This document compares the constant strain triangular (CST) element and the linear strain triangular (LST) element in finite element analysis. It states that the CST element has constant strains inside each element but strains are not continuous across boundaries. In contrast, the LST element has linear strains inside each element and is preferred for stress analysis due to its higher accuracy. The document recommends using LST elements over multiple CST elements for better representation of stresses and displacements.

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
1. Three nodded triangular element is called as constant
strain triangular element.
2. 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
4. The displacement function is linear.
5. Strains and stresses are constant.
6. The strains and stresses are NOT continuous across
element boundaries
7. Avoid CST in critical areas of structures (e.g., stress
concentrations, edges of holes, corners)
8. 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
1. Six nodded triangular element is called as Linear
strain triangular element.
2. 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
4. This element is also called quadratic triangular
element.
5. The displacements functions are quadratic.
6. Strains and Stresses are linear
7. 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.