不同类型结构中楼梯受力性能研究

通过对有楼梯的框架结构、框架-剪力墙结构和剪力墙结构的地震反应分析,研究了不同类型结构中楼梯构件的受力性能。结果表明,在框架结构中当楼梯与主体结构共同工作时,楼梯中梯段板、梯梁和梯柱等构件的内力显著增大,且受力状态复杂,从而造成楼梯构件不同程度的破坏;在框架-剪力墙结构和剪力墙结构中,当楼梯与主体结构共同工作时,楼梯中梯段板的内力明显增大,且受力状态复杂,易造成梯段板的破坏;而梯梁、梯柱等所受内力较小,不易产生破坏。     

框架结构中现浇楼梯的抗震性能分析

本文研究了框架结构的楼梯在汶川地震中出现的多种震害状况,如梯段板的断裂,框架角柱的短柱破坏,楼梯间梯柱、平台梁和平台板等构件的破坏。结合《建筑抗震设计规范(GB 50011-2001)》部分规定和工程中楼梯的设计方法,分析了震害出现的原因,指出了GB 50011-2001规范中有关楼梯设计方法和构造措施的不足,给出了今后框架结构中楼梯设计和施工的相关建议。     

隔震防倒塌支座及楼梯间位置对框架结构抗震性能的影响研究

为研究梯段板下端设置隔震防倒塌支座和楼梯间位置对钢筋混凝土框架结构抗震性能的影响,利用ETABS软件建立不包括、包括隔震防倒塌支座的3种楼梯间布置方案,6个框架结构计算模型。通过模态分析、反应谱分析和Pushover分析,研究隔震防倒塌支座和楼梯间位置对框架结构的振型、内力及破坏机制的影响。结果表明:梯段板下端设置隔震防倒塌支座后,楼梯间位置对钢筋混凝土框架结构的扭转效应影响较小,且框架结构在两个主轴方向的动力特性比较接近;楼梯间框架柱内力均显著降低,但楼梯间布置在最边跨时,在垂直于梯跑方向地震作用下,框架结构边柱内力较大;框架梁对整体框架结构的耗能贡献较多,增强了框架结构的抗震性能,大震时楼梯构件严重破坏较晚,设置隔震防倒塌支座可保证楼梯整体稳定性。     

基于ETABS的钢筋混凝土框架与楼梯共同工作性能分析

本文利用大型结构分析软件ETABS设计了4种包含和不包含楼梯的钢筋混凝土框架计算模型,分别采用底部剪力法、反应谱法和时程分析法对各模型进行了弹性阶段地震反应特性对比计算分析.结果显示:楼梯参与结构整体计算后,结构出现抗侧刚度明显增加、结构扭转振动显著、梯间框架柱剪力突变等现象;建议结构设计时采用包含楼梯的层间结构计算模型(M-4),使用振型分解反应谱法进行结构抗震分析计算.     

大震作用下板式楼梯框架弹塑性地震反应分析

有关大震作用下楼梯与框架共同工作方面的研究还很少,采用结构有限元软件Midas/Gen,对一个5层钢筋混凝土现浇板式楼梯框架办公楼模型进行了弹塑性分析,对模型在大震作用下的受力情况进行了详细研究.通过对楼梯和框架共同工作性能的研究,并与不考虑楼梯影响的框架的工作性能进行了对比,分析了板式楼梯框架的失效机制和受力特点,指出了楼梯与框架共同工作时的受力不利部位.结果表明:楼梯相较于框架梁柱是模型的薄弱部位;模型的失效是从楼梯发展到框架,由下层发展到上层.最后根据模型的失效机制特点提出了相应的抗震措施.     

考虑梁端耗能能力影响的钢框架结构易损性分析

一般采用梁柱焊接节点钢框架结构在遭遇强烈地震地震作用下,结构倒塌破坏可能由于是耗能能力不足所导致。以某钢框架结构为算例,选取20条实际地震动记录,对结构进行易损性分析,对比不同损伤指标和不同梁端构造形式的钢框架结构抗震性能差异。研究显示:对梁柱焊接的普通钢框架结构,其倒塌破坏是由于结构耗能能力不足所导致的,评价结构抗震性能不仅需考虑结构变形能力,尚需同时考虑结构耗能能力;对于改进形式的钢框架结构,结构耗能能力得到显著提高,使得位移首超破坏先于累积损伤破坏,此时基于变形的评价结果更加可靠。     

芦山地震框架结构震害分析

根据芦山地震现场考察结果,介绍了框架结构房屋填充墙、楼梯、柱、梁、板、玻璃幕墙、飘窗和吊顶的震害特征,并为增强框架结构房屋防震减灾能力提出建议:(1)经过抗震设计并且按照规范施工的钢筋混凝土框架结构房屋具有良好的抗震性能,值得推广应用;(2)框架结构楼梯间墙体震害相对较重,建议完善框架结构楼梯间的设计方法和抗震构造措施;(3)注意填充墙对整体结构的抗震贡献和影响,要加强填充墙与框架梁柱的构造连接措施,可以选用轻质材料与框架柔性连接,并避免填充墙倒塌伤人;(4)要重视玻璃幕墙与主体结构的连接构造,避免玻璃幕墙脱落伤人;(5)对吊顶和广告牌等非结构构件,要做好构造和连接,防止坠落造成人员伤害。     

芦山7.O级地震中钢筋混凝土框架结构震害分析

2013年4月20日四川芦山7.0级地震给震区建筑结构造成了严重破坏.本文选择不同烈度区典型震害的钢筋混凝土框架结构,介绍了结构梁柱、填充墙、其他附属构件及地基等的破坏特点,分析了各类震害特征与破坏机理.结果显示,钢筋混凝土框架结构在本次地震中表现出了良好的抗震性能,除了极震区个别建筑框架柱发生了结构性破坏外,地震区绝大部分均为非结构性破坏,如填充墙及其他附属构件破坏,且大部分破坏不影响结构框架承重体系继续使用.最后针对该次地震中钢筋混凝土框架结构存在的主要问题,给出了一些钢筋混凝土框架结构设计与建设改进建议.     

梯段板不同构造对框架结构地震反应的影响

为检验混凝土框架结构设置楼梯隔震防倒塌支座的效果,利用ETABS有限元软件建立计入楼梯、不计入楼梯、设置滑动支座和隔震防倒塌支座的4个框架结构模型,进行地震作用下梯段板下端不同构造措施对框架结构地震反应影响的对比分析。研究结果表明:与不考虑楼梯作用相比,设置隔震防倒塌支座后,钢筋混凝土框架结构的周期、振型、地震作用、层间位移、框架梁柱和楼梯梁柱的地震内力等均未明显变化,表明隔震防倒塌支座能有效地卸去梯段板的斜撑作用;与滑动支座结构相比,隔震防倒塌支座结构沿地震动输入方向的水平滑动位移基本相同,同时减小了梯段板竖向翘起位移。     

耗能支撑钢筋混凝土框架结构抗震性能研究

本文通过普通钢筋混凝土框架、耗能支撑钢筋混凝土框架结构１／８比例模型的地震模拟振动台对比试验,研究两类框架结构在地震作用下的破坏形态和动力特征,揭示了耗能支撑钢筋混凝土框架结构良好的抗震性能;对试验模型进行了弹塑性时程分析,理论分析和试验结果符合较好;结合扬州电厂二期主厂房框排架结构,研究了其纵向框架结构采用耗能支撑体系时结构的抗震性能,为该类结构型式的工程应用提供依据     

Discontinuous Steady‐State Analytical Solutions of the Boussinesq Equation and Their Numerical Representation by Modflow

Known analytical solutions of groundwater flow equations are routinely used for verification of computer codes. However, these analytical solutions (e.g., the Dupuit solution for the steady‐state unconfined unidirectional flow in a uniform aquifer with a flat bottom) represent smooth and continuous water table configurations, simulating which does not pose any significant problems for the numerical groundwater flow models, like MODFLOW. One of the most challenging numerical cases for MODFLOW arises from drying‐rewetting problems often associated with abrupt changes in the elevations of impervious base of a thin unconfined aquifer. Numerical solutions of groundwater flow equations cannot be rigorously verified for such cases due to the lack of corresponding exact analytical solutions. Analytical solutions of the steady‐state Boussinesq equation, associated with the discontinuous water table configurations over a stairway impervious base, are presented in this article. Conditions resulting in such configurations are analyzed and discussed. These solutions appear to be well suited for testing and verification of computer codes. Numerical solutions, obtained by the latest versions of MODFLOW (MODFLOW‐2005 and MODFLOW‐NWT), are compared with the presented discontinuous analytical solutions. It is shown that standard MODFLOW‐2005 code (as well as MODFLOW‐2000 and older versions) has significant convergence problems simulating such cases. The problems manifest themselves either in a total convergence failure or erroneous results. Alternatively, MODFLOW‐NWT, providing a good match to the presented discontinuous analytical solutions, appears to be a more reliable and appropriate code for simulating abrupt changes in water table elevations.     

梁板分离式分层隔震结构减震原理研究

为了拓宽隔震技术的应用范围,提出了梁板分离式分层隔震结构概念,其核心思想是将框架结构或框架剪力墙结构中的所有楼层或某些楼层的全部或部分楼板通过橡胶隔震支座支承于梁上。建立了分层隔震结构的动力分析模型,利用自编程序按时程分析法和振型分解反应谱法分别计算了不同工况下分层隔震结构的地震反应,运用隔震技术的基本原理和振型分析法分析了刚度比和场地条件等因素对减震效果的影响。发现了刚度比变化过程中分层隔震结构的两个极限状态,并利用其中之一初步判断减震效果。     

Spatial differences in denitrification and bacterial community structure of streams: relationships with environmental conditions

In streams, benthic bacterial communities are integral to multiple aspects of ecosystem function, including carbon and nitrogen cycles. Variation both in terms of bacterial community structure (based on taxonomic and/or functional genes) and function can reveal potential drivers of spatiotemporal patterns in stream processes. In this study, the abundance and diversity of 16S rRNA genes and abundance of nosZ genes, encoding for nitrous oxide reductase, were related to denitrification and environmental conditions. Denitrification rates varied among the three streams examined, and within a given stream there were significant longitudinal differences. Likewise, bacterial community structure based on analysis of the 16S rRNA gene also differed significantly among streams. However, variation in denitrification rate was not well correlated with environmental or biological variables measured. In addition, relatively large numbers of denitrifiers occurred when denitrification rates were low. In conclusion, although the streams differed in environmental conditions as well as bacterial community structure, these differences did not explain much of the spatial variation in denitrification rates.     

江苏地区220 kV标准变电站抗震性能评估

220 kV变电站建筑在电网系统中地位非常重要,其承载能力安全性,尤其是其抗震能力,对电网系统稳定有决定性影响。为评估变电站结构抗震承载能力,明确其倒塌机理,从而为新建变电站结构抗震设计提供技术支撑。以国家电网江苏公司220 kV标准变电站结构为例,选取3条地震波,采用弹塑性时程法,分析结构在不同地震波不同输入方式下的响应。研究结果发现:三向地震波输入下变电站结构地震响应很大;结构的损伤、失效主要发生于结构薄弱部位;现有220 kV变电站结构的抗震承载力不高,鉴于其重要程度,其安全度应增强。     

Shaking-table tests and numerical simulations on a subway structure in soft soil

Shaking table tests were performed to investigate the damage mechanisms of a subway structure in soft soil while experiencing strong ground motions. The seismic responses of the structure and soil were found to be more sensitive to input motions with richer low-frequency components. The excess pore pressure ratio of soil increased slightly, and the distribution of the excess pore pressure surrounding the structure showed clear spatial effects. The frequency spectrum characteristics of input ground motions clearly influenced the lateral displacement of the structure. In addition, the structure was most severely damaged at the top or the bottom of the interior columns. Finite element analyses were conducted by using the modified Martin–Seed–Davidenkov viscoelastic and the rate-independent plastic-damage constitutive models for soil and concrete, respectively. Satisfactory agreement was observed between the simulation and test results, the difference between these results was discussed in detail. The results provide insight into how the characteristics of strong ground motion might influence and present a simplified analysis method to quantitatively evaluate the damage of subway structures in soft soil.     

Statistics on the sizes and internal structures of rainshowers

A large sample of radar reflectivity data from essentially a full summer of operation was analyzed to determine the horizontal extents and internal structure of rain areas observed at altitude levels from 2 to 10 km. Results are given on the size distributions of individual cells or patches defined by reflectivity thresholds approximately 4 dBz apart, on the dependence of mean size on altitude and reflectivity threshold, and on the interior structure of the patches as characterized by the number and sizes of higher-threshold patches contained in each echo. In a more detailed analysis of internal structure, the data were restricted to convective echoes in which certain prescribed reflectivities, ranging from about 30 to 50 dBz, were exceeded. It was found that the dependence of mean quantities, such as patch area, on reflectivity and altitude could be approximately described by simple functions, but that the scatter of observations about the mean was usually large.     

二级结构地震反应的实验研究

本文针对结构顶部的附属结构在正弦激励和地震动作用下的反应，设计了多层结构模型并研究了附属结构的多种情况。实验结果表明，附属结构在地震作用下可对主体结构产生不同的影响，根据附属结构的参数的不同可能导致主体结构的反应增大或减小，因此得出结论：在结构设计时对主体结构和附属结构进行整体考虑，能使结构的地震反应控制在最佳的水平。     

Response of the zooplankton community to extreme hydrological variations in a temporary lake in a neotropical floodplain system

Extreme events can cause species substitution or biodiversity losses. In floodplains, flood and drought phases are considered disturbances when their amplitude or intensity are atypical. These unpredictable events can affect the structure of aquatic communities. In this context, we evaluated the response of the zooplankton community to two extreme droughts that occurred from 2001−2002 and 2014−2016. We assessed species richness and composition on three occasions: before extreme drought (phase 1); during the phase after extreme drought (phase 2) characterized by floods, and lastly, after flood (phase 3), when the fluctuations in water levels in the lowlands stabilized. We hypothesized that (i) zooplankton composition in the lake is distinct in the phases before extreme drought and flood, as the extreme drought event causes changes in the community structure and (ii) after the flood (phase 3), the composition of species in the lake would be more similar to the phase 1, with a large number of species shared in these. Contrary to what we expected, similarity in the species composition of the lake was greater between the phase 1 and phase 2, which may indicate the resilience capacity of the community, through specialized adaptations capable of tolerating extreme. The lowest similarity was observed between the phase 1 and phase 3 and this difference may be a consequence of the dilution effect of the community in the flood (phase 2). Our results suggest that the community structure in the lake can be considered more resilient to extreme drought. We also highlight the importance of the hydrological dynamics of a floodplain for the structure of communities, considering atypical droughts in periods of different climatic events.     

沿海地区一次多单体雷暴电荷结构时空演变

利用闪电放电辐射源三维时空分布测量,分析了山东低海拔地区一次多单体雷暴过程的电荷结构演变以及与回波强度的关系.结果表明对流云区电荷结构是典型的上正下负电偶极结构,且随着雷暴发展正负电荷层强度增大,高度抬升.负电荷区处在40 dBz以上的强回波区域中,正电荷层处在约40 dBz区域中.层状云区也有类似结构,只是强度弱,高度低.观测到的四层电荷结构是出现在对流区消散阶段,此时,由于云体不同部位的不同消散程度,电荷结构发生断裂,云体前部正负电荷区下沉,云体中部正负电荷区高度变化不大,但负电荷区域变薄,呈现出四层电荷结构.从本例结果说明,雷暴优势起电机制通常能形成电偶极或三极性结构,多极结构可能不是起电形成.本文还分析了一次负地闪传输过程,和宏观电荷结构很好吻合,说明利用三维定位系统观测,可以较好地描述雷暴宏观电荷结构.     

Magnetotelluric sounding and geothermics in Central and Eastern Europe: a comparison

In eight areas of Central and Eastern Europe elevated electrical conductivity horizons determined from magnetotellurics, heat flow densities and crustal structure were identified. Based on these data, it was determined whether good conducting horizons are the consequence of elevated temperatures or not. In three areas investigated the thermal activation was detectable; these areas are Alpine subsidences. In the five other areas no thermal activation was found, the good conducting layers on these areas have been caused by other disturbing effects, such as material inhomogeneities or near surface disturbances.