Lect14

CST Vs LST in FEM

1. Dr. A. S. Sayyad Professor & Head Department of Structural Engineering Sanjivani College of Engineering, Kopargaon 423603. (An Autonomous Institute, Affiliated to Savitribai Phule Pune University, Pune ) Finite Element Method In Civil Engineering Constant Strain Triangular Element (CST) CST Vs LST Linear Strain Triangular Element (LST)

2. Constant strain triangular (CST) element Three nodded triangular element is called as constant strain triangular element. Inside each element, all components of strain are constant; hence the name Constant Strain Triangle . Displacement field in terms of generalized coordinates 3. DOF per node: 02 ( u , v ), Total DOF: 06 Resulting strain field is

3. Constant strain triangular (CST) element The displacement function is linear. Strains and stresses are constant. The strains and stresses are NOT continuous across element boundaries Avoid CST in critical areas of structures (e.g., stress concentrations, edges of holes , corners ) In general CSTs are not recommended for general analysis purposes as a very large number of these elements are required for reasonable accuracy .

4. Linear Strain Triangular ( LST ) element Six nodded triangular element is called as Linear strain triangular element. Inside each element, all components of strain are Linear, hence the name Linear Strain Triangle . Displacement field in terms of generalized coordinates Resulting strain field is 3. DOF per node: 02 ( u , v ), Total DOF: 12

5. Linear Strain Triangular ( LST ) element This element is also called quadratic triangular element . The displacements functions are quadratic. Strains and Stresses are linear Quadratic elements are preferred for stress analysis, because of their high accuracy and the flexibility in modeling complex geometry, such as curved boundaries . For a given number of nodes, a better representation of true stress and displacement is generally obtained using LST elements than is obtained using the same number of nodes a finer subdivision of CST elements. For example, a single LST element gives better results than four CST elements.