Investigation of the soil amplification factor in the Adapazari region

Turkey is located on the highly active Eurasian plate. A very active strike slip fault, the North Anatolian Fault Zone (NAFZ), crosses Turkey from east to west; earthquakes occurred on this fault on August 17, 1999 (Kocaeli) and November 12, 1999 (Düzce). Regional geology and subsoil conditions can significantly change the characteristics of ground motion. For this reason, determining soil amplification during an earthquake, especially for soft soils, is a very important topic for researchers. In this study, one dimensional ground response analyses were performed for selected Adapazari sites using the August 17, 1999 Kocaeli earthquake strong ground motion record with SHAKE2000 software. Soil characteristics and depth to engineering bedrock at the selected sites are different and the observed level of structural damage at these sites during the Kocaeli earthquake was also different. Calculated soil surface response spectrums at these sites were compared with the recommended design spectra of the Turkish Earthquake Code and the Eurocode 8. According to one dimensional ground response analyses, the calculated response spectra of the selected sites exceed the recommended design spectra of the Turkish Earthquake Code and the Eurocode 8. Calculations show that higher amplification ratios occur at higher periods due to soil behaviour. Results of this study indicate that local geological conditions may amplify ground motion at some periods and, due to this amplification, the calculated response spectra may exceed the recommended design spectra. Therefore, it is clear that local site conditions must be considered for earthquake-resistant engineering designs on soft alluvial soil deposits.     

支架式水塔的水平地震作用的计算

利用流体力学的理论 ,推导出了支架式水塔附加地震作用的计算式 ,给出了晃动水的动力放大系数反应谱的部分计算统计结果 ,对《建筑抗震设计规范》(GBJ 11- 89)中支架式水塔水平地震作用的计算式提出了修改的建议 ,并给出了一个具体计算例 ,验证了在水塔的抗震计算中考虑附加地震作用的必要性。     

长周期结构弹塑性时程分析的地震波选取

长周期结构在大震作用下进入弹塑性状态,结构刚度退化,周期延长,地震波对应的反应谱与规范反应谱在长周期段的拟合程度对结构的安全性判 断有较大影响。提出长周期反应谱拟合系数作为长周期结构在弹塑性时程分析中地震波选取的依据,通过六千多条强震记录的统计分析,得到不同场地条件 下适用于长周期结构弹塑性时程分析的地震波库,保证所选取地震波对应的反应谱与规范反应谱在3~6s段统计意义上相一致。     

Assessment of the site amplifications and predominant site periods for Saruhanlı, in an earthquake-prone region of Turkey

An earthquake-resistant design should include the effect of local site conditions on the seismic ground motions. In this study, ground response analyses in 22 locations around the developing town of Saruhanlı in the Aegean Region of Turkey were undertaken using SHAKE software. The ground response analyses for a typical soil profile considered various modulus reduction and damping curves including effective confining stress and a plasticity index dependent model. The confining stress-dependent soil models and shear-wave velocity profile resulted in higher amplification ratios and lower predominant periods. High acceleration ratios (>3) and lower predominant site periods were found in the eastern part of the site such that buildings of ten or more storeys would be severely damaged.     

桥梁抗震设计规范与建筑抗震设计规范的比较

对我国现行<公路工程抗震设计规范>与<建筑抗震设计规范>进行了较为详细的对比,分别从抗震设计的基本思想、设计地震动参数、地震反应分析和计算方法、构造细节等方面对这两本规范进行了比较,并指出了今后我国各行业工程结构抗震设计规范宜逐步统一.     

地震波三维斜入射作用下隧道#br# 对场地地表地震动的影响

利用2.5维有限元-边界元耦合方法,以饱和土场地中圆形隧道为例研究了地下隧道对场地地表地震动加速度的放大效应,主要讨论了地震波入射角的影响。假定地震波在基岩面三维斜入射,用水平入射角θh和竖向入射角θv两个角度来表示地震波的入射方向。研究表明,地震波斜入射时的场地地表地震动加速度放大系数显著大于地震波垂直入射情况,且地震波入射角对场地地表加速度反应谱的幅值、形状以及卓越频率也均有一定程度的影响,尤其对竖向加速度反应谱卓越周期的影响显著。此外,针对本文算例,θh< 30°且θv> 30°时,场地地表地震动竖向加速度与水平加速度的比值大于规范推荐的0.65,且此时竖向加速度反应谱的幅值可能会大于水平加速度反应谱的幅值。     

Geo-engineering properties and settlement of peaty soils at an industrial site (Turkey)

Peats consist of the partly decomposed remains of vegetation, which have accumulated in waterlogged areas. They are often unsuitable for supporting structures of any kind due to their high water content, high compressibility, low shear strength and high degree of spatial variability. The paper reports a preliminary study on peats from industrial sites in the city of Kayseri, Turkey. The soils in the study area are classified as peat to muck. The peats are fibrous at shallow depth and become amorphous as they extend to some 8 m depth. The ranges of geo-engineering properties are generally consistent with those reported in the literature, with some variation due to their higher mineral soil contents. The behavior of the peats is essentially frictional, with high friction and relatively small cohesion. The direct shear tests yielded higher shear strengths than those from the triaxial tests, due to the fact that the peat specimens used in the direct shear tests were rich in fibers and mineral soils. Back analysis of the settlement of heavy rolls of metal wires laid on the peat generally confirmed the consolidation properties of the soil determined in laboratory.     

改进的简化能力谱法在铁路桥梁中的应用

依据现行的《铁路工程抗震设计规范》,合理地选取大量强震记录作为地震动输入,采用单自由度弹塑性动力分析程序,对不同固有周期的弹塑性单自由度体系进行非线性动力时程响应分析,得到与我国现行《铁路工程抗震设计规范》相容的具有统计意义的弹塑性需求谱和强度折减系数谱,进而对简化能力谱法作了改进,并应用于某客运专线双柱式桥墩的抗震性能评估中,再将所求得的结构性能点转化为结构的非线性地震响应,并与80条强震记录非线性时程分析计算结果的平均值进行比较,从中可以看出:改进的简化能力谱法可以用较少的计算工作量得到比较精确的结构非线性地震响应。这也验证了将改进的简化能力谱法应用于我国铁路桥梁工程抗震性能评估的可行性。     

福州市区场地类别划分的初步研究

利用现场实测波速和钻孔资料,根据中国建筑抗震设计规范(GB50011-2001)和美国FEMA编制的NEHRP(2000)以及欧洲抗震规范(EUROCODE8,1998)关于场地分类划分的标准,对福州市区典型场地进行了场地类别划分,讨论了划分结果的适用性。文章认为,对福州市区带有软弱夹层土的场地,简单的划分方法可能对长周期地震动估计不足,应当考虑用其他方法估计地震动。     

国外减隔震桥梁的失效分析

近年来国外一些减隔震桥梁在地震下的倒塌事件,为我们提出了"灾后分析、处理和规范修正"的重要课题。本文主要介绍国外几座安置了减隔震装置的桥梁,因为减隔震装置的使用不当而造成桥梁失效的案例。着重对土耳其的Bolu高架桥以及日本隔震桥梁在实际地震中会失效的原因进行了综述性的归纳和总结。Bolu高架桥1号线的失效原因主要在于地震隔离系统的设计没有遵照相关的规范要求,而日本采用的橡胶隔震支座的冷冻硬化导致了桥梁超载。分析失效的原因,作好抗震加固、更新和改造,为我们提供了宝贵的经验教训。     

The chronology of anthropogenic,atmospheric Pb deposition recorded by peat cores in three minerogenic peat deposits from Switzerland

Peat cores were collected from three minerogenic peatlands in Switzerland: La Tourbière des Genevez (TGE), in Canton Jura; Gola di Lago (GDL), in Canton Ticino; and Mauntschas (MAU), in Canton Grisons. Chemical analyses of the pore waters and the peats document the increasingly minerogenic character with depth. In particular, the Sr concentration profile in the peats reflects the growing importance of mineral sediment dissolution with increasing distance below the peat surface. Despite this circumstance, Pb concentrations are greatest in the surface layers, and decrease with depth. Thus, dissolution of the basal sediments at these sites appears to be an unimportant source of Pb, compared with atmospheric deposition. Twenty-one new radiocarbon age dates for the three cores provide a chronology of Pb enrichment, and these are consistent with the record of atmospheric Pb deposition recorded by the ombrotrophic peat bog 'Etang de la Gruère' (EGR). Sediment samples from TGE and EGR were reacted at pH 5 with ammonium acetate to dissolve the carbonate fraction, filtered, and the residues analyzed using XRF. These analyses show that much of the Ca, Mg, Sr and Mn is lost when the carbonate fraction is dissolved, but this process does not measurably affect Pb. This finding suggests that carbonate dissolution dominates the weathering of the sediments underlying these peat deposits, but this fraction does not contain significant concentrations of Pb. Minerogenic peat deposits such as those described here, therefore, can serve as reliable archives of atmospheric Pb deposition, provided that mineral dissolution in the underlying sediments does not contribute measurably to the Pb inventory of the peat profile.     

Development of mean site-dependent response spectra for new bridge designs in Turkey

Bridges in Turkey have been designed using a modified version of AASHTO Load Factor Design Specifications. In this paper, a new design spectrum is being analysed to address the characteristics of the Turkish earthquake records. The main contribution of this study is to suggest a mean Turkish site-dependent response spectra especially for the constant velocity region by analysing a number of Turkish earthquake records. The findings are compared to the two different design spectra of AASHTO. The mean site-dependent response spectra normalised with the peak ground accelerations are analysed for certain soil conditions and for a given range of moment magnitude values. The mean site-dependent response spectra corresponding to the largest moment magnitude range is observed to lie above the design spectra for periods larger than 1.0 s. Response spectrum analyses and time history analyses are performed on selected bridges using AASHTO design spectra and the mean site-dependent response spectra to observe the differences in corresponding structural responses. Results from analyses indicate that design spectrum is conservative for small to moderate moment magnitude levels. However, for the largest moment magnitude range considered, structural responses from mean site-dependent spectra are higher than those obtained from the design spectra.     

建筑抗震设计的新概念--对《建筑工程抗震性态设计通则》的理解

《建筑工程抗震性态设计通则》(CECS160:2004)已经中国工程建设标准化协会批准试用。《通则》总结了近几年来国内外的最新抗震科研成果和工程经验,提出了抗震性态设计、设计地震加速度、结构弹塑性地震反应、结构影响系数、结构弹塑性侧移、高频结构竖向地震反应、建筑抗震设计类别等诸多抗震设计新概念和新方法,对提高我国建筑抗震设计水平将起到积极的推动作用,也为今后修订国家标准《建筑抗震设计规范》提供了较完整的资料。     

美国NEHRP规范中地震作用的比较研究

从1985年第一版推荐性的NEHRP规范出版以来,它已渐渐成为美国各样板规范和其他地方性建筑规范的主要参考资料之一。本文从设计加速度反应谱的最大值和长周期下降段形状等方面,对不同版本的NEHRP规范进行了比较。从中看出,在确定设计加速度反应谱时,分别考虑了场地条件在长、短周期的影响;控制长周期幅值的下降段的下降速率逐渐增大等。这些有望为我国建筑抗震设计规范的修订提供一些启示。     

多层冷弯薄壁型钢住宅体系动力时程分析

在采用有限元方法验证三层冷弯薄壁型钢房屋振动台试验结果的基础上,建立了多层冷弯薄壁型钢结构住宅空间整体模型,分析了模型前3阶自振频率、振型以及双向地震作用下的加速度、位移响应和水平地震剪力,考察了多层房屋的抗震性能。结果表明:《低层冷弯薄壁型钢房屋建筑技术规程》推荐的基频计算方法适用于多层冷弯薄壁型钢结构体系;随着输入地震波峰值加速度的增加,模型各层加速度幅值、相对位移和最大剪重比均增大,而各层峰值加速度放大系数有降低的趋势;随着结构高度的增加,模型各层峰值加速度放大系数、相对位移和最大剪重比均增大;多层冷弯薄壁型钢结构体系在多遇地震和罕遇地震作用下结构X向和Y向的水平地震剪力和最大层间位移角满足《建筑抗震设计规范》的要求,具备较好的抗震性能。     

Seismic performance factors for low‐ to mid‐rise steel diagrid structural systems

Diagrids are known as an esthetically pleasing and structurally efficient system. The current design codes and provisions, however, provide no specific guidelines for their design under extreme events such as earthquakes. This paper presents a comprehensive investigation of the performance of steel diagrid structures to evaluate their key seismic performance factors. Nonlinear static, time‐history dynamic, and incremental dynamic analyses are used to assess diagrid performance and collapse mechanisms in a high seismic region. Seismic performance factors including response modification factor, ductility factor, overstrength factor, and deflection amplification factor are quantified using 4 different methodologies. Four archetype groups of diagrid buildings ranging in height from 4 to 30 stories have been investigated. An R factor in the range of 4 to 5 is recommended for steel diagrid frames in the range of 8 to 30 stories unless supplementary analyses are conducted to find the optimal diagonal angle. For low‐rise steel diagrids (under 8 stories), an R factor in the range of 3.5 to 4 is recommended. Further, an overstrength and ductility of 2.5 and 2 are recommended. This paper lays the groundwork for including steel diagrids in design provisions.     

《室外给水排水和燃气热力工程抗震设计规范》GB50032-2003的几点修订建议

本文将《室外给水排水和燃气热力工程抗震设计规范》GB50032-2003与《建筑抗震设计规范》等国内主要工程抗震规范进行了原则比较,从抗震设防目标、设防分类和设防标准、地震作用计算、抗震性能化设计、地震动参数等方面进行了分析,并提出了一些修订建议,可供规范修订参考。同时通过一个典型清水池的试设计,建议开展高于"小震弹性"抗震设防目标的研究工作,并建议研究和增加中震、大震位移角限值的相关规定。     

Accumulation of organic carbon over the past 150 years in five freshwater peatlands in western and central Europe

Under predicted scenarios of global climate change, peatlands may become a net source of greenhouse gases which will accelerate warming of the atmosphere. Comparative studies of peat bogs along present climatic gradients may provide an insight into the future response of boreal and subarctic peatlands to changing temperature and moisture. Three maritime peat bogs in the British Isles, and two high-elevation peatlands in the Czech Republic were studied. All sites were relatively wet, the mean annual temperatures were higher by up to 6 degrees C at the British/Irish sites than at the Czech sites. Cumulative carbon content in (210)Pb-dated Sphagnum-dominated vertical peat cores increased from the warmer to the colder sites when evaluated for the most recent decades (since ca. 1950). That would correspond to formation of thinner, more highly decomposed peat deposits over the long-term in warmer conditions, and deeper peat bogs in colder conditions. However, when cumulative carbon content was evaluated for the last ca. 150 years, no relationship was found between mean annual temperature and the carbon pool size. Even along broad present-day climatic gradients, site-specific factors controlled organic carbon preservation in peat. Pollen analysis was instrumental in corroborating the (210)Pb dates, identifying wet and dry periods in the past, and it also provided evidence for increasing nitrogen loads in wetland areas.     

建筑场地地震力影响单因素分析

通过给定某些特定假设条件,利用反应谱原理计算出不同场地类型、设防烈度、自振周期和阻尼比情况下的地震力,利用这些计算结果来分析判断各因素与地震力之间的作用关系,计算结果表明:利用抗震设计反应谱计算出的地震力,当诸多因素中只有唯一变量时,其与自振周期成反比,与阻尼比成反比,与设防烈度成正比,与场地类型成正比。