Numerical analysis of the thermal active restrained shrinkage ring test to study the early age behavior of massive concrete structures

Several tests, devoted to the study of cracking due to autogenous and drying shrinkage, exist in the literature. They are generally not relevant for the study of massive structures for which thermal strains plays a key role. Therefore, an active ring test has been developed to study cracking due to restrained thermal shrinkage. This test is an evolution of the restrained shrinkage ring test which allows us to take into account both autogenous and thermal shrinkage. With this test, the early age cracking due to thermal restrained shrinkage (effect of the temperature rate), the influence of reinforcement and construction joints have been studied (Briffaut et al. (2011) [1]).Nevertheless, in this test, several phenomena occur simultaneously (hydration, shrinkage, creep…) and their effect cannot be easily decoupled. So, complementary tests have been performed to study each phenomenon separately and the ring test has been numerically simulated in order to identify coupling between creep and damage and to quantify the strength decrease due to construction joints. A good agreement between experimental and numerical results has been obtained for ring with reinforcement and construction joints. With the proposed model and the identified materials parameters validated on the active restrained ring test, numerical simulations of the construction of a real massive structure have been performed, and a parametric study has been achieved to highlight the creep effect.     

Ecotoxicological tests assessment of soils polluted by chromium (VI) or pentachlorophenol

Carbon mineralisation and plant germination and growth (Lactuca sativa seeds) tests have been performed in two soils of different properties, experimentally spiked with pentachlorophenol (PCP) or Cr (VI), in concentrations between 0.001 and 1000 mg kg(-1). The evaluation has been done considering the following parameters of carbon transformation test: soil cumulative basal respiration after 14 days incubation, substrate induced respiration after 12 h of glucose addition, and, in the plant germination and growth test: number of germinated seeds, root elongation and total biomass produced. The most sensitive assay found in our work has been carbon mineralisation test, from which the lowest toxic concentrations were obtained (especially substrate induced respiration test). In the plant germination and growth test, the measurement of root elongation has shown the best sensitiveness, followed by plant biomass and seed germination numbers. Regarding the contaminants, the highest toxicity, considering the minimum concentration with toxic effect, has been found in PCP (0.01 mg kg(-1)) in C mineralisation test in the granitic soil. For Cr, the minimum concentration with toxic effect has been 0.1 mg kg(-1), also in the C mineralisation test and the granitic soil. The granitic soil has shown more vulnerability to the pollutants assayed in the respiration test, whereas the calcareous soil has shown more vulnerability in the plant germination and growth test.     

The deformation modulus of rock masses — comparisons between in situ tests and indirect estimates

Three methods of in situ deformation modulus (Em) measurements of rock masses have been described, analysed and compared. The plate jacking (PJT) test, where the deformations are measured by extensometers in drill holes, gives generally the best results. A factor of 2.5 has been found between PJT and the Goodman jack test, and the plate loading test. From analyses of the results it has been pointed out that the damage from blasting of the test adit reduces the magnitude of test results with a factor between 2 and 4. The existing equations for indirect estimates of the rock mass deformation modulus from classification systems have been analysed and adjustment suggested. Taking into consideration the uncertainties connected to in situ deformation measurements caused by blast damage, test procedure and test method, a good characterization of the ground may give comparable, or possibly better Em values, using the RMi or the RMR system than the in situ tests. The RMR system gives, however, values that are too high for Em in massive rock.     

Modified Stanley's approach for statistical analysis of compression strength test data of rock specimens

A very wide scatter is usually observed in laboratory compressive strength test (uniaxial and triaxial) data of rock specimens due to randomness in the number, orientation and distribution of micro-cracks. This leads to an uncertainty in choosing the representative design strength which leads to the need for a probabilistic approach to the analysis of test data. An attempt has been made in this paper to propose such an approach which is a modified version of Stanley's approach and employs Weibull's statistical strength theory. Uniaxial compressive strength (UCS) test data from three sources have been analyzed and results compared with those from Weibull's theory. As the proposed approach employs Weibull's parameters, goodness-of-fit tests have been performed to check the fitness of tests data to Weibull's distribution. Further, the proposed approach for uniaxial conditions has been extended to triaxial stress conditions. Corresponding cumulative distribution functions of the applied stress level have been obtained which have been subsequently invoked to correlate the applied stress level at failure with the associated risk of failure. For the UCS test data, the proposed approach yields higher design strengths than does Weibull's theory when Weibull's m parameter is greater than unity. Strength under triaxial stress condition can be predicted by employing the proposed approach even though triaxial tests cannot be conducted, provided the UCS test data are available.     

某边坡工程预应力锚索试验研究

结合某边坡预应力锚索支护工程实例,对预应力锚索进行了试验研究。根据实际工程坡面状况,共设置了三组试验孔,结果表明:(1)土层压力分散型锚索主要破坏形式为位移不收敛;(2)岩层永久拉力型锚索,受施工现场工艺控制,很难保证锚索筋体与锚垫板之间严格垂直,从而在一定程度上降低了钢绞线材料的极限破坏荷载;(3)锚固段是否设置波纹钢套管,锚固力没有明显差别。     

波速测试的工程应用

波速测试作为地基土动力特性测试项目之一,已广泛应用于水利水电、公路铁路、工业与民用建筑等众多岩土工程勘察领域,取得了良好的应用效果。文章阐述了国产武汉岩海RS-1616K（S）型基桩动测仪进行波速测试的基本原理、测试方法、波形的判读和数据整理、波速测试成果的应用和工程实例。     

Calculation of the heating rate of an unprotected steel member in a standard fire resistance test

ENV.1991-2-7 is the new ‘European standard code of practice for actions on structures exposed to fire’. The document recommends a standardized procedure for the calculation of the fire resistance of a structural member. For each member state of the EU, a national application document (NAD) is being drafted to provide values of those parameters used in the calculations described in the code of practice. The first part of this paper provides a justification o f the values recommended for test piece surface and furnace emissivities as well as the safety factors in the UK version of the NAD.

ENV.1991-2-7 is designed to have a working life of only three years, after which its contents will be reviewed in the light of the experience gained during its use, before being issued as a final EN standard. The second part of this paper attempts to identify the most important developments needed during this three year period. There is an urgent need to develop a reliable means of measuring and controlling the total heat flux incident on a specimen during a standard fire resistance test. The availability o f total heat flux control would allow modification of EN. 1363-1 (the standard fire resistance test) to achieve harmonization of fire test results across the whole EU.

A method has been developed by which existing fire resistance test data can be used to calculate the total heat flux incident on the specimen at any instant during the test. The method has been used to compare the total incident heat flux/time characteristics of beam testing. furnaces at the Warrington Fire Research Centre (WFRC) and TNO (Delft) as well as the column furnace at the Borehamwood laboratory of the Loss Prevention Council (LPC). These characteristics have then been compared with those implied in the draft UK-NAD for ENV.1991-2-7. The latter has been shown to use heat flux/time characteristics very similar to those derived from standard test data.     

Comparison of toxic product yields of burning cables in bench and large-scale experiments

Toxic product yields from five commercial cables obtained from a steady state tube furnace (SSTF) method (IEC 60695-7-50, Purser furnace) are compared with results from a large-scale test, which uses the physical fire model in the proposed prEN50399-2-2 test, with the addition of effluent gas analysis, using Fourier transform infrared (FTIR), and for further comparison, a static tube furnace method (NF X 70-100). This work represents one of the first attempts to establish a relationship between bench- and large-scale toxic product yields for burning cables. This is difficult because the cables have been formulated for low flammability, and therefore do not burn consistently. The tube furnace burns the cable completely, whereas the large-scale test effluent is the result of a combination of flame spread and toxic product yields, both of which are fire scenario dependant. There is significant differentiation between cable types based on composition, and arising because only a portion of the cables burn in the large-scale test, accompanied by possible decomposition of hydrate sheaths. The fire stage of the large-scale test appears to have been replicated in an appropriate manner, given the correspondence of the CO₂/CO ratios. The yields of CO₂, CO, HCl and smoke show reasonable agreement, given the differences in the extent of burning, and the accuracy of the mass-loss data available for the large-scale test. The yields and extent of burning have been combined to demonstrate the estimation of toxic hazard for a particular fire scenario based around the large-scale test, which shows only marginal sensitivity to the differences in toxic product yield between the SSTF and the large-scale test.     

非黏性土的振动密实试验研究(英文)

通过室内模型和现场振冲试验,研究了无填料振冲加固细砂吹填土的适用性。在模型试验中,进行了孔隙水压力测试和静力触探试验,研究了孔隙水压力变化规律和振冲间距对振冲效果的影响。通过回归分析,得出了孔隙水压力消散的经验公式。另外在现场进行了单点振冲,双点振冲及三点振冲试验。室内模型试验和现场试验的结果表明,无填料振冲法可以应用在细砂的地基处理中,并可以取得很好的效果。     

港深西部通道钢箱梁低温CTOD试验

为有效控制大型钢箱梁焊接接头质量,运用裂纹尖端张开位移(CTOD)试验技术,按英国BS7448标准,对焊接接头进行低温(-20℃)韧性测定。评定了两种拟用焊接工艺:自动埋弧焊和手工电弧焊工艺,解决了港深西部通道后海湾大桥钢箱梁焊接接头韧性控制这个关键技术问题。介绍了CTOD的概念、试验方法、钢箱梁的低温CTOD试验过程及其结果。     

Toxicity of the 13 priority pollutant metals to Vibrio fisheri in the Microtox chronic toxicity test

The Microtox Acute Toxicity Test has been successfully used to measure the toxicity of metals and other pollutants at high concentrations (ppm) in selected environmental samples. However, metals and other toxicants are often found in much lower concentrations (ppb) in many municipal wastewaters and receiving waters. In order to assess the toxicity of these pollutants in these samples, a more sensitive toxicity assay is needed. The Microtox chronic toxicity test has been developed to measure the sublethal effect of toxicants over multiple generations of the test species, Vibrio fisheri. In this study, the toxicity of the 13 priority pollutant metals [i.e. As, Se, Cd, Cr (III and VI), Cu, Pb, Sb, Ag, Tl, Zn, Be, Hg and Ni] to V. fisheri was evaluated using the Microtox chronic toxicity test. In this test, the inhibitory concentration (IC), lowest observable effect concentration (LOEC), and no observable effect concentration (NOEC) were obtained after 22-h of incubation at 27+/-1 degrees C, by comparing the light output of the control to that of the test sample. Among the 13 priority pollutant metals, beryllium (Be) was found to be the most toxic in the test (LOEC=0.742-1.49 microg/l) while thallium (Tl) was the least toxic (LOEC=3840-15300 microg/l). The LOECs for copper (as Cu) and lead (Pb) in reagent (ASTM Type I) water were 6.78-13.6 microg/l and 626-1251 microg/l, respectively. The toxicity of copper sulfate (as Cu) in reagent water was shown and significantly reduced with the addition of natural organic matter (fulvic acid) or EDTA to the sample. The LOEC values for the 13 priority pollutant metals in this test were comparable to or lower than those reported for commonly used aquatic toxicity tests, such as the Ceriodaphnia dubia assay.     

Prediction of pullout interaction coefficient of geogrids by extreme gradient boosting model

Geogrids embedded in fill materials are checked against pullout failure through standard pullout testing methodology. The test determines the pullout interaction coefficient which is critical in fixing the embedment length of geogrids in mechanically stabilized earth walls. This paper proposes prediction of pullout interaction coefficient using data driven machine learning regression algorithms. The study primarily focusses on using extreme gradient boosting (XGBoost) method for prediction. A data set containing 220 test results from the literature has been used for training and testing. Predicted results of XGBoost have been compared with the results of random forest (RF) ensemble learning based algorithm. The predictions of XGBoost model indicates 85% accuracy and that of RF model shows 77% accuracy, indicating significantly superior and robust prediction through XGBoost above RF model. The importance analysis indicates that normal stress is the most significant factor that influences the pullout interaction coefficients. Subsequently pullout tests have been performed on geogrid embedded in four different fill materials at three normal stresses. The proposed XGBoost model gives 90% accuracy in prediction of pullout interaction coefficient compared to laboratory test results. Finally, an open-source graphical user interface based on the XGBoost model has been created for preliminary estimation of the pullout interaction coefficient of geogrid at different test conditions.     

Flexible Automation for Servo-Controlled Testing

The paper presents an efficient method of flexibly automating test control and data acquisition functions for servo-controlled testing. A systems analysis approach coupled with structured design is used in developing the system. With hardware that includes (a) a personal computer, (b) a servo-controlled electrohydraulic testing machine equipped with a special type of digital function generator, and (c) a multipurpose data acquisition board, an automated test control and data acquisition system for servo-controlled materials/structural/mechanical testing has been developed. The servo-controlled materials/structural/mechanical testing system allows (1) automated control of the test, (2) rapid and reliable acqusition of several channels of data from static or fast-rate tests subject to periodic or nonperiodic loading, and (3) realtime (or nearly real-time) graphics of the test characteristics in order to allow the operator to monitor the test. The communication and postprocessing options allow user-supplied software to be incorporated into the automated system for advanced non-real-time functions. These options include noise filtering, signal averaging, mathemtical analyses and processing, report quality graphics, and file transfer features. The system features have been validated through a series of load-controlled direct tension tests on an aluminum specimen. The system has been used for successfully carrying out an elaborate research program on fracture toughness testing of fiber-reinforced concrete in a flexural loading configuration.     

岩石钻孔原位测试技术的应用与改进

 如何确定岩体工程力学特性是工程设计中的重要问题,也是长期困扰工程界的难题。由于原位测试技术可克服室内试验扰动性及尺寸效应等缺点,逐渐发展成为一种重要的岩体力学参数取值手段。钻孔剪切试验技术近年来被广泛应用于土体现场直剪试验中,但其在岩石工程中的应用较为少见。对所引进的岩石钻孔剪切仪进行工程现场岩体钻孔剪切试验应用尝试,得到有益的试验结果。针对岩石钻孔剪切仪在工程实际应用中所存在的问题及不足,对其进行改进与完善。在此基础上,研制开发新的岩石原位测试设备--钻孔剪切弹模原位测试系统,实现同步获取岩体力学及变形参数,为岩体钻孔高效利用以及岩体工程力学参数的确定提供新的途径。     

Modellierung des Single Burning Item Tests

Modelling the Single Burning Item Test Harmonisation in Europe led to new standards, tests and classification of building products in fire safety. The Single Burning Item (SBI) test is the new reaction to fire test for the intermediate level. In the test a developing fire caused by a single burning item, e.g. a burning waste paper basket, is simulated. Numerical investigations of the SBI test have been performed by the Federal Institute for Materials Research and Testing (BAM) in cooperation with Technical University Berlin. Two CFD (Computational Fluid Dynamics) codes, Fluent and FDS, have been used to develop models of the SBI test. Data of our own experiments and literature has been used to validate the numerical models. Variation of ventilation in the burning room and variation of ambient air temperature lead to significant changes in temperatures and flow velocities in the burning room. The SBI standard EN 13823 allows the ventilation and ambient air temperature to be in a range. New experiments are necessary to show the effect of one single parameter like ambient air temperature. But the used data and the numerical results give reason to think about narrowing the ranges for ventilation and ambient air temperature in the standard.     

椭圆空心截面梁侧向失稳分析

分析椭圆空心截面(EHS)构件弯曲时的侧向稳定性。对8根截面(高厚比为2)的无侧限EHS梁进行三点弯曲试验,并记录试件的试验设备、材料性质、截面几何形状、残余应力以及荷载、变形响应。使用数值模拟方法对试验数据进行补充,并依据试验结果验证其正确性。数值分析用于评估截面高厚比和构件长细比对侧向稳定性的影响。基于结构特性相关数据建立椭圆空心截面梁的侧向扭转屈曲曲线。提出限制长度以下时,侧向扭转屈曲(LTB)可不考虑。     

Simulation of air flow in the IEA Annex 20 test room—validation of a simplified model for the nozzle diffuser in isothermal test cases

The modeling of air supply devices has been identified from the International Energy Agency (IEA) Annex 20 project as one of the most important problems in applying computational fluid dynamics (CFD) to predict air flow pattern and air distribution in buildings, and the complicated HESCO nozzle diffuser used in the IEA Annex 20 test room has been proved to be particularly difficult to model. In a previous study, a simplified model for this diffuser was developed and validated against experimental data. It has been shown that this model can yield good prediction for the wall jet flow issued from the diffuser, but whether this model is capable of correctly predicting the global flow pattern in the whole test room was not known. In this paper, the benchmark data of the IEA Annex 20 Test Cases B2 and B3 were used to evaluate the performance of the model for the prediction of the global air flow pattern in the test room. It was demonstrated that this model can predict the air flow pattern in the whole test room for both the Test Cases B2 and B3 with reasonable accuracy. The significance of a velocity correction when comparing the numerical prediction with experimental data obtained using omni-directional anemometers was also discussed.     

Microstructure characteristics of cement-stabilized sandy soil using nanosilica

An experimental program was conducted to explore the impact of nanosilica on the microstructure and mechanical characteristics of cemented sandy soil.Cement agent included Portland cement type II.Cement content was 6% by weight of the sandy soil.Nanosilica was added in percentages of 0%,4%,8% and 12% by weight of cement.Cylindrical samples were prepared with relative density of 80% and optimum water content and cured for 7 d,28 d and 90 d.Microstructure characteristics of cementnanosilica-sand mixtures after 90 d of curing have been explored using atomic force microscopy(AFM),scanning electron microscopy(SEM) and X-ray diffraction(XRD) tests.Effects of curing time on microstructure properties of cemented sandy soil samples with 0% and 8% nanosilica have been investigated using SEM test.Unconfined compression test(for all curing times) and compaction test were also performed.The SEM and AFM tests results showed that nanosilica contributes to enhancement of cemented sandy soil through yielding denser,more uniform structure.The XRD test demonstrated that the inclusion of nanosilica in the cemented soil increases the intensity of the calcium silicate hydrate(CSH) peak and decreases the intensity of the calcium hydroxide(CH) peak.The results showed that adding optimum percentages of nanosilica to cement-stabilized sandy soil enhances its mechanical and microstructure properties.     

Interpretation of International Parallel Test on the Measurement of Gmax Using Bender Elements

This report summarizes the results of international parallel test on the measurement of the elastic shear modulus at very small strains, G_max, using bender elements which was carried out from 2003 to 2005 by technical committee, TC29 (Stress-strain and Strength Testing of Geomaterials) of the International Society of Soil Mechanics and Geotechnical Engineering. The purpose was to evaluate the consistency of the bender element test results obtained by applying the exactly similar test material as well as the test method besides identifying the various existing hardware and software being used in this test. It was decided that the domestic TC29 group of Japanese Geotechnical Society (TC29-JGS) was expected to lead this international co-operation. By 2005, reports of the test results were obtained from 23 institutions from 11 countries. This report has been prepared by TC29-JGS taking a leading role from the beginning. A standard test method is proposed here in order to obtain more accurate data from the bender element test by examining various test methods adopted at different institutions worldwide and the effects of various factors on the test results.     

Laboratory assessment of Alaska aggregates using Micro-Deval test

Aggregates suitable for use in asphalt concrete (AC) pavement construction must meet durability criteria. Thus, it is critical to select appropriate tests to properly characterize aggregate durability. In Alaska, durability tests currently being used for aggregates in AC pavement include Los Angeles (LA) abrasion test, sulfate soundness test and Washington degradation test. However, there have long been concerns arising over Washington degradation test used as an acceptance tool, motivating pavement practitioners to seek more suitable alternatives. This paper presents a study to investigate the feasibility of using Micro-Deval test, commonly used in other states, to evaluate the durability of Alaskan aggregates in AC pavement as well as its potential to replaceWashington degradation test. Micro-Deval test,Washington degradation test and other tests currently specified in Alaska were conducted on aggregates from 16 batches representing statewide sources. Based on the testing results, it is found that using Micro-Deval test for durability assessment of Alaska aggregates was feasible and reproducible, and a high potential was revealed to use Micro-Deval test to replace Washington degradation test in Alaska. It is recommended that Micro-Deval test be considered as an additional test for a certain period, but in the long run should be used along with current LA abrasion and sulfate soundness tests to provide a more desirable durability assessment of Alaska aggregates used in AC pavement.