节理峰值后归一化位移软化模型

切向荷载作用下贯通节理岩体峰值强度后的剪切应力、位移变形规律一般呈双曲线形式发展,即峰值后强度衰减速率逐步变小而趋于0,到达残余强度。直剪试验表明,非贯通节理岩体峰值后剪切应力、位移呈“S”型趋势发展,即强度衰减速率先是逐步增大,到达一定程度后逐步减少,最后趋于稳定达到残余强度值。贯通节理岩体峰值强度后的本构关系并不适合于描述该特征。提出一个新的非线性归一化位移软化本构模型,通过归一化剪切应力R与归一化剪切位移D的指数函数关系体现峰值后剪切应力、位移的发展趋势,即模型采用无量纲表达式。归一化剪切应力R是峰值后强度降? p-? 与峰值强度、残余强度差值? p-? r的比值;归一化位移D是峰值后剪切位移、峰值位移差值? -? p与残余位移、峰值位移差值? r -? p的比值。对含不同起伏角的非贯通节理岩体在常法向荷载条件下的直剪试验数据进行拟合分析,模型预测结果与实测值具有相当高的吻合度,验证了模型的正确性     

Field Study on the Behavior of Destructive and Non-Destructive Piles Under Compression

This paper presents a series of full-scale load tests on long bored piles instrumented with strain gauges along the shafts, including eight field tests of piles loaded to failure and one non-destructive pile load test. The load-displacement response, skin friction, end resistance, and the threshold of the pile-soil relative displacement for fully mobilizing skin resistance were discussed. A simple softening model was proposed to describe the degradation behavior of the skin friction along the pile-soil interface and the load-displacement relationship developed at the pile base. It is found that the shaft resistance degradation investigated in the non-destructive load test only occurs at a shallow depth, and the skin friction of deeper soil is not fully developed. However, unlike the results of the non-destructive load tests, the softening is accompanied by a reduction in skin friction and observed to be along the whole pile depth. The thresholds of pile-soil relative displacement for fully mobilizing skin resistances in different soils have been found to be in the range 0.6% to 2.4% of the pile diameter. Moreover, in practical applications, a bilinear model is assumed to be feasible in analyzing the load-settlement relationship developed at the end of non-destructive pile, whereas the load transmission curve of the soils below the pile base corresponds to a softening model in the field tests of piles loaded to failure.     

Field and Theoretical Analysis on the Response of Destructive Pile Subjected to Tension Load

Most field tests are carried out using working piles for verification purposes in China, and loading tests are terminated before achieving true pile capacity. In this work, two full-scale destructive loading tests on tension piles instrumented with strain gauges were conducted to capture true pile capacity. The load-displacement response, load transfer, and threshold of the pile-soil relative displacement for fully mobilizing skin resistance in the uplift case were discussed. It was found that the shaft resistance degradation is observed to be along the pile depth with a reduction factor of 0.905 to 0.931, and the thresholds of pile-soil relative displacement for fully mobilizing skin resistance of the tension pile in different soils are found to be in the range 0.67% to 1.34% of the pile diameter. Based on the field test results, a simple softening model was proposed to describe the degradation behavior of skin friction along the pile-soil interface. Further study was conducted to assess the influence of the threshold of pile-soil relative displacement for fully mobilizing skin friction and the reduction factor on the skin friction. As to the analysis of the response of single pile subjected to tension load, a highly effective iterative computer program was developed using the proposed skin friction softening model. Comparisons of the load-settlement response for the well-instrumented tests were given to demonstrate the effectiveness and accuracy of the proposed simple method.     

Critical Top Tension for Static Equilibrium Configuration of A Steel Catenary Riser

This paper aims to present the critical top tension for static equilibrium configurations of a steel catenary riser（SCR） by using the finite element method. The critical top tension is the minimum top tension that can maintain the equilibrium of the SCR. If the top tension is smaller than the critical value, the equilibrium of the SCR does not exist. If the top tension is larger than the critical value, there are two possible equilibrium configurations. These two configurations exhibit the nonlinear large displacement. The configuration with the smaller displacement is stable, while the one with larger displacement is unstable. The numerical results show that the increases in the riser＇s vertical distances, horizontal offsets, riser＇s weights, internal flow velocities, and current velocities increase the critical top tensions of the SCR. In addition, the parametric studies are also performed in order to investigate the limit states for the analysis and design of the SCR.     

法向承力锚拖曳安装过程的整体模拟

法向承力锚(Vertically Loaded Plate Anchor,VLA)是一种适用于深水的新型系泊基础,它的拖曳安装过程直接决定了其系泊定位的精度和锚体的最终承载能力。综合考虑VLA锚体、锚泊线和上部船体的运动,建立了一种新的准静力整体分析模型。模型包括不断贯入海床的锚体、锚泊线(土中反悬链段和水中悬链段)和安装船体三部分,针对确定的锚泊线长度,安装船运动张紧锚泊线进行安装的过程,计算了此过程中锚体的运动轨迹、锚泊线形态和作用在船体上的锚泊线张力矢量的变化,重点分析了不同抛链长度和海床土体的参数对安装过程控制的影响,发现链长与水深之比达到5时,接近极限贯入深度。     

Marine reserve establishment and on-going management costs: A case study from New Zealand

While there is considerable international research focused on the conservation outcomes of marine protected areas (MPAs) and marine reserves (MRs) there is little information on the economic cost to establish and manage these protected areas. This study estimated the MR pre-establishment and establishment costs for the Taputeranga Marine Reserve (TMR) in New Zealand (NZ) and determined the annual management costs for this reserve and four further NZ MRs. Finally, the cost to local rock lobster fishers resulting from the displaced fishing effort once the TMR had been established was estimated. This research found that the TMR pre-establishment cost was approximately NZ$508,000, and the establishment process cost was approximately NZ$353,000. The annual management costs across the five reserves ranged between NZ$43,200 and NZ$112,500 between 2008/09 and 2010/11. The annual fishers displacement cost at TMR was approximately NZ$22,000 per annum. This research showed that on a unit area basis, small MRs in NZ are just as expensive to maintain as large MRs. This study also highlighted how volunteer effort helped to considerably reduce the monetary cost of the MR pre-establishment process. This research increases our understanding of establishment and management costs, and supports future planning of MRs both within NZ and internationally.     

长江口沙波统计特征及输移规律

利用多波束测深系统对长江口南港、北槽、横沙通道和北港水下地貌进行测量,对沙波波高、波长、迎流倾角、背流倾角、水深和沉积物特征进行统计,并根据流速、沉积物粒径及水深估算其潮周期内净位移。结果表明:长江口沙波基本都为大型沙波,且沙波大小与其所在区域沉积物粒径呈正比关系;长江口各个区域沙波的对称性不同,涨、落潮优势流越明显,则沙波对称性越差,净位移越大;沙波对称性能反映此区域水动力强弱及潮周期内沙波净位移大小。     

框架剪力墙结构模态静力非线性抗震分析方法研究

本文在模态pushover分析方法基础上推导建立了模态静力非线性分析方法,对一栋10层框架剪力墙结构进行了静力非线性分析,提出了目标位移求解的等效单自由度体系弹塑性时程分析迭代法,计算结果与相应时程分析结果进行了比较,表明两者吻合较好,验证了本文计算方法的有效性。另外,对同一结构,计算分析了在不同水平荷载模式下的静力非线性分析结果,比较不同荷载模式对计算结果的影响,为静力非线性分析方法的推广使用提供参考。     

既有基坑延深开挖稳定性评价与支护方案确定

以北京市某特殊基坑工程为背景,采用FLAC3D软件,选用Mohr-Coulomb准则,对基坑在现有支护方案条件下进行延深开挖,计算分析桩锚支护体系的变形、受力情况。结果表明,基坑在现有支护方案条件下进行延深开挖将导致护坡桩抗弯性能不足、支护结构水平位移过大、锚固体系失效等问题,要保证基坑延深开挖后的安全稳定,必须对护坡桩增设支点,增加支护力。根据设计变更要求及施工现场实际条件,对多种加固支护方案进行比选,最终选用对护坡桩增设锚索的方案进行延深基坑的预加固。采用数值方法模拟分析上述加固方案后的基坑延深开挖力学行为,预测基坑及支护结构的变形情况,并与现场监测数据进行对比分析。结果表明,基坑延深开挖预加固支护方案合理有效,表明该方法对于类似工程的设计优化及现场施工具有重要的参考意义。     

A note on the useable dynamic range of accelerographs recording translation

Since the late 1970s, the dynamic range and resolution of strong motion digital recorders have leaped from 65 to 135 dB, opening new possibilities for advanced data processing and interpretation. One of these new possibilities is the calculation of permanent displacement of the ground or of structures, associated with faulting or with non-linear response. Proposals on how permanent displacements could be recovered from recorded strong motion have been published since 1976. The analysis in this paper concludes that permanent displacements of the ground and of structures in the near-field can be calculated provided all six components of strong motion (three translations and three rotations) have been recorded, and the records are corrected for transducer rotation, misalignment and cross-axis sensitivity.