ường hầm vỏ hoạt động dọc theo môi trường đàn hồi, được coi là siêu hệ thống tĩnh với cao cấp và phức tạp. Tính toán của hệ thống này trong trường hợp chung: đường hầm vỏ có nhiều loại hình dạng, độ dày của vỏ đường hầm được thay đổi bởi trên thực tế điều kiện làm việc và chúng tôi không thể hiển thị yếu tố này trong thực tế để tính toán. Do đó, để xác định các lực lượng phần, chúng ta có thể sử dụng phương pháp gần đúng, được gọi là: phương pháp thay thế cho thanh hệ thống. | TAÏP CHÍ PHAÙT TRIEÅN KH&CN, TAÄP 11, SOÁ 05- 2008 COMPUTE AND DEFINE EXACTLY THE REGION OF ELASTIC REACTION FORCE FOR CALCULATING THE SECTION FORCE OF UNDERGROUND CONSTRUCTION BY FINITE ELEMENT METHOD Nguyen Quoc Tuyen, Le Van Nam University of Technology, VNU-HCM OUTLINE OF COMPUTING THE UNDERGROUND CONSTRUCTION BY THE METHOD OF REPLACING TO BAR SYSTEM Tunnel shell works along surround the elastic environment, which is considered as the super static system with high grade and complex. The computation of this system in general case: tunnel shell has many type of shape forms, the tunnel shell’s thickness is changed by in fact working condition, and we can not show these factor in fact for calculation. Therefore, to define the section forces, we can use the approximate method, called: the method of replacing to bar system. Principles of this method: - Replacing the continuous curve of tunnel shell’s structure by polygonal line segment. - Each line segment’s stiffness (EF) is considered as constant. - Replacing the distribute load of stratum pressure q and p by the concentrate load at nodes at point of polygonals. The tunnel shell’s seft weight is also replaced by concentrate load at the beginning and end point of bar. - The elastic environment is replaced by elastic bearings setting at point of polygonals which direct to curve’s radius. q x x o a b k α1 1 X1 a 2 α3 2 3 p o Xo c 2ϕο α2 1 b k c a X2 3 X3 4 y X4 4 y Figure elastic foundation model ELEMENT STIFFNESS MATRIX The most basic point in solving the underground structure problem by finite element method is building the element stiffness matrix. Then assembling the element equations based on the continuous conditions, the boundary conditions to make the system of equation and next step is solving this system of equation. The beam element on elastic foundation: Contains the modulus of elasticity E, the cross section area A, the moment of inertia I, the spring stiffness
