【作者】 吴小勇；

【导师】 熊光晶；

【作者基本信息】 汕头大学 ， 结构工程， 2011， 博士

【摘要】 混凝土柱是关系结构安全性、耐久性的关键构件,目前常用的三种加固方法:加大截面法、外包钢法和纤维复合材料法都有各自的不足,譬如加大截面法施工复杂、体积增加较大,外包钢法技术要求高、耐久性较差,纤维复合材料法费用高、耐热耐火性较差。研发中的钢丝网砂浆加固法可克服上述常用加固法的不足,但不能明显提高柱的承载能力;研发中的钢筋网砂浆加固法可显著提高柱的承载力,但延性和耐久性尚不尽人意。为既大幅度提高柱的承载能力,又大幅度提高延性、抗震性能和耐久性,本文提出钢筋(大直径)钢丝网砂浆加固混凝土柱的新方法,并进行了较系统的试验研究。1.钢筋钢丝网砂浆加固混凝土圆柱的轴压试验研究分别制作钢筋钢丝网砂浆(SW)、钢筋网砂浆(S)和纤维复合材料(FRP)加固混凝土圆柱共74根。以承载力和延性为指标,以不同加固方法、钢筋和钢丝网相对用量为主要影响因素,进行了对比试验研究。研究结果表明,与S和FRP加固法相比,SW既能大幅度提高混凝土圆柱的极限承载力,又能显著提高其位移延性。如SW2(钢筋网加两层钢丝网)试件在承载力比S(钢筋网)试件高51%的情况下,SW2试件的位移延性达S试件的2.05倍;主要原因之一是SW试件优越的配筋分散性使得加载过程中出现大量纵横交错的细小裂缝(≈网格间距)而大量耗能。提出了SW加固混凝土圆柱极限承载力计算公式,经比较与试验结果吻合较好。此外还探索了测量圆柱外表面砂浆环向应变的方法。2.钢筋钢丝网砂浆加固混凝土圆柱的小偏压试验研究分别制作SW和S加固混凝土圆柱共18根,进行了以小偏心距为影响因素的抗压对比试验研究。结果表明,偏心距对各加固柱的极限承载力有显著影响;S和SW加固法均不能有效提高小偏心受压试件的位移延性;实测SW试件极限承载力显著高于既有偏压承载力公式计算值。3.钢筋钢丝网砂浆加固混凝土方柱的抗震滞回试验研究分别制作钢筋钢丝网砂浆(FS)、钢筋网砂浆(S)加固混凝土方柱和对比柱(O)6根,进行抗震滞回试验研究。结果表明,FS既能显著提高混凝土方柱的滞回耗能能力和侧向位移延性,又能明显增强试件的侧向承载力和刚度。在FS加固试件的配筋率仅比S加固试件高11%的情况下,FS试件的总耗能是S试件的1.61倍;主要原因之一是钢丝网的优越配筋分散性避免了受力主筋与混凝土/砂浆的脱粘破坏,且在一定程度上使砂浆层保持裂而不碎,裂缝两侧砂浆相互摩擦挤压耗能。本文还探讨了柱底塑性铰长度问题;并指出将能量耗散系数与总能耗结合才能合理评价构件的抗震性能。最后,结合研究现状及试验过程中所遇到的问题,提出了今后的研究设想。整个研究表明,钢筋钢丝网砂浆加固法是一种可靠的加固方法,加之经济、施工简易(不需支模和大型施工机具),非常适合城乡中小学校舍的抗震加固,应用前景广泛,很可能取得不同以往的实质性效果。更多还原

【Abstract】 Concrete column is the key member in the construction framework which affects its safety and durability greatly. Enlarging concrete section by using new concrete, enveloping steel and strengthening with fiber-reinforced polymer (FRP) are three widely-used methods to strengthen concrete column, but these methods have their own disadvantages, such as construction complex and volume increase of enlarging section method, high technical needs and poor durability of enveloping steel, and the high cost and poor fire proof of FRP method. In order to improve the seismic performance, ductility and durability of concrete columns significantly while improving the bearing capacity greatly, this thesis put forward a new method for strengthening concrete columns with ferrocement including steel bars (large diameter) and its experimental study was carried out.a. The axial compression performanceA total of 74 circular concrete columns were strengthened by using ferrocement including steel bar (SW), steel bar (S) and FRP respectively. Comparative test was performed under axial compressive load, the effect such as different strengthening methods and the area ratios between steel bar and wire mesh were studied according to the index of bearing capacity and ductility. The results showed that, SW not only improved the bearing capacity dramatically, but also improved the displacement ductility significantly comparing with S and FRP methods. For example, on the premise that the bearing capacity of the SW2 (with two layers of wire mesh) columns was 51% higher than the S columns, the ductility of the SW2 columns was still 2.05 times of the S columns. One of the main reasons is that the superior reinforcement dispersion of the SW columns induces a massive criss-cross of tiny cracks during the loading process, leading to a great energy dissipation. The formula of the ultimate load of the SW columns was proposed, the calculated results show a good agreement with experimental data. In addition, a method for measuring the stain of mortar surface was explored.b. The eccentric loaded performance18 circular concrete columns strengthened by SW and S were tested under eccentric loading, and the effect of the eccentricity (small) was studied. The results show that, eccentricities have a significant effect on the ultimate bearing capacity of each strengthened column. Both S and SW methods can not improve the ductility effectively. The measured ultimate load of the SW column was much higher than that by using the code formula.c. The seismic performanceAn experimental study of 6 square concrete columns strengthened by ferrocement including steel bar (FS) and steel bar (S) was carried out under the cyclic loading. The results show that, the FS can not only improve the hysteretic energy dissipation and ductility of square concrete column significantly, but also enhance the bearing capacity and rigidity greatly. When the reinforcement ratio of the FS column was only 11% higher than that of the S column, the total energy dissipation of the former was as much as 1.61 times of the latter. One of the main reasons is that the wire mesh with superior reinforcement dispersion protects the bond between longitudinal bars and concrete/mortar well, meanwhile it makes the mortar keep cracked but not broken, friction and extrusion of the mortar on both sides of the cracks lead to a large energy dissipation. The plastic hinge length at the column bottom was discussed. In addition, it was pointed out that a reasonable evaluation could only be drawn out based on a comprehensive analysis on both the energy dissipation coefficient E and the total energy dissipation.Further research issues were put forward at the end of the thesis.The whole research shows that, ferrocement (including steel bar) strengthening is a reliable strengthening method, coupled with low cost, construction easily (no need of moulds and large construction tools), which is suitable for seismic retrofit of the primary and secondary school buildings in urban and rural China. With broad application prospects, this method will probably get different concrete results.更多还原