不锈钢管混凝土短柱轴压承载力试验研究

对9根奥氏体型和9根双相型不锈钢管混凝土短柱进行轴压试验,测得了短柱在轴压作用下的极限荷载、纵向应变和环向应变等,重点考察了钢管壁厚和混凝土强度对短柱承载性能的影响,并参考普通钢管混凝土设计规程欧洲规程(Eurocode 4)、美国规程(ACI 318-99)、日本规程(AIJ-CFT),我国相关规程DBJ 13-51―2003、DL/T5085―1999和CECS 28:2012计算了不锈钢管混凝土短柱的承载力并进行对比分析。结果表明,不锈钢管混凝土轴压短柱在核心混凝土强度等级相同的情况下,构件承载力随钢管壁厚的增加而增大,混凝土强度对其有影响。6种规程在计算不锈钢管混凝土短柱承载力时偏于安全,其中CECS28:2012更接近试验结果,该文成果对不锈钢管混凝土短柱承载力的设计有一定的参考意义。     

自攻螺钉双面剪切连接抗剪性能研究

该文通过ABAQUS有限元软件对自攻螺钉双面剪切连接抗剪性能进行了研究,通过已有试验结果验证了有限元模型的准确性,基于此模型讨论了钢材强度等级、钢板厚度、螺钉直径以及不同中间钢板厚度对螺钉双面剪切连接的破坏模式和抗剪承载力的影响。结果表明:螺钉双面剪切连接构件的破坏模式可分成3类,分别为:承压破坏、承压-剪切破坏和剪切破坏。螺钉双面剪切连接抗剪承载力随着钢材强度等级和钢板厚度的增加而提高并趋于稳定;随着螺钉直径的增加,螺钉双面剪切连接抗剪承载力呈线性增加;在一定范围增加中间钢板厚度也可显著提高螺钉双面剪切连接抗剪承载力。将数值模拟结果与中美欧规范计算值进行比较分析得出,当钢板发生承压破坏时,中国、欧洲和AISC规范公式计算值偏于保守,AISI规范计算值较接近有限元值;当螺钉发生剪切破坏时,AISI和中欧规范过于保守。AISC规范公式计算值与有限元值吻合较好,因此,当螺钉发生剪切破坏时,使用AISC规范公式计算具有一定参考价值。     

预制装配型钢混凝土梁受剪承载力试验与计算方法研究

为了深入研究预制装配型钢混凝土梁的受剪机理并提出可准确预测其受剪承载力的计算公式,该文完成了2个足尺预制装配型钢混凝土梁试件的静力剪切性能试验。通过分析试件的破坏过程、荷载-位移曲线和应变发展规律,对不同剪跨比下试件的破坏形态和承载能力进行了研究。基于变形协调桁架-拱模型和Nakamura模型建立了该种预制装配型钢混凝土梁及普通现浇型钢混凝土梁共同适用的受剪承载力计算模型。通过与75个发生剪切破坏的型钢混凝土梁试验结果对比可得:该文提出的计算方法可较好反映型钢混凝土梁的剪切破坏机理,试验值与计算值吻合良好;规范AISC 360-2010和JGJ 138-2016建议的受剪承载力计算公式较为保守。     

基于不同混凝土本构模型的混凝土双向板火灾行为分析

为考查本构模型对混凝土双向板火灾行为的影响,建立不考虑骨料类型影响的混凝土高温本构模型,编程对混凝土试验板火灾行为进行分析,验证了本构模型的有效性。在此基础上,基于EC2、ASCE和该文模型,分析本构模型、火灾工况、板厚和骨料类型等参数对混凝土双向板火灾行为的影响规律。结果表明,与EC2和ASCE模型计算结果相比,该文模型所得结果均趋于保守。     

不锈钢压弯构件整体稳定性能有限元研究与承载力计算方法

该文采用有限元软件ANSYS建立了焊接不锈钢压弯构件有限元模型,并基于试验结果验证了该模型的有效性。采用经验证的有限元模型分析了残余应力和几何初始缺陷对构件整体稳定性能的影响,并在广泛的截面等级、荷载偏心和长细比组合下进行了参数分析以产生足够的数据点。最后,利用有限元分析结果对我国现行《不锈钢结构技术规程》（CECS 410―2015）中的计算方法进行评价,并给出了提高计算精度的改进方法。结果表明:CECS 410―2015中的计算方法对于不锈钢焊接工字形和箱形截面压弯构件整体稳定承载力的预测均偏于保守,改进的计算方法能够更精确地预测不锈钢焊接工字形和箱形截面压弯构件的整体稳定承载力。     

不锈钢焊接箱形截面压弯构件弯曲屈曲试验研究

为了研究不锈钢焊接箱形截面压弯构件的弯曲屈曲,该文对5根奥氏体型和5根双相型不锈钢焊接箱形截面柱进行了偏心受压试验,试件长细比在55~85,荷载偏心距分别设计为50 mm、60 mm、70 mm,并且在试验前对试件的初始弯曲和荷载初偏心进行了测量。根据试验结果对构件静力承载性能进行了分析,并将试验结果分别与CECS 410:2015《不锈钢结构技术规程》和欧洲规范EN 1993-1-4中不锈钢压弯构件承载力的计算值进行了对比。结果表明:所有构件均发生平面内的整体弯曲失稳,且整体失稳前没有发现明显的局部板件屈曲;构件承载力随着偏心距、长细比的增大而降低;对于双相型不锈钢压弯构件,依据CECS 410:2015和EN 1993-1-4的计算值较试验结果均偏于安全;对于奥氏体型不锈钢压弯构件,依据EN 1993-1-4的计算值较试验结果均偏于安全,依据CECS 410:2015的个别试件计算结果略低于试验结果,但整体偏于安全。     

基于纤维模型的钢筋混凝土柱应变率效应研究

该文基于钢筋混凝土柱构件的快速加载试验数据,分别采用CEB规范和Kulkarni和Shah建议的考虑应变率效应的混凝土动力本构关系,运用纤维模型建立了其动力纤维单元模型,并对单调快速加载下的构件的恢复力特性进行了数值模拟。与试验结果的比较表明所采用的两种动力本构模型均能够反映钢筋混凝土柱承载力随加载速率的提高而提高的特...     

压型钢板-高延性水泥基材料组合楼板纵向剪切性能及承载力研究

通过2组8个压型钢板-高延性水泥基材料(ECC)组合楼板静力加载试验,研究上述试件破坏模式、承载力、刚度、应变分布及滑移等受力性能。试验结果表明：峰值荷载时,端部设置栓钉的压型钢板-ECC组合楼板试件滑移值较大,达到峰值荷载后,试件承载力下降平缓,表现为延性剪切破坏;而端部未设置栓钉的试件表现为脆性剪切破坏。分析了剪跨、压型钢板厚度、组合楼板截面高度及端部栓钉等因素对压型钢板-ECC组合楼板纵向剪切性能及剪切承载力影响规律。在试验研究基础上,分别基于欧洲规范(Eurocode-4)和组合楼板设计与施工规范(CECS273:2010)的m-k法,提出适用于压型钢板-ECC组合楼板的纵向剪切承载力计算公式,经比较分析计算结果与试验结果吻合较好。     

钢管再生混凝土长柱偏压性能研究

对10个圆钢管再生混凝土和10个方钢管再生混凝土长柱进行偏压静力单调加载试验,考虑了再生粗骨料取代率、长细比、偏心距3个变化参数,观察了试件受力的全过程和试件破坏形态,绘制出荷载-变形、荷载-应变等一系列重要关系曲线,给出了截面应变沿高度分布情况,并分析了变化参数对试件极限承载力的影响规律,采用国内外常用的8部相关规程计算两种截面形式试件的极限承载力。研究结果表明:钢管再生混凝土偏压长柱受力过程均经历了弹性阶段、屈服阶段和破坏阶段,破坏形态主要为弹塑性失稳破坏;建议采用规程DL/T5085-1999和DBJ13-51-2003设计圆钢管再生混凝土偏压长柱试件的极限承载力,采用规程CECS159:2004、DBJ13-51-2003设计方钢管再生混凝土偏压长柱试件的极限承载力。     

测量活动管控效果的模糊综合评定法

鉴于靶场试验测量活动大多为现场测量,尤其需要注重管控,其效果与满足测量要求的程度直接相关,是信任测量结果的主观前提。该文依据GJB 9001B——2009和GJB 2725A——2001等标准,运用模糊综合评价法,建立涵盖岗位人员、测量设备、测量过程、测试方法和环境条件5个方面的测量活动管控效果评价模型,并给出评分指南。最后,为方便模型应用,开发基于移动应用的评定工具APP程序。APP程序的试用结果表明:该方法具有严谨的评价准则和指标,既可以在线评定,使靶场一线测量活动得到规范,又可以事后评定,确认试验测量结果是否值得被信任。     

Experimental study on FRP-to-concrete bonded joints

The behaviour of bond between FRP and concrete is a key factor controlling the behaviour of concrete structures strengthened with FRP composites. This article presents an experimental study on the bond shear strength between FRP and concrete using a near-end supported (NES) single-shear pull test. The test results are found to be in close agreement with the predictions of Chen and Teng's [J. Struct. Eng. 127(2001) 784] bond strength model, which mutually verifies the reliability of both the test method and the Chen and Teng model in general. The NES single-shear pull test, given its simplicity and reliability, is therefore a good candidate as a standard bond test. The test results also showed that Chen and Teng's [J. Struct. Eng. 127(2001) 784] bond strength model is slightly conservative when the FRP-to-concrete width ratios are at the two extremes, but this small weakness can be easily removed when more test results of good quality become available.     

基于Campbell模型的卡车与防撞柱最大碰撞力修正计算方法

为探究卡车冲击防撞柱过程中的最大碰撞力,开展了63组碰撞数值试验。根据碰撞后卡车变形特征分析,采用卡车等效变形对Campbell模型进行参数修正,提出了卡车与防撞柱最大碰撞力的修正计算方法,并对国内外相关规范建议的最大碰撞力计算方法的适用性进行了评估。研究表明,碰撞后卡车变形沿宽度呈中间大、两端小的不均匀分布。卡车等效变形不仅受卡车碰撞速度影响,还与防撞柱高度和直径、钢管屈服强度和厚度以及基础深度有关。与实车碰撞试验和数值模拟试验得到的最大碰撞力对比表明,《欧规1》附录B建议方法计算结果严重偏小,《欧规1》附录C和《公路规范》建议方法计算结果离散性较大,该文建议方法计算结果更加准确保守,适用于防撞柱结构设计。     

Optimal efficiency factor in strut-and-tie model for FRP-reinforced concrete short beams with (1.5 < <Emphasis Type="Italic">a/d </Emphasis>< 2.5)

A new model for the efficiency factor of the concrete strut in the strut-and-tie model is proposed in this study for FRP-reinforced concrete short beams with (1.5 < a/d < 2.5). The ultimate load capacity of tested FRP-reinforced short beams was evaluated using the proposed model along with other models for the efficiency factor used in strut-and-tie models of design codes such as the ACI, CSA, and AS3600. It was found that efficiency factor models used in existing reinforced concrete design codes do not predict the ultimate load capacity of FRP-reinforced short beams as accurately as they do for steel-reinforced short beams. This can be attributed to not accounting for the effect of the shear span to effective depth ratio, a/d and the axial stiffness of the flexural reinforcement on the efficiency factor of the concrete strut in reinforced concrete short beams. Ultimate shear load capacity predictions by the proposed model were in agreement with experimental data obtained on 15 GFRP and CFRP-reinforced concrete short beams tested in the laboratory. The proposed model for the efficiency factor was shown to be statistically more accurate yielding the lowest standard deviation and coefficient of variation compared to those of the ACI, AS3600, and CSA A23.3 models. It was also found that shear equations recommended for FRP-RC beams by design guidelines such as the CSA S806-02, ISIS, JSCE, and ISE render very conservative predictions of the ultimate load capacity of FRP-reinforced short beams.     

Simulation of industrial refrigeration plants under variable load conditions

A method to simulate industrial refrigeration systems with several independent, time-variable heat loads is described. The method uses a combination of ordinary differential and algebraic equations to describe both the refrigeration plant, and its interaction with the product in each application. Numerical integration of the differential equations with respect to time allows the various processes to be simulated. Models for freezers, chillers, cold stores and controlled atmosphere work areas are discussed. Assumptions made in these models are realistic from a practical viewpoint, so provided accurate data are available close correlation between predictions and measurements would be expected. The simulation could have applications in both refrigeration system and control system design as it will predict the interactions between different parts of a plant when operating under time-variable conditions. When considering system changes or changes to product specifications the suitability of particular alternatives can be assessed by simulating each in turn.     

Simulation of industrial refrigeration plants under variable load conditionsSimulation d'installations frigorifiques industrielles à des charges variables

A method to simulate industrial refrigeration systems with several independent, time-variable heat loads is described. The method uses a combination of ordinary differential and algebraic equations to describe both the refrigeration plant, and its interaction with the product in each application. Numerical integration of the differential equations with respect to time allows the various processes to be simulated. Models for freezers, chillers, cold stores and controlled atmosphere work areas are discussed. Assumptions made in these models are realistic from a practical viewpoint, so provided accurate data are available close correlation between predictions and measurements would be expected. The simulation could have applications in both refrigeration system and control system design as it will predict the interactions between different parts of a plant when operating under time-variable conditions. When considering system changes or changes to product specifications the suitability of particular alternatives can be assessed by simulating each in turn.     

Plastic collapse moment equations of throughwall axially cracked elbows subjected to in-plane bending moment

A throughwall axial crack may develop in an elbow or pipe bend due to service related degradation mechanism. It is very important to know the plastic collapse moment (PCM) of an elbow in the presence of a throughwall axial crack. The existing PCM equations of throughwall axially cracked (TAC) elbows are based on very few test data points of Griffiths without detailed analyses and also the range of applicability of their proposed equations are limited. Further, they do not differentiate between closing and opening modes of bending although deformation characteristics under these two modes are completely different. Therefore, the present study has been undertaken to investigate through 3D elastic-plastic finite element analysis. A total of 84 elbows with various sizes of axial cracks (a/D_m = 0-1), different wall thickness (R/t = 5-20), different elbow bend radii (R_b/R = 2, 3) and two different bending modes, namely closing and opening have been considered in the analysis. Elastic-perfectly plastic stress-strain response of material has been assumed. Both geometric and material non-linearity are considered in the analysis. Crack closing is observed in most of the cases. To capture the crack closure effect, contact analysis has been performed. Plastic collapse moments have been evaluated from moment-end rotation curves by twice-elastic slope method. From these results, closed-form equations are proposed to evaluate plastic collapse moments of elbows under closing and opening mode of bending moment. The predictions of these proposed equations are compared with the test data available in the literature. Matching between predictions and experimental results is found to be satisfactory.     

Predicting creep crack initiation in austenitic and ferritic steels using the creep toughness parameter and time-dependent failure assessment diagram

Methods for evaluating the creep toughness parameter,   K ^mat _c   , are reviewed and   K ^mat _c   data are determined for a ferritic P22 steel from creep crack growth tests on compact tension, C(T), specimens of homogenous parent material (PM) and heterogeneous specimen weldments at 565 °C and compared to similar tests on austenitic type 316H stainless steel at 550 °C. Appropriate relations describing the time dependency of   K ^mat _c   are determined accounting for data scatter. Considerable differences are observed in the form of the   K ^mat _c   data and the time-dependent failure assessment diagrams (TDFADs) for both the 316H and P22 steel. The TDFAD for P22 shows a strong time dependency, but is insensitive to time for 316H. Creep crack initiation (CCI) time predictions are obtained using the TDFAD approach and compared to experimental results from C(T) specimens and feature components. The TDFAD based on parent material properties can be used to obtain conservative predictions of CCI on weldments. Conservative predictions are almost always obtained when lower bound   K ^mat _c   values are employed. Long-term test are generally more relevant to industrial component lifetimes. The different trends between long- and short-term CCI time and growth data indicate that additional long-term test are required to further validate the procedure to predict the lifetimes of high temperature components.     

DEPOSITION OF SUBMICRON AEROSOL PARTICLES DURING INTEGRATED CIRCUIT MANUFACTURING: THEORY

Submicron (≤1μm) particle contamination can produce unacceptably low yields in the manufacture of integrated circuits. Calculations were made to predict deposition velocities of 0·01-lOμm particles, incorporating gravitational, dlffusional, and electrostatic effects. The results were summarized in equations that correlate non-dimensional deposition (Sherwood number) with convective-diffusion (Peclet number) and with electrostatics (Boltzmann and Fuchs charge distributions). These equations were used In conjunction with particle size distributions to predict particle deposition. In a companion paper |25| the predictions were shown to compare well with limited experimental data. To reduce deposition product surfaces should not be electrically charged and, where possible, these surfaces should be at higher temperatures than the ambient gas. For quality control purposes, the deposition flux predictions could serve to link the specifications of gas cleanliness with the specifications of surface cleanliness.     

腹板并合双肢冷弯薄壁Σ型钢压弯构件畸变性能试验研究

为研究腹板并合双肢冷弯薄壁Σ型钢拼合钢柱的畸变屈曲性能及其相关作用,并评估现行各国规范计算方法适用性,设计制作了22根构件进行压弯试验。以Σ型加劲、腹板孔位、偏心荷载作用位置、柱长等为主要参数,考察其对试件屈曲行为、破坏特征和极限承载能力的影响。结果表明：试验主要发生畸变屈曲或畸变-整体、畸变-局部相关屈曲,Σ型加劲有效地防止了腹板局部屈曲;腹板开孔不会影响屈曲模式的改变;关于强轴和弱轴的偏压位置及偏心距离对试件畸变屈曲行为有显著影响。采用中美技术标准包括中国规范GB50018-2002、JGJ/T 421-2018以及北美规范NAS 100-2016计算的承载力结果与试验结果进行了对比分析,结果表明：荷载绕强轴偏心作用时,中美规范计算结果均偏于安全;荷载绕弱轴偏心作用时,GB 50018-2002和NAS 100-2016计算结果偏于安全,而JGJ/T 421-2018计算值较为保守,试验与其比值约为1.64,该文建议腹板双肢并合截面整体协同工作下绕弱轴稳定承载力可按全截面计算。