钢纤维钢筋混凝土梁柱节点抗震设计方法

基于压杆模型和软化桁架模型,提出钢纤维钢筋混凝土梁柱节点的一种新的抗震设计方法.掺入节点核心区的钢纤维可被等效为部分水平和竖向剪力筋.在节点核心区与梁或柱相交端截面处建立平衡方程、协调方程和本构方程,可以求出传给节点压杆模型和软化桁架模型的地震作用.提出的设计方法能够对节点的水平和竖向抗剪承载力进行设计,其可靠性得到七个钢纤维钢筋混凝土梁柱外节点试验数据的验证.     

梁柱节点混凝土的施工

在钢筋混凝土结构中,高层建筑框架结构的梁柱节点比较复杂,本文将就混凝土的施工方法及裂缝处理,谈几点个人看法。     

浅谈高层建筑梁柱节点混凝土的施工

在钢筋混凝土结构中,高层建筑框架结构的梁柱节点比较复杂,高层建筑框架梁柱节点区混凝土如何浇注才能满足要求,本文将就混凝土的施工方法及裂缝处理,谈几点个人看法。     

梁柱节点不同强度等级混凝土的施工

高层建筑的框架结构节点处,经常会出现柱混凝土强度等级比同一层梁板高的情况,通常的施工方法是先浇节点处混凝土强度等级高的核心部分,然后于初凝前再浇梁板混凝土。本文讨论了关于梁柱节点不同强度等级混凝土的施工问题。     

梁柱节点不同强度等级混凝土施工

高层建筑框架结构的梁柱节点比较复杂,要求同一层的竖向结构(柱、墙)混凝土强度等级高于水平结构(梁、板)的混凝土强度等级.介绍梁柱节点不同强度等级混凝土施工方法,分析了梁柱节点处裂缝产生的原因分析并给出了相应的预防措施.     

对建筑工程梁柱节点混凝土强度的分析

本文在分析建筑结构施工中存在问题的基础上,就梁柱节点不同强度等级混凝土的常见施工方法进行了探讨,并提出了控制和消除梁柱节点位置裂缝的操作手段,旨在为提高建筑施工的质量,做出理论层面的参考。     

自复位超弹性SMA筋梁柱节点数值模拟研究

为提高框架结构的耗能能力和自恢复能力,提出了基于超弹性SMA筋的功能自恢复梁柱节点.基于OpenSees有限元软件平台,采用SMA材料自复位双旗形本构模型,建立了自复位SMA筋混凝土梁柱节点有限元数值模型,进行了低周往复作用下有限元模拟,得出节点的滞回曲线与骨架曲线.通过与现有试验结果的对比,验证了节点分析模型的有效性...     

有缺陷的装配式混凝土梁柱节点抗震性能试验研究

为了明确装配式混凝土框架结构节点缺陷对于节点抗震性能的影响,该文考虑了三种典型装配式梁柱节点核心区缺陷,对5个装配式混凝土梁柱节点和1个全现浇混凝土梁柱节点进行了拟静力试验,分析了其对破坏形态、滞回性能、骨架曲线、刚度退化、耗能能力等性能的影响。采用OpenSees非线性有限元分析程序模拟钢筋粘结滑移关系和节点区域剪切性能,讨论了装配式混凝土梁柱节点钢筋粘结削弱的影响。结果表明:核心区内部混凝土浇筑缺陷将使得钢筋过早出现滑移现象,对节点的强度及耗能能力产生影响;粗糙面的缺陷及柱底接缝灌浆层缺陷对于节点抗震性能的影响较小;有限元模型通过考虑节点域的钢筋粘结滑移关系,可以有效模拟装配式节点钢筋粘结削弱效应,从而为进一步研究装配式节点抗震性能不确定性,并进行地震易损性分析奠定基础。     

火灾后型钢混凝土梁柱节点抗震性能试验研究

通过4个火灾后型钢混凝土柱-型钢混凝土梁节点试件及2个常温未受火对比试件的低周反复加载试验,研究火灾后该类节点的滞回特性、延性、耗能性能、承载力与刚度退化规律,分析了受火时间、轴压比对火灾后该类节点的抗震性能的影响。结果表明：火灾后试件与常温未受火试件的破坏过程和破坏形态基本一致。经历火灾损伤后,型钢混凝土梁柱节点的滞回曲线仍然饱满,但试件承载力降低、变形增大、延性减弱,受火时间越长,承载力下降程度越高、变形增加程度越大、延性系数越小。反复荷载下型钢混凝土梁柱节点的强度出现衰减,加载初期的衰减系数随位移的增大而减小,加载后期的衰减系数随位移的增大总体保持稳定,体现出良好的抗荷载循环能力。与常温未受火试件相比,高温后试件加载初期的刚度降低、等效阻尼比增大,受火时间越长,刚度降低和等效阻尼比增大的程度越高。随着加载的进程,高温后试件的刚度与常温未受火时间刚度逐渐趋向一致,但等效阻尼比相比常温未受火试件减小,受火时间越长,减小程度越高。轴压比对火灾后节点的抗震性能产生一定影响,随着轴压比的增大,试件强度和刚度有所提高,但延性下降。     

钢纤维自密实混凝土梁抗弯性能的数值模拟方法

钢纤维自密实混凝土梁的抗弯性能与钢纤维的取向有密切关系,而基于钢纤维取向对其抗弯性能进行的数值模拟研究较少.借助Moldex3D软件模拟并分析了浇筑完成后钢纤维的取向概率,在此基础上由Final-v11有限元软件建立钢纤维自密实混凝土梁模型并进行数值计算,通过与试验对比结构的荷载位移曲线、裂缝开展过程等方面,验证了该数...     

Simulated seismic loading on reinforced concrete beam/column connections

Laboratory tests to investigate the seismic behaviour of five reinforced concrete external beamlcolumn connection specimens, by subjecting the beams to a series of slow load reversals, are described. The first three tests were undertaken as an extension of a static (non-seismic) test programme and were primarily carried out for the purposes of rig development. The two further test specimens contained additional links in the connection zone to make them representative of current seismic practice in the U.S.A. These two specimens were subjected to a series of slow load reversals specifically intended to simulate seismic effects.
With the first three specimens, complete destruction of the connection zone was achieved after only four or five cycles; the last two specimens withstood ten and twelve cycles respectively. One of these latter specimens failed due to the development of a plastic hinge at the beaml column junction, the other by plastic hinges forming in the column above and below the beam. Detailed information regarding the form of the reinforcement strain distributions developed during these tests is presented, data being obtained using reinforcement internally strain gauged with electric resistance strain gauges. Each specimen contained around 230 such gauges.     

Fatigue behaviour of steel fiber reinforced concrete

The results of an experimental investigation on the fatigue characteristics and residual strength of steel fiber reinforced concrete (SFRC) are reported. The testing program included flexural specimens as well as split-cylinders and cubes reinforced with two fiber types at a low volume content. One of the fibers was of the deformed slit-sheet type available at aspect ratios of 45 and 60. It is shown that SFRC has a better fatigue response than plain concrete and that the deformed slit-sheet fiber has an effect almost identical to hooked-end fiber of similar dimensions. There is no increase in residual strength measured by split-tension when specimens are subjected to fatigue stress above the endurance limit. Fatigue characteristics of SFRC from this testing program as well as previous works can be interpreted as a function of the fiber factor (i.e. a parameter accounting for volume fraction, aspect ratio and fiber type) to provide design charts. More experimental work is needed to provide an acceptable database for fatigue design of SFRC.     

Thermo-mechanical properties of fiber reinforced raw perlite concrete

The effect of hooked steel, wavy steel and polypropylene fibers on the thermo-mechanical properties of raw perlite aggregate concrete was investigated. In order to determine the effect of fiber ratio on the thermo-mechanical properties of 100% raw perlite concrete, 0.25%, 0.75%, 1.25%, and 1.75% fiber ratios were used by volume of the sample and also, 350 kg/m³ cement dosage and 3 ± 1 cm slump were used. When compared to the control sample that contains no fiber, (1) with the increase of steel fiber ratio in the mixtures thermal conductivity (TC), unit weight, splitting-tensile strength, and flexural strength of concretes increased, (2) with the increase of steel fiber ratio in the mixtures compressive strength of concretes decreased, and (3) with the increase of polypropylene fiber ratio in the mixtures TC, unit weight, compressive strength, splitting-tensile strength, and flexural strength of concretes decreased.     

纳米SiO2对钢纤维/混凝土高温后力学性能及微观结构的影响

研究了掺纳米SiO2的钢纤维混凝土(NSFC)、钢纤维混凝土(SFRC)和普通混凝土(NC)三种材料在不同加热温度后的抗压、劈裂和抗折强度等力学性能,对不同温度热处理后的微观结构进行了SEM分析,对钢纤维与过渡区界面的相结构进行了XRD分析.结果表明:在测试温度范围内,NSFC的抗压、劈裂和抗折强度均高于SFRC和NC的强度,且在400℃时达到最大值.在常温下,NSFC的抗压、劈裂和抗折强度较NC分别提高27.01％、63.28％和54.12％,400℃高温热处理后比NC分别高35.09％、84.62％和87.23％; SEM分析表明,在钢纤维与过渡区的界面处,致密度提高,显微硬度提高.由于固相反应,使界面区结构发生变化,在钢纤维表层形成扩散渗透层(白亮层),即化合物层,呈锯齿状,XRD分析证明,白亮层主要由FeSi2和复杂的水化硅酸钙组成,从而增强了钢纤维与基体的粘结力,提高了混凝土的高温力学性能.     

Corrosion process and abatement in reinforced concrete wrapped by fiber reinforced polymer

The corrosion performance of steel reinforcement embedded in concrete samples encased by carbon fiber reinforced polymer (CFRP) wraps was investigated experimentally. Concrete samples were wrapped with 0−3 fabric layers impregnated with one of two different epoxies. To accelerate corrosion, samples were subjected to an impressed current and a high salinity solution. Current flow measurements dynamically monitored corrosion activity during exposure, while reinforcement mass losses were measured following exposure. Theoretical predictions of total mass loss were compared with actual corrosion mass loss values. Test results indicated that CFRP wrapped specimens had prolonged test life, decreased reinforcement mass loss, and lower corrosion rates. The performance of wrapped specimens was superior to that of either control samples or those coated only with epoxy. Results indicated that the level of corrosion abatement provided by the CFRP wraps was influenced both by the type of epoxy used and the number of wrap layers.     

Experimental investigation of steel fiber reinforced concrete box beams under bending

Reduction of dead weight of a reinforced-concrete (RC) structure without too much concession in its load carrying capacity has always been an attractive study subject because it engenders (1) a decrease in dimensions of the members, (2) a decrease in the reinforcement steel, and (3) a decrease in lateral inertia forces during severe earthquakes. In this study, nine RC beams of outer dimensions of 300 × 300 × 2000 mm, six of which are box beams, designed and produced using a C20 class steel fiber concrete, (SFRC) with the commonly used steel fiber type of Dramix-RC-80/0.60-BN at a dosage of 30 kg/m³, are tested under bending. The mechanical behaviours of all these nine beams under bending are recorded from the beginning of the test till the ultimate failure of the tensile reinforcement in a two-point beam-loading setup. The proportions of (1) loss in ultimate load versus reduction in dead weight and (2) (ultimate experimental load)/(ultimate theoretical load) of the SFRC box beams are determined for two different box thicknesses. Dimensionless behaviour relationships of all the SFRC beams are determined, and the experimentally obtained relationship between the ratio of (actual ultimate load)/(theoretical ultimate load) and the ratio of (wall thickness)/(beam height) for the SFRC box beams is expressed diagrammatically.     

Ductility of 3D printed concrete reinforced with short straight steel fibers

ABSTRACT

With the number of 3D printed concrete structures rapidly increasing, the demand for concepts that allow for robust and ductile printed objects becomes increasingly pressing. An obvious solution strategy is the inclusion of fibers in the printed material. In this study, the effect of adding short straight steel fibers on the failure behaviour of Weber 3D 115-1 print mortar has been studied through several CMOD tests on cast and printed concrete, on different scales. The experiments have also been simulated numerically. The research has shown that the fibers cause an important increase in flexural strength, and eliminate the strength difference between cast and printed concrete that exists without fibers. The post-peak behaviour, nevertheless, has to be characterised as strongly strain-softening. In the printed specimens, a strong fiber orientation in the direction of the filament occurs. However, this has no notable effect on the performance in the tested direction: cast and printed concrete with fibers behave similarly in the CMOD test. For the key parameters, no scale effect was found for the specimens with fibers, contrary to the ones without. Numerical modelling of the test by using the Concrete Damage Plasticity material model of Abaqus, with a Thorenfeldt-based constitutive law in compression and a customised constitutive law in tension, results in a reasonable fit with the experimental results.     

Fatigue behavior of externally bonded steel fiber reinforced polymer (SFRP) for retrofit of reinforced concrete

Steel fiber reinforced polymer (SFRP) strips comprised of multiple high-strength wires have been introduced into the repertoire of the structural engineer in recent years. The deleterious effects of fatigue loading on FRP-to-concrete bond have been identified in previous studies by the author; therefore the effect of fatigue loading on the bond behavior of SFRP is investigated. Four large-scale beam specimens (4.9 m long) having externally bonded SFRP retrofits are tested. These specimens are paired with unretrofit and CFRP-retrofit companion specimens allowing a number of direct comparisons to be made. Of the SFRP specimens, one is tested in monotonic loading to failure while the remaining three are tested at various fatigue load levels ranging from service load level to an extreme load level. Service load fatigue is cycled for 2 million cycles and the specimen is then tested monotonically to failure to assess the effects of fatigue conditioning on the ultimate performance of the beam. Extreme loading is selected to result in fatigue-induced failure of the internal reinforcing steel.     

基于荷载时程分析法的钢筋混凝土与钢板混凝土墙冲击响应对比分析

为对比核电站核岛厂房钢筋混凝土结构(RC)与钢板混凝土结构(SC)外墙的抗冲击性能,基于荷载时程分析法,用显示非线性动力分析软件ANSYS/LS-DYNA仿真分析1/7.5比例飞机模型撞击RC、SC墙的冲击实验。将RC、SC墙破坏模式、混凝土碎片残余速度及背部钢板变形等计算结果与飞射物-靶体相互作用分析法计算结果及实验结果以及同厚度不同结构类别墙的计算结果进行对比。结果表明,基于荷载时程分析法计算结果有一定保守性,与实验结果吻合较好,且SC墙抗冲击性能优于RC墙,尤其背部钢板能有效约束混凝土撞击方向的运动及限制混凝土碎片飞溅。用于抗飞机撞击的SC结构墙体厚度可适当减薄。     

Strain distribution along lapped joints in reinforced concrete

Strain measurements along lapped joints in reinforced concrete tension members were obtained using a method of internally strain gauging the reinforcing rods. Strain concentration gauges, installed at the lap ends of some specimens, demonstrated the localised nature of force transfer prior to crack formation.
Results from ten test specimens of varying lap length and rod diameter have been produced. The changes observed in the longitudinal strain distributions, and the associated bond and concrete stresses as cracks developed are presented.