截面空心系数对空心桥墩抗震性能的影响分析

为了研究空心桥墩的墩高及空心截面对其抗震性能的影响,选用有限元软件OpenSees建立三组不同墩高、截面空心尺寸及类型的空心墩模型。引入空心系数来表示截面空心尺寸。采取Pushover拟静力分析方法进行数值模拟,根据基底剪力—位移曲线,分析空心桥墩的抗震性能。结果表明随着墩高增加,空心桥墩承载力明显下降,但变形能力增加。截面空心系数对空心桥墩的抗震性能影响明显,在0.2～0.4之间承载力明显提升,但空心系数持续增加,承载力增幅降低。空心系数相同时,方形空心截面的空心墩承载力极限优于矩形空心截面的空心墩,但变形能力下降。考虑到经济效应,建议空心桥墩抗震设计时,考虑空心系数在0.3～0.6之间的矩形空心桥墩。     

现浇混凝土空心楼盖的技术经济分析

针对新型的现浇混凝土空心楼盖技术,介绍了将空心楼盖简化为等效实心楼盖进行计算的设计原理,总结了混凝土空心楼盖的力学性能,分析了混凝土空心楼盖的综合经济优势,概括了混凝土空心楼盖施工控制要点,指出了抗浮是混凝土空心楼盖施工的关键技术措施.     

新型钢筋混凝土双向叠合空心板

提出了一种新型双向叠合空心板的形式即空心箱板,并对双向叠合空心板与现浇钢筋混凝土双向空心板进行对比分析,现浇钢筋混凝土双向空心板取自具体工程实例,使空心箱板条件与其相同,并用PKPM对此空心箱板进行计算,最后通过计算材料用量,对比分析两种板的经济性。     

温州国际会展中心展厅大跨空心楼盖设计与施工

近年来空心楼盖体系得到了越来越多的应用,而平时我们接触更多的是单管空心楼盖,对叠合空心管楼盖的研究较少。叠合空心管楼盖是无梁现浇空心楼盖结构体系的一种,该文以温州国际会展中心展厅为例介绍了叠合薄壁空心管现浇混凝土空心楼盖的特性、技术原理和具体施工方法和流程以及其中需要注意的问题。     

现浇混凝土空心楼盖施工技术

文鼎广场综合楼工程采用现浇混凝土空心楼盖结构,内置BDF空心管,通过合理设计施工流程,按排管详图排放空心管,严格控制空心管的抗浮固定、空心管破损及与管线冲突时的处理等施工工艺,保证了施工质量。     

宽扁梁现浇空心楼板竖向受力性能研究

通过对湖南某高层建筑中局部两开间布置带宽扁梁的大跨度现浇空心楼板进行现场水箱加载试验,研究空心楼板在竖向荷载作用下的竖向位移、裂缝开展及分布特征,同时引入空心层分层壳模型对该空心楼板进行了有限元受力性能分析。结果表明,在设计活荷载作用下,带宽扁梁的大跨度现浇空心楼板具有足够的抗弯刚度和抗裂能力,能够满足现行规范正常使用极限状态的要求。但由于宽扁梁与空心楼板刚度比为1.5,宽扁梁对空心楼板无法形成有效嵌固而导致竖向荷载作用下,两开间试验现浇空心楼板的竖向位移曲线、裂缝分布与单块板基本相似。分析结果亦表明,空心层分层壳模型能较好地实现对空心楼板受力性能的模拟,当宽扁梁高与空心楼板厚度比h_b/h_s≥2时,宽扁梁可实现对空心楼板的有效约束,可供实际工程选用。     

GBF管空心板楼盖施工

为了保证GBF高强薄壁管空心板楼盖的施工质量,从GBF管空心板楼盖模板工程、GBF管空心楼盖梁板钢筋工程以及GBF管空心楼盖梁板混凝土施工等方面分别阐述了其施工要点,积累了GBF管空心楼盖的施工经验。     

桥梁空心板裂缝监测方案

本文针对目前国内空心板桥裂缝类病害较多、对桥梁安全运营构成危胁的实情,介绍一种简单、实用的空心板裂缝监测方法 ,以了解其状态和发展趋势,科学决策安排对空心板的维修加固,保证空心板桥的正常服役,延长空心板桥的使用寿命。     

空心砌块的传导传递函数系数计算与验证

根据空心砌块的频域热特性辨识其s多项式传递函数,并进一步求取空心砌块的CTF系数。根据空心砌块动态热特性实验结果对采用CTF系数计算空心砌块热特性的可靠性进行了验证。结果表明,在边界条件趋于周期性稳定后,采用CTF系数和实验得到的空心砌块内外表面温度曲线非常吻合。因此,CTF系数能准确的计算空心砌块的动态热特性,是一种分析空心砌块动态热特性的有效方法。     

浅谈大直径钻埋预应力混凝土空心桩

阐述了大直径空心桩的产生过程及其三个特殊工序,归纳总结了大直径空心桩的特点,从成桩的角度入手,介绍了大直径空心桩的类型,并研究了大直径空心桩的发展方向,对推广大直径钻埋预应力混凝土空心桩具有重要意义。     

Alteration of arsenopyrite in soils under different vegetation covers

The weathering of arsenopyrite (FeAsS) has been monitored in soils using an in situ experimental approach. Arsenopyrite in nylon experimental bags was placed in individual horizons in soils in spruce (litter, horizons A, B, and C), beech (litter, horizons A, B, and C) and unforested (horizons A, B, and C) areas and left in contact with the soil for a period of 1 year. The individual areas on the ridge of the Krušné hory Mts., Czech Republic, had the same lithology, climatic and environmental conditions. Scorodite (FeAsO₄·2H₂O) was identified as a principal secondary mineral of arsenic (As) formed directly on the surface of the arsenopyrite. Scorodite was formed in all the areas in all soil horizons. The amount of scorodite formed decreased in the series beech, spruce and unforested areas. In forested areas, there was a larger amount of scorodite on arsenopyrites exposed in organic horizons (litter, A horizon). The greater rate of arsenopyrite alteration in organic horizons in the beech stand compared to spruce stand is probably a result of faster mineralization of organic material with resulting production of nitrate and better seepage conditions of soil in this area. Speciation of As determined using the sequential extraction technique demonstrated that As was bonded in the soils primarily in the residual fractions prior to the experiment. The As content in the mobile fractions increased in the organic horizon in the forested areas after the experiments.     

探究“虚实”空间关系，创造个性化的城市空间场所

作者利用空间的“虚、实”概念,结合格斯塔心理学的“图底”关系,类比分析中国水墨画的留白艺术手法及生态系统中的细胞繁衍规律,通过张家界城市绿化广场周边地段的概念设计的创作实践,提出创造个性化的城市空间场所工作中虚实空间的理念与原则目标。     

中国绿道规划建设实践——从提级统筹到制度并轨

绿道在中国经过多年实践发展,在理论内涵、规划选线、综合效益等各方面都已有许多成果支撑.基于可公开获取的一系列文献资料,立足于绿道在中国各省市近20年的具体实践过程,梳理绿道在规划体系中的角色转变、在指标设置中的逐步细化和在管控上的落实方式,总结绿道实践在中国从提级统筹、常态认同到制度并轨3个阶段的发展变化,在展望绿道后...     

Polycyclic aromatic hydrocarbons (PAHs) in agricultural soil and vegetables from Tianjin

Several types of vegetables were collected from two contaminated sites in Tianjin, China. The bulk soil and the rhizosphere soil samples were also collected from the same plots. Sixteen PAHs in the samples were measured. The total concentrations of PAH16 in the bulk soil from the two sites were 1.08 and 6.25 microg/g, respectively, with similar pattern. The concentrations of PAH16 and individual compounds in the rhizosphere were significantly higher than those in the bulk soil with mean values of 2.25 and 7.82 microg/g for the two sites, respectively. The contents of both total and dissolved organic matter in the rhizosphere were also higher than those in the bulk soil. Almost all PAH compounds studied were detected in both roots and aerial parts of the vegetables studied. Abundance of higher molecular weight PAHs in vegetable, however, was lower than that in soil. Concentrations of PAH16 in vegetable were higher than those reported in the literature for other areas. It appears that agricultural soils and vegetables in Tianjin, especially those from the site located immediately next to an urban district and irrigated with wastewater for several decades, are severely contaminated by PAHs. Among the eight types of vegetable studied, the highest concentration of PAHs was found in cauliflower. By average, the concentration of PAH16 in the aerial part of vegetables was 6.5 times higher as that in vegetable root, suggesting that foliar uptake is the primary transfer pathway of PAHs from environment to vegetables.     

Factors affecting bulk to total bacteria ratio in drinking water distribution systems

Bacteria in drinking water systems can grow in bulk water and as biofilms attached to pipe walls, both causing regrowth problems in the distribution system. While studies have focused on evaluating the factors influencing the bacteria in bulk water and in biofilms separately, there is a need for understanding biofilm characteristics relative to the bulk water phase. The current study evaluated the effects of chlorine and residence time on the presence of culturable bacteria in biofilms relative to that in bulk water. The results showed that when no chlorine residual was present in the system, the median ratio of bulk to total bacteria was 0.81, indicating that 81% of the bacteria were present in bulk water, whereas only 19% were present in the biofilm. As chlorine concentration increased to 0.2, 0.5, and 0.7 mg/L, the median percentage of bacteria present in bulk water decreased to 37, 28, and 31, respectively. On the other hand, as the residence times increased to 8.2, 12, 24, and 48h, the median percentage of bacteria present in bulk water increased to 7, 37, 58, and 88, respectively, in the presence of a 0.2mg/L chlorine residual. The common notion that biofilms dominate the distribution system is not true under all conditions. These findings suggest that bulk water bacteria may dominate in portions of a distribution system that have a low chlorine residual.     

Health assessment of artisanal gold miners in Indonesia

Small scale miners use mercury to extract gold from ore in many countries. An environmental and health assessment was performed in Indonesia in two regions, Galangan in Central Kalimantan and Talawaan in Northern Sulawesi. The environmental assessment showed severe mercury contamination of the sediments, and increased mercury levels in local fish. For the health investigation 281 volunteers were recruited and examined by a standardized questionnaire, a neurological examination and neuro-psychological tests. A medical score was used consisting of significant factors of mercury intoxication. Mercury exposed workers showed typical symptoms of mercury intoxication, such as movement disorders (ataxia, tremor, dysdiadochokinesia, etc.). Blood, urine and hair samples were taken from any participant and analyzed for mercury. The mercury concentration in the biomonitors was high, partly extreme high in the working population, increased in the population living in the same habitat and low in the control group. By a standard protocol which includes a combination of threshold values of mercury in the biomonitors and a medical sum score the diagnosis of chronic mercury intoxication was made for highly burdened workers (amalgam smelters) in 55% in Sulawesi and in 62% in Kalimantan. Less exposed mineral processors and the general population in the mining areas were also intoxicated to a high percentage.     

城外造景：清末广州景园营造与岭南 园林的近代转型

清末广州中西交汇,景园营造新旧共存互动,推 动岭南园林的近代转型。其中,在繁荣的中西贸易和文化交 流,以及书院文化、士绅文化等的影响下,清末岭南形成了 以广州为中心、十三行行商为代表、官商士绅竞相造园的特 殊历史时期,其造园数量、规模、意匠等均在该时期达到岭 南古典园林发展的巅峰。这一时期也是岭南园林近代转型的 关键时期。在西方文化和清末洋务运动思想的影响下,广州 开始出现洋务花园、公园、市政绿化,以及校园绿地等新型 园林形式。这些具有公共性质的城市景致与新建私园一道广 泛分布在城墙以外,成为清末广州城市空间拓展与风景体系 形成的重要参与者。由于清末广州城外造景的繁荣,从时间 上开启了岭南园林的近代转型,在空间上使岭南园林的地域 性特征得以形成和辨识,其空间性与时间性界定了清末岭南 园林近代转型的物质及文化维度。梳理了清末广州具有代表 性的景园营造活动,在分析其动力机制的同时,探讨城外造 景之于岭南园林近代转型的意义。     

混凝土板裂缝产生的原因与防治

混凝土在现代工程建设中占有重要的地位。而在现代混凝土工程中裂缝几乎无所不在。尽管我们在施工中采取各种措施,但裂缝时有出现,究其原因,发现产生裂缝的原因是多方面的。首先,在施工中混凝土常常出现温度裂缝,影响到结构整体性和耐久性;其次,施工工艺不熟,浇注方式的变化也会导致现浇钢筋混凝土楼板产生裂缝;第三,在运转过程中,温度变化对结构的应力状态具有显著的不容忽视的影响,另外施工单位为赶进度,在现浇混凝土未达到设计强度时即拆模,或板上施工堆载过重,也会导致板开裂,出现穿透性裂缝。本文以近年来部分住宅楼用户投诉件为例,针对混凝土裂缝的成因,从脆性和不均匀性、施工工艺、温度应力形成过程、混凝土的早期养护等方面进行分析,提出现场混凝土温度的控制和预防裂缝的措施。     

Heterotrophic and mixotrophic growth of Micractinium pusillum Fresenius in the presence of acetate and glucose: effect of light and acetate gradient concentration

The main objective of this study was to determine the importance of secondary mechanism of organic carbon utilization (mixotrophic and heterotrophic modes) in addition to CO2 fixation (photoautotrophic mode) in the green alga, Micractinium pusillum Fresenius (chlorophyta), isolated from a waste stabilization pond. The growth was studied in the presence of acetate and glucose. The incorporation rate of 14C- acetate was measured in the light and in the dark at different concentrations. Finally, in order to underline the role of photosynthesis and respiration processes in the acetate assimilation, the effect of two specific metabolic inhibitors, a specific inhibitor of photosystem II (DCMU) and an uncoupler respiratory (DNP), has been studied. The obtained results showed that M. pusillum grows in the presence of organic substrates, i.e., glucose and acetate, in the light (mixotrophic growth) as well as in the dark (Heterotrophic growth). The growth was much more important in the light than in the dark and more in the presence of glucose than of acetate. In the light, the presence of acetate led to a variation of growth parameters mumax, iotaopt, and beta. The effect of acetate gradient on the growth of the microalga was severe as soon as its concentration in the medium was higher. The acetate uptake followed a Michaelis-Menten kinetic in the light as well as in the dark. The capacity of assimilation was slightly higher in the dark. The utilization of DNP and DCMU indicates that acetate incorporation is an active process depending on both anabolic (photosynthesis) and catabolic (respiration) metabolisms, corroborating the model of the Michaelis-Menten kinetic.     

化学溶液和干湿循环作用下砂岩抗剪强度劣化试验及化学热力学分析

 为研究化学溶液和干湿循环共同作用下砂岩抗剪强度的劣化机制,在不同pH环境下,通过不同干湿循环次数后的单轴、三轴试验,计算出砂岩的黏聚力和内摩擦角,同时得到其与循环次数的关系式,进而获得砂岩在浸泡环境下抗剪强度随干湿循环次数的变化公式。根据砂岩的组成矿物及其百分含量,得到各种主要组成矿物在中性、碱性、酸性溶液中溶解的化学反应方程式,利用化学热力学的基本原理,确定各主要矿物在中性、碱性、酸性溶液浸泡下能否稳定。为了验证分析的正确性,对浸泡溶液中的部分离子(Ca2+,SiO2,Na+,K+)浓度进行测试。结果表明,酸性环境下,砂岩抗剪强度劣化最为严重,碱性次之,中性最轻。在酸性环境中,对抗剪强度影响较大的胶结物主要组成成分(长石、方解石)的性质不稳定,溶解反应能自发进行,而碱性环境中,对强度影响较小的骨料主要组成成分(石英)的性质不稳定,溶解反应能自发进行。酸性浸泡液中,方解石、钾长石、钠长石溶解出的Ca2+,K+,Na+的浓度明显高于中性和碱性液中Ca2+,Na+,K+的浓度,而碱性溶液中,石英溶解出的SiO2的浓度明显高于中性和酸性液中SiO2的浓度,与热力学分析结果一致。