The Testing Strength Curves of Lightweight Aggregate Concrete by Rebound Method and Ultrasonic-rebound Combined Method

The strength curves of lightweight aggregate concrete （LWAC） were tested based on detecting LWAC with density of 1 400-1 900 kg/m3 and LWAC with strength grade of LC15-LC50 by rebound method and ultrasonic-rebound combined method.The results show that the common measured strength curves tested by above two methods can not satisfy the required accuracy of LWAC strength test.In addition,specified compressive strength curves of testing LWAC by rebound method and ultrasonic-rebound combined method are obtained,respectively.

Experimental p-y curves for liquefied soils from centrifuge tests

The present study aims to obtain p-y curves(Winkler spring properties for lateral pile-soil interaction)for liquefied soil from 12 comprehensive centrifuge test cases where pile groups were embedded in liquefiable soil.The p-y curve for fully liquefied soil is back-calculated from the dynamic centrifuge test data using a numerical procedure from the recorded soil response and strain records from the instrumented pile.The p-y curves were obtained for two ground conditions:(a)lateral spreading of liquefied soil,and(b)liquefied soil in level ground.These ground conditions are simulated in the model by having collapsing and non-collapsing intermittent boundaries,which are modelled as quay walls.The p-y curves back-calculated from the centrifuge tests are compared with representative reduced API p-y curves for liquefied soils(known as p-multiplier).The response of p-y curves at full liquefaction is presented and critical observations of lateral pile-soil interaction are discussed.Based on the results of these model tests,guidance for the construction of p-y curves for use in engineering practice is also provided.

Determination of Material Parameters of EVA Foam under Uniaxial Compressive Testing Using Hyperelastic Models

The objective of this research was to determine the mechanical parameter from EVA foam and also investigate its behavior by using Blatz-Ko,Neo-Hookean,Mooney model and experimental test.The physical characteristic of EVA foam was also evaluated by scanning electron microscopy(SEM).The results show that Blatz-Ko and Neo-Hookean model can fit the curve at 5%and 8%strain,respectively.The Mooney model can fit the curve at 50%strain.The modulus of rigidity evaluated from Mooney model is 0.0814±0.0027 MPa.The structure of EVA foam from SEM image shows that EVA structure is a closed cell with homogeneous porous structure.From the result,it is found that Mooney model can adjust the data better than other models.This model can be applied for mechanical response prediction of EVA foam and also for reference value in engineering application.

Dynamic Characteristics of a Curved Cable-stayed Bridge:Operational Modal Testing and FE Modeling

This paper summarizes the analytical and experimental dynamic analyses carried out to assess the actual dynamic behaviour of a curved cable-stayed bridge,recently erected in the commercial harbour of Porto Marghera ( Venice,Italy). Ambient vibration tests were carried out to determine the dynamic characteristics of the bridge and more than 20 modes were identified in the frequency range 0～10Hz. In the theoretical study,a 3D FE model of the bridge was developed using an integrated CAD-FEA approach; subsequently,the information obtained from the field tests,combined with simple manual tuning,provided a linear elastic model,accurately fitting the modal parameters of the bridge in its present condition.

Calculation of phase transformation latent heat based on cooling curves in end-quench test and its application in nickel-based superalloy

To obtain the phase transformation latent heat corresponding to different cooling rates with low test workload and cost,the Newton thermal analysis method and the improved Newtonian thermal analysis method were discussed based on the cooling curve obtained in the end-quench test.The validity of two methods was given by the latent heat calculation of 45^(#) steel.The results show that the relative error of latent heat is 5.20%through the improved Newtonian thermal analysis method,which is more accurate than the Newtonian thermal analysis method.Furthermore,the latent heat release of phase transformation of the self-designed CSU-A1 powder metallurgy nickel-based superalloy increases from 4.3 to 12.29 J/g when the cooling rate decreases from 50.15 to 33.40℃/min,because there is more sufficient time for the alloy microstructure to complete the phase transformation process when the cooling rate is smaller.

Testing the Hypothesis of J Curve for Turkish Economy

The purpose of this paper is to find the relationship between balance of foreign trade and real exchange rate in econometrics concept by using time series method. The authors used annual data of foreign trade deficit, real exchange rate, gross domestic product （GDP） of Turkey from 1989 to 2014, and analyzed the long-term relation of them by using ARDL bound testing method. By the result of test method; although there was a long-term relationship between balance of foreign trade, real exchange rate, GDP of Turkey and of the world, the coefficient of real exchange rate was insignificant in terms of statistical methods. Turkey and the world as well as being statistically significant coefficient of GDP, it was concluded that there was significant relationship with the economic aspects.

Seismic performance of double- skin steel- concrete composite box piers: Part Ⅰ——Bidirectional quasi-static testing

To study the seismic performance of double-skin steelconcrete composite box（ DSCB） piers, a total of 11 DSCB pier specimens were tested under bidirectional cyclic loading. The effects of the loading pattern, the steel plate thickness, the axial load ratio, the slenderness ratio and the aspect ratio were taken into consideration. The damage evolution process and failure modes of the tested specimens are presented in detail. Test results are also discussed in terms of the hysteretic curve, skeleton curve, ductility and energy dissipation capacity of DSCB pier specimens. It can be concluded that the hysteretic performance of DSCB piers in one direction is affected and weakened by the cyclic loading in the other direction. DSCB piers under bidirectional cyclic loading exhibit good performance in terms of load carrying capacity, ductility, and energy dissipation capacity. Overall, DSCB piers can meet the basic aseismic requirements. The research results can be taken as a reference for using DSCB piers as high piers in bridges in strong earthquakeprone areas.

Stress-deformed state of cylindrical specimens during indirect tensile strength testing

In this study, the interaction between cylindrical specimen made ofhomogeneous, isotropic, and linearlyelastic material and loading jaws of any curvature is considered in the Brazilian test. It is assumed thatthe specimen is diametrically compressed by elliptic normal contact stresses. The frictional contactstresses between the specimen and platens are neglected. The analytical solution starts from the contactproblem of the loading jaws of any curvature and cylindrical specimen. The contact width, correspondingloading angle （2 ^0）, and elliptical stresses obtained through solution of the contact problems are used asboundary conditions for a cylindrical specimen. The problem of the theory of elasticity for a cylinder issolved using Muskhelishvili＇s method. In this method, the displacements and stresses are represented interms of two analytical functions of a complex variable. In the main approaches, the nonlinear interactionbetween the loading bearing blocks and the specimen as well as the curvature of their surfacesand the elastic parameters of their materials are taken into account. Numerical examples are solved usingMATLAB to demonstrate the influence of deformability, curvature of the specimen and platens on thedistribution of the normal contact stresses as well as on the tensile and compressive stresses actingacross the loaded diameter. Derived equations also allow calculating the modulus of elasticity, totaldeformation modulus and creep parameters of the specimen material based on the experimental data ofradial contraction of the specimen.

Cyclic testing of moment-shear force interaction in reinforced concrete shear wall substructures

Previous quasi-static cyclic tests of shear walls,which routinely used an incremental lateral displacement test protocol with a constant axial load,failed to reflect the character of moment-shear force interaction of prototype buildings.To study the effect of the moment-shear force interaction on the seismic performance of shear walls,three identical 2-story shear wall specimens with different loading patterns were constructed at 1/2 scale,to represent the lower portion of an 11-story high-rise building,and were tested under reversed cyclic loads.The axial force,shear force and bending moment were simultaneously applied to simulate the effects of gravity loads and earthquake excitations on the prototype.The axial force and bending moment delivered from the upper structure were applied to the top of the specimens by two vertical actuators,and the shear force was applied to the specimens by two horizontal actuators.A mixed force-displacement control test program was adopted to ensure that the bending moment and the lateral shear were increased proportionally.The experimental results show that the moment-shear force interaction had a significant effect on the failure pattern,hysteretic characteristics,ductility and energy dissipation of the specimens.It is recommended that moment-shear force interaction should be considered in the loading condition of RC shear wall substructures cyclic tests.

On the Distribution of Type II Errors in Hypothesis Testing

When a statistical test of hypothesis for a population mean is performed, we are faced with the possibility of committing a Type II error by not rejecting the null hypothesis when in fact the population mean has changed. We consider this issue and quantify matters in a manner that differs a bit from what is commonly done. In particular, we define the probability distribution function for Type II errors. We then explore some interesting properties that we have not seen mentioned elsewhere for this probability distribution function. Finally, we discuss several Maple procedures that can be used to perform various calculations using the distribution.

Rating Curve Modification at Low Discharges Using Physical Model Tests

Hydraulic structure is designed based on hydraulic theories or guidelines. To ensure performance, physical model tests are often used at high discharges. However, high discharge in river is rare. Physical model tests at high discharges will probably lead biased hydrological relationship. To improve hydrological relationship at low discharges, in this study, we considered the diversion rating curve of the Yuanshanzi Diversion Work. The 1/100-scaled physical model tests at low and high discharges (90 - 1620 m3/s) were performed and coupled the diversion discharges of 5 flood events (2009-2010) in field. The official diversion rating curve was built only based on physical model tests at high discharges (837 - 1620 m3/s). The results of physical model tests in this study suggested the official diversion rating curve should be modified considering all tests. The modifications showed the official diversion rating curve was over-estimated. A complete series of physical model tests and considering field situations, in this study, indicated expanded physical model tests and constantly field measurements were therefore necessary for hydraulic structure, which provided information to modify used hydrological relationship to fit real situations.

Compressive Strength of Basic Magnesium Sulfate Cement Coral Aggregate Concrete(MCAC)on Non-Destructive Testing

Basic magnesium sulfate cement coral aggregate concrete(MCAC)is a new type of concrete consisting of basic magnesium sulfate cement,coarse coral aggregate,coral reef sand and seawater.The rebound hammer(RH),the ultrasonic pulse velocity(UPV)and the compressive strength(fcu)tests of 14 sets of cube specimens of the MCAC after 28 d of aging were conducted.The impact of the content and length of sisal fiber on the relationship between the fcu-RH and the fcu-UPV was determined.A mathematical model was established to predict the strength of the MCAC using the UPV,RH,and comprehensive UPV/RH methods and to obtain the curves of test strength.The applicability of the test strength curves of ordinary portland concrete(OPC),light-weight aggregate concrete(LAC),and coral aggregate concrete(CAC)to MCAC was assessed.The results showed that the test strength curves of OPC,LAC and CAC were inappropriate to determine the strength of MCAC using non-destructive method.The relative standard error of the curves of test strength of the RH method and the comprehensive method met the specifications,whereas that of the UPV method did not.

Hardness-Based Non-destructive Method for Developing Location Specific S-N Curves for Fatigue Life Evaluation

This paper first describes the importance of using location specific S-N curves for fatigue damage assessment of existing steel structures. It discusses the existing concepts and methods for developing S-N curves using empirical formulae and monotonic strength parameters, such as the ultimate tensile strength and hardness. It also discusses relationships among these monotonic parameters. Then it presents formulae for developing hardness-based full range S-N curves for medium strength steels. The formulae are verified using experimental data obtained from both monotonic and cyclic testing. Finally, it describes the advantages of these hardness-based formulae for developing location specific S-N curves as hardness testing is a non-destructive test which can be carried out on specific locations in structures.

Comparison of Procedures to Evaluate the Cyclic Stress-Strain Curve from Incremental Step Test

The design of structural components in low-cycle fatigue field often requires the knowledge of the cyclic properties of the material, which are commonly described by the classical relation of Ramberg-Osgood. In order to obtain the cyclic curve using experimental data from incremental step tests, four methodologies are described and critically discussed. Three methods differ in the procedure of evaluation of the elastic modulus, while in the last one the experimental data are interpolated with a single non-linear regression. The various techniques were applied to data obtained from tests carried out on stainless steel specimens, and the resulting differences were analysed and quantified. An average behaviour was evaluated considering the total set of data obtained from experimental tests. The choice of the most suitable method is related to both the strain range of interest and the goal for which the results are used.

Stress—strain curves for different loading paths and yield loci of aluminum alloy sheets

To carry out biaxial tensile test in sheet metal, the biaxial tensile testing system was established. True stress—true strain curves of three kinds of aluminum alloy sheets for loading ratios of 4:1, 4:2, 4:3, 4:4, 3:4, 2:4 and 1:4 were obtained by conducting biaxial tensile test in the established testing systems. It shows that the loading path has a significant influence on the stress—strain curves and as the loading ratio increases from 4:1 to 4:4, the stress—strain curve becomes higher and n-value becomes larger. Experimental yield points for three aluminum alloy sheets from 0.2% to 2% plastic strain were determined based on the equivalent plastic work. And the geometry of the experimental yield loci were compared with the yield loci calculated from several existing yield criteria. The analytical result shows that the Barlat89 and Hosford yield criterion describe the general trends of the experimental yield loci of aluminum alloy sheets well, whereas the Mises yield criterion overestimates the yield stress in all the contours.

WEIGHTED LEAST SQUARE METHOD FOR S-N CURVE FITTING

An S-N curve fitting approach is proposed based on the weighted least square method, and the weights are inversely proportional to the length of mean confidence intervals of experimental data sets. The assumption coincides with the physical characteristics of the fatigue life scatter. Two examples demonstrate the method. It is shown that the method has better accuracy and reasonableness compared with the usual least square method.

全程曲线拟合法和Aquifertest水文地质求参

抽水试验是获取含水层水文地质参数的主要方法,求参结果直接影响对调查区水文地质条件的认识和地下水开发利用。传统求参方法存在主观影响大、求参时间长、易受外界影响和抽水阶段数据的不足等问题。通过全程曲线拟合法和Aquifertest软件分别从配线法和水位恢复法两个角度进行求参,并结合全程曲线拟合法确定最终取值。结果表明,采用Aquifertest软件求参便捷、准确,与水位恢复法求参结果的差异相对较小,全程曲线拟合法求参值具有唯一性和可靠性,多种方法结合求参能更真实反映水文地质情况。

海上风电单桩基础小变位水平静力承载特性研究

针对海上风电桩径9m的超大直径单桩基础,采用离心模型试验与数值仿真相结合方法,研究砂土地基中不同锚固深度工况下单桩基础在小变位条件下的水平静力承载特性。结果表明,随锚固深度增加,桩身旋转中心逐渐下移,且桩身水平位移与倾角沿桩身分布的非线性趋势逐渐增强。不同锚固深度工况下桩侧p-y曲线间的差异随深度逐渐加大,在趋势上,p-y曲线随锚固深度增大由外凸型向内凹型转变;在量值上,同一深度处初始割线模量间可相差4倍。这一差异的原因在于,同一深度处桩体发生相同侧位移时,锚固更浅的桩体周围土体内部径向位移、环向位移的影响范围较小,土体应变较大,进而呈现较大的水平抗力。研究成果有助于深化对大直径单桩基础承载机制的认识,进而为桩体设计优化提供理论基础。

土工格室加筋非饱和土三轴试验

为探索加筋非饱和土结构的变形和破坏特征,测试了非饱和土的土-水特征曲线;同时,基于固结排水三轴试验测得不同净围压下基质吸力分别为30、80和130 kPa时非饱和素土和土工格室加筋土的应力-应变曲线,对比分析了不同基质吸力下素土和加筋土变形模量和抗剪强度指标;此外,基于三轴试验结果分析了土工格室对非饱和土的约束围压大小。结果表明:随着轴向应变的增加和净围压的减小,土工格室加筋土的变形模量提高幅度逐渐增大;非饱和土的有效内摩擦角受土工格室加筋作用的影响较小,由于土工格室的约束作用,加筋土的黏聚力和反映基质吸力对强度贡献的内摩擦角均有提高;随着非饱和土基质吸力的增加和净围压的减小,由于剪胀趋势的增强,土工格室加筋土的变形模量和表观黏聚力提高幅度逐渐增加。

放电状态对锂离子电池在机械滥用条件下力学响应和失效行为的影响

为厘清放电状态对锂离子电池动态力学响应和失效模式的影响规律,系统地开展了锂离子电池在不同放电状态下的准静态压缩特性及其安全性的实验分析。通过预设电池至特定的放电电量,并在放电过程中、放电后静置1和24 h的时间节点上实施压缩测试,深入探究了电池的力-位移响应特性、最大承载力及安全性表现。实验结果显示,相较于其他状态,放电状态下的电池展现出较低的力-位移曲线,表明其刚度在静置之后相比于放电过程中有所提升。此外,放电状态下的电池展现出显著高于静置后状态的最大承载力,且在放电过程中进行压缩测试更容易使电池发生爆炸,而静置后的电池则表现出显著提升的安全性。借助扫描电子显微镜分析,进一步确认了放电状态下电池内部电极颗粒的破损程度更剧烈,观测到的现象被归因于放电过程中产生的扩散诱导应力,该应力在电池内部累积,加剧了电池在机械压缩下的损伤风险。