Study On Mechanical Properties Of Steel Box Girder Based On Remote Intelligent Health Monitoring

Box girder bridges have the characteristics of short construction cycle and high degree of prefabrication,especially for projects with high construction period requirements,and the monitoring of engineering safety is crucial.Based on this,this paper takes a grade separation bridge as the background and builds an intelligent monitoring system for steel box girder on the basis of summing up the research results at home and abroad;based on the intelligent monitoring data,analyze the stress of the steel box girder at different construction stages,and verify the finite element model.Through the results of finite element analysis,it provides guidance for the next construction to ensure the smooth construction progress.The main research and conclusions are as follows:1.Building a refined finite element model of fish-belly steel box girder section.Based on the actual engineering conditions and the structural characteristics of the steel box girder,determine the monitoring parameters,the layout of the measuring points and the monitoring scheme,and establish a remote intelligent health monitoring system for the steel box girder.The instrument installation and on-site debugging results show that the installed acquisition instrument operates normally and meets actual engineering requirements.2.Lo Ra is used as the node gateway for various types of sensor data transmission,and the monitoring data volume of each sensor node is networked and packaged,and sent to the platform through wireless 4G technology.Set up a sensor subsystem and a data transmission subsystem to provide strong technical support for later data analysis.3.Based on time span,construction phase,different components,and external environmental conditions,the site monitoring data is divided into different working conditions and discussed.In the initial stage of construction,which the effect of the load on the bridge deck is small,the steel box girder has a stress distribution state of up and down pressure and the average top stress of upper roof is 10 MPa.Compared with the upper roof,the bottom roof is affected by the constraints of the support and cannot be deformed freely,thereby generating compressive stress;with the increase of the construction load,a common state of upper and bottom stress occurs.The pressure value of the upper roof is within 70-80 MPa,and the tensile force value of the bottom roof is within 60-70 MPa.In the process of removing the temporary support,the change in stress value of the middle bin is small,and the change of stress value of the bins on both sides is large.The whole steel box girder has sufficient safety reserves,and the construction safety is high.The results show that during the construction phase,necessary monitoring and control work needs to be implemented.4.Based on monitoring stress and temperature,different parts of the steel box girder are analyzed at different times.It is found that the daily temperature of the upper roof changes greatly,and the highest daily temperature difference is about 30 ° C;the temperature of the bottom roof changes little and is close to the outside temperature.The change in temperature is positively related to the change in stress on the upper roof and negatively related to the bottom roof;When the temperature rises by 6?,the compressive stress on the upper roof can reach 30 MPa.The results show that structural stress changes caused by temperature changes cannot be ignored.5.A partial improvement method for the finite element model based on the measured temperature.The numerical analysis of the stress value is in good agreement with the measured value;Based on an improved finite element model,it reveals the force,deformation and stress distribution of steel box girder.It is found that when the steel box girder reaches the design deformation limit of 0.1m,the average stress of the upper roof is-130 MPa,the average value of the bottom roof is 91.52 MPa,and the average stress at the support is-180.47MPa;When the steel box girder reaches yield,the deflection in the mid-span reaches 0.36 m.Numerical simulation results show that when the steel box girder reaches the design deformation limit,there is still a large distance from the yield limit,and it has a certain safety reserve.The analysis results can also be used as a basis for setting the pre-alarm value in the structural health monitoring system.