火灾后空间混凝土框架结构的受力性能模拟

为了分析火灾后空间混凝土框架结构损伤、修复和加固后的力学性能,基于纤维单元模型和分层壳单元模型,将梁、柱构件截面划分成多个纤维,将板沿截面厚度方向划分成多个层,可以考虑各个构件截面的不均匀温度场分布以及受火损伤或修复、加固后材料力学性能的变化。以ABAQUS通用有限元软件为开发平台,利用Python脚本语言对其进行二次开发,建立混凝土框架火灾受损分析系统(ASFCF)。进一步以一个多层多跨空间混凝土框架结构为例,利用该系统对框架在受火损伤、修复和加固后的力学反应进行了研究和对比分析。结果表明,ASFCF系统可以较为准确地进行火灾后空间混凝土框架的损伤、修复与加固后的力学性能分析。研究成果可作为评估混凝土整体框架结构火灾后的残余力学性能及修复、加固后的力学性能的理论参考。

火灾后混凝土结构损伤的属性识别

应用属性数学理论建立火灾后混凝土结构损伤程度评价的属性识别模型。选择影响火灾后混凝土质量的4个参数,如抗压强度损伤系数、抗渗透性损伤系数、爆裂损伤系数以及裂纹损伤系数等作为综合评判指标,通过构造属性测度函数以计算单指标属性测度和样本综合属性测度,应用置信度准则对火灾后混凝土样本的质量状况进行属性识别,从而建立了火灾后混凝土结构损伤程度综合评判的属性识别模型。在工程实例研究中,通过属性测度分析和计算,得到了火灾后混凝土样本损伤程度的评价结果,并分别与模糊综合评价和物元可拓评判法评价结果进行了比较,结果有较好的一致性。由于属性数学理论能很好地解决具有多个模糊属性问题的综合评价,且置信度准则是根据评价集具有有序性这一特点而提出的,因而可使评价结果更为可靠。

火灾损伤钢筋混凝土电化学再碱化技术的研究

混凝土电化学再碱化方法主要是应用电解和电渗原理，在直流电的作用下，使混凝土内钢筋周围产生OH^-．同时使Na^+等碱性阳离子渗入到混凝土内部，恢复钢筋周围的碱性环境，使钢筋从新钝化。通过对预制钢筋混凝土试件的再碱化试验，实现了再碱化法在火灾混凝土上的应用，提出了火灾损伤钢筋混凝土再碱化修复的关键参数值，为该项技术的推广应用奠定了基础。

某热处理车间局部火灾后鉴定与修复

通过对某热处理车间局部火灾的检测、鉴定与加固,对火灾后结构的安全性进行了评定,并对受损部位提出了相应的处理方案。本工程典型之处在于火灾发生部位既有混凝土构件,也有钢结构构件,可供同行业人士参考。

高温下型钢混凝土构件粘结性能研究

型钢混凝土柱在很多国家得到普遍使用,本文从目前型钢混凝土国内外研究现状出发,通过对国内外研究学者的研究成果进行分析,指出当前型钢混凝土粘结性能研究存在的不足,进一步对型钢混凝土粘结性能的热点问题做了研究。通过11个型钢混凝土柱试验(包括3个未加热试件和8个在ISO835标准火灾中加热90min或180min试件),研究了火灾下型钢混凝土的剩余粘结性能。

高温后静置混凝土抗压强度的人工神经网络预报

根据本文的试验结果,应用人工神经网络(ANN)方法对火灾高温静置后的混凝土抗压强度进行了预报,预报值与试验值吻合良好.探讨了火灾温度、火灾后静置时间及冷却和养护方式对火灾后混凝土抗压强度的影响.此外,利用该网络模型分析了火灾下混凝土的抗火性能.

碳纤维加固钢筋混凝土梁的应用研究

利用CFRP对混凝土结构进行修复加固及补强,是近几年发展较快的一项新型高效的技术。该项技术在建筑物、桥梁特种结构物等各类土木工程中均有大量成功应用的实例。本文以钢筋混凝土梁为研究对象,列举了碳纤维对既有结构的钢筋混凝土梁分别进行抗弯加固及抗剪加固的实例,并通过试验探讨了碳纤维加固火灾后受损钢筋混凝土梁的加固效果,所得结论对类似工程具有一定的参考价值。

火灾损伤钢筋混凝土电化学再碱化技术的研究

混凝土电化学再碱化方法主要是应用电解和电渗原理,在直流电的作用下,使混凝土内钢筋周围产生OH-,同时使Na+等碱性阳离子渗入到混凝土内部,恢复钢筋周围的碱性环境,使钢筋重新钝化。通过对预制钢筋混凝土试件的再碱化试验,实现了再碱化法在火灾混凝土中的应用,提出了火灾损伤钢筋混凝土再碱化修复的关键参数值,为该项技术的推广应用奠定了基础。

Unified strength model based on the Hoek-Brown failure criterion for fibre-reinforced polymer-confined pre-damaged concrete columns with circular and square cross sections

Fibre-reinforced polymer(FRP)has the advantages of high strength,light weight,corrosion resistance and convenient construction and is widely used in repairing and strengthening damaged concrete columns.Most of the existing strength models were built by regression analysis of experimental data;however,in this article,a new unified strength model is proposed using the Hoek-Brown failure criterion.To study the strength of FRP-confined damaged and undamaged concrete columns,900 test data were collected from the published literature and a large database that contains the cross-sectional shape of each specimen,the damage type,the damage level and the FRP-confined stiffness was established.A new strength model using the Hoek-Brown failure criterion was established and is suitable for both circular and square columns that are undamaged,load-damaged and fire-damaged.Based on the database,most of the existing strength models from the published literature and the model proposed in this paper were evaluated.The evaluation shows that the proposed model can predict the compressive strength for FRP-confined pre-damaged and undamaged concrete columns with good accuracy.

Stress redistribution of simply supported reinforced concrete beams under fire conditions

This study presents experimental and numerical investigations of simply supported steel reinforced concrete(RC)beams under fire.The temperature field of cross sections,the vertical deflection at mid-span,and specifically the axial expansion displacement at beam-ends were measured during the fire tests.A novel finite element(FE)model of a RC beam under fire was developed,in which the water loss in the heat transfer analysis and the concrete transient strain in the mechanical analysis were considered.Based on the validated FE model proposed in this study,parametric studies were conducted to investigate the effects of the beam type,the protective layer thickness,and the load ratio on the thermal and mechanical behavior of simply supported RC beams.It was found that greater fire resistance and fire performance of girder beams in comparison to secondary beams contributed to the non-structural reinforcements,which effectively compensated for the reduced tensile capacities of structural reinforcements because of the degradation of the material properties.In addition,the history of normal stress distributions of concrete under fire can be divided into three phases:expansion,stress redistribution and plateau phases.

Post-fire cyclic behavior of reinforced concrete shear walls

The effects of fire exposure,reinforcement ratio and the presence of axial load under fire on the seismic behavior of reinforced concrete(RC) shear walls were investigated.Five RC shear walls were tested under low cyclic loading.Prior to the cyclic test,three specimens were exposed to fire and two of them were also subjected to a constant axial load.Test results indicate that the ultimate load of the specimen with lower reinforcement ratio is reduced by 15.8%after exposure to elevated temperatures.While the reductions in the energy dissipation and initial stiffness are 59.2%and 51.8%,respectively,which are much higher than those in the ultimate load.However,this deterioration can be slowed down by properly increasing reinforcement due to the strength and stiffness recovery of steel bars after cooling.In addition,the combined action of elevated temperatures and axial load results in more energy dissipation than the action of fire exposure alone.

Fire's effect on chloride ingress related durability of concrete structure

This paper describes the effects of fire on durability of reinforced concrete structures, and points out that fire not only damages the chemical composition and physical structure of concrete by high temperature, but also leads to an additional risk due to the generation of polyvinyl chloride (PVC) combustion gases. A mathematical model is proposed to calculate chloride ingress profiles in fire damaged concrete, so as to explore the service life prediction of the structure. Rapid Chloride Migration (RCM) test was carried out to determine the chloride diffusion coefficients for the application of the mathematical model. Finally, the detected results of a reported case testified to the validity of the mathematical model.

Post-fire Behavior of Ordinary Concrete Reinforced with Short Steel Fibers

Concrete is a widely used material in civil construction and may be submitted to high working temperatures under various circumstances. Many factors influence the behavior of this material at high temperatures, which usually leads to the evaporation of the hydrated cement. The dehydrated cement undergoes a contraction, simultaneously with the thermal expansion of the inert fraction of the material. As a consequence of these conflicting expansions and contractions, the material cracks and its strength and modulus of elasticity decrease significantly. On the other hand, the addition of short metallic fibers to the material increases its toughness, probably due to its action on the cracking behavior of the composite. It is thus expected that a concrete containing metallic fibers should maintain its original properties even after exposure to elevated temperatures. This paper presents an evaluation of the influence of steel fibers on the microstructure and toughness of concretes submitted to high tenaperatures. The bending behavior, under strain rate control, of concretes with a strength of 30 MPa and containing short steel fibers, submitted to a previous treatment at 500 ℃, was analyzed. It was observed that, after both heat treatments, the addition of metallic fibers to concrete was able to maintain the pseudo-ductility and load-carrying capacity of this composite material.