【作者】 魏华；

【导师】 吴智敏；

【作者基本信息】 大连理工大学 ， 结构工程， 2009， 博士

【摘要】 纤维增强复合材料(FRP)由于其优越性能在混凝土结构补强和加固中得以广泛应用,其中一个主要的应用是对混凝土柱整体缠绕碳纤维布(CFRP)以增强其强度和延性。然而实际工程中,混凝土由于冻害,老化,施工质量等原因易产生混凝土的劣化,结构的局部强度产生削弱,给结构的安全性和耐久性留下隐患。针对结构局部强度不足的现象,若进行整体加固势必产生人力物力财力的浪费,而关于局部补强加固的研究一直没引起各类专家的关注,相关的规范标准还没有形成。本文针对FRP对混凝土结构中部分强度不足的区域进行局部补强加固试验和理论研究,分析和掌握受FRP约束的含有局部强度缺陷的混凝土柱,在轴心荷载和偏心荷载作用下的力学性能,探讨FRP进行局部补强加固的可行性和可靠性,以期进一步扩大FRP的应用范围,为局部强度不足的混凝土受压构件加固提供科学合理的理论依据。本文针对含有强度削弱区域的素混凝土和钢筋混凝土,使用碳纤维布进行局部加固后,进行了轴心和偏心荷载作用下其力学性能的试验,并根据试验结果及众多学者的分析结果提出了轴压和偏压状态下的承载力计算方法,提出了局部加固碳纤维布加固量的确定方法及步骤。主要的研究内容如下:(1)对15根含有局部强度不足的素混凝土方柱进行轴心受压试验,观测了不同纤维布约束下,局部强度不足区域的混凝土受力性能,考察了局部加固对混凝土强度和延性的改善程度,评估整个试验柱极限承载力的提高效果是否达到预期的加固效果。试验结果表明:仅在局部强度不足的区域缠绕不同含量的碳纤维布同样可以提高该薄弱区域的强度和延性,从而达到增强整柱承载力的目的。根据碳纤维布加固量的不同,试验柱表现出的破坏方式不同,碳纤维布不能提供充足约束时,试验柱表现出薄弱区域混凝土被压碎;碳纤维布能提供充足的侧向约束力,受约束混凝土处于强约束状态时,破坏表现为未削弱区域混凝土被压碎,表明使用局部加固达到预期的加固效果。同时验证对局部强度不足的带有强度缺陷的混凝土,使用碳纤维布进行局部加固是一种行之有效的方法。(2)在轴心荷载作用下,对5根含有薄弱区段的钢筋混凝土方柱进行碳纤维布局部加固的受压试验,分析了碳纤维布含量对加固效果的影响。结果表明:由于碳纤维布有效地约束了薄弱段混凝土的横向变形,使其处于三向受压状态,延缓了混凝土裂缝的开展,使纵向钢筋的塑性变形得到充分发挥,提高了受约束混凝土的极限抗压强度,从而提高整柱的承载力。试验构件的承载力随纤维布加固量的增加而增加,但其承载力增长大幅度却随着碳纤维布加固量的增加而减慢,即碳纤维布存在一个层间利用率的问题。同时,在强度不足区域局部包裹的碳纤维布后,无论是与局部强度不足的混凝土对比柱还是与原目标对比柱相比,受局部约束的试验柱其延性均有明显改善。(3)综合分析已有的FRP约束加固混凝土柱的应力应变关系模型,研究各个影响因素对加固效果的影响,对碳纤维布局部加固含有强度缺陷的混凝土柱轴心受压承载力计算进行了理论探讨,理论计算值与试验值进行对比发现,本文提出的承载力计算公式得出的计算结果与试验结果吻合较好,可以用来预测局部强度不足的混凝土柱使用碳纤维布局部加固时的轴心受压极限承载力,基于承载力计算公式探讨了局部加固碳纤维布用量的计算思路和计算步骤。(4)在偏心荷载作用下,对16根CFRP加固的含有薄弱段的钢筋混凝土方柱进行了试验,分析了碳纤维布加固量、加固方式及偏心距对局部加固效果的影响。结果表明:使用碳纤维布进行局部加固后,受约束混凝土柱的承载力和延性均有一定提高,但加固效果不如轴心受压柱加固效果明显;加固柱的延性提高与碳纤维布加固量并不成比例关系;对于偏心距较小的柱子采用横向外包FRP的加固效果较明显,随着偏心距的增大,承载力提高幅度有限,但延性仍较高;加固后柱截面应变分布仍满足平截面假定;由于混凝土的不均匀受压膨胀外包纤维存在明显的拉应变梯度;加固后试件的轴向力偏心距增大系数实测值与按规范计算值相差很大。(5)根据约束截面的应变分布和应变梯度规律,引入考虑偏心距的应变梯度影响系数,通过修正受压区等效应力矩形图形的参数,以及根据约束混凝土峰值应变得到的界限破坏时受压区高度,提出了局部强度不足的混凝土柱在局部包裹碳纤维布加固的情况下,偏心受压柱的正截面承载力计算公式。通过与试验数据的比较分析,表明该方法具有较高的精度,可作为实际工程中针对局部强度缺陷的钢筋混凝土矩形柱偏压加固设计时的理论参考。更多还原

【Abstract】 Fiber reinforced polymer(FRP) composites are used in strengthening concrete columns frequently due to their superior advantages.Most applications in the past focused on the entirely wrapping,while in practice,partial strength deterioration of concrete columns occurs occasionally.Frost damage,aging or construction quality might lead to the concrete strength be deteriorated.In these cases,wrapping CFRP is considered as an effective approach to maintain the regular service.However,the whole columns confinement including intact and deteriorated parts has been regarded as a waste.Few literatures involved in partial confinement only to the defect parts.This paper aims to present an effective method to partial deteriorated strength columns,and to investigate the mechanical behavior of the defect columns.For concrete columns and RC concrete columns with partial deteriorated strength, wrapping with CFRP only in the strength deteriorated regions,then axial and eccentric compressive loading were applied to all specimens.Based on generalization and experimental results of many former researchers,this paper analysized the formula to calculated bearing capacity of concrete columns sufferred from axial or eccentric compressive loading,and then derived the procedure how to determine CFRP amount.The research contents and results are as follows:Five groups totally 15 of 150×150 mm plain square columns are cast;each specimen has two different strengths,the lower strength in the middle segment and higher strength in both ends.The lower strength is to simulate the status of partial deteriorated region.Different layers of CFRP sheets have been wrapped just on the lower strength part to gain the reinforcement with CFRP sheets,and to verify the practicability of partial confinement. Specimens are subjected to monotonic axial compression until failure.Axial load,axial and transverse strains are measured to compare the different behaviors between the two parts. Experimental results show that partial confinement can significantly enhance the strength and the ductility of the deteriorated strength part,then,the bearing capacity of the whole column can be increased subsequently.Test data indicate that the ultimate load of the confined column is higher than that of the original column without deterioration;partial confinement on weakness is a feasible approach.Findings of this paper prove that partial confinement on deteriorated parts of concrete columns would develop as an alternative to avoid cost and time consumption in practice.Similar to the plain concrete columns,5 steel reinforced concrete columns with partial deteriorated strength were cast and suffered from axial compressive loading until failure. Wrapped with different amount of CFRP,the columns presents good performance compared with the columns without CFRP reinforcement.Experimental results show that because CFRP effectively limited the concrete’ lateral deformation,the ultimate compressive strength and deformation capacity of concrete have been prominently enhanced,the plastic distortion capability of steel bar can be made full use of and has the positive attributes to improving the carrying capacity and ductility of structure.Meanwhile,The experimental results indicate that the ultimate beating capacity and ductility of the whole column increase as the CFRP layer increase,but the increasing rate of beating capacity reduces while CFRP layers increases, which means there was a utilization ratio for different layer of CFRP.Besides,wrapping with CFRP,the ductility of columns with strength deficiency were improved greatly compared with not only the control columns with strength deficiency but also the control colulmns with original strength.Generalized the existed stress-strain models of FRP reinforced concrete presented by the former researchers,the paper analysized the factors influencing the partial reinforcement.And then analysized the formula to calculated bearing capacity of concrete columns sufferred from axial compressive loading,the calculaty results are agree well with the experimental ones, which means that using this formular could predict the bearing capacity of strength deficient concrete columns reinforced by CFRP.Based on the calculation of bearing capacity,then the paper derived the procedure how to determine the CFRP amount.16 partial deteriorated strength RC columns confined with CFRP were tested under eccentric compression.Based on the destructive tests,this paper analyzed the strengthening effect with the parameters such as different CFRP amount,different strengthening mode and different eccentricity.The experimental results indicate that the ultimate bearing capacity and ductility of the specimen have a certain increase as the amount of transverse CFRP increases, but it is not in linear relationship.Actually,the increasing ratio of bearing capacity reduces with CFRP layers increases.The results also show that CFRP can enhance the strength and ductility of columns with small eccentricity effectively,but the enhancement of capacity is very small and ductility is still high for columns with critical eccentricity;the distribution of sectional strain accords with plain section assumption;the tensile strain of external FRP exists distinct strain gradient due to uneven dilation of compressed concrete,and the testing value of axial magnifying coefficient of eccentricity is far different from the calculating value according to concrete code,and so on.Analysized the distribution of sectional strain,introduced the strain gradient factor caused by eccentricity,modified the parameters considered with equivalent rectangular stress distribution,and so on,this paper focused on bearing capacity calculation of CFRP wrapped deficient columns over the eccentrical loading.With comparation theoretical results and the experimental results,the theoretical value has the higher accuracy and was more conservative, which is more favorable for predicting bearing capacity of columns in practice.The research results show very usful for the practical engineering,and the authors hope it can be developed as guide for more comprehensive application.更多还原