Studies On Collapse-Resistant Performance Of Frame Structures Subjected To Blast Loads

Recently accidental explosions often occur due to gas leakage or improper storage of explosive materials, resulting in the collapse of building structures subject to blast loads. Frame structures have been widely used for civil infrastructure in China. And once the girders and columns of a frame structure are damaged by blast loads, the local regions of the structure could fail due to the loss of the load bearing capacity. Such failure might induce the progressive collapse of the structure, which would cause serious loss of lives and significant impact on the society. Therefore, studies on the collapse-resistant performance of frame structures under blast loads have shown their importance in both theoretical research and practical applications. However, so far most of studies are carried out within the static analysis framework. Research related to blast loads is very limited in the literature. Due to it, with the aid of numerical simulations this thesis attempts to investigate the collapse-resistant performance of a laboratory-scale reinforced concrete frame subjected to blast loads. The primary contributions of this thesis are listed as follows.(1) Firstly within the static analysis framework, the existing method based on importance coefficients of components has been improved in order to analyze the collapse sequence of the RC frame subject to specific static loads. Meanwhile, the same collapse procedure has been simulated using the ANSYS/LS-DYNA program and the predicted displacements were compared to the measured ones. On the other hand, the theoretical results given by the static analysis were also compared with the numerical predictions in the aspect of the collapse sequence. By these means, the accuracy of the frame model has been validated.(2) Secondarily, the basic theories related to blast loading simulations have been summarized, including the classification of blast loads, parameter definitions, time history curves of pressure attenuation, the basic concepts of blast waves and the calculation methods of blast loads. After detailed investigations, the blast loading method suitable for this study has been established. At the same time, the constitutive models for concrete and steel materials, the boundary and connection conditions and the mesh size for air and explosive elements have also been investigated for the subsequent numerical simulations.(3) Thirdly, the collapse mechanism of the RC frame subjected to blast loads has been analyzed using the ANSYS/LS-DYNA program. The analyses focused on three aspects of a) the interaction effects between the blast waves and the structural components; b) the dynamic responses of structural components under blast loads; c) the progressive collapse mechanism of the frame after the failure of some regional components.(4) Lastly, the frame was locally reinforced on its critical components for the purpose of collapse prevention. The numerical analyses demonstrated that the collapse-resistant performance of the frame could be significantly improved by means of a) narrowing the distances between stirrups; b) increasing the longitudinal reinforcement ratios of the girders and c) setting the external rebars for tying adjacent girders. On the other hand, the increase of the longitudinal reinforcement ratios of the columns showed little effects.As a conclusion, this thesis presents a successive analysis procedure for the sake of a comprehensive investigation. The frame model was first validated from a static point of view. Then it was adopted as the baseline model for the subsequent dynamic analyses under the blast loading. Lastly, design proposals have been given in the interest of improving the collapse-resistant performance of the frame structure.