汽车质量和速度对上跨桥桥墩撞击特性的影响

基于车桥撞击事故的严重性,文中开发一种新颖的重型卡车等效模型。通过G1011 K302+095分离立交桥受撞桥墩验证计算模型的可靠性,采用数值模拟方法分析重型卡车的载重和撞击速度对撞击力和桥墩应力的影响。研究结果表明,随着卡车质量和撞击速度的增加,撞击力峰值增大。受撞桥墩应力较高的区域集中在桥墩根部和撞击位置,与桥墩轴线成45°的斜向贯通裂缝。文中的研究揭示了卡车的质量和撞击速度对桥墩撞击力和Mises应力的影响机理,为桥墩的防撞设计提供了新的理论基础。     

桥梁地震碰撞的三维撞击模型及非线性响应分析

为合理模拟地震时相邻桥梁间发生的碰撞响应,提出适用于桥梁多维碰撞响应分析的三维Kelvin接触-摩擦撞击模型,即将Kelvin-Voigt模型和库伦摩擦模型相结合,通过一个摩擦元件来模拟发生纵向碰撞后,接触点间的横向和竖向的相对摩擦作用,以真实地模拟结构接触位置的三维撞击行为。进而将该三维撞击模型引入所建立的结构精细化模拟分析平台FENAP中,与纤维梁柱单元模型良好结合,实现对桥梁的多维碰撞响应分析。通过对一钢筋混凝土连续梁桥在双向地震作用下的碰撞响应分析,结果表明:所提出的三维撞击模型能够模拟邻梁间的纵向和横向碰撞响应;纵向碰撞对刚度较大的桥梁影响较大,会增大墩底剪力和墩顶位移,加剧桥墩的塑性发展;横向碰撞对桥梁的碰撞响应影响较大,不可忽略。     

事故型撞击作用下钢筋混凝土安全壳防冲切计算

根据事故型撞击下钢筋混凝土壳的变形,建立单自由度体系的刚塑性模型,研究安全壳局部贯穿后塞块的动力响应。该模型中,将纵向钢筋设想为具有相应强度特征和应变特征的钢筋膜,并考虑了安全壳所有结构要素混凝土、箍筋、纵筋和钢衬套的影响作用。根据单自由度模型,建立运动方程。采用数值分析来考虑纵向钢筋含量与刚衬套厚度对事故型撞击下安全壳动力响应的影响。     

横向撞击荷载作用下压弯H型钢柱的破坏模式和动态响应

钢结构受碰撞冲击的过程是一个复杂的非线性过程。采用Abaqus/Standard模拟H型钢压弯柱的平衡状态,再以此为初始状态在Abaqus/Explicit模块中执行横向撞击的数值模拟,通过考察系统能量转化关系和沙漏能占比验证有限元模型的合理性,研究了压弯柱受横向撞击的破坏模式并进行了动态响应的参数分析。结果表明:压弯H型钢柱受横向撞击的破坏是翼缘局部失稳引起的整体失稳破坏,是否破坏主要取决于撞击动能;撞击动能、撞击质量、撞击速度、撞击位置距固端约束的距离和轴压力的增加都会加剧H型钢柱的动态响应;存在减弱压弯柱动态响应的轴压力-弯矩荷载组合,但随着叠加弯矩值的增大,柱的变形开始加剧直至失稳破坏。     

钢骨混凝土桥墩撞击抗剪强度计算模型

为了研究钢骨混凝土桥墩的抗撞击性能,进行5根钢骨混凝土桥墩和1根钢筋混凝土桥墩水平撞击试验。试验结果表明:内置钢骨的加入对混凝土桥墩斜裂缝具有较好的抑制作用;钢骨混凝土桥墩相比钢筋混凝土桥墩具有较高的抗撞击强度。基于修正压力场理论,考虑应变率效应,分析受压区混凝土以及横向钢骨对撞击抗剪强度的影响,提出钢骨混凝土桥墩撞击抗剪强度计算模型,该模型通过斜压应力角θ和平均纵向应变εx考虑不同因素对撞击抗剪强度的影响。将不同计算模型与试验结果进行对比分析,本文模型计算结果与试验结果误差为13.10%,与试验结果较符合,可为钢骨混凝土桥墩的抗撞击设计提供参考。     

受火后内配型钢方钢管混凝土构件抗侧向撞击性能试验研究

为了研究火灾后内配型钢钢管混凝土构件的抗侧向撞击性能，进行了9个受火后构件的侧向撞击试验，考察了受火时间、撞击高度、边界条件对构件破坏形态和撞击响应的影响。分析了受火后构件的温度场、撞击过程、破坏形态、撞击力时程、挠度发展和能量吸收，基于等效塑性铰模型给出侧向撞击下构件跨中最大挠度的简化计算方法。试验结果表明：火灾后内配型钢方钢管混凝土构件在侧向撞击下发生整体弯曲破坏，表现出较好的抗撞性能。与未受火内配型钢的构件相比，受火60 min后构件所受撞击力平台值下降23.9%,跨中最大挠度和撞击持续时间分别增大38.2%和41.5%。随着撞击高度从1.0 m增加至2.6 m,受火后构件跨中最大挠度增加114.7%,撞击力平台值提高14.2%。在钢管混凝土中配置型钢可以显著提高构件所受撞击力平台值，减小构件的破坏程度和跨中挠度，内配型钢对受火后构件的抗撞击性能提升更显著。     

钢框架结构竖向撞击响应数值模拟分析

多层钢框架结构在工程中得到较为广泛的应用。文中通过建立有限元数值模型,对竖向撞击荷载作用下多层钢框架结构进行数值模拟,分析其在撞击荷载作用下的结构响应,并分析撞击速度和撞击物质量对结构响应的影响。结果显示,竖向撞击下,多层钢框架结构受到一个极大的瞬时撞击力,受撞击处发生明显的振动,并产生较大的塑性残余变形。随着撞击速度或撞击物质量的增大,撞击力峰值随之近似呈线性增大,受撞处变形也随之增大,且增长趋势逐渐增强。     

某石质牌楼受撞击后主体结构应力水平分析

某石质牌楼的雀替受到车辆撞击破坏并脱落,需要对其主体结构撞击后的应力水平进行分析。本文通过试验确定了牌楼石材材料特性,建立了牌楼结构的三维实体有限元模型。对实体结构进行了动力特性检测,将结构基频实测结果与模型模拟结果进行了对比,校核了有限元模型的精度。分析了牌楼雀替受撞击后达到石材抗拉强度极限值时,牌楼主体结构的应力状态。分析结果表明,牌楼主体结构在雀替撞击破坏的情况下,未达到石材抗拉强度极限值。     

岩石撞击过程中的升温机理分析

分析了岩石在撞击过程中的能量转化及其升温机理,推导出了理论升温公式。同时,采用TVS–2000MKII高精密度红外热成像系统,测量了大理岩和砂岩在撞击过程中的升温值,并给出了其升温值与岩石质量和撞击角度的关系曲线。最后,得出了岩石撞击过程中的升温的主要因素为:岩石破坏时释放热量、撞击时摩擦生热和岩石受压缩而升温等三个方面,同时通过实验进行了验证。     

车辆撞击下桥墩动力响应与撞击荷载研究

为研究城市桥墩抗撞性能,采用LS-DYNA有限元软件建立精细化车辆-桥墩碰撞模型,分析桥墩动力响应与撞击荷载。该模型考虑了应变率效应对钢筋与混凝土非线性材料力学性能的影响。基于40个车-桥碰撞工况,研究了撞击速度、撞击质量对撞击荷载和桥墩变形的影响,分析了撞击能量和桥墩破坏模式之间的关系。根据40个撞击荷载样本,提出撞击荷载经验公式与半正弦荷载时程曲线,用来计算撞击荷载峰值与反应时撞击荷载时程。将撞击荷载峰值分别与3种等效静力荷载和《公路桥涵设计通用规范》荷载限值进行对比。结果表明:规范中撞击荷载限值偏于不保守;采用等效静力荷载作为撞击荷载对城市桥墩进行抗撞评估偏于不安全。     

某工程基础大体积混凝土施工工艺

结合某工程基础大体积混凝土的施工工艺,从开始的施工部署、大体积混凝土的施工方法、大体积混凝土温度的监测等等方面对基础大体积混凝土的施工工艺进行了较为详细的介绍,以供从事大体积施工工艺的人员参考借鉴。     

Prediction of strength and deformability of an interlocked blocky rock mass using UDEC

The accurate prediction of strength and deformability characteristics of rock mass is a challenging issue.In practice,properties of a rock mass are often estimated from available empirical relationships based on the uniaxial compressive strength(UCS).However,UCS does not always give a good indication of in situ rock mass strength and deformability.The aim of this paper is to present a methodology to predict the strength and deformability of a jointed rock mass using UDEC(universal distinct element code).In the study,the rock mass is modelled as an assemblage of deformable blocks that can yield as an intact material and/or slide along predefined joints within the rock mass.A range of numerical simulations of uniaxial and triaxial tests was conducted on rock mass samples in order to predict the equivalent mechanical properties for the rock mass under different loading directions.Finally,results are compared with the deformability parameters obtained by analytical methods.     

节理岩体强度参数损伤张量模型多维估算

Hoek-Brown强度准则因可较好实现对节理岩体稳定性分析及参数估算,正逐渐被广泛应用于岩体工程评价中。在对其进行力学参数估算时,采用一维损伤因子D将岩体视为各向同性损伤材料进行分析,而实际上,节理岩体损伤呈现为多维度特征,对其整体损伤效应予以准确把握有赖于建立多维度损伤表示方法。本文基于Hoek-Brown强度准则实现对岩体强度参数估算,充分考虑损伤效应的多维度特征,建立损伤张量表示模型,并结合节理裂隙空间分布参数,实现对损伤张量因子确定化表示;基于节理岩体损伤张量表示结果,结合某露天铜矿边坡节理岩体统计窗测试结果,实现了对强度参数系统估算。损伤张量模型具有表示节理岩体空间损伤特征,可较好用于对节理岩体强度参数的多维度估算。     

Investigation of fracture behaviour during rock mass failure

The main characteristic behaviour of rock mass fractures are studied. Their importance in the application and investigation of rock mass failure is demonstrated through some preliminary investigation of rock mass fracture mechanics by the authors. Firstly, in the study of rock fracture features, the mechanisms and non-linear phenomenon of a fragmented belt of rock fracturing have been investigated. Several new ideas can be used to construct a new system of rockmass fracture mechanics. Secondly, in the investigation of rock mass structure controlled rock mass fracturing, the importance of true mixed mode fracturing is emphasized. A primary criterion to predict the propagation of rock mass cracks has been established. Thirdly, in the investigation of non-singular stress effects on rock mass fracture, a new fracture criterion for the generalized crack opening displacement of rock is proposed. This can be used to analyze the influence of the normal stress and the crack orientation on the fracturing process in a rock mass. Finally, the rock mass fracture mechanics investigation and methodology was used to analyze the stability of the Mabukan high slope in the upper reaches of a large hydro-power station in the south-west of China. It is shown that the results of this study have created a more solid foundation for the application of rock mass fracture mechanics to rock engineering.     

Coupling of thermal mass and natural ventilation in buildings

The coupling of thermal mass and natural ventilation is important to passive building design. Thermal mass can be classified as external thermal mass and internal thermal mass. Due to great diurnal variation of ambient air temperature and solar radiation intensity, heat transfer through building envelopes, which is called external thermal mass, is a complex and unsteady process. Indoor furniture are internal thermal mass, affecting the indoor air temperature through the process of absorbing and releasing heat. In this paper, a heat balance model coupling the external and internal thermal mass, natural ventilation rate and indoor air temperature for naturally ventilated building is developed. In this model, the inner surface temperature of building envelopes is obtained based on the harmonic response method. The effect of external and internal thermal mass on indoor air temperature for six external walls is discussed of different configurations including lightweight and heavy structures with and without external/internal insulation. Based on this model, a simple tool is developed to estimate the indoor air temperature for certain external and internal thermal mass and to determine the internal thermal mass needed to maintain required indoor air temperature for certain external wall for naturally ventilated building.     

大体积混凝土温度裂缝控制综合措施

分析了大体积混凝土温度裂缝的形态及原因,阐述了大体积混凝土的定义及其温度裂缝控制的基本方法,并结合具体工程实例研究了大体积混凝土温度裂缝控制的综合措施。强调大体积混凝土裂缝控制要想取得好的效果,必须“抗”与“放”结合,从多方面考虑,采用综合措施。     

结合结构面统计的侧向岩石压力计算方法

岩体抗剪强度取决于结构面分布及其性质,侧向岩石压力的计算常用岩体等效内摩擦角参数,而边坡规范中岩体等效内摩擦角的取值难以反映实际岩体结构面分布及其性质的影响。为确定合理的支挡结构侧向岩石压力值,提出对现场岩体结构面性质包括产状、隙宽、迹长、间距、粗糙度进行统计,进而结合现场结构面统计的蒙特卡洛随机模拟结果和RMR地质评价系统,对岩体结构面进行定量评价。利用评价结果和Hoek-Brown准则拟合得到岩体等效摩尔库伦强度参数,由此计算侧向岩石压力。通过与现有方法进行对比发现,采用本方法得到的岩体等效内摩擦角计算所得的侧向压力更符合实际。     

Critical heat flux and mass loss rate for extinction of flaming combustion of timber

The critical mass loss rate and critical heat flux for self-extinction of flaming combustion during steady-state burning of timber was measured in this study for a range of timber species. A vertical mass loss calorimeter was used to provide the external heat flux and to measure the mass loss of the timber samples. The results showed that the critical mass loss rate was dependent upon the timber species but did not show a clear dependency with the timber density. Critical mass loss rates and heat fluxes for self-extinction exist for each of the timber species tested for both the solid timber and cross laminated timber (CLT). Debonding of both the char layer and the individual lamella of the CLT caused increased mass loss rates, re-ignition after self-extinction and increased flame lengths. Both char and ply fall-off were observed.     

煤体振动方法防治冲击地压的机理研究

 研究了一种新的冲击地压控制方法, 即煤体振动方法的机理。在实验上, 采用分形几何方法, 研究了煤体在受振后裂隙的变化规律, 发现受振后煤体的分形维数增大, 表明煤体的裂隙增加, 且经过一定振动时间后, 分形维数趋于稳定; 研究了振动对煤体力学性质的影响, 发现受振后煤体的抗压强度、弹性模量和降模量降低, 且受振时间越长或初应力水平越高, 振动对煤体力学性质的影响越明显。应用采煤工作面和巷道冲击地压的分析结果, 从理论上证明了煤体受振后煤岩体的稳定性增加。     

Determination of geological strength index of jointed rock mass based on image processing

The geological strength index(GSI) system,widely used for the design and practice of mining process,is a unique rock mass classification system related to the rock mass strength and deformation parameters based on the generalized Hoek-Brown and Mohr-Coulomb failure criteria.The GSI can be estimated using standard chart and field observations of rock mass blockiness and discontinuity surface conditions.The GSI value gives a numerical representation of the overall geotechnical quality of the rock mass.In this study,we propose a method to determine the GSI quantitatively using photographic images of in situ jointed rock mass with image processing technology,fractal theory and artificial neural network(ANN).We employ the GSI system to characterize the jointed rock mass around the working in a coal mine.The relative error between the proposed value and the given value in the GSI chart is less than 3.6%.