Study On Safety Evaluation Of Column Replacement By Joist In High-rise Building

With the vigorous development of China’s economic construction,the construction industry has also made considerable progress,but at the same time,all kinds of construction accidents are endless.At the same time,some existing buildings have reached or will reach the service life,and some structures or components will not be able to meet the bearing capacity requirements.Therefore,it is necessary to reinforce and reconstruct the problematic or defective buildings.As an important measure in the reinforcement technology,the underpinning technology is in response to the requirements for the construction industry in the national dual carbon target and in line with the new requirements for green building development put forward by the State and Gansu Province.But for high-rise buildings,the change of beam and column has a great risk of safety,from the initial simulation,the pressurization of jacks,the truncation of old columns,the cast-in-place of new columns and so on,it will cause the collapse of buildings and cause great losses to people’s lives and property.In order to better manage and control the safety status of high-rise building beam replacement column construction process,accident cause theory and grey theory are used to analyze the safety status.First of all,based on a large number of references and relevant standards and specifications(mainly including the Work Safety Law of the People’s Republic of China,Work Safety Licensing Regulations,and Construction Safety Inspection Standards),and in combination with the construction technical points of beam support and column replacement(mainly including: floor opening,steel tube support installation,steel cushion beam processing,jack installation,jack unloading,steel cushion beam temporary support,concrete replacement,replacement column concrete removal,reinforced concrete column reinforced steel construction,reinforced concrete column template installation,grouting construction,template removal and stacking,etc.),as well as the circular of the General Office of the Ministry of Housing and Urban-Rural Development on the work safety accidents of housing municipal engineering in 2020,the main types of safety accidents in the circular mainly include five types,such as falling from high places,object strike,lifting injury,collapse accident,mechanical injury,etc.,and other types of safety are relatively few,and mainly focus on electric shock.Based on seven principles,namely,simplicity,scientificity,feasibility,representativeness,comparability,independence,and combination of quality and quantity,this paper preliminarily constructs the evaluation index system for the construction safety of beam and column replacement of high-rise buildings,determines 44 initial indexes,optimizes and screens the indexes through questionnaire survey and expert evaluation,and finally forms five first-grade indexes,namely,the influence factors of personnel,articles,technical management measures,management system and environment.From the operator,the scene commander to the building own condition and so on 13 secondary targets.From the post qualification,operating capacity,building inclination,uneven settlement,wall column cracks,beam cracks,foundation cracks and other 43 tertiary indicators.Secondly,in view of the poor objectivity of subjective weighting method,the objective weighting method is used only to determine the index weight,which sometimes deviates from the actual situation of the index and leads to the deviation of the index weight.AHP and entropy weight method are used to assign weights,and the comprehensive weights of each index are determined by the principle of minimum information entropy.Then,through the grey clustering theory,the safety evaluation model is established.The smaller the index is,the better the function is.The bigger the index is,the better the function is.At the same time,7 qualitative indices are evaluated according to the measured data,36 quantitative indices are evaluated according to the results of expert scoring.Finally,taking a high-rise project under construction as an example,the grey clustering model is used to evaluate the safety grade of the project,and the safety risk grade of the project is Grade II,that is,"relatively safe".The safety grade of the whole project is relatively high.However,there are still some indexes in the evaluation result with low evaluation value.There are 8 indexes of medium safety in Grade III indexes,which are mainly in the aspects of on-the-spot commanders,installation of jacks,safety management system and on-the-spot construction environment method.These aspects need to be further improved and promoted,and the safety of buildings shall be increased.There are 3 indexes of relatively dangerous,and the influence of general safety on buildings shall be very great,and these indexes shall be strictly controlled near the dangerous edge.These indexes mainly include the installation of steel bars,the fastness of nodes of templates,and the safety production responsibility system.The corresponding control measures are given for these three indexes.