Study On Progressive Collapse Resistance Of Reinforced Concrete Structures Considering Slabs & Infill Walls

Progressive collapse refers to the phenomenon that the structure is partially damaged due to accidental sudden loads,resulting in the domino effect and the overall collapse of the structure.In the nearly 60 years since the Progressive collapse of the Ronan Point apartment in the United Kingdom in 1968,a series of consecutive structural collapse events have continuously attracted the attention of experts and scholars from all over the world on the study of Progressive collapse.In recent years,the continuous innovation of building structures and design concepts in various countries,the continuous upgrading of research platforms and research tools,and the continuous optimization of analysis techniques and program algorithms have brought more new propositions and new ideas to the study of structural progressive collapse.However,the current research on progressive collapse of structures has not yet formed a widely recognized design standard and evaluation mechanism.The existing research on progressive collapse of reinforced concrete frame structures mostly focuses on plane frame structures,rarely considers the spatial effects caused by floor slabs and infill walls,and mostly adopts deterministic analysis and static analysis,which fails to reflect the discreteness of structural parameters and the instantaneity of progressive collapse.There is still a large space for further exploration in the study of structural progressive collapse.Therefore,in view of the vacancies and deficiencies of the existing research,this paper carries out the analysis and evaluation of the progressive collapse resistance of reinforced concrete structures considering floor slabs and infill walls.The main research contents and conclusions are as follows:(1)A complete analysis framework for the progressive collapse of spatial reinforced concrete frames based on Open Sees was built,and the spatial effects of spatial beams,floor slabs,infill walls were comprehensively considered.Various simplified modeling methods for three-dimensional spatial structures were systematically sorted out and key techniques of spatial structure modeling were disassembled,such as material constitutive,fiber section,element type,nodal constraints,coordinate transformation,mass definition and load combination,etc.Multilevel comparative analysis was carried out to verify the accuracy and reliability of the modeling methods for beam-column components,floor slabs and infill walls,and to provide modeling references for progressive collapse studies considering the effect of floor slabs and infill walls.(2)The incremental dynamic analysis was used to quantify and compare the progressive collapse resistance of different two-dimensional and three-dimensional structures,revealing the improvement law of different spatial effects on the collapse resistance of the structure,and decoupling the contribution of different spatial effects to the collapse resistance.Studies have shown that secondary and/or non-structural elements such as floor slabs and infill walls significantly improve the structural resistance to successive collapses,and their respective characteristics were amplified due to coupling effects in the spatial frames.(3)A fragility analysis model for structural progressive collapse assessment is established.Through the interactive use of multiple softwares(Matlab/Open Sees/Python),the wholeprocess integrated probability assessment of spatial structural systems considering uncertainty was realized.The research shows that the progressive collapse mechanism of floor slab and infill wall was different.In the process of progressive collapse,the infill wall significantly improves the initial stiffness of the structure and plays an early role until it reaches the peak capacity,while the floor slab continues to act through the membrane effect until the middle and later stage of the development of progressive collapse.(4)A machine learning-based rapid assessment method for the progressive collapse resistance of reinforced concrete structures is proposed.Based on the previous research,taking the research results of the infilled frames with floor slabs which consider the random parameters and spatial effects as the data source,a variety of single learning models and integrated learning models are used to predict the progressive collapse resistance of the five-level damage state,Multi-dimensional and comprehensive performance evaluation and comparative analysis are carried out on the prediction results.The results show that the rapid evaluation method proposed in this paper has strong operability,high calculation accuracy and operation efficiency.