Seismic performance parameters of RC beams retrofitted by CARDIFRC

A new high performance fibre-reinforced cementitious composite material (designated CARDIFRC^®), to be used for retrofitting concrete members, has been developed at Cardiff University. The material is compatible with concrete and possesses favourable strength and ductility properties desirable for seismic retrofit. It overcomes some of the problems associated with the current techniques based on externally bonded steel plates and fibre-reinforced polymer (FRP) laminates caused mainly by the mismatch of their tensile strength and stiffness with that of the concrete member being retrofitted.

This paper reports on the results of three-point and four-point flexure tests conducted on a number of non-ductile and ductile small scale RC beams retrofitted with externally bonded CARDIFRC^® strips. A number of different strip configurations and two strip thicknesses are investigated and their effect on the retrofitting process examined. Some strength and seismic performance parameters including toughness and ductility are evaluated for each retrofitted beam and compared with those of the corresponding control beams. It is shown that precast CARDIFRC^® strips, adhesively bonded to the surface of the RC beam can greatly increase the strength and ductility of the retrofitted beam; hence, they can be used successfully to enhance the seismic performance of both damaged and undamaged RC beams.     

悬伸梁和双跨连续梁的整体稳定承载力试验研究

为了研究悬伸梁和双跨连续梁在集中荷载作用下的整体稳定性能,对两种单轴对称截面形式(上翼缘加强、下翼缘加强)、两种悬伸长度(1200mm、1600mm)共计5根悬伸梁,以及一种单轴对称截面形式(上翼缘加强)、三种相邻跨度之比(1∶0.48、1∶0.64、1∶1)共3根双跨连续梁进行了试验研究。在进行破坏试验前,对悬伸梁进行了三种荷载作用位置的弹性试验,对连续梁进行了三种加载比例的弹性试验,并利用Southwell法确定了临界荷载。试验研究结果表明:当最大弯矩出现在悬伸梁的简支跨且上翼缘受压时,上翼缘加强构件稳定承载力明显高于同尺寸的下翼缘加强构件;悬伸长度为1600mm的构件承载力明显高于悬伸长度为1200mm的构件承载力;荷载作用在简支梁段跨中时构件稳定承载力最低,荷载作用点离中间支座越近构件稳定承载力越高。双跨连续梁中,在等比例加载时,相邻跨度之比越大,构件稳定承载力越高。此外,对试验进行了有限元模拟,计算结果与试验结果吻合良好。     

螺纹孔单边螺栓T形连接节点受拉性能研究(Ⅰ)——试验研究

单边螺栓连接技术广泛应用于钢梁与钢管柱的高强螺栓端板连接。通过试验研究了单边螺栓T形连接节点的拉伸性能,共发现3种破坏模式:T形翼缘完全屈服、T形翼缘屈服伴随螺栓断裂和螺纹破坏。试验结果表明:1)增加T形翼缘的厚度可以提高节点的极限承载力,并增大节点的刚度;2)即使在T形翼缘较薄时,螺纹孔仍可提供足够的锚固力以确保节点不发生螺纹破坏;3)增加螺母并不能提高T形节点的屈服强度,但可以防止翼缘屈服后上下翼缘板完全脱开;4)节点是发生螺纹破坏还是螺杆断裂,取决于螺杆直径与锚固螺纹长度的大小。     

Dynamic and static axial crushing of axially stiffened cylindrical shells

The axial impact of cylindrical tubes, which incorporate axial stiffeners, is examined in this paper. For comparison purposes, the effect of static loading is also studied. An examination is made into the influence of stiffener depth (T), number of stiffeners (N) and the effect of placing the stiffeners externally or internally.

The experimental results on mild steel specimens show that there are considerable differences between the static and dynamic modes of failure, and that an optimum T/D ratio may exist for a given value of N.     

Experimental collapse of thin cylindrical shells submitted to internal pressure and pure bending

A thin-walled pressurised cylindrical shell is sensitive to buckling phenomena when it experiences locally a compressive stress. It is often considered that its behaviour under bending is rather similar to pure compression, but very few are the experimental investigations that precise the real behaviour of a thin pressurised cylinder submitted to a bending load. A large amount of experimental results is presented here, obtained on thin shells (550<R/t<1450) of moderate length (L/R≈2). The evolution of the cylinders' behaviour that has been recorded when internal pressure increases is outlined. It is shown that one must distinguish between local buckling and global collapse of the structure. A comparison of our experimental data to design recommendations given by two standards (NASA SP8007 and Eurocode 3) is finally achieved, putting in advance safety margins provided by these codes.     

钢管杆塔新型内外法兰受弯性能试验研究及有限元分析

提出了一种适用于钢管杆塔的内外法兰连接型式,阐述了该法兰的特点,对节点的设计进行了系统分析,提出了节点螺栓拉力计算模型,指出确定计算螺栓拉力旋转轴的位置是整个新型法兰的研究重点。为考察新型内外法兰的受力性能、节点破坏模式、内外圈螺栓拉力及法兰螺栓群的受力分界线,以白花洞钢管杆工程为背景,进行了2个缩尺法兰模型的静力试验。同时,对试验模型进行了非线性有限元分析,试验结果与有限元分析结果吻合较好,分析结果均表明：这种法兰构造合理、安全可靠,可用于实际工程。最后,结合试验与有限元参数分析结果,给出了内外法兰受弯时的设计方法,建议计算螺栓拉力的旋转轴位置可取在距钢管中心0.7r处(r为钢管半径)。     

局部可更换钢框架梁-柱节点受力性能研究

基于保险丝和塑性铰外移理念,将外伸端板连接、削弱型和拼接型连接的优点进行整合,提出一种局部可更换钢框架梁-柱连接节点。选取端板连接和拼接节点2个典型试验进行模拟,验证有限元建模过程的可靠性,然后对试件进行变参数分析,研究短梁翼缘削弱深度、削弱长度、短梁长度对节点承载力、耗能能力及延性的影响。结果表明:通过对H型短梁翼缘削弱,实现了塑性铰外移的目的,使地震作用下的塑性变形主要集中于短梁上,其他构件保持弹性,具有良好的震后恢复能力; 参数对节点力学性能的影响程度由大到小依次为削弱深度、削弱长度、短梁长度,随着翼缘削弱深度的增大,节点的承载力有明显降低,而耗能能力和延性有所提高; 同时随着翼缘削弱长度的增大,节点的最大承载力有所减小,而延性系数有所增大; 短梁长度对节点力学性能的影响基本可忽略不计。     

基于位错理论的饱和土渗流特性CPTU评价研究

孔压静力触探（CPTU）测试数据通常用于土层划分和岩土工程设计参数评价。国际上CPTU测试技术的最新进展之一在于采用测得的锥尖阻力、侧壁摩阻力和孔隙水压力快速、连续地获得饱和土的渗透系数,以避免孔压消散试验费时的缺点。首先简要回顾了基于CPTU测试资料确定饱和土渗透系数的的研究成果,并进行了分析与改进,提出了基于位错理论和圆柱面径向流模型的水平向渗透系数预测新方法。选取典型场地进行了CPTU测试,并在黏性土场地采用薄壁取土器获得无扰动的原状试样,进行室内水平向渗透试验,在无黏性土场地进行现场钻孔抽水试验。以室内渗透试验和现场抽水试验的结果为参考,对3种基于CPTU连续评价饱和土渗透系数的方法进行了对比分析。研究表明,位错理论适用于评价饱和土的原位渗透系数,然而准确性与所采用的渗流模型有关。对国际标准CPTU探头,孔压过滤环位于锥肩（u₂）位置时,采用圆柱面的径向流模型能够获得最为准确的水平向渗透系数预测结果,采用球面流或半球面流模型时趋于低估土层的渗透性。     

Structural behaviour of perforated shear connectors with flange heads in composite girders: an experimental approach

Perforated shear connector with flange head (PSCFH) as a new type of connector behaves high bearing capacity and excellent ductility in steel-concrete composite girders. In this paper 15 groups, totally 45 push-out test specimens, were conducted to investigate the effects of plate thickness, connector height, flange length, flange number, hole diameter on the web, diameter of reinforcing bars and concrete strength on structural behaviour of PSCFH. In the push-out tests, failure mode, load versus slip curve and bearing capacity of all the specimens were obtained. Based on the results of push-out tests, bearing mechanism was analyzed and a calculation model of the shear bearing capacity was proposed with respect to the failure modes. Calculation results based on the proposed model agree well with the experimental values.     

Fire performance of cold-formed steel wall panels and prediction of their fire resistance rating

Recent research at the Queensland University of Technology has investigated the structural and thermal behaviour of load bearing Light gauge Steel Frame (LSF) wall systems made of 1.15 mm G500 steel studs and varying plasterboard and insulation configurations (cavity and external insulation) using full scale fire tests. Suitable finite element models of LSF walls were then developed and validated by comparing with test results. In this study, the validated finite element models of LSF wall panels subject to standard fire conditions were used in a detailed parametric study to investigate the effects of important parameters such as steel grade and thickness, plasterboard screw spacing, plasterboard lateral restraint, insulation materials and load ratio on their performance under standard fire conditions. Suitable equations were proposed to predict the time–temperature profiles of LSF wall studs with eight different plasterboard-insulation configurations, and used in the finite element analyses. Finite element parametric studies produced extensive fire performance data for the LSF wall panels in the form of load ratio versus time and critical hot flange (failure) temperature curves for eight wall configurations. This data demonstrated the superior fire performance of externally insulated LSF wall panels made of different steel grades and thicknesses. It also led to the development of a set of equations to predict the important relationship between the load ratio and the critical hot flange temperature of LSF wall studs. Finally this paper proposes a simplified method to predict the fire resistance rating of LSF walls based on the two proposed set of equations for the load ratio–hot flange temperature and the time–temperature relationships.     

方钢管混凝土柱-H形钢梁不同构造隔板贯通节点力学性能研究

为研究具有不同连接形式、隔板厚度和外伸长度的隔板贯通节点的力学性能,使用ABAQUS对不同构造节点进行数值模拟研究。基于试验结果验证了建模方法的准确性,并分别建立了全焊接、腹板栓接-翼缘焊接、下栓上焊、全螺栓四种连接形式的隔板贯通节点模型,对比了不同连接形式节点的力学性能,对产生差异的原因进行了机理分析。并进一步针对下栓上焊连接形式节点的隔板厚度、外伸长度对力学性能的影响进行了参数化分析。研究发现,具有翼缘螺栓连接形式的节点承载力更高且塑性铰远离节点核心区,基于此且考虑到施工因素,认为下栓上焊的连接形式具有显著优势;隔板过薄或隔板外伸长度过长均会降低该种节点的承载力和延性,隔板也会发生明显变形导致在核心区形成塑性铰,劣化节点受力性能。推荐工程中采用的隔板厚度宜比钢梁翼缘厚度厚3mm左右,隔板外伸长度宜控制在50~75mm。     

Flange/web distortional buckling of cold-formed steel sections in bending

Recent experimental tests of cold-formed steel C- and Z-sections in bending have revealed unconservative results in the prediction of the bending moment resistance, using the current North American Design Standards. The failure mode of these tests was identified as flange/web distortional buckling. This mode of failure initially involves a rotation of the lip/flange component about the flange/web corner, which typically occurs for short half-wavelength distortional buckling. Near ultimate failure, an apparent lateral movement of the flange/web corner, which includes transverse bending of the web, is experienced. Various analytical methods that predict the moment resistance of sections which experience short half-wavelength distortional buckling were investigated and compared with the applicable test data. The modified Lau and Hancock 2 Model, with S136-94 Standard calculated effective section modulus, is recommended for use as the North American predictor model for the flange/web distortional buckling moment resistance of cold-formed steel sections in bending.     

Mechanical properties of roller bent wide flange sections — Part 1: Experimental investigation

Arched roofs are built more and more with roller bent wide flange sections, serving as structural elements. Roller bent wide flange sections are manufactured from straight hot-rolled wide flange sections by a process called roller bending. The material is cold worked during forming, inducing a new distribution of mechanical properties across the section which is different compared to its original state. For the design of arches the use of original or nominal strength properties of the straight material neglects the influence of the roller bending process. This may lead to conservative or nonconservative designs. This paper presents the results of an extensive experimental investigation of the mechanical properties of roller bent wide flange sections. It comprises tensile tests and compression tests on coupons taken from roller bent sections and their straight counterparts. The results show that the roller bending process alters the mechanical properties of the material non-uniformly over the cross-section. In this paper the experimental results are presented. In a companion paper the experimental results are used to arrive at a set of equations that yields different stress-strain curves for specific zones across the roller bent steel section.     

翼缘宽度对预期损伤部位采用FRC增强的梁柱组合件破坏机制影响的试验研究及数值模拟

为研究现浇板翼缘宽度和纤维增强混凝土（FRC）材料对框架结构破坏机制的影响,设计制作一组纵梁腹板两侧各6倍和8倍板厚翼缘宽度,且带有横交梁的梁柱组合件,试件的预期损伤部位采用FRC材料,柱梁抗弯承载力比分别取1.2和1.4|对试件进行拟静力试验,考察试件的破坏过程和破坏形态,分析其破坏机制和翼缘板内钢筋的应变分布,研究试件的变形和耗能能力、强度和刚度退化等抗震性能。在试验研究基础上,对试件原型破坏过程进行数值模拟,并进行了参数分析。结果表明,预期损伤部位范围内的梁、柱和板采用FRC材料,在一定程度上可以减小板对梁抗弯承载力影响的范围,易于实现“强柱弱梁”的破坏机制|考虑8倍板厚翼缘宽度的梁柱组合件更易于实现“强柱弱梁”的破坏机制,并且能显著降低其强度退化系数,提高其耗能能力。     

Einfluss imperfekter Ringflanschverbindungen auf die Ermüdungsfestigkeit von kreiszylindrischen Stützen

Bei Seilbahnen, Windenergieanlagen, Kaminen etc. werden oft turmartige Stahlkonstruktionen aus kreiszylindrischen oder konischen Rohrabschnitten verwendet, welche mittels L‐förmiger Flanschverbindungen verschraubt sind. Auf Grund von Imperfektionen zufolge Schweißverzug und hohen dynamischen Beanspruchungen werden häufig die Grenzen der Beanspruchbarkeit der Flanschverbindungen erreicht. In vielen Fällen ist nicht der Nachweis der Traglast (ULS) von Bedeutung, vielmehr ist der Grenzzustand der Ermüdung (FLS) maßgebend für die Dimensionierung. Der vorliegende Beitrag beinhaltet die Untersuchung imperfekter Ringflanschverbindungen von kreisförmigen Seilbahnstützen auf Ermüdung. An einem Bauteilversuch im Maßstab 1 : 1 wurde die Ermüdungsfestigkeit der gesamten Flanschverbindung (Schrauben, Schweißnaht, Rohrmantel) untersucht. Parallel durchgeführte FE‐Berechnungen dienen als Vergleich zu den Laborergebnissen. Zum Abschluss wird eine Möglichkeit der Berücksichtigung der Flanschimperfektionen für die praktische Bemessung aufgezeigt. Effects of imperfect ring flange connections on the fatigue resistance of cylindrical columns. For cableway installations, wind turbines, chimneys etc. often tower‐like steel constructions from cylindrical or conical tubing sections are used, which are bolted by means of L‐shaped flange connections. Due to imperfections from welding distortion and high dynamic loads the resistance of the flange connections will be frequently achieved. In many cases the ultimate load (ULS) proof becomes less important and the fatigue assessment (FLS) is determining the dimensions. This contribution contains investigations of imperfect flange connections of circular cable car towers on fatigue. A large scale test was performed to prove the fatigue strength of the entire flange connection (bolts, welding seam, tube section). Parallel accomplished FE‐computations serve as comparison to the laboratory test results. As conclusion a possible procedure to consider flange imperfections for the practical dimensioning is pointed out.     

Shear assessment of compression flanges of structural concrete T-beams

In T-beams the force transfer from the web into the flange has to be studied. The general design procedure is based on a strut-and-tie (or a stress field) model which comprises spreading compressive and transverse tensile forces. As is known, strut-and-tie models represent the force flow within a structural member at ultimate. This procedure is sufficient for design purposes and in general, leads to safe results. For the assessment of a structure it may be worthwhile to improve the accuracy. For this purpose both web and flange have to be looked at more in detail. An advanced method for the analysis of webs in shear is the Generalized Stress Field Approach [1]. This approach can be utilized for treating flanges, where the classical assumptions have to be adapted; in particular by considering the strain dependence of the concrete compressive strength and thus, defining a representative strain value. In the present contribution background and details of these aspects are given, and the corresponding calculation procedure is described. Theoretical results are compared with experimental data and show a reasonably good agreement. However, as the number of sufficiently documented tests is very limited no concluding findings are attained.     

Slenderness limits normal to the plane of bending for beam-columns in plastic design

This paper describes a theoretical approach for identifying the spacing of lateral restraints to the compression flange for beams, and beam-columns with limited axial force, in regions of moment gradient, in order to achieve an identified rotation capacity of the plastic hinge within this length. The predictions obtained from this approach are compared with the results of tests conducted by Smith and Adams. It is acknowledged that the analytical technique which is used is rather simplistic and could be expanded into a more sophisticated model, although the non-linear nature of the solution may make this cumbersome. Nevertheless a favourable comparison is obtained and it is possible to recommend appropriate formulae for design purposes.     

住宅钢结构梁翼缘材料削弱型节点的有限元分析

提出一种利用低屈强比钢实现住宅钢结构节点梁翼缘削弱的新方法。采用非线性静动态有限元方法,分析和比较梁翼缘材料削弱前后节点的极限承载能力和滞回性能,研究梁翼缘削弱位置和削弱长度等对节点承载能力、塑性铰发生位置、节点抗震性能等的影响。分析表明:梁翼缘材料削弱会造成节点承载能力小幅度降低,并使节点局部应力重分布,实现塑性铰外移;梁翼缘削弱后,节点的滞回曲线更为饱满,节点耗能性能和延性性能增强;梁翼缘削弱位置和削弱长度的变化对节点承载能力和抗震性能都有一定影响,需要对削弱参数进行综合考虑。     

凯威特型索穹顶结构多种张拉成形方案模型试验研究

张拉成形技术属于索穹顶结构的关键技术。为分析比较各种张拉成形方案的施工可行性和方便性,同时深入理解预应力生成机理,对一凯威特型索穹顶结构模型进行了逐步张拉外圈斜索成形、一次性张拉外圈斜索成形及由外及里逐步调节压杆到原长成形等三种成形方案的张拉成形试验,跟踪了张拉成形全过程。试验研究表明：三种张拉成形方案都是可行有效的,其中一次性张拉外圈斜索成形方案施工较为方便;逐步调节压杆长度到原长成形方案精度相对较高;控制构件原长的张拉成形控制技术不仅适用于单整体自应力模态体系,也适用于多整体自应力模态体系;体系预应力伴随着构件的逐步张拉到位而逐步生成。