Study on Fracture Delay of High-Strength Bolts in Road Bridge Maintenance

In the maintenance work of highway and bridge engineering structures,the fracture delay of high-strength bolts is a content that needs to be focused on and researched.Based on this,the paper analyzes the fracture delay of high-strength bolts in highway bridge maintenance,including an overview of the fundamental research on fracture delay and related specific studies.It is hoped that this study can provide scientific reference for the reasonable maintenance of high-strength bolts,so as to ensure the overall maintenance effect of highway bridge projects.

Deformation-softening behaviors of high-strength and high-toughness steels used for rock bolts

In deep ground engineering,the use of high-strength and high-toughness steels for rock bolt can significantly improve its energy absorption capacity.However,the mechanisms and effects of rock loading conditions on this kind of high energy-absorbing steel for rock bolt remain immature.In this study,taking Muzhailing highway tunnel as the background,physically based crystal plasticity simulations were performed to understand the effect of rock loading rate and pretension on the deformation behaviors of twinning induced plasticity(TWIP)steel used for rock bolt.The material physical connecting to the underlying microscopic mechanisms of dislocation glide and deformation twinning were incorporated in numerical modeling.The rock loading conditions were mimicked by the real-time field monitoring data of the NPR bolt/cable equipment installed on the tunnel surrounding rock surface.The results indicate that the bolt rod exhibits pronounced deformation-softening behavior with decrease of the loading rate.There is also a sound deformation-relaxation phenomenon induced by the dramatic decrease of loading rate after pre-tensioning.The high pretension(>600 MPa or 224 k N)can help bolt rod steel resist deformation-softening behavior,especially at low loading rate(<10~(-1)MPa/s or 10~(-2)kN/s).The loading rate was found to be a significant factor affecting deformation-softening behavior while the pretension was found to be the major parameter accounting for the deformation-relaxation scenario.The results provide the theoretical basis and technical support for practical applications.

Research on Loose Reason of Fixing Bolt of Step Connector based on Finite Element Analysis

There are two connection modes between escalator step and step drive chain of outer roller,connector type A and type B.Connector type B after a period of running was found that the fixing bolt on the connector has loosened,which causes safety risks.In order to eliminate this security issue,the finite element modeling is proposed to analyze the relationship between the force generated by the connector type A or type B during the step band running and the assembly clearance or the assembly mode.So as to find out the root cause of fixing bolt loosening phenomenon,by redesigning the assembly clearance between the connector shaft and the chain hole,the fixing bolt of the connector is prevented from loosening during the step band running,ensuring the safe operation of escalators to avoid injury accidents.

Numerical Model Research on Rotational Performance of Beam-Column High-Strength Bolt Extension End-Plate Connection Node

The high-strength bolted end plate connection is widely used in the construction industry with its green environmental protection and excellent seismic performance. The joints of the joints are semi-rigid, the force performance is extremely complicated, and the experimental research cost is relatively high, and the cycle is very long. Therefore, the establishment of an efficient numerical model is of great significance for evaluating the force performance of high-strength bolt end plates. In this paper, the influence of different material models on the rotation performance of the joint is studied by numerical simulation, and the bending moment-rotation curve is obtained. The numerical simulation and the experimental results are in good agreement, so as to provide a reference for the design and application of this kind of joint.

不同螺栓等级下共享铁塔挂载连接件承载性能研究

为研究螺栓等级对挂载连接件承载性能的影响,选取了4.8级普通螺栓(KL-4.8)与8.8级摩擦型高强螺栓(KL-8.8)连接的挂载连接件进行静力试验研究。采用ABAQUS有限元分析软件对其受力性能进行模拟,使用可靠的数值模型系统分析螺栓等级和螺栓直径对连接件承载性能的影响。结果表明:在水平荷载作用下,两种不同螺栓等级连接的挂载连接件节点处均未出现滑移;两种连接件的破坏模式基本一致,左右两侧方钢管底部及右侧方钢管顶部均出现断裂;KL-8.8的整体刚度、极限承载能力以及变形能力均高于KL-4.8;当采用4.8级普通螺栓连接且承载力低于74.13 kN时,螺栓直径不宜小于18 mm,否则螺栓杆会发生剪切变形;当采用8.8级和10.9级高强螺栓连接时,双板件连接处节点偏于刚性连接,挂载连接件的整体刚度和极限荷载主要取决于方刚管、挂载铁杆等其他部件;挂载连接件在承载过程中通过双板件与主材之间的摩擦力和螺栓抗剪来抵抗外载,实际工程中应根据挂载重量合理选择螺栓参数。

钢-混凝土组合梁螺栓连接件受剪性能试验研究

传统螺栓连接件的直径小于钢梁预留孔的孔径,导致螺栓与孔壁存在间隙,容易引发钢梁与上部混凝土板间发生相对滑移使组合梁挠度增大。为尽量减小或消除上述间隙,本文引入铰制孔螺栓和螺纹孔螺栓作为组合结构的剪力连接件,并提出锥套自锁螺栓连接件。设计并开展了8个螺栓连接件推出试验,基于各试件的荷载-滑移曲线,研究了3种螺栓连接件与传统螺栓连接件间的抗剪承载力、滑移能力及抗剪刚度等受剪力学性能的具体差异。研究结果表明:3种螺栓连接件的破坏形态与传统螺栓连接件表现一致,均为螺栓杆剪断,混凝土无压溃现象;3种螺栓连接件的抗剪承载力均接近于传统螺栓连接件的抗剪承载力;基于试件的荷载-滑移曲线,3种螺栓连接件均可分为弹性阶段、塑性阶段及破坏阶段;3种螺栓连接件的延性系数和抗剪刚度均明显优于传统螺栓。综合考虑力学性能、施工性能和经济性,本文建议选用铰制孔螺栓用于组合结构的剪力连接件。

可拆卸式钢-预制UHPC组合梁中高强螺栓剪力键的抗剪性能试验

试验共设计16个推出试件,探究螺栓直径、螺栓等级、螺栓预紧力和剪力键类型对钢-预制超高性能混凝土(ultra-high performance concrete,UHPC)组合梁中高强螺栓剪力键抗剪性能的影响.试验结果表明,推出试件以剪力键剪断为主要破坏模式.螺栓剪力键的抗剪性能随螺栓的直径和螺栓等级的增大而提高;螺栓预紧力仅对初始抗剪刚度有影响;相比于传统焊钉剪力键,螺栓剪力键的单栓抗剪承载力有所下降,但整体抗剪性能仍满足结构性能要求.结合试验结果和国内外规范公式,提出一条更精确的计算公式用以预测钢-预制UHPC组合梁中螺栓剪力键的抗剪承载力.

矿山法隧道初期支护中栓钉型钢与喷射混凝土界面黏结滑移本构模型与试验研究

[目的]为探明矿山法隧道初期支护中栓钉型钢与喷射混凝土界面黏结滑移本构关系。[方法]以栓钉长度、直径和布置形式为变化参数,设置4组不同工况,进行腹板带栓钉的型钢-喷射混凝土短柱推出试验,分析其破坏模式、荷载-滑移特性和承载力等。[结果及结论]栓钉试件的破坏模式受栓钉数量和强度影响,分为拉裂破坏和胀裂破坏两类;典型的平均黏结强度-相对滑移曲线可分为无滑移段、曲线上升段、曲线下降段和水平残余段;室内试验证明栓钉直径和布置形式是影响承载能力的主要因素;根据受力机制建立带栓钉的型钢与喷射混凝土界面的黏结滑移本构模型,并经室内试验和数值模拟双重验证,表明提出的黏结滑移本构模型精度较高。研究结果可为矿山法隧道型钢与喷射混凝土支护结构设计提供理论支持。

钢-预制UHPC组合梁中高强螺栓剪力键群的抗剪性能试验研究

为研究高强螺栓作为钢-预制UHPC组合梁剪力键的抗剪性能,共设计15个推出试件,探究螺栓间距和螺栓数量对试件的破坏模式、荷载-滑移曲线、极限承载力、延性和初始抗剪刚度的影响。试验结果表明,推出试件的主要破坏模式为螺栓剪力键剪断,同时在螺栓剪切面下端有局部UHPC受压剥落,UHPC预制板只在剪力槽四周出现细微裂缝。减小螺栓间距会导致试件的抗剪性能降低;而增加螺栓数量可以有效地提高试件的抗剪性能,但也会导致单栓初始抗剪刚度下降。分析国内外现行钢-混凝土组合梁中剪力键的抗剪承载力计算公式,并以此提出一条更适用于钢-预制UHPC组合梁中高强螺栓剪力键群的抗剪承载力计算公式。对比提出公式的计算值与试验值,两者的平均比值、标准差和变异系数分别为1.02、0.02和0.02。

装配式腹板开洞组合梁受力性能试验研究

为研究高强螺栓连接腹板开洞组合梁的受力性能,文中以高强螺栓间距为变化参数,对3根装配简支组合梁试件进行了跨中单调集中加载试验。研究包括高强螺栓在组合梁装配中的受力表现、试件极限承载力、试件的破坏形态及其变形特征。结果表明高强螺栓连接的组合梁试件破坏形态为典型的剪切破坏;螺栓间距对装配式组合梁的整体刚度有较大影响,高强螺栓布置的间距越小,组合梁的组合作用越强,整体刚度也越大,破坏时变形小;高强螺栓的预紧力和螺栓孔容差对组合梁的荷载-滑移性能也有较大影响。研究可为洞口上方高强螺栓连接件的设计、施工以及加固补强提供参考。

新型不锈钢螺栓连接件疲劳后力学性能退化研究

为探究装配式组合梁中新型不锈钢螺栓连接件疲劳后的力学性能,开展螺栓连接件疲劳后力学性能仿真方法研究。首先,基于当前螺栓连接件存在的问题与不足,设计了一种耐锈蚀、方便拆卸的新型螺栓连接件。其次,进行1组静载推出试验,4组不同疲劳加载次数后的静载推出试验,分析了试件破坏特征以及力学性能退化规律。最后,基于材料剩余强度理论,引入考虑疲劳损伤的混凝土和螺栓连接件的材料退化本构模型,建立不同疲劳加载次数后的螺栓连接件力学性能退化仿真计算流程,并对仿真结果进行了验证。结果表明:新型螺栓连接件疲劳加载270万次后剩余承载力退化了12.1%,且疲劳后破坏模式为螺栓剪断。采用的材料本构退化模型的仿真计算值与试验结果吻合较好,能够合理地反映螺栓在疲劳后的力学性能退化状况。

可拆装配化钢板组合梁桥总体设计与选型研究

将可拆高强螺栓连接件应用在钢混组合梁中,可提高组合梁的管养效率,降低维修成本,但目前尚缺乏全面的相关研究和设计规范。为此,将UHPC-NC叠合桥面板代替预制桥面板,采用高强螺栓代替预制板剪力钉,形成的新型组合梁桥,并通过有限元模拟进行深入研究验证其可行性。结果表明:该梁桥成桥状态钢主梁墩顶压应力水平从原有的208.8MPa减小到195.6MPa,跨中的拉应力水平从183.4MPa增大到193.9MPa,满足设计要求。为新型可拆装配化钢板组合梁设计提供了参考。

Influence of anchorage length and pretension on the working resistance of rock bolt based on its tensile characteristics

In coal mining roadway support design,the working resistance of the rock bolt is the key factor affecting its maximum support load.Effective improvement of the working resistance is of great significance to roadway support.Based on the rock bolt’s tensile characteristics and the mining roadway surrounding rock deformation,a mechanical model for calculating the working resistance of the rock bolt was established and solved.Taking the mining roadway of the 17102(3)working face at the Panji No.3 Coal Mine of China as a research site,with a quadrilateral section roadway,the influence of pretension and anchorage length on the working resistance of high-strength and ordinary rock bolts in the middle and corner of the roadway is studied.The results show that when the bolt is in the elastic stage,increasing the pretension and anchorage length can effectively improve the working resistance.When the bolt is in the yield and strain-strengthening stages,increasing the pretension and anchorage length cannot effectively improve the working resistance.The influence of pretension and anchorage length on the ordinary and high-strength bolts is similar.The ordinary bolt’s working resistance is approximately 25 kN less than that of the high-strength bolt.When pretension and anchorage length are considered separately,the best pretensions of the high-strength bolt in the middle of the roadway side and the roadway corner are 41.55 and 104.26 kN,respectively,and the best anchorage lengths are 1.54 and 2.12 m,respectively.The best anchorage length of the ordinary bolt is the same as that of the high-strength bolt,and the best pretension for the ordinary bolt in the middle of the roadway side and at the roadway corner is 33.51 and 85.12 kN,respectively.The research results can provide a theoretical basis for supporting the design of quadrilateral mining roadways.

高强螺栓连接铝合金框架梁柱节点抗震性能试验研究及数值分析

为研究高强螺栓连接铝合金框架梁柱节点的抗震性能,设计了采用铝合金和不锈钢两种材料角型连接件的节点循环加载试验。结果表明,全铝合金角型件节点的延性发展严重不足,延性系数最大仅为2.25,破坏征兆不明显,在抗震结构中偏不安全。顶底不锈钢角型件节点最大塑性转角均在0.04rad以上,满足美国规范FEMA350不小于0.03rad的延性设计要求,表现出良好的塑性变形及耗能能力。对于顶底不锈钢角型件节点,梁腹板采用铝合金或不锈钢角型件对滞回全过程及各项性能指标无显著影响。采用有限元分析软件ABAQUS对节点抗震性能试验进行有限元模拟,有限元分析和试验结果吻合良好,可以很好地模拟节点的受力全程。

无湿接缝装配式组合梁力学性能研究

【目的】为实现钢-混凝土组合梁的无湿接缝装配化,使组合梁结构易于拆卸和更换。【方法】采用ABAQUS有限元分析软件对高强螺栓连接钢-混凝土组合梁的力学性能进行研究,建立了准确可靠的有限元模型。在此基础上,改进了预制混凝土板无湿接缝的连接方式,并研究螺栓预紧力、拼接间隙对组合梁刚度与滑移的影响。【结果】组合梁抗弯刚度随预紧力的增大而提高,随拼接间隙的增加先降低后不变。对钢-混凝土交界面滑移过程进行了传力机理分析,阐明了增加预紧力提高组合梁刚度的原理,通过拟合与试验结果对比证明了所提出的改进方法对提高组合梁抗弯刚度的有效性与可行性。

栓接装配式钢-混凝土组合梁及其抗剪键的力学性能研究

为了探究摩擦型高强度螺栓在装配式钢-混凝土组合梁中的适用性,采用ABAQUS有限元软件建立推出试件和简支梁试件的有限元模型。在试验结果验证模拟可靠性的基础上,研究螺栓预拉力、螺栓孔径、混凝土强度和螺栓强度等因素对单个抗剪键及整体组合梁的影响。分析结果表明:抗剪键的受力过程分为摩擦、滑移、承压和破坏4个阶段;螺栓预拉力、混凝土强度的增大有利于提高摩擦型高强度螺栓的极限承载力和承压抗剪刚度,较大的混凝土孔隙显著降低了螺栓抗剪刚度;提高螺栓预紧力或提高混凝土强度均可增强钢与混凝土部件的组合作用,相反,在抗剪连接程度不变的情况下,提高螺栓等级导致界面刚度分布不均,不利于滑移控制。

Hydrogen-induced delayed fracture of Cu-containing high-strength bolt steel

The hydrogen-induced delayed fracture(HIDF)behavior of a 1300-MPa-grade high-strength bolt steel 42CrMoV containing 0.42 wt.%Cu was investigated by constant load tensile test in a pH 3.5 Walpole solution.It is shown that the addition of Cu is beneficial to enhance the HIDF resistance by~13%.The observation of the fracture surface revealed that the area fraction of brittle crack initiation zone decreased remarkably for the Cu-added steel.Both the corrosion pit depth and the corrosion rate of the Cu-added steel in the Walpole solution are notably decreased,which is primarily because of the formation of a Cu-rich protective compact rust layer and slightly higher corrosion potential.As a result,the absorbed hydrogen content in that solution was also decreased by~21%.It is concluded that the improvement in the HIDF resistance of the tested steel is primarily due to the increase in corrosion resistance and resultant decrease in the absorbed diffusible hydrogen content in the acidic condition.

一种插转式连接装置的受力承压特性数值仿真

为明确软质输送管线中插转式软管连接装置的受力承压特性,保障输送介质的安全运输,通过分析其结构特点构造三维模型,运用仿真的方法,研究了插转式软管连接装置在工作压力和爆破压力下的临界螺栓预紧力,并分析了螺栓预紧力对软管的力学影响。结果表明,若保证插转式软管连接装置不发生拉脱,在工作压力下的临界螺栓预紧力需达到1.1628×104N以上,在爆破压力下的临界螺栓预紧力需达到3.5409×104N以上。此外,在工作压力下,软管所受最大等效应力随螺栓预紧力增大而不断增大。

新型不锈钢可拆卸螺栓连接件疲劳后剩余力学性能研究

为适应装配式组合梁的发展,研发一种新型不锈钢可拆卸螺栓连接件,并对其疲劳荷载作用下的力学性能退化规律开展研究。首先,通过文献和市场调研,充分考虑现有螺栓的优缺点,设计制作一种新型不锈钢可拆卸螺栓连接件用于装配式组合梁;其次,制作6组新型螺栓连接件的推出试件,进行静载和疲劳试验,对比静载与不同疲劳加载次数后试件的破坏形态,重点分析新型螺栓连接件在疲劳加载过程中剩余承载力、残余滑移量、抗剪刚度及延性系数的退化规律;最后,基于疲劳累积损伤理论和材料剩余强度模型,确定新型螺栓连接件在疲劳加载过程中的损伤度,进而建立新型螺栓连接件的剩余承载力计算模型。结果表明:新型螺栓连接件在静力和疲劳作用下呈现不同的变形及断面破坏特征;在疲劳荷载作用下,新型螺栓连接件的各项力学性能均呈现不可逆的退化,在该试验中试件在疲劳加载270万次后剩余承载力退化12.1%,延性系数退化67.6%,抗剪刚度退化12.9%,退化较为明显;建立的新型螺栓连接件剩余承载力计算模型计算结果与试验值吻合良好。

An ultra-thin bolt tension sensor and online monitoring system:For application in hydropower plant unit

The condition of bolted connections significantly affects the structural safety.However,conventional bolt tension sensors fail to provide precise measurements due to their bulky size or inadequate stability.This study employs the piezoresistive effect of crystalline silicon material to fabricate an ultrathin sensor.The sensor exhibits a linear relationship between pressure and voltage,an exceptional stability at varying temperatures,and a superior resistance to corrosion,making it adaptable and user-friendly for applications of high-strength bolt tension monitoring.A monitoring system,incorporating the proposed sensor,has also been developed.This system provides real-time display of bolt tension and enables the assessment of sensor and structural conditions,including bolt loosening or component failure.The efficacy of the proposed sensor and monitoring system was validated through a project carried out at the Xiluodu Hydropower Plant.According to the results,the sensor and online monitoring system effectively gauged and proficiently conveyed and stored bolt tension data.In addition,correlations were created between bolt tensions and essential unit parameters,such as water head,active power,and pressures at vital points,facilitating anomaly detection and early warning.