Experimental and numerical investigation on the dynamic shear failure mechanism of sandstone using short beam compression specimen

In this study,a novel testing method is proposed to characterize the dynamic shear property and failure mechanism of rocks by introducing the short beam compression(SBC)specimen into the split Hopkinson pressure bar(SHPB)system.Firstly,the stress distribution of SBC specimen is comprehensively analyzed by finite element method(FEM),and the results show that the optimal notch separation ratio of SBC specimen is C/H?0.2 to achieve successful dynamic simple-shear tests.Then,dynamic shear tests are conducted on sandstone using the SBC-SHPB method.Via careful pulse shaping technique,the dynamic force balance is guaranteed for SBC specimens,and the testing results show that the dynamic shear strength of sandstone is significantly rate-dependent.Combining the results of dynamic compression and tension tests,the failure envelopes of sandstone under different loading rates are obtained in the principle stress plane.It is found that the failure envelope of sandstone constantly expands outwards with increasing loading rate.Moreover,the energy partition of SBC specimen is quantified by virtue of high-speed digital image correlation(DIC)technique.The results show that the kinetic energy portion is non-negligible,and the shear fracture energy increases with increasing loading rate.In addition,the microscopic shear cracking mechanism of SBC specimen is analyzed by the thin section observation:the intra-granular(TG)fracture of minerals dominates the dynamic shear failure of sandstone,and the portion of TG fracture increases with increasing loading rate.This study provides a convenient and reliable method to investigate the dynamic shear property and failure mechanism of rocks.

Short beam shear properties and failure modes of the wood-based X-type lattice sandwich structure

A wood-based X-type lattice sandwich structure was manufactured by insertion-glue method.The birch was used as core,and Oriented Strand Board was used as panel of the sandwich structure.The short beam shear properties and the failure modes of the wood-based X-type lattice sandwich structure with different core direction(vertical and parallel),unit specification(120 mm×60 mm and 60 mm×60 mm),core size(50 mm and 60 mm),and drilling depth(9 mm and 12 mm)were investigated by a short beam shear test and the establishment of a theoretical model to study the equivalent shear modulus and deflection response of the X-type lattice sandwich structure.Results from the short beam shear test and the theoretical model showed that the failure modes of the wood-based X-type lattice sandwich structure were mainly the wrinkling and crushing of the panels under three-point bending load.The experimental values of deflection response of various type specimens were higher than the theoretical values of them.For the core direction of parallel,the smaller the unit specification is,the shorter the core size is,and the deeper the drilling depth is,the greater the short beam shear properties of the wood-based X-type lattice sandwich structure is.

Long-and short-term average intensity for multi-Gaussian beam with a common axis in turbulence

With the help of the extended Huygens-Fresnel principle and the short-term mutual coherence function, the analytical formula of short-term average intensity for multi-Gaussian beam （MGB） in the turbulent a^mosphere has been derived. The intensity in the absence of turbulence and the long-term average intensity in turbulence can both also be expressed in this formula. As special cases, comparisons among short-term average intensity, long-term average intensity, and the intensity in the absence of turbulence for flat topped beam and annular beam are carried out. The effects of the order of MGB, propagation distance and aperture radius on beam spreading are analysed and discussed in detail.

三软煤层沿空留巷顶板结构模型及合理支护研究

为了揭示三软煤层沿空留巷围岩变形机理,探索适用于三软煤层巷道围岩控制的新技术,通过切顶沿空留巷物理相似模拟实验,研究了不切顶普通支护、切顶高强支护和切顶普通支护3种条件下顶板岩层断裂演化过程,构建了三软煤层切顶留巷顶板结构力学模型,给出了支护阻力计算方法,在韩城矿区象山煤矿进行了现场工业性试验验证。研究表明:切顶技术切断了顶板的应力传递,巷内采用高强支护,使顶板形成稳定的“短悬臂-砌体梁”结构。现场监测结果显示,不切顶普通支护的留巷顶底板平均移近量1000~1200 mm,两帮平均移近量600~700 mm;切顶高强单体支护的留巷顶底板平均移近量200~300 mm,两帮平均移近量200~300 mm;切顶组合式支架支护的留巷顶底板平均移近量50~100 mm,两帮平均移近量100~200 mm。组合式支架高强支护能够较好地控制三软煤层沿空切顶留巷围岩变形,可实现留巷二次复用无返修。

基于LSTM的多站点协作波束切换算法

毫米波频段拥有非常丰富的频谱资源,支持更高速的数据传输,因此成为通信领域近年来的研究热点。基于大规模输入输出(Massive Multiple Input Multiple Output,mMIMO)的波束成形技术可以有效补偿毫米波的高路损,是5G毫米波通信中的一项关键技术。但是在高速移动场景下,信道变化加速,必须进行频繁的波束切换才能保证良好的通信质量,故而大大增加了信令开销与资源消耗。如何在高动态场景下降低波束切换开销、提升波束切换速度与效率成为关键问题。针对直射径(Light of Sight,LOS)被遮挡情况下的复杂信道环境,文中提出了一种基于长短期记忆(Long Short Term Memory,LSTM)网络的多站点协作波束切换算法,根据过去一段时间的波束信息,学习信道环境与服务波束序号的内在联系,并预测当前时刻切换的最佳波束。仿真结果表明,与基于当前信道环境信息的遍历搜索算法相比,所提波束切换算法在上行发射功率较高时性能接近,在上行发送功率较低时,性能更优,体现了所提算法的优势。

预应力混凝土梁桥短线匹配法的抗差估计方法

针对预应力混凝土梁桥短线匹配法线形控制问题,充分考虑节段梁控制点测量值中可能出现的随机误差与粗差,提出一种附有条件限制的总体最小二乘抗差估计方法,适用于短线匹配法线形控制;推导了解算方法,并给出了具体的解算步骤;以黄茅海跨海通道工程6×60 m连续刚构中的某一跨为基准进行了数据模拟。结果表明:该方法可以实时地修正施工中各类误差导致的预制线形变化,有效地阻止了施工误差与测量误差在后续节段梁中的不断积累;与既有算法相比,所提算法的计算结果准确度最高,不仅在终端节段末端与基准线形的差值均值最小,而且在代表整体线形连续性的偏差平方和均值上与最小二乘法的结果相近,优于传统的选点控制方法。

多因素作用下混凝土梁长期性能时变劣化规律

为了探究混凝土梁在锈蚀、疲劳、徐变等多因素长期作用下的性能劣化规律,对21根试验梁开展了锈蚀、疲劳和徐变的正交分组试验,通过对钢筋锈蚀深度、梁的刚度和疲劳寿命的测量计算,研究了钢筋混凝土梁长期性能的时变劣化规律。研究结果表明:相较于无损梁,在2.5%、15.0%、60.0%疲劳寿命比和3、6个月持续荷载作用下,损伤混凝土梁的锈蚀深度扩大了1.337~1.934倍;随着钢筋锈蚀和疲劳损伤程度的加深,损伤梁的刚度下降了1.694 kN·m^(2),在持续荷载作用下,其刚度仅为无损梁的34.1%;在锈蚀和徐变相继作用后,损伤梁的疲劳寿命仅为无损梁的16.14%。根据试验研究结果,给出了损伤混凝土梁的临界锈蚀深度衰减系数、短期刚度降低系数、刚度退化系数和疲劳寿命衰减系数,以反映复杂荷载与环境作用对混凝土梁长期性能的影响,为混凝土结构的长期性能评估提供了科学依据。

气象数据驱动的拉林铁路简支T梁温致变形预测

为快速、准确预测日照环境下高原铁路桥梁的温度变形效应,基于长短期记忆神经网络(LSTM)提出了一种气象数据驱动的桥梁温度变形智能预测模型。以拉林铁路简支T梁为背景,采用热力耦合有限元仿真分析,构建了“气象数据—温度变形”映射的样本数据库,以此训练预测模型并对桥梁温致变形进行预测。结果表明,LSTM模型表现出了较高的精度和优势,其梁体竖向挠度预测的决定系数(R2)超过0.97,平均绝对误差(MAE)和均方根误差(RMSE)较反向传播神经网络(BP)模型提升超过70%,较随机森林(RF)模型分别提升了24%和27%。预测挠度与真实值在趋势和数值方面均基本一致,表明所提出的预测方法性能优异,为高原铁路轨道平顺性变化规律研究及动态检测数据评价提供参考。

预制钢-UHPC组合梁中橡胶-短栓钉剪力件的抗剪性能试验研究

为了探究钢-UHPC组合梁中橡胶-短栓钉剪力件的抗剪性能,试验设计并制作了10个推出试件,研究橡胶套筒尺寸和加载制度对其抗剪性能的影响规律。试验结果表明:试件以栓钉剪断为主要破坏形式,并伴随栓钉附近局部混凝土压碎。橡胶套筒厚度对剪力件的抗剪承载力影响较小,橡胶套筒厚度为2mm的组合剪力件承载力为普通剪力件的94%。随着橡胶套筒厚度的增加,剪力件的抗剪刚度随之下降,最小为普通剪力件的87%;相对滑移则随着厚度增加而增加,最大为普通剪力件的142%。而随着橡胶套筒的高度增加,剪力件的抗剪承载力随之减少,橡胶套筒高度为50mm的组合剪力件承载力为普通剪力件的89%;随着橡胶套筒高度的增加,剪力件的抗剪刚度随之下降,最小为普通剪力件的75%;相对滑移则随着高度的增加而增加,最大为普通剪力件的137%。

锥形术CT测量分析下颌第一磨牙拟种植区剩余牙槽嵴的骨量

背景:随着口腔领域的发展与进步,口腔种植技术逐渐成为替代传统义齿的主流选择。近年来,多种骨增量技术的成熟以及口腔数字化领域的不断发展,使种植适应证不断扩大,种植手术的成功率也越来越高。但是种植手术前使用锥形术CT对剩余牙槽嵴骨量进行准确测量并且个性化制定合适的种植方案,成为一部分临床医师的难题。目的:采用锥形束CT对下颌第一磨牙拟种植区剩余牙槽嵴骨量进行测量分析,为优化下颌第一磨牙区种植方案的设计提供参考。方法:采用回顾性研究设计,纳入205例下颌第一磨牙缺失患者的锥形术CT影像,测量下颌第一磨牙拟种植区剩余牙槽嵴高度及宽度,并将剩余牙槽嵴形态分为Ⅰ、Ⅱ、Ⅲ、Ⅳ4类(Ⅱ、Ⅲ、Ⅳ类剩余牙槽嵴为骨量不足),统计分析下颌第一磨牙剩余牙槽嵴高度、宽度、形态频数分布,不同性别患者下颌第一磨牙剩余牙槽嵴高度和牙槽嵴顶宽度的差异,剩余牙槽嵴高度与剩余牙槽嵴顶宽度、剩余牙槽嵴底宽度的相关性,年龄与剩余牙槽嵴顶宽度、高度的相关性。结果与结论:①下颌第一磨牙拟种植区剩余牙槽嵴高度平均为(12.14±2.96)mm,其中<12 mm者占43.41%(89/205),下颌第一磨牙拟种植区牙槽嵴顶宽度平均为(6.80±1.65)mm,其中<6 mm者占26.34%(54/205);②男性下颌第一磨牙剩余牙槽嵴高度高于女性,但差异无显著性意义(P>0.05),男性下颌第一磨牙剩余牙槽嵴顶宽度宽于女性,差异有显著性意义(P<0.01);③剩余牙槽嵴高度与剩余牙槽嵴顶宽度和剩余牙槽嵴底宽度呈负相关(P<0.05);年龄与剩余牙槽嵴顶宽度呈正相关(P<0.05),与剩余牙槽嵴高度无明显相关性(P>0.05);④剩余牙槽嵴形态Ⅰ类占58.05%(119/205),Ⅱ类占9.27%(19/205),Ⅲ类占20.49%(42/205),Ⅳ类占12.19%(25/205),其中多数为Ⅲ类剩余牙槽嵴骨量不足,临床医生需要根据剩余牙槽嵴类型个性化设计最佳的种植方案。

基于奇异值分解与四控制点的短线法节段梁轻量化线形控制方法

短线法是目前广泛使用的节段预制拼装桥梁施工方法,其预制线形控制通常采用六控制点方式,坐标系的变换求解方法正由二维简化向三维空间变换发展。然而,当前线形控制方法仍存在一些问题,如控制点冗余大、预制误差识别与修正过程繁琐、精度控制效果差异大等。以某城市地铁高架节段U梁桥为例,提出一种基于奇异值分解空间坐标变换理论的四控制点短线法节段预制线形控制方法,并开发了轻量化算法,跳过了梁段里程、轴线和高程误差的独立识别与修正过程,直接求解匹配节段的理论匹配坐标。预制线形控制结果表明,修正后的节段接缝处左右端点实际坐标与理论坐标基本重合,表明该算法可直接有效地修正预制误差,是一种可行的预制线形控制新方法。

浅埋深大采高工作面矿压显现规律研究

以三道沟煤矿85214工作面为工程背景,对浅埋深大采高工作面矿井的矿压显现规律进行研究,利用理论分析的方法,建立固支梁和悬臂梁模型,确定工作面初次来压步距和周期来压步距分别为104.91和19.90 m。基于覆岩浅埋结构性质,建立短砌体梁和台阶岩梁模型,确定支护阻力分别为5 624和14 461 kN;利用现场试验的方法,对井下支架工作阻力数据实测分析,确定工作面初次来压步距106 m,周期来压步距16.8 m,月平均次数11次,平均支架载荷37.5 MPa,支承压力主要分布于工作面中部区域。研究结果证明了来压步距模型的合理性和有效性,并确定了浅埋深条件下覆岩结构呈现短砌体梁结构和台阶岩梁结构的破断特点,可为矿井生产提供依据。

浅谈智能机械立体车库结构设计

智能机械立体车库建筑设计除满足正常使用功能、消防、疏散等方面的要求,还要满足设备的运行安装要求。结构设计在满足建筑设计全部功能的前提下,还要保证结构安全、经济合理、施工简便。江西省南昌市渊明北路停车场项目采用垂直移动立体车库和巷道堆垛类立体车库两种停车方式,论文以该项目为例,分析智能机械立体车库结构设计的特点和可以采取的结构措施。

SE短槽式干挂陶土板施工技术

北京市房山区青龙湖综合性商业金融服务项目使用了SE短槽式干挂陶土板施工技术,成功实现了幕墙装饰板材的工厂化加工、现场干挂式安装,起到了提高工作效率、增加外观装饰美感、降低工程成本的良好效果。

考虑功率反馈的短波发射机波束自动控制方法

由于传统相位或幅度控制方法无法实时监测短波发射机输出功率,导致波束指向控制精度较低。文章提出考虑功率反馈的短波发射机波束自动控制方法,构建短波发射机数学模型作为被控对象,监测并调制短波发射机的输出功率信号,将监测信号传输到自动调谐控制器中,控制器根据监测信号与目标信号之间的偏差,对短波发射机放大器的增益进行调整,实现对发射机波束指向的自动控制。实验结果表明,在该设计方法控制下短波发射机波束指向偏移量为0.6°,控制效果良好。

短台背工况下的预制梁架桥机安装技术应用研究

先简支后连续桥梁上部结构预制梁安装普遍采用在桥台背后长路基段落拼装架桥机,然后配重预制梁体过孔,再安装预制梁。中珠排洪渠桥上部结构为(5×23)m的双T梁,桥梁台背两侧为短距离路基,路基紧邻两侧被交道路深基坑,桥梁上部结构双T梁架桥机安装及喂梁场地长度不足,无法采用常规台背长路基段落安装工艺施工。文章分析了短台背工况安装难点,介绍了一种短台背距离工况下的双T梁架桥机安装方法,以期为其他类似项目提供借鉴。

20m以内的预应力钢束张拉质量控制关键措施研究与实践

20m以内预应力钢束的张拉质量控制一直是一个技术难题,施工过程中,普遍存在张拉关键指标超出规范要求的现象。本文通过研究短束预应力张拉过程中的张拉控制应力的确定、理论伸长值的计算、张拉工艺的设计和张拉设备的选型等关键工序和设备,并在工程实际中进行了实践应用,总结出20m以内短束预应力张拉的质量控制关键措施和方案,实现保证张拉质量、提高桥梁的安全性和耐久性的目的,也可为短束预应力张拉控制提供参考。

水工软弱围岩隧洞台阶法开挖支护工艺浅析

软弱围岩隧洞采用台阶法掘进较为普遍,为保证施工进度与安全,在工程实际应用中,采用“短进尺、强支护”的方式组织施工,在拱脚处施设锁脚锚杆和地脚连系梁,保障了隧洞开挖安全,适度提升了施工进度,取得了较好的施工效果,并适度节约了施工成本。

Self-modulation and anomalous collective scattering of laser produced intense ion beam in plasmas

The collective interaction between intense ion beams and plasmas is studied by simulations and experiments,where an intense proton beam produced by a short pulse laser is injected into a pre-ionized gas.It is found that,depending on its current density,collective effects can significantly alter the propagated ion beam and the stopping power.The quantitative agreement that is found between theories and experiments constitutes the first validation of the collective interaction theory.The effects in the interaction between intense ion beams and background gas plasmas are of importance for the design of laser fusion reactors as well as for beam physics.

An elastic-plastic analysis of short-leg shear wall structures during earthquakes

Short-leg shear wall structures are a new form of building structure that combine the merits of both frame and shear wall structures. Its architectural features, structure bearing and engineering cost are reasonable. To analyze the elastic-plastic response of a short-leg shear wall structure during an earthquake, this study modified the multiple-vertical-rod element model of the shear wall, considered the shear lag effect and proposed a multiple-vertical-rod element coupling beam model with a new local stiffness domain. Based on the principle of minimum potential energy and the variational principle, the stiffness matrixes of a short-leg shear wall and a coupling beam are derived in this study. Furthermore, the bending shear correlation for the analysis of different parameters to describe the structure, such as the beam height to span ratio, short-leg shear wall height to thickness ratio, and steel ratio are introduced. The results show that the height to span ratio directly affects the structural integrity; and the short-leg shear wall height to thickness ratio should be limited to a range of approximately 6.0 to 7.0. The design of short-leg shear walls should be in accordance with the ＂strong wall and weak beam＂ principle.