碳纤维布加固钢筋混凝土板的耐火极限分析

编制了碳纤维布加固钢筋混凝土板的高温全过程分析程序,程序的有效性得到了试验结果的初步验证。针对不同构件尺寸、防火涂料厚度、受拉纵筋配筋率、碳纤维布加固量、混凝土保护层厚度、荷载比等共计6400种工况,进行了碳纤维布加固钢筋混凝土板的高温反应分析,考察了各主要参数对该类加固构件耐火极限的影响规律。在此基础上,建立了该类加固构件耐火极限的实用计算方法。研究结果表明：高温下碳纤维布加固钢筋混凝土板的耐火极限随板的厚度、防火涂料厚度和混凝土保护层厚度的增加逐渐增大,而随碳纤维布加固量和荷载比的增加逐渐减小;其中荷载比的影响最为显著,受拉纵筋配筋率对该类加固构件的耐火极限影响较小。     

碳纤维布抗弯加固钢筋混凝土梁的耐火极限分析

编制了碳纤维布抗弯加固钢筋混凝土梁的温度场计算程序和耐火极限分析程序,通过数值分析结果与试验结果的对比,初步验证了程序的有效性。利用上述程序,针对高温下加固梁的受弯破坏形态,就不同构件跨高比、防火涂料厚度、受拉纵筋配筋率、碳纤维布加固量、混凝土保护层厚度、荷载比等共计1728种工况进行了大量计算分析,同时考察了各参数对加固梁耐火极限的影响规律。在此基础上,建立了加固梁的耐火极限简化预测方法。研究结果表明,加固梁的耐火极限随防火涂料厚度、混凝土保护层厚度和受拉纵筋配筋率的增加而逐渐增大,同时随荷载比、碳纤维布加固量和跨高比的增加而逐渐减小,其中荷载比的影响最为显著。     

浅谈提高钢筋混凝土构件的耐火极限

阐述了钢筋混凝土结构倒塌破坏的主要原因，对钢筋、混凝土及钢筋混凝土构件等相关建筑材料及构件的耐火性能作了分析，提出了提高钢筋混凝土构件耐火极限应采取的措施。     

承重构件的耐火极限与荷载的关系

本文认为，承重构件试验中所加荷载越大，构件的耐火极限越小。为保证构件在火灾中安全可靠而不倒塌，建议《建筑构件耐火试验方法》第３．３．１条工作荷载应不小于设计荷载的７０％。     

钢筋混凝土梁式简支构件耐火极限计算

通过耐火试验破坏过程分析，本文认为，影响钢筋混凝土单向受弯构件耐火极限的主要因素是钢筋混凝的应力系数（σ/σs），钢筋保护层厚度和截面高度，并由33组试验结果回归得到计算公式，平均相对误差为4.9%。     

混凝土砌体构件的耐火极限

前言 混凝土砌体为不燃体,具有持久的耐火性能,同时又施工经济,因此被广泛地指定为防火墙和防火屏障的构件. 在《国际建筑规范》(IBC)[2]～[3]第7章中,对结构性耐火和隔火的材料及构件有具体规定.本TEK文件是在《混凝土和混凝土砌体构件耐火性能的评定》ACI216.1/TMS-021 6[1](以下简称《标准》)规定基础上,介绍混凝土砌体构件耐火极限的计算过程.     

建筑构件的耐火极限试验

简单介绍了建筑构件的定义及其耐火极限的判定条件,分别阐述了建筑构件耐火试验的具体过程及操作要点,并指出了影响耐火极限的因素及提高构件耐火极限的具体措施,以指导实践。     

建筑构件的耐火极限

目前,作为指导我国建筑防火设计的两本主要规范是《建筑设计防火规范》(GBJ 16-87)(简称建规)和《高层建筑设计防火规范》(GB 50045-95)(简称高规),这两本规范在执行过程中也经过数次的修订,以适应并满足不断发现的问题与市场发展的需求。但无论是《建规》还是《高规》对建筑物的耐火等级及建筑构件耐火极限的要求一直以来并未有过多的变化,它是一种按火灾统计而形成的一种预测式的要求,也即根据大多数火灾持续时间在1h到2h之间这样一个概念并按照构件在建筑中所起的作用而确定的。     

碳纤维布加固钢筋混凝土板的耐火性能试验研究

在ISO834标准升温条件下,进行3块设置不同防火材料的碳纤维布加固钢筋混凝土板,以及1块未加固板的耐火性能对比试验。分析不同防火措施对高温下碳纤维布加固钢筋混凝土板的破坏形态、跨中挠度及耐火极限的影响。试验结果表明:(1)只要采取适当的防火措施,在使用荷载明显增大的情况下,碳纤维布加固钢筋混凝土板仍具有与未加固板大体相当甚至更长的耐火极限;(2)与薄型防火涂料相比,水泥砂浆的防火保护效果相对较弱;(3)厚度5 mm的薄型防火涂料的防火效果相对较好。为确保实际工程中碳纤维布加固钢筋混凝土板具有足够的耐火能力,科学合理地选择防火材料及其厚度是十分重要的。     

具有端部约束的碳纤维布加固混凝土梁耐火性能试验研究

在ISO834标准升温条件下,开展了具有端部约束的7根碳纤维布加固混凝土梁和1根未加固混凝土梁的耐火性能试验,考察了梁端轴向和转动约束、防火涂料厚度、荷载比等参数对约束梁高温变形及内力的影响。试验结果表明:约束梁的轴向变形最大值随轴向约束刚度比和防火涂料厚度增大而减小,附加轴力最大值随轴向约束刚度比增加或防火涂料厚度减小而增大,梁端附加弯矩最大值随防火涂料厚度减小而增大,但防火涂料厚度在10~20mm范围内变化时影响幅度有限;降温后约束梁的附加轴力仅少量恢复,梁端附加弯矩却较大幅度回落;与非加固梁相比,加固梁的梁端附加弯矩最大值不仅数值更小,而且出现时刻明显偏晚。     

Experimental study on fire protection methods of reinforced concrete beams strengthened with carbon fiber reinforced polymer

In this paper, two reinforced concrete (RC) beams strengthened with carbon fiber reinforced polymer (CFRP) and attached with thick-painted fire resistant coating were tested for fire resistance following the standard fire testing procedures. The experimental results show that the specimen pasted with the insulated layer of 50 mm in thickness could resist fire for 2.5 h. It is also demonstrated that the steel wire mesh embedded in the insulated layer can effectively prevent it from cracking and eroding under firing. __________ Translated from Journal of Tongji University (Natural Sciences), 2006, 34(11): 1452–1456 [译自: 同济大学学报 (自然科学版)]     

碳纤维布加固混凝土轴心受压柱的试验研究

进行了8根碳纤维布加固混凝土柱的轴心受压试验研究,着重探讨了不同转角曲率半径、混凝土开裂程度等因素对加固效果的影响。试验结果表明,《碳纤维片材加固混凝土结构技术规程》中“转角处的曲率半径不小于20mm”的规定是合理的,转角处的曲率半径并不是越大越好,一般在20-50mm为宜。混凝土出现少量裂缝时,进行及时加固,其极限承载力仍有较大的提高。     

预应力碳纤维板加固钢筋混凝土梁的受弯性能

为研究预应力碳纤维板加固钢筋混凝土梁的受弯性能,进行3根碳纤维板加固钢筋混凝土梁和1根对比梁的试验研究。研究预应力以及梁底锚固方式对混凝土梁的受弯承载力、刚度、裂缝发展情况、碳纤维板利用率的影响。试验结果表明:预应力碳纤维板加固可明显提高试件的受弯承载力,提高碳纤维板的利用率,减小裂缝宽度,其延性有所下降,在加固构件设计时需特别关注;两种锚固方式均满足正常使用要求,综合考虑无需开槽的MJ-2锚具适用性更强。     

Failure modes of reinforced concrete beams strengthened with carbon fiber sheet in fire

It is shown that elevated temperature may cause a change in the failure mode of reinforced concrete (RC) beams strengthened with carbon fiber sheet (CFS), as flexural failure at room temperature can be transformed into shear failure in fire. In this paper, an analysis procedure for flexural capacity and shear capacity of RC beams strengthened in flexure using CFS at high temperature is discussed and validated by test results from literatures. A parametric study is conducted for the critical situation (i.e., flexural failure and shear failure occur simultaneously in fire) of the strengthened beams with fire insulation. The influences of some parameters, such as span-to-height ratio, confinement ratio, rich degree of shear capacity, thickness of concrete cover, thickness of fire insulation, and strengthening ratio, on the tensile reinforcement ratio related to the critical situation are examined. Based on the aforementioned analysis procedure and extensive numerical results, recommendations for fire-safety design of the flexurally strengthened and insulated beams are discussed preliminarily. It is important to recognize that increasing of the thickness of fire insulation is not always good for the fire performance of the strengthened beams. To account for the adverse influence of concrete shear cracks on shear capacity of the strengthened beams exposed to fire, an additional reduction factor may be considered for the shear resistance of steel stirrups at high temperature.     

纤维增强复合材料加固钢筋混凝土单向板受弯性能研究

通过纤维增强复合材料（FRP）布加固钢筋混凝土单向板的受弯性能试验,研究了FRP布种类、层数、宽度、粘贴方式和锚固措施等因素对加固效果的影响。结果表明：在板底粘贴CFRP布和高强GFRP布均可明显提高钢筋混凝土单向板的受弯承载力和纵筋屈服后刚度。当采用横向粘贴1层U形CFRP布条作为端部锚固措施时,所有加固单向板试件的破坏模式均为跨中弯曲裂缝引起的剥离破坏。当FRP布宽度和层数相同时,采用CFRP布加固效果优于高强GFRP布加固。与对比试件相比,FRP布加固钢筋混凝土单向板试件的位移延性略有降低。高强GFRP布加固钢筋混凝土单向板的位移延性优于CFRP布加固钢筋混凝土单向板。FRP布的粘贴方式对FRP加固钢筋混凝土单向板的位移延性也有影响,单层FRP布加固单向板试件的延性较好。通过对试验结果的分析,提出了FRP布加固钢筋混凝土单向板构件受弯破坏模式的判别方法,验证了已有文献和GB 50608-2010《纤维增强复合材料建设工程应用技术规范》中给出的跨中弯曲裂缝引起的FRP剥离应变计算公式对FRP布加固混凝土单向板的适用性,建立了FRP布加固钢筋混凝土单向板受弯承载力计算方法。     

碳纤维布加固钢筋混凝土梁试验研究

共进行了6根碳纤维布加固钢筋混凝土梁和1根未加固梁的正截面承载力对比试验,研究了碳纤维布加固钢筋混凝土梁的破坏机理、应变分布情况、承载力、刚度和延性,分析了碳纤维布的粘贴层数、粘贴锚固方式、二次受力对加固效果的影响,并进行了试验梁的正截面承载力理论计算,与试验结果比较一致,验证了现行规范所提供的计算理论和构造措施的合理性。     

基于可靠度的FRP加固混凝土结构设计方法研究

为进一步完善FRP加固混凝土结构的设计方法,通过对新颁布的《纤维增强复合材料工程应用技术规范》GB50608中各类FRP加固混凝土结构在不同破坏模式下的设计方法进行可靠度校核,明确现阶段设计方法所能达到的可靠度水平,并探讨规范中FRP材料分项系数的作用。在此基础上,通过引入附加抗力系数γβ修正荷载-抗力分项系数表达式,并在可靠度分析的基础上确定附加抗力系数取值。计算结果表明,附加抗力系数可较好地调整不同类型加固构件的可靠度,使加固构件满足目标可靠度的要求,且可靠度指标具有较好的一致性。     

Post‐earthquake fire resistance of CFRP strengthened reinforced concrete structures

Post‐earthquake fire (PEF) presents a high risk to buildings that have been partially damaged in a prior earthquake, particularly in urban areas. As most standards and criteria ignore the possibility of fire after earthquake, buildings are not adequately designed for that possibility, and thus, PEF is a high‐risk load needed to be scrutinized further, codified and become part of a routine design. An investigation based on sequential analysis inspired by FEMA356 is performed here on two RC frames, of three and five stories, at the Life Safety performance level and designed to the ACI 318‐08 code, after they have been subjected to a spectral peak ground acceleration of 0.35 g. A fire analysis of the weakened structures follows, from which the time it takes for the damaged structures to collapse is determined. As a point of reference, the fire resistance is also determined for undamaged structures and before the occurrence of earthquake. The results show that structures previously damaged by the earthquake and exposed to PEF are considerably more vulnerable than those that have not been damaged previously. A method using carbon fiber‐reinforced polymer as a means of relocation of plastic hinges away from the column faces towards the beams is introduced as a function of the time required for fire extinguishment or evacuation. This is carried out to increase the structural load‐carrying capacity, thus reducing the potential damage for the anticipated earthquake and thereby improve the PEF resistance. The results show a considerable improvement in the PEF resistance of the frames. While the investigation and the proposition relate to a certain class of structures (ordinary buildings, intermediate RC structures, three and five stories) and the results can therefore be applied only to the cases investigated, it is hoped that this study paves the way for further research into this very important phenomenon and leads to an eventual revision of codes. Copyright © 2013 John Wiley & Sons, Ltd.     

火灾后钢筋混凝土构件材料性能检测的探讨

火灾后的现场检测要根据火灾构件的温度场分布规律和损伤规律,采取符合实际的采样方法,才能准确判断构件的材料性能.本文提出火灾后钢筋混凝土构件材料性能检测方法和注意事项.