Study On Ground Pressure Distribution Of Large Crawler Grane And Its Engineering Application

To ensure the safety and economy while hoisting components with crawler crane during process of construction,it is important to determine the ground pressure correctly.The existing calculation model has greatly simplified the pressure distribution under the crawler track,and the influence of its own fuselage structure is not taken into consideration.Thus the calculated ground pressure ratio often differs greatly from the actual value,and may have potential safety hazard or even cause safety accident when it is adopted to guide the hoisting operation.Aiming at the deficiency of the traditional calculation model,a new calculation model,elastic foundation calculation model,is proposed through analyzing the basis structure of the crane and considering the form of force received by the crane on the elastic foundation;the track frame on the elastic foundation is simplified into the multi-span continuous beam with spring support,a new method called “five-moment equation” suitable for solving the end reaction,i.e.the track roller reaction force of the crawler crane,is derived.The track shoe is simplified into rectangular plate with four free edges on the elastic foundation,and Winkler foundation model is adopted to obtain the ground pressure.A software coded with MATLAB is developed to make the calculation more efficiently.The FEM model of frame-track frame-track roller system is established,and the influence of various factors on the reaction force distribution of the track roller is discussed.The analysis result indicates that when the stiffness of the foundation is relatively small,the reaction force of the track roller shows non-linear distribution when the crane is under the action of symmetrical load,and the maximum value appears at the track roller near the ear plate;under the eccentric load,the distribution of the reaction force of tract roller shows the shape of polylines.With the increase of the foundation stiffness,the reaction force of the track roller near the ear plate are increased,and the reaction forces at both ends of the frame are gradually reduced.The FEM model of the track roller-creeper tread and elastic foundation system is established,and the influence of multiple factors on the contact pressure under the creeper tread is discussed.The analysis shows that,the load of the track roller only has influence on the creeper tread in the range of the adjacent track rollers;and the maximum contact pressure under the track shoe increases with the increase of soil stiffness.To meet the project practice needs,the special situation of crawler crane operation on raft is analyzed,and the measures to increase the partial pressure ratio by sand cushion are put forward.FEM models of welded grillage slabs-sand cushion-raft system are established to explore the factors that affect the partial pressure effect.The analysis shows that,laying the sand cushion can reduce the ground pressure of the raft surface effectively;and increasing the thickness of the sand cushion can improve the partial pressure effect,which,however,will no longer change when the thickness is increased to above 30 cm.The recommend thickness of sand cushion is suggested.