Behavior of steel-concrete composite slabs subjected to standard fire

Finite element method is employed to calculate the temperature fields for two kinds of steel concrete composite slabs: composite slab with profiled steel sheeting and LJMB composite slab. The calculated results are in good agreement with those of tests. Fire resistance of the two kinds of composite slabs is calculated by using a numeric method. The results show that: due to heat absorbing of concrete, the performance of composite slabs under fire is better than that of unprotected steel structure, and fire resistance of composite slabs mentioned in this paper is at least 30 min subjected to standard fire. Parameters related to the fire resistance are discussed. It was found that with increasing of concrete strength and thickness of slab, fire resistance increases, and with increasing of steel strength and steel ratio, fire resistance decreases. Also thickness of fire proof is calculated by a numeric method. The results obtained in this paper may be referenced for practical engineering.

Experimental investigation of engineered geopolymer composite for structural strengthening against blast loads

The recent increase in blast/bombing incidents all over the world has pushed the development of effective strengthening approaches to enhance the blast resistance of existing civil infrastructures.Engineered geopolymer composite(EGC)is a promising material featured by eco-friendly,fast-setting and strain-hardening characteristics for emergent strengthening and construction.However,the fiber optimization for preparing EGC and its protective effect on structural elements under blast scenarios are uncertain.In this study,laboratory tests were firstly conducted to evaluate the effects of fiber types on the properties of EGC in terms of workability,dry shrinkage,and mechanical properties in compression,tension and flexure.The experimental results showed that EGC containing PE fiber exhibited suitable workability,acceptable dry shrinkage and superior mechanical properties compared with other types of fibers.After that,a series of field tests were carried out to evaluate the effectiveness of EGC retrofitting layer on the enhancement of blast performance of typical elements.The tests include autoclaved aerated concrete(AAC)masonry walls subjected to vented gas explosion,reinforced AAC panels subjected to TNT explosion and plain concrete slabs subjected to contact explosion.It was found that EGC could effectively enhance the blast resistance of structural elements in different scenarios.For AAC masonry walls and panels,with the existence of EGC,the integrity of specimens could be maintained,and their deflections and damage were significantly reduced.For plain concrete slabs,the EGC overlay could reduce the diameter and depth of the crater and spallation of specimens.

Experimental study on seismic behaviors of steel-concrete composite frames

Steel-concrete composite frames are seeing increased use in earthquake region because of their excellent structural characteristics, including high strength, stiffness, and good ductility. However, there exist gaps in the knowledge of seismic behavior and the design provisions for these structures. In order to better understand the seismic behaviors of composite frame systems, eight steel-concrete composite frames were designed. These composite frames were composed of steel-concrete composite beams and concrete filled steel tube columns. The axial compression ratio of column, slenderness ratio and linear stiffness ratio of beam to column were selected as main design parameters. The low reversed cyclic loading tests of composite frame system were carried out. Based on test results, the seismic behaviors of composite frames such as failure mode, hysteresis curve, strength degradation, rigidity degradation, ductility and energy dissipation were studied. Known from the test phenomenon, the main cause of damage is the out-of-plane deformation of steel beam and the yielding destruction of column heel. The hysteretic loops of composite frame appear a spindle shape and no obvious pinch phenomenon. The results demonstrate that this type of composite frame has favorable seismic behaviors. Furthermore, the effects of design parameters on seismic behaviors were also discussed. The results of the experiment show that the different design parameter has different influence rule on seismic behaviors of composite frame.

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.

Mechanical performance of shear studs and application in steel-concrete composite beams

This work experimentally investigates the effects of shear stud characteristics on the interface slippage of steel-concrete composite push-out specimens. ABAQUS is used to establish a detailed 3D finite element(FE) model and analyze the behavior of push-out specimens. The modeling results are in good agreement with the experimental results. Based on parametrical analysis using the validated FE approaches, the effects of important design parameters, such as the diameter, number, length to diameter ratio, and yield strength of studs, concrete strength and steel transverse reinforcement ratio, on the load-slip relationship at the interface of composite beams are discussed. In addition, a simplified approach to model studs is developed using virtual springs with an equivalent stiffness. This approach is demonstrated to be able to predict the load-displacement response and ultimate bearing capacity of steel-concrete composite beams. The predicted results show satisfactory agreement with experimental results from the literature.

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.

Bending Stiffness of Truss-Reinforced Steel-Concrete Composite Beams

This paper is concerned with a special steel-concrete composite beam in which the resisting system is a truss structure whose bottom chord is made of a steel plate supporting the precast floor system. This system works in two distinct phases with two different resisting mechanisms: during the construction phase, the truss structure bears the precast floor system and the resisting system is that of a simply supported steel truss;once the concrete has hardened, the truss structure becomes the reinforcing element of a steel-concrete composite beam, where it is also in a pre-stressed condition due to the loads carried before the hardening of concrete. Within this framework, the effects of the diagonal bars on the bending stiffness of this composite beam are investigated. First, a closed-form solution for the evaluation of the equivalent bending stiffness is derived. Subsequently, the influence of geometrical and mechanical characteristics of shear reinforcement is studied. Finally, results obtained from parametric and numerical analyses are discussed.

Improved methods for decreasing stresses of concrete slab of large-span through tied-arch composite bridge

Mechanical behavior of concrete slab of large-span through tied-arch composite bridge was investigated by finite element analysis (FEA). Improved methods to decrease concrete stresses were discussed based on comparisons of different deck schemes, construction sequences and measures, and ratios of reinforcement. The results show that the mechanical behavior of concrete slab gets worse with the increase of composite regions between steel beams and concrete slab. The deck scheme with the minimum composite region is recommended on condition that both strength and stiffness of the bridge meet design demands under service loads. Adopting in-situ-place construction method, concrete is suggested to be cast after removing the full-supported frameworks under the bridge. Thus, the axial tensile force of concrete slab caused by the first stage dead load is eliminated. Preloading the bridge before concrete casting and removing the load after the concrete reaching its design strength, the stresses of concrete slab caused by the second stage dead load and live load are further reduced or even eliminated. At last, with a high ratio of reinforcement more than 3%, the concrete stresses decrease obviously.

A tunable corner-pumped Nd:YAG/YAG composite slab CW laser

A corner-pumped Nd：YAG/YAG composite slab continuous-wave laser operating at 1064 nm,1074 nm,1112 nm,1116 nm,and 1123 nm simultaneously and a laser that is tunable at these wavelengths are reported for the first time.The maximum output power of the five-wavelength laser is 5.66 W with an optical-to-optical conversion efficiency of 11.3%.After a birefringent filter is inserted in the cavity,the five wavelengths can be separated successfully by rotating the filter.The maximum output powers of the 1064 nm,1074 nm,1112 nm,1116 nm,and 1123 nm lasers are 1.51 W,1.3 W,1.27 W,0.86 W,and 0.72 W,respectively.

Vibration Serviceability of Large-Span Steel–Concrete Composite Beam with Precast Hollow Core Slabs Under Walking Impact

A large-span steel–concrete composite beam with precast hollow core slabs(CBHCSs)is a relatively new floor structure that can be applied to various long-span structures.However,human-induced vibrations may present serviceability issues in such structures.To alleviate vibrations,both the walking forces excited by humans and the associated floor responses must be elucidated.In this study,150 load–time histories of walking,excited by 25 test participants,are obtained using a force measuring plate.The dynamic loading factors and phase angles in the Fourier series functions for one-step walking are determined.Subsequently,walking tests are performed on seven CBHCS specimens to capture the essential dynamic properties of mode shapes,natural frequencies,damping ratios,and acceleration time histories.The CBHCS floor system generally exhibits a high frequency(>10 Hz)and low damping(damping ratio<2%).Sensitivity studies using the finite element method are conducted to investigate the vibration performance of the CBHCS floor system,where the floor thickness,steel beam type,contact time,and human weight are considered.Finally,analytical expressions derived for the fundamental frequency and peak acceleration agree well with the experimental results and are hence proposed for practical use.

The Study of Force and the Mechanical Characteristic of Incremental Launching Construction Method on a Steel-Concrete Continuous Beam Bridge

The usage of steel-mixed composite beams is quite extensive today.During an event of constructing steel-mixed composite bridges,the incremental launching construction method is generally adopted.This paper mainly analyzes the force of incremental launching construction on a steel-concrete continuous beam bridge,the classification of incremental launching construction,the application of incremental launching construction in steel-mixed composite beams,the temporary facilities existing in incremental launching construction as well as their existing problems.Lastly,the analysis of the stress of composite beams in incremental launching construction is described by using the reference for the construction of mixed composite continuous beam bridges provided.

Research review on steel–concrete composite joint of railway hybrid girder cable-stayed bridges

Purpose–This study aims to research the development trend,research status,research results and existing problems of the steel–concrete composite joint of railway long-span hybrid girder cable-stayed bridge.Design/methodology/approach–Based on the investigation and analysis of the development history,structure form,structural parameters,stress characteristics,shear connector stress state,force transmission mechanism,and fatigue performance,aiming at the steel–concrete composite joint of railway long-span hybrid girder cable-stayed bridge,the development trend,research status,research results and existing problems are expounded.Findings–The shear-compression composite joint has become the main form in practice,featuring shortened length and simplified structure.The length of composite joints between 1.5 and 3.0 m has no significant effect on the stress and force transmission laws of the main girder.The reasonable thickness of the bearing plate is 40–70 mm.The calculation theory and simplified calculation formula of the overall bearing capacity,the nonuniformity and distribution laws of the shear connector,the force transferring ratio of steel and concrete components,the fatigue failure mechanism and structural parameters effects are the focus of the research study.Originality/value–This study puts forward some suggestions and prospects for the structural design and theoretical research of the steel–concrete composite joint of railway long-span hybrid girder cable-stayed bridge.

Flexural stiffness characterization of the corrugated steel-concrete composite structure for tunnel projects

Corrugated steel–concrete(CSC)composite structures are increasingly used in tunnel and culvert projects due to their good mechanical properties.The design of CSC composite structures is often governed by deflection limits in service,hence it becomes crucial to evaluate accurately their flexural stiffness.In this work,the deflection deformation mechanism of CSC composite structure is studied by experimental and numerical methods,and a simplified formula for calculating the flexural stiffness is established.In addition,the deflection results obtained by different methods are compared and analyzed.It is found that:(1)the flexural stiffness of the CSC composite structure is constant only when the load is small,and after the bending moment exceeds a certain value,the flexural stiffness will gradually become smaller as the bending moment increases.(2)The value of the bending moment corresponding to the end of the elastic stage of the bending moment-deflection curve increases with the increase of the axial force in the composite structure.(3)As the axial force of the composite structure increases,the flexural bearing capacity of the structure increases first and then decreases.

钢纤维细石混凝土-钢组合板抗弯性能试验研究

钢纤维细石混凝土是一种具有优异力学性能和良好工作性的高性能混凝土复合材料。本试验针对正交异性钢桥面铺装层裂缝病害问题,对4组采用不同钢筋配筋率和保护层厚度的横桥向钢纤维细石混凝土-钢组合桥面板进行了抗弯破坏试验,研究了组合板的荷载-挠度关系与裂缝开展特征;用等效截面法计算了开裂应力、裂缝宽度和钢筋应力,验证了钢纤维细石混凝土-钢组合板的抗裂性能。结果表明:60 mm厚钢纤维细石混凝土铺装层在小配筋率(2.6%)和低于规范要求的保护层厚度(15 mm)条件下呈现出多缝开裂的破坏形态,具备较高的延性和开裂应力,满足规范和工程应用的要求。

预应力UHPC槽形节段与整体式混凝土板组合梁受剪性能

将预制的UHPC槽形节段通过干缝连接和预应力张拉形成槽形梁,再与整体现浇的混凝土板组合成的组合梁,称为预应力UHPC槽形节段与整体式混凝土板组合梁(PUCS-MCS组合梁)。它是一种能充分发挥不同材料的性能、施工方便且整体性能好的新型桥梁结构。为探究其抗剪性能,开展了9根模型梁的试验。分析了接缝数、接缝处剪力键数、剪跨比、UHPC钢纤维体积率、配箍率和纵筋率等参数对试件变形、破坏模式、抗剪承载力的影响;基于试验研究结果,提出了PUCS-MCS组合梁抗剪承载力计算方法。结果表明:PUCS-MCS组合梁均为剪压破坏,所有梁在开裂前的荷载-挠度曲线差异不大,在开裂后刚度不断下降;PUCS-MCS组合梁的抗剪承载力随接缝处剪力键数、UHPC钢纤维掺量、配箍率和纵筋率的增大而增大,随干接缝数量增加和剪跨比的增大而减小,其中影响最显著的是干接缝和剪力键,影响最小的是钢纤维掺量和配箍率,因此PUCS-MCS组合梁可不配箍筋,并可采用较低钢纤维掺量的UHPC。

栓钉型弧形双钢板混凝土组合板的抗爆性能试验与数值分析

弧形双钢板混凝土组合结构由钢板、混凝土与连接件协同作用,具有更优异的抗震和抗爆性能,被应用于超高层结构、海洋平台和核电设施中。利用试验和数值分析方法研究了栓钉型弧形双钢板混凝土组合结构的破坏模式和损伤机理,参数化分析了爆炸距离、钢板厚度、拱高和栓钉间距对其抗爆性能的影响。结果表明:在爆炸荷载下,栓钉型弧形双钢板混凝土组合板整体表现良好,仍具有较高的承载能力。增加爆炸距离和钢板厚度能有效减小混凝土的损伤和组合板的跨中挠度;减小拱高,混凝土损伤区域从以压缩破坏为主逐渐转换为以拉伸破坏为主,混凝土损伤更严重,组合板跨中挠度变大;减小栓钉间距会增大混凝土塑性损伤程度,但组合板的跨中挠度减小。研究结果可为弧形双钢板混凝土组合结构的设计提供参考。

双向受力的开槽混凝土叠合板力学性能试验研究

为了解决双向受力的叠合板拼缝处外伸的胡子筋容易与其他部件产生冲突从而影响施工的问题,采用了一种双向受力的开槽混凝土叠合板,在板件拼缝位置预留槽口,并在槽口处放置附加钢筋进行预制板之间的连接,共设置了3个试件对其力学性能进行试验研究.试验结果表明,双向受力的开槽混凝土叠合板与现浇混凝土板的承载力、刚度比分别达到0.99和1.08,延性系数达到9.59,且二者破坏形态一致,增加槽口数量对试件弹性刚度、开裂荷载、极限承载力的影响有限,但是可以提升叠合板的延性.双向受力的开槽混凝土叠合板可以实现拼缝处的有效传力,具有与现浇混凝土板一致的力学性能,在应用于实际工程时,可以提高施工效率、降低钢筋用量、提升经济效益,具有广阔的应用前景.

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。