基于不同地面特性的混凝土框架结构的抗震性能评估

基于3层普通抗震混凝土框架结构,采用能力谱法评估了矩形框架结构的抗震性能,从实验结果中获取能力曲线,并利用在地面特性条件下的各站记录的地震地面运动建立需求曲线。评估结果表明,3层混凝土框架可以抵抗地面条件为1和2的所有地震带A,B,C,D和E的地震荷载;对于地面条件3,混凝土框架在地震带A,B,C和D中的实验结果令人满意;对于地面条件4,混凝土框架只对地震带A和B有效。     

基于多项式拟合均匀荷载面曲率曲线的结构损伤识别方法

为仅利用结构损伤状态的柔度矩阵对结构进行损伤程度识别,先对损伤状态的均匀荷载面曲率曲线进行最小二乘法拟合。根据曲率曲线差判断结构的损伤位置,对损伤位置的点进行剔除后,再利用未损伤位置上的点进行局部最小二乘法拟合,代替损伤前的均匀荷载面曲率曲线,用于结构的损伤定位与定量。通过一简支梁数值算例,先以理论的二次多项式进行拟合,考虑单损伤和多损伤的情况,进行损伤识别分析,再分析多项式次数、测点数目以及不同噪声水平对损伤定量精度的影响。结果表明:在一定范围内,次数越高拟合误差越小,但差别不明显,采用理论的二次多项式拟合即可满足结构损伤识别要求,无噪声的情况下,测点数目减半不影响损伤识别的精度,该方法具有一定的抗噪声能力。     

砂土中单桩静载室内模型试验及颗粒流数值模拟

通过自行设计的可视化模型箱,进行了单桩静载室内模型试验,考虑了不同桩径、不同土体密实度等影响因素,研究了单桩的沉降模式、桩侧摩阻力和桩端阻力的发挥性状及随沉降的发展模式,并通过拍摄跟踪和图像处理技术,研究了桩端和桩周土体的孔隙率的变化规律;对二维颗粒流程序进行开发,模拟了单桩静载过程中桩端阻力和桩周土体孔隙率的变化情况。结果表明,颗粒流数值模拟能够较好地模拟单桩静载过程,研究成果进一步揭示了单桩静载过程的宏细观机制。     

Development of the cyclic p–y curve for a single pile in sandy soil

Pile foundations that support transmission towers or offshore structures are dominantly subjected to cyclic lateral load induced by wind and waves. For a successful design, it is crucial to investigate the effect of cyclic lateral loads on the pile behavior that is loaded laterally. Although the p–y curve method is generally utilized to design the cyclic laterally loaded pile foundations, the effect of cyclic lateral loads on the pile has not been properly implemented with the p–y curve. This reflects a lack of consideration of the overall stiffness change in soil–pile interaction. To address this, a series of model pile tests were conducted in this study on a preinstalled aluminum flexible pile under various sandy soil conditions. The test results were used to investigate the effect of cyclic lateral loads on the p–y behavior. The cyclic p–y curve, which properly takes into account this effect, was developed as a hyperbolic function. Pseudo-static analysis was also conducted with the proposed cyclic p–y curve, which showed that it was able to properly simulate cyclic laterally loaded pile behavior in sandy soil.     

Behavior of soil plugs in open‐ended model piles driven into sands

Calibration chamber tests were conducted on open‐ended model piles driven into dried siliceous sands with different soil conditions in order to clarify the effect of soil conditions on load transfer mechanism in the soil plug. The model pile used in the test series was devised so that the bearing capacity of an open‐ended pile could be measured as three components: outside shaft resistance, plug resistance, and tip resistance. Under the assumption that the unit shaft resistance due to pile‐soil plug interaction varies linearly near the pile tip, the plug resistance was estimated. The plug capacity, which was defined as the plug resistance at ultimate condition, is mainly dependent on the ambient lateral pressure and relative density. The length of wedged plug that transfers the load decreases with the decrease of relative density, but it is independent of the ambient pressure and penetration depth. Under several assumptions, the value of earth pressure coefficient in the soil plug can be calculated. It gradually reduces with increase in the longitudinal distance from the pile tip. At the bottom of the soil plug, it tends to decrease with increase in the penetration depth and relative density, and to increase with the increase of ambient pressure. This may be attributed to (1) the decrease of friction angle as a result of increase in the effective vertical stress, (2) the difference in the dilation degree of the soil plug during driving with ambient pressures, and (3) the difference in compaction degree of soil plug during driving with relative densities. Based on the test results, an empirical equation was suggested to compute the earth pressure coefficient to be used in the calculation of plug capacity using one‐dimensional analysis, and it produces proper plug capacities for all soil conditions.     

自重湿陷性黄土地区桩基设计探讨

根据自重湿陷性黄土的特点、《湿陷性黄土地区建筑规范》（GB50025—2004）和《建筑桩基技术规范》（JGJ94—94）中关于桩基设计的对比分析，通过自重湿陷性黄土场地工程实例分析计算，依据负摩擦产生的机理——中性点理论，论述了自重湿陷性黄土场地中桩基设计应考虑中性点，而不应全部计入负摩阻的观点。     

极限荷载作用下临近基坑c-土地基的破坏模式

与地面水平时地基土体的对称破坏模式不同,临近基坑（边坡）地基土体的破坏模式呈现明显的非对称性.利用FLAC-3D数值模拟技术,研究了在竖向极限荷载作用下临近基坑c-ψ土地基不同工况时的破坏模式,得出了与J.Graham所假设的边坡附近无黏性土地基破坏模式相一致的结论.最后将数值模拟结果与大尺寸模型试验数据以及J.Graham的基于应力特征线法的非对称滑动破坏模式的地基承载力理论解进行了分析对比.结果表明,采用叠加计算方法得到的承载力系数Nγq偏于安全.     

打滑地层新型孕镶金刚石钻头

在分析打滑地层特点的基础上,指出了钻进该地层所存在的问题,提出了用于打滑地层钻进的新型孕镶金刚石钻头的设计思路,在钻头工作层中采用主、辅两种磨料,并对这两种磨料的工作机理、处理工艺以及该新型钻头的制造进行了阐述.钻头的室内钻进试验结果表明:在钻进极坚硬致密的锆刚玉时,相对于普通金刚石钻头,新型孕镶金刚石钻头的钻进时效提高1.93倍,平均磨损量增加38%,具有高时效、相对寿命长的优点,是打滑地层钻进的理想钻头.     

车辆荷载作用下隔震沟隔震效率影响因素分析

基于动力学基本方程,运用有限单元法（FEM）和Newmark隐式积分方法,对隔震沟对车辆荷载（FWD荷载）引起的地基振动的隔震效率的影响因素进行了弹塑性数值分析。考虑到人工边界上波反射对计算结果的影响,分别用有限单元和半无限单元离散计算区域内部和边界,分析中主要考虑了隔震沟的位置、深度、宽度三个主要影响因素,基于计算结果总结出其影响规律。