索承式桥梁腐蚀吊索安全性能评估

腐蚀蚀坑是索承式桥梁吊索力学性能退化的主要原因。基于断裂力学和蚀坑等效,考虑腐蚀蚀坑影响,以吊索在荷载作用下的安全系数小于2.5作为吊索失效判据,建立腐蚀吊索承载力安全性能评估方法,并以袁州大桥钢丝腐蚀速率数据为基础,进行参数敏感性分析和算例计算,研究了各工况下吊索失效时的断丝数量和安全系数小于2.5的时间。结果表明,该方法相比较均匀腐蚀理论模型,考虑了钢丝腐蚀蚀坑对吊索承载力的影响,能够预测钢丝断裂数量和安全系数小于2.5的时间。     

高速铁路隧道基底软岩动力累积损伤特性

利用相似材料模拟高速铁路隧道基底软岩,采用荷载控制和非对称正弦波循环加载方式对软岩试件进行动三轴疲劳与损伤检测综合试验。通过试验结果分析,建立了软岩3参数多项式疲劳寿命计算模型和4参数多项式累积损伤参量计算模型,获得了软岩疲劳损伤特性,即：软岩疲劳破坏表现为端部拉-剪复合破坏和中部压-剪复合破坏两种模式;疲劳破坏全过程表现为初始微孔隙压密、裂纹发生与稳定扩展以及损伤裂纹加速发展3个发展阶段;软岩疲劳寿命主要取决于本身强度和动应力水平,强度愈高、动力应力水平愈低,其疲劳寿命就越长;当动应力水平相同时,软岩疲劳寿命与其弹性模量呈线性增长关系。     

钢砼组合结构PBH剪力键的疲劳性能

为了研究钢箱-砼组合结构中PBH剪力键在反复荷载作用下的疲劳性能,设计制作了PBH剪力键试验模型,进行了24万次疲劳推出试验。在疲劳破坏形态和试验滑移及应变数据分析的基础上,利用数值工具开展肋板开孔孔径、穿入钢筋直径、混凝土强度3个参数的PBH剪力键疲劳寿命影响因素分析。研究表明：PBH剪力键的疲劳破坏形态与静载破坏相似,表观表现为混凝土面多处斜向劈裂裂缝、内部榫孔混凝土压碎、穿入钢筋局部屈服;疲劳破坏演化过程分为疲劳损伤开始、发展、破坏3个阶段,其中疲劳发展阶段占整个疲劳阶段的91.7%,结构刚度在疲劳损伤开始和发展阶段退化较慢,在疲劳破坏阶段退化较快;肋板开孔孔径、穿入钢筋直径、混凝土强度3个参数对PBH剪力键疲劳寿命影响均有明显影响,其中穿入钢筋直径对疲劳寿命的影响尤为突出。     

酸雨环境下老旧砖砌体的抗压性能

为研究酸雨环境下老旧砌体抗压力学性能退化规律，实验室配置了PH值分别为1.5、2.5和3.5的3种硫酸和硝酸混合溶液来模拟酸雨环境，采用完全浸泡加速腐蚀的试验方法对砖、砂浆和砖柱进行不同程度的腐蚀，并测定其抗压强度。试验表明，随着腐蚀时间的增加，砂浆试块抗压强度先增大后降低；砖试块抗压强度随腐蚀时间的增加而降低；模拟酸雨溶液PH值越小，砂浆和砖试块抗压强度降低程度也愈大；砖柱极限承载力和弹性模量均随腐蚀时间的增加而降低，且模拟酸雨溶液PH值越小，降低程度愈大；随着腐蚀时间的增加，砖柱初始刚度逐渐减小，极限破坏位移增大；模拟酸雨溶液PH值越小，砖柱在达到峰值荷载时的变形值越小，脆性愈大；基于试验结果，建立了酸雨环境下砖柱应力应变曲线上升段统一数学表达式及酸雨侵蚀后普通烧结粘土砖砌体剩余抗压强度回归公式。     

CT test analysis of meso damage and fracture process of concrete under tensile loading

对静力、动力拉伸荷载条件下混凝土的细观破损过程进行了CT试验研究,获得了试样内部裂纹萌生、扩展、贯通的全过程CT图像。通过对CT图像及图像兴趣区中整体统计区域、局部统计区域CT 数均值的分析,研究了混凝土拉伸荷载条件下细观破损过程。结果表明：静力拉伸荷载条件下,裂纹在界面的薄弱区域形成后逐渐往相邻的薄弱部位扩展,两个统计区域CT 数均值呈降低趋势,试样破坏时伴有少量骨料被拉断的现象;动力拉伸荷载条件下,裂纹从界面薄弱区域形成后追随最快的路径扩展,局部统计区域CT 数均值呈下降趋势,而整体统计区域CT数均值变化幅度较小,破坏后骨料沿界面脱离砂浆粘结,且试样破裂面更为平整;由于加载速率的提高,骨料被拉断的现象非常显著。     

复合岩体的TBM破岩机理数值模拟

为了指导TBM刀盘刀具的研制和不同地质条件下刀盘刀具的选型,TBM破岩机理的研究成为核心。在TBM滚刀的作用下,岩体中裂纹的生成、扩展和连接规律是深刻理解TBM破岩机理的前提,因此,TBM滚刀破岩机理的研究具有重要的工程应用价值。目前,TBM滚刀破岩机理的研究主要集中在单一岩体中,但在TBM施工过程中会遇到各种复杂的地质条件。笔者采用离散元方法,研究了复合岩体的破岩机理,复合岩体中岩片的形成不同于单一岩体,其裂纹的最终连接是由起裂于复合岩体交界面上的微裂纹的扩展,将两滚刀之间的赫兹裂纹连接,最终形成岩片。因此,在一定情况下复合岩体更有利于TBM隧道施工。     

基于缺口应力法的焊接接头多轴疲劳分析

鉴于当前焊接接头疲劳评估曲线只适用于单轴加载情况，基于缺口应力法对焊接接头进行了多轴疲劳分析。通过联合焊接接头的多轴疲劳试验名义应力数据和有限元法所计算的缺口应力集中系数，获得了5种焊接接头的各向缺口应力；根据Von Mises、ⅡW和EESH 3种多轴疲劳准则计算出等效缺口应力并将其统一在同一坐标系统下；最后采用最小二乘法拟合出适用于多轴疲劳评估的缺口寿命曲线。与ⅡW标准推荐的单轴曲线相比，这些多轴缺口疲劳曲线具有更低的倾斜度和更高的疲劳等级，即多轴加载时明显降低了10³~10⁶次中周范围内的疲劳强度值，而对10⁶~10⁷次高周疲劳范围的影响则相对有限。     

决定种子寿命的生理机制研究进展

以前对种子寿命的研究主要集中于环境因子、贮藏方法对寿命的影响，形态结构与寿命关系等方面。近年对决定种子寿命的生理机制进行了一些研究，本文从种子寿命的预测，耐脱水性与寿命的关系，脂质过氧化对寿命的作用，种子蛋白成熟加工酶、蛋白修复酶、Ubiquitins、HSPs、Chaperones、LEA蛋白的作用等方面概述了这一领域的研究进展。     

冷却剂参数对铣槽喷管低周疲劳寿命的影响

采用有限体积流固耦合计算方法、非线性有限元热结构耦合分析方法和局部应变法研究大面积比铣槽喷管三维再生冷却槽道在循环工作条件下的热结构变形与低周疲劳寿命,并对比分析了冷却剂质量流量与入口温度对铣槽喷管疲劳使用寿命的影响。计算结果表明,铣槽喷管热结构响应呈现复杂的三维效应,应变较大位置主要分布在与肋连接的内衬区域,喷管中部的残余应变量最大;冷却槽道低周疲劳寿命分布和热结构响应基本一致,最小寿命位于喷管中部与肋相连的内衬区域燃气侧;随冷却剂质量流量增加,铣槽喷管低周疲劳寿命不断提高;随冷却剂入口温度增加喷管尾部低周疲劳寿命值不断降低,而喷管中前部的低周疲劳寿命值却不断提高,当冷却剂入口温度为280K左右时,本文的铣槽喷管总体使用寿命达到最大。      

混凝土在硫酸盐溶液中的腐蚀模型

混凝土在硫酸盐溶液中的腐蚀破坏是一种常见的混凝土破坏形式,研究混凝土抗硫酸盐腐蚀破坏对于混凝土工程具有重要意义。混凝土在硫酸盐溶液中受腐蚀的过程是一个循序渐进的过程,这个过程包括固液界面的表面吸附、硫酸盐溶液的扩散过程以及硫酸盐在混凝土试件内部的化学反应和物理结晶等物理化学过程。研究表明：可以采用Fick第二扩散定律来描述硫酸盐在混凝土中的扩散过程;硫酸盐溶液中,混凝土试件的固液相界面处发生物理吸附和化学吸附,并存在表面化学反应。     

Prediction of material fatigue life based on industrial CT images

A two dimensional gray image of the material fault can be obtained without destruction by industrial computer tomography (ICT). This process is used to distinguish the seizure and the expansion of cracks within the initiation section. A fatigue life prediction method based on industrial CT images was studied. First, the crack initiation and expansion processes were divided into three phases: micro scale thinness sight crack, CT scale crack, and macroscopic crack. Second, different crack initiation and expansion standards were adapted to calculate material fatigue life. The fatigue life of the material was the sum of the three phase's fatigue lives. Compared with other methods, such as the fatigue cumulative damage theory method and the nominal stress method, the fatigue life predicted by this method is more precise.     

Experimental Investigation and Finite Element Analysis on the Hysteretic Behavior of New Steel Beam-to-Column Connections

By the hysteretic experiments and the finite element analysis of the proof-of-concept connections, the mechanical properties and energy dissipation capacity of the new steel beam-to-column connections are investigated. These connections are semi-rigid ones improved by adding threaded rods into the angle connections and can be designed to limit the structural damage only to the angles and threaded rods. It is found, by the comparative analysis of six connections tested with the same loading sequence, that the performance degradation of the connections may be resulted from the plastic damage, crack propagation of the angles and the buckling and fatigue crack of the rods. The rotation capacity and failure modes of the connections with threaded rods depend on the ability of anti-fatigue crack of the rods, and the better ductility the rods have, the better energy dissipation capacity the connections have. In addition, the hysteretic behavior and the deformation modes of the connections prior to the significant strength degradation or the fracture of the rods could be well simulated by the finite element method. Meanwhile, the stiffening effect from pre-stressing the angles, the plastic distribution of the angles and the degradation induced by the rod buckling were strongly verified by the FEA. Finally, the advantages and disadvantages of such new beam-to-column dissipative connections were analyzed, and the proposal for further connection improvement and in-depth study was made.     

Effect of welding on high strain and low cycle fatigue behavior of hot-rolled H-beam

Low cycle fatigue(LCF)properties of H-beam as hot-rolled and welded are studied, and the cyclic stress-strain relationship and cyclic response characterization are determined. Based on the Coffin-Manson formula, the strain-fatigue life relationship is obtained. Finally, the cyclic toughness, which is the product of strain range at LCF life of 100 cycles and the stress amplitude, are calculated. The test results show that the cyclic toughness as welded H-beam is 62% of that as hot-rolled. Hot-rolled materials exhibit cyclic stability, and welded materials show cyclic softening followed by fracture. The scanning electron microscope(SEM) micrograph of fracture surfaces reveals that the fatigue crack initiates from the coarse grain area of welding joint, and the fine dimple is observed in the fracture surface, which indicates the welding joint remains a good ductility.     

Low-Cyclic Fatigue Behavior of Reinforced Concrete Columns Subjected to Non-Symmetric Displacement Cycling

For the sake of setting up more rational damage criteria for RC structures based on the relationship between displacement amplitude after yielding and low-cyclic fatigue life, this paper Presents six RC columns test results focusing on development of cumulative damage and low-cyclic fatigue life varying with displacement amplitude and positive/ negative displacement ratio. On this basis, expression is provided to describe the relation between low-cyclic fatigue life and positive/negative displacements amplitude ratio under different displacement levels.     

钢筋非均匀锈蚀引起混凝土保护层内裂分析

根据自然环境下保护层锈胀开裂前的钢筋锈蚀形态，将锈蚀层简化为半椭圆状的非均匀分布，从而建立了钢筋非均匀锈蚀理论模型。经过求解得到了混凝土中锈胀应力理论解，并与有限元计算结果对比，验证了理论解的精确性。根据理论解可知最大周向应力在水平轴上，因此锈蚀层的发展会首先引起保护层内部水平裂纹的产生。增加钢筋直径可有效减低锈胀应力，提高结构抗锈裂的能力。与均匀锈蚀理论模型对比结果表明：均匀锈蚀要远小于非均匀锈蚀条件下的临界锈蚀层厚度，均匀锈蚀的计算结果偏于保守。因此，对锈胀问题进行理论分析时，应采用更接近真实锈蚀形态的非均匀锈蚀模型。     

Reinforced Concrete Beam's Stiffness Degeneration Regulation and its Calculation Formula Under the Action of Fatigue Load

Fatigue failure is a fatal damage for the reinforced concrete structure bearing fatigue load repeatedly. That how to estimate or describe the degree of fatigue damage is a challenge in areas of structure damage and lifespan estimation. Structure's stiffness degenerates irreversibly along with the damage progress. There is a certain inherent relevance between stiffness degeneration and fatigue damage. A series of fatigue tests were carried out to study stiffness degeneration regulation due to its simplicity and feasibility. According to the test results, reinforced concrete beam's stiffness degeneration presents a three-stage rules obviously, and the stiffness degeneration curves accord with "S" style. Based on the stiffness degeneration regulation, the reinforced concrete beams' stiffness degeneration calculation formula is obtained by fitting experimental data. The formula has a perfect goodness of contact area with 10 test beams' experimental results, and it can describes reinforced concrete beams' stiffness degeneration perfectly. The formula can be used to forecast the deformation developing. Meanwhile, the residual life of the structure can be used to decision structure's fatigue fracture and the degree of performance degradation.     

THE STUDY OF STRAIN FATIGUE CRACK PROPAGATION BEHAVOURS OF VANADIUM BEARING HSLA STEEL

In this paper, the strain fatigue: crack propagation rates of vanadium bearing HSLA steel with different micro-structures are measured under constant load conditions, and the relationship between the crack propagation rate and the microstructures of steel is also studied.     

对称式基坑渗流涌水量的计算方法

随着地铁、越江隧道等地下工程的日益增多，涌现出了大量的对称式基坑。基于共形映射理论，推导了对称式基坑涌水量计算表达式，并对其计算参数进行分析。研究表明，对称式基坑的单宽涌水量与渗透系数、基坑内外水头差成正比，与（相对）隔水层层顶到坑底的距离和基坑两侧止水帷幕间距的比值、止水帷幕嵌固深度和（相对）隔水层层顶到坑底距离的比值、基坑内外水头差和（相对）隔水层层顶到坑底距离的比值成反相关。