Damage Identification Of Reinforced Concrete Axial And Eccentric Compression Columns After Fire Based On Modal Measurement

Fire is one of the most frequent natural disasters in human life.More than 200,000 fires occur every year in China,and more than half of them are construction fires.Unlike the fire damage phenomenon of other structures(wood structure,steel structure,etc.),reinforced concrete structures rarely suffer from complete damage or collapse after fire.Therefore,to study the damage identification and repair and reinforcement technology of building structures after fire,it is of great economic value and social benefit to find an effective and applicable structural damage identification and evaluation method for structural members.At present,structural damage identification technology based on dynamic characteristics has received a lot of attention,and it has been widely applied and matured in the fields of machinery,aeronautical engineering and bridge structure.The damage identification of reinforced concrete structures after fire based on dynamic characteristics is mainly concentrated on beam-slab members,and the research on reinforced concrete columns is less.Based on the design principle of “strong column weak beam”,the column is the most important component in the structure,and its damage may cause the overall collapse of the building structure.Therefore,it is of great significance to study the damage identification of reinforced concrete columns after fire based on dynamic characteristics.The main work done in this paper is as follows:(1)Through the literature to understand the high temperature thermal and mechanical properties of steel and concrete materials,the influence of the change of thermal parameters of materials and the deterioration of mechanical properties on the physical properties of the structure is analyzed,so as to understand the temperature field,physical properties and dynamic fingerprint of reinforced concrete structures.The relationship provides a theoretical basis for the subsequent fire damage identification study of reinforced concrete columns.(2)The fire test was carried out on the designed reinforced concrete axial center and eccentric compression column specimens.Through the observation of the apparent phenomenon after the fire of the test piece and the analysis of the test data,the reinforced concrete axial center and the eccentric compression column were studied.The difference between the temperature field and the depth of damage.(3)Before and after the fire,the modal measurement tests were carried out on the reinforced concrete axial and eccentric compression column specimens,and the modal parameter changes of the specimen were obtained.The reinforced concrete axial center and the eccentric compression column dynamics were analyzed after the fire.Differences in characteristics.(4)The static load test was carried out on the reinforced concrete axial center and the eccentric compression column test piece and the normal temperature comparison column test piece after the fire,and the bending rigidity reduction range of the reinforced concrete axial center and the eccentric compression column after the fire was analyzed.And the degree of load reduction.(5)Based on the change of the mode shape parameters of the reinforced concrete column specimen after fire,the damage position of the reinforced concrete axial center and the eccentric compression column specimen was identified by the coordinate modal confidence criterion COMAC.(6)By analyzing the relationship between the frequency change rate of reinforced concrete axial and eccentric compression column specimens before and after fire,the relationship between high temperature damage depth,stiffness reduction and bearing capacity reduction,based on modal frequency parameters for post-fire reinforcement The degree of damage of the concrete column specimens was identified.(7)According to the damage identification of reinforced concrete axial and eccentric compression column specimens after fire,with reference to relevant standards and literatures,a reinforced concrete axial center based on modal vibration mode and modal frequency is proposed.Eccentric compression column damage identification and evaluation method.