摘要
近年来,随着土木工程、水利水电工程、铁路隧道工程等的迅速发展,钢筋混凝土结构的应用越来越广,对于钢筋混凝土结构的研究也越来越多,这些研究主要集中在钢筋混凝土的变形和极限强度问题上,而对于钢筋混凝土结构破坏全过程的研究较少。目前国内外有一些钢筋混凝土结构破坏的实验研究,但由于钢筋混凝土结构力学性能的复杂性,试验和量测手段的局限性,无法从试验中得到结构的全部力学性能,因此,需要其它方法与试验相结合来分析结构的力学性能,在试验研究的同时出现了数值模拟研究。20世纪60年代美国学者把有限元法引进到钢筋混凝土结构数值模拟分析中来,开始了钢筋混凝土结构的数值研究,取得了一定成果。但有限元模型的解决方法仍有不足之处,基于有限元基本理论的数值模拟方法的结构计算要求变形连续协调,对于钢筋和混凝土之间存在的不连续介质力学问题,应用有限元法很难计算。
由东北大学岩石破裂与失稳中心开发的复合材料破坏全过程分析系统MFPA2D,为研究钢筋混凝土结构的破坏提供了一种可行的方法。MFPA系统数值模型采用具有残余强度的弹脆性本构模型,引入统计分布函数,反映了混凝土的非均匀性影响；认为单元应力达到破坏准则发生破坏,并对破坏单元进行刚度退化处理,故可以以连续介质力学方法处理物理非连续介质问题。
采用MFPA2D数值模拟系统,对钢筋混凝土结构破坏全过程进行数值模拟,研究内容及结果包括以下三方面：
首先,对钢筋混凝土梁进行数值模拟。选用参考文献的试验模型,对钢筋混凝土梁施加对称集中荷载的四点弯曲受力形式进行数值模拟,给出模拟结果,主要有结构破坏过程的应力、位移变化及破坏形式,还有试验很难获得的声发射能量与声发射次数等。通过数值模拟结果与相应试验结果的比较分析,发现数值模拟结果在一定程度上和试验结果有着较好的一致性。在数值模拟中,采用了文献中的500MPa高强钢筋作为梁的受力筋,同时也进行了用普通钢筋HRB335作为受力钢筋的梁的数值模拟,对两者的模拟结果进行对比,发现500MPa高强钢筋混凝土梁与普通钢筋混凝土梁的受力性能、变形规律、裂缝发展等破坏过程基本相同,从而为高强钢筋在钢筋混凝土梁中的应用研究提供了一定的参考。
其次,对钢筋混凝土柱进行数值模拟。模拟主要考虑了大偏心受压和小偏心受压两种情况,模拟结果包括应力、位移和声发射能量等。该模拟也采用了相应的试验模型作为模拟的数值模型,目的是便于和试验进行比较分析。通过两种偏压形式的模拟结果比较,得出大小偏心受压的各自受力、变形和破坏特点,与试验结果基本吻合。
最后,对钢筋混凝土框架结构进行数值模拟。数值模拟了钢筋混凝土单层框架的受力变形和破坏,为框架结构的研究提供了一定参考。
通过上述三方面的数值模拟研究,证实了MFPA2D数值模拟在钢筋混凝土梁、柱、框架等方面研究具有一定的参考价值,为钢筋混凝土结构的研究提供了一种新的方法。
In recent years, with the rapid development of civil engineering, hydroelectic engineering and railway tunnel engineering, the reinforced concrete structure has become more widely used, the researches on reinforced concrete structure become more and more. These researches mainly concentrated on the deformation and limit strength of reinforced concrete, but rarely studied the whole failure process of reinforced concrete structure. At present, there are some researches on the failure of reinforced concrete structure at home and abroad. However, the complication of mechanics property of reinforced concrete structure and the limitations of tests and measures made it difficult to obtain all property data from the tests. Therefore, tests combined with other methods are required to analyze the mechanics property of structure. In the meantime of the tests, the numerical simulation research emerged. In 1960's, American scholars introduced the finite element method to the numerical simulation analysis of reinforced concrete structure, started the numerical research on reinforced concrete structure and gained a certain achievements. But the method for finite element model still had some deficiency. The structure calculation of numerical simulation method based on the finite element theory required that the deformation is continuous and harmonious, but for the uncontinuous medium mechanics existing between the reinforcing bar and the concrete, it is hard to use the finite element method to solve the problem.
The whole failure process analysis system of composite material-MFPA2D developed by Centre for Rock Instability and Seismicity Research, Northeasten University provided a feasible method of studying the failure of reinforced concrete structure. The numerical model of the MFPA system utilizes elastic damage constitutive model with residual strength, and introduced statistical distribution function, reflected the concrete heterogeneity. It showed that when the unit stress reached the point of failure, the failure produced, and the failure unit was treated to soften the rigidity, thus the physical uncontinuous medium problem can be solved by the continuous medium mechanics.
By the MFPA2D numerical simulation system, the numerical simulation of the whole failure process of reinforced concrete structure was conducted. The research and conclusions contain the following three aspects:
First, numerical simulation of reinforced concrete beam. The test model was selected from the reference documents, and the numerical simulation of four point-bend loading mode of the reinforced concrete beam subjecting symmetrical concentrated load was performed. The simulation results mainly included the variation of stresses and displacement, the failure mode, and the energy and times of Acoustic Emission hardly obtained from test, etc. By comparing the results of numerical simulation with those of corresponding tests, it was found that, to certain extent, there is a good agreement between the results of numerical simulation and those of the corresponding tests,. During the numerical simulation, the 500MPa high-strength reinforced bar from the reference document was selected as the loaded bar. Meanwhile, the numerical simulation of regular reinforced bar HRB335 was also carried out. Through comparing the results from the two numerical simulations, it indicated that the failure process of loading feature, deformation pattern and crack development of the 500MPa high-strength reinforced bar was basically identical to that of regular reinforced bar. Thereby, it provided a certain reference for the research on the reinforced concrete beam with high-strength reinforced bar.
Second, Numerical simulation of reinforced concrete column. The simulation mainly considered two cases-large eccentric loading and small eccentric loading. The simulation results included stress, displacement and the energy of Acoustic Emission, etc. The simulation also chose the corresponding test model as the numerical simulation model in order to make it convenient for comparing with the results of the corresponding test. By comparing the results between the two eccentric loading cases, it showed that the respective loading, deformation and failure feature of the large eccentric loading and small eccentric loading are basically identical to those of test.
Third, Numerical simulation of reinforced concrete frame. It simulated the deformation and failure of single reinforced concrete frame. It offered a certain reference for the research on the frame structure.
By the numerical simulation research on the three aspects above, the certain referense of the numerical simulation-MFPA2D was verified, therefore, it provided a new method for the research on reinforced concrete beam, column and frame.
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