覆盖型岩溶地面塌陷防治与应急处置

覆盖型岩溶地面塌陷是覆盖型岩溶区可溶岩上覆盖层中部分土颗粒在外部因素触发下向岩溶通道和(或)溶洞中运移,导致的土体变形而产生的地面反应。土体是地面塌陷的主体,岩溶通道和(或)溶洞为土颗粒运移和储存提供了条件,外部因素通过水的不良作用、外加荷载和土洞顶板抗力降低等方式触发地面塌陷。地面塌陷的预防应采取控制触发因素、适当的工程措施以及重点监测与群测群防相结合的措施。地面塌陷的治理应根据沙漏型、土洞型和泥流型3个塌陷机理修复有缺陷的岩溶地质结构。地面塌陷应急处置应在突变、缓变和暂时稳定阶段分别采取应急自救、外界救援和工程处理措施。     

某工程冲孔灌注桩充盈系数偏高原因分析及对策

冲孔灌注桩近年在广东等沿海地区高层建筑和桥梁基础中应用较广泛,但施工过程中常会遇到因混凝土充盈系数偏高而导致工程成本增加、利润降低的问题.文中分析某基础工程施工冲孔灌注桩混凝土充盈系数偏高的原因,探讨其解决对策,及其实施效果和经济、社会效益.     

Mechanism of evolution of stress–structure controlled collapse of surrounding rock in caverns: A case study from the Baihetan hydropower station in China

During the excavation of the underground powerhouse in the Baihetan hydropower station, which is currently still under construction, stress–structure controlled collapse has occurred frequently. In order to study the mechanism behind the evolution of this kind of collapse, an in situ experiment involving microseismic (MS) monitoring was carried out in the left main/auxiliary powerhouse. In this paper, the spatiotemporal characteristics of stress–structure controlled collapse are summarized and presented. A field survey, scanning electron microscopy and MS monitoring have been used to investigate a typical stress–structure controlled collapse that occurred during the monitoring period. These methods provided a consistent set of results, namely, that tensile fracturing is the rock-mass fracturing mechanism that is most active during the process of evolution of stress–structure controlled collapse. In addition, the evolution of the microseismicity during the development of the studied collapse was also obtained. The results provide a direct case history that will assist the prediction and support of stress–structure controlled collapse disasters and contribute to excavation of deeply-buried caverns in the field.     

Mesozoic contraction deformation in the Yanshan and northern Taihang mountains and its implications to the destruction of the North China Craton

Mesozoic contraction deformation in the Yanshan and Taihang mountains is characterized by basement-involved thrust tectonics,basement-cored buckling anticlines and ductile thrust and nappe tectonics.Most of these deformations are orientated west-east,west-northwest and northeast to north-northeast.The contraction deformations began in the Permian,continued through the Triassic and Jurassic and terminated in the Early Cretaceous,and constitute an important part of the destruction of the North China Craton.It...     

杂填土条件下混凝土灌注桩塌孔的预防措施

对塌孔原因进行了分析，提出了避免群机近距离作业、调整泥浆比重、加干红土造浆护壁等预防混凝土塌方的措施，达到了比较好的效果，解决了在杂填土层上塌孔的问题.     

Generalised capacity curves for stability and plasticity: Application and limitations

In recent decades, the resistance of a structure has been thought of as well defined by the outcome of a geometrically and materially nonlinear analysis with explicitly modelled imperfections (GMNIA). But when this is the only analysis that is performed on a complex structural system, it is sometimes difficult to interpret the result. The outcome must be seen in the context of those from simpler analyses, which can define appropriate reference quantities.     

Effects of eccentric steel bracing systems on seismic fragility curves of mid-rise R/C buildings: A case study

In this study, the seismic reliability of a mid-rise reinforced concrete (R/C) building retrofitted using eccentric steel braces is investigated through fragility analysis. As a case study, a six storey mid-rise R/C building was selected. The design of selected sample building was made with reference to 1975 version of the Turkish Seismic Code. The effectiveness of using different types of eccentric steel braces in retrofitting the building was examined. The effect of distributing the steel bracing over the height of the R/C frame on the seismic performance of the retrofitted building was studied. For the strengthening of the original structure, D, K, and V type eccentric bracing systems were utilized and each of these bracing systems was applied with four different spatial distributions in the structure. For fragility analysis, the study employed a set of 200 generated earthquake acceleration records compatible with the elastic code design spectrum. Nonlinear time history analysis was used to analyze the structures subjected to this set of earthquake accelerations generated in terms of peak ground accelerations (PGA), whilst monitoring four performance limit states. The fragility curves were developed in terms of PGA for these limit states; namely: slight, moderate, major, and collapse with lognormal distribution assumption. The improvement of seismic reliability achieved through the use of D, K, and V type eccentric braces was evaluated by comparing the median values of the fragility curves of the existing building before and after retrofits. As a result of this study, the improvement in seismic performance of this type of mid-rise R/C building resulting from retrofits by different types of eccentric steel braces was obtained by formulation of the fragility reduction.     

Response modification factor of elevated water tanks with reinforced concrete pedestal

A probabilistic method based on FEMA P695 is employed for validating the response modification factor of reinforced concrete pedestals in elevated water tanks. In the current codes and standards, the response modification factor of elevated water tanks is mainly based on engineering judgement. Ten models of elevated water tanks with different tank sizes and pedestal heights are selected for the investigation. Initially, the prototypes are designed based on the current codes and standards. Next, the finite element models of the prototypes are developed. By performing incremental dynamic analysis, the probability of collapse for each prototype is calculated under different seismic loading conditions and system uncertainties. The results of the study validate and confirm the current response modification factor values and show that the tank size has a significant effect on the nonlinear seismic response behaviour of elevated water tanks. In addition, it is revealed that heavy tank sizes that are designed in accordance with codes and guidelines are more vulnerable under seismic loading compared with light and medium tank sizes.     

超高层建筑受飞机撞击后坍塌过程模拟分析

为了解飞机撞击超高层建筑并引起油箱爆炸所致建筑坍塌的特征，使用基于颗粒流的PFC 3D分析程序对其撞击、爆炸及坍塌过程进行模拟。以核心筒-框架结构的超高层建筑为研究对象建立了飞机撞击模型，并引入三维爆炸模型。设计飞机撞击速度为900 km/h，撞击高度为建筑正面250 m和100 m处。对两种高度撞击后的建筑坍塌过程进行模拟，结果表明：两种坍塌都包含撞击和爆炸两种作用，直接撞击作用并不能造成建筑的坍塌，爆炸是建筑坍塌的直接原因。但两者坍塌至稳定的时间不同，撞击高度250 m所用时间为151.28 s，而撞击高度100 m所用时间为196.08s；最终残骸的分布不同，前者分布于撞击反方向，后者分布于四周；坍塌过程不同，前者为倒塌，后者为坐塌,即上部建筑结构重力作用导致下部结构坐塌破坏；最终坍塌结果不同，前者下部建筑结构完好，后者完全破坏。     

钢筋混凝土烟囱拆除切口中脊高度的计算

拆除钢筋混凝土烟囱时,拆除切口中脊高度的合理选择是拆除成功的重要因素。根据钢筋混凝土烟囱在倒塌至拆除切口闭合时,倾覆力矩大于薄弱面的抵抗力矩的原则来确定钢筋混凝土烟囱定向倒塌的条件及拆除切口中脊高度对其定向倒塌的影响。在考虑烟囱是变截面筒体的情况下,通过对上述条件的分析,得到拆除切口中脊高度的计算公式,与烟囱的结构尺寸、拆除切口薄弱面位置、拆除切口所对圆心角、余留支撑体轴筋承受的拉力有关,不仅仅与烟囱的壁厚有关,与传统的经验公式是有较大差别的。