洛塘河双层高架特大桥护栏碰撞条件与评价标准

合理确定护栏碰撞条件及评价标准是新型护栏设计的重要工作。护栏碰撞条件由碰撞车型、车辆质量、碰撞速度和碰撞角度这四大基本要素组成，四种要素组合确定了护栏的防撞能力和防撞等级，这些因素是护栏设计的基础，且护栏的安全评价标准则是判断护栏在已定碰撞条件下能否达到安全防护目标的一系列技术参数指标。依据洛塘河双层高架特大桥自身特点，参阅国内外相关标准，对防撞护栏碰撞条件、评价标准重新进行研究。其中，碰撞条件中最大碰撞能量达到894kJ，远远高于现行标准规范的最大碰撞能量520kJ；而在碰撞标准的研究中，洛塘河双层特大桥对于工作宽度有明确的限制条件，即W≤65cm，而国内现行标准并没有对过桥墩处扩栏工作宽度进行特殊规定。因此对有特殊防护需求的护栏的碰撞条件及评价标准进行研究具有足够的必要性。     

Development and structural testing of a composite-reinforced timber highway guardrail

Various government agencies install timber guardrails on scenic highways and roads in lieu of conventional steel guardrails for aesthetic reasons. Most acceptable timber guardrails rely on a continuous steel backing member to carry the large tensile forces caused by vehicle impact and transfer load to the posts. However, these guardrails are relatively expensive and heavy due to their use of large, solid-sawn timber sections. This study focuses on the development and structural testing of a novel timber guardrail that consists of a hardwood glued-laminated member strengthened with a fiber-reinforced polymer (FRP). The FRP acts in place of steel to carry the impact-induced tension and the guardrail is significantly shallower and lighter than conventional timber guardrails. This paper details the analysis of the guardrail response under vehicle impact, the development and testing of a unique and easily installed rail-to-rail field splice connection capable of carrying the tensile forces caused by vehicle impact, and the evaluation of guardrail durability in exterior conditions. In addition, the structural performance of the guardrail was assessed using experiments that produced the simultaneous tension and flexure forces expected during vehicle impact using a single hydraulic actuator and a three-point bending test apparatus. Based on the development and testing documented in this paper, the FRP-reinforced timber guardrail is expected to be capable of passing required vehicle crash tests.     

振动荷载对砂岩峰后损伤变形特性的影响

岩石峰后力学特性的理论研究对于深部煤炭的安全开采至关重要。开展粉砂岩的峰后振动循环和加卸载试验:首先以0.1 MPa/s的速率将围压增至20 MPa,然后以60 kN/min速率施加轴向荷载直至峰值q,再进行轴向卸载至0,最后轴向施加10~80次的正弦振动荷载。通过总结振动荷载对粉砂岩强度、变形、损伤和弹性模量的作用规律,研究了振动荷载对砂岩峰后损伤变形特性的影响。结果表明:少量的振动荷载有利于粉砂岩变形损伤的闭合,可以提高岩石的弹性模量,使岩石变得相对坚硬;但过多次数的循环荷载会引起岩石的变形进一步发展,产生新的损伤,同时也会使岩石变软。峰后阶段的振动荷载会促进新裂纹的产生、发展和贯通,最终产生多组破裂面。     

铝合金护栏的设计与研究

本文在确保铝合金隔离护栏原有的防护效果的基础上,开发研究了一种新型轻量化铝合金材质隔离护栏。该设计利用铝合金护栏全程组装无焊接的特点,采用铆接与角码的连接方式,其严密无缝的节点,更为的可靠与安全,从外形上看富有美观时尚且不易生锈的品质,并且铝合金自带绿色环保寿命长的特点也得到了充分的体现。     

内环线高架道路中间隔离护栏结构改进形式的冲击试验研究

本文主要通过两种类型的原中间护栏改造的冲击试验比较,分析了改进后的护栏抗冲击作用的效果,研究表明护栏的改造方案是可行的。     

钢筋锈蚀对钢筋混凝土结构固有频率和阻尼比影响的试验研究

针对钢筋锈蚀使钢筋混凝土结构的抗震性能和耐久性能退化,并且对结构动力特性产生影响的现象,采用电化学加速锈蚀方法,通过法拉第定律控制锈蚀程度,将钢筋的理论锈蚀率分为5%,10%,15%三个锈蚀阶段,在实验室中模拟了钢筋混凝土梁中钢筋的锈蚀过程。根据悬臂梁的自由振动衰减特性,采用自由衰减法采集了钢筋混凝土梁的固有频率和阻尼比,研究了钢筋锈蚀对钢筋混凝土梁固有频率和阻尼比的影响。结果表明:钢筋锈蚀对钢筋混凝土梁的固有频率和阻尼比有显著影响,钢筋混凝土梁的固有频率随着钢筋锈蚀程度的加深而呈减小趋势,阻尼比随着钢筋锈蚀程度的加深而呈增大趋势,因此阻尼比可以作为损伤指标用于混凝土结构腐蚀损伤检测。     

Experimental study on a large aircraft impacting reinforced concrete nuclear containment structure model

美国9·11恐怖袭击事件后，核电厂房抵御大型商用飞机恶意撞击成为核安全领域备受关注的热点问题。为真实准确地研究大飞机撞击下核电厂房结构的损伤破坏及振动特性，基于某新型反应堆核电厂房结构，设计了大飞机撞击钢筋混凝土核安全壳模型试验，获得了核安全壳结构遭受大飞机撞击时相对完整的试验数据及物理参数。试验结果表明：当大飞机模型以我国核电厂厂址选择安全导则中建议的基准速度100 m/s撞击时，安全壳模型发生局部碎甲破坏，但壳体的主筋整体性能完好，钢筋网有效阻止了大飞机模型的侵入破坏。依据试验结果研究了钢筋混凝土安全壳结构在大飞机撞击作用下的损伤破坏规律和特点，分析了结构的撞击振动反应特性。根据试验结果反演至原型结构，安全壳结构的环梁牛腿处和筒体与穹顶连接处峰值加速度较大，分别为39.5g和47.2g，底板处水平和竖向峰值加速度相对较小，但仍达到3.45g和4.37g。壳体直接撞击区钢筋发生屈服，而在壳体碎甲区之外，各测点的钢筋应变均小于屈服应变，钢筋未发生屈服，钢筋混凝土壳体未发生由振动导致的破坏。     

大飞机撞击钢筋混凝土核安全壳模型试验研究增强出版（附加材料可在文章详情页“评审附件”下载）

美国9·11恐怖袭击事件后,核电厂房抵御大型商用飞机恶意撞击成为核安全领域备受关注的热点问题。为真实准确地研究大飞机撞击下核电厂房结构的损伤破坏及振动特性,基于某新型反应堆核电厂房结构,设计了大飞机撞击钢筋混凝土核安全壳模型试验,获得了核安全壳结构遭受大飞机撞击时相对完整的试验数据及物理参数。试验结果表明：当大飞机模型以我国核电厂厂址选择安全导则中建议的基准速度100 m/s撞击时,安全壳模型发生局部碎甲破坏,但壳体的主筋整体性能完好,钢筋网有效阻止了大飞机模型的侵入破坏。依据试验结果研究了钢筋混凝土安全壳结构在大飞机撞击作用下的损伤破坏规律和特点,分析了结构的撞击振动反应特性。根据试验结果反演至原型结构,安全壳结构的环梁牛腿处和筒体与穹顶连接处峰值加速度较大,分别为39.5g和47.2g,底板处水平和竖向峰值加速度相对较小,但仍达到3.45g和4.37g。壳体直接撞击区钢筋发生屈服,而在壳体碎甲区之外,各测点的钢筋应变均小于屈服应变,钢筋未发生屈服,钢筋混凝土壳体未发生由振动导致的破坏。     

Detection of damage due to corrosion in prestressed RC beams by static and dynamic tests

In this paper, the behaviour of pre-stressed RC beams with compressive concrete subjected to damage due to reinforcement corrosion has been experimentally investigated. The experimental static and dynamic analysis is described. The results of static bending tests show that the corrosion leads to an increase of curvature for prestressed RC section, a decrease of stiffness and, as evident, a non linear behaviour of damaged beam under low service loads. Dynamic tests allow to record variations of frequency response both for undamaged and damaged beams at different modes of vibration. Finally, a damage coefficient has been evaluated for damaged beams.     

黑麦草根系加固粘土的剪切强度性能研究

植被在增强边坡稳定性方面有着积极的作用,其作为一种兼顾生态保护和边坡治理的护坡方式,在工程实践中得到了广泛的应用.为了研究植物根系加筋土的抗剪特性,以室内培育的黑麦草根系为加筋土的筋材,制备了不同含根量和含水率的重塑试样,通过直剪试验分析其抗剪强度特性的变化规律.研究结果表明:黑麦草根系加筋增强了土体的抗剪强度,表现为...     

The impact vibration-based fatigue damage assessment of steel and steel fiber reinforced concrete composite girder

The steel-concrete composite girder has been usually applied in the civil structures. The current fatigue damage assessment on the composite girder, especially the negative bending region, mainly bases on the crack observation and deflection measurement. It is not stable sometimes, thus the impact vibration-based fatigue damage assessment was considered instead. A 3.3m steel-steel fiber reinforced concrete (SFRC) composite girder was designed and tested. The fatigue load, the impact load, and the static load were applied in the test. It showed that the local fatigue damage reflected by the tensile SFRC cracks may not be easily evaluated through observing the global mechanical change. However, the vibration modal parameters such as the vibration frequency, vibration mode, damping ratio might be useful for this. In particular, the vibration mode variation, which can be expressed by the Modal Assurance Criterion (MAC) value, may reflect the local fatigue damage on the composite girder.     

卷板式护栏端头正面碰撞分析

为了解卷板式护栏端头安全性能,本文建立有限元仿真模型,运用碰撞试验对仿真模型进行可靠性验证后,对卷板式护栏端头进行正面碰撞分析。结果表明:仿真与碰撞试验结果相符,验证了仿真方法的可靠性;不同速度正面中心碰撞,端头卷板吸能效果良好,但加速度峰值随速度增加有较大增加;不同角度正面碰撞,车辆姿态良好,加速度峰值变化不大;不同位置正面碰撞端头,端头吸能效果良好,加速度峰值变化不大;卷板器质量是加速度峰值产生的最主要因素。卷板式端头可有效降低事故严重程度,保护乘员安全。     

Exploring the impact of chloride-induced corrosion on seismic damage limit states and residual capacity of reinforced concrete structures

A non-linear finite element (FE) framework for time-dependent capacity assessment of corroded rectangular reinforced concrete (RC) columns is developed. The proposed non-linear FE model includes the impact of corrosion on inelastic buckling and low-cycle fatigue degradation of longitudinal reinforcement. The proposed non-linear FE model is validated against a set of experimental data and then extended to evaluate the impact of corrosion on damage limit states to be used in seismic performance and evaluation of corroded structures. This is done through a parametric study on hypothetical RC columns, varied in axial force ratios, mass loss ratios, cover crack widths and confinement levels. Moreover, the application of the proposed model in seismic collapse capacity assessment of corroded structures is shown through non-linear dynamic analyses of prototype columns. Results show that, depending on the axial force ratio, corrosion changes the failure mechanism of the columns. The results of this study suggest that in seismic fragility analysis of corroded structures, the damage limit states should be considered as time-variant parameters.     

Blast vibration damage to underground coal mines from adjacent open-pit blasting

A study was conducted to evaluate the effect of heavy blasting in open-pit coal mines on the stability of adjoining underground coal mine workings. Investigations were carried out at seven coal mines in India. Strata monitoring instruments, viz. borehole extensometers, convergence indicators, strain bars, stress capsules and load cells were installed in the roof and pillar. Monitoring of strata behaviour was carried out before and after the blasts. Arrangements were made to mount the transducers of seismographs in the roof and pillars to monitor vibration. Altogether, 202 production blasts were conducted and 622 vibration data were recorded.

The maximum peak particle velocity (PPV) recorded was 372.8 mm/s with the associated frequency of 78 Hz. At this magnitude of vibration, a coal block of 0.38 m³ detached from the roof. Minor damage in the form of loosened coal chips falling from the roof and the pillars was noticed at PPV level of 113 mm/s. Major damage was observed when the magnitude of PPV exceeded 181.9 mm/s. The damage is classified into three groups, viz. major damage, minor damage and no damage. The vibration levels in no damage zone are taken as safe level of vibration, The threshold value of vibration for the safety of underground workings is recommended based on the RMR of the roof rock.

It was also observed that the roof of underground roadways vibrated with 1.1–2.58 times higher amplitude of vibration compared to the pillars, The amplification was further higher at junctions. Monitoring of underground strata behaviour indicated, in all the mines, some amount of divergence between the roof and floor just after the blast, but, later on it was followed by convergence and most of the divergence that occurred was restored.     

基于植被根系分形维数的生态边坡位移场研究

植物根系与土的相互关系非常复杂,本文将根土复合体当作由土体、根系所联系起来的有机体,提出基于根系形态特征的固土机理数值分析方法,研究在雨水侵蚀力和坡面径流侵蚀力作用下,不同根系形态对土体位移场的影响。同时根据根系形态特征,研发了计算不同植物根系分形维数的分形软件Fractal 1.0,利用该软件能计算不同植物根系分形维数。选择常见护坡植物夹竹桃(Nenium indicum)作为研究对象,依据数值模拟中根系模型与实测根系形态分形维数的关系,研究了植物根系分形维数与边坡土体位移场的关系,给出了分形维数与边坡位移量的定量关系。随着分形维数的增大,根系生长活性增大,根系分枝数量和分枝长度逐渐增大,植入边坡土体后,边坡表层位移量能够有效减小,因此植物根系分形维数大小能够反映根系对边坡土体位移场的影响。     

Transfer learning and deep convolutional neural networks for safety guardrail detection in 2D images

Safety has been a concern for the construction industry for decades. Unsafe conditions and behaviors are considered as the major causes of construction accidents. The current safety inspection of conditions and behaviors heavily rely on human efforts which are limited onsite. To improve the safety performance of the industry, a more efficient approach to identify the unsafe conditions on site is required to supplement the current manual inspection practice. A promising way to supplement the current manual safety inspection is automated and intelligent monitoring/inspection through information and sensing technologies, including localization techniques, environment monitoring, image processing and etc. To assess the potential benefits of contemporary technologies for onsite safety inspection, the authors focused on real-time guardrail detection, as unprotected edges are the ones cause for workers falling from heights.In this paper, the authors developed a safety guardrail detection model based on convolutional neural network (CNN). An augmented data set is generated with the addition of background image to guardrail 3D models and used as training set. Transfer learning is utilized and the Visual Geometry Group architecture with 16 layers (VGG-16) model is adopted to construct the basic features extraction for the neural network. In the CNN implementation, 4000 augmented images were used to train the proposed model, while another 2000 images collected from real construction jobsites and 2000 images from Google were used to validate the proposed model. The proposed CNN-based guardrail detection model obtained a high accuracy of 96.5%. In addition, this study indicates that the synthetic images generated by augment technology can be used to create a large training dataset, and CNN-based image detection algorithm is a promising approach in construction jobsite safety monitoring.     

高速公路施工防撞护栏的施工经验

简单介绍了高速公路防撞护栏的施工特点,结合施工经验,从准备工作、施工放线定位、设备选用、施工注意事项等方面详细地阐述了防撞护栏的施工,以保证防撞护栏的施工质量,从而保证高速公路的交通安全.     

Monitoring the effects of impact damages on modal parameters in carbon fiber entangled sandwich beams

The aim is to study the impact toughness of two types of entangled sandwich materials (heavy and light) with the help of vibration testing. A simple case of symmetrical impacts is studied in this article as no literature is available regarding impact tests on entangled sandwich materials. The variation of modal parameters with two levels of damage (BVID and Damage not apparent on the surface) is studied. Vibration test results show that the light entangled specimens possessing good damping capabilities seem more sensitive to impact damage than the heavy ones. Furthermore, damping is found to be more sensitive to damage than the stiffness variations, so it is reasonable to assume that damping may be used instead of natural frequency as a damage indicator tool for structural health monitoring purposes.     

Analytical demonstrations to assess residual bearing capacities of steel plate girder ends with stiffeners damaged by corrosion

Many field surveys depict that steel plate girder ends tend to corrode due to the leakage of water from construction joints and/or detention of rain water near bearing regions. In many cases, buckling failures of plate girders were observed due to the excessive loss of material at the bottom portion of bearing stiffeners. In this study, the effect on the buckling strength of steel plate girder due to the corrosion damage at bearing stiffeners was investigated. Full-scale experimental tests were performed on two plate girder ends to determine the bearing capacity. Bearing capacity and failure modes were also verified by numerical analyses. Initial imperfections and welding residual stresses were also taken into account in analytical models. The simulation of the model was extended to the various corrosion damages, considering different damaged heights and thicknesses of the bearing stiffener near weld seam. All results were plotted in terms of remaining bearing capacity versus damage thickness ratio keeping the damage height of the stiffener constant. In this study, a damage parameter Reduced Thickness Ratio was used to assess the ultimate capacity and buckling of steel plate girder end with various corrosion levels.     

Experimental and numerical evaluation of bearing capacity of steel plate girder affected by end panel corrosion

The present study deals with the effect of uniform and non-uniform local corrosion damages at the bearing stiffener and nearby web on the bearing capacity of plate girder. Five plate girder ends simulated with different uniform and non-uniform types of corrosion damage, at the base of the bearing stiffener are used in the experimental program. The experimental results are modeled and verified on a Finite Element (FE) software ABAQUS, considering shell-solid coupling elements formulation. The study is further extended to various damage cases i.e., stiffener damage, stiffer plus web damages etc. considering different damage heights and residual thicknesses. The study concludes that minimum thickness within any damage height may be used to simulate the corrosion damage in a FE analysis. At the end, some empirical relationships are also proposed to estimate the bearing strength of the plate girder affected by the local corrosion damage at plate girder end.