Modal testing as a means of quantitative monitoring of damage progression in a model FRP rehabilitated bridge deck system

Although substantial research has been conducted on the application of externally bonded fibre reinforced polymer (FRP) materials as a means of strengthening deficient and deteriorating concrete components most studies, and even field monitoring, have been at the component level. There is lack of data regarding the systems level response of strengthening. This paper reports on the results of an investigation of the effect of progressive strengthening of a slab-girder system through initial flexural strengthening of the decks followed by shear strengthening of the central girder. The progression of damage after each phase of loading was assessed through a process of forced vibration based modal testing. The paper focuses on modal testing and model updating procedures as a means of structural health monitoring and indicates that the process can be used effectively to accurately show changes in both local and global response through the different stages of loading. The procedures not only provide an assessment of damage progression and load redistribution in the rehabilitated components, but also enable an accurate representation of response at the systems and local (through support locations) levels.     

Reliability-based service life assessment for deteriorating reinforced concrete buildings considering the effect of cumulative damage

Most engineering systems used in maintenance strategies must consider deterioration and seismic structural damage. To identify the effects of deterioration and earthquakes simultaneously on structural performance, this study applies an integral simulation method. Compared with that of previous studies, the feature of the proposed method is its analysis of the time-dependent structural capacity of a deteriorating reinforced concrete (RC) building and the simulation of life-cycle earthquake events within a specified service period, while considering cumulative damage induced by deterioration and earthquakes. In addition, the proposed assessment method is applied to derive the reliability-based service life of a deteriorating RC building located in a region with high seismic hazard. Briefly, for deteriorating RC buildings, the proposed reliability-based service life assessment method provides useful information related to maintenance based on both serviceability and safety.     

Application of singular spectrum analysis to structural monitoring and damage diagnosis of bridges

Singular spectrum analysis (SSA) is a novel technique and has proven to be a powerful tool for time series data analysis. Through singular value decomposition of Hankel matrix data, the time series of data can be decomposed into several simple, independent and identifiable components from singular values and singular vectors. It has already been widely applied to process climatic, meteorological, geophysical and economic data. In this paper, we demonstrate that the coupling degree of the 1st and 2nd singular values in SSA contains useful indications on the feature and composition of the analysed signal. The proposed method is successfully applied to the monitoring of structure, such as damage detection of the simulated dynamic system, experimental steel frame, bridge foundation scouring and pier settlement in the laboratory and on-site bridge monitoring during typhoon strike. The proposed algorithm is simple and suitable for structural health monitoring in the field.     

Structural system identification of cable-stayed bridges with observability techniques

Cable-stayed bridges are highly statically redundant, light and flexible structures. This complexity highlights the role of the structural system identification (SSI) method in the calibration of the actual properties of the simplified models of these structures. This study proposes the first application of observability techniques to SSI of cable-stayed bridges. This method enables to define which subset of actual structural variables should be measured on site to identify mechanical properties, such as Young's modulus, area and inertia, or stiffnesses (EA and EI) of deck, pylon and stay cables. The effects of the inclination and inertia of the stay cables and the existence of pylon and deck cracking in the observability of different cable-stayed bridges are studied. The results obtained are validated by the models of actual cable-stayed bridges.     

Regional loss estimation due to hurricane wind and hurricane-induced surge considering climate variability

This paper presents a framework to assess the potential hurricane damage risks to residential construction. Studies show that hurricane wind, frequency and/or hurricane-induced surge may change as a result of climate change; therefore, hurricane risk assessments should be capable of accounting for the impacts climate change. The framework includes a hurricane wind field model, hurricane-induced surge height model and hurricane vulnerability models. Three case study locations (Miami-Dade County, FL; New Hanover County, NC and Galveston County, TX) are presented for two types of analyses: annual regional loss estimation and event-based regional loss estimation. Demographic information, such as median house value and changes in house numbers, and distribution of houses for different exposures, is used to estimate the time-dependent probability of damage with or without possible climate change-induced change in wind speed, frequency and/or surge height. Through both analyses, it was found that climate change may have a significant impact on regional hurricane damage losses.     

Robustness of corroded reinforced concrete structures – a structural performance approach

The aim of this work is to provide new contributions in order to define more accurately the structural robustness concept, particularly when applied to corroded reinforced concrete (RC) structures. To fulfil such a task, several robustness indicators are analysed and discussed with special emphasis on structural-performance-based measures. A new robustness definition and a framework are then proposed for its analysis, based on the structural performance lost after damage occurrence. The competence of the proposed methodology is then tested comparing the robustness of two RC foot bridges under corrosion. The damage considered is the longitudinal reinforcement corrosion level, and load carrying capacity is the structural performance evaluated. In order to analyse corrosion effects, a finite element (FE) based on a two-step analysis is adopted. In the first step, a cross-section analysis is performed to capture phenomenons such as expansion of the reinforcement due to the corrosion products accumulation; damage and cracking in the reinforcement surrounding concrete; steel–concrete bond strength degradation; effective reinforcement area reduction. The results obtained are then used to build a 2D structural model, in order to assess the maximum load carrying capacity of the corroded structure. For each foot bridge, robustness is assessed using the proposed methodology.     

壳聚糖季铵盐修饰的辅酶Q10纳米结构脂质载体的制备及表征

为了增强运载辅酶Q10的纳米结构脂质载体(CoQ10-NLC)的透皮效果,采用促渗剂——壳聚糖季铵盐(QCS)对CoQ10-NLC进行了表面修饰,并结合QCS分子链的自聚集行为,明确了壳聚糖季铵盐修饰的包载辅酶Q10的纳米脂质体(QCS-CoQ10-NLC)的形成机制,得到了粒径在500 nm左右的脂质载体。进一步通过体外透皮实验,考察了QCS-CoQ10-NLC的透皮吸收效果。结果显示,经质量分数0.5%的QCS修饰后,脂质载体可将CoQ10在皮肤中的渗透总量由1.36μg/cm~2显著增加至5.14μg/cm~2。     

碳纤/环氧复合材料层合板低速冲击损伤机理研究

对[0/90/0/90]_(2s)和[+45/-45/0/90]_(2s)以及平纹布铺层方式的T300/环氧复合材料层合板进行低速冲击实验,在圆形试样的基础上比较不同铺层结构的复合材料在冲击性能方面的差异,从冲击能量传播的角度分析不同铺层结构复合材料的冲击破坏机理。并在ABAQUS有限元模拟的基础上分析冲击破坏的能量传播机理。结果表明冲击能量的传播与复合材料层合板中织物沿厚度方向的铺层结构有关,也与每一层织物内纤维的方向和纤维的空间结构有关。冲击能量在排列很直的纤维中传播很快,沿纤维轴向的损伤更容易传递,所以单向布铺层的复合材料与平纹布铺层的复合材料相比,冲击中心区域的损伤小,但是损伤的范围大,纤维的弯曲会降低冲击能量沿纤维轴向的传播速度,平纹织物中每一层纤维存在交织点,冲击能量集中在冲击中心区域,使得平纹布铺层的复合材料冲击损伤集中于冲击中心处且损伤程度比单向布铺层的复合材料大,出现更多的纤维断裂情况。在铺层复合材料中纤维排列的方向越多,沿纤维轴向传播的能量方向也就越多,冲击能量在每一层的面内传播更均匀,有利于减轻复合材料受冲击的损伤程度。     

循环加载下复合材料胶接面变形与破坏实验研究

复合材料胶接结构损伤变形和演化行为的实时表征对其服役的安全性和可靠性评估具有重要的意义。结合数字图像相关(Digital Image Correlation,简称"DIC")和声发射(Acoustic Emission,简称"AE")技术,研究循环拉伸加载条件下复合材料单搭接界面的损伤变形与破坏行为。依据单向拉伸失效载荷均值,取准静态破坏载荷的70%和80%分别进行循环拉伸加载实验。通过不同阶段复合材料胶接界面的损伤变形场、应变场信息及演化过程中获取的AE信号,分析循环加载下复合材料单搭接界面损伤破坏的力学机制与实时变形和AE特征信号的对应关系。结果表明,复合材料单搭接试件损伤破坏的实时微位移场特征和AE相对能量、撞击累积数及幅度谱等反映了胶接界面微裂纹的萌生及扩展行为。随应力水平的升高,复合材料单搭接试件破坏前的循环次数呈递减趋势。