Experimental Research And Theoretical Analysis On Progressive Collapse Resistance Of Frame With Specially Shaped Columns

The frame structure with specially shaped columns has been widely used in high-rise buildings in recent years owing to the advantages of significantly expanding the usable floor area of the building and improving the flexibility of furniture layout.Compared with the rectangular column section,the column section of specially shaped column is irregular,the mechanical performance is more complex,and the progressive collapse performance of these two kinds frames is also inevitably to have some similarities and differences.In this paper,the progressive collapse-resistant behavior of RC frame structure with specially shaped columns was studied through experimental study and theoretical analysis,which can provide a reference for the collapse resistant design of frame structure with specially shaped columns.The progressive collapse resistance,failure mechanisms and failure modes of a space RC frame with specially shaped columns was studied through a collapse experiment.The results of dynamic collapse experiment show that the influence of dynamic response on structure was not significant.The structure was still in the elastic stage and collapse did not occur,indicating that RC frame with specially shaped columns designed according to Chinese codes has a good behavior against progressive collapse.The results of static loading test show that the frame eventually collapsed due to the failure of beam-column joints.The beam-column joints are proved to be a weak area of the structure to resist progressive collapse and will require further enhancements.At the same time,the spatial connection action of the lengthways beams and slabs significantly increased the progressive collapse resistance of structure.The contribution of the floor should be considered in the collapse resistant design of structureThe finite element analysis results show that the dynamic response at the moment of column failure is related to the failure time of vertical member.Proper protection to the key load-carrying members of the structure to delay the failure time can reduce the dynamic response and the risks of progressive collapse of structure due to local damage.The study also shows that the progressive collapse resistance of frame structure with specially shaped columns mainly depends on the flexural strength and compressive arch action of frame beams.The reinforcement of beams are the main factors influencing the collapse resistance of the structure,the collapse resistance of the structure increased with the increase of reinforcement of the beams.Improving the seismic fortification intensity during the design of frame can significantly enhance the progressive collapse resistance of frame with specially shaped columns.The comparative analysis results of the frame with specially shaped columns and frame with rectangular columns show that the progressive collapse resistance of these two kinds frames is very close during the small deformation stage when the frame beam section and reinforcement are exactly the same.During the large deformation stage,the beam-column joints of the frame with specially shaped columns damaged before the frame,the structure can't give full play to the catenary action and improve the antiprogressive collapse bearing capacity of the overall structure.Unable to make full use of the carrying capacity of the catenary action is the main difference between the frame with specially shaped columns and frame with rectangular columns.The proposed damage model based on materials can more accurately evaluate the damage state of concrete,steel bars,structural members and the whole structural system during the collapse process of frame structure with specially shaped columns.The corresponding relationship between the damage degree and damage index values were determined by comparing with test results.It can provide a reference for the subsequent collapse damage evaluation of frame with specially shaped columns.