Experimental study of the seismic behavior of partially concrete‐filled steel bridge piers under bidirectional dynamic loading     

Huihui Yuan  Ji Dang  Tetsuhiko Aoki 《地震工程与结构动力学》2013,42(15):2197-2216

The seismic behavior of steel bridge piers partially filled with concrete under actual earthquake conditions was investigated by using 20 square section specimens subjected to static cyclic loading tests and single‐directional and bidirectional hybrid loading tests. Acceleration records of two horizontal NS and EW directional components for hard (GT1), medium (GT2), and soft grounds (GT3), obtained during the 1995 Kobe earthquake, were adopted in dynamic tests. Experimental results clearly showed that maximum and residual displacements under actual earthquake conditions cannot be accurately estimated by conventional single‐directional loading tests, especially for GT2 and GT3. A modified admissible displacement was proposed on the basis of bidirectional loading test results. The concrete fill can effectively improve the seismic resistance performance if the concrete inside the steel bridge piers is sufficiently high in quantity. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Long‐term seismic performance of reinforced concrete bridges under steel reinforcement corrosion due to chloride attack     

Yu‐Chen Ou  Hong‐Da Fan  Nguyen Dang Nguyen 《地震工程与结构动力学》2013,42(14):2113-2127

This work presents a new seismic evaluation methodology for corroded reinforced concrete bridges on the basis of nonlinear static pushover analysis. Corrosion of steel reinforcement by chloride attack is considered. At the material level, the effects of corrosion are considered by modeling the degradation of the mechanical properties of steel reinforcement, softening of cover concrete under compression, degradation of core concrete due to confinement steel corrosion, and reduction of bond strength between concrete and steel reinforcement. At the structural level, the effects of corrosion on both flexural behavior and shear behavior, and their interaction are considered. Eleven bridges of various structural types in Taiwan that are located within 6.5 km of their nearest coastline are analyzed to identify their long‐term seismic performance. Relationships between the yield and collapse peak ground accelerations (PGAs), and service time and corrosion level are established for each bridge. Analysis results show that chloride corrosion starts in 2–32 years. The transverse steel reinforcement typically starts corroding before the longitudinal steel reinforcement, as the former has a thicker cover. Research results show that collapse PGA reduces by 0.94% or 1.23% per 10 years when the mean value plus 1 or 2 standard deviation of the collapse PGA values are considered, respectively. Therefore, we suggest increasing the design PGA from 4.70% to 6.15% for a bridge adjacent to a coastline to ensure adequate long‐term seismic performance for 50 years, the typical design life span of a regular bridge. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

黔东南那哥铜铅多金属矿床的矿化时空结构          下载免费PDF全文

刘安璐  张均  范建强  徐志永  陈学峥 《地质找矿论丛》2014,29(3):368-374

黔东南那哥铜铅多金属矿床位于扬子陆块与华夏陆块的过渡带上,该区经历了自四堡期以来的多期构造活动,岩浆活动频繁,变形-变质强烈,构造形迹复杂;通过深入剖析矿床地质特征,结合区域地质演化史,从铜铅矿化的时空结构分析入手,系统研究了矿体空间定位规律。研究结果表明,在时间结构上,成矿与重大地质事件关系密切,具有多阶段成矿的特点;在空间结构上,矿体主要受控于尾硐溪断裂,赋存于断裂带走向上的弧形转弯处、断裂面的凹凸变化部位,矿体具膨大狭缩、尖灭再现特点,在空间上具有向W侧伏的趋势。  相似文献   

长螺旋压灌反插钢筋笼成桩工艺在吉大二院基坑支护工程中的应用     

谢贵明  李洪 《吉林地质》2014,(3):116-119

结合吉大二院基坑支护工程实例,论述了长螺旋成孔压灌混凝土成桩后反插钢筋笼的施工工艺,介绍了配套振笼器装置的反插钢筋笼工作原理及施工工法预案与解决方法。  相似文献   

四川盆地南部早古生代海相页岩微观孔隙特征及发育控制因素   总被引：6，自引：0，他引：6  

张廷山  杨洋  龚其森  梁兴  魏祥峰 《地质学报》2014,88(9):1728-1740

利用环境扫描电镜(ESEM)、原子力显微镜(AFM)、比表面积分析仪对四川盆地南部早寒武世筇竹寺组以及早志留世龙马溪组页岩气储层的微观孔隙类型、结构特征进行了系统研究。四川盆地南部筇竹寺组和龙马溪组页岩气储层微观储集空间类型多样,包括黏土矿物层间孔、有机质孔、晶间孔、矿物铸模孔、次生溶蚀孔等基质孔隙。ESEM和AFM两种方法结合,能客观地反映页岩气储层的微观孔隙结构特征,具有互补性。本区筇竹寺组和龙马溪组页岩气储层以极为发育的微孔为主,为页岩气储层提供了大量孔体积和表面积,但是筇竹寺组页岩比表面积和孔体积都较龙马溪组的小。笔者认为有机碳含量、黏土矿物类型及其含量、干酪根类型及其热演化程度是控制本区筇竹寺组和龙马溪组页岩气储层微观孔隙结构的主要因素,其中,热演化程度的影响最为明显。在一定范围内,热演化程度与比表面积、孔体积与黏土矿物中伊/蒙间层含量具有正相关性,随着热演化程度、有机碳含量、Ⅱ型干酪根含量的增加,表现为微观孔隙数量增加,比表面积和孔体积增大。  相似文献   

Distinctive erosional and depositional structures formed at a canyon mouth: A lower Pleistocene deep‐water succession in the Kazusa forearc basin on the Boso Peninsula,Japan     

Makoto Ito  Kazuaki Ishikawa  Naohisa Nishida 《Sedimentology》2014,61(7):2042-2062

The canyon mouth is an important component of submarine‐fan systems and is thought to play a significant role in the transformation of turbidity currents. However, the depositional and erosional structures that characterize canyon mouths have received less attention than other components of submarine‐fan systems. This study investigates the facies organization and geometry of turbidites that are interpreted to have developed at a canyon mouth in the early Pleistocene Kazusa forearc basin on the Boso Peninsula, Japan. The canyon‐mouth deposits have the following distinctive features: (i) The turbidite succession is thinner than both the canyon‐fill and submarine‐fan successions and is represented by amalgamation of sandstones and pebbly sandstones as a result of bypassing of turbidity currents. (ii) Sandstone beds and bedsets show an overall lenticular geometry and are commonly overlain by mud drapes, which are massive and contain fewer bioturbation structures than do the hemipelagic muddy deposits. (iii) The mud drapes have a microstructure characterized by aggregates of clay particles, which show features similar to those of fluid‐mud deposits, and are interpreted to represent deposition from fluid mud developed from turbidity current clouds. (iv) Large‐scale erosional surfaces are infilled with thick‐bedded to very thick‐bedded turbidites, which show lithofacies quite similar to those of the surrounding deposits, and are considered to be equivalent to scours. (v) Concave‐up erosional surfaces, some of which face in the upslope direction, are overlain by backset bedding, which is associated with many mud clasts. (vi) Tractional structures, some of which are equivalent to coarse‐grained sediment waves, were also developed, and were overlain locally by mud drapes, in association with mud drape‐filled scours, cut and fill structures and backset bedding. The combination of these outcrop‐scale erosional and depositional structures, together with the microstructure of the mud drapes, can be used to identify canyon‐mouth deposits in ancient deep‐water successions.  相似文献   

Sedimentological and deformational criteria for discriminating subglaciofluvial deposits from subaqueous ice‐contact fan deposits: A Pleistocene example (Ireland)     

Edouard Ravier  Jean‐François Buoncristiani  Sylvain Clerc  Michel Guiraud  John Menzies  Eric Portier 《Sedimentology》2014,61(5):1382-1410

A pit located near Ballyhorsey, 28 km south of Dublin (eastern Ireland), displays subglacially deposited glaciofluvial sediments passing upwards into proglacial subaqueous ice‐contact fan deposits. The coexistence of these two different depositional environments at the same location will help with differentiation between two very similar and easily confused glacial lithofacies. The lowermost sediments show aggrading subglacial deposits indicating a constrained accommodation space, mainly controlled by the position of an overlying ice roof during ice‐bed decoupling. These sediments are characterized by vertically stacked tills with large lenses of tabular to channelized sorted sediments. The sorted sediments consist of fine‐grained laminated facies, cross‐laminated sand and channelized gravels, and are interpreted as subglaciofluvial sediments deposited within a subglacial de‐coupled space. The subglaciofluvial sequence is characterized by glaciotectonic deformation structures within discrete beds, triggered by fluid overpressure and shear stress during episodes of ice/bed recoupling (clastic dykes and folds). The upper deposits correspond to the deposition of successive hyperpycnal flows in a proximal proglacial lake, forming a thick sedimentary wedge erosively overlying the subglacial deposits. Gravel facies and large‐scale trough bedding sand are observed within this proximal wedge, while normally graded sand beds with developed bedforms are observed further downflow. The building of the prograding ice‐contact subaqueous fan implies an unrestricted accommodation space and is associated with deformation structures related to gravity destabilization during fan spreading (normal faults). This study facilitates the recognition of subglacial/submarginal depositional environments formed, in part, during localized ice/bed coupling episodes in the sedimentary record. The sedimentary sequence exposed in Ballyhorsey permits characterization of the temporal framework of meltwater production during deglaciation, the impact on the subglacial drainage system and the consequences on the Irish Sea Ice Stream flow mechanisms.  相似文献   

Analysis of circular tunnels due to seismic P-wave propagation,with emphasis on unreinforced concrete liners     

《Computers and Geotechnics》2014

A set of closed-form expressions to calculate tunnel liner forces due to compressional seismic P-wave propagation is presented. The results are compared against a state-of-practice method that considers only shear S-waves, and verified against dynamic numerical analyses. Under the realistic assumption of full-slip conditions at the liner-rock mass interface, it is shown that P-waves can lead to significantly higher axial hoop forces compared to S-waves, and can be critical for tunnels bored through areas of irregular topography/geological stratigraphy. The findings are of particular interest for the analysis of unreinforced concrete tunnel liners, where earthquake effects can be a governing factor.  相似文献   

河南宜阳地区陆相二叠系—三叠系界线附近 微生物成因沉积构造特征及意义   总被引：2，自引：0，他引：2  

张利伟  杨文涛  牛永斌 《地质论评》2014,60(5):1051-1060

有关微生物成因沉积构造及其生物地质过程的研究近年来发展迅速,成为深刻认识地球早期生命演化以及生物与环境相互作用过程的重要桥梁。目前报道的微生物成因沉积构造主要集中在海相沉积中,而陆相碎屑岩沉积中的微生物成因沉积构造研究较少。本文介绍了河南省宜阳地区二叠系—三叠系界线附近陆相碎屑岩中发育的以微生物席生长特征、微生物席破坏特征为主的微生物成因沉积构造,认为这些沉积构造的发育与二叠纪末地质灾变事件造成的特殊水体化学环境和严重退化的生态系统相关,属陆相环境中的"错时相"沉积。研究区微生物成因沉积构造的发现对于二叠纪末地质灾变期生物绝灭与复苏奥秘的探索、陆相地层的划分、海相—陆相地层的对比均具有重要意义。  相似文献   

Tectonic repetitions of the Early Cretaceous Agrio Formation in the Chos Malal fold-and-thrust belt,Neuquén Basin,Argentina: Geometry,kinematics and structural implications for Andean building     

《Journal of South American Earth Sciences》2014

The Neuquén Basin, developed in a retroarc setting in the central-west of Argentina, contains more than 6000 m of Mesozoic marine and continental sedimentary rocks. These rocks were deformed during the Andean orogeny leading to several thick and thin-skinned fold-and-thrust belts. The Early Cretaceous Agrio Formation is composed by a thick marine succession predominantly of black shales in which highlights a thin fluvial-aeolian sandy interval named Avilé Member. The Avilé Member, one of the most important hydrocarbon reservoirs of the Neuquén Basin, constitutes an excellent structural marker. At the Chos Malal fold-and-thrust belt, the strong mechanical anisotropy given by the contrasting lithology of the Avilé Member within the Agrio Formation favored the location of detachments along the shales and ramps affecting the sandstones during the Andean compression. Detailed field mapping at the Chacay Melehue area allowed us to recognize tectonic repetitions of the Avilé Member, which form imbrications in the simplest case whereas in other places constitute a more complex combination of imbrications, including fault-bend folding that duplicates stratigraphic sequences and fault-propagation folding that deforms more intensely the duplicated units. Along three structural cross-sections we illustrate the geometry of these tectonic repetitions of the Agrio Formation, which in the northern area have an eastward-vergence and in the central and southern regions show a clear westward-vergence. A tear fault along the arroyo Chacay Melehue could explain this vergence change. Forward modeling of the structures at the central cross-section, where a backthrust system produced imbrication, duplication and folding of the Agrio Formation, allows us to propose a balanced kinematic reconstruction of this complex structure and to compare the features produced at different stages of the deformation sequence with field observations. Our kinematic interpretation shows that the tectonic repetitions of the Agrio Formation involve 3 km of shortening above a basal detachment within the lowermost black shales. Based on a regional balanced cross-section constructed from the basement-cored Cordillera del Viento anticlinorium toward the east, across the thin-skinned sector of the Chos Malal FTB, it is possible to connect the backthrust system with east-vergent fault-bend folds that involve the stratigraphic units below the Agrio Formation. Finally, we propose a regional structural model considering the Cordillera del Viento as a basement wedge related to a low angle Andean thrust that is inserted into the sedimentary cover producing structures of different order, which evidence a strong relationship between thick and thin-skinned structures during the Andean orogeny.  相似文献