双语推荐：“桥梁疲劳断裂和长寿命设计与运维”主题

近年来桥梁疲劳断裂病害增长较快，诱发的工程事故时有发生，危及桥梁运营安全。桥梁结构疲劳损伤的过早出现，使其无法达到设计使用年限，给桥梁安全性与耐久性带来了极大挑战。服役桥梁延寿、新建桥梁增寿，实现桥梁结构长寿命化是新世纪桥梁工程创新发展的重要方向之一。

本期精选发表于《交通运输工程学报》的7篇双语文章，内容涵盖新型管节点疲劳性能试验、拉索腐蚀疲劳评估、钢桥疲劳限载分析、超高性能混凝土（UHPC）组合梁耐久承载性能试验等方面的最新科研成果，希望能为相关领域的专家学者提供新的思路和见解，欢迎阅读。

01

在役钢桥面板纵肋与顶板焊根疲劳裂纹内焊加固方法

Internal welding reinforcement method for fatigue crack at weld root on rib-to-deck of in-service steel bridge deck

【摘要】为实现纵肋与顶板焊根疲劳裂纹的有效加固,提出了能够满足在役钢桥面板加固需求的内焊加固方法,研发了自动化焊接机器人和相关关键装备;设计了4个试验模型对方法和装备的有效性和适用性进行研究,验证了纵肋与顶板焊根产生疲劳裂纹的开裂模式;使用所研发的专用焊接设备在纵肋内部进行焊接加固,进行了加固结构的疲劳破坏试验;对比了试验结果与有限元模拟结果,分析了加固后结构的疲劳性能,验证了内焊加固方法的有效性。研究结果表明:内焊加固方法能够将既有的焊根裂纹转化为内部缺陷,研发的装备能够实现原位加固,有效抑制疲劳裂纹的扩展,使已开裂焊接细节的疲劳寿命提高了66%～157%;由于各开裂模式具有不同程度疲劳损伤累积,加固后焊接细节会发生主导开裂模式迁移;对于包含多开裂模式的焊接细节,加固后的剩余疲劳寿命与各开裂模式的实际疲劳损伤累积程度以及加固方法对各开裂模式受力特性的扰动程度两方面的因素密切相关。

【Abstract】To achieve effective reinforcement of fatigue crack at weld root on rib-to-deck, an internal welding reinforcement method was proposed to meet the requirements of in-service steel bridge decks, and automated welding robots and associated key equipment were developed. Four test models were designed to study the effectiveness and applicability of the method and equipment. The cracking mode of fatigue crack at weld root on rib-to-deck was validated. The developed specialized welding equipment for internal welding reinforcement was used internally within the rib, and fatigue failure tests on the reinforced structure were conducted. The results of experiment and finite element simulation were compared. The fatigue performance of the structure after reinforcement was analyzed, and the effectiveness of internal welding reinforcement method was confirmed. Research results indicate that the internal welding reinforcement method can transform the existing weld root cracks into internal defects. The developed equipment enables in-site reinforcement, effectively suppressing the expansion of fatigue cracks, and enhancing the fatigue lives of the cracked welded joints by 66%–157%. Due to the different degrees of fatigue damage accumulation in various cracking modes, a transition in the dominant cracking mode of the welded joints occurs after reinforcement. For welded joints containing multiple cracking modes, the remaining fatigue life after reinforcement is closely related to the actual fatigue damage accumulation levels of each cracking mode and the degree of disturbance of reinforcement methods on the stress characteristics of each cracking mode.

02

钢管混凝土KK型节点疲劳性能试验

Fatigue performance experiment of concrete-filled steel tubular-KK joint

【摘要】为研究钢管混凝土KK(CFST-KK)型节点疲劳性能,开展了CFST-KK型节点模型疲劳试验,分析了CFST-KK型节点热点应力分布规律和疲劳性能演化过程;建立了CFST-KK型节点实体有限元模型,结合试验和有限元结果,分析了CFST-KK型节点与钢管混凝土K(CFST-K)型节点疲劳性能的差异性;研究了不同参数对KK型节点疲劳性能影响,探讨了适用于CFST-KK型节点疲劳寿命的评价方法。研究结果表明:采用二次外推方式计算的CFST-KK型节点,最大热点应力位于受拉支管相贯焊缝的主管侧冠点偏外鞍点15°处;计算CFST-KK型节点应力集中系数时,支管名义应力可仅考虑轴力和面内弯矩的影响而不考虑面外弯矩的影响,其应力集中系数为6.36,比CFST-K型节点大80.2%;CFST-KK型节点的疲劳裂纹萌生于最大热点应力处,在反复加载过程中裂纹沿焊趾根部向两侧与主管壁厚方向延伸,裂纹向外鞍点扩展的速度要略快于向内鞍点扩展的速度,停止反复加载后裂纹并未贯穿主管管壁;受支管面外弯矩与支管间空间效应的影响,CFST-KK型节点的抗疲劳性能与CFST-K型节点有明显差异;主管内填混凝土能提升CFST-KK型节点径向刚度,缓解应力集中情况;支管面外夹角增大会增大支管间空间效应的影响;考虑钢管内混凝土影响的CFST-K型节点的热力应力与疲劳寿命曲线在评价CFST-KK型节点疲劳寿命时具有良好的精度。

【Abstract】In order to study the fatigue performance of concrete-filled steel tubular-KK (CFST-KK) joint, a fatigue test on CFST-KK joint models was conducted, and the stress distribution pattern and fatigue performance evolution of CFST-KK joints were analyzed. A solid finite element (FE) model of CFST-KK joint was established. In combination with the results of the test and FE models, the difference in the fatigue performance between the CFST-KK joint and the concrete-filled steel tubular-K (CFST-K) joint was revealed, the influences of different parameters on the fatigue performance of KK joint were analyzed, and an appropriate fatigue life evaluation method for the CFST-KK joint was discussed. Research results show that the maximum hotspot stress of CFST-KK joint calculated by the quadratic extrapolation method is located 15° away from the crown point on the chord side of tension brace to the chord intersecting weld towards the outer saddle point. In calculating the stress concentration factor (SCF) of CFST-KK joint, the nominal stress of the brace only takes into account the influence of axial force and in-plane bending moment regardless of the impact of out-of-plane bending moment, and the SCF of CFST-KK joint is 6.36, 80.2% higher than that of CFST-K joint. The fatigue crack in the CFST-K joint originates at the location with the highest stress concentration, extends towards the two sides and wall thickness of the chord along the weld to the root during repeated loading, and expands slightly faster towards the outer saddle point than the inner saddle point. However, it does not penetrate the chord wall after stopping the repeated loading. The fatigue resistance of CFST-KK joint differs significantly from that of CFST-K joint, primarily due to the presence of out-of-plane bending moment in the brace and the spatial interaction between the braces. Filling the tub with concrete can enhance the radial stiffness of CFST-KK joint and reduce the stress concentration. Augmenting the angle beyond the branch face can enhance the spatial interaction between the braces. Taking into account the impact of filled concrete, the hot spot stress and fatigue life curve of CFST-K joint has high precision in assessing the fatigue life of CFST-KK joint.

03

氯盐环境下预损伤UHPC-HPC组合梁抗弯性能

Flexural behavior of pre-damaged UHPC-HPC composite beams in chloride corrosion environment

【摘要】为了提高普通钢筋混凝土梁的耐久性,设计了一种超高性能混凝土(UHPC)-高性能混凝土(HPC)组合梁新型结构,开展了锈蚀后UHPC-HPC组合梁的抗弯性能试验,研究了氯盐侵蚀后组合梁抗弯承载力降低的机理,分析了腐蚀程度、截面形式与预损伤对其抗弯性能的影响;引入钢筋屈服强度折减系数、截面积折减系数与混凝土预损伤系数,提出了锈蚀后UHPC-HPC组合梁抗弯承载力计算方法,并验证了计算方法的可行性。分析结果表明:锈蚀后梁体抗弯承载力降低主要原因为钢筋抗拉强度下降,梁体刚度退化与韧性减弱,钢纤维阻裂效果削弱;锈蚀后UHPC-HPC组合梁的破坏表现为跨中附近出现1条主裂缝或加载点附近出现2条主裂缝;UHPC-HPC组合梁的受力过程分为线弹性、裂缝发展和屈服3个阶段,梁体截面混凝土应变基本符合平截面假定;侵蚀时间越长,组合梁的开裂荷载和承载力降低越大,通电快速侵蚀10d时,降幅分别达16.2%和10.9%;锈蚀后T形梁比矩形梁开裂早,前者的开裂荷载比后者降低8.1%,后期刚度下降较快;预损伤显著影响梁的整体刚度,预加载后梁的整体刚度降低,混凝土损伤后的预损伤系数为0.984;锈蚀率越大,钢筋的屈服强度与截面积折减系数越小,变化趋势符合二次抛物线;锈蚀后UHPC-HPC组合梁抗弯承载力的计算值与实测值吻合良好,两者之比的平均值为0.998,标准差为0.020。

【Abstract】To improve the durability of ordinary reinforced concrete beams, a new structure of ultra-high performance concrete (UHPC)-high performance concrete (HPC) composite beam was designed, and the flexural behavior of the UHPC-HPC composite beam after chloride corrosion was tested. The decrease mechanism of flexural capacity of the composite beam after chloride erosion was studied, and the effects of erosion degree, section form and pre-damage on the flexural behavior were analyzed. The yield strength reduction coefficient, cross-sectional area reduction coefficient of steel bar and pre-damage coefficient of concrete were introduced to propose the calculation method of flexural capacity of the UHPC-HPC composite beam after corrosion, and the feasibility of the calculation method was verified. Analysis results show that the main reasons for the decrease in the flexural capacity of the beam after corrosion are the decrease in the tensile strength of steel bars, the degradation of the stiffness and toughness of the beam, and the weakening of the crack resistance effect of steel fibers. The failure of the UHPC-HPC composite beam after corrosion is characterized by one main crack near the mid-span or two main cracks near the loading point. The stress process of the UHPC-HPC composite beam is divided into three stages: linear elasticity, crack development and yield. The concrete strain of the beam section basically conforms to the assumption of plane section. The longer the erosion time is, the more the cracking load and the flexural capacity reduce. When the beam is energized and eroded rapidly for 10 d, the reductions reach 16.2% and 10.9%, respectively. The T-beam cracks earlier than the rectangular beam, the cracking load of the former is 8.1% smaller than that of the later, and the stiffness decreases faster in the later stage after corrosion. The pre-damage significantly affects the overall stiffness of the beam, the overall stiffness decreases after pre-loading, and the pre-damage coefficient after the concrete damage is 0.984. The larger the corrosion rate is, the smaller the yield strength and the cross-sectional area reduction coefficient of the steel bar are, and the change trend conforms to the quadratic parabola. The calculated flexural capacity of the UHPC-HPC composite beam after corrosion is in good agreement with the measured value, the average ratio of the two is 0.998, and the standard deviation is 0.020. 10 tabs, 14 figs, 31 refs.

04

矩形截面型钢混凝土梁抗弯极限承载力

Ultimate flexural capacity of steel reinforced concrete beams with rectangular section

【摘要】采用JGJ138—2016、СИ3-78、YB9082—2006、AISC360-16、叶列平公式,计算了所收集的51个矩形截面型钢混凝土(SRC)梁试件的抗弯极限承载力,并将计算结果与试验值进行比较;分析了所收集试件的参数范围及现有计算方法出现计算误差的原因,讨论了现有计算方法在计算理论等方面存在的局限性,并进行理论推导,提出了矩形截面SRC梁抗弯极限承载力计算方法;采用所提出的计算方法,计算了所收集试件的抗弯极限承载力。分析结果表明:现有计算方法的计算值与试验值均存在一些偏差;СИ3-78中的受压区高度取值不合理,且该方法的计算误差随混凝土强度提高而增大;JGJ138—2016未考虑中性轴与型钢位置的相对关系对计算结果的影响,存在局限性;YB9082—2006与AISC360-16未考虑型钢与混凝土相互作用及型钢的布置方式等问题;叶列平公式计算结果较为保守;采用提出的抗弯极限承载力计算方法得到的计算值与试件试验值的比值均值为0.953,方差为0.015,计算值与试验值吻合较好;所收集SRC梁试件的含钢率为1.77%～5.77%,小于YB9082—2006所建议的合理含钢率范围,因此,今后还需进一步开展高含钢率试件的补充试验,以便完善矩形截面SRC梁的抗弯极限承载力计算方法。

【Abstract】JGJ 138—2016, СИ 3-78, YB 9082—2006, AISC 360-16, and YE Lie-ping’s formulas were used to calculate the ultimate flexural capacities of 51 collected specimens of steel reinforced concrete (SRC) beams with rectangular sections. The calculated results were compared with the test values. The ranges of parameters of the collected specimens and the reasons for the calculation errors of the existing calculation methods were analyzed. The limitations of the existing calculation methods were discussed in terms of the calculation theory and other aspects. Theoretical derivations were performed, and a method for calculating the ultimate flexural capacities of SRC beams with rectangular sections was proposed. The ultimate flexural capacities of the collected specimens were calculated by using the proposed method. Analysis results show that some deviations are found between the calculated values obtained by the existing calculation methods and the test values. The height value of the compression zone in СИ 3-78 is not appropriate, and the calculation error of this method increases with the increase in concrete strength. The impact of the relative relationship between the neutral axis and the position of the structural steel on the calculation results is not considered in JGJ 138—2016, and limitations exist. YB 9082—2006 and AISC 360-16 do not take into account the interaction between structural steel and concrete or the arrangement of the structural steel. The YE Lie-ping’s formulas produce conservative results. The average ratio of the values calculated by the proposed method for the ultimate flexural capacity to the test values of specimens is 0.953, with a variance of 0.015. The calculated values agree well with the test values. The steel ratios of the collected SRC beam specimens range from 1.77% to 5.77%, which is smaller than the reasonable steel ratio range suggested by YB 9082—2006. Therefore, it is necessary to carry out further supplementary tests of specimens with high steel ratios in the future, so as to improve the calculation method for the ultimate flexural capacity of SRC beams with rectangular sections. 1 tab, 10 figs, 31 refs.

05

基于Harris特征与NDT-ICP算法的钢箱拱预制件尺寸智检方法

Intelligent dimensional inspection method for steel box arch prefabricated components based on Harris features and NDT-ICP algorithm

【摘要】针对桥梁建造时传统人工尺寸检测在面对海量桥梁预制件时效率低、成本高的难题,使采用地面激光扫描(TLS)技术的智能尺寸检测突破现有数据处理算法的精度与效率瓶颈,建立了基于建筑信息模型(BIM)-TLS的桥梁钢预制件尺寸智检框架,包含构件几何尺寸检测与数字预拼装2个环节;二次开发了BIM点云化处理技术,构建了参照点云模型,采用直通滤波、统计去噪(SOR)滤波、体素化网格(VG)处理等算法预处理点云数据,实现了基于k近邻(kNN)算法的尺寸检测指标评价;通过3D-Harris特征点检测、正态分布变换(NDT)粗配准与迭代最近点(ICP)精配准提出了基于Harris特征与NDT-ICP算法的快速配准尺寸智检策略,并结合工程需求应用于某大跨拱梁组合结构钢箱拱预制件尺寸智检中。研究结果表明:采用提出的智检方法对2个相邻节段钢箱拱进行尺寸检测的最大偏差分别为1.689和1.571mm,均满足制造偏差(小于2mm)要求;与传统NDT-ICP算法相比,该方法将点云整体配准精度提高了35.3%,效率提高了61.88%,可见该方法表现高效且结果准确,促进了钢预制件几何尺寸检测智能化;基于该方法的拱肋数字预拼装监测点最大检测拼装偏差为1.9533mm,符合拼装偏差(小于2mm)要求,实现了精准偏差检测,为后续桥位顺利架设提供了良好保障,且为相似结构的尺寸检测提供了参考。

Abstract:In response to the challenges of low efficiency and high cost of traditional manual dimensional inspection in the face of massive bridge prefabricated components during the bridge construction, and to break through the accuracy and efficiency bottlenecks of existing data processing algorithms in the intelligent dimensional inspection using the terrestrial laser scanning (TLS) technology, an intelligent dimensional inspection framework for bridge steel prefabricated components was established based on the building information modeling (BIM)-TLS, including two links: geometric dimensional inspection and digital pre-assembly of components. The BIM point cloud processing technology was customized, and the reference point cloud model was constructed. The point cloud data were preprocessed by using the straight-through filtering, statistical outlier removal (SOR) filtering, voxel grid (VG), and other algorithms. The dimensional inspection index evaluation based on the k-nearest neighbor ( kNN) algorithm was realized. Through the 3D- Harris feature point inspection, normal distributions transform (NDT) coarse registration, and iterative closet point (ICP) fine registration, a fast registration intelligent dimensional inspection strategy based on the Harris feature and NDT-ICP algorithm was proposed and applied to the intelligent dimensional inspection of steel box arch prefabricated components of a large-span arch beam composite structure in combination with the engineering requirements. Research results show that the maximum deviations of the proposed intelligent inspection method for the dimensional inspection of two steel box arches at adjacent segments are 1.689 and 1.571 mm, respectively, and meet the requirement of the manufacturing deviation (less than 2 mm). Compared with the traditional NDT-ICP algorithm, the proposed method improves the overall registration accuracy of the point cloud by 35.3% and the efficiency by 61.88%. It can be seen that the method is efficient, and the results are accurate. It promotes the intelligence of the geometric dimensional inspection of steel prefabricated components. Based on the method, the maximum inspection assembly deviation of the digital pre-assembly monitoring point for the arch rib is 1.953 3 mm, and meets the requirement of the assembly deviation (less than 2 mm). The method realizes the accurate deviation inspection. It provides a good guarantee for the smooth erection of subsequent bridge positions and a reference for dimensional inspections of similar structures.

06

腐蚀-疲劳荷载耦合作用下桥梁拉索高强钢丝自漏磁信号变化规律

Variation laws of self-magnetic flux leakage signals of high-strength steel wires in bridge cables under coupling effect of corrosion–fatigue loads

【摘要】为增强桥梁拉索高强钢丝漏磁检测的实用性,开展了腐蚀、应力单一因素作用试验与预腐蚀-疲劳-腐蚀、预疲劳-腐蚀-疲劳三阶段交互作用试验,阐述了腐蚀-疲劳耦合作用对自漏磁信号的影响机制。研究结果表明:腐蚀区域的自漏磁信号极值随腐蚀时间的增加而增加,且变化特征越发明显,腐蚀缺陷引起的异常自漏磁信号最大变化可达50000nT;随着疲劳加载循环次数的增加,无锈蚀高强钢丝自漏磁信号整体呈现先增加后稳定的趋势,当疲劳加载循环次数大于10000时,磁场强度的增加速率降低且趋于平缓;预腐蚀后施加的交变应力场会削弱腐蚀缺陷引起的自漏磁信号,再次腐蚀后的磁场信号变化与预腐蚀程度有关,预腐蚀9h后施加疲劳荷载,之后再腐蚀3h,与单一腐蚀12h相比,自漏磁信号强度削弱了32%;施加预疲劳交变应力场可强化磁场,导致腐蚀后自漏磁信号极值增加,当预疲劳加载循环次数从1000增加至100000时,自漏磁信号强度增大了30%。由此可见,早期腐蚀引起的高强钢丝异常自漏磁信号可被疲劳作用掩盖,考虑单一腐蚀与应力变化难以反映高强钢丝自漏磁检测效果,需综合考虑腐蚀-疲劳的耦合效应,以获得桥梁拉索高强钢丝自漏磁信号变化规律,从而为桥梁拉索无损检测提供分析依据。

【Abstract】To enhance the practicality of magnetic flux leakage detection for high-strength steel wires in bridge cables, the corrosion and stress single factor tests, as well as three-stage interaction tests of pre-corrosion–fatigue–corrosion and pre-fatigue–corrosion–fatigue were conducted, and the mechanism for the influence of corrosion-fatigue coupling effect on the self-magnetic flux leakage signal was explained. Research results show that the extreme self-magnetic flux leakage signals in the corroded area increase with the corrosion time, and the variation characteristics are becoming more and more obvious. The maximum variation in the abnormal self-magnetic flux leakage signals caused by the corrosion defect can reach up to 50,000 nT. As the fatigue loading cycle number increases, the self-magnetic flux leakage signal of non-corroded high-strength steel wires is on an overall increasing trend before getting stabilized. When the fatigue loading cycle number exceeds 10,000, the increasing rate of magnetic field intensity decreases and tends to be stable. The alternating stress field applied after the pre-corrosion weakens the self-magnetic flux leakage signal caused by the corrosion defect, and the variation in the magnetic field signal after the second corrosion is related to the degree of pre-corrosion. Under the fatigue load after the pre-corrosion for 9 h, and the ninthe second corrosion for 3 h, the strength of the self-magnetic flux leakage signal reduces by 32% compared with that in the single corrosion for 12 h. Applying a pre-fatigue alternating stress field can strengthen the magnetic field, leading to an increase in the extreme self-magnetic flux leakage signal after the corrosion. When the pre-fatigue loading cycle number increases from 1,000 to 100,000, the strength of the self-magnetic flux leakage signal increases by 30%. It follows that the abnormal self-magnetic flux leakage signals of high-strength steel wires caused by the initial corrosion can be masked by the fatigue effect, making it difficult to reflect the detection effect of self-magnetic flux leakage of high-strength steel wires by just considering a single factor of variation in the corrosion or stress. Therefore, it is necessary to comprehensively consider the corrosion-fatigue coupling effect, to obtain the variation laws of self-magnetic flux leakage signals of high-strength steel wires in bridge cables, thereby providing an analytical basis for the non-destructive test of bridge cables.

07

钢-ECC/UHPC组合梁负弯矩区力学性能研究

Investigation on mechanical properties of steel-ECC/UHPC composite girders in negative moment regions

【摘要】为改善钢-混组合梁负弯矩区混凝土易开裂缺点,引入工程水泥基复合材料(ECC)和超高性能混凝土(UHPC)代替普通混凝土(NC)形成钢-ECC/UHPC组合梁,展开了1片钢-NC组合梁、1片钢-ECC组合梁和2片钢-UHPC组合梁的负弯矩区静力试验;结合有限元分析方法对比了不同类型混凝土的应变、裂缝扩展与分布特点,分析了混凝土类型和配筋对钢-混组合梁破坏形态、承载能力与变形能力影响规律。研究结果表明:钢-混组合梁在负弯矩作用下整体协同工作性能良好,破坏形态均为弯曲破坏;ECC和UHPC裂缝呈现纤细的特点,ECC尤为明显;与钢-NC组合梁相比,钢-ECC组合梁和钢-UHPC组合梁的开裂荷载分别提高了2.00和2.75倍,抗弯刚度分别提高了17.23%和35.73%,抗弯承载力分别提高了9.00%和6.81%,表明UHPC抗裂能力更强,可以有效改善钢-混组合梁负弯矩区桥面板抗裂性能,ECC与UHPC代替NC可以提高钢-混组合梁的抗弯刚度和承载力;配筋与无筋钢-UHPC组合梁的开裂荷载和前期刚度无显著差异,无筋钢-UHPC组合梁破坏时形成贯通裂缝,其承载力相比配筋钢-UHPC组合梁下降了13.39%;ECC强度增加,钢-ECC组合梁承载力提高较显著,UHPC强度变化对钢-UHPC组合梁承载力影响不明显;配筋率对钢-UHPC组合梁承载力影响可分为2个阶段,当配筋率小于1.6%时承载力显著增长,当超过1.6%时承载力增幅趋缓。

【Abstract】In order to improve the concrete cracking defect in the negative moment regions of steel-concrete composite girders, the engineered cementitious composite (ECC) and ultra-high performance concrete (UHPC) were introduced to replace the normal concrete (NC) to form the steel-ECC/UHPC composite girders. The tests of static mechanical properties in the negative moment regions were carried out, involving one steel-NC composite girder, one steel-ECC composite girder, and two steel-UHPC composite girders. The finite element analysis method was utilized to compare the strain, crack propagation, and distribution characteristics of different types of concretes. The influences of concrete type and reinforcement on the failure mode, bearing capacity and deformation capacity of steel-concrete composite girders were analyzed. Research results show that the steel-concrete composite girders have good overall cooperative performance under negative moments, and the failure modes are all bending failures. Cracks in the ECC and UHPC are delicate, especially in the ECC. Compared with the steel-NC composite girder, the cracking loads of steel-ECC and steel-UHPC composite girders increase by 2.00 and 2.75 times, the flexural stiffnesses increase by 17.23% and 35.73%, and the flexural capacities increase by 9.00% and 6.81%, respectively. Therefore, the UHPC has stronger crack resistance, effectively improving the crack resistance of bridge decks in the negative moment regions of the steel-concrete composite girders. Moreover, using the ECC and UHPC to replace the NC can enhance the flexural stiffness and bearing capacity of steel-concrete composite girders. There is no significant difference in the cracking load and early stiffness between the reinforced and unreinforced steel-UHPC composite girders. When the unreinforced steel-UHPC composite girder fails, the through cracks form, and its bearing capacity decreases by 13.39% compared to the reinforced steel-UHPC composite girder. As the ECC strength increases, the bearing capacity of the steel-ECC composite girder improved significantly. The influence of UHPC strength on the bearing capacity of steel-UHPC composite girder is not obvious. The impact of reinforcement ratio on the bearing capacity of steel-UHPC composite girder can be divided into two stages. When the reinforcement ratio is below 1.6%, the bearing capacity increases significantly, and when it exceeds 1.6%, the growth rate of bearing capacity slows down.

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