Difference between Determinate and Indeterminate Structure

A determinate structure is structure in which the unknown external reaction or internal components may be determined only by the equilibrium conditions whereas an indeterminate structure is structure in which the unknown forces cannot be identified just by static equilibrium conditions.

It will necessitate a study of the compatibility conditions of various elements of the structure for a thorough analysis.

Here are some of the main differences between determinate and indeterminate structures to help you understand how both differ:

Determinate Vs Indeterminate Structure:

Determinate Structure:

A statically determinate structure is the structure in which the responses at the supports and internal forces in the members may be determined by static equilibrium requirements.

A structure that is statically definite is neither better nor worse than a system that is statically indeterminate.

They may be stronger or weaker based on the options of the two systems.

Indeterminate structure:

A statically indeterminate structure is the structure in which statically equilibrium cannot define the reactions at the supports and internal forces in the members.

 A statically indeterminate are as follows:

Continuous beams and frames are two examples of externally indeterminate structures.

Trusses are an example of an internally indeterminate structure.

Trussed beams and continuous trusses are both externally and internally indeterminate structures.

The indeterminate structure has lower stresses than determinate structure.

Due to increased stiffness, indeterminate structures have less Deflection.

A statically indeterminate structure can be used to disperse loads.

If a component (or member or support) of such a structure fails, the entire structure does not necessarily collapse, and the loads are shifted to nearby components of the structure.

What is Difference between Determinate and Indeterminate Structure?

Determinate structures are analysed by using only simple equilibrium equations whereas Indeterminate structures cannot be analysed using only fundamental equilibrium equations.

Let’s discuss the difference between them as follows:

Determinate structure	Indeterminate structure
Equilibrium conditions are adequate to identify unknown forces and moments.	Equilibrium conditions are insufficient to identify unknown forces and moments.
The bending moment or shear force at any segment is unaffected by the material qualities of the structure.	The qualities of a material determine the bending moment or shear force at any section.
At every location, the bending moment or shear force is independent of the cross-section or moment of inertia.	The cross-section or moment of inertia determines the bending moment or shear force at each point in space.
In this determinate structure, temperature changes do not induce stress as compared to the indeterminate structure.	Temperature changes create stress.
There are no strains as a result of a lack of fit.	Stress is induced by an inability to fit.
Additional requirements such as displacement compatibility are not necessary to examine the structure.	Additional requirements, such as displacement compatibility are necessary to examine the structure in addition to the equilibrium equations.
Determined structures include simply supported beams, cantilever beams, single and double overhanging beams, three-hinged arches, and others.	Indeterminate structures include fixed beams, continuous beams, fixed arches, two-hinged arches, gates, multistorey frames, and others.

Also read: Moment Frame | Types of Structures | Shear Wall

Conclusion:

The determinate structure has just enough limitations and restraints to keep them stable and in static equilibrium, while the indeterminate structure has constraints and restraints that make them overly stable.

The equilibrium equations cannot aid in the determination of force in each member because they do not provide any rule for the distribution of forces in members that exceed what is required to maintain equilibrium.