钢纤维混凝土静力损伤及疲劳损伤研究

发布时间：2018-07-26 14:55

【摘要】：钢纤维混凝土(SteelFiberReinforcedConcrete,简写为SFRC)是在普通混凝土中掺入乱向分布的短钢纤维所形成的一种新型复合材料。它不仅具有普通混凝土的优良特性，同时由于钢纤维的存在限制了裂缝的开展，从而使原来本质上是脆性的混凝土材料呈现出很高的抗裂性能并能推迟裂缝的出现、使混凝土具有较大的延性和韧性以及优良的抗拉、抗折、抗冲击、耐磨损、抗疲劳等特性。近年来，钢纤维混凝土得到广泛的应用和深入的研究。根据国内外已有的研究成果，本文对钢纤维混凝土静力损伤和疲劳损伤进行了研究，主要研究内容及结论如下： 1、给出了将试验得到的4点弯曲梁的荷载－挠度曲线转化为相应的应力－应变曲线的方法；根据能量等效原理和weibull统计分布理论推导了钢纤维混凝土在单向荷载作用下的本构模型及其损伤模型，只要能准确的测定出试件的弹性模量、峰值应力以及相应的峰值应变，就能得到其单向荷载作用下的本构方程和损伤演变方程。 2、静载破坏可看成是特殊的疲劳破坏，即极限强度加载下，承受一个循环的疲劳破坏。在此过程中，损伤也是一个逐步累积的过程。借鉴疲劳损伤的分析方法，基于损伤力学推导了单轴加载作用下描述损伤变量与应变关系的损伤演变方程。根据应变等效原理，得到对应的本构方程。 3、对钢纤维再生混凝土和钢纤维卵石混凝土弯曲疲劳性能进行了试验研究，得到不同应力水平（S=0.7,0.75,0.8,0.85）下的疲劳寿命。分析结果表明：应力水平S与对数疲劳寿命lgN成直线关系，相关系数在0.99以上，因钢纤维和粗骨料之间的界面连接强度不同，在任何应力水平下钢纤维再生混凝土的疲劳寿命都比钢纤维卵石混凝土大。综合已有文献回归得到的弯曲疲劳载荷作用下的疲劳寿命方程，可作为弯曲疲劳荷载作用下疲劳寿命的估算。钢纤维再生混凝土和钢纤维卵石混凝土弯曲疲劳应变演化曲线呈现三阶段发展规律，随着循环比的增加，钢纤维再生混凝土的疲劳应变比钢纤维卵石混凝土的疲劳应变发展慢。由此可见，利用再生骨料作为粗骨料的钢纤维再生混凝土不仅能“变废为宝”，减少环境污染，实现资源的重复利用，而且其疲劳寿命和疲劳应变发展都优于钢纤维卵石混凝土。 4、利用威布尔分布和对数正态分布对钢纤维再生混凝土和钢纤维卵石混凝土的疲劳寿命试验结果进行检验，结果表明本次试验的弯曲疲劳寿命较好地服从对数正态分布和两参数威布尔分布。不同存活率P和应力水平S下，单对数疲劳方程和双对数疲劳方程的线性关系是成立的，其相关系数R均在0.99以上；存活率P对钢纤维卵石混凝土的回归系数B和b影响很小，可取其平均值作为通用结果，而存活率P对钢纤维卵石混凝土各回归系数影响很小，可取其平均值作为通用结果。 5.通过对二级配钢纤维混凝土疲劳试验数据进行回归，提出了二级配钢纤维混凝土弯曲疲劳方程，，其回归系数可以达到0.971以上，比采用其他拟合公式更接近试验结果。 6.提出了描述钢纤维混凝土的疲劳应变演化曲线的疲劳应变方程，结果显示，拟合曲线与试验曲线能很好吻合。根据疲劳模量与疲劳应变幅值成反比的关系，由疲劳应变演化方程得到疲劳模量演化方程。利用疲劳模量演化方程对已有疲劳模量试验结果进行拟合，结果显示，该式表达的疲劳模量演化曲线与相应的试验曲线吻合很好，其相关系数均在0.99以上，说明该式适合描述钢纤维混凝土的疲劳模量演化曲线。 7、分别用疲劳应变和疲劳模量定义钢纤维混凝土疲劳损伤，得到的典型的损伤变量演化曲线显示，由最大疲劳应变和疲劳残余应变定义的损伤变量演化曲线基本一致，且相差很小；而由疲劳模量定义的损伤变量演化曲线明显大于由疲劳应变定义的损伤变量演化曲线，当循环比为0.9时，由疲劳应变定义的损伤变量约0.35左右，而疲劳模量定义的损伤变量约为0.77，当初始循环时，疲劳模量定义的损伤变量就达到0.34左右，而疲劳应变定义的损伤变量接近0。也就是说，由疲劳模量定义的损伤变量自始至终都比疲劳应变定义的损伤变量大。 8、基于损伤力学推导了钢纤维卵石混凝土和钢纤维再生混凝土弯曲疲劳损伤方程，结果显示，由疲劳损伤方程得到的回归曲线与疲劳损伤演化曲线吻合很好。 9、根据材料的宏观量的变化与疲劳损伤演变有本质联系，故由损伤变量推导得到钢纤维混凝土剩余疲劳寿命和剩余弯曲强度的表达式。通过该式，可求得给定疲劳应力水平、不同损伤状态下的剩余疲劳寿命和剩余弯曲强度，为有损结构的安全评估及决策提供参考。由剩余疲劳寿命随损伤变量以及循环比的变化曲线可知，随着损伤变量的增大，剩余疲劳寿命曲线下降，损伤变量为0.3以内时，剩余疲劳寿命降幅较大，且应力水平越低，降幅越明显，应力水平为0.7时，曲线急剧下降；随着循环比的增加，剩余疲劳寿命近似直线下降，且应力水平越低，降幅越明显。由剩余弯曲强度随循环比以及损伤变量的变化曲线可以看出，随循环比的不断增加，剩余弯曲强度逐渐降低，近似呈直线变化，当接近破坏时，剩余弯曲强度急剧下降，另外，循环比相同时，应力水平的变化对剩余弯曲强度的影响较小；而剩余弯曲疲劳强度随损伤变量近似呈直线变化，损伤变量相同时，应力水平越高，剩余弯曲强度越大。
[Abstract]:Steel fiber reinforced concrete (SteelFiberReinforcedConcrete, SFRC) is a new type of composite made of short steel fiber mixed with random distribution in ordinary concrete. It not only has excellent properties of ordinary concrete, but also restricts the development of cracks because of the existence of steel fiber, so that it is essentially a brittle coagulation. Soil materials have high cracking resistance and can postpone the appearance of cracks, make concrete have great ductility and toughness, excellent tensile, fracture resistance, impact resistance, wear resistance, fatigue resistance and so on. In recent years, steel fiber reinforced concrete has been widely used and studied in depth. The static damage and fatigue damage of concrete are studied. The main contents and conclusions are as follows:
1, the method of converting the load deflection curve of the 4 point bending beam to the corresponding stress strain curve is given, and the constitutive model and the damage model of the steel fiber reinforced concrete under unidirectional load are derived according to the energy equivalence principle and the Weibull statistical distribution theory, so long as the elastic modulus of the specimen can be accurately measured. The constitutive equation and damage evolution equation under uniaxial loading can be obtained by volume, peak stress and corresponding peak strain.
2, the static load failure can be regarded as a special fatigue failure, that is, under the ultimate strength loading, it bears a cyclic fatigue failure. In this process, the damage is also a cumulative process. Based on the fatigue damage analysis method, the damage evolution equation describing the relationship between the damage variable and the strain is derived based on the damage mechanics. According to the strain equivalence principle, the corresponding constitutive equation is obtained.
3, the flexural fatigue behavior of steel fiber recycled concrete and steel fiber cobble concrete was tested and the fatigue life under different stress levels (S=0.7,0.75,0.8,0.85) was obtained. The results showed that the stress level S was linear with logarithmic fatigue life lgN, the number of related lines was above 0.99, and the interface between steel fiber and coarse aggregate The fatigue life of steel fiber recycled concrete at any stress level is larger than that of steel fiber reinforced concrete. The fatigue life equation under the bending fatigue load obtained by the existing literature can be used as an estimate of fatigue life under the action of bending fatigue load. Steel fiber recycled concrete and steel fiber pebble. The bending fatigue strain evolution curve of concrete presents three stages of development. With the increase of cycle ratio, the fatigue strain of steel fiber recycled concrete is slower than that of steel fiber pebble concrete. Therefore, the steel fiber recycled concrete using recycled aggregate as coarse aggregate can not only "change waste into treasure", reduce environmental pollution. To achieve the reuse of resources, the development of fatigue life and fatigue strain is better than steel fiber pebble concrete.
4, using Weibull distribution and logarithmic normal distribution to test the fatigue life test results of steel fiber recycled concrete and steel fiber gravel concrete. The results show that the bending fatigue life of this test is well obeying log normal distribution and two parameter Weibull distribution. Under different survival rates P and stress level S, single logarithmic fatigue square The linear relationship between the path and the double logarithmic fatigue equation is established. The correlation coefficient R is above 0.99, and the survival rate P has little effect on the regression coefficient B and B of the steel fiber gravel concrete. The average value should be used as the general result, while the survival rate P has little influence on the number of the regression lines of steel fiber gravel concrete, and the average value should be used as a general junction. Fruit.
5. through the regression analysis of the fatigue test data of two graded steel fiber reinforced concrete, the bending fatigue equation of two graded steel fiber reinforced concrete is proposed. The regression coefficient can reach more than 0.971, which is closer to the test results than the other fitting formulas.
6. the fatigue strain equation describing the fatigue strain evolution curve of steel fiber reinforced concrete is presented. The results show that the fitting curve is in good agreement with the test curve. According to the inverse ratio of fatigue modulus to fatigue strain amplitude, the fatigue modulus evolution equation is obtained from the evolution equation of fatigue strain. The results of the model test are fitted. The results show that the fatigue modulus evolution curve of the formula is in good agreement with the corresponding test curve, and the correlation coefficient is above 0.99. It shows that the formula is suitable for describing the fatigue modulus evolution curve of steel fiber concrete.
7, the fatigue damage of steel fiber reinforced concrete is defined by fatigue strain and fatigue modulus. The typical damage variable evolution curve shows that the damage variable evolution curve defined by the maximum fatigue strain and the fatigue residual strain is basically consistent, and the difference is very small, and the damage variable evolution curve defined by the fatigue modulus is obviously larger than that by the fatigue. The damage variable evolution curve defined by strain strain, when the cycle ratio is 0.9, the damage variable defined by the fatigue strain is about 0.35, and the damage variable defined by the fatigue modulus is about 0.77. When the initial cycle, the damage variable defined by the fatigue modulus is about 0.34, and the damage variable defined by the fatigue strain is close to 0., that is to say, fatigue. The damage variable defined by the model is always greater than the damage variable defined by fatigue strain.
8, based on the damage mechanics, the bending fatigue damage equations of steel fiber gravel concrete and steel fiber recycled concrete are derived. The results show that the regression curve obtained by the fatigue damage equation is in good agreement with the fatigue damage evolution curve.
9, the expression of residual fatigue life and residual bending strength of steel fiber concrete is derived from the damage variable according to the change of macroscopic quantity of the material and the evolution of fatigue damage. By this formula, the given fatigue stress level, residual fatigue life and residual bending strength under different damage states are obtained, which are damaged structures. The residual fatigue life with the damage variable and the change curve of cycle ratio shows that the residual fatigue life curve decreases with the increase of the damage variable and the damage variable is less than 0.3, and the lower the stress level, the more obvious, the stress level is 0.7, the curve is urgent. With the increase of the cycle ratio, the residual fatigue life decreases approximately linearly, and the lower the stress level, the more obvious. The residual bending strength decreases with the cycle ratio and the damage variable curve, and the residual bending strength decreases gradually with the continuous increase of the annular ratio. At the same time, the change of the stress level has little effect on the residual bending strength, while the residual bending fatigue strength approximated to the damage variable, and the higher the stress level, the greater the residual bending strength.
【学位授予单位】：华南理工大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU528.572

【参考文献】