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桩基础是松软深厚地基上高层建筑的主要基础形式,其长度直接影响高层建筑的抗震性能。尽管桩基础有较广的应用范围,但桩长与结构整体抗震性能的相关性研究还颇为少见。根据上海某高层建筑地基基础结构数据建立软土地基上桩基础高层建筑平面动力有限元计算模型,以横观各向同性材料模拟软土地基,弹性阻尼人工边界模拟地基半无限体,薄膜单元模拟桩土间接触滑移性能,并考虑桩-土-结构共同作用,采用上海地铁某车站地震监测数据作为地震波输入,在其他条件不变的情况下选择各种桩长进行计算,根据计算结果分析讨论在该模型条件下桩长选择对上部结构以及桩基础整体抗震性能的影响,提出优化方案。 相似文献
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对广州地区一例地基-基础-隔震板柱结构动力相互作用体系进行了计算分析.通过与常规设计方法及非隔震体系的比较,研究了该体系地震反应的变化规律,并分析了阻尼比、地基土特性、基础刚度、基础型式、基础埋深、土体深度、上部结构刚度和地震波等因素对相互作用体系动力特性及地震反应的影响. 相似文献
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为探索非一致地震波动输入对大型钢筋混凝土框架结构地震响应的影响,基于OpenSees软件平台建立二维钢筋混凝土框架结构\|地基动力相互作用有限元模型。将El-Centro地震波按P波波形分别以0°、15°、30°和35°角入射该有限元模型进行计算,对比分析框架柱内力和楼层层间位移的地震响应。研究发现非一致地震波输入方法对于大型钢筋混凝土框架结构建筑动力响应影响明显,随着地震波入射角的增大,钢筋混凝土框架结构底层柱的轴力幅值减小,剪力幅值增大,而弯矩幅值变化较小,楼层层间位移幅值也随之增大。研究结果对于大型钢筋混凝土框架结构抗震设计具有参考意义。 相似文献
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本文依托河海大学岩土所独立研发的程序WWCC,以广东省广珠东线中（山）-江（门）高速公路为工程背景,选取一处地基土层为基本模型,在三条不同地震波（人工波,汶川波E,汶川波N）作用下,通过动力有限元计算分析,对加载路基堆荷前后的地基土抗液化能力进行对比分析。结果表明公路地基在相同地震荷载作用下,增加路基堆荷后的抗液化能力明显提高,抗液化安全系数随着土层深度的增加逐渐增大,并通过改变路基的高度进一步分析路基荷载对地基土液化特性的影响。结果表明路基越高,地基土的抗液化能力越大。本文通过研究路堤对地基土液化特性的影响,证明路基荷载对公路工程抗液化是偏安全的。 相似文献
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针对振动台试验,采用u-p形式控制方程表述饱和砂土的动力属性,选用土的多屈服面塑性本构模型刻画饱和砂土和黏土的力学特性,引入非线性梁-柱单元模拟桩,建立试验受控条件下液化场地群桩-土强震相互作用分析的三维有限元模型,并通过试验结果验证数值建模途径与模拟方法的正确性。以实际工程中常用的2×2群桩为例,建立桩-土-桥梁结构强震反应分析三维有限元模型。基于此,针对不同群桩基础配置对液化场地群桩-土强震相互作用影响展开具体分析。对比发现,桩的数量相同时,桩排列方向与地震波输入方向平行时比垂直时桩基受力减小5%~10%,而对场地液化情况无明显影响;相同排列形式下,三桩模型中土体出现液化的时间约比双桩模型延缓5s,桩上弯矩和剪力减小33%~38%。由此可见,桩基数量增加,桩-土体系整体刚度更大,场地抗液化性能显著,桩基对上部桥梁结构的承载性能明显增强,其安全性与可靠性更高。这对实际桥梁工程抗震设计具有一定的借鉴意义。 相似文献
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为了研究不同基础形式下河水对成层软土地基上建筑物地震反应的影响,构建了结构-基础-土-河水体系动力相互作用的非线性完全有限元计算模型,在考虑土体重力的前提下,对筏片基础、桩筏基础、箱形基础、桩箱基础相互作用体系进行了时域数值分析。计算结果表明,建筑物靠近河水时,筏基和箱基体系顶部位移发生了向河水一侧的偏移,而采用桩基和桩箱基础时其偏移度明显减小。同种基础形式下,建筑物距河水越远,其框架剪力峰值越大,而不同基础形式的同种工况,桩箱基础时柱剪力最大,筏片基础时最小。单纯筏基和箱基时,基础周围土体均大量进入塑性,上部结构仍保持弹性;而采用下部有桩基础的筏基或箱基时,地基土体只有很少量进入塑性,上部框架结构进入了塑性。 相似文献
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高速铁路中的桥梁常采用灌注桩基础以控制沉降,地震作用是桩基础的设计工况之一。建立桥梁-桥墩-桩基础-地基为一体的耦合系统非线性三维数值分析模型,以典型地震波为输入,考虑上部结构和基础的共同工作、土-结构动力相互作用、材料非线性和土层对桩的侧阻及端阻作用,开展三向地震作用下的动力有限元计算,并对地基主要土层压缩模量、桩体材料弹性模量、桩径和桩长进行参数敏感性分析。计算结果表明:现行的桩基础设计方案能有效控制地震荷载作用下桥梁的变形;地震过程中的不同时刻,桩侧阻发挥程度不同且不可忽略,以单纯的梁单元模拟桩的动力学行为的适用性值得商榷;桩长和地基主要土层压缩模量对桥梁地震反应影响最大,桩体材料弹性模量的影响次之,桩径的影响最小。 相似文献
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This paper presents the results of dynamic centrifuge model tests conducted to investigate the liquefaction mechanism in non-homogeneous soil deposits. Four types of model tests were conducted: one model test involved a uniform soil deposit; one involved continuous layered soil deposit; and two involved discontinuous layered soil deposits. Non-homogeneity in the tests was incorporated by including periodically distributed discontinuous silty sand patches. It was found that more excess pore water pressure (EPWP) remains for a longer period of time in the discontinuous region in non-homogeneous soil deposits compared with the continuous layered and uniform soil deposits. The generation of pore water pressure ceases the supply of a new mass of water after seismic excitation; therefore the dissipation of EPWP becomes the dominant factor for settlement after seismic excitation. The rapid dissipation of EPWP through the discontinuous part in the non-homogeneous soil deposits manifests as a larger settlement in the discontinuous part, causing non-uniform settlements. 相似文献
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Three groups of dynamic triaxial tests were performed for saturated Nanjing fine sand subjected to uniform cyclic loading.
The tested curves of the excess pore water pressure (EPWP) ratio variation with the ratio of the number of cycles are provided.
The concept of the EPWP increment ratio is introduced and two new concepts of the effective dynamic shear stress ratio and
the log decrement of effective stress are defined. It is found that the development of the EPWP increment ratio can be divided
into three stages: descending, stable and ascending. Furthermore, at the stable and ascending stages, a satisfactory linear
relationship is obtained between the accumulative EPWP increment ratio and natural logarithm of the effective dynamic shear
stress ratio. Accordingly, the EPWP increment ratio at the number of cycles N has been deduced that is proportional to the log decrement of effective stress at the cycle number N-1, but is independent of the cyclic stress amplitude. Based on the analysis, a new EPWP increment model for saturated Nanjing
fine sand is developed from tested data fitting, which provides a better prediction of the curves of EPWP generation, the
number of cycles required for initial liquefaction and the liquefaction resistance. 相似文献
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Liquefaction macrophenomena in the great Wenchuan earthquake 总被引：3，自引：2，他引：1
Longwei Chen Xiaoming Yuan Zhenzhong Cao Longqing Hou Rui Sun Lin Dong Weiming Wang Fanchao Meng Hongjuan Chen 《地震工程与工程振动(英文版)》2009,8(2):219-229
On May 12, 2008 at 14:28, a catastrophic magnitude M 8.0 earthquake struck the Sichuan Province of China.The epicenter was located at Wenchuan (31.00°N, 103.40°E). Liquefaction macrophenomena and corresponding destruction was observed throughout a vast area of 500 km long and 200 km wide following the earthquake. This paper illustrates the geographic distribution of the liquefaction and the relationship between liquefaction behavior and seismic intensity, and summarizes the liquefaction macrophenomena, including sandboils and waterspouts, ground subsidence, ground fissures etc., and relevant liquefaction features. A brief summary of the structural damage caused by liquefaction is presented and discussed. Based on comparisons with liquefaction phenomena observed in the 1976 Tangshan and 1975 Haicheng earthquakes, preliminary analyses were performed, which revealed some new features of liquefaction behavior and associated issues arising from this event. The site investigation indicated that the spatial non-uniformity of liquefaction distribution was obvious and most of the liquefied sites were located in regions of seismic intensity Ⅷ. However, liquefaction phenomena at ten different sites in regions of seismic intensity Ⅵ were also observed for the first time in China mainland. Sandboils and waterspouts ranged from centimeters to tens of meters, with most between 1 m to 3 m. Dramatically high water/sand ejections,e.g., more than 10 m, were observed at four different sites. The sand ejections included silty sand, fine sand, medium sand,course sand and gravel, but the ejected sand amount was less than that in the 1976 Tangshan earthquake. Possible liquefaction of natural gravel soils was observed for the first time in China mainland. 相似文献
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The present work deals with 1D and 2D ground response analysis and liquefaction analysis of alluvial soil deposits from Kanpur region along Indo-Gangetic plains. Standard penetration tests and seismic down hole tests have been conducted at four locations namely IITK, Nankari village, Mandhana and Bithoor at 1.5 m interval up to a depth of 30 m below the ground surface to find the variation of penetration blows and the shear wave velocity along the depth. From the selected sites undisturbed as well as representative soil samples have been collected for detailed soil classification. The soil profiles from four sites have been considered for 1D and 2D ground response analysis by applying the free field motions of three Himalayan earthquakes namely Chamba earthquake (Mw—5.1), Chamoli earthquake (Mw—6.4) and Uttarkashi earthquake (Mw—6.5). An average value of Peak Ground Acceleration (PGA) obtained from 1D and 2D analysis is considered for liquefaction analysis and post-liquefaction settlement. The excess pore water pressure ratio is greater than 0.8 at a depth of 24 m from ground surface for IITK, Nankari village, Bithoor sites. More than 50% of post liquefaction settlement is contributed by layers from 21–30 m for all sites. In general, the soil deposits in Kanpur region have silty sand and sand deposits and are prone to liquefaction hazards due to drastic decrease of cyclic resistance ratio (CRR) at four chosen sites in Kanpur. 相似文献
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Compaction or densification of loose saturated soils has been the most popular method of reducing earthquake related liquefaction potential. Such compaction of a foundation soil is only economical when limited in extent, leading to a case of an ‘island’ of improved ground (surrounded by unimproved ground). The behavior of the densified sand surrounded by liquefied loose sand during and following earthquakes is of great importance in order to design the compacted area rationally and optimize both safety and economy. This problem is studied herein by means of dynamic centrifuge model tests. The results of three heavily-instrumented dynamic centrifuge tests on saturated models of side-by-side loose and dense sand profiles are discussed. The test results suggest the following concerns as relates to ‘islands’ of densified soil: (1) there is a potential strength degradation in the densified zone as a result of pore pressure increase due to migration of pore fluid into the island from the adjacent loose liquefied ground; (2) there is a potential for lateral deformation (sliding) within the densified island as the surrounding loose soil liquefies. 相似文献
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Mitsutoshi Yoshimine Hiroto Nishizaki Kei Amano Yasuyo Hosono 《Soil Dynamics and Earthquake Engineering》2006,26(2-4):253-264
This paper intended to evaluate the behavior of saturated sand and sloped ground subjected to flow failure with seepage of pore water in the ground after earthquake and the resultant liquefaction. Triaxial compression tests of sand with constant deviator stress but changing of pore pressure and volume of the specimens were conducted in this study. It was revealed that the relation between the volume change and the amount of shear strain during deformation depended on the initial density of the sand but it did not much depend on shear stress and initial confining stress levels. Based on this test results and numerical analysis of the seepage of pore water in liquefied ground, a methodology was proposed to predict the deformation of inclined ground due to liquefaction. 相似文献
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Damage of embankments during earthquakes is widely attributed to the liquefaction of foundation soil. Previous studies have investigated the dynamic response of embankments by mainly considering uniform sand foundation and a single earthquake event. However, the foundation of an embankment consists of many sublayers of soil from liquefiable sand to relatively impermeable layer, and during earthquakes a mainshock may trigger numerous aftershocks within a short time which may have the potential to cause additional damage to soil structures. Accordingly, the investigation of liquefaction-induced deformation of earthen embankments on various liquefiable foundation conditions under mainshock–aftershock sequential ground motions is carried out by a series of dynamic centrifuge tests in this study. The liquefiable foundation includes uniform sand profile, continuous layered soil profile, and non-homogeneous soil profiles. Effects of various foundation conditions on embankment deformations are compared and analyzed. From the test results, it is found that the embankment resting on non-homogeneous soil deposits suffer more damage compared to the uniform sand foundation of same relative density. The test results also suggest that the sequential ground motions have a significant effect on the accumulated deformation of embankment. 相似文献
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An energy-based liquefaction potential evaluation method (EBM) previously developed was applied to a uniform sand model shaken by seismic motions recorded at different sites during different magnitude earthquakes. It was also applied to actual liquefaction case histories in Urayasu city during the 2011 M9.0 Tohoku earthquake and in Tanno-cho during the 2003 M8.0 Tokachi-oki earthquake. In all these evaluations, the results were compared with those by the currently used stress-based method (SBM) under exactly the same seismic and geotechnical conditions. It was found that EBM yields similar results with SBM for several ground motions of recent earthquakes but has easier applicability without considering associated parameters. In Urayasu city, the two methods yielded nearly consistent results by using an appropriate coefficient in SBM for the M9.0 earthquake, though both overestimated the actual liquefaction performance, probably because effects of plasticity and aging on in situ liquefaction strength were not taken into account. In Tanno-cho, EBM could evaluate actual liquefaction performance due to a small-acceleration motion during a far-field large magnitude earthquake while SBM could not. 相似文献
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During the 1999 Chi-Chi, Taiwan earthquake, many sand boiling phenomena were observed in central Taiwan, which caused severe ground settlement and structure damages. According to the installed accelerograms, the peak ground surface horizontal accelerations in the liquefaction-affected areas range from 774.42 to 121.3 gal. The writers carried out an extensive investigation of soil liquefaction in this earthquake. In this paper, we present results of the CPT exploration and post-earthquake liquefaction analysis. Two hundred and seventy five (275) cone penetration test data were collected from the liquefaction-affected areas, and 46 liquefaction case histories and 88 non-liquefaction case histories were derived that can be used to evaluate the accuracy of existing liquefaction evaluation models. In addition, the strength of the liquefied soils after earthquake and the implication of its liquefaction potential in the future event are discussed. 相似文献