高强不锈钢绞线网-渗透性聚合砂浆加固梁抗弯承载力试验研究

高强不锈钢绞线网-渗透性聚合砂浆加固技术是一项新型加固工艺,具有耐火、耐腐蚀、耐老化等优点。针对采用高强不锈钢绞线网-渗透性聚合砂浆加固的河北沧州某大桥,采用缩尺比例模型,对4根由该工艺加固的钢筋混凝土T型梁和1根对比梁的抗弯性能试验进行对比研究,分析加固梁抗弯承载力的影响因素及其破坏模式。在试验研究的基础上,提出此类加固梁的抗弯承载力计算公式。     

碳纤维布加固损伤混凝土梁抗弯性能试验研究

本试验采用5根钢筋混凝土梁,其中1根对比梁加载至破坏,其余4根梁加载至最大裂缝宽度达到0.2mm~0.3mm后卸载采用碳纤维布进行加固且用U形箍锚固,然后进行抗弯试验。试验结果表明,采用U形箍锚固措施对损伤钢筋混凝土梁极限承载力有不同程度的影响。在试验研究和理论分析基础上对碳纤维布加固损伤钢筋混凝土梁抗弯承载力计算方法进行了分析,给出了损伤混凝土梁抗弯承载力折减系数;并对加固损伤钢筋混凝土梁挠度进行分析。计算结果表明,理论计算结果与试验值吻合较好。     

碳纤维加固材料加固受损混凝土梁受弯性能试验及设计方法研究

基于碳纤维加固材料(CFRP)布加固疲劳损伤后的钢筋混凝土梁和预应力混凝土梁进行的竖向荷载作用下试验,研究了CFRP布加固疲劳损伤后的混凝土梁受弯性能和抗弯承载力。试验结果表明:预应力钢筋明显减小加固梁的跨中挠度及CFRP布应变值;混凝土梁的疲劳损伤降低了CFRP布加固钢筋混凝土梁的极限抗弯承载力,且混凝土梁加固前损伤程度越大,加固后极限抗弯承载力降低的幅度亦越大;采用GB50367—2013《混凝土结构加固设计规范》和GB 50608—2010《纤维增强复合材料建设工程应用技术规范》中提出的抗弯承载力计算式(均未考虑梁加固前损伤程度),所得计算值均高于试验结果,表明加固前梁产生的疲劳损伤对加固后抗弯承载力的影响不可忽略。     

火灾下CFRP加固RC梁抗弯性能的试验研究

正葡萄牙研究人员开展了火灾下碳纤维增强复合材料(CFRP)加固钢筋混凝土(RC)梁抗弯性能的试验研究。其目的是评价在不同防火保护方式下,采用该类加固方式的钢筋混凝土梁的耐火性能。加固梁的耐火性能试验采用的防火保护方式     

碳纤维片材加固火灾后钢筋混凝土梁抗弯承载力

研究碳纤维片材加固火灾后钢筋混凝土梁抗弯承载力的计算方法,采用截面分析法分析碳纤维片材加固火灾后钢筋混凝土梁的抗弯承载力.考虑的火灾作用位置包括受拉区受火和受压区受火,提出了碳纤维片材加固火灾后钢筋混凝土梁的计算方法,建议了碳纤维片材的允许应变值,并根据试验结果对提出的计算方法进行了验证.结果表明,本文的计算方法可较准确地计算碳纤维片材加固火灾后钢筋混凝土梁的抗弯承载力,计算值有一定的安全储备.     

钢丝网水泥砂浆加固混凝土梁高温后的抗弯性能

对钢丝网水泥砂浆加固钢筋混凝土梁高温后抗弯性能进行试验,研究受热温度对钢丝网水泥砂浆加固钢筋混凝土梁高温后抗弯性能的影响规律。研究结果表明:采用钢丝网水泥砂浆加固法能有效提高梁的抗弯刚度,减少跨中挠度;随着受热温度的升高,钢丝网水泥砂浆加固梁的承载力有一定程度的降低,当受热温度在450℃以下时,加固梁承载力的降低不超过5%。也即采用钢丝网水泥砂浆加固混凝土梁具有良好的抗火能力。     

钢板-混凝土组合加固带损伤钢筋混凝土T梁的抗弯性能试验

为了研究钢板-混凝土组合加固钢筋混凝土T梁在静载作用下的抗弯性能,对带损伤的2片混凝土T梁组合加固后进行了抗弯承载力试验,得到了构件破坏时的极限抗弯承载力以及受力特性,揭示了钢板-混凝土组合加固钢筋混凝土T梁的弯曲破坏机理;建立了钢板-混凝土组合加固钢筋混凝土T梁的有限元模型,并进行了非线性静力计算。结果表明:考虑材料非线性的静力计算结果与试验结果吻合良好;采用塑性分析方法建立的试验梁极限抗弯承载力简化计算公式的计算结果与试验结果吻合良好。     

芳纶纤维布加固钢筋混凝土梁的抗弯性能

通过3根芳纶纤维布加固钢筋混凝土梁和1根基准混凝土梁的抗弯性能试验,研究了芳纶纤维布层数对加固混凝土梁的抗弯承载力、刚度和破坏特征的影响.试验结果表明,粘贴芳纶纤维布可以有效地提高被加固梁的抗弯承载力.根据不同的破坏模式,给出了芳纶纤维布加固钢筋混凝土梁的抗弯承载力计算公式,计算结果与实测结果符合良好.     

复合砂浆钢丝网加固RC受弯构件的试验研究

本文对用无机材料钢丝网复合砂浆加固的钢筋混凝土梁进行了正截面抗弯试验研究,研究了这种新的加固技术对钢筋混凝土梁的抗弯承载力的影响和作用。试验包括13根用钢丝网加固的试件和两根未加固的对比试件。加固的形式包括U形三面加固及一面加固两种。试验的主要目的是研究采用该加固方法后,试件可能产生的破坏形式,正截面抗弯承载力的提高程度等等。试验中测量了受弯构件的开裂荷载、极限荷载、钢筋应变及钢丝网应变。试验结果表明,钢丝网复合砂浆薄层可以明显地提高钢筋混凝土梁的抗弯承载力,提高抗裂性能,增强构件的抗弯刚度。试验结果说明该技术是一种有效的加固方法。     

碳纤维加固锈蚀钢筋混凝土梁抗弯承载力

为研究碳纤维对锈蚀钢筋混凝土梁加固后抗弯承载力的变化情况,采用碳纤维对一根锈蚀率为9%的梁正截面进行加固,计算加固后的抗弯承载力。分析结果表明:钢筋锈蚀到一定程度后,无法满足承载力要求;采用碳纤维布进行加固后,梁抗弯承载力显著提升,满足承载力要求;在适用条件下,抗弯承载力随着碳纤维布用量的增加而增加。     

三面受火情况下钢筋混凝土梁极限承载力的计算与分析

根据对火灾作用下钢筋混凝土梁可能破坏截面的应力、应变及内力分析的基础上,编制了火灾下钢筋混凝土梁截面极限承载力的计算程序.运用该程序对钢筋混凝土梁可能破坏截面的高温极限承载力的变化进行计算、分析,由此得出混凝土梁在火灾作用下极限承载力随时间下降变化的一般规律,可用于指导工程结构的耐火设计及火灾营救.     

均匀受火钢筋混凝土框架极限承载力分析

对火灾高温作用下钢筋混凝土梁、柱可能破坏截面的应力、应变及内力进引分析。在此基础上,编制了钢筋混凝土梁、柱在高温作用下截面极限承载力的计算程序。运用该程序对同时受到荷载和均匀受火条件下的简单框架梁、柱可能破坏截面的极限承载力的变化及其相互影响进行计算、分析和讨论,据此提出钢筋混凝土框架在均匀受火时也要像抗震设计一样尽量满足"强柱弱梁"的要求,即"耐火强柱弱梁"的延性设计原则,为火灾抗倒塌设计提供参考。     

火灾下钢梁悬索效应分析研究

为了研究高温下钢梁的大变形性能．本文使用ABAQUS有限元程序建立了分析模型。通过与有关的试验结果对比，验证了有限元分析程序计算的准确性和可靠性。在利用程序进行大量参数分析，包括跨度、应力比、边界条件、温度分布等参数分析的基础上,发现梁的水平支撑对其抗火承载力有很大的影响。为了在实际设计中应用钢梁的悬索效应，本文导出了计算钢梁变形和悬索力的简化计算方法。     

A Numerical Study on the Thermo-mechanical Response of a Composite Beam Exposed to Fire

This study presents an analytical framework for estimating the thermo-mechanical behavior of a composite beam exposed to fire. The framework involves: a fire simulation from which the evolution of temperature on the structure surface is obtained; data transfer by an interface model, whereby the surface temperature is assigned to the finite element model of the structure for thermo-mechanical analysis; and nonlinear thermo-mechanical analysis for predicting the structural response under high temperatures. We use a plastic-damage model for calculating the response of concrete slabs, and propose a method to determine the stiffness degradation parameter of the plastic-damage model by a nonlinear regression of concrete cylinder test data. To validate simulation results, structural fire experiments have been performed on a real-scale steel–concrete composite beam using the fire load prescribed by ASTM E119 standard fire curve. The calculated evolution of deflection at the center of the beam shows good agreement with experimental results. The local test results as well as the effective plastic strain distribution and section rotation of the composite beam at elevated temperatures are also investigated.     

火灾中考虑整体性的钢梁破坏形态研究

1990年英国broadgate火灾之后,结构整体性以及由于温度而在整体结构中产生的附加应力得到了人们的重视。处于整体结构中的梁的破坏形态与单个构件的梁的破坏形态有较大差别,当考虑梁的悬链线效应时其抗火承载力明显提高。文章采用大型通用有限元程序ANSYS,对T.C.HLiu所做试验进行了验证,表明了有限元计算悬链线效应的可靠性,同时通过计算分析,提出了处于整体结构中钢梁在火灾中破坏的5个阶段,并给出了钢结构防火的概念设计建议。     

A round robin study on modelling the fire resistance of a loaded steel beam

This paper details a round robin study of the calculated response of structures in fire. In this instance, the study is based on one of two fire tests which were conducted on steel beams in a horizontal fire resistance furnace. The two specimens in the tests were identical having come from the same cast flow. The tests were conducted according to EN 1365-3 and the steel beams had a total length 5.4 m, spanning 5.2 m. These tests also formed a part of a testing round robin, reported elsewhere.The calculations were conducted by round robin participants in two stages. In the first instance a prediction of the response was made without knowledge of the measured temperatures of the steel beam and with only the grade of steel and details of the test setup. In the second instance the participants were also given the measured elastic limit of the steel, which differed significantly from the elastic limit implied by the grade, as well as measured temperatures from the steel beam and the plate thermometers from the furnace and asked to refine their model.Statistical analysis of the round robin results are presented to illustrate the variation which arises in the results of calculations. The results of the round robin study serve to illustrate the fire research and testing community's capability for modelling this simple case as well as the uncertainty in the calculation results. The results of the calculation round robin are also compared with the testing round robin to illustrate the comparative certainty between testing and calculations.     

Fire response of exterior reinforced concrete beam-column subassemblages

Investigating the structural response of reinforced concrete beam-column sub-assemblies at elevated temperatures is the purpose of this paper. This goal was achieved by conducting the ISO-834 standard fire test on two identical one-third scaled reinforced concrete beam-column subassemblage test specimens. The test specimens, which each consisted of one reinforced concrete cantilever beam anchored at the mid-height of a reinforced concrete column, were installed together in a full scale furnace and subjected to downward and upward service loads, respectively. The fire compartment fully engulfed the cantilever beams (except the beams’ top face and the loading points), the beam-column connections and the lower columns. The fire test terminated after 74 min as soon as the tensile longitudinal steel bars of the upward-loaded cantilever beam attained the predefined critical temperature 530 °C. The lower columns exhibited partial concrete spalling and typical diagonal cracks appeared at the beam-column connections. Based on the recorded internal temperature distributions at the joint cores it was found that the material strength loss in the fire had insignificant impact on the load bearing mechanism of the joints. On the other hand, the gradual decrease in rotation capacity of the beam ends during the fire course considerably influenced the load-deflection relationship. A detailed numerical work has been carried out to simulate the response of the test specimens and will be published elsewhere.     

蠕变模型对约束钢梁抗火性能分析的影响

钢材在高温和荷载作用下产生明显蠕变变形,影响火灾中结构的变形和受力性能。现有的蠕变模型较多,但没有一个广泛适用的蠕变模型。不同的蠕变模型对钢结构抗火分析结果有很大影响。为了量化蠕变模型对约束钢梁抗火性能分析的影响,对5种常用的蠕变模型进行了对比分析。采用编写的约束钢梁计算程序,分别计算5种蠕变模型下约束钢梁的抗火性能并与试验数据进行对比。结果表明,采用Norton蠕变模型的计算结果与试验数据吻合最好。最后对影响约束钢梁抗火性能参数进行了研究,研究发现,Harmathy蠕变模型对约束梁抗火性能分析结果影响最大;不同蠕变模型对不同荷载比、约束刚度下的约束钢梁抗火性能影响程度均不同。     

Behaviour of headed stud shear connectors for composite steel-concrete beams at elevated temperatures

The behaviour of composite steel-concrete beams at elevated temperatures is an important problem. A three-dimensional push test model is developed herein with a two-dimensional temperature distribution field based on the finite element method (FEM) and which may be applied to steel-concrete composite beams. The motivation for this paper is to increase the awareness of the structural engineering community to the concepts behind composite steel-concrete structural design for fire exposure. The behaviour of reinforced concrete slabs under fire conditions strongly depends on the interaction of the slabs with the surrounding elements which include the structural steel beam, steel reinforcing and shear connectors. This study was carried out to consider the effects of elevated temperatures on the behaviour of composite steel-concrete beams for both solid and profiled steel sheeting slabs. This investigation considers the load-slip relationship and ultimate load behaviour for push tests with a three-dimensional non-linear finite element program ABAQUS. As a result of elevated temperatures, the material properties change with temperature. The studies were compared with experimental tests under both ambient and elevated temperatures. Furthermore, for the elevated temperature study, the models were loaded progressively up to the ultimate load to illustrate the capability of the structure to withstand load during a fire. It is concluded that finite element analysis showed that the shear connector strength under fire exposure was very sensitive. It is also shown that profiled steel sheeting slabs exhibit greater fire resistance when compared with that of a solid slab as a function of their ambient temperature strength.     

Behaviour and design of restrained steel column in fire,Part 1: Fire test

This is the first of the three companion papers dealing with the restrained steel column behaviours in fire. This paper reports the results of two new fire tests on axially and rotationally restrained steel columns that have different axial restraint stiffness. Axial and rotational restraints were applied by a restraint beam. The external applied axial load was kept constant during the fire test. The increase and decrease in axial force in the restrained steel column was borne by the restraint beam. Test results included the temperature, the axial displacement and the lateral deflection of the test column. It was found that the axial restraint reduced the buckling temperature of a restrained column. The effects of axial restraint to the failure temperature depended on the load ratio and the axial restraint stiffness ratio. A Finite Element Method (FEM) model was built to simulate the fire test. The damping factor fitting for simulating behaviours of restrained steel column in fire was selected through parametric analysis. The validated FEM model was used to perform parametric studies on the behaviour of restrained steel column in Part 2, results of which were used to develop a practical design method for restrained steel column in fire in Part 3.