Safety Analysis Of A Frame Building With Cracks Caused By Additional Equipments

A main part six-floored and part five-floored concrete frame structure of a university in Dalian was transformed by setting up two tanks and three units at the roof five years ago.Nowadays.a mass of cracks was found in the rooms of fifth floor.In this paper,through the field survey and theoretical calculation simulation.explore the reason of cracking and evaluate the safety of the building.In view of these problems to carry out the following aspects of the work,the main contents of the study include:(1)This paper introduced the general situation of the building structure,and the layout of the roof size and additional equipments.Measured roof additional equipment layout and determined additional equipment load.cracks generated by the length of the general situation of housing and distribution of field measurements,crack depth measuring instrument and crack width measuring instrument used to measure the depth and width of cracks,and draw the schematic diagram of the distribution of the fracture.The length and distribution of the crack were measured in the field.The depth and width of the crack were measured by the crack depth measuring instrument and the crack width measuring instrument.Through the comparison of the depth and width of the wall crack,it is concluded that the crack of the second beam is more serious.(2)This paper mainly introduced the established material and cross-section model parameters.According to the characteristics of the structure,the unit is modeled according to the condition of the structure.Two kinds of load conditions were applied to the model.Case I is the original design load,that is,not including the roof of additional equipment load.Case II is the full load.The deformation analysis of the whole structure and the secondary beam under two working conditions are carried out.The strength analysis of the whole structure.the second beam and the wall under the second beam under the two cases.Compared the first principal stress of the secondary beam before and after loading,bending moment of secondary beam and the third main stress of the second beam under the wall.Through bending moment calculation,the maximum stress of the second beam has exceeded the cracking strength of concrete.Finally,the strength of the structure is evaluated comprehensively,and the cracking of the secondary beam is obtained.The stress of the wall under the second beam exceeds the design value,and the crack is produced.(3)Three models of finite element analysis of reinforced concrete structures are introduced.which are the integral model.the separate model and the combined model.The constitutive relation and constitutive model of concrete and steel bar are introduced.In order to make the analysis result more accurate.considering the coupling effect of the reinforced concrete,the finite clement model of the five floor is established by the method of separate modeling.After the strength analysis and deformation analysis.compared the analysis results of the two models.It was found the analytical results of the separation model are basically consistent with the results of the analysis of the isotropic.It is concluded that the main reason of the crack is caused by the deficiency of bearing capacity.(4)ANSYS is used to carry on the modal analysis and the steps.the modal analysis is carried out.the 70 order natural frequencies and modes are obtained,and the natural frequencies are compared before and after the loading.This paper describes the content and principle of dynamic test.the dynamic signal acquisition and analysis system is used to test the vibration of building structure under the working condition of additional equipment,and finally the data analysis is carried out.From the results of the data analysis,there is not much correlation between the crack and the vibration of the five floor and the wall.