Monitoring of water quality from roof runoff: Interpretation using multivariate analysis

The quality of harvested rainwater used for toilet flushing in a private house in the south-west of France was assessed over a one-year period. Temperature, pH, conductivity, colour, turbidity, anions, cations, alkalinity, total hardness and total organic carbon were screened using standard analytical techniques. Total flora at 22 °C and 36 °C, total coliforms, Escherichia coli and enterococci were analysed. Overall, the collected rainwater had good physicochemical quality but did not meet the requirements for drinking water. The stored rainwater is characterised by low conductivity, hardness and alkalinity compared to mains water. Three widely used bacterial indicators - total coliforms, E. coli and enterococci - were detected in the majority of samples, indicating microbiological contamination of the water. To elucidate factors affecting the rainwater composition, principal component analysis and cluster analysis were applied to the complete data set of 50 observations. Chemical and microbiological parameters fluctuated during the course of the study, with the highest levels of microbiological contamination observed in roof runoffs collected during the summer. E. coli and enterococci occurred simultaneously, and their presence was linked to precipitation. Runoff quality is also unpredictable because it is sensitive to the weather. Cluster analysis differentiated three clusters: ionic composition, parameters linked with the microbiological load and indicators of faecal contamination. In future surveys, parameters from these three groups will be simultaneously monitored to more accurately characterise roof-collected rainwater.     

Characterization of a local aerosol on a rural site of the Po Valley

A site was chosen in the Po Valley (Northern Italy) that could be considered representative of the whole eastern part of the Valley. High volume aerosol samples were collected during periods characterized by weak pressure gradients over the region, so that any influence by external sources, over the aerosol composition, could be reasonably excluded. The measured total concentration of airborne particles appears notably high in a rural atmosphere. The following aerosol characteristics were determined: a) concentration of water soluble and insoluble material; b) concentration of ether soluble organic material; c) chemical element balance. Synoptic and local meteorological data were also collected during the samplings.The results are discussed from the point of view of the contribution of various sources to the total particulate matter.     

An Assessment of the Impact of Inland Surface Water Input to the Bacteriological Quality of Coastal Waters

The introduction of ultraviolet disinfection in Jersey has achieved significant improvements in water quality. However, bathing waters in St Aubin's Bay and shellfish flesh have failed to comply with microbial standards. Streams and seepages from coastal structures were investigated as potential indicator organism sources (total and faecal coliforms, faecal streptococci). Seepages were an unimportant bacterial source as concentrations were low. Geometric mean concentrations in streams were up to four orders of magnitude higher than in final sewage-treatment works effluent, and concentrations increased significantly at high stream discharge. Rainfall-induced pulses of poor water quality occurred two to three times per week during the 1993 summer season. Natural discharges from island catchments thus contribute significantly to the bacterial load received at the coast, especially during high flow events. These observations have implications for other UK and European schemes using tertiary disinfection technology to attain water quality targets in coastal waters.     

Defining the sources of low-flow phosphorus transfers in complex catchments

Nutrient transfers from the land to rivers have the potential to cause persistent eutrophic impacts at low flows even though the transfers may constitute a minor percentage of total annual fluxes. In rural catchments, the contribution from agricultural soils during storm events can be particularly large and untangling the relative contributions from multiple sources that vary in time and space is especially problematic. In this study, the potential for domestic septic tank system pollution during low flows was investigated in 3 small catchments (3 to 5 km(2)) using an integrated series of methods. These included septic system surveys, continuous (10 min) total phosphorus (TP) monitoring at the outlet of each catchment, repeated low-flow water quality surveys in sub-catchments upstream of the catchment outlets and single day river-walk water quality surveys. A series of faecal matter and grey-water fingerprinting techniques were also employed. These included determining sterol ratios in stream sediments, monitoring the presence of proteins, E. coli and enterococci bacterial signatures and boron. The total density and density of poorly maintained septic systems mirrored the magnitude of frequent TP concentrations in the catchments although this relationship was less apparent in the nested sub-catchments. The exception was possibly related to the simple hydraulics in one particular catchment and indicated temporary effluent attenuation in the other catchments. Repeated low-flow and river-walk water quality surveys highlighted discrete areas and reaches where stepped changes in nutrient concentration occurred. Bio-chemical fingerprinting showed that between 7% and 27% of sediments were contaminated with human faecal material and correlation matrices indicated that, at least during low flows, P fractions were positively correlated with some markers of faecal and grey-water contamination.     

Indoor airborne bacterial communities are influenced by ventilation,occupancy, and outdoor air source

Architects and engineers are beginning to consider a new dimension of indoor air: the structure and composition of airborne microbial communities. A first step in this emerging field is to understand the forces that shape the diversity of bioaerosols across space and time within the built environment. In an effort to elucidate the relative influences of three likely drivers of indoor bioaerosol diversity – variation in outdoor bioaerosols, ventilation strategy, and occupancy load – we conducted an intensive temporal study of indoor airborne bacterial communities in a high‐traffic university building with a hybrid HVAC (mechanically and naturally ventilated) system. Indoor air communities closely tracked outdoor air communities, but human‐associated bacterial genera were more than twice as abundant in indoor air compared with outdoor air. Ventilation had a demonstrated effect on indoor airborne bacterial community composition; changes in outdoor air communities were detected inside following a time lag associated with differing ventilation strategies relevant to modern building design. Our results indicate that both occupancy patterns and ventilation strategies are important for understanding airborne microbial community dynamics in the built environment.     

凉都体育中心体育馆屋盖CFD数值分析

采用计算流体力学软件Fluent得到凉都体育中心体育馆屋盖的风压力分布,进而得出体育馆屋盖的风压系数分布.对建筑间风遮挡效应进行了讨论,两体量相近的建筑物相邻时,下游建筑受到的风荷载往往更为不利.屋盖在风荷载作用下受向上的风吸力,屋盖不同位置的风压系数都不相同,且分布规律复杂,为简化设计计算过程,建议凉都体育馆屋盖体型系数可取为-0.9.     

Contribution of different sources to the pollution of wet weather flows in combined sewers

Experiments performed on "Marais" catchment, in central Paris, aimed to follow up the quality of wet weather flows from the entry to the exit of a combined sewer network. SS, VSS, COD, BOD5, Cd, Cu, Pb, Zn concentrations were measured for an important number of rain events in roof, yard, street runoff, as well as in dry and wet weather flows at the catchment outlet. Mass entry-exit totals, at the scale of the catchment, were calculated over 31 rain events in order to evaluate the contribution of different types of runoff, of sanitary sewage and of sewer sediments to the total wet weather pollutant loads at the catchment outlet. The erosion of in-sewer pollutant stocks was found to be the main source of particles and of organic matter in wet weather flows, whereas heavy metal loads mainly originated from roof runoff, due to the corrosion of metallic roofs. Particles eroded inside the sewer during rain events were found to be quite different from the particles constituting the main part of sewer sediments: they are organic and biodegradable, with rather important settling velocities and seem to accumulate during dry weather periods. A change of the chemical form of heavy metals was noticed during the transport in the sewer and it is suspected that a fraction of the dissolved metals from the runoff is adsorbed on sewer sediments.     

Reliability analysis of roof sheathing panels exposed to a hurricane wind

Light-frame wood roofs are frequently used in the US for residential and commercial construction. High wind events, such as hurricanes, may cause severe damage to these structures by breaking the roof envelope and allowing penetration of wind-driven rain. Most previous wood panel reliability studies have used static, uniform wind pressure load models and code-specified load distribution rules for analysis. This study re-estimates the reliability of roof sheathing panels exposed to a specific hurricane event using actual wind pressure data and a more refined structural analysis model. The objective is to examine the adequacy of the simplified wind load and structural analysis models used for roof panel reliability analysis. In the procedure here, panel failure behavior is modeled by individual fastener extraction from the panel as dynamic wind pressure is increased. For reliability analysis, the limit state is based on panel pull-off. The results show that the use of a refined model provides some significant differences in panel reliability found from simplified techniques.     

Influence of an upstream building on the wind-induced mean suction on the flat roof of a low-rise building

The effect of an upstream building on the suction forces on the flat roof of a low-rise building placed in the wake of the former is analyzed. The analysis has been performed by wind tunnel testing of a flat roof, low-rise building model equipped with pressure taps on the roof and different block-type buildings (only configurations where the upstream building is as high or higher than the downstream one are considered in this paper). The influence of the distance between both buildings on the wind loads on the downstream building roof is analyzed, as well as the height of the upstream one and the wind angle of incidence. Experimental results reveal that the wind load increases as the relative height of the upstream building increases, the wind load being highest for intermediate distances between buildings, when a passage between them is formed.     

大型场馆异形钢结构屋面概念设计若干问题探讨

本文提出了大型场馆异形钢结构屋面的概念设计问题。对于周边墙体封闭的“馆”类建筑,屋面风的体型系数一般为负,即受风吸作用。对于“场”类建筑,则应根据屋盖各部分形状与风向的相对关系来确定屋面受风吸还是风压。对于异形屋面排水问题,屋面形状应尽可能满足快捷排水的要求。排水路径要短,水流要向结构的支座处会聚,尽量避免聚向悬挑端。评定一个结构是否是空间结构,看其在结构效应中,是以弯曲为主还是以轴向拉压为主。如果是前者,则结构的厚度和跨度之比就要求较大;而对于以拉压效应为主的空间结构,则其厚度和跨度之比可以较小。铸钢节点用于杆件交汇数量多、交角小的节点,可以避免较大的应力集中。但对于少量几根钢管之间的连接,不太适合使用铸钢节点,采用相贯线焊接,也同样能满足受力要求。     

北大体育馆屋盖结构风荷载分布特性的试验研究

风荷载是控制大跨度钢屋盖结构设计的主要荷载之一。结合北京大学体育馆屋盖结构的风洞模拟试验,以屋盖上的平均风荷载和脉动风荷载为研究对象,对屋盖上的风荷载分布特性进行了详尽的分析。结果认为:整个屋盖所受风荷载主要以负压为主,屋盖悬挑部分在迎风时产生“上吸下顶”的叠加作用,其他风向为“上吸下吸”的抵消作用;屋盖角部的风荷载一般也很大,在结构设计时应采取必要的构造措施;脉动风荷载对于总的设计风荷载来说不能忽略,准定常理论不适合用来计算大跨度屋盖的风振响应。     

Full-scale validation of vortex suppression techniques for mitigation of roof uplift

Widespread damage to roofs in hurricanes and other high wind events has highlighted the need for improving the wind performance of roofs, including both new construction and retrofit on existing buildings. Effective and economical methods to mitigate wind effects on roof components are sought to reduce accumulated losses from frequently recurring low- and moderate-intensity events. An experimental study was carried out in the 6-fan Wall of Wind (WoW) testing apparatus to assess the effectiveness of aerodynamic edge devices at full scale in reducing wind effects over the roof corner and edge regions. Two sets of tests, roof gravel scour testing and pressure testing, were carried out to visualize the development of edge vortices and compare roof uplift pressures with and without aerodynamic edge shapes, thus allowing the estimation of the effects of such shapes in alleviating wind damage of roofing material as well as high uplift pressures on roofs. Probabilistic estimates of peak pressures indicated that the use of such mitigation devices resulted in significant reductions in uplift within the instrumented area, which according to the US wind load specifications (ASCE 7-05) represents a corner section of the roof that will experience the highest suction. The largest reduction was achieved with the Flat Roof AeroEdge Guard (FRAG1). This research demonstrates the potential for substantial reduction of roof uplift pressures through the development and application of mitigation techniques to lessen or prevent hurricane-induced damage to new and existing roofs.     

平面T形低矮房屋风荷载特性风洞试验与数值分析

对复杂体型的平面T形低矮双坡屋面房屋的风荷载特性进行了风洞试验研究,得到了屋面风压系数以及各屋面体型系数的变化规律;采用计算流体力学软件FLUENT建立了数值风洞模型,在数值分析结果与风洞试验结果吻合良好的基础上,对影响屋面平均风压系数及体型系数的风攻角、屋面坡角、檐口高度、房屋几何尺寸和屋面形式等参数进行了详细分析。结果表明:屋面坡角和风攻角对屋面风压系数的影响显著;在不同风攻角作用下,迎风屋面屋檐及屋脊附近形成较高负压;当屋面处于背风区域时,风压系数分布较均匀;四坡屋面坡角为30°时屋脊背风区域易形成较大负压,局部更易遭受破坏。     

钢筋混凝土柱实腹屋面钢梁结构体系设计中的几个问题探讨

钢筋混凝土柱人字形实腹钢梁结构体系中竖向构件采用钢筋混凝土构件,屋面梁采用实腹钢梁.根据材料性能和结构的受力特性,通过实例计算,分析竖向荷载、水平荷载(风荷载)、屋面坡度、柱子刚度对梁内力、柱内力、柱顶水平位移、结构项部竖向位移、斜梁相对位移的影响,给出了风荷载、屋面坡度和柱截面的合理取值.     

Chemical and microbial effects of atmospheric particles on the performance of steep-slope roofing materials

The reflectivity of a roof is a critical component in design of strategy to reduce overall building energy usage. Airborne particulate matter that settles on a roof can either reflect or absorb incoming solar radiation. The light scattering and absorption processes occur within a few microns of the surface that affects the solar reflectance of the roof. The long-term loss of roof reflectivity appears driven by the ability of the atmospheric particulate matter to cling onto the roof and resist being washed off by wind and or rain. Contaminants collected from samples of roof products exposed at seven California sites for about one and a half years were analysed for major and trace elements and carbons to assist characterization of the chemical profile of the atmospheric particles that soil each roof sample. The chemical composition of the accumulated particles was very similar across the state of California; there was no clear distinction from one region to another. Elemental carbon did not contribute significantly to the loss of solar reflectance as initially expected. Dust particles and organic carbon compensated for the loss of solar reflectance due to elemental carbon possibly because some crystalline forms of these elements were light reflecting and contributed to the solar reflectance. Differences in microbial communities and biomass were seen between the various materials. Abundance of microbial biomass on roof tiles appears to be related to the composition/surface structure of the tile. Cyanobacteria or fungi represent the dominant player.     

《屋盖围护结构风荷载标准》的制订依据及相关规定

为配合新编行业标准JGJ/T 481—2019《屋盖结构风荷载标准》的推广、应用,对屋盖围护结构风荷载的制订依据及相关规定进行了介绍。在对比国内外规范风荷载条文规定的基础上,以围护结构风荷载全风向最小值和最大值作为确定其标准值的依据,引入围护结构风压系数极值表达围护结构的风压标准值;根据风压系数时程样本的不同数量规定了风压系数极值的估计方法,对比了各国规范中封闭式低矮双坡屋盖的风压系数极值。新编标准以风荷载理论为依据制订了屋盖围护结构风荷载条文,完善和发展了我国标准的相关规定,提供了相对简单、合理的风压系数极值计算方法。     

双层马鞍型空间网壳屋盖风振系数非线性模态叠加法计算

非线性模态叠加法将非线性项作为外部荷载处理,结合与荷载相关的Ritz向量后可快速、准确求解简化的模态方程组.以一大跨度马鞍型屋盖刚性模型风洞试验为例,利用非线性模态叠加法计算风振响应时程,进而求得相应风振系数,并与直接时程积分计算结果比较,表明在选择一定数量参振振型后该方法准确、可靠.分析表明该屋盖风振系数受风向影响显著,在0°、180°风向角下由于大拱曲边涡脱效应出现风振系数极值.     

秦皇岛体育场膜结构挑篷的抗风分析与设计

结合秦皇岛体育场膜结构挑篷的风洞试验研究,以挑篷上的典型膜面的风荷载特性和风荷载响应为研究对象,直接采用风洞试验测量所得到的风荷载数据,对膜面进行了详尽的静力风荷载响应分析和非线性风振响应分析;试验结果分析表明,挑篷前缘膜面的负压风荷载数值最大,是膜结构挑篷设计的控制荷载。非线性分析表明,通过设置抗风索可以有效提高膜结构的抗风性能;膜面的风振动力效应并不显著,可以近似采用阵风系数来考虑脉动风的瞬时增压作用。这些结果可为类似结构的抗风设计提供参考。     

大跨度屋盖结构的风荷载特征

分析了封闭型和敞开型两种大跨结构屋面风荷载的分布特征。对于封闭型,屋面的迎风区域由于受柱状涡和锥形涡的作用而产生极大的负风压,其他区域风压较小;对于敞开型,迎风时上下表面呈"上吸下顶"的风压叠加组合,背风时呈"上吸下吸"的风压抵消组合。同时讨论了附近的构筑物对屋面风荷载的气动干扰作用,在不同的风向下,干扰体与屋面的相对位置产生不同的干扰效果。     

波纹状悬挑大跨屋盖的风荷载特性

采用同步测压风洞试验技术,对相同尺寸的波纹状悬挑屋盖、光滑表面悬挑屋盖风荷载进行了研究,重点讨论了波纹形状对悬挑屋盖风荷载的影响。风压分布云图表明,波纹形状没有改变风荷载的主要作用机制,但加剧了来流在屋盖前缘的分离。通过积分得到了对屋盖主体结构抗风设计起控制作用的弯矩系数,相对于光滑表面悬挑屋盖,最不利风向角下波纹状悬挑屋盖的平均弯矩系数增加23%,脉动弯矩系数增加20%,但波纹形状减缓了脉动风荷载在折算频率0.1~0.2范围内的能量集中。波纹形状对风压极值影响较大,特别是对围护结构抗风设计起控制作用的负压极值,波纹状悬挑屋盖较光滑表面悬挑屋盖增加13%。进行波纹状悬挑屋盖抗风设计时,不考虑波纹形状的影响是不安全的。