Instability mechanism of mining roadway passing through fault at different angles in kilometre-deep mine and control measures of roof cutting and NPR cables

The angle α between the fault strike and the axial direction of the roadway produces different damage characteristics. In this paper, the research methodology includes theoretical analyses, numerical simulations and field experiments in the context of the Daqiang coal mine located in Shenyang, China. The stability control countermeasure of "pre-splitting cutting roof + NPR anchor cable"(PSCR-NPR) is simultaneously proposed. According to the different deformation characteristics of the roadway, the faults are innovatively classified into three types, with α of type I being 0°-30°, α of type II being 30°-60°, and α of type III being 60°-90°. The full-cycle stress evolution paths during mining roadway traverses across different types of faults are investigated by numerical simulation. Different pinch angles α lead to high stress concentration areas at different locations in the surrounding rock. The non-uniform stress field formed in the shallow surrounding rock is an important reason for the instability of the roadway. The pre-cracked cut top shifted the high stress region to the deep rock mass and formed a low stress region in the shallow rock mass. The high prestressing NPR anchor cable transforms the non-uniform stress field of the shallow surrounding rock into a uniform stress field. PSCR-NPR is applied in the fault-through roadway of Daqiang mine. The low stress area of the surrounding rock was enlarged by 3-7 times, and the cumulative convergence was reduced by 45%-50%. It provides a reference for the stability control of the deep fault-through mining roadway.

Dynamic Characteristics of a Curved Cable-stayed Bridge:Operational Modal Testing and FE Modeling

This paper summarizes the analytical and experimental dynamic analyses carried out to assess the actual dynamic behaviour of a curved cable-stayed bridge,recently erected in the commercial harbour of Porto Marghera ( Venice,Italy). Ambient vibration tests were carried out to determine the dynamic characteristics of the bridge and more than 20 modes were identified in the frequency range 0～10Hz. In the theoretical study,a 3D FE model of the bridge was developed using an integrated CAD-FEA approach; subsequently,the information obtained from the field tests,combined with simple manual tuning,provided a linear elastic model,accurately fitting the modal parameters of the bridge in its present condition.

Initial pre-stress finding procedure and structural performance research for Levy cable dome based on linear adjustment theory

The cable-strut structural system is statically and kinematically indeterminate. The initial pre-stress is a key factor for determining the shape and load carrying capacity. A new numerical algorithm is presented herein for the initial pre-stress finding procedure of complete cable-strut assembly. This method is based on the linear adjustment theory and does not take into account the material behavior. By using this method,the initial pre-stress of the multi self-stress modes can be found easily and the cal-culation process is simplified and efficient also. Finally,the initial pre-stress and structural performances of a particular Levy cable dome are analyzed comprehensively. The algorithm has proven to be efficient and correct,and the numerical results are valuable for practical design of Levy cable dome.

Initial Pre-stress Finding and Structural Behaviors Analysis of Cable Net Based on Linear Adjustment Theory

The tensile cable-strut structure is a self-equilibrate pre-stressed system.The initial pre-stress cal- culation is the fundamental structural analysis.A new numerical procedure was developed.The force density method is the cornerstone of analytical formula,and then introduced into linear adjustment theory;the least square least norm solution,the optimized initial pre-stress,is yielded.The initial pre-stress and structural performances of a particular single-layer saddle-shaped cable-net structure were analyzed with the developed method,which is proved to be efficient and correct.The modal analyses were performed with respect to various pre-stress levels.Finally,the structural performances were investigated comprehensively.

Test analysis of stress characteristics on reinforcing rock slope with group anchorage cable

To research the reinforcement effect of a rock slope with group anchorage cables and the stress characteristics of pre-stressed anchorage cables in the fractured surface, the rock slope calculated model of a wedge block within the double-slide face was established by using the finite difference software according to the actual slope project combined with indoor model test. The pre-stress loss rule of the anchorage cable and the distribution of axial force and the force-transferring mechanism of the anchorage cable were analyzed during simulation. Also, based on the displacement contour and the safety factor of the calculated results, the quantitative analysis for the reinforcement ef- fect of the rock slope with group pre-stressed anchorage cable was discovered. The results computed by the software conform with the data in the experiment, which can prove the effectiveness and correctness of parameter selection and model building. Keywords group anchorage reinforcement, rock slope, joint fissure, pre-stressed anchorage cable, stress characteristics

Cosserat Dynamic Modeling and Simulation of Mobile Cable on Satellite

Mainly for the problems that the configuration of the mobile cable on the satellite is very easy to change,the motion trajectory and dynamic characteristics of the cable can not be accu-rately predicted,which affects the laying quality seriously,the dynamic modeling and simulation of mobile cable on the satellite are carried out.On the basis of referring to the previous papers,the existing mathematical model is improved.The equations of the base vector of the cable section principal axis coordinate system with respect to the arc coordinate s,the distribution force of cable balance equation,the matrix expression of the base vector after the rotation motion transformation in the section principal axis coordinate system,the angular velocity of cable,the section elastic strain and velocity calculation equations are given,and the Cosserat dynamic modeling of the mobile cable is established.Finally,the dynamic simulation model of the mobile cable assembly of the kinematic mechanism is established,and the changes of the force and torque on the cable con-straint end are obtained,which provides a reference for the dynamic modeling and simulation of the mobile cable on satellite.

常泰长江大桥组合索塔锚固结构钢-混传剪构造足尺模型试验研究

常泰长江大桥索塔锚固结构采用钢箱-核芯混凝土组合结构,为研究该新型组合索塔锚固结构钢-混传剪构造的受力特性,进行钢-混传剪构造足尺模型试验研究。制作2个锚固结构足尺节段试验模型,通过压剪试验研究锚固结构的荷载~滑移曲线及应力、应变分布等受力特性,并通过有限元模型分析锚固结构的传力机理和各组件的内力分配比例,推导剪力钉剪力计算方法。结果表明:在2.14倍单索最大索力荷载作用下,锚固结构保持弹性状态,钢壁板未产生明显滑移,钢-混界面最大滑移不超过0.25 mm,该锚固结构中钢-混传剪构造至少具有2.14倍的安全系数;荷载作用下,剪力钉剪力从上至下逐渐增大,锚腹板附近底部3排剪力钉剪力较大,钢-混传剪构造至少存在剪力钉和界面摩擦力2种传剪机制,钢-混传剪构造的承载能力显著提高;钢-混传剪构造受力过程分为粘结力传力阶段和局部滑移阶段,剪力钉剪力分布不仅与沿剪切方向长度分布有关,也与荷载的大小线性相关。

缆线在铅垂面内弯曲的大变形曲线微分方程及其数值解法

针对民用与工业应用中经常用到的自然弯曲的软管和柔缆,归纳出5个共同特点,作为本文研究缆线的基本假设。从这些假设出发,根据受力和应力分析,首次推导了缆线在铅垂面内弯曲的大变形曲线方程。列出了多种端部约束条件下相对应的求解大变形曲线的方程组。证明了悬链线与纯弯曲线都是本文的特例。提出了获得数值解的递进法,并针对两端夹持约束的情形给出了具体算例。说明了存在多解的原因以及比较不同解稳定性的方法。

圆弧曲梁人行桥阻尼索减振研究

圆弧曲梁人行天桥在城市桥梁建设中得到了应用,曲线桥梁存在弯、扭耦合而更易在人行激励下发生大幅振动。为降低人行天桥的人致激励响应,该文提出了一种由阻尼器、复位弹簧并联后与主索串联而成的阻尼索装置,进行圆弧曲梁人行桥-阻尼索减振的理论分析与试验研究。首先,建立两端固支圆弧曲梁的振动微分方程,采用微分变换法获得曲梁面外振动的振型与特征频率;然后,采用模态分析法获得阻尼索为曲梁提供的附加阻尼比;最后,制作两端固支半圆弧曲梁模型,实测了阻尼索在不同的安装位置及不同阻尼器黏性系数下曲梁附加阻尼比。研究结果表明:阻尼索提供的圆弧曲梁附加阻尼比的理论分析结果与试验实测结果吻合;阻尼索可以大幅增加圆弧曲梁的附加阻尼比,很好地抑制曲梁的振动。

考虑嵌固段桩前土体弹塑性变形的锚索微型桩群计算模型研究

锚索微型桩群在中小型边坡治理及边坡紧急抢险工程中的应用越来越广泛,但现有的计算模型对嵌固段桩前土体塑性变形及桩侧土体受力变形连续性考虑较少。针对这一问题,首先根据锚索微型桩群加固土质边坡的特点,以潜在滑裂面位置为分界线,将微型桩群分为受荷段与嵌固段进行分析。对于受荷段,将桩间土简化为水平土弹簧,有效考虑桩间土力的传递作用;对于嵌固段,采用理想弹塑性p-y曲线分析桩-土相互作用。其次,将冠梁处预应力锚索简化为弹性支座,将其作用力转移至后排桩桩顶,再由桩顶冠梁重分配至各排桩桩顶处,从而达到对桩顶位移的约束作用。最后,以帕斯捷尔纳克(Pasternak)双参数地基梁法为基础,建立考虑嵌固段桩前土体弹塑性变形及桩侧土体受力变形连续性的锚索微型桩群有限差分计算模型,并迭代求解得到该结构的水平位移与内力。利用该计算模型分别对微型桩群与锚索微型桩群加固土质边坡进行算例计算,与试验、数值模拟结果对比分析,验证该模型的合理性,并探讨土体剪切刚度、锚索束及桩径对该锚索微型桩群水平位移与内力的影响。研究表明:嵌固段桩前土体塑性变形及桩侧土体受力变形连续性对微型桩的水平位移与内力有较大影响;随着锚索束的增加,桩身最大正弯矩及水平位移均不断减小,可通过增设锚索束达到控制桩身变形与内力的目的。

拉索高强钢丝疲劳寿命与疲劳裂纹萌生机理

高强钢丝作为桥梁拉索的核心受力构件,极易受到疲劳荷载和表面腐蚀的损伤,影响拉索的正常使用。本文通过研究影响高强钢丝疲劳寿命S‑N曲线的主要因素,给出拉索与高强钢丝的S‑N曲线和疲劳强度极限,并采用FORTRAN编写可记录疲劳累积损伤量的代码,内置于有限元软件的用户子程序中进行模拟分析,探究高强钢丝的疲劳裂纹萌生与扩展过程及疲劳寿命。结果表明:高强钢丝的疲劳寿命受应力范围和强度等级的影响程度较大,其余参数的影响效果相对较小;高强钢丝的裂纹萌生寿命约占总寿命的85%~97%,裂纹萌生寿命占比随着应力范围的增大而减小,且在高应力范围作用下裂纹扩展速度显著加快,裂纹扩展寿命占比随之减小。

高能脉冲磁弹仪器研制及其索力表征实验研究

针对在役桥梁钢索的索力检测需求,基于磁弹效应检测机理,首先,设计了便携式脉冲磁弹索力检测仪器,其可输出0~600 V电压可调、电流峰值高达60 A的高能尖峰脉冲信号,实现了对不同直径钢索的充分磁化,仪器主要包括上位机(含软件)、具有反馈控制的脉冲磁弹仪下位机和基于多芯线缆的改进磁弹传感器;其次,对公称直径17.8 mm的七芯钢绞线进行加载和卸载索力检测实验,实现了钢绞线的饱和磁化,磁弹传感器绕制效率是传统方法的8倍,分析了传统索力表征参量与索力之间的线性相关性;最后,在此基础上,提出一种索力表征参量--饱和磁导率μs,其线性拟合优度大于95%,且灵敏度(0.05)高于传统参量。通过对索力表征误差分析,该参量相较于传统参量在索力表征方面显示出较低的预测误差(3.7%)和迟滞误差(±1.54%)。该研究提出的参量可为脉冲磁弹法检测索力提供新的表征方法。

地震下三塔悬索桥主缆-鞍座摩擦滑移行为及其影响

三塔悬索桥中塔两侧主缆并未直接与锚锭连接,中塔处主缆的纵向约束较弱,地震下主缆-鞍座易发生显著的摩擦滑移。为了揭示三塔悬索桥中主缆-鞍座摩擦滑移及其对结构地震响应的影响规律,本文依托浔江大桥实际工程,建立了三塔悬索桥的非线性有限元模型,利用摩擦单元重现了主缆-鞍座界面的摩擦滑移行为,揭示了地震下主缆在边塔和中塔处的不同滑移变位,分析了摩擦系数对于界面滑移、主塔内力等响应量的影响规律。分析结果表明:摩擦系数大于0.1,在设计地震下主缆-索鞍界面无摩擦滑移,而在罕遇地震和极罕遇地震下,有一定的摩擦滑移,最大摩擦滑移量随着摩擦系数增大而减小;主缆-索鞍界面在地震作用下会发生明显滞回现象,最大可提供约2.0%的等效阻尼比;边塔顶剪力对塔底弯矩的贡献率达到了50%~70%,而中塔由于设置阻尼器,剪力贡献率仅为20%~40%;适当减小摩擦系数有利于降低塔的响应,但摩擦系数降低至0.001时,主缆将失去对塔变形的约束能力,将显著改变塔的变形模式与动力效应。

大跨曲线矮塔斜拉桥主梁锚固区蝶形应力区及优化配筋研究

为了探究曲线矮塔斜拉桥主梁局部锚固区受弯扭耦合效应的影响,优化局部配筋方案,以王家河大桥为工程背景,从应力、变形及预应力施加效率3个层面,对成桥和最大悬臂工况下直桥和弯桥局部节段模型开展对比计算,提出弯扭耦合效应造成的锚固区蝶形剪应力集中区域。结果表明:弯扭耦合效应增大了锚固区主梁各构件的主拉应力;同时,增大蝶形剪应力集中区域的面积约40%,在该区域可采用非对称配筋方案,适当增加锚固处弯曲侧抗剪钢筋比例;弯扭耦合效应会使主梁锚固区横向位移明显增大,增幅接近30%,但对挠度无显著影响;弯扭耦合效应下主梁锚固区预应力施加效率小幅度提升,在配束计算时应予以考虑。

斜拉桥曲面钢塔内部合理构造设计与受力分析

为了给斜拉桥曲面钢桥塔内部构造设计提供思路和方法,以石家庄滹沱河大桥为依托工程,在综合考虑施工可行性的前提下,提出了三种桥塔截面内部构造布置形式,并通过有限元分析,结合桥塔受力特性,得出桥塔的经济性对比结果。进一步应用有限元数值分析、理论推导和规范相结合的方式得到整体稳定折减系数计算流程,并针对三种截面进行整体稳定性分析对比。为保证曲面钢板的加劲的合理布置和板厚的选择,引入曲面局部稳定折减系数计算方法,总结计算流程,并对依托工程的曲塔壁厚和加劲布置进行多参数对比计算,得出推荐的壁厚与加劲间距的对应关系。桥塔的锚固形式多样,需要根据索力大小、内部操作空间及传力路径等多方面进行比选,最终选择与桥塔相适应的锚固构造。

考虑不确定性斜拉桥参数的重要性与易损性分析

许多结构参数对桥梁数值模型的计算结果产生影响,结构的恒载、阻尼以及相关材料特性等参数涉及的不确定性被称为建模不确定性。研究表明建模不确定性的存在使得结构易损性曲线的偏差程度达到70%,因此在地震易损性分析中考虑不确定性很有必要。文章采用一种基于随机森林(random forest,RF)模型的概率地震需求模型(probabilistic seismic demand model,PSDM)易损性计算方法,分析桥梁构件的材料特性、荷载条件和构件几何特性等不确定因素对桥梁易损性的影响,并从中筛选出重要的不确定性参数。借助随机森林模型的学习与预测功能对结构易损性曲线进行预测。

曲面异形“内混凝土外钢”塔柱施工方法研究

曲面异形“内混凝土外钢”斜拉桥主塔结构新颖,桥塔具有构造复杂、造型奇异等特点。桥塔施工面临钢结构吊装节段多、安装精度要求高、混凝土浇筑难度大等诸多难题。文章结合海花岛跨海3#桥工程实例,总结了塔柱施工重难点,研究了主塔总体施工方案及施工工艺措施,包括钢结构拼装及吊装工艺、桥塔安装控制测量等方面,可为同类工程提供参考。

单索面曲梁人行悬索桥设计探讨

单索面曲梁人行悬索桥桥型新颖美观,空间异型曲面结构受力复杂。单侧悬吊曲梁承受偏心力矩和水平分力,通过调整三角形截面桁架梁的重心位置和主梁悬吊点的高度,桁架梁上弦杆和下弦杆的水平径向抵抗力均指向曲线外,实现曲线杆件以轴向受拉为主,提高其稳定性。单侧倾斜空间索面布置于曲梁外侧,利用有限元迭代计算修正空间主缆节点坐标、内力及吊索张拉力,得到成桥线形。斜塔两侧主缆形成水平夹角,通过在塔顶张拉2根背索平衡主缆水平分力,确保主塔的整体稳定性。结合跨径300 m单索面曲梁人行悬索桥设计,有限元模型计算结果表明,承载力和变形满足规范要求,为同类型桥梁设计提供参考。

空间曲塔大跨斜拉桥抗风性能研究

跨江大桥跨径较大,桥位风速较高,抗风问题至关重要。随着桥梁造型逐渐复杂,规范中一般公式无法适用其抗风计算,因此针对某主跨为238 m的跨江空间曲塔斜拉桥的抗风性能进行了研究。研究内容包括:利用虚拟风洞试验技术获取了主梁的静气动力系数、气动导数以及桥塔分段的模拟风荷载;利用三维颤振稳定性分析方法检验了主梁颤振性能;对主梁的涡激共振进行了数值模拟,得到了不同风攻角下的振幅-风速曲线;分析了结构静风荷载下的位移响应。结果表明,该桥主体结构的抗风性能均满足规范要求。