Structural Damage Assessment Research And Elastoplastic Analysis Of An Irregular Frame-shear Wall Structure

With the vigorous development of China’s economy, complex architectural appearance andmulti-function had became the trend of requirements of modern high-rise buildings, and thereconsequently emerged a large number of high-rise buildings with such characteristics. However,complex architectural form and functions may easily lead to structural irregularity of plane andvertical layout, and complicated mechanical characteristics during earthquakes. As shown byextensively domestic and overseas surveys of damages induced by earthquake, deformation andenergy accumulation tend to be found at or near structural irregularity, which may lead to localfailure or even overall instability. However deflection is the only indicator to determine the stateof structural destruction defined in the code for earthquake resistant, in which the maximumdeformation is the main concern, while accumulated damages induced by earthquakes may beneglected. Therefore, for the structure with irregularity, the imperfection of single indicator inthe code is highlighted by complex mechanical performances. As damage indicator is the keyassessing structural performances of structures with irregularity, a frame-shear wall structurewith irregularity was taken as an example. The theories and computational methods of variousdamage indicators were studied and compared, and the applicability of all the damage indicatorsto the structures with irregularity in practical engineering will be verified.The main works and conclusions are as follow:(1)3D seismic loads should be employed in the time-history analysis of irregular structure,while a reasonable way for3D seismic loading is crucial to assess the earthquake responses ofthe structure correctly. There are two methods of loading3D seismic in practical engineeringmainly. The first method: after modulated according to the1:0.85:0.65of PGA, exerte theamplitude of seismic oscillation on the structure in the two horizontal directions and the vertical direction; the second method: input the three ground motion component records of the sameselected seismic event and same seismic observatory into the structure in the original ratioamong such three records. A contrast analysis between such two methods, which involved stress,deformation, energy dissipation and structural damage, had been done and showed that it’sunreasonable to use the first method in an irregular structure time history analysis because itcan easily lead to the underestimation earthquake influence or the overestimation of thestructural seismic capacity. Therefore, it is advised to use the second method for the loading ofthree-dimensional ground motion.(2) Choosing the right damage indicator is the most important part of the damageassessment for practical engineering. This paper researches into the computation conditions ofactual engineering and concludes that the damage indicator should be of necessary accuracyand practicality in actual engineering. In consideration of the above two conditions, this paperhad made comparison among damage indicators based on various failure criterions and pickedup4of it. They are the twice POA index, which is based on rigidity degeneration, the Park-Ang’s index, which includes double parameters, the harmful inter-story drift indicator and theinter-story drift indicator.Considering the complex seismic response of the irregular structure and the undefinedapplicability of the4damage indicators above, taking an irregular frame-shear wall structureas an example, comparison analysis between the damage assessment results has been done. Theanalysis above involved the global damage assessment and the story damage assessment. Theanalysis results indicates that to the global damage assessment, inter-story drift indicator is themost conservative one among the four. The twice POA index takes the second place and Park-Ang’s index is the forth. Besides, because of the insufficiency in sensibility, the harmful inter-story drift indicator is not suitable for overall damage assessment of the irregular frame-shearwall structures. In addition, because the irregular structure is seriously affected by the highorder mode and the Park-Ang’s index only includes the top displacement for structuraldeformation, it is unwise to choose Park-Ang’s index for irregular structure global damageassessment either. For the purpose of accuracy and reliability, the twice POA index and inter-story drift indicator have been recommended for the global damage assessment of this kind ofstructure and the max value of the two results should be taken as the final result.(3) When conducting the inter-story damage assessment, this research shows that the Park-Ang’s damage index for the underparts of the structure appears to be more exceeding than thenormally safe value, making the result for these specific parts the most reliable. While the harmful inter-story drift damage indicator is exceeding to be safer as well, but in a lower profilethan the Park-Ang’s damage index. Whereas the inter-story drift damage indicator is converselysmaller than the expected safe value, making the result tend to be dangerous and unreliable. Inthe meantime, though identical laws for the Park-Ang’s damage index and harmful inter-storydrift damage indicator is also found in the upper parts of the structure, the safest value analyzedchanged to appear in the inter-story drift damage indicator.By studying the damage index curve, this paper finds that the Park-Ang damage index andthe harmful inter-story drift damage indicator can always accurately reflect the vulnerable partsof the structure. However, the inter-story drift damage indicator can’t reflect the exactly realinformation about the vulnerability. So the inter-story drift damage indicator is not suitable forstory damage assessment. What’s more, the deformation pattern of the structure fails to meetthe assumption drawn from the harmful inter-story drift damage indicator, so the calculatingresult turns out to be smaller, which explains why this damage indicator is not suitable fordamage assessment, either. To sum up, considering the accuracy and safety, the Park-Angdamage index is proposed to apply into the inter-story damage assessment for irregular frame-shear wall structures.