Dynamic thermo-mechanical responses of road-soft ground system under vehicle load and daily temperature variation

A complete road-soft ground model is established in this paper to study the dynamic responses caused by vehicle loads and/or daily temperature variation.A dynamic thermo-elastic model is applied to capturing the behavior of the rigid pavement,the base course,and the subgrade,while the soft ground is characterized using a dynamic thermo-poroelastic model.Solutions to the road-soft ground system are derived in the Laplace-Hankel transform domain.The time domain solutions are obtained using an integration approach.The temperature,thermal stress,pore water pressure,and displacement responses caused by the vehicle load and the daily temperature variation are presented.Results show that obvious temperature change mainly exists within 0.3 m of the road when subjected to the daily temperature variation,whereas the stress responses can still be found in deeper places because of the thermal swelling/shrinkage deformation within the upper road structures.Moreover,it is important to consider the coupling effects of the vehicle load and the daily temperature variation when calculating the dynamic responses inside the road-soft ground system.

The Effect of the pH of Ammonum Nitrate Solution on the Susceptability of Mild Steel to Stress Corrosion Cracking (SCC) and General Corrosion

This work investigates the relative aggressiveness of nitrate solutions at different pH values on mild steel towards stress corrosion cracking (SCC) and general corrosion. Electrochemical behavior and stress corrosion cracking sus-ceptibility measurements were carried out in 52 Wt% ammonium nitrate solutions at 368° K and various pH values ranging from 0.77 to 9.64. Constant load stress corrosion test at 90% yield stress was conducted. Tested specimens were prepared and examined using the scanning electron microscope (SEM). The potentiodynamic polarization curves for different pH values again emphasized the validity of the gravimetric measurements and hence the mechanism of cracking was attributed to the stress that assisted the dissolution process.

Effect of Temperature and Concentration of Ammonium Nitrate Solution on the Succeptibility of Mild Steel to Stress Corrosion Cracking

The effect of varying the temperature and the concentration of ammonium nitrate solution on the stress corrosion cracking (SCC) susceptibility of mild steel is studied. An increase in the temperature causes a decrease in the stress corrosion life. It appears that the susceptibility in the range 368 K to 380 K was greater than at other temperatures. Near the boiling point corrosion and stress corrosion occurs, at the boiling point, the cracking was associated with a high rate of general corrosion. Microscopic examination after stress corrosion testing in 10Wt%, 20Wt%, and 52Wt% NH4NO3 solution revealed that in all cases there was severe intergranular attack, especially at the high concentration.

Finite element analysis of couple effect of soil displacement and axial load on single inclined pile

The couple effect of soil displacement and axial load on the single inclined pile in cases of surcharge load and uniform soil movement is discussed in detail with the methods of full-scale field tests and finite element method. Parametric analyses including the degree of inclination and the distance between soil and pile are carried out herein. When the displacement of soil on the left side and right side of a pile is identical, deformation of a vertical pile and an inclined pile is highly close in both cases of surcharge load and uniform soil movement. When the couple effect of soil displacement and axial load occurs, settlement of an inclined pile is greater than that of a vertical pile under the same axial load, and bearing capacity of an inclined pile is smaller than that of a vertical pile. This is quite different from the case when the inclined pile is not affected by soil displacement. For inclined piles, P-Δ effect of axial load would lead to a large increase in bending moment, however, for the vertical pile, P-Δ effect of axial load can be neglected. Although the direction of inclination of piles is reverse, deformation of piles caused by uniform soil movement is totally the same. For the inclined piles discussed herein, bending moment(-8 m to-17 m under the ground) relies heavily on uniform soil movement and does not change during the process of applying axial load. When the thickness of soil is less than the pile length, the greater the thickness of soil, the larger the bending moment at lower part of the inclined pile. When the thickness of soil is larger than the pile length, bending moment at lower part of the inclined pile is zero.

Experimental Study on Fatigue Performance of Reinforced Concrete Beams in Corrosive Environment with Cyclic Loads

In marine environments,reinforced concrete bridge structures are sub-jected to cyclic loads and chloride ingress,which results in corrosion of the rein-forcing bars,early deterioration,durability loss,and a considerable reduction in the fatigue strength.Owing to the complexity of the problem and the difficulty of testing,there are few studies on the fatigue performance of concrete structures under the combined action of corrosion environment and cyclic load.Therefore,a coupling test device for corrosion and cyclic load is designed and fatigue tests of reinforced concrete beams in air environments and chlorine salt corrosive envir-onments are carried out.The fatigue corrosion process,damage mode,and corro-sion features of the test beams as well as chloride ion content in concrete are analyzed.The relationships of deflection,crack,and number of cycles in the dif-ferent environments are given.Results show that the fatigue life of the beam is.greatly reduced under coupled effects of the cyclic load and corrosive environ-ment,the failure fom of the beam is corrosion fatigue damage.The deflection and crack keeps growing with the increase in loading cycles.Under the coupling of cyclic load and corrosion env ironment,the content of chloride ion in concrete is low and there is less variety along the direction of penetration.

Size and temperature effects on band gaps in periodic fluid-filled micropipes

A new model is proposed for determining the band gaps of flexural wave propagation in periodic fluid-filled micropipes with circular and square thin-wall cross-sectional shapes, which incorporates temperature, microstructure, and surface energy effects. The band gaps depend on the thin-wall cross-sectional shape, the microstructure and surface elastic material constants, the pipe wall thickness, the unit cell length, the volume fraction, the fluid velocity in the pipe, the temperature change,and the thermal expansion coefficient. A systematic parametric study is conducted to quantitatively illustrate these factors. The numerical results show that the band gap frequencies of the current non-classical model with both circular and square thin-wall cross-sectional shapes are always higher than those of the classical model. In addition,the band gap size and frequency decrease with the increase of the unit cell length according to all the cases. Moreover, the large band gaps can be obtained by tailoring these factors.

Principal axes of M-DOF structures PartⅡ:Dynamic loading

This paper is the second in a two-part series that discusses the principal axes of M-DOF structures subjected to static and dynamic loads.The primary purpose of this series is to understand the magnitude of the dynamie response of structures to enable better design of structures and response modification devices/systems.Under idealized design condi- tions,the structural responses are obtained by using single directinn input ground motions in the direction of the intended response modification devices/systems,and by assuming that the responses of the structure is deconpleable in three mutual- ly perpendicular directions.This standard practice has been applied to both new and retrofitted structures using various seis- mic protective systems.Very limited information is available on the effects of neglecting the impact of directional couplings (cross effects of which torsion is a component)of the dynamic response of structures.In order to quantify such effects,it is necessary to examine the principal axes of structures under both static and dynamic loading.In this twn-part series,the first paper is concerned with static loading,which provides definitions and fundamental formulations,with the conclusion that cross effects of a statically loaded M-DOF structure resulting from the lack of principal axes are of insignificant magnitude. However,under dynamic or earthquake loading,a relatively small amount of energy transferred across perpendicular direc- tions is accumulated,which may result in significant enlargement of the structural response.This paper deals with a formu- lation to define the principal axes of M-DOF structures under dynamic loading and develops quantitative measures to identify cross effects resuhing from the non-existence of principal axes.

腐蚀疲劳交替下2A12-T4航空铝合金的寿命分析研究

基于飞机服役期间经历“地面腐蚀与空中疲劳”的交替损伤模式,考虑载荷间的相互作用,研究了航空铝合金2A12-T4在预腐蚀与“腐蚀+疲劳”交替模式下疲劳寿命的退化与损伤累积规律。同级加载条件下提出利用腐蚀疲劳耦合损伤指数和迟滞载荷用来描述考虑交替腐蚀疲劳损伤模式,用各级疲劳损伤间的相互影响及腐蚀损伤与疲劳损伤在服役工作期间的耦合作用来描述腐蚀、疲劳间的相互促进、加速劣化的现象。基于损伤力学和非线性累积理论,考虑载腐蚀疲劳耦合指数与迟滞载荷对传统的Miner线性累积损伤理论进行修正。建立了飞机结构材料的寿命计算模型,并将模型计算结果与试验结果进行对比验证。确定了腐蚀实验中的腐蚀耦合损伤,并利用低载锻炼效应理论得出均匀分布的迟滞载荷。计算结果表明,本文提出的寿命计算模型的结果与实验结果比较吻合。

循环加卸载条件下考虑温度的煤体本构模型

随着煤炭资源深部开采趋于“常态化”,深入了解处于高地应力和高地温环境中深部煤体在扰动条件下的力学性质及其损伤演化规律,对煤矿深部开采具有重要意义。选取平煤十二矿己16-17-17200工作面的煤体为研究对象,开展了在不同温度条件下三轴循环加卸载试验,分析了温度对试件峰值强度、变形模量、泊松比等基本力学参数的影响。将不同加卸载速率相关的应力-应变问题转化为时间-应力-应变问题,同时引入分数阶导数理论和连续介质损伤理论,提出了一个考虑了热-力耦合作用的分数阶粘弹塑性本构方程,通过试验数据验证了其有效性。结果表明:煤体变形模量随着循环次数的增加呈出现线性减小的趋势,而煤体泊松比减速上升,在峰值应力处达到极值,然后降低,表明循环加卸载作用对煤体基本力学性能有劣化作用。随着温度的升高,煤体峰值强度非线性减小,损伤累积变缓,对应的应变逐渐增大,表明升温能增强煤体延性变形能力,加速煤体损伤的发展。在循环加卸载过程中,输入能密度、弹性能密度和耗散能密度在煤体破坏失稳阶段随温度升高呈现出明显的衰减现象,说明高温加剧了煤体内部的损伤,降低了煤体强度,使得破坏所需外界输入能量减少。考虑温度影响的分数阶粘弹塑性模型可以较好地描述深部煤体在循环加卸载条件下的力学行为。模型适用于热力耦合下深部煤体的复杂应力状态。

浮式风机风载荷与浮式基础运动相互影响研究

本文定量研究浮式风机系统风载荷与浮式基础运动间的相互影响。建立了浮式风力机系统一体化耦合动力学分析模型,对比分析了风载荷对系缆力、浮式基础运动、机舱加速度的影响及浮式基础运动对叶片相对流速、叶片推力和发电功率的影响。结果表明,风载荷显著影响浮式基础纵荡/纵摇平均值,对其标准差影响较小;风载荷对系缆力的平均值和标准差都有一定影响,而机舱加速度受风载荷的影响并不大;浮式基础运动对叶片相对风速的标准差有显著影响,离轮毂越远位置的相对风速受基础运动影响越大,这导致浮式风机叶片推力和发电功率有很大波动。为保证平稳发电,对浮式风机控制设计时,需考虑浮式基础运动的影响。

风浪流单独及耦合作用下15 MW级浮式基础动力特性研究

了解风浪流等环境荷载效应对浮式基础设计及优化至关重要,为此,以15 MW级漂浮式基础为研究对象,系统性定量分析风浪流环境荷载单独及耦合作用下对浮式基础运动及系泊系统受力的影响。首先,以INOWINDMOOR 12 MW和TaiDa 15 MW浮式基础为原型设计新的15 MW级浮式基础,并在ANSYS-AQWA建立水动力分析模型,风力荷载及海流荷载通过风力系数、流力系数添加;其次,针对风浪流等环境荷载单独及耦合作用下浮式基础运动和系泊受力等特征开展分析。结果表明:浮式基础运动及系泊受力主要受风力和流力的影响,波浪会加剧浮式基础运动及系泊受力的往复性,并加大运动幅度及系泊受力;流荷载对浮式基础运动及系泊受力影响较大,特别是风、浪与流耦合作用时会导致系泊受力明显增加,实际工程设计时,流荷载应给与重点关注。

铁尾矿粉混凝土在荷载与硫酸盐干湿循环耦合作用下的性能劣化机理

铁尾矿粉作为矿物掺合料应用于混凝土有助于固废高值化利用和节能减排,而关于铁尾矿粉混凝土抗硫酸盐侵蚀性能的研究,大多只考虑了单一条件或者加速条件环境,其在多种环境耦合下的劣化特征尚未得到探究.本文将铁尾矿粉作为矿物掺合料应用于混凝土中,以相对动弹性模量、质量损失率为性能指标,研究荷载-硫酸盐干湿循环耦合作用下铁尾矿粉混凝土劣化过程,探究铁尾矿粉掺量和荷载率对铁尾矿粉混凝土内部劣化的影响,结合扫描电镜(SEM)、X-ray衍射分析(XRD)、压汞(MIP)等微观手段揭示铁尾矿粉混凝土在耦合作用下损伤劣化机理.结果表明:适量铁尾矿粉的掺入有利于其与矿粉的协同水化作用,提高混凝土水化程度和基体密实度,减少硫酸根离子传输路径,提高混凝土抗硫酸盐侵蚀能力;荷载的施加使试块内部微裂纹宽度和数量增加,为硫酸根离子的进入提供更多渗透路径,加速铁尾矿粉混凝土损伤劣化过程;耦合作用使得铁尾矿粉混凝土内部损伤不断累积,在微观上表现为结构的疏松和裂缝的衍生扩展,在宏观上表现为力学性能的衰减和整体结构完整性的下降.

移动荷载作用下层状横观各向同性饱和土中排桩的隔振效应

利用有限元-边界元耦合法评估了移动荷载下层状横观各向同性饱和土体中排桩的隔振效果。利用有限元法将排桩离散成单桩以及桩单元,基于Bernoulli-Euler梁理论得到桩的有限元矩阵方程;在桩-土边界,土体单元与桩单元进行了等节点离散,并以层状饱和地基的解析层元基本解作为核函数,利用边界积分法得到桩-土界面处地基的柔度矩阵;基于两阶段理论,将侧摩阻力响应与移动荷载直接引起的振动进行耦合,结合边界元法得到饱和地基的边界元方程;考虑Bernoulli-Euler梁和土体之间不发生相对滑移和脱开的位移协调条件,耦合有限元和边界元方程,得到排桩的动力响应方程;计算有无排桩隔振下某一观测点的位移,即可结合隔振理论分析排桩的隔振效率。在验证所提方法准确性的基础上,分析了桩长、桩身刚度、移动荷载速度以及横观各向同性参数对排桩隔振效应的影响。结果表明:最优桩长约等于2倍瑞利波长,超过该值隔振效果提高不大;桩与地基的刚度差越大,隔振效果越好;荷载速度超过剪切波速,桩基隔振表现反而更好。

多向荷载耦合作用下复合基础承载特性分析

针对水下石油生产系统复合基础在不同方向荷载耦合作用下的承载特性,分析复合加载模式下的破坏包络线。采用非线性有限元数值模拟方法,通过固定位移比法绘制竖向—倾覆、水平—扭转、竖向—水平—倾覆、竖向—水平—扭转荷载空间内的地基承载力破坏包络线,分析不同长径比和桩间距对不同方向荷载耦合作用下地基承载力包络线的影响,并分别将归一化处理后的竖向—倾覆、水平—扭转荷载包络线拟合为关于长径比和桩间距的包络线数学表达式。结果表明:随竖向荷载分量的增大,基础在二维荷载空间内包络线尺寸有所减小。结合实际工程应用,通过绘制地基承载力破坏包络线,对基础设计方案校核和评估,能很好指导工程实践与设计。

铜缓蚀剂及其与硅烷复合自组装膜耐腐蚀性能

目的解决铜及铜合金在海水介质中的腐蚀问题。方法采用自组装技术在铜表面制备了甲基-1H-苯并三唑(TTA)、十六烷基三甲基溴化铵(CTAB)、L-精氨酸和L-组氨酸4种缓蚀剂的自组装膜,并将这4种缓蚀剂分别与双-[γ-(三乙氧基硅)丙基]四硫化物(Si-69)进行组合制备了复合自组装膜,通过电化学方法研究了铜表面自组装膜的耐腐蚀性能。结果所有缓蚀剂及其复合膜层均具有一定的耐腐蚀性,不同缓蚀剂自组装膜的缓蚀效率从大到小为:CTAB(78.78%)>TTA(61.00%)>组氨酸(56.03%)>精氨酸(46.38%)。相比空白铜样品的水接触角(76.9°),CTAB自组装膜的接触角达100.7°。缓蚀剂与Si-69复配的自组装膜性能比单一缓蚀剂或硅烷更加优异,且在4种缓蚀剂中CTAB效果最好,其缓蚀效率达96.91%,其余依次为TTA(85.38%)、组氨酸(84.91%)和精氨酸(82.09%)。CTAB与硅烷复合膜层的水接触角为105.6°。结论在铜表面制备CTAB、TTA、组氨酸、精氨酸4种自组装膜可以有效提高材料的耐蚀性。将4种缓蚀剂与硅烷复配时缓蚀效率均有提高,硅烷的加入能够改善缓蚀剂自组装膜层结构,提高耐蚀性。结果表明,利用缓蚀剂与硅烷复配的协同效应来提高膜层性能是一种可行的思路。

钢框架-灌浆轻钢剪力墙结构抗震性能试验研究

对钢框架-灌浆轻钢剪力墙结构足尺试件进行了水平低周往复加载试验,研究了灌浆轻钢剪力墙与钢框架的耦合效应,分析了结构的破坏模式、受力特征和耗能机理,得到了结构的承载能力、抗侧刚度、延性及耗能能力等。通过与纯钢框架及冷弯薄壁型钢灌浆墙体结构的试验结果对比,发现灌浆轻钢剪力墙通过自攻螺钉采用内嵌的方式与钢框架连接,二者具有良好的协同工作性能,框剪结构的抗剪承载力和抗侧刚度分别是钢框与墙体对应值之和的1.50倍和1.64倍,结构延性系数达5.42,抗震性能优良,研究结果可为该类结构的设计研究提供科学基础。

Synergistic effects of sodium hypochlorite disinfection and iron-oxidizing bacteria on early corrosion in cast iron pipes

Corrosion in drinking water distribution systems(DWDSs)may lead to pipe failures and water quality deterioration;biocorrosion is the most common type.Chlorine disinfectants are widely used in DWDSs to inhibit microorganism growth,but these also promote electrochemical corrosion to a certain extent.This study explored the independent and synergistic effects of chlorine and microorganisms on pipeline corrosion.Sodium hypochlorite(NaOCl)at different concentrations(0,0.25,0.50,and 0.75 mg/L)and iron-oxidizing bacteria(IOB)were added to the reaction system,and a biofilm annular reactor(BAR)was employed to simulate operational water supply pipes and explain the composite effects.The degree of corrosion became severe with increasing NaOCl dosage.IOB accelerated the corrosion rate at an early stage,after which the reaction system gradually stabilized.When NaOCl and IOB existed together in the BAR,both synergistic and antagonistic effects occurred during the corrosion process.The AOC content increased due to the addition of NaOCl,which is conducive to bacterial regrowth.However,biofilm on cast iron coupons was greatly influenced by the disinfectant,leading to a decrease in microbial biomass over time.More research is needed to provide guidelines for pipeline corrosion control.

不同双轴加载路径下T形截面RC剪力墙抗震性能试验研究

为了探究复杂多维地震作用下带翼缘剪力墙的损伤机理和抗震性能,进行了5个T形截面RC剪力墙的水平单、双轴拟静力试验,研究双轴加载对T形墙破坏模式、滞回性能、承载力、延性与耗能能力的影响,考察T形墙在不同双轴加载路径下的受力机理和多维抗震性能。结果表明:T形墙在单、双轴加载下的破坏均发生在墙肢自由端底部,双轴加载加剧了裂缝的开展和混凝土的剥落,且对翼缘的损伤影响更大;T形墙两正交方向的受力行为存在明显的相关性,双轴耦合受力产生的内力重分布和局部附加应力会改变T形墙的局部受力机理和整体性能,表现为一个方向受荷时,其正交方向在位移不变的情况下荷载会产生突变;相较于单轴加载,双轴加载下T形墙各方向承载力平均降低了6.90%,极限变形能力平均降低了11.28%,单个方向破坏时的累积耗能减小,且双轴耦合效应按“十”字形、“8”字形、矩形加载路径的顺序依次增强。鉴于地震动的随机性以及结构响应的多维耦合性会显著改变带翼缘RC剪力墙在实际地震作用下的抗震能力,建议在剪力墙结构抗震设计时合理考虑承载力的折减并适当减小层间位移角限值。

基于层内力等效的偏心高层建筑三维等效静力风荷载

对于质心和刚心不重合的偏心高层建筑,由于结构三维振型耦合与气动力耦合等因素的影响,其等效静力风荷载的评估变得十分复杂.基于振型加速度法,推导了考虑三维气动力耦合和振型交叉项贡献的偏心高层建筑各层拟静力项和惯性力项内力(剪力和弯矩)响应计算方法 .在此基础上,基于各层内力响应等效,建立了能合理反映荷载沿高分布信息的结构三维等效静力风荷载评估方法.随后,结合3种典型矩形截面高层建筑刚性模型测压风洞试验,分析了荷载相关性、结构偏心率和截面长宽比对偏心结构三维等效静力风荷载的影响.研究表明:对于偏心截面高层建筑,振型交叉项和荷载相关性对结构风致响应与等效静力风荷载的贡献不可忽视,若忽略两者则会低估偏心高层建筑三维等效静力风荷载,特别是扭转向等效静力风荷载.此外,偏心率和截面长宽比同样影响偏心高层建筑等效静力风荷载的大小和分布情况.相关研究可为偏心高层建筑的抗风设计提供一定的指导.

锈蚀-疲劳耦合作用下钢筋混凝土梁挠度计算方法研究

为探究锈蚀-疲劳耦合作用下钢筋混凝土梁的结构力学行为及刚度退化规律,设计了3组不同应力幅作用的钢筋混凝土梁锈蚀-疲劳耦合持荷试验,分析了各试验梁的疲劳寿命及刚度演化规律。结果表明,钢筋、混凝土疲劳和钢筋的锈蚀耦合作用下,钢筋混凝土构件的疲劳寿命显著降低,疲劳梁和锈蚀疲劳耦合梁的挠度发展曲线均呈现“突增-稳定-突增”的变化规律,且锈蚀疲劳耦合梁在第二阶段的挠度发展速率要远大于同应力幅下的疲劳加载梁。该方法在既有规范基础上分别改进了现有疲劳梁和锈蚀疲劳耦合作用下结构的挠度计算方法,可以有效考虑钢筋疲劳作用、外荷载应力幅、混凝土模量退化、钢筋锈蚀等因素的影响,其计算值与试验值吻合较好,验证了该文提出的刚度计算模型的有效性。