土木工程专业英语课件教学PPT作者陈瑛1.2.课件.ppt

1.2 Determinate and Indeterminate Structures 静定和超静定结构 Statically Determinate Structures Structures are said to be statically determinate when the forces and reactions produced by a given loading can be calculated using only the equations of equilibrium. Statically Determinate Structures The simply supported beam shown in Figure 1.3 is statically determinate. We can solve for the three unknown reactions using the equations of equilibrium and then calculate the internal forces such as bending moment, shear force, and axial force at any given location along the length of the beam. Statically Indeterminate Structures Four unknown reactions Three independent equilibrium equations Statically Indeterminate Structures Force Method 力法 The force method (also called the flexibility method) is used to calculate internal forces and reactions in statically indeterminate structures due to loads and imposed deformations. Force Method 力法 The steps in the force method 1．Determine the degree of statical indeterminacy of the structure. Parameter n will be used to denote the degree of indeterminacy. 确定超静定次数 The steps in the force method 2 Transform the structure into a statically determinate system by releasing a number of statical constraints equal to the degree of statical indeterminacy,n. The steps in the force method This is accomplished by releasing external support conditions creating internal hinges. The system thus formed is called the primary system. Number the released constraints from 1 to n. 3．For a given released constraint j, introduce an unknown redundant [ri5dQndEnt] force Xj corresponding to the type and direction of the released constraint. 多余未知力redundant force 基本体系沿多余未知力方向的位移应与原结构位移相同 4．Apply the given loading or imposed deformation to the primary system. Calculate displacements due to the given loading at each of the released constraints in the primary system. These displacements are called Δ1P , Δ2P , ΔnP .., . 5．For a given released constraint