The prediction of the fracture mechanism for RC portal frame
Date Issued
2016
Date
2016
Author(s)
Wang, Weng-Hone
Abstract
This thesis studies were produced by the department for the failure pattern of concrete structures, analysis and discussion, except by laboratory tests, but still based on the concept of material mechanics and plastic mechanics. The structure for the generation of cracks, stretch and the final failure pattern are derived, analyzed and proven. The finite element analysis program, SAP, is adopted by cylindrical concrete splitting test to attain stress, principal stress and strain energy that can be analyzed to obtain cracks stretch and mathematical proof of failure pattern. The HHT method is also adopted by analysis the change situation of the structure characteristic value before and after the failure pattern of the structure for structural safety was assessed. In this paper, the research work in addition to splitting failure pattern of the cylindrical concrete splitting test specimen for discussion, the one floor, two-span structures for real-scale tests to investigate the failure pattern of concrete structures. When the cylindrical concrete splitting test was be done, the crack distribution of the failure pattern along the parallel loading diameter of the cylindrical concrete specimen according to ASTM C496 was recognized. Because the cylindrical concrete element is compression parallel to the diameter of the cylindrical concrete and tension perpendicular to the diameter of the cylindrical concrete, the combination of the mechanics behavior lead to the failure pattern of compression and tension. In this study, in addition to the cylindrical concrete splitting test was be done to investigate the development situation of fracture pattern, the analysis of the elastic analysis by the stress distribution parallel and perpendicular to the direction of the diameter, and the finite element method analyzed energy distribution, stress, etc of the test specimen cross-section are also finished. The failure pattern of cylindrical concrete splitting test is gained with the gradient direction of equal principal stress and equal energy distribution line. The historic data of displacement, velocity and acceleration is attained by setting sensors on the one floor and two bays concrete structure. The analysis data is gained from before and after seismic table test, white noise(WN1、WN2), seismic table test, and before and after reaction wall test, ambient test1(AT1、AT2). The structure principal frequent, phase angle, stiffness, and damping ratio changes in different stages of environmental influence can be searched by the HHT method is adopted to transform the time domain to the frequent domain. As described above, the safety estimation of the structure can be done. The gradient direction of the equal maximum principal stress, the equal minimum principal stress and equal unit strain energy that analyzed by cutting the concrete network elements, the cracks happen, stretch, and form the tension crack core from the gradient of the maximum principal stress on which the higher tension stress is distributed, then finally the compression arch is formed along the gradient of the minimum principal stress on which the higher compression stress is distributed. The gradient directions of equal unit strain energy stored in the concrete structure include two parts of unit stain energy formed according to the maximum principal stress and the minimum principal stress. The analysis results from the gradients of equal strain energy are the same as the theorem and effect of the compression arch. In addition to the traditional stead and linear analysis, and the promotion non-stead and nonlinear analysis in the frequent domain are adapted according to the HHT method, and the white noise existed in the natural environment is filtered by dealing with the energy spectrum with concepts of orthogonal and flattening, the promotion non-stead and nonlinear analysis in the frequent domain is finished. According to the results of the HHT method, the principal stress of concrete structure attenuate between before and after of the concrete structure failure pattern happen. The effects of seismic resistance to the concrete structure are gained and estimated from the analysis of Hysteresis loop of reaction wall about the loading linear stiffness, unloading linear stiffness, the unit strain energy and damping ratio, and the safety estimate of the concrete structure and functions of the concrete structure arranged with damper can be reached. The prediction about the failure pattern of the concrete structure is already important state to the much more earthquakes existed in our environment. According to the failure pattern research of the concrete structure by establishing the feasible prediction and model of the failure pattern, the safety estimate of the concrete structure can be used.
Subjects
equal stress line
equal energy line
compression arch
Hubert-Huang Transform
Type
thesis
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