Experimental study on hysteretic behavior of prestressed truss concrete composite beams

This paper describes an experimental study of the hysteretic behavior of prestressed truss concrete composite beams （PTCCBs） under cyclic loading. Five beam models were designed and tested, in which the testing parameters include the global reinforcement index β0, the prestress level 2 and the ratio of stirrup ρsv in the potential plastic hinge zones. Based on the test results, the failure mode and hysteretic behavior of the tested models are obtained. In addition, the P-△ and sectional M-φ hysteretic models for the PTCCBs at the midspan are established. The P-△ hysteretic model shows good agreement with the test results.

Experimental research on mechanical properties of prestressed truss concrete composite beam encased with circular steel tube

Tests of 4 simply supported unbonded prestressed truss concrete composite beams encased with circular steel tube were carried out. It is found that the ratio of the stress increment of the unbonded tendon to that of the tensile steel tube is 0.252 during the using stage,and the average crack space of beams depends on the ratio of the sum of the bottom chord steel tube's outside diameter and the secondary bottom chord steel tube's section area to the effective tensile concrete area. The coefficient of uneven crack distribution is 1.68 and the formula for the calculation of crack width is established. Test results indicate that the ultimate stress increment of unbonded tendon in the beams decreases in linearity with the increase of the composite reinforcement index β0. The pure bending region of beams accords with the plane section assumption from loading to failure. The calculation formula of ultimate stress increment of the unbonded tendon and the method to calculate the bearing capacity of normal section of beams have been presented. Besides,the method to calculate the stiffness of this sort of beams is brought forward as well.

Mechanical Response of All-composite Pyramidal Lattice Truss Core Sandwich Structures

The mechanical performance of an all-composite pyramidal lattice truss core sandwich structure was investigated both theoretically and experimentally.Sandwich structures were fabricated with a hot compression molding method using carbon fiber reinforced composite T700/3234.The out-of-plane compression and shear tests were conducted.Experimental results showed that the all-composite pyramidal lattice truss core sandwich structures were more weight efficient than other metallic lattice truss core sandwich structures.Failure modes revealed that node rupture dominated the mechanical behavior of sandwich structures.

Mechanical behavior of concrete-filled rectangular steel tubular composite truss bridge in the negative moment region

Concrete-filled rectangular steel tubular(CFRST)composite truss bridge is a new type of structure composed of a CFRST truss and concrete deck slab.This new type of bridge has the advantages of high structural force-transferring efficiency,rapid assembly construction speed and excellent total life cycle,which meets the construction concept of green,recyclable and sustainable development.Due to the broad application prospects,experiment on the flexural behavior of CFRST composite truss bridge in the negative moment region was reported by authors previously.This paper thus presents a finite element analysis(FEA)modelling verified by the reported test data to further investigate the detailed analytical behavior of this structure.The structural response and failure mechanism of CFRST composite truss beam in the negative moment region are studied.In addition,the important structural design parameters on the flexural performance of the CFRST composite truss beam are also investigated,including the height to span ratio,the brace-to-chord wall thickness ratio,the reinforcement ratio of steel reinforcements and prestressed tendons and the strength grade of concrete infill in chords.Finally,the reasonable structural design parameters range are proposed for the optimum design of the CFRST composite truss bridge.

Flexural behaviour of SFRRAC two-way composite slab with different shapes

To promote the application of green renewable materials in concrete composite slabs(CCSs)and study the flexural behavior of CCSs with different shapes,the bending performances of three CCSs with a SFRRAC base plate,one cast-in-site concrete slab of ordinary concrete and one CCS of ordinary concrete by steel bar truss(as recommended in the technical specification for precast concrete structures in Chinese)were compared through experiments.The carrying capacity,flexural behaviour and bi-directional mechanical properties of the specimens were systematically analyzed from the failure modes,load-deflection curves,load-bar strain curves,load-slip curves and crack distributions.Results show that the bending failure process of CCSs with a SFRRAC base plate is similar to that of the cast-in-site concrete slab of ordinary concrete and CCS of ordinary concrete by steel bar truss,as all of them went through the plastic phase,elastic plastic phase and failure phase with fully developed cracks and deflection.No sudden breakage or horizontal cracking of the connecting interface between the base plate and concrete topping was observed.The shape of the base plate has a major impact on the bearing capacity of the CCS with the SFRRAC base plate.When calculating the ultimate bearing capacity with the plastic yield line theory,the influence of the base plate shape on the plastic yield line position should be taken into account.

A review on application of composite truss bridges composed of hollow structural section members

Composite truss with hollow structural section(HSS) members is deemed as the structure applicable to large-span and heavily-loaded bridges. To promote the application of composite truss bridge with HSS members in China, this paper described its structural characteristics and technology in details. Besides, not only were 32 typical design cases of composite truss bridges with HSS members collected, but also the corresponding historical development was summed up. Comparisons on structural components, characteristics and engineering applications were made among composite truss bridges with HSS members in different structural forms. Then, the analysis on the characteristics of composite truss bridges with concrete-filled steel tubular(CFST) chords was conducted, and the challenges on the aspects of complicated joints and interfacial debonding were pointed out. To address these problems, the concrete-filled rectangular hollow section(CFRHS)stiffened with PBLs(Perfobond Ribs) was proposed to improve the reliability of confinement effect in CFST member and force transfer in joints. The advantages on the mechanical properties of CFRHS structure stiffened using PBLs were systematically expounded with respect to the behaviors of steel plate, interface, member and joint. Moreover, the structure design, construction technology, structural calculation and economic efficiency of the practical bridge with CFRHS chords stiffened using PBLs were comprehensively analyzed.The results demonstrated that composite truss bridge with PBL-stiffened CFRHS members was competitive in mechanical performance and construction.

Study on support mechanism of pre-stressed truss cable and its application

The truss cable support technology was put forward to control the large mining height and composite mudstone strata roadway. This technique makes the steady rock in roadway slantwise top be anchor points, makes the truss cable be steady support structure through special implement, and supplied rock in anchor area with horizontal and vertical pressure which strengthens the surrounding rock＇s anti-strain capability, so it can solve the support problem in roadway with the large cross section and large mining height with mudstone strata. The support mechanism of truss cable about how to make the soft strata stabilize is analyzed by use of the mechanical method. Based on the mechanism and numerical simulation method, the truss cable support project was designed and used to the large mining setting room in eleventh mining area of Bailong Mine successfully.

航天器复合材料桁架连接增强方法与验证

大型航天器主承载复合材料桁架局部承受过大的轴向拉伸载荷时,存在接头与杆件拉脱破坏的风险。基于胶接桁架碳纤维分层破坏机理,提出了外套管增强胶接、锥面配合增强胶接和组合增强胶接3种连接增强方案,通过优化传力路径达到降低层间应力的目的。针对3种连接增强方案,投产了相应的试件开展性能测试。经试验验证,胶接增强设计方法能够有效提高承载能力33%~66%,极限拉脱力达到200 kN,可为大型航天器主承载桁架研制提供参考。

叠加空腹桁架的钢-钢骨混凝土组合转换桁架设计分析与监测

针对某上弦为钢骨构件、腹杆及下弦为型钢的钢-钢骨混凝土组合转换桁架结构,采用PKPM软件对组合转换桁架和其上空腹桁架进行了多个整体模型的弹性对比分析及静力推覆分析。结果表明,施工模拟方式、楼面板刚度模拟方式、混凝土空腹桁架构件徐变、中大震下出铰情况对转换桁架和空腹桁架分担的转换荷载计算值均有较大影响,相关因素应予包络、准确地考虑。对多个子结构组合而成的结构体系,应明晰各子结构在整体中发挥的作用,以及各子结构在相关因素变动情况下的定量变化情况,以保证各子结构性能稳定性和整体结构的安全。工程施工阶段监测表明,叠加空腹桁架的组合转换桁架结构变形及构件应变基本与设计预期相符,转换结构安全合理。

深江铁路洪奇沥公铁大桥主桥设计关键技术

研究目的:洪奇沥公铁大桥是深江铁路的控制性工程,主桥采用主跨808 m公铁合建斜拉桥一跨跨越洪奇沥水道,上层布置8车道城市快速路,下层布置4线铁路。结合建设条件、结构特点及使用性能,对主桥结构体系、主梁横断面及结构形式、索-塔锚固结构、施工方法等关键技术展开研究,确定技术合理可行和经济节约的设计方案。研究结论:(1)首创了短边跨叠合板-桁组合梁斜拉桥结构体系,主桥长度减少20%,节省工程投资;(2)首次在4线铁路公铁合建斜拉桥上采用倒梯形双主桁截面,桥面布置紧凑、受力明确;(3)提出的边跨主梁采用矩形钢管混凝土叠合板-桁组合结构,集结构受力和锚固压重于一体,施工便捷;(4)发明了“自平衡交叉锚固+齿块锚固”的索-塔混合锚固方式,技术经济性高;(5)钢主梁创新采用“纵向大节段+横向分块”施工方法,解决了超宽超高超重整节段钢桁梁运输受既有桥净空限制的难题;(6)本研究成果可为公铁合建桁梁斜拉桥设计提供参考或借鉴。

公铁合建斜拉桥钢桁-混凝土板组合梁受力特性

以某主跨808 m的公铁合建新型钢桁-混凝土板组合梁斜拉桥为背景,采用ANSYS软件建立局部组合梁细化的全桥多尺度有限元模型,分析其在不同工况下双层组合梁的受力传力特性和混凝土桥面板荷载分配比,并讨论混凝土桥面板厚度t_(b)、横梁刚度变化系数λ_(K)和钢与混凝土弹性模量比λ_(E)对组合梁受力传力的影响规律。结果表明:最不利组合工况下,钢桁架最不利Von Mises应力为183.6 MPa,混凝土桥面板最大拉应力为5.3 MPa,均满足结构受力要求;沿纵向路径,钢桁架和混凝土桥面应力在节间横梁间均呈“波形”分布;上下层混凝土桥面板顶、底面应力沿横向近似呈“W”和“M”状分布,表明桥面板承受一定沿横向不均匀分布弯矩;公路及铁路混凝土桥面最大剪力滞系数分别为1.45、1.36,更宽的公路混凝土桥面剪力滞效应更显著;公路及铁路混凝土桥面分别承担上、下层结构57.46%~79.99%和33.21%~62.81%的轴向荷载,为组合梁的主要传力构件;混凝土桥面板的应力随t_(b)及λ_(K)的增大而增大,随λ_(E)的增大而逐渐减小;混凝土桥面每层平均荷载分配比ξ与t_(b)成正比,与λ_(K)及λ_(E)成反比;当t_(b)、λ_(K)和λ_(E)参数的取值范围分别为0.8~1.4、0.4~1.6以及4~10时,组合梁混凝土桥面应力及荷载分配比ξ较为合理。

梁桁组合结构高铁斜拉桥的收缩徐变分析——以西十高铁汉江特大桥为例

梁桁组合结构高铁斜拉桥中,混凝土收缩徐变对桥面线性的平顺性及行车的舒适性有直接影响,是桥上能够铺设无砟轨道的关键因素。因此,为分析收缩徐变对梁桁组合结构受力和变形的影响,依托新建西安至十堰高铁汉江特大桥工程,采用CEB-FIP90徐变计算模型,通过建立有限元模型分析收缩徐变影响下主要构件的内力和变形,评价各主要受力构件刚度变化对徐变变形的贡献程度,研究改善收缩徐变变形措施。结果表明:(1)收缩徐变引起主梁跨中下挠、桥塔向跨中侧偏移,同时引起主梁和桥塔的压缩变形,5年完成的收缩徐变变形占前10年的70%以上,且主梁产生的收缩徐变贡献超过50%;(2)收缩徐变引起斜拉索索力松弛,运营30年的最大变化率在5%以内;(3)收缩徐变引起主梁应力及上下缘应力差变化,随着运营时间增加主梁跨中区域应力差增大明显,主要表现在下缘压应力储备降低;(4)随着桥塔刚度、主梁刚度、加劲钢桁刚度增大,收缩徐变引起的变形有所减小,而斜拉索刚度则产生相反的趋势。(5)延长铺轨时间、适当增加底板钢束面积、增加斜拉索索力以及在跨中加劲钢桁上弦灌注混凝土可有效降低主梁跨中徐变下挠。

带钢筋桁架楼承板的PRC连梁抗震性能试验研究及数值分析

为适应超高层建筑以及现代工业化住宅建筑体系迅速发展的需要,提出了一种带钢筋桁架楼承板的新型钢板-混凝土组合(plate-reinforced composite,PRC)连梁。通过拟静力试验,分析了不考虑楼板作用、带普通钢筋混凝土(reinforced concrete,RC)楼板及带钢筋桁架楼承板PRC连梁的破坏形态、承载能力、变形能力和耗能能力等。在此基础上,采用ABAQUS软件分析在不同峰值荷载作用下钢筋桁架楼承板PRC连梁的混凝土、钢板和钢筋骨架的应力发展情况。研究结果表明:钢筋桁架楼承板的设置能显著提高小跨高比PRC连梁的受剪承载力、耗能能力和延性,设置楼板能显著提高连梁的峰值荷载,且带钢筋桁架楼承板对PRC连梁承载力的提升比带普通RC楼板更强,其连梁试件PRC-S3的正向峰值荷载比不带楼板连梁PRC-NS1和带普通RC楼板连梁PRC-S2分别提升了31%和18%,但带楼板连梁在梁板交界处产生通缝之后连梁的刚度退化较为严重;带钢筋桁架楼承板的PRC连梁具有优越的耗能能力,在连梁跨度范围内均出现了显著的对角压杆,主压杆及其衍生压杆共同构成桁架作用来承受剪力;楼承板桁架上下弦钢筋以及连梁纵筋均在连梁根部位置出现应力集中,且连梁试件PRC-S3破坏点对应的累积耗能是不带楼板试件PRC-NS1的1.39倍。

混凝土叠合板分类及研究综述

叠合板因为施工方便快捷、整体性好,近几年在我国得到快速发展和应用。开展叠合板的研究,可以进一步优化叠合板相关性能,拓宽叠合板应用范围,推动其在装配式建筑中的应用,有利于加速推进建筑工业化发展进程。根据底板构造形式不同将叠合板分为平板型、钢筋桁架型、预制带肋型、空心底板型、双向密肋夹芯叠合板几大类,全面系统地论述了不同类型叠合板的研究进展,并对各类型叠合板以及不同类型板间连接技术的优缺点进行了归纳总结,提出现阶段叠合板研究中的问题和不足。

公铁混合布置大跨度斜拉桥主梁断面形式研究--以赣江公铁大桥西支主桥设计为例

以赣江公铁两用大桥西支主桥设计为例,研究一种适应上层8车道公路、下层对称双线铁路+4车道公路混合布置的主梁断面形式。提出带挑臂双索面箱桁组合断面、带挑臂单索面箱桁组合断面、矩形箱桁组合断面、矩形钢桁梁断面4种主梁断面方案,采用有限元软件分析各方案静动力性能及受力特点,综合考虑方案构造特点、技术指标、工程数量、公铁运营安全、景观效果等,确定该桥选用带挑臂双索面箱桁组合断面。该桥斜拉索最大索力16000 kN,锚固在下层钢箱梁两侧,通过有限元实体分析对锚拉板和钢锚箱式两种索梁锚固形式进行比选研究,钢锚箱形式受力合理、应力水平低、经济性好,设计采用钢锚箱形式。带挑臂双索面箱桁组合断面桥面空间布置合理、下层公铁行车干扰小、梁端竖向变形最小、经济性好,是一种适应公铁混合布置大跨度斜拉桥主梁断面形式。

胶合木与钢筋桁架混凝土板界面连接抗剪性能试验研究

为提高构件预制率,将钢筋桁架楼承板应用到传统的木混凝土组合梁中,形成一种新型组合结构——木钢筋桁架混凝土组合梁。基于木混凝土组合梁中常用的螺钉、榫钉和植钢板连接,对采用钢筋桁架楼承板的木混凝土界面连接的抗剪性能进行了推出试验,并与普通配筋的木混凝土界面连接的抗剪性能进行了对比。推出试验结果表明:与混凝土板采用普通配筋的推出试件相比,引入钢筋桁架楼承板后,不同连接方式下新型组合梁推出试件的界面连接抗剪承载力和滑移刚度得到明显提升。本文所提出的新型组合梁在提高构件工业化水平和施工效率的同时,其界面连接的抗剪性能得到明显改善,有利于促进木混凝土组合结构在木结构领域的应用。

异形钢木组合空腹式桁架拱精密装配技术

天府农业博览园主展馆室外棚架工程结构形式为异形钢木组合空腹式桁架拱结构。上弦杆为双拼欧洲落叶松胶合木,下弦杆为欧洲云杉胶合木,腹杆为钢板切割组焊的四角锥结构。此种结构体系因其为异形几何体,组拼与安装难度极高。通过一种先进的拼装支架及预装配工法,采用数字化模型精确定位,可实现钢木组合桁架拱精密装配。该技术解决了钢木组合结构装配公差的技术难题,同时满足了各工序间的衔接,加快了整体施工进度。

异形双曲面楼承板节点构造及施工方法

为解决异形双曲面钢筋桁架组合楼板施工的难题,对某工程异形双曲面楼承板施工过程中的几种技术措施进行分析和总结,形成较为完整的施工工艺。总结的单元化、以直代曲等技术可为滑雪场、商业楼等异形双曲面钢筋桁架组合楼板施工提供借鉴。

大跨梁桁组合结构高铁斜拉桥主梁施工方案比选

西十高铁汉江特大桥主桥为(67+70+73+420+73+70+67) m斜拉桥,主梁采用预应力混凝土箱梁和加劲钢桁架组成的梁桁组合结构,钢桁架下节点与预应力混凝土箱梁采用PBL键连接。边跨及塔区混凝土主梁采用支架现浇施工,为选择合理的中跨混凝土主梁施工方案,提出5 m节段悬浇施工、10 m节段悬浇施工、5 m节段预制悬拼施工3种方案,从建设条件、结构受力、行车动力性能、桥面线形、施工工期和投资等方面对3种方案进行对比。结果表明:5 m节段预制悬拼施工方案的工期最短,但投资最高,且受建设场地和运输条件的制约;节段悬浇施工技术成熟,技术风险及质量风险低,相比5 m节段,10 m节段悬浇施工方案虽然投资略高,但能够有效节省工期达5个月,且结构受力性能、行车安全性及舒适性、桥面线形均满足相关要求,在保证施工监控精度的前提下,成桥线形也在可控范围内,该桥最终选择10 m节段悬浇施工中跨混凝土主梁。

宜宾新市金沙江大桥主桥总体设计

宜宾新市金沙江大桥主桥为(304+680+304)m双塔双索面钢桁梁斜拉桥,采用半飘浮体系,在桥塔横梁顶设置含限位功能的纵向阻尼器,两岸边跨各设置1个辅助墩。桥塔采用宝瓶形钢筋混凝土塔,四川岸和云南岸塔高分别为290.2 m和297.5 m,由上、中、下塔柱和上、中、下横梁及下塔柱横向连接隔板组成。主梁采用钢桁梁与钢-混组合桥面板的板桁结合型式,主桁横向中心距28 m,桁高6.8 m,标准节间长6.8 m,上、下弦杆与腹杆呈“N”形布置,采用焊接整体节点。桥面板采用钢-混组合桥面板。斜拉索采用环氧喷涂钢绞线体系,疲劳应力幅280 MPa,斜拉索在主桁上采用锚拉板锚固方式,在桥塔上采用钢锚梁锚固方式。采用桥面全回转吊机进行主桁、横桁单元件安装;钢-混组合桥面板滞后主梁2个节段施工。