碳纤维布加固钢筋混凝土梁受力性能

随着国民经济的发展,交通运输任务量大幅度增长,行车密度及车辆载重越来越大,对桥梁的承载能力要求越来越高。而现有在役桥梁中,部分桥梁(特别是八十年代以前修建的桥梁)由于当初设计标准低,或结构陈旧老化,致使承载能力降低,已不能满足交通发展的需要,严重危及桥梁正常运行。此外,80年代后修建的桥梁由于设计或施工质量原因,亦有一部分桥梁出现不同程度的病害和损伤。因此,我国需加固改造的旧有桥梁的数量很大,任务繁重。在这种工程背景下,研究人员和工程师亟需研究开发一种快速、简捷、安全、可靠、经济、适用的旧有结构物加固改造方法。碳纤维材料作为一种新型复合材料,以其抗拉强度高、质量轻、耐腐性好、施工方便等优点,受到广大工程界人士的青睐。本文从2002年开始,对CFRP布加固钢筋混凝土梁的受力性能进行了较系统的试验研究和理论分析,共进行了16片抗弯梁、5片锚固梁、3片疲劳试验梁及3个温度试件的试验研究,研究内容包括CFRP布加固钢筋混凝土梁抗弯性能分析、刚度分析、附加锚固分析、温度应力分析及低温疲劳性能分析等。 本文通过碳纤维布加固钢筋混凝土梁与未加固梁的抗弯试验,分析了碳纤维布对加固梁的抗弯承载力、刚度、裂缝分布及钢筋应变等的影响;验证了CFRP布加固钢筋混凝土梁平面变形假设仍然成立;探讨了混凝土标号、碳纤维层数、配筋率等参数对加固效果的影响;根据非线性有限元原理采用分层法编制了碳纤维布加固钢筋混凝土梁极限承载力计算机仿真程序,并应用此程序对试验梁进行了仿真分析,在此基础上重点研究了碳纤维极限拉应变折减系数;对碳纤维布加固钢筋混凝土梁的极限破坏状态进行了分析,叙述了各种破坏状态下极限承载力的实用计算方法;采用《桥规》规定的材料强度取值,应用简化公式对试验梁及其他作者的试验梁进行计算,探讨了简化公式的安全储备。 本文在试验梁结果基础上,分析了碳纤维布加固钢筋混凝土梁截面刚度变化规律;参照结构设计原理中的钢筋混凝土梁刚度计算方法,考虑碳纤维布的约束作用,推导了使用阶段在短期荷载效应组合作用下加固梁刚度Bs的计算公式,并与试验值及其它计算方法进行了对比分析;利用分层法,编制了计算钢筋屈服至梁破坏阶段挠度计算的计算机仿真程序,并将程序计算结果与试验结果进行了对比分析。 本文分析了碳纤维布加固钢筋混凝土梁产生剥离的原因,并通过5片锚固梁的试验,分析了梁的破坏形态,探讨了U型箍条宽、间距等因素对碳纤维布加固梁抗剥离效果的影响。 本文通过3个温度试件的试验,分析了碳纤维布加固混凝土梁温度应力的变化规律;根据变形协调原理,推导了碳纤维布加固混凝土构件温度应力的解析解,并采用ANSYS软件对碳纤维布加固混凝土构件的温度应力进行了仿真分析。 本文利用低温自然环境,采用偏心起振机对试验梁施加疲劳荷载,通过低温疲劳试验分析了碳纤维布加固钢筋混凝土梁的低温疲劳性能。 最后,对论文的研究成果进行总结,指出本文的创新点及值得进一步研究的问题。
工业羊毛毡
With development of national economy and fast increase of traffic flow, running vehicle density and vehicle load capacity are becoming higher and higher, requiring higher bearing capacity of bridges. Among existing bridges, part of them can no longer meet the demand for traffic development due to inferior design in the past years or old and aged structures, endangering normal operation of the bridges. In addition, diseases and damages took place to some bridges built in the 80s due to inferior design or construction quality. Therefore, we have a lot of existing bridges that need to be reinforced or transformed in our country. This is a heavy task. In such engineering background, it is urgent for researchers and engineers to develop a fast, simple, safe, reliable, low-cost, and applicable method for reinforcing and transforming old structures. As a new-type compound material, carbon fiber polymer material has become a favorite of all people in the engineering circle due to its advantages in high tensile strength, light weight, good anti-corrosion performance, and simplicity in construction. We began systematic test study and theoretical analysis on performances of CFRP reinforced concrete beam against stresses by this paper from 2002. We carried out tests and study on 16 bending beams, 5 anchoring beam, 3 fatigue test beams, and 3 temperature test pieces. The scope of our study covers analysis on stress performances, rigidity, attached anchorage, temperature strain, and low- temperature fatigue performances of CFRP reinforced bending beam.Through bending tests on reinforced beam and unreinforced beam by this paper, the influences of carbon fiber reinforcement on bending bearing capacity, rigidity, crack distribution, and steel bar strain of the beams are analyzed. It is proved that the assumption of plane deformation of CFRP strengthened reinforced concrete beam is tenable. The influences of concrete grade number, number of layers of carbon fiber, ratio of reinforcement and other parameters on effect of reinforcement are studied. A computer simulation program has been worked out to calculate the ultimate bearing capacity of carbon fiber reinforced beam by hierarchical method on basis of non-linear finite element principle. The program is used to carry out simulation analysis on the test beams. On such basis, focus is put on study of ultimate tensile strain reduction coefficient of carbon fiber polymer. Analysis is made on the ultimate failure state of carbon fiber polymer reinforced beam. Practical calculation methods for the ultimate bearing capacity under various failure states are described. The specified strength values of materials by the "Codes of Bridge" are adopted to make calculation with simplified formula for our test beams and other authors’ test beams. The safety reserves of the simplified formula are discussed.Based on the result of test beams, the law of change of rigidity of carbon fiber polymer reinforced beam cross-section is analyzed. In reference to the calculation method for rigidity of steel reinforced concrete beam in conformity to the structure design principles and taking intoconsideration of the constraint function of carbon fiber polymer, a formula for calculating the rigidity of reinforced beam Bs under combination of short-term load effect during service period is derived, and comparison and analysis are made to the test values and results of other calculation methods. A computer simulation program has been worked out to calculate the deflection of the beam from yield state of steel bars to failure state of the beam. Comparison and analysis are made on the results of calculation by the program and test results.Reasons for spalling of carbon fiber polymer reinforced beams are analyzed by this paper. Through tests on 5 anchoring beams, the forms of failure of the beams are analyzed, and influences of the width and spacing of U-shape strain strakes on the anti-spalling effect of carbon fiber polymer reinforced concrete beam are analyzed.Through tests on three groups of temperature test pieces, the law of change of temperature strain of carbon fiber polymer reinforced concrete beam is analyzed. Based on the principle of compatibility of deformation, analytic solution for the temperature strain of carbon fiber reinforced concrete structural members is derived. Also Ansys software is used to make simulation analysis on temperature strain of carbon fiber polymer reinforced concrete structural members.Under natural low-temperature environment and with fatigue load applied to the test beams by eccentric vibrator, the low-temperature fatigue performances of carbon fiber polymer reinforced concrete beams are analyzed through low-temperature fatigue tests.At last, summary is made on the results of research by this paper, highlighting the innovative points of this paper and problems that are worth further studying.