Internal Force Distribution in Steel-Concrete Composite Structure for Pylon of Cable-Stayed Bridge

Adopting a steel-anchor beam and steel corbel composite structure in the anchor zone on pylon is one of the key techniques for the design of Jintang bridge, a cable-stayed bridge in Zhoushan, China. In order to ensure the safety of the steel-concrete composite structure, a stud connector model for the joint section was put forward. Experiments were conducted to obtain the relation between load and slip of specimen, the failure pattern of stud connector, the yield bearing capacity and ultimate bearing capacity of a single stud, etc. The whole process of the structural behavior of the specimen was comprehensively analyzed. The features of the internal force distribution in the steel-concrete composite structure and the strain distribution of stud connector under different loads were emphatically studied. The test results show that the stud connector is applicable for the steel-concrete composite structure for pylon of Jintang bridge. The stud has a good ductility performance and a obvious yield process before its destruction. The stud connector basically works in a state of elasticity under a load less than the yield load.

Influence of Binder Composition and Concrete Pore Structure on Chloride Diffusion Coefficient in Concrete

The influence of binder composition and pore structure of concrete on chloride diffusion coefficient in concrete were investigated by the natural immersion test, MIP test, SEM and EDS test, respectively. The experimental results showed that the effect of binder composition on chloride diffusion coefficient was the comprehensive result of concrete pore structure and binder hydration products, and the porosity and pore size distribution were the main factors that influence the changes of diffusion coefficient. The chloride diffusion coefficient decreased with increasing the curing temperature and the relative humidity. The hydration degree were promoted by improving curing temperatures, and then the porosity of concrete decreased and the proportion of gel pore and transitional pore increased, respectively. But the water evaporation decreased with increasing the relative humidity and then decreased porosity and increased the proportion of gel pore and transitional pore. Additionally, The chloride diffusion coefficient of concrete got the lower value when the appropriate replacement of fly ash in the ranges of 10%-20%, when the double-adding fly ash and slag content was 50%. The porosity increased and the ratio of C/S in C-S-H decreased with further increasing the fly ash content, which led to increase the chloride diffusion coefficient in concrete.

Development of high performance and high strength heavy concrete for radiation shielding structures

Heavy concrete currently used for construction contains special materials that are expensive and difficult to work with.This study replaced natural aggregate（stones） in concrete with round steel balls,which are inexpensive and easily obtainable.The diameters of the steel balls were 0.5 and 1 cm,and their density was 7.8 kg/m3.Dense packing mixture methods were used to produce heavy concrete with densities of 3500 and 5000 kg/m3.The various properties of this concrete were tested according to the standards of the American Society for Testing and Materials（ASTM）.The results indicated that the construction slump of the concrete could reach 260-280 mm and its slump flow could reach 610-710 mm.More important,its compressive strength could reach 8848 MPa.These results will significantly alter traditional construction methods that use heavy concrete and enhance innovative ideas for structural design.

Evaluation of Current Design Practices on Estimation of Axial Capacity of Concrete Encased Steel Composite Stub Columns： A Review

This paper presents the design assessment of concrete encased I-sections composite column based approaches given in Eurocode, ACI Code, BS Code and AISC-LRFD. This study includes comparison of various design parameters and evaluation of design strength based on the procedures predicted in the various codes of practices. A practical example has been assumed and calculation has been shown to evaluate their potentiality in understanding in predicting the potentiality of various procedures. The obtained results based on the methods varies widely, because of the different design considerations adopted by the different codes. As such, they have hardly considered the effect of confinement of the concrete due to the presence of longitudinal reinforcements as well as lateral ties. The study has attempted to throw light on critical review and their potentiality in assessing the strength of such concrete encased composite column under purely axial loads.

Static behavior of semi-rigid thin-walled steel-concrete composite beam-to-column joints with bolted partial-depth flush end plate:experimental study

A new type of semi-rigid thin-walled steel-concrete composite beam-to-column joint has been proposed in this paper.Five semi-rigid composite beam-to-column joint specimens subjected to hogging moments under monotonic loading were tested to study the static behavior of this new type of joint.The main variable parameters for the five joint specimens were the longitudinal reinforcement ratio and the joint type.The experimental results designated that the magnitude of extension of the longitudinal reinforcement is the most important factor that influenced the moment-rotation characteristic of the new type of joint.The concrete slabs could resist 3.8%-19.1% of the total shear load applied to the cross-sections near the beam-to-column connection.The edge stiffened elements,such as the flange of the lipped I-section thin-walled steel beam,were capable of having considerable inelastic deformation capacity although they had comparatively large width-to-thickness ratios.The shear failure of the concrete cantilever edge strip must be taken into account in practical design because it has significant influence on the anchorage of the longitudinal reinforcement in the new type of external joints.

Technological development and engineering applications of novel steel-concrete composite structures

In view of China's development trend of green building and building industrialization,based on the emerging requirements of the structural engineering community,the development and proposition of novel resourcesaving high-performance steel-concrete composite structural systems with adequate safety and durability has become a kernel development trend in structural engineering.This paper provides a state of the art review of China's cutting-edge research and technologies in steel-concrete composite structures in recent years,including the building engineering,the bridge engineering and the special engineering.This paper summarizes the technical principles and applications of the long-span bi-directional composite structures,the long-span composite transfer structures,the comprehensive crack control technique based on uplift-restricted and slip-permitted (URSP)connectors,the steel plate concrete composite (SPCC)strengthen technique,and the innovative composite joints.By improving and revising traditional structure types, the comprehensive superiority of steel-concrete composite structures is well elicited.The research results also indicate that the high-performance steel-concrete composite structures have a promising popularizing prospect in the future.

Mode-I fracture and durability of FRP-concrete bonded interfaces

In this study, a work-of-fracture method using a three-point bend beam （3PBB） specimen, which is commonly used to determine the fracture energy of concrete, was adapted to evaluate the mode-I fracture and durability of fiber-reinforced polymer （FRP） composite-concrete bonded interfaces. Interface fracture properties were evaluated with established data reduction procedures. The proposed test method is primarily for use in evaluating the effects of freeze-thaw （F-T） and wet-dry （W-D） cycles that are the accelerated aging protocols on the mode-I fracture of carbon FRP-concrete bonded interfaces. The results of the mode-I fracture tests of F-T and W-D cycle-conditioned specimens show that both the critical load and fracture energy decrease as the number of cycles increases, and their degradation pattern has a nearly linear relationship with the number of cycles. However, compared with the effect of the F-T cycles, the critical load and fracture energy degrade at a slower rate with W-D cycles, which suggests that F-T cyclic conditioning causes more deterioration of carbon fiber-reinforced polymer （CFRP）-concrete bonded interface. After 50 and 100 conditioning cycles, scaling of concrete was observed in all the specimens subjected to F-T cycles, but not in those subjected to W-D cycles. The examination of interface fracture surfaces along the bonded interfaces with varying numbers of F-T and W-D conditioning cycles shows that （1） cohesive failure of CFRP composites is not observed in all fractured surfaces; （2） for the control specimens that have not been exposed to any conditioning cycles, the majority of interface failure is a result of cohesive fracture of concrete （peeling of concrete from the concrete substrate）, which means that the cracks mostly propagate within the concrete; and （3） as the number of F-T or W-D conditioning cycles increases, adhesive failure along the interface begins to emerge and gradually increases. It is thus concluded that the fracture properties （i.e., the critical load and fracture energy） of the bonded interface are controlled primarily by the concrete cohesive fracture before conditioning and by the adhesive interface fracture after many cycles of F-T or W-D conditioning. As demonstrated in this study, a test method using 3PBB specimens combined with a fictitious crack model and experimental conditioning protocols for durability can be used as an effective qualification method to test new hybrid material interface bonds and to evaluate durability-related effects on the interfaces.

Behavior of eccentrically loaded concrete-filled GFRP tubular short columns

The glass fiber reinforced polymer (GFRP) tube is an effective material that can increase the bearing capacity and ductility of concrete.To study the mechanical behavior of this composite structure,twenty-one concrete-filled GFRP tubular short columns were tested under an eccentric load.The principle influencing factors,such as the eccentricity ratio,concrete strength and ratio of longitudinal reinforcement were also studied.In addition,the course of deformation,failure mode,and failure mechanism were analyzed by observing the phenomena and summarizing the data.The test results indicated that the strength and deformation characteristics of core concrete increase as a result of the addition of the GFRP tube.However,the gain in strength due to the addition of the GFRP tube decreases as the ratio of e /d increases.An increase in the longitudinal steel ratio can improve the bearing capacity of the composite short column effectively.Furthermore,the study showed that the constraint effect of the GFRP tube on high-strength concrete is not as effective as that on common concrete.The reason is that the lateral deformation of the high-strength concrete is less than that of the common concrete when the concrete column was tested under the same axial compression ratio.

Function-Integrative Textile Reinforced Concrete Shells

This paper presents the development and technological implementation of textile reinforced concrete (TRC) shells with integrated functions, such as illumination and light control. In that regard the establishment of material, structural and technological foundations along the entire value chain are of central importance: From the light-weight design idea to the demonstrator and reference object, to the technological implementation for the transfer of the research results into practice. The development of the material included the requirement-oriented composition of a high-strength fine grained concrete with an integrated textile reinforcement, such as carbon knitted fabrics. Innovations in formwork solutions provide new possibilities for concrete constructions. So, a bionic optimized shape of the pavilion was developed, realized by four connected TRC-lightweight-shells. The thin-walled TRC-shells were manufactured with a formwork made of glass-fibre reinforced polymer (GFRP). An advantage of the GFRP-formwork is the freedom of design concerning the formwork shape. Moreover, an excellent concrete quality can be achieved, while the production of the precast concrete components is simple and efficient simultaneously. After the production the new TRC-shells were installed and assembled on the campus of TU-Chemnitz. A special feature of the research pavilions are the LED light strips integrated in the shell elements, providing homogeneous illumination.

Identification of Connection Flexibility Effects Based on Load Testing of a Steel-Concrete Bridge

In the case of composite girders, an effective cooperation of both parts of the section is influenced by deformability of connectors. Limited flexural stiffness of welded studs, used commonly in bridge structures, does not provide full interaction of a steel beam and a concrete slab. This changes strain distribution in cross-sections of a composite girder and results in redistribution of internal forces in steel and concrete element. In the paper partial interaction index defined on the basis of a neutral axis position, which can be used for verification of steel-concrete interaction in real bridge structures rather than in specimens is proposed. The range of the index value changes, obtained during load testing of a typical steel-concrete composite beam bridge, is presented. The investigation was carried out on a motorway viaduct, consisting of two parallel structures. During the testing values of strains in girders under static and quasi-static loads were measured. The readings from the gauges were used to determine the index, characterizing composite action of the girders. Results of bridge testing under movable load, changing position along the bridge span is presented and obtained in-situ influence functions of strains and index values are commented in the paper.

Fe_(2)O_(3)-MWNTs Composite with Reinforced Concrete Structure as High-performance Anode Material for Lithium-ion Batteries

A Fe_(2)O_(3)-MWNTs(multi-walled carbon nanotubes)composite with a reinforced concrete structure was fabricated employing a two-step method which involves a sol-gel process followed by high-temperature in situ sintering.This Fe_(2)O_(3)-MWNTs composite,intended to be used as an anode material for lithium-ion batteries,maintained a reversible capacity as high as 896.3 mA·h/g after 100 cycles at a current density of 100 mA/g and the initial coulombic efficiency reached 75.5%.The rate capabilities of the Fe_(2)O_(3)-MWNTs composite,evaluated using the ratios of capacity at 100,200,500,1000,2000 and 100 mA/g after every 10 cycles,were determined to be 904.7,852.1,759.0,653.8,566.8 and 866.3 mA·h/g,respectively.Such a superior electrochemical performance of the Fe_(2)O_(3)-MWNTs composite is mainly attributed to the reinforced concrete construction,in which the MWNTs function as the skeleton and conductive network.Such a structure contributes to shortening the transport pathways for both Li+and electrons,enhancing conductivity and accommodating volume expansion during prolonged cycling.This Fe_(2)O_(3)-MWNTs composite with the designed structure is a promising anode material for high-performance lithium-ion batteries.

双壁波纹钢管混凝土构件短柱轴压力学性能

为改善空心钢筋混凝土柱(HRC)的使用与受力性能,提出一种双壁波纹钢管混凝土(CFDCST)构件。本文共进行了4个大尺寸双壁波纹钢管混凝土短柱与2个空心钢筋混凝土短柱的轴压试验,关键试验参数为试件类型与波纹钢管类型。分析构件的破坏模式,对比不同参数下构件的承载力、峰值应变、延性系数等关键力学指标,获得荷载-波纹钢管应变关系曲线以揭示试件的约束机理并验证外波纹钢管类型的影响。试验结果表明:外波纹钢管可为夹层混凝土提供约束作用,且螺旋角越小,外波纹钢管的约束作用越强;内波纹钢管则主要为夹层混凝土内壁提供有效支撑,以保持截面的完整性。名义约束效应系数与空心率相近时,由于咬口滑移影响,大螺旋角双壁波纹钢管混凝土比小螺旋角双壁波纹钢管混凝土的峰值应力、峰值应变与延性系数分别降低15.5%、21.8%与16.7%。在总用钢量相近的情况下,小螺旋角双壁波纹钢管混凝土柱的承载力、峰值应变与延性系数分别比空心钢筋混凝土柱提高10.6%、36.2%与50.0%。基于试验结果,检验了3种典型承载力公式的适用性,并提出了相应设计建议。

Numerical analysis of tunnel segments strengthened by steel-concrete composites

In order to study the feasibility of strengthening of segmental tunnel linings by using steel-concrete composites(SCC),a three-dimensional(3D)finite element(FE)model is proposed in this paper.The nonlinear mechanical behavior of concrete is described by a plastic-damage model.The nonlinearity,resulting from the interface of the SCC and reinforced concrete(RC)segments,is simulated with the help of a system of springs.The analysis results are compared with those obtained from a full-scale test of a tunnel segment.Their agreement validates the usefulness of the 3D FE model.Numerical re-analysis of the test shows that the interfacial connectors govern both the strengthening effect of SCC and the failure pattern of the strengthened segments.Thus,the force-transmitting capacity of the interfacial connectors should be concerned in design activities.As regards the circular segments,the interfacial connectors refer to both the shearing and the stripping connectors.The composite effect of the SCC and RC segments increases with the increasing number of these connectors.The latter,therefore,results in the increases of the bearing capacities and stiffnesses of the strengthened segments.Those increases become insignificant as the number of these connectors is sufficient to ensure a perfect composite effect of the SCC and RC segments.In addition,the numerical simulations show that using high-performance steel shell(HPS)or/and ultra-high-performance concrete(UHPC)is an effective way to increase the strengthening effect of SCCs.

3D fracture modelling and limit state analysis of prestressed composite concrete pipes

In this manuscript,we study fracture of prestressed cylindrical concrete pipes.Such concrete pipes play a major role in tunneling and underground engineering.The structure is modelled fully in 3D using three-dimensional continuum elements for the concrete structure which beam elements are employed to model the reinforcement.This allows the method to capture important phenomena compared to a pure shell model of concrete.A continuous approach to fracture is chosen when concrete is subjected to compressive loading while a combined continuous-discrete fracture method is employed in tension.The model is validated through comparisons with experimental data.

Analysis and design of steel-concrete composite sandwich systems subjected to extreme loads

This paper presents the design guide based on analytical,numerical and experimental investigation of Steel-concrete-steel(SCS)sandwich structural members comprising a lightweight concrete core with density ranged from 1300 to 1445 kg/m3 subjected to static,impact and blast loads.The performance of lightweight sandwich members is also compared with similar members with normal weight concrete core and ultra high strength concrete core(fc=180 MPa).Novel J-hook shear connectors were invented to prevent the separation of face plates from the concrete core under extreme loads and their uses are not restricted by the concrete core thickness.Flexural and punching are the primary modes of failure under static point load.Impact test results show that the SCS sandwich panels with the J-hook connectors are capable of resisting impact load with less damage in comparison than equivalent stiffened steel plate panels.Blast tests with 100 kg TNT were performed on SCS sandwich specimens to investigate the key parameters that affect the blast resistance of SCS sandwich structure.Plastic yield line method is proposed to predict the plastic capacity and post peak large deflection of the sandwich plates.Finally,an energy balanced model is developed to analyze the global behavior of SCS sandwich panels subjected to dynamic load.

Rational permeability coefficient of a permeable lining for composite tunnel lining structures

Various factors influence the tunneling are simplified considering the axial symmetry of the composite lining structure.The analytical expressions for the seepage field,stress,and displacement in the surrounding rock and those for the grouting circle,permeable lining,and ordinary lining are obtained according to the principle of effective stress.The seepage discharge,plastic zone,stress,and displacement around a tunnel affected by the different permeability coefficient ratios between the permeable lining and surrounding rock are studied.The reasonable value of permeability coefficient for the permeable lining are discussed.The results show that the grouting circle controls the tunnel seepage discharge well and has a reasonable permeability coefficient and an optimal radius.The grouting circle controls the plastic zone development in the surrounding rock,i.e.,the thicker the grouting circle,the smaller the plastic zone in the surrounding rock.The tunnel seepage discharge and the effective stress in the grouting circle and lining increase gradually with the increasing of permeability coefficient ratio and tend to be stable after the ratio reaches 0.1.Comprehensive analysis on the factors such as the stability of tunnel seepage discharge,the plastic zone of the surrounding rock and the stress around the tunnel indicates that it is relatively reasonable for the permeability coefficient ratio to be greater than or equal to 0.1.

STUDY ON STABILITY OF UNDERGROUND STRUCTURAL ENGINEERING BY ACOUSTIC EMISSION MONITORING SYSTEM

A simulation acoustic emission (AE) signal was processed. And an effective algorithm was presented to obtain the useful signal about the place information from the simulation signal. This paper introduces the artificial monitoring system, its application at underground roadway and its monitoring results, and tries to explore theoretically analyzing method of stability of underground concrete roadway by AE parameters. A simulation AE signal was processed. And an effective algorithm was presented to obtain the useful signal about the place information from the simulation signal It shows the nice future of the application in the active damage detection of composite material.

常泰长江大桥组合索塔锚固结构钢-混传剪构造足尺模型试验研究

常泰长江大桥索塔锚固结构采用钢箱-核芯混凝土组合结构,为研究该新型组合索塔锚固结构钢-混传剪构造的受力特性,进行钢-混传剪构造足尺模型试验研究。制作2个锚固结构足尺节段试验模型,通过压剪试验研究锚固结构的荷载~滑移曲线及应力、应变分布等受力特性,并通过有限元模型分析锚固结构的传力机理和各组件的内力分配比例,推导剪力钉剪力计算方法。结果表明:在2.14倍单索最大索力荷载作用下,锚固结构保持弹性状态,钢壁板未产生明显滑移,钢-混界面最大滑移不超过0.25 mm,该锚固结构中钢-混传剪构造至少具有2.14倍的安全系数;荷载作用下,剪力钉剪力从上至下逐渐增大,锚腹板附近底部3排剪力钉剪力较大,钢-混传剪构造至少存在剪力钉和界面摩擦力2种传剪机制,钢-混传剪构造的承载能力显著提高;钢-混传剪构造受力过程分为粘结力传力阶段和局部滑移阶段,剪力钉剪力分布不仅与沿剪切方向长度分布有关,也与荷载的大小线性相关。

装配式轻钢框架-轻钢骨架轻混凝土墙板结构抗震性能

为研究装配式轻钢框架-轻钢骨架轻混凝土墙板结构抗震性能,对1个足尺轻钢框架结构试件和3个足尺轻钢框架-轻钢骨架轻混凝土墙板结构试件进行了低周反复荷载下的抗震性能试验及理论分析,试件变量包括:2种装配构造,即内嵌式装配墙板、外贴式装配墙板;2种轻钢骨架轻混凝土墙板,即框架式轻钢骨架轻混凝土墙板、桁架式轻钢骨架轻混凝土墙板。研究了各试件的破坏特征和损伤演化过程,分析了结构滞回特性、承载力、变形能力、刚度退化、耗能性能和应变。结果表明:装配式轻钢框架-轻钢骨架轻混凝土墙板结构共同工作性能良好,其水平承载力相比轻钢框架提高了204.7%~210.4%,抗侧刚度提高了257.3%~512.5%,结构变形及耗能能力有显著提高;内嵌墙板的自攻钉连接构造以及外贴墙板的螺栓连接构造传力性能可靠,结构具备2道抗震防线的受力特征;基于简化塑性分析模型以及拉压杆软化桁架模型,对试件承载力进行了计算,计算结果与试验符合较好。

装配式型钢混凝土叠合框架梁连接节点构造设置与安全分析

住房和城乡建设部印发《“十四五”建筑业发展规划》提出大力发展装配式建筑、推动生产和施工智能化升级的主要任务。而国内目前采用的预制叠合框架梁存在着跨度大自重大吊装成本高、预制梁柱节点位置易发生钢筋碰撞吊装定位难度大等问题,限制了装配式建筑结构的发展。结合实际工程项目,提出一种新型的装配式型钢混凝土叠合框架梁,并对该叠合梁的构造设置、连接方式及安全性进行分析,从而为装配式框架结构、框架—剪力墙结构等装配式建筑中框架梁的深化设计提供一种新的拆分方案。