高钛重矿渣混凝土破坏机理及数值模拟

进行了高钛重矿渣混凝土和普通混凝土配合比试验设计,分别制作了4组混凝土立方体试块和棱柱体试块并进行强度测试,通过PFC离散元软件标定了高钛重矿渣混凝土与普通混凝土试件的细观力学参数,模拟了高钛重矿渣混凝土和普通混凝土棱柱体试件受压破坏,分析了高钛重矿渣混凝土棱柱体试件破坏现象和破坏机理。研究结果表明,高钛重矿渣骨料内部的孔洞会削弱骨料的强度;高钛重矿渣骨料的粗糙表面会提高界面过渡区的粘结强度;高钛重矿渣混凝土破坏形态与普通混凝土破坏形态不一致,高钛重矿渣混凝土破坏时形成的破坏面会穿越骨料与硬化砂浆,而普通混凝土破坏时形成的破坏面会沿着界面过渡区穿越硬化砂浆。     

结构面岩体爆破破坏机理探究

岩体多属于各向异性的复杂不连续体。岩体中主要结构面在爆破时,会对岩石的破坏和最终的爆破效果产生影响。总结了结构面岩体爆破破坏机理的研究现状,并从应力波传播、岩体破坏方式等方面研究了结构面岩体爆破的影响。在研究结构面岩体爆破破坏作用机理的基础上,提出改善爆破效果的技术措施,供同类型矿山参考。     

采场顶板岩层塑性破坏机理与塑性分析

本文运用梁的塑性变形理论,对采场直接顶板岩层进行了塑性破坏分析,并据此建立了岩层梁处于极限承载状态时的数学模型;在分析模型的基础上,提出了相应的顶板维护措施。模型的建立对采场结构与支护设计有一定的指导意义。     

复吹溅渣转炉炉衬破坏机理初探

介绍了实施溅渣护炉后转炉的炉衬破坏机理及危害,提出了解决办法及思路.     

梅山铁矿盲竖井破坏机理及防治

针对梅山铁矿盲竖井的特点，把围岩作为位移计算的关键，利用弹塑性理论及数值分析，对盲竖井井壁位移进行分析计算，并对井壁变形进行了现场实测，提出了井筒破坏的机理及控制的有关措施。     

浅析混凝土冻融破坏的机理和影响因素

混凝土的冻融破坏,是北方地区混凝土遭受雨雪浸湿后破坏的常见弊病.本文对混疑土冻融破坏的机理和影响因素进行了分析和阐述.     

矿区土地的破坏机理与治理措施研究

根据煤炭开采对地表的破坏规律,即下沉、倾斜、曲率、水平移动和水平变形,结合土地自身的属性,多角度分析了煤炭开采对土地的破坏机理,并提出了矿区土地的破坏等级划分和具体的矿区土地复垦治理措施.     

尾砂胶结充填体的破坏机理及其损伤本构方程

本文从细观力学角度，分析了尾砂胶结充填体的物理组成，单轴压缩时的破坏机理，并运用损伤力学方法建立了其本构方程。结果表明，理论曲线与实验曲线吻合得较好。     

贵州印江长坡村官船滑坡地质灾害变形破坏及机理分析

人类工程活动是诱发滑坡复活并导致滑坡整体或局部失稳破坏的重要因素之一,滑坡在西南山区极其发育,特别是在近年贵州经济社会高速发展的过程中,受工程活动和极端气候的影响滑坡更是频发。文章以贵州印江长坡村官船片区滑坡地质灾害为例,通过实地调查,对地质环境进行详细分析,阐述了该滑坡的基本特征和变形破坏机理,认为地质构造、地层岩性、岩体结构是该滑坡形成的主要原因,人类工程活动及降雨等诱发了滑坡的加剧变形。并对其提出“抗滑桩板墙+锚索+截（排）水+监测”的主动防护措施,以保障人民群众生命财产安全。     

短炭纤维增强C和SiC双基体材料的力学性能及破坏机理

以短炭纤维为增强纤维,以炭粉、Si粉和树脂为基体来源,采用温压—原位反应法制备C/C-SiC材料,研究该材料的力学性能及破坏机理。结果表明:C/C-SiC制动材料的纵向和横向抗弯强度分别为76 MPa和62 MPa,以韧性断裂为主,弯曲破坏表现为裂纹偏转、纤维桥接、纤维拔出和界面脱粘。纵向抗压强度达112 MPa,纵向压缩破坏表现为韧性断裂,以对角剪切破坏方式为主;横向抗压强度达84 MPa,横向压缩破坏主要表现为脆性断裂,以多层复合剪切破坏方式为主。材料的冲击韧性为3.1 kJ/m2。     

Damage Detection of FRP-Strengthened Concrete Structures Using Capacitance Measurements

In this study, a new concept for detecting air voids, water intrusion, and glue infiltration damages in fiber-reinforced polymers (FRPs)-strengthened concrete structures was developed. The concept, based on detecting the local dielectric permittivity variations, was employed to design coplanar capacitance sensors (CCSs) to detect such defects. An analytical model was used to introduce the sensor operation theory and analyze the influence of different sensor parameters on the output signals and to optimize sensor design. Two dimensional finite element (FE) simulations were performed to assess the validity of the analytical results and to evaluate other sensor design-related parameters. To experimentally verify the FE model, dielectric properties of various materials involved in FRP-strengthened concrete systems were measured. In addition, two concrete specimens strengthened with FRP laminates and containing preinduced defects were constructed and inspected in a laboratory setting. Good agreement was found between experimental capacitance measurements and those predicated by the FE simulations. The proposed CCS design, coupled with commercially available portable capacitance meters, would facilitate field implementation of the proposed technique for rapid inspection of FRP-strengthened concrete structures without the need for sophisticated data analyses usually required by other more expensive and time consuming methods.     

Nondestructive Assessment of Reinforced Concrete Structures Based on Fractal Damage Characteristic Factors

Nondestructive damage assessment of civil engineering structures has become a focus of increasing interest for recent decades. Its core is to extract effective damage characteristic information capable of reflecting structural damage status. In this study, fractal theory is adopted to extract the fractal damage characteristic factors of a reinforced concrete structure by characterizing its surface-crack distributions. The concentrated and even load spaces are generalized as applicable spaces for employing fractal-to-structural damage assessment. As demonstrated in the damage assessment of reinforced concrete beams under four-point bending and aged crossbeams of an operation bridge in a sluice, the surface-crack distributions of reinforced concrete structures exhibit monofractal character in the concentrated load space, and multifractal character in the even load space. The physical damage interpretations of the extracted monofractal and multifractal damage characteristic factors in the respective load spaces are then established by analyzing the correlations between the monofractal dimension and the natural frequency, and between the multifractal singular spectrum and the average carbonized depth and residual material intensity, respectively. The closely linear fitting relationships between the fractal quantities and traditional damage characteristic factors indicate that the fractal (i.e., monofractal and multifractal) quantities can serve as viable and novel damage characteristic factors in the online damage assessment of concrete structures. It is significant that the proposed fractal damage characteristic factors overcome some disadvantages of traditional damage characteristic factors in practical applications, and they extend the technique of fractal into the meaningful damage assessment of reinforced concrete materials.     

某工业构筑物混凝土基座腐蚀损伤检测

工业构筑物混凝土基座由于介质的不断侵蚀,造成了混凝土构件腐蚀损伤。需对此类混凝土结构进行检测,确定其腐蚀损伤程度,为后续隐患治理提供技术依据。这也是加固维修前的必要工作。总结了工业构筑物混凝土结构腐蚀损伤检测内容、检测方法,对类似因工业介质侵蚀的混凝土结构工程的检测鉴定具有借鉴意义。     

Use of Microwaves for Damage Detection of Fiber Reinforced Polymer-Wrapped Concrete Structures

Jacketing technology using fiber reinforced polymer (FRP) composites is being applied for seismic retrofit and rehabilitation of reinforced concrete (RC) columns designed and constructed under older specifications. In this study, the authors develop an electromagnetic (EM) imaging technology for detecting such damage as voids and debonding between the jacket and the column, which may significantly weaken the structural performance of the column otherwise attainable by jacketing. This technology is based on the reflection analysis of a continuous EM wave sent toward and reflected from layered FRP–adhesive-concrete medium: Voids and debonding areas will generate air gaps which produce additional reflections of the EM wave. In this study, dielectric properties of various materials involved in the FRP-jacketed RC column were first measured using a plane-wave reflectometer. The measured properties were then used for a computer simulation of the proposed EM imaging technology. The simulation demonstrated the difficulty in detecting damage by using plane waves, as the reflection contribution from the voids and debonding is very small compared to that from the jacketed column. In order to alleviate this difficulty, dielectric lenses were designed and fabricated, focusing the EM wave on the bonding interface. Finally, three concrete columns were constructed and wrapped with glass–FRP jackets with various voids and debonding conditions artificially introduced in the bonding interface. Using the proposed EM imaging technology involving the especially designed and properly installed lenses, these voids and debonding areas were successfully detected. This technology can be used to assess the jacket bonding quality during the initial jacket installation stage and to detect debonding between the column and the jacket caused by earthquake and other destructive loads.     

火灾后损伤混凝土结构构件检测鉴定与评级探讨

随着火灾事故的不断增加,火灾后导致建筑结构构件产生不同程度损伤,因此,针对火灾后建筑物的检测鉴定是必要的。《火灾后建筑结构鉴定标准》中虽然有混凝土结构检测鉴定评级,但是是初步评级,无法对其他检测内容进行评级。为此笔者利用若干次火灾后检测鉴定工程实践,并根据现行国家相关鉴定规范和相关研究成果,有针对性的提出了火灾后受损伤混凝土结构构件鉴定评级标准,解决了火灾后受损伤混凝土结构构件的分项评级和综合评级问题。     

Evaluating Safety of Concrete Gravity Dam on Weak Rock: Scott Dam

Scott Dam is owned and operated by Pacific Gas & Electric Co. (PG&E) as part of the Potter Valley Project. Although it is an unimpressive concrete gravity dam [233 m (765 ft) long with maximum water surface 33.4 m (110 ft) above tailwater], the dam has unusually complex and weak foundation rocks; this condition caused design changes during construction, numerous subsequent special investigations, and several corrections and additions. A main stumbling block to clarification of the dam safety issue for Scott Dam has always been difficulty in characterizing the foundation material. This paper discusses an approach to this problem as well as how the safety of the dam was subsequently confirmed, following a comprehensive program of research, investigations, and analysis from 1991 to 1997.     

Case Study: Dillon Dam Trashrack Damage

In 1986 the trashracks on the intake to the outlet works at Dillon Dam in Colorado were damaged due to filling the intake tunnel too rapidly. As the air from the tunnel was discharged through the intake structure, high velocities displaced two horizontal trashracks and removed one vertical trashrack from its guides. This damage was discovered through an underwater inspection in 1996. The addition of an air vent and the establishment of a filling procedure provided a solution to the problem. The quantity of air in the intake tunnel was reduced through the installation of a 102 mm (4 in.) diam air valve and 63.5 mm (2??in.) vent hole in the crown of the intake tunnel at the control tower. Since the vent could not remove all the air in the tunnel, the tunnel was filled by opening the emergency gate 7.9 mm ( in.) and letting the conduit fill over a 12 h period.     

Anisotropic Damage Model for Concrete

In this paper, a damage constitutive model accounting for induced anisotropy and bimodular elastic response is applied to two-dimensional analysis of reinforced concrete structures. Initially, a constitutive model for the concrete is presented, where the material is assumed as an initial elastic isotropic medium presenting anisotropy and bimodular response (distinct elastic responses, whether tension or compression stress states, prevail) induced by damage. Two damage tensors govern the stiffness under prevailing tension or compression stress states. Criteria are then proposed to characterize the dominant states. Finally, the proposed model is used in plane analysis of reinforced concrete beams to show its potential for use and to discuss its limitations.     

Slip-Form Application to Concrete Structures

Because of superior speed and productivity, slip forms were extensively utilized as a potential formwork candidate in constructing concrete structures for the past few decades. Typical projects that employ this formwork technique are: Core of high-rise buildings, silos, telecommunication towers, cooling towers, heavy concrete offshore platforms, etc. The research presented in this paper aims at studying slip-form application to cores and silos, assessing its productivity, and determining its appropriate speed as well as auxiliary resource combinations. Simulation models are developed in which the potential control units in a slip-form system are described for cores and silos. Data are collected from several case study projects. A set of charts has been developed to predict productivity considering different stoppages, core cross section area, slipping (jacking) rate, and concrete placing methods. These charts play an essential role in managing slip-form application to cores and silos. Results show that the developed simulation models predict the productivity of case study projects with 99.70 and 99.30% accuracy for cores and silos, respectively. The presented research is relevant to both researchers and practitioners. It provides practitioners with charts that assist in scheduling and managing the required resources for slip-form application. In addition, it provides researchers with simulation models and framework for implementing slip forms to core and silo construction.