Pre- and post-beach response to engineering hard structures using Landsat time-series at the northwestern part of the Nile delta,Egypt

Analyses have been undertaken to examine shoreline positions established from remote sensing data along the northwestern part of the Nile delta from the Abu Qir Bay to Gamasa embayment (∼143 km length). The image data used (MSS, TM and ETM+ sensors) are acquired at unequal intervals between 1972 and 2006, i.e., covering a time span of 34 years. Automated waterline positions extracted from Landsat satellite images during this period of time were computer generated. A digital shoreline analysis software was used to calculate the annual rate of beach changes at 1,432 cross-shore transects prior to (1972–1990) and after protection (1993–2006). On comparison, rates estimated from three statistical approaches (the end point rate, the Jackknife and a weighted linear regression) at corresponding positions are successfully validated with those measured from ground survey. Before protection, results reveal longshore patterns wherein erosion along a coastal stretch gives way to accretion in an adjacent stretch, refining the sub-cells previously identified within the littoral system of the delta. Maximum shoreline retreat occurs along the Rosetta promontory (−138.52 m/year) and along the central bulge of the delta at Burullus headland (−6.07 m/year). In contrast areas of shoreline accretion exist within saddles or embayments between the promontories at west Abu Qir Bay (20.04 m/year), Abu Khashaba saddle (16.17 m/year) and Gamasa embayment (20.68 m/year). These rates of changes have been significantly altered by the construction of intensive shoreline protective structures built from 1990 to combat areas of rapid erosion at both the Rosetta promontory and Burullus–Baltim headland, ∼15-km length in total.     

酸雨对混凝土建筑物和文物损坏机理的研究

介绍了酸雨对混凝土建筑物和文物损坏机理的宏观分析,水泥中加入少量石膏,可延缓凝结时间,但当加入量大,将引起水泥膨胀,以致溃裂,探讨了酸雨对混凝土建筑物与文物损坏的微观分析,特别是酸雨等生成各种硫酸盐,通过从化学反应原理上分析了酸雨中二氧化硫与混凝土中钙离子反应生成石膏机理,从石膏特性上探讨了酸雨对混凝土建筑物和文物侵蚀机制,并由此提出了酸雨条件下保护混凝土建筑物和文物应对措施。     

A Decade of Geomorphic and Hydraulic Response to the La Valle Dam Project,Baraboo River,Wisconsin

We investigate stream response to the La Valle Dam removal and channel reconstruction by estimating channel hydraulic parameter values and changes in sedimentation within the reservoir. The designed channel reconstruction after the dam removal included placement of a riffle structure at the former dam site. Stream surveys undertaken in 1984 by Federal Emergency Management Agency and in 2001 by Doyle et al. were supplemented with surveys in 2009 and 2011 to study the effects of the instream structure. We created a model in HEC‐RAS IV and surface maps in Surfer© using the 1984, 2009, and 2011 surveys. The HEC‐RAS IV model for 2009 channel conditions indicates that the riffle structure decreases upstream channel shear stress and velocity, causing renewed deposition of sediment within the former reservoir. We estimate by 2009, 61% of former reservoir sediments were removed during dam removal and channel reconstruction. Between 2009 and 2011 renewed sedimentation within the former reservoir represented approximately 7.85% of the original reservoir volume. The HEC‐RAS IV models show the largest impacts of the dam and riffle structure occur at flood magnitudes at or below bankfull. Thus, the riffle and the dam similarly alter channel hydraulics and sediment transport. As such, our models indicate that the La Valle Dam project was a dam replacement rather than a removal. Our results confirm that channel reconstruction method can alter channel hydraulics, geomorphology, and sediment mobility.     

郑州新郑国际机场航站楼钢结构屋盖施工稳定性控制技术研究

郑州新郑国际机场航站楼工程,由于建筑造型需要,采用了大跨度曲线连续空间桁架屋盖钢结构。此结构形式跨度大、施工工艺复杂,工程难度较大。施工过程中,通过采用分段制作、地面拼装、高空成型、积累滑移等工艺,成功地解决了大跨度曲线连续空间桁架屋盖施工的技术难题。通过对在原有的滑移工艺进行多方面的改进和突破,该工程在经济、技术水平和缩短工期方面都取得了明显的进步和提高,对类似屋盖工程施工具有一定的参考和借鉴意义。     

臭氧/陶瓷膜对生物活性炭工艺性能和微生物群落结构影响

利用处理量为120m3/d的臭氧/陶瓷膜-生物活性炭(BAC)组合工艺处理微污染原水, 对工艺性能和BAC中的微生物多样性和种群结构进行了研究.结果显示,组合工艺可有效去除微污染原水中的有机物和氨氮.臭氧曝气提高了溶解氧浓度,改善了后续BAC工艺对氨氮的去除效果.组合工艺对氨氮和CODMn的总去除率分别约为90%和84%,其中BAC在污染物的去除中发挥了重要作用.组合工艺和传统工艺中BAC床层共检测到36个门类的细菌.与传统BAC工艺相比,臭氧/陶瓷膜降低了后续BAC中微生物群落结构的多样性和均匀度.组合工艺BAC中存在丰度较高的亚硝化单胞菌属和硝化螺旋菌属,可能对氨氮的去除具有重要的作用.臭氧/陶瓷膜对后续BAC中致病菌和条件致病菌有很好的预处理和抑制作用,显著降低了其相对丰度,提高了饮用水的生物安全性.     

高温后不同类型混凝土力学性能试验研究

对高温后C40和G50普通混凝土以及C80高性能混凝土的力学性能进行了试验研究,描述了试验现象,探讨了火灾温度、恒温时间、试件尺寸、冷却方式和混凝土类型等因素对高温后混凝土力学性能的影响,提出了高温后不同类型混凝土的轴心抗压强度、弹性模量、峰值应变等经验计算公式和高温后混凝土轴压应力-应变关系曲线表达式.试验研究表明,随着火灾温度的升高和恒温时间的增加,高温后混凝土立方体抗压强度、轴心抗压强度、弹性模量等整体上呈降低趋势,而峰值应变逐渐增加;在火灾温度、恒温时间恒定时,试件尺寸越大越不利,喷水冷却不如自然冷却,高性能混凝土不如普通混凝土.     

薄膜结构在动风荷载下的安全性能分析

从理论和实践两方面对薄膜结构在风荷载下的安全性能进行了研究。根据随机过程理论 ,用计算机模拟生成具有空间相关性的风场。发展建立了膜结构几何非线性动力响应问题的有限元公式 ,并以此为基础对一具体的膜结构进行了动力时程响应分析。通过观察膜结构在不同风速下的位移时程曲线 ,笔者发现 :当外界风速小于一定的临界风速时 ,结构的位移响应会逐渐趋于稳态 ,结构的振动逐渐趋于稳定 ,这时结构是安全的 ;当外界风速超过或接近临界风速时 ,结构的振幅会逐渐增大 ,膜结构将可能发生驰振损坏。进而提出了通过增大膜内预应力或提高膜曲面的曲率来防止膜结构风振破坏的方法 ,并指出了在设计和施工中为保证膜结构的风振安全应当采取的措施。     

砖木结构类保护性建筑的灾害分析与防治对策

系统阐述了砖木结构类保护性建筑的灾害机理,分析了邻近工程施工对这类保护性建筑的影响,讨论了砖木结构类保护性建筑的结构抗震性能和建筑防火问题.同时,针对砖木结构类保护性建筑的灾害机理,提出了这类保护性建筑的维护与防治对策.     

基于振动的土木工程结构损伤诊断研究进展

评估土木工程结构的安全状况已成为当前国际上土木工程师十分关心的问题,也是当前国际上的研究热点.在综述近几年国内外有关结构损伤诊断研究进展的基础上,重点介绍了基于振动的结构损伤诊断方法的发展,并对相关问题进行了讨论和评述.最后对基于振动的结构损伤诊断的未来研究提出了几点建议与展望.     

MODELING THE LONG TERM IMPACTS OF USING RIGID STRUCTURES IN STREAM CHANNEL RESTORATION1

Abstract: Natural channel designs often incorporate rigid instream structures to protect channel banks, provide grade control, promote flow deflection, or otherwise improve channel stability. The long term impact of rigid structures on natural stream processes is relatively unknown. The objective of this study was to use long term alluvial channel modeling to evaluate the effect of rigid structures on channel processes and assess current and future stream channel stability. The study was conducted on Oliver Run, a small stream in Pennsylvania relocated due to highway construction. Field data were collected for one year along the 107 m reach to characterize the stream and provide model input, calibration, and verification data. FLUVIAL-12 was used to evaluate the long term impacts of rigid structures on natural channel adjustment, overall channel stability, and changing form and processes. Based on a consideration of model limitations and results, it was concluded that the presence of rigid structures reduced channel width-to-depth ratios, minimized bed elevation changes due to long term aggradation and degradation, limited lateral channel migration, and increased the mean bed material particle size throughout the reach. Results also showed how alluvial channel modeling can be used to improve the stream restoration design effort.