A combined local damage index for seismic assessment of existing RC structures

A new local damage index for existing RC structures is introduced, wherein deterioration caused by all deformation mechanisms (flexure, shear, anchorage slip) is treated separately for each mechanism. Moreover, the additive character of damage arising from the three response mechanisms, and the increase in degradation rate caused by their interaction, are fully taken into consideration. The proposed local damage index is then applied, in conjunction with a finite element model developed previously by the authors, to assess seismic damage response of several RC column and frame test specimens with substandard detailing. It is concluded that in all cases and independently from the prevailing mode of failure, the new local damage index describes well the damage pattern of the analysed specimens. Copyright © 2012 John Wiley & Sons, Ltd.     

Optimum lateral load pattern for seismic design of elastic shear‐buildings incorporating soil–structure interaction effects

Recently, several new optimum loading patterns have been proposed by researchers for fixed‐base systems while their adequacy for soil–structure systems has not been evaluated yet. Through intensive dynamic analyses of multistory shear‐building models with soil–structure interaction subjected to a group of 21 artificial earthquakes adjusted to soft soil design spectrum, the adequacy of these optimum patterns is investigated. It is concluded that using these patterns the structures generally achieve near optimum performance in some range of periods. However, their efficiency reduces as soil flexibility increases especially when soil–structure interaction effects are significant. In the present paper, using the uniform distribution of damage over the height of structures, as the criterion, an optimization algorithm for seismic design of elastic soil–structure systems is developed. The effects of fundamental period, number of stories, earthquake excitation, soil flexibility, building aspect ratio, damping ratio and damping model on optimum distribution pattern are investigated. On the basis of 30,240 optimum load patterns derived from numerical simulations and nonlinear statistical regression analyses, a new lateral load pattern for elastic soil–structure systems is proposed. It is a function of the fundamental period of the structure, soil flexibility and structural slenderness ratio. It is shown that the seismic performance of such a structure is superior to those designed by code‐compliant or recently proposed patterns by researchers for fixed‐base structures. Using the proposed load pattern in this study, the designed structures experience up to 40% less structural weight as compared with the code‐compliant or optimum patterns developed based on fixed‐base structures. Copyright © 2012 John Wiley & Sons, Ltd.     

Shear behaviour of fractured rock as a function of size and shear displacement

This paper presents laboratory results regarding the shear behaviour of an artificial tensile fracture generated in granite. We used a direct shear rig to test fractures of different sizes (from 100 mm to 200 mm) under various shear displacements up to 20 mm and cyclic shear stresses with constant normal stress of 10 MPa. To determine the evolution of surface damage and aperture during shear, cyclic loading was performed at designated shear displacements. These changes in the surfaces topography were measured with a laser profilometer ‘non-contact surface profile measurement system’. In addition, changes were also measured directly by using pressure-sensitive film.

The results showed that the standard deviation (SD) of the initial aperture of the sheared fracture significantly increases with both shear displacement and size, which result in an increase in the non-linearity of the closure curve (since the matedness of the fracture surfaces decreases with shear displacement). Therefore, we concluded that shear dilation is not only governed by the surfaces sliding over each other, but is also strongly influenced by the non-linearity of closure with shear displacement. Furthermore, while the shear stiffness of the fracture during the initial stage decreases with fracture size, it increases with fracture size in the residual stage. This can be attributed to the fact that only small asperities with short wavelengths were mainly damaged by shearing. Moreover the result showed that the damaged zones enlarge and localise with shear displacement, and eventually tend to form perpendicular to the shear displacement.     

“五·一二”地震在同一山体两侧边坡发生两种不同破坏模式成因机制研究

“五·一二”汶川大地震诱发多处地质灾害.该边坡形成地质灾害的主要诱因是“五·一二”大地震,该滑坡在地震作用下,两侧山脊产生两种不同的灾害类型:一种是高位滑坡,另一种是崩塌.在分析两种地质灾害的地质特征、变形特征的基础上,对两种地质灾害的成因机制进行了较深入地分析.通过对两种地质灾害成因机制的分析,进一步阐述了形成两种不同破坏模式的因素.     

聚苯乙烯和四溴联苯醚对黑褐新糠虾抗氧化防御系统的联合效应

本文以黑褐新糠虾(Neomysis awatschensis)为受试生物,分别研究两者单独及联合暴露21 d后的氧化应激效应,并结合综合生物标志物响应(Integrated Biomarker Response,IBR)评估其毒性。结果表明:PS单独暴露时,过氧化氢酶(Catalase,CAT)、谷胱甘肽硫转移酶(Glutathione S-transferase,GST)、超氧化物歧化酶(Superoxide dismutase,SOD)和谷胱甘肽过氧化物酶(Glutathione peroxidase,GPX)活性随暴露浓度升高被显著抑制,丙二醛(Malondialdehyde,MDA)含量随暴露浓度增加逐渐上升,而谷胱甘肽(Glutathione,GSH)含量仅在97.4μg·L^-1暴露下显著上升;BDE-47单独暴露时,CAT、GST和GSH含量均被抑制,MDA和GPX活性仅在较高浓度下被显著诱导,SOD活性在低浓度被诱导,在最高浓度下恢复至空白水平。联合暴露时,CAT和SOD活性随PS投加浓度升高表现出先诱导后抑制的效应,且均显著高于BDE-47单独暴露组,MDA含量随PS投加浓度升高表现出诱导效应。GST和GPX活性与空白水平相近,低浓度PS暴露组中的GSH含量也有相似的变化规律。可见,PS能减缓BDE-47对黑褐新糠虾抗氧化防御系统的氧化胁迫,在低浓度PS联合暴露组中尤其显著。     

半潜式海洋平台结构的疲劳失效概率计算研究

本文根据Ｍｉｎｅｒ线性累积损伤原理，引入随机变量，客观地分析了半潜式平台结构因疲劳引起损伤的情况，提出了平台结构在设计寿命期间的疲劳可靠性分析方法，通过算例，验证了方法的可靠性，并得出有意义的结论。     

深海顶张紧式立管涡激振动疲劳可靠性研究

以深海顶端张紧式立管为研究对象,基于圆柱体受迫振荡实验数据和能量平衡原理预报立管涡激振动响应及其诱发的疲劳损伤度,各主要参数随机化,应用响应面法建立了涡激振动疲劳安全系数与极限状态方程关系,研究了疲劳安全系数对结构可靠性的影响,并分析了各随机变量的灵敏度。研究结果表明:1)随着疲劳安全系数的增大,结构失效概率逐渐减小,且失效概率的减小幅度随疲劳安全系数的增加而趋缓。疲劳安全系数SF无需超过20。2)增加疲劳安全系数SF可降低疲劳载荷不确定量B、S-N曲线参数A、顶张力、流速、外径和壁厚等立管及环境随机变量对结构涡激振动疲劳损伤可靠性的影响。3)立管各参数中,流速、外径和壁厚均值越大,立管结构安全度越低,顶张力对结构影响相反;各参数的标准差越大,结构可靠度越低。均值灵敏度由大到小依次为顶张力、流速、外径和壁厚,标准差灵敏度由大到小依次为流速、张力、外径和壁厚。4)壁厚对深海顶张紧式立管涡激振动所致疲劳损伤影响很小,可忽略其影响。研究成果可为深海顶张紧式立管涡激振动疲劳安全系数的选取提供参考。     

GPR survey to confirm the location of ancient structures under the Valencian Cathedral (Spain)

This paper describes the ground-penetrating radar (GPR) survey performed inside the Cathedral of Valencia, Spain. It is part of historical studies performed in the Cathedral in order to add information to old maps and documents in the Cathedral Archives and also to analyze the extent and importance of potentially destructive moisture areas that were appearing on the floor. The construction of the Cathedral of Valencia occurred in three stages, all of which are well-documented in the Cathedral Archives with detailed drawings, maps, and charts. The radar data were successful in locating crypts, ossuaries, sepulchers, and graves, and the location of ancient walls that existed before the final Cathedral expansion. Three cultural layers corresponding to the three periods of construction were also identified corresponding to the Roman, Arabian and Middle Age Epochs. Measurements of relative sub-floor moisture were obtained by comparing dielectric permittivity changes and radar velocity differences between materials in humid and non-humid areas.     

八所港矿砂码头混凝土腐蚀现状分析

针对海南八所港矿砂码头服役近30年的混凝土梁、柱和70年的甬道等结构腐蚀状况进行现场调研,发现钢筋混凝土结构出现钢筋锈蚀、混凝土剥落,部分混凝土严重破损。测量了其混凝土梁、柱、甬道等不同位置混凝土和铁锈中氯离子含量,分析了局部环境对氯离子分布的影响。根据调研结果总结分析了其破损原因。结果表明混凝土中氯离子分布呈现规律性变化,且铁锈中的氯离子含量远小于混凝土中氯离子含量。     

云南漾濞6.4级地震交通系统震害调查分析

2021年5月21日21时48分34秒,云南省大理州漾濞县发生6.4级地震,中国地震局组织专家迅速进入灾区开展烈度评定和损失评估等现场应急工作。为加深业内同行对交通系统地震破坏的认识和理解,本文主要针对此次地震中交通系统的破坏情况进行宏观性描述,展现地震中交通系统的地震破坏现象,对道路和桥梁的主要震害特征进行总结,对典型震害的形成原因进行了探讨。最后,结合此次地震的破坏特点,为我国交通系统的抗震策略提出思考与建议。