Study On Variation Of Dynamic Characteristics Of RC Structural Members In The Process Of Earthquake Damage

Earthquake disaster has the huge destructive effect, earthquake led to a large number of buildings damaged in different degree. The damage process of structures under earthquake is the current hot issues in the study of earthquake resistance of structure. The natural frequencies of the structure is able to accurately reflect the property parameters, structure performance status based on this, this paper carried out the members of reinforced concrete structures in seismic damage in the process of dynamic characteristics of structure, in order to reveal the mechanism of damage cause by earthquakes, and earthquake damage identification and quantitative structure foundation.Based on the National Natural Science Fund Project "RC based hysteresis energy consumption based on variable structure stochastic response of incomplete information dynamic reliability research" (51108044), the research of dynamic characteristics of reinforced concrete columns in the process of seismic damage is conducted through pseudo static test. In the experiment,20 specimens of different strength and stiffness are divided into two groups, and then tested by MTS servo loading system of horizontal reciprocating loading to measure the natural frequency in the process of component damage. The specimens of the same strength and stiffness are tested by changing the applied seismic load and seismic load cycle amplitude to explore the impact of seismic loads, seismic load cycle on the dynamic characteristics of the damage. The test also uses cras7.0 software to measure the natural frequency of specimens before and after damage.In this paper, the main work and conclusions are as follows:1.Three groups of different loading cycles,1.875s,2.4s and 3.0s are designed in the experiment and test results show that:the loading cycle has certain effect on the decline of natural frequency of under damage specimens. The natural frequency decreases slowest when the loading cycle is 2.4s, and the natural frequency will decrease faster when the loading period decreases to 1.875s or increases to 3.0s.2. Cras7.0 measurements show that:before the injury and after the injury, the first three frequencies are significantly reduced. And with the higher order, the reduce amplitude becomes larger. The natural frequency decreases rapidly in the earlier stage of damage process, and then decreases slowly in the later stage of damage process.3. The damage degree is defined through the natural frequency and the definition formula is used to analyze and process the test data. According to the formula of natural frequency definition, the formula between load, displacement and natural frequency is obtained and is used to process data.4. Using MATLAB fitting the fitting equation of natural frequency of specimen damage process change, the natural frequency changes in expression of N T and the number of loading cycles of loading amplitude and loading of the A equation, the fitting equation shows that the effect of loading amplitude and loading frequency A N on the changes of natural frequency is a linear, effect of loading cycle of T changes in natural frequency is three times.5. On the natural frequency equation for a derivative, a numerical specimen damage rate, the absolute value of the derivative value the greater that damage faster, results show that:the specimen damage, damage rate and loading time proportional to the number of absolute value, large loading 40 weeks before the derivative values, natural frequency decreases faster, smaller absolute value by numerical loaded in 40 weeks, the natural frequency decreases slowly.6. Comparison of two groups of different stiffness specimens shows that:the greater stiffness the specimen is of, the more significantly the natural frequency changes, namely the bigger damage degree the specimen is of.7. Variables of natural frequency, squared and load capacity are analyzed, and the corresponding relationship is conducted.