic steel deck on the basis of the executed test results, numerical simulations and the strain-time history data from the online structural health monitoring system implemented on the studied bridge.

Development of a 1200-mm-Diameter Round Panel Test for Post-Crack Assessment of Fiber-Reinforced Concrete

AbstractThe ASTM C1550 round panel test is now used widely to assess the post-crack performance of fiber-reinforced concrete (FRC) and fiber-reinforced shotcrete (FRS) and is firmly established as the most repeatable means of post-crack performance assessment available for these materials. However, the 75-mm standard specimen thickness for this test method has limited its application to relatively thin-walled structures such as FRS linings in mines and tunnels. The performance characteristics of FRC in bending depend on the thickness of a member, and thus a specimen with a thickness close to that in the intended application should be used for representative performance assessment. For this reason, tests such as ASTM C1609/C1609M, based on a 150-mm-deep beam, are typically used for thick-walled applications such as FRC tunnel linings and pre-cast elements. Unfortunately, the high single-operator variability characteristic of performance parameters obtained using beam tests has burdened the construction industry with unnecessarily expensive FRC designs, because the resulting margin between target performance and design requirements becomes excessively large. In response to this, demand has arisen for an enlarged version of the 75-mm-thick ASTM C1550 panel that can be used as a quality assurance tool for thick-walled FRC applications. The present paper describes the development of a version of the ASTM C1550 round panel 150 mm thick and 1200 mm in diameter with specific emphasis on developing thickness correction factors and characterizing the single-operator variability for these large test specimens. It also establishes a correlation between residual strengths measured using ASTM C1609/C1609M beams and using 1200-mm-diameter round panels at comparable crack widths.

Role of specimen size upon the measured toughness of cellular solids

It is well known that the mechanical properties of cellular solids depend critically upon the specimen size and that a 'sufficiently' large test specimen is needed to obtain representative bulk values. Notwithstanding, the fracture toughness of cellular solids is still measured experimentally based on standards, such as the ASTM E399 and E813, developed for solid materials that do not possess an intermediate, 'cell-level' length scale. Experimental data in the literature appears to show that the toughness of stochastic 3D foams is, also, size-dependent. This paper presents the results of a detailed finite element (FE) study that will quantify, and identify the physical origin of, the size-dependent effect. Three-point bending of a single-edge notched (or SEN(B)) specimen, with a 2D Voronoi micro-architecture, is modelled numerically to obtain estimates of fracture toughness which are compared to those obtained with a 'boundary-layer' analysis.

A higher‐order method for determining quasi‐brittle tensile fracture parameters governing the release of slab avalanches and a new tool for in situ indexing

The tensile fracture of heterogeneous earth materials such as snow, ice, and rocks can be characterized by two fracture parameters—the fracture toughness and the fracture process zone length. The latter length scale characterizes the zone of microcracking surrounding a crack tip in a heterogeneous material. For alpine snow, these two fracture parameters influence the release dimensions and thus destructive potential of slab avalanches. In general, it is difficult to determine these parameters concurrently, and most experimental methods are based on first‐order scaling laws that have considerable errors unless very large test specimens are used. Here we introduce a simple experimental method based on a higher‐order quasi‐brittle scaling law that has never been applied to snow nor any other geophysical material. We conducted hundreds of beam bending experiments using natural cohesive snow samples to produce the most comprehensive measurements to date of the tensile fracture toughness and effective process zone length of snow. We also adopt a new penetration resistance gauge to index the fracture toughness data, addressing a longstanding need for better proxy measurements to characterize snow structure. The peak penetration resistance met by a thin blade proved better than the bulk snow density for predicting fracture toughness, a finding that will improve field predictions and facilitate comparisons of results across studies. The tensile fracture process zone, previously a highly uncertain length scale related to avalanche fractures, is shown to be about 5–10 times the snow grain size, implying nonlinear fracture scaling for the majority of avalanches.

Fire resistance tests of large glazed aluminium curtain wall test specimens – results comparison

Four test specimens, glazed aluminium curtain walls in full configuration, were tested. Curtain walls had the same transom – mullion structure, with: • transoms and mullions made of the same aluminium profiles, with two types of insulation inserts (in each test one type of the insulation inserts), • glass panes of the same glass product group and dimensions of: ◦ 1680× 3198mm (width × height) for biggest glass pane orientated vertically, ◦ 1980× 1628mm (width × height) for biggest glass pane orientated horizontally. • non-transparent panels of the same construction and dimensions, • similar design (profiles, and consequently glass panes and panels of the same construction on the exposed area). Two test specimens were tested for external fire exposure, and two for standard fire exposure. Dimensions of exposed surfaces were 5000× 4500mm (width × height) for external fire exposure and 5000× 4800mm (width × height) for internal fire exposure. As a result the heated area was over 2 times greater than the minimum heated area required in EN 1364-3:2006 [3]. The distance between the mullion fixing anchors was 5000mm in both cases. All tested specimens were of the same transom – mullion structure with aluminium profiles sections of 50× 115mm (transoms) and 50× 130mm (mullions), fig. 1. Two types of insulations inserts were used in profiles, each type for pair of tests (external and internal fire exposure). Two types of glass panes were used in test specimens, each type for pair of tests (external and internal fire exposure). Glass panes were of symmetrical structure.

Interacting stability behaviour of steel I-girders with corrugated webs

Due to its advantages corrugated steel plates are widely used in various applications. Engineers realized a potential application field in bridges, especially in composite bridges. When such a bridge is incrementally launched, the girder is subjected to combined action of bending moment, shear and transverse forces, resulting in a complex stress field and interacting instability phenomena. The current paper focuses on the experimental and numerical investigation of the structural behaviour of the girders with corrugated webs under all of the above mentioned actions. 12 large scale test specimens are investigated under combined patch load and bending moment. Based on the experimental investigations a numerical model is developed and the structural behaviour of the girders with corrugated web is analysed under the complex loading situation due to combined bending moment, shear force and patch loading.

대형 보형 실험체의 다점 다하중 가력을 위한 실험장치 구성에 관한 연구

구조실험에서 정확성과 효율성을 높이기 위해서는 적절한 실험장치를 적용하는 것은 중요한 요소이다. 특히, 대규모의 구조 실험에서 적절한 실험장치는 비용과 시간을 절감할 수 있다. 액츄에이터와 유압잭 및 UTM은 실험체의 휨 능력을 평가하는 데 일반적으로 적용되고 있다. 그러나, 대규모 실험체에서 다점 다하중 가력하중이 적용되어야 하는 경우에는 기존의 UTM 등을 이용하는 실험방법은 정확한 하중을 가력하기에 어려움이 많다. 이를 해결하기 위하여 본 연구에서는 실험결과의 정확성과 효율성을 높이기 위하여 기존의 실험장치로 조합된 새로운 방법을 개발하였다. In the field of structural test, it is a very important factor to apply with an appropriate test jig to enhance test accuracy and efficiency. Especially in the large scale structure test, proper test apparatus scheme will reduce overall cost and time of the test project. Actuators, oil jack and UTM is generally used to evaluate the flexural capacity of the test beam. But in the case of multiple loading point or asymmetric loading of large scale test specimen, existing test method such as UTM have a difficulty in giving an accurate load. In this study new test method which is composed of existing test apparatus will be developed to improve test accuracy and economic efficiency.

BEHAVIOR CHARACTERISTICS OF BUCKLING-RESTRAINED BRACES USING ROUND STEEL BAR CORES AND DOUBLE STEEL TUBES

In the previous research by the authors, the buckling restrained braces (BRBs) using round steel bar cores and double steel tubes were developed and some loading tests revealed that the BRBs have sufficient capability as hysteretic dampers. However the test specimens were relatively small and limited to the rigid connection type. The present paper firstly presents evaluation of the rotation characteristics of the outer tube end and loading tests using the element specimens. Then some full-scale tests are conducted using rather large test specimens in which the pin connection type BRBs are employed in addition to the rigid connection type ones. The test results reveal the behavior of the inner tubes, influence of the number of contraction allowance parts, energy dissipation capacity and behavior characteristics of the pin connection type BRBs. Finally, the design conditions of the outer tubes are discussed considering the evaluation results of the rotation characteristics of the outer tube end.

Effective Porosity Measurement of a Marine Clay

Effective porosity commonly represents only the voids in soils or rock that contribute to the advective transport of groundwater. In the extreme case, all the pores or fractures are interconnected and contribute to the transport of groundwater. However, in most cases, some pores or fractures are dead-ended or isolated and, therefore, do not contribute to the advective movement of water through the soil or rock mass. The effective porosity is often estimated to be some fraction of the total porosity. The purpose of this study was to compare a glacial marine clay deposit’s effective and total porosities. The inner connection of the soil pores and the importance of the clay minerals on the pore spaces are at the root of the effective porosity testing described herein. Based on the results of three tracer tests on a low-plasticity, glacial marine clay, the effective porosity was found to be approximately equal to the total porosity within an error of less than 10%. Based on visual appearance of this uniform clay, the longitudinal dispersivity was assumed to be small compared to the tracer specimen length. However, it was found that larger test specimens would have made the tracer breakthrough curves less complicated.

EXPERIMENTAL INVESTIGATION OF THE EFFECT OF MECHANICAL LOADING ON THERMAL TRANSPORT IN CERAMIC MATRIX COMPOSITES

This paper presents the results of experimental measurements of transverse thermal diffusivity for six different industrial Ceramic Matrix Composite materials under the action of in-plane uni-axial mechanical loading. Measurements have also been taken using a one-dimensional Laser Flash technique on 8 mm diameter disc specimens without mechanical load. These results have been used to benchmark data obtained using a three-dimensional Laser Flash rig developed to operate on large mechanical test specimens whilst being loaded in a test machine. The latter facility has been used to measure the degradation of transverse thermal diffusivity with uni-axial strain. For five of the composites tested the degradation of transverse thermal diffusivity was small; and the degradation of transverse thermal diffusivity was linear with strain. One composite showed evidence of fibre pullout, and a decrease of transverse thermal diffusivity to a low value. The different behaviours observed were believed to be associated with the weave type/composite lay-up, and the selection of composite constituent materials, although insufficient data is available to make general conclusions.

Ultrasonic Imaging Methods for Investigation of Post-tensioned Concrete Structures: A Study of Interfaces at Artificial Grouting Faults and Its Verification

This paper presents the progress of successful location of grouting faults in tendon ducts with ultrasonic imaging. The examples were obtained in the research group FOR 384 funded by DFG (German Research Foundation). The co-operation of experimental research and modeling allowed imaging and identification of grouted and ungrouted areas of tendon ducts (including strands) in a large test specimen (40 m2). In addition to the criteria for indicating grouting faults in post-tensioned ducts known until now the phase evaluation of reflected ultrasonic pulses is described. Experiments and modeling of wave propagation are presented for reflections at metal plates in concrete (thickness range 0.5 mm to 40 mm) and for tendon ducts including strands. The main part of the progress was achieved by automated measurements using dry contact transducers, 3D-SAFT reconstruction including phase evaluation and modeling considering wave propagation for typical elastic parameters and exact experimental site conditions. The results for shear waves as well as for pressure waves are compared in the frequency range from 50 kHz to 120 kHz.