Strength Performance Analysis Of Concrete Wet Shotcrete Telescopic Boom

Shotcrete support is one of the three pillars of NATM technology system in tunnel and underground engineering.It is widely used for its simple technology,timely support and low cost.Shotcrete mixes concrete mixtures in a certain proportion into the hopper of the wet sprayer.The mixtures are conveyed to the nozzle along the pipeline by the wet sprayer.The high-speed jet is formed by compressed air in the nozzle.At the same time,the accelerator is added to fill the special concrete by slurry jet and the aggregate is impacted and compacted.The spraying technology has three kinds: dry spraying,tidal spraying and wet spraying.The wet spraying technology has the technical and economic advantages of reducing dust,reducing springback and ensuring quality,so it has been widely applied.With the social development and technological progress,shotcrete has basically realized mechanized construction.The key equipment for mechanized construction of shotcrete is the wet shotcrete unit,and the boom is the key component of the wet shotcrete unit.Whether the structure is reasonable or not directly affects the performance of the unit and the accuracy of the end operation(nozzle trajectory).Because the working environment of wet jet unit is very complex,and the boom is a typical multi-input,multi-output,highly non-linear and rigid coupling complex multi-body system,the dynamic response characteristics of the boom restrict the performance of the whole machine to a certain extent,so the research has practical significance.Through research,it is found that the main cause of structural failure is fatigue failure.When the mechanism suddenly accelerates,decelerates or rotates,a transient impact load will occur,and the vibration of the mechanism will be inevitable.At this time,the strain amplitude and the stress amplitude will appear correspondingly.If the strain amplitude and the stress amplitude will exceed a certain value.The boundaries will cause fatigue failure in the organization.In order to study the dynamic performance of the mechanism at this moment,the Rayleigh damping coefficient must be known.Its frequency range is obtained by modal analysis,and then it is calculated accordingly,and the mechanism vibration is considered.The effect of the frequency range.After analyzing the transient dynamics of the structure,the vibration response of the structure subjected to the impact load is obtained,and it is used as the load spectrum.The fatigue life of the structure is calculated by the fatigue analysis software FE-SAFE.After analyzing the structure of the fatigue life,we can find that the selected calculation method is different,the average stress correction method is different,and the fatigue life is different,so we should consider the application of the formula when we choose,so that we can get Reasonable structure.After studying the influence of the fatigue life of the structure on the damping ratio,we found that there is a linear relationship between the fatigue life and the damping ratio in the logarithmic coordinate system.In the case of initial cracks in the structure,we usually use the damage tolerance method to calculate the fatigue life of the structure.The expressions of stress intensity factor and fracture toughness can be obtained by referring to some relevant manuals and materials.Then the fatigue life of the telescopic arm upper cover plate under the action of alternating load can be calculated with the application of Paris formula under the condition of initial crack.