《地震载荷下钢结构焊接接头断裂行为的研究及评估》由会员分享，可在线阅读，更多相关《地震载荷下钢结构焊接接头断裂行为的研究及评估（84页珍藏版）》请在金锄头文库上搜索。
1、天津大学硕士学位论文地震载荷下钢结构焊接接头断裂行为的研究及评估姓名：卢庆华申请学位级别：硕士专业：材料加工工程指导教师：张玉凤20031201摘 要钢结构重量轻、抗震性能好，在工业生产领域和高层建筑中得到广泛的应用。但近几次大地震中，许多抗弯钢结构的梁柱焊接节点并未像设计时所预期的那样发挥良好的延性性能，而是出现了脆性破坏，可以看出有一个潜在的危险胜没有考虑。同时，在强烈地震条件下，钢结构将承受剧烈的冲击。钢材对冲击载荷很敏感，它容易受强烈冲击而损伤，从而导致钢结构的强度和承载能力下降。有鉴于此，本文主要模拟地震载荷，对钢结构焊接接头在预应变及动载下的断裂行为等问题进行了一系列的研究。以常用
2、建筑结构钢Q345和Q235B为研究对象，通过不同温度下的夏比冲击试验研究预应变对母材和焊缝冲击性能的影响。结果表明：材料在预应变下无论是母材还是焊缝夏比冲击韧度均有所降低，韧一脆转变温度有所提高。Q345母材和焊缝5预应变后的韧一脆转变温度均低于OV，10预应变后低于室温，因此都可在室温下安全使用；而Q235B钢，除5预应变后的焊缝的韧一脆转变温度较低外，其它经过预应变后的韧一脆转变温均高于室温。为建立客观的材料韧度指标和进行更有效的安全分析时，预应变应作为一个考虑因素。测试了Q345和Q235B母材与焊缝在无预应变与10预应变下的力学性能，得出随着预应变增加，材料的屈服强度与抗拉强度均有所
3、提高的结论。同时，验证了按公式推导出的预应变与屈服强度的关系与试验结果吻合，并进一步推导出在5预应变下材料的力学性能。测试了Q345和Q235B两种材料的母材与焊缝在5预应变和10预应变静态下的CTOD值，研究预应变对CTOD断裂韧度的影响。对Q345和Q235B在地震载荷作用下的动态断裂韧度与静态断裂韧度进行比较分析。计算不同加载速率下焊缝和母材的CTOD。结果表明，常温下动载对Q345钢焊缝和母材的断裂韧度有利，而对Q235B则产生不利影响。最后，介绍了两种目前最新的危险评估方法，这两种危险评估方法可以使工程技术人员对结构的脆性断裂危险性进行有效的评估，对已遭破坏的结构决定修补措施，从而使
4、危险降至最低程度。并运用该方法对不同预应变下的Q345和Q235B进行评估。可以看出加工制造与检测环节对结构的安全性影响很大；当材料已经有了大的应力应变，则温度对危险性的影响甚微。建议：对于需要考虑抗震能力的钢结构的重要部件建议采用Q345钢制造。关键词：预应变；冲击韧度；力学性能；动态CTOD；危险评估方法ABSTRACTBecause of its light weight and good earthquake resistant performance，the steelstructure is widely used in the industrial fields and hi业r
5、ise buildingsBut in recentgreat earthquakes，it is brittle fractures not the ductile fractures as expected whendesigned that happened in the welded beam-to-column connections in many steelmoment frames，It Can be seen that a potential risk factor has not been considered，Inintensive earthquake，the stee
6、l structure will undertake a severe impact which the steelis very sensitive toUnder the strenuous impact，the structure will be damaged easilyIt will lead to the falling ofthe strengths and the bearing capacity ofthe structureSo，the main purpose of this paper is to aim the fracture behavior under pre
7、strainand dynamic load of the connections to perform extensive researchThe effects of prestrain on the impact toughness of base metal and weld metal ofstructural steels Q345 and Q235B were investigated experimentally by use of theCharpy notch impact test at different testing temperaturesThe results
8、of the testsshow that：the impact toughness of both base metal and weld metal decreases withdecreasing temperature and the ductilebrittle transition temperature of the two kindsof material increases a little under prestrain111e ranges of ductilebrittle transitiontemperature of the base metal and weld
9、 metal of Q345 steel under 5and 10prestrain arelowerthan0C andthe roomtemperature(20。C)respectively,atwhichit Can be used safelyThe ductilebridle transition temperature of Q235B steel underprestrain is higher than 20except that of the weld metal under 5prestralnTheconclude Call be drawn that the pre
10、straining effect should be considered whenestablish an objective toughness standard and carry out more effective safety mmlysis，The mechanical property tests of the base metal and weld metal on structuralsteels(Q345 and Q235B steel)are carried out under nO prestrain and 10prestrainThe results show t
11、hat：both the yield strength and tensile strength increase underprestrainThe formula derivation result of the relationship between prestrain and theyield strength is consistent with the testSo，we deduce the mechanical property under5prestrainThe value of CTOD of the base metal and weld metaI of the t
12、wo steel under 5prestrain and 10prestrain have been gottenAnd the effect of prestrain on theCTOD has been investigatedThe dynamic and static toughness of welds and base metal of Q345 and Q235Bsteel have been compared and analysedFrom the result of CTOD under difierentIIloading rate，it can be conclud
13、ed that the dynamic loading is beneficial to the Q345steel but disadvantage to the Q235B steelAt last，this paper provides two stateof-theart Risk Assessment Procedures(RAPs)They are designed to enable all engineer to assess qualitatively the risk ofbrittle fractureThe procedures call also be used to
14、 determine measures to be used in arepair situation to reduce future risks to an acceptable levelThe material of Q345 andQ235B under different prestrain has been assessed by using the two Risk AssessmentProceduresIt Can be shown that the effect of fabrication and testing is great Butwhen the materia
15、l has sustained high stressstrain，the temperature has almost noimpact on riskIt can be suggested that the important components of steel structure should benlade in Q345 steelKey words：prestrain；impact toughness；mechanical property；dynamic CTOD；Risk Assessment ProceduresIII独创性声明本人声明所呈交的学位论文是本人在导师指导下进
16、行的研究工作和取得的研究成果，除了文中特别加以标注和致谢之处外，论文中不包含其他人已经发表或撰写过的研究成果，也不包含为获得鑫盗盘堂或其他教育机构的学位或证书而使用过的材料。与我一同工作的同志对本研究所做的任何贡献均已在论文中作了明确的说明并表示了谢意。学位论文作者签名： 产灰牛 签字日期：乒3年，毒月；。日学位论文版权使用授权书本学位论文作者完全了解盘注盘茎有关保留、使用学位论文的规定。特授权墨盗盘鲎可以将学位论文的全部或部分内容编入有关数据库进行检索，并采用影印、缩印或扫描等复制手段保存、汇编以供查阅和借阅。同意学校向国家有关部门或机构送交论文的复印件和磁盘。(保密的学位论文在解密后适用本授权说明)学位论文作者签名：于走等 导师签名：各宅危1祝签字日期：h)3年文月3。曰 签字日期：堋年l卫月)u日第一章绪论1,1引言第一章绪论地震是一种危害性极大的自然灾害，堪称群灾之首，具有突发性、难以预测性、范围广、破坏性大等特点，由地震产生的
