Fire Performance Of Concrete-encased Concrete Filled Steel Tubular Column-RC Beam Joints

It is well known that structures using concrete-encased CFST(concrete filled steel tube)columns are gaining popularity in the fields of high-rise buildings and industrial plants.However,related designing codes have no specific provisions on fire design or post-fire assessment of structures using concrete-encased CFST columns.Therefore,it is of essential importance to study the fire performance of this kind of structures,including the performance in fire situation and after exposure to fire.A thoroughly understanding of the their behaviour in the full-range fire acts as the basis of scientific fire design and post-fire assessment of structures using concrete-encased CFST columns.Typical concrete-encased CFST column and concrete-encased CFST column to RC(reinforced concrete)beam joints from practical engineering were selected as the research objects,in which the concrete-encased CFST columns have a outer square cross section with encased circular CFST component.This dissertation systematically investigates their working mechanism in the combined full-range loading process and the full-range fire.The research work conducted is as follows:1.Experimental investigation of concrete-encased CFST columns were conducted subjected to the combined loading and full-range fire.The parameters include cross-secitonal dimensions,load ratio,and heating time ratio.Th e experiment investigates the development of fire resistance,post-fire residual loading bearing capacity,failure modes,temperature distrib ution and structural deformation of concrete-encased CFST columns.The finite element analysis(FEA)model of concrete-encased CFST columns was established with consideration of the influence of reinforcement confined concrete and the concrete properties variations during the cooling stage.The predicted results of the FEA model show good agreement with the test results.2.Experimental investigation of concrete-encased CFST column to RC beam joints was conduted subjected to the combined loading and full-range fire.The parameters include beam cross-sectional dimensions,column load ratio,beam load ratio and heating time ratio.The experiment investigates the developments of the joints’ fire resistance,post-fire residual load bearing capacity,failure modes,temperature distribution and deformations,which provides a better understanding of the joint’s mechanism subjected to the full-range fire.3.The FEA model of concrete-encased CFST column to RC beam joints subjected to the combined loading and full-range fire was established.This FEA model was utilized to investigate the mechanism of concrete-encased CFST column to RC beam joints subjected to the combined loading and full-range fire.The developments of temperature distribution,failure mode,deformation,s tress and strain distribution,internal force distributions and the joint bending moment versus the relative rotation were obtained and analysed.The influence of concrete explosive spalling,the properties of interface,and construction method on the performance of the joint were also analysed.4.The influencing parameters of the bending moment versus the relative rotation relation of concrete-encased CFST column to RC beam joints subjected to the combined loading and full-range fire,such as heating time,column load ratio,beam load ratio,steel ratio,strength of materials et al.,were investigated.The joint residual rotational stiffness indexes,joint residual loading bearing capacity indexes and deformation indexes after the combined loading and full-range fire were obtained corresponding to different parameters.Simpilified calculation methods for these indexes were proposed.