Experimental study on seismic reinforcement of bridge foundation on silty clay landslide with inclined interlayer

A shaking table test for a bridge foundation reinforced by anti-slide piles on a silty clay landslide model with an inclined interlayer was performed.The deformation characteristics of the bridge foundation piles and anti-slide piles were analyzed in different loading conditions.The dynamic response law of a silty clay landslide with an inclined interlayer was summarized.The spacing between the rear anti-slide piles and bridge foundation should be reasonably controlled according to the seismic fortification requirements,to avoid the two peaks in the forced deformation of the bridge foundation piles.The“blocking effect”of the bridge foundation piles reduced the deformation of the forward anti-slide piles.The stress-strain response of silty clay was intensified as the vibration wave field appeared on the slope.Since the vibration intensified,the thrust distribution of the landslide underwent a process of shifting from triangle to inverted trapezoid,the difference in the acceleration response between the bearing platform and silty clay landslide tended to decrease,and the spectrum amplitude near the natural vibration frequency increased.The rear anti-slide piles were able to slow down the shear deformation of the soil in front of the piles and avoid excessive acceleration response of the bridge foundation piles.

Experimental investigation on seismic performance of rigid frame tied-arch bridge with split-piers

A novel seismic design method, namely split-pier seismic design, is proposed. A vertical gap and connect elements are set in split-piers. The lateral stiffness of piers is reduced by cracking of the connect elements under severe earthquake, and the seismic response of bridges is reduced by avoiding the site predominant periods. A model of tied-arch rigid frame bridge with split-piers was designed. Seismic performance was investigated by pseudo-static experimentation on the scale model, The failure process of split-piers, the hysteresis characteristic and the effect of split-piers on the superstructure are presented. Results show that the split-pier has better seismic performance than common ductile piers do.

Improved methods for decreasing stresses of concrete slab of large-span through tied-arch composite bridge

Mechanical behavior of concrete slab of large-span through tied-arch composite bridge was investigated by finite element analysis (FEA). Improved methods to decrease concrete stresses were discussed based on comparisons of different deck schemes, construction sequences and measures, and ratios of reinforcement. The results show that the mechanical behavior of concrete slab gets worse with the increase of composite regions between steel beams and concrete slab. The deck scheme with the minimum composite region is recommended on condition that both strength and stiffness of the bridge meet design demands under service loads. Adopting in-situ-place construction method, concrete is suggested to be cast after removing the full-supported frameworks under the bridge. Thus, the axial tensile force of concrete slab caused by the first stage dead load is eliminated. Preloading the bridge before concrete casting and removing the load after the concrete reaching its design strength, the stresses of concrete slab caused by the second stage dead load and live load are further reduced or even eliminated. At last, with a high ratio of reinforcement more than 3%, the concrete stresses decrease obviously.

Deflection Measurement for Bridges Based on Secant Inclination

Deflection is a significant indicator of bridge’s strength and its whole stiffness, so the research on deflection measurement is an important aspect of bridge health monitoring. There have existed many measurement methods of bridge deflection so far, while inclination method is gradually catching more and more attention for its fair obviously comprehensive advantages. However, the inclination method at present focuses on measuring the rotation of bridge’s section at testing point, that is, the tangent angle of deflection curve. With the tangent angle, the deflection curve can be determined by the methods of curve fitting or (and) integration or conjugate beam. The methods mentioned above, are not only complicated in calculation, but also bad in accuracy. The deflection measurement method proposed by this paper is based on measuring the inclination of two points initiatively in horizontal line, that is, the secant angle of the deflection curve, and on the simple triangle function operation. The proposed method is simple in theory, but good in accuracy for either static or dynamic load. The numerical simulation suggests that the error of the proposed method is less than 1%.

Simulation and Experiment Study on the Bridge Deflection Measuring Method Based on Secant Inclination

Deflection is the most direct indicator that reflects the bearing capacity of the bridge and the overall stiffness. There are many ways to measure the deflection of Bridges, and the inclination angle method is the most commonly used indirect method, but the existing theory of inclination angle method is relatively complicated. Based on the facts of the bridge small inclination, this article proposes the method of obtaining the bridge deflection by the inclination of the secant line constructed from the adjacent measurement points. Firstly, according to the bending deformation curve of general simply supported beam, the deflection calculation formula of each measuring point is derived based on the assumption of small deformation and the inclination Angle of measuring point. Secondly, a large commercial finite element software ANSYS 10.0 is used to carry out numerical simulation on the simply-supported beam under concentrated load in mid-span, and the deflection results of the numerical simulation are compared and verified with the theoretical results of the proposed method. Finally, the measured deflection results of the simply-supported beam model under mid-span load are compared with the theoretical results of the proposed method. The verification results show that if the actual model is consistent with the theoretical model, the proposed method has good accuracy.

Mechanical response of bridge piles in high-steep slopes and sensitivity study

The bridge piles located in high-steep slopes not only endure the loads from superstructure, but also the residual sliding force as well as the resistance from the slope. By introducing the Winkler foundation theory, the mechanical model of piles-soils-slopes system was established, and the equilibrium differential equations of pile were derived. Moreover, an analytic solution for identifying the model parameters was provided by means of power series method. A project with field measurement was compared with the proposed method. It is indicated that the lateral loads have great influences on the pile, the steep slope effect is indispensable, and reasonable diameter of the pile could enhance the bending ability. The internal force and displacements of pile are largely based upon the horizontal loads applied on pile, especially in upper part.

Proposing a New Model of Hangers in Pedestrian Suspension Bridges to Solve Hangers Slackness Problem

The hangers of suspension bridges can be placed in two forms: vertical or inclined form. Inclined hangers are more liable to fatigue. Vertical hangers are subjected to greater fluctuations of stress resulting from bridge wind loads. To improve aerodynamic stability, inclined hangers can be used instead of vertical ones. Some inclined hangers show considerable signs of distress and some of them show slackness due to their location against loads. In this paper a pedestrian suspension bridge with vertical hangers has been studied as a case study. Then, the same bridge has been studied with inclined hangers. To reduce internal forces, fatigue and slackness in hangers, horizontal cables have been added to inclined hangers. This modification is proposed by the present authors. The added horizontal cables transfer the tensile load from overstressed hangers to adjacent slacked hangers. Three different hanger patterns have been analyzed under nonlinear static analysis for symmetrical and nonsymmetrical live load plus dead load. Results showed that the modified hanger system had been improved considerably in comparison with vertical or inclined hangers and wherever that there is no improvement some solutions have been proposed.

大倾角钢箱提篮拱桥总体设计

考虑施工技术、经济性和景观效果等方面,陕西蔡家坡渭河特大桥主桥采用(35+210+35) m大倾角钢箱提篮拱桥。该桥采用摩擦摆和环向钢丝绳阻尼支座综合减隔震约束体系,以降低结构的地震响应。拱肋为单室等宽钢箱截面,采用主、副拱肋2条悬链线,主、副拱肋共面,设计为横向内倾20°的大倾角,在提高桥梁景观效果的同时,又有效提高了结构的整体稳定性;拱肋设钢-混结合段连接拱脚与混凝土拱座。桥面系采用自重较轻的正交异性钢桥面板结构。吊杆采用抗拉强度1 860 MPa的环氧柔性钢绞线。基础采用Φ2.5 m的钻孔灌注群桩,以抵抗软弱地质条件下荷载的竖向及水平作用力。该桥总体采用先梁后拱的施工方案。整体及局部有限元分析结果表明,桥梁结构力学性能均满足规范要求,设计安全可靠。

斜撑钢管板桩直立式海堤结构受力分析

某填海工程的实施可能影响邻近桥梁的安全性,拟采用斜撑钢管板桩直立式海堤结构,通过Plaxis 3D岩土有限元分析软件模拟该海堤结构的受力特性及变位,以及其对邻近桥梁桩基变位的影响。结果表明,该直立式海堤结构受力特性较好、变位较小,且对邻近桥梁桩基变位的影响较小。

城市隧道入口上跨斜交阴影效应对驾驶人眼动影响

文中在武汉黄龙山隧道开展实车试验,以驾驶人注视持续时间和频率、扫视持续时间和频率为指标,分析普通路段、桥下阴影段、以及隧道入口段的变化规律,并构建驾驶负荷评价模型,对隧道入口区域进行评价.结果表明:驾驶人在桥下阴影段的注视、扫视持续时间总体较普通路段高,但较隧道入口段低,而注视、扫视频率呈相反变化趋势;当隧道入口区域前存在阴影效应时,视觉指标离散度增大,初次阴影效应会使驾驶人视觉指标短时发生较大变化,连续阴影效应会使驾驶人眼动行为逐渐趋于不良状态,在隧道入口段黑洞效应的出现会导致视觉指标突变,阴影效应和黑洞效应会显著提高驾驶负荷.

极值风环境下空间缆索体系悬索桥吊索耐久可靠度分析

空间缆索悬索桥是一种主缆、吊索等缆索系统向横桥向内侧倾斜或是外侧倾斜的悬索桥体系,其中吊索是重要的传力构件,但是其抗力会随着桥梁服役期的增加而下降,这会导致构件失效概率的增加和结构安全性问题。以主跨1666 m的整体式钢箱梁悬索桥为工程背景,采用不同的主缆内倾角度,试设计了7个空间缆索体系悬索桥方案。通过建立吊索抗力时变概率模型、恒载内力时变概率模型以及风载内力时变概率模型,分析比较了在恒载和极值静风荷载作用下,空间缆索悬索桥吊索可靠度指标随服役期的变化规律。分析结果表明:受均匀腐蚀与点蚀影响的吊索抗力在钢丝体开始腐蚀后的10年内,吊索的抗力不拒绝伽马分布;在第10年到第30年间,吊索抗力不拒绝韦布尔分布。吊索风载内力在服役期40年内不拒绝对数正态分布。悬索桥吊索的时变可靠度与空间缆索体系的内倾角度不相关,且同一悬索桥不同位置处的吊索耐久可靠度变化形式一致。

吊杆损伤对大跨径斜靠式拱桥稳定性影响

斜靠式拱桥作为一种新型结构的拱桥值得研究,并且由于其独特的吊杆布置方式,吊杆损伤对稳定性影响目前需要不够了解。以跨径130m,高26m,宽44.4m的斜靠式系杆拱桥为例,采用有限元模拟的方法对拱桥不同位置吊杆损伤以及应力变化情况做出具体研究和分析。得到结论,在斜靠式拱桥4号吊杆位置处吊杆断裂对拱桥稳定性影响最大,并且偏荷载使得拱桥安全系数整体下降,在偏荷载一侧桥型屈曲波动较大。主拱吊杆在吊杆断裂时受到的应力更大,也更容易发生断裂,在靠近拱脚处的短吊杆受到的应力最大断裂后向相邻吊杆释放的冲力也越大。稳定拱吊杆在一定程度上影响拱桥稳定性,但是在断裂后向相邻位置稳定拱吊杆和对应位置主拱吊杆冲力更小,不容易发生连锁性破坏。最后得出结论,主拱吊杆承载应力更大也更容易发生破坏,需要着重加固靠近拱脚位置吊杆。

温州瓯江北口大桥施工期索夹抗滑移控制

温州瓯江北口大桥为主跨2×800 m的三塔四跨双层钢桁梁悬索桥,主跨钢桁梁采用1000 t缆载吊机大节段吊装,施工期索夹受力大、索夹螺杆紧固力损失大,索夹滑移风险高。为给施工期索夹滑移风险评估和抗滑移控制措施提供依据,在《公路悬索桥设计规范》(JTG/T D65-05—2015)索夹抗滑移系数计算公式的基础上,考虑索夹上临时荷载、主缆轴力增加引起的主缆直径变小和主缆丝股重新排列、螺杆时变效应造成的索夹螺杆紧固力损失,提出适用于大跨悬索桥施工期的索夹抗滑移系数计算方法,分析主要参数对施工期索夹抗滑移系数的影响,并评估该桥施工期索夹抗滑移风险,提出索夹抗滑移控制措施。结果表明:钢桁梁吊装过程中,索夹倾角变化大,应采用当前施工阶段索夹倾角计算施工期索夹抗滑移系数,主缆轴力增加引起主缆直径变小是造成索夹滑移的主要原因之一;该桥除主跨跨中钢桁梁节段对应索夹抗滑移系数满足规范要求外,其余索夹抗滑移系数均不满足规范要求。根据索夹滑移风险评估结果,采取紧固索夹螺杆的抗滑移控制措施,并明确了该桥索夹螺杆紧固次数和时机。该桥采取索夹抗滑移控制措施后,施工过程中索夹均未出现滑移现象。

半分离式斜腹板双箱梁大跨单肋拱桥颤振临界风速分析

为研究低扭弯频率比大跨度桥梁的颤振性能,以某主跨180 m的半分离式斜腹板双箱梁大跨单肋拱桥为背景(主梁扭弯频率比接近1.0),进行颤振临界风速分析。采用有限元法分析该桥动力特性,计算桥梁颤振稳定性;对比《公路桥梁抗风设计规范》(JTG/T 3360-01—2018)推荐的3组理想平板颤振临界风速估算公式,基于Scanlan半逆解法的理想平板颤振临界风速,考虑主梁形状与攻角修正系数确定颤振临界风速范围;采用强迫振动数值模拟识别颤振导数,获得精确颤振临界风速,进一步计算半分离式斜腹板双箱梁的形状和攻角系数。结果表明:该桥主梁扭弯频率比较低,颤振稳定性低于500 m级大跨度双肋拱桥;规范推荐的理想平板颤振临界风速估算公式在小扭弯频率比时差异较大;半分离式斜腹板双箱梁形状修正系数小于分离式双箱梁而大于P-K梁、带斜腹板箱梁,攻角修正系数略大于这3种形式主梁。

五峰山长江大桥南锚碇倾斜基岩地质条件分析

五峰山长江大桥南锚碇位于五峰山山壑间,采用圆形扩大基础,外径90 m,场地内地形变化大,岩土层分布复杂,合理设置适应于地质条件的锚碇基础方案,对工程安全性、经济性意义重大。为了充分利用南锚碇场地内工程性能良好的微风化凝灰质砂岩地基,准确评价岩土体稳定性及对工程的适宜性,采用了露头调查、钻探、物探、原位测试及室内试验的综合勘察手段。基于地质成因分析及赤平投影方法,发现岩面、风化面总体产状具有一致性,倾角约18°,沿倾斜方向分布较稳定;通过进一步分析倾斜岩体及其风化面分布与锚碇基坑的相互作用关系,评价采用台阶式基础方案的可行性,并分析了其对岩石地基的利用优势,针对性提出了锚碇基坑的施工建议。经优化,考虑倾斜基岩工程地质条件的锚碇基础设计可减少约4万m3的微风化岩石开挖量,使工程兼具安全性与经济性。

大跨度悬索桥多对刚性中央扣受力性能研究

中央扣对改善大跨度悬索桥动力特性、短吊杆弯折、主梁纵向位移等具有显著作用,但现有文献少见对中央扣自身力学行为的研究。该文以中央扣为研究对象,通过力学方法推导了中央扣侧移刚度的计算公式,通过敏感性分析确认了杆身倾角α以及杆身轴向刚度j是影响中央扣侧移刚度的主要因素;对设置多对刚性中央扣的情况进行了研究,因主缆与中央扣杆身轴向刚度相差不大,主缆对多对中央扣协调受力影响较大,中央扣与主缆组成串、并联弹簧体系,受力分配更加复杂,可通过调整杆身倾角及杆身轴向刚度,设置具有不同侧移刚度的多对中央扣以实现协调受力。

含缓倾结构面的岩质桥址边坡地震稳定性评价及加固优化

桥址边坡地震稳定性评价在桥梁建设中十分重要,山区岩质桥梁桥址边坡稳定性多受结构面控制.文中依托某公路桥梁典型桥址边坡,利用有限元数值模拟技术,考虑了岩土材料应变软化特性,研究了含缓倾软弱结构面桥址边坡地震作用下安全稳定性.结果表明:考虑岩土材料应变软化的有限元数值仿真技术能较好地揭示含缓倾结构面的桥址边坡的多级潜在滑动特征.地震荷载作用加剧了坡内多级滑面的渐进发展趋势,多级滑面发育的时空顺序为:一级主滑面-二级主滑面-次级滑面,安全设计需要依据墩台部位的上下边坡地震工况下的稳定性进行.根据该桥主墩位置上下边坡地震的稳定性和变形特征,提出了针对缓倾结构面注浆加固和预应力锚索联合加固优化方案.

矮腿小倾角V形刚构桥梁设计方法

文中首先对矮腿小倾角V形刚构桥梁特点进行简单阐述,随后以某桥梁工程项目为例,对其设计方法进行深入研究,主要分析项目设计方案模型、设计参数、设计重点以及设计效果等内容。结果表明,矮腿小倾角V形刚构桥梁设计方法在实际应用中具有良好的可行性与安全性。

佛山富龙西江特大桥主桥桥塔中塔柱施工控制关键技术

佛山富龙西江特大桥主桥为主跨580 m的双塔双索面混合梁斜拉桥,“白鹭”造型桥塔高194.3 m,塔柱采用液压爬模法分节段施工,中塔柱直线段内倾12.5°,布置5道主动横撑(G1~G5)。建立主桥施工全过程杆系有限元模型和中塔柱塔肢结合部位实体模型,通过计算确定主动横撑安装位置、顶推力、横撑拆除顺序及中塔柱节段横向预偏量;确保横撑顶推前后塔柱根部最大拉应力不超过1 MPa;制定先从上往下拆除G3、G2、G1横撑、再从下往上拆除G4、G5横撑的拆除顺序;加大G4、G5横撑钢管规格,并在G2横撑下方增设竖向支撑;中塔柱节段向外侧设置横向预偏,抵消自重及施工荷载作用下塔柱内倾的影响。在每道横撑顶推施工期间对横撑钢管表面应力、对顶口相对位移、塔肢顶部偏位和根部截面应力进行精细化监测,确保横撑顶推力有效施加到塔柱上。施工中桥塔线形和内力状态控制良好,符合设计要求。

主桁倾角对倒梯形钢桁梁气动特性的影响分析

针对主桁倾角变化对倒梯形钢桁梁气动特性有较大影响的问题,以某公铁两用连续钢桁梁为例,针对不同的主桁倾角,采用计算流体力学(CFD)的方法建立简化的三维分析模型,对钢桁梁节段进行风场模拟,分析不同主桁倾角下的钢桁梁断面静风气动力系数、涡振性能以及流场特性的差异。结果表明:升力系数和力矩系数受主桁倾角变化影响明显,主桁倾角为10°时,钢桁梁的升力系数较优,此时钢桁梁承受较小的竖向风荷载;主桁倾角为0°时,钢桁梁的力矩系数较优,此时钢桁梁承受较小的扭转风荷载;主桁倾角对钢桁梁在0°和6°风攻角条件下的涡激性能影响明显,涡振性能在主桁倾角为2.5°和5°时较优;随着主桁倾角的增大,钢桁梁内部风速存在的减速现象减弱,有利于内部行车稳定;主桁倾角的变化对湍动能的分布影响明显,随着主桁倾角的增大,钢桁梁内部湍动能的增大效果减弱,而钢桁梁背风侧湍动能的增大效果加强;通过综合对比多类气动特性,主桁倾角为5°的钢桁梁的气动特性较优。研究得出了主桁倾角变化对倒梯形钢桁梁主梁气动特性和空间流场特性的影响规律,可为后续钢桁梁的抗风设计提供参考。