Current research on Concrete filled steel tubular (CFST) structures mainly on the single members and joints. Based on these studies, when designing a CFST truss beam, it is usually discretizes the CFST truss structure into members and joints for calculating the bearing capacity. In this paper, two full-scale models of CFST truss beam with and without prestressed steel strands were subjected bending to explore the effects of setting prestress. The flexural behaviors of the two beams during elastic stage, elastoplastic stage, plastic stage and failure stage were observed and compared. Experimental results indicated that setting prestress in the bottom chord could increase the flexural bearing capacity with 14.8% and enhance flexural stiffness of the CFST truss beam, while not affect the failure mode of which. Furthermore, a simplified prediction method for flexural bearing capacity was proposed based on the plane section assumption, which improved the calculation efficiency of the bearing capacity of such beams. The relative error of this method is 2.93% validated against the experimental results, which satisfies the precision requirements of engineering design.

The Guantang Bridge in Liuzhou City, with a main span of 457 m, is a through steel box arch bridge. The MIDAS/Civil three-dimensional finite element calculation and analysis software is used to establish a spatial dynamic calculation model, conduct structural dynamic characteristics analysis, and use response spectrum analysis and time history analysis methods to conduct structural seismic response analysis. The results show that the bridge has good dynamic and seismic performance.

For reinforced concrete arch bridges formed by the strong skeletal method, when calculating the non-strong skeletal structure, only the steel tubes are considered as ordinary reinforcement without accounting for composite force effects, which has a minimal impact and leans towards safety. However, for strong skeletal structures, if composite force effects are not considered, the calculation results are excessively conservative. In this paper, taking the Xining River Extra Large Bridge as a background, the influence of composite force effects of the strong skeletal structure on the ultimate load-bearing capacity of the arch ring is analyzed under the influence of dual nonlinearity.

Based on the difficulties encountered during the construction period of the Sichuan Hejiang Yangtze River Third Bridge with a main span of 507 m—Concrete filled steel tube (CFST) Tied Arch Bridge, technical research has been conducted on the mechanical properties of ultra-high strength CFST (≥ C70), the structural construction of large-span CFST tied arch bridge, and the installation process of the main arch. Based on the research results, this report introduces the calculation method of ultra-high strength CFST, the structural system design of CFST tied arch bridge with a main span of 507 m, the stiffness matching design of the main arch suspension system, the structural design of composite transverse brace, the installation and hanging system of the main arch, and the design of the main arch concrete pouring.

Fifth Yangtze River Bridge in Luzhou is an extra-long span half-through steel box arch bridge with thrust. The main girder deck system is subject to the direct action of vehicles, pedestrians, rail transit and other loads. At the same time, it produces a huge horizontal thrust to the arch base foundation through the slings and arch ribs. Therefore, the selection of the main girder structural type is directly related to the comfort of traveling, the steel consumption economy and the arch base foundation engineering volume. The three main girder schemes are compared from the structural form of the rail transit, the stiffness demand, the deformation limit and the force performance. The two-side box type flat steel box girder is finally selected as the deck system.

The main bridge of Shuiluohe Bridge on the Gulin Jinsha Expressway is a deck reinforced concrete arch bridge, and the main arch ring is constructed using cantilever casting method. Due to the influence of terrain and geological conditions, in order to reduce excavation of the mountain, the main arch adopts a “slope arch”, and the elevation of the arch line on Jinsha Bank is 6.7m higher than that on Gulin Bank. The main arch adopts a catenary curve non-hinge arch with a span of 335m, a rise-span ratio of 1/4.2, and an arch axis coefficient of 1.8. The main bridge adopts a left and right split design, and the arch ribs of both bridges adopt two octagonal single box single chamber structures, with transverse diaphragms connecting the arch ribs. The upper structure adopts a span of 11 × A 31.75m prestressed concrete simply supported I-shaped beam and composite bridge deck, supported by columns and cover beams on the arch. The arch base adopts open excavation to expand the foundation.

To investigate the matching relationship between steel ratio and core concrete strength in the ultra-high strength concrete-filled steel tubular (UHSCFST) columns, a total of 40 stub column specimens, considering eight different steel ratios (ranging from 5.97% to 38.72%) and three grades of high-strength concrete (C60, C80, and C100), were tested under axial compression. The results revealed that under axial compression loads, as the steel ratio of the cross-section increased from low to high, the local buckling characteristics on the surface of UHSCFST stub columns gradually diminished, transitioning from shear failure to local buckling and bulging failure. With the improvement of the strength grade of the core concrete, the steel ratio that ensures the full confining effect of the steel tube should also be increased significantly. For the specimens filled with C60, C80, and C100 concrete, the threshold value of the steel ratio that can ensure the axial compressive strength of the specimen does not decrease after reaching the peak load was 13.87%, 20.24%, and 27.16%, respectively. By comparing with the experimental data, it is found that the CFST composite strength formula recommended by the current Chinese code did not apply to UHSCFST members. Based on the regression fitting of experimental data, the formula for calculating the composite strength of UHSCFST members and the ultimate strength of UHSCFST stub columns were proposed.

The beam end of the railway bridge is the crucial part of the whole bridge, and the earthquake will cause damage to the beam end. In order to ensure the safety of the bridge and track system. To investigate the risk of seismic deformations at the beam end in railway bridges, a three-span continuous rigid frame bridge was taken as a case study and a three-dimensional finite element model of the whole bridge was established in ABAQUS. The deformation angle of the beam end was selected as the damage index, and the seismic vulnerability and risk curves of the beam end were calculated by the incremental dynamic analysis (IDA) method using 22 scaled ground motion time histories. The results show that in the same range of peak ground accelerations (PGAs), the influence of cross-bridge ground motion on the corner deformations of the beam end was much greater than that of the along-bridge ground motion. Under the along-bridge seismic excitation, the damage probabilities for the rotation angles in X, Y and Z-directions did not exceed 50 %. In different damage states, increasing in PGA correlated positively with the beam end damage probability. The vulnerability curves for PGA can be used for the seismic risk assessment of the beam end and can also provide decision support for prioritizing the seismic reinforcement of bridges.

为研究钢管混凝土相贯焊接节点在轴力和弯矩共同作用下,管内混凝土对节点疲劳寿命的贡献,制作钢管混凝土桁梁桥K型相贯焊接节点1:2缩尺模型并建立实体有限元模型,开展空管、仅弦管灌注混凝土、弦管和腹管均灌注混凝土3类构件相贯焊接节点受力分析与疲劳试验验证.结果表明:弦管与腹管灌注混凝土可提高结构刚度和调整结构内力,中弦管到边弦管的传力路径由单一的斜腹管变为斜腹管与水平腹管共同传力,斜腹管内力由轴力变为轴力与弯矩的组合形式.疲劳试验测得的相贯焊接节点最大应力位置、大小及应力分布状态与有限元计算结果吻合.弦管与腹管灌注混凝土使相贯焊接节点整体应力及峰值应力均降低,改善了相贯焊接节点的应力分布状态,延缓了裂纹发展速度,延长了相贯焊接节点疲劳寿命.

The jacking and pouring of concrete in the main arch pipe is a key process and technical difficulty in the construction of CFST arch bridge. The concrete in the pipe of long-span CFST arch bridge has large volume, high strength, long pumping distance and long pouring time, it is prone to block and burst. Several accidents have occurred on many bridges in China. In order to reduce the construction risk of concrete pouring in the main arch pipe, the experimental research on the technology of concrete jacking and pouring in the pipe of long-span CFST arch bridge is carried out, and the influence rules of the construction process of concrete jacking and pouring in the pipe on the slump, expansion, plastic viscosity, movement mode and pumping resistance of concrete are discussed. The result shows that（1） The slump, expansion and plastic viscosity of the concrete in the pipe are reduced after the high-pressure pumping process, and the influence on the compressive strength is not obvious.（2） Under the condition of high pump pressure, the air content of concrete increases, while it decreases at the end of pumping process.（3） The movement modes of concrete in large-diameter main arch steel pipe and small-diameter pump pipe are obviously different. The former moves very slowly, mainly with the shear movement of the concrete in the pipe itself, while the latter moves faster, mainly with the piston type overall push movement.（4） The different movement modes of concrete in the pipe leads to different calculation methods of pumping pressure.The pumping resistance of concrete in the large-diameter main arch steel pipe is mainly to overcome gravity and do work, while the pumping pressure of concrete in the small-diameter pump pipe is mainly to overcome the pipe wall friction resistance and its own shear force. The calculation methods of concrete pumping pressure in the pipe of small-diameter pump pipe and large-diameter main arch steel pipe are put forward through the test, and the applicability is verified by project examples.

钢筋混凝土拱桥因受力合理、全寿命周期维护成本低,成为深沟峡谷、地震多发等地区最具竞争力的桥型.特别是劲性骨架成拱的钢筋混凝土拱桥,无需支架、施工安全、截面参与施工受力,已成为大跨钢筋混凝土拱桥建造最优技术之一.原有劲性骨架法成拱技术,受到主拱结构构造差、骨架强度低、刚度小、外包混凝土施工环节多等诸多因素限制,国内建设数量较少.为攻克技术难题,依托320 m官盛渠江特大桥,对劲性骨架钢筋混凝土拱桥再创新,提出强劲骨架建造特大跨钢筋混凝土肋拱桥的建造技术,该技术提出的新结构、新材料、新工艺和新装备等科技成果,可简化特大跨钢筋混凝土拱桥施工流程、降低施工风险、节约施工工期,结构设计合理、材料利用率高、节约工程造价,社会经济效益十分显著.

直线布筋先张法预应力混凝土箱梁中的预应力筋不能对梁端混凝土提供预剪力,不能有效控制混凝土斜裂缝的发展.通过在箱梁端部布置混凝土堵头板可以提高梁端截面的抗剪能力,但堵头板的存在会使箱梁内模板不便于拆除,降低施工的便利性,也造成了模板的浪费.为了研究设置箱梁堵头板的必要性和对梁端受力的影响,建立ABAQUS空间箱梁模型,分析堵头板设置与否、堵头板截面形式和厚度的变化分别对梁端附近截面的剪应力沿梁高分布情况的影响.结果表明:在直线布筋先张法预应力混凝土箱梁梁端布置堵头板具有必要性,综合考虑堵头板改善梁端受力性能的效率和经济因素后,建议采取厚度为 60 cm的开方孔堵头板.

高原山区的桥梁工程建设环境恶劣,工程技术要求高,钢混组合桥梁中盖梁的跨径及承受的外部荷载重量正逐步突破现有技术水平.通过加强设计或者加大施工投入以维持桥梁的正常施工与运营,不仅成本耗费巨大,更会造成资源浪费,与当前社会发展战略思想相悖.本研究依托马塘特大桥,开展超大跨预应力钢箱混凝土组合盖梁设计技术创新,提出了超大跨盖梁的设计和建造技术,为项目桥梁以及相同场景的桥梁建设提供技术支撑.

Based on the project of the Guansheng Qujiang Bridge, the flexural mechanical properties of an ultrahigh strength concrete filled steel tube (UHSCFST) were discussed. A total of six UHSCFST beam specimens were tested, and the cube strength (fcu) of the core concrete reached 80.3–115.2 MPa. The effects of concrete strength on flexural bearing capacity, deformation characteristics, and failure modes of UHSCFST specimens were discussed. Test results showed that the bending failure modes of UHSCFST specimens were the same as those of ordinary ones. The failure of UHSCFST specimens was attributed to excessive deflection, and local buckling occurred in the compression zone. Moreover, the bending capacity of the specimens did not decrease, even if they had yielded. Although ultrahigh strength concrete was poured, all of the specimens displayed outstanding bending ductility. The main function of core concrete was to provide radial restraint for the steel tube to avoid premature buckling. When the steel content of the specimen section was constant, the strength increases of core concrete had a slight impact on the bending failure mode, bearing capacity and ductility of UHSCFST specimen. The research results can deepen the understanding of the mechanical behaviors of the UHSCFST composite truss structure.

当前工程应用的预填集料混凝土其集料粒径大且组成单一,混凝土强度偏低,应用范围受限.为提高预填集料混凝土抗压强度,本文试验研究制备方式、浆体材料类型、粗集料级配组成等对预填集料混凝土抗压强度的影响.结果表明:分层填筑、振动灌浆比自填充灌浆更有利于提高预填集料混凝土抗压强度;粗集料堆积程度越紧密、空隙率越小,预填集料混凝土的抗压强度越高;采用高流动性砂浆为灌浆料比用净浆为灌浆料制备的预填集料混凝土强度高;利用非连续级配粗集料(10～20?mm:20～25?mm=2:8,空隙率37.0％)与高强高流动性砂浆(流动度330?mm、28?d抗压强度72.2?MPa),一次振动成型可制备出28?d抗压强度达69.4?MPa的预填集料高强混凝土.

回顾了美兰法100多年的发展历程,讨论了相关专业术语及其内涵与外延;调查分析了美兰拱桥在中国的应用现状,总结了美兰法的技术发展要点和历史经验;指出了美兰法技术与美兰拱结构的研究现状与发展方向.研究结果表明:美兰法在19世纪末和20世纪上半叶从欧美起源,20世纪下半叶传到中国和日本;按所采用的埋置拱架类型,其在中国的发展可分为半劲性拱架、(一般)钢管混凝土(CFST)拱架和强劲CFST拱架3个阶段;美兰拱桥为混凝土拱桥的一种,美兰法所用的埋置拱架以服务施工为主,成桥后对混凝土的增强作用为辅;截至2021年5月,收集到的中国已建成或在建的美兰拱桥有57座,2007年以来,跨径250 m以上的混凝土拱桥均采用此法修建,其中最大跨径为600 m;美兰拱桥主要应用在中国西南山区的公路桥梁中,近年在铁路桥中的应用增多,以上承式双肋组拼拱为主,矢跨比集中在1/4～1/6,拱轴线多采用悬链线;CFST拱架截面积在主拱截面中的占比、钢管直径、钢管和混凝土材料强度均随时间的推移和跨径的增大而不断提高;应用美兰法时要综合考虑有限的用钢量、受控的结构受力和简便的施工这3种因素;预埋拱架从最早的型钢向类桁式、箱式、桁式发展,目前以桁式为主,桁式钢管拱架多采用悬臂法架设,转体法也有应用且形式多样;为减少用钢量,并控制施工过程中结构的受力与变形,中国创新地引入了CFST桁式结构作为埋置拱架,并采用预压、辅助锚索、多点平衡浇筑、斜拉索等调载方法;近年来,通过采用强劲CFST拱架,外包混凝土横向分环浇筑工序减少至3环及以下;在美兰法应用方面,应以强劲CFST拱架为核心,继续开展材料、结构与施工技术方面的研究;在美兰拱结构方面,应加强钢管增强混凝土结构、超高性能材料、钢腹板(杆)-混凝土组合拱受力性能研究;同时,还应深入研究美兰拱桥的耐久性,从而为新建桥梁的设计和既有桥梁的维修养护服务.

PAC has the advantages of high coarse aggregate content, low glue consumption, good volume stability and durability.However, many factors, such as the grouting process and the filling compactness, the working performance, mechanical properties and volume stability of the grouting material, the grading composition and voids of coarse aggregate, may affect the microstructure and macroscopic mechanical properties of PAC.In order to understand the status of PAC research and engineering application, the development and application process of PAC were summarized.The characteristics of current construction technology and preparation method were analyzed.The influence of grouting material and aggregate characteristics on PAC was summarized, and the existing problems and development trend of PAC research and application were discussed.

为满足金阳河特大桥钢管外包混凝土高程泵送低与收缩高抗裂要求,保障施工质量与结构长期耐久性.通过利用旋转黏度仪和平板开裂法与接触法研究了配合比参数、减缩剂、钢纤维与聚丙烯腈纤维对混凝土泵送、开裂、收缩性能的影响.结果表明:减缩剂与纤维均能提升混凝土抗裂等级、降低混凝土干燥收缩率.采用减缩剂制备出的低收缩高抗裂混凝土,90 d总收缩率为75×10-6,抗裂等级达到I级,其浆体黏度值为840 MPa·s,在实际工程应用时,工作性能良好,能满足泵送要求,完工后未发现裂缝.

为解决高强钢管混凝土组合结构高墩的主管内高抛混凝土与大流动性、低收缩协同提升的难题,研究了胶凝材料组成体系、骨料母岩强度对混凝土工作性和力学性能的影响,探究了膨胀剂掺量对混凝土体积稳定性的影响,并通过SEM分析了高强钢管混凝土的微观结构.结果表明:硅灰与粉煤灰微珠复掺能有效降低混凝土的黏度;母岩强度较高的玄武岩能保证后期强度稳定增长;掺35 kg/m3的膨胀剂能保证混凝土的体积稳定性;微观结构显示混凝土具有致密的结构、饱满的界面过渡区.掺硅灰、粉煤灰微珠与适量膨胀剂,利用玄武岩碎石能制备性能优异的自密实补偿收缩高强混凝土,并将其成功应用于四川凉山金阳河特大桥组合结构桥墩.

四川山区处在极其特殊的地理位置,桥梁建设面临巨大挑战,开展桥梁防震的相关研究具有重要意义.文章总结了近年来四川桥梁建设面临的地震引发的直接和间接灾害,归纳总结了四川省内已建桥梁防震主要措施,对山区桥梁建设具有借鉴意义.