What makes a truss statically determinate

Since a statically determinate truss cannot have more members than the number required for stability, it is not a fail-safe structure.

This means that if one member of the truss were to fail, then the truss will collapse. This is a major reason for introducing redundant members in truss structures, especially when public safety is of primary concern. Key Observation Since a statically determinate truss cannot have more members than the number required for stability, it is not a fail-safe structure. Subscribe to: Post Comments Atom. Blast Resistant Design. Construction Management. Construction Materials.

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The beam shown in figure 3 a is statically indeterminate to one degree because there are three unknown reactions and statics has only two reactions. The beam in figure 3 b is statically redundant to two degree. The beam in figure 3 c is redundant to three degree and the beam in figure 3 d is redundant to four degrees. A portal frame is statically determinate if there are only three external reactions, because there are three conditions of equilibrium for such a system.

The portal frame shown in figure 4 are statically determinate because there are only three reactions to be determined. If a portal frame has more than three reactions it is statically indeterminate, the degree of indeterminacy or redundancy being equal to the number of redundant or extra reactions to be determined.

Therefore, the portal frames of figure 5 a and b are redundant by one degree, that of figure 5 c is redundant by two degrees, that of figure 5 d is redundant by three degrees, and that of figure 5 e is redundant by 5 degrees.

The statically indeterminate beams and frames can be analysed by strain energy method, three moment equation, slope deflection method or moment distribution method.

A truss having more than 2j — 3 members is statically indeterminate or redundant, the degree of indeterminacy or redundancy being equal to the number of extra members. Thus the truss shown in figure 6 a is statically redundant by one degree because there are 14 members and 8 joints.

The internally indeterminate trusses can be analysed by strain energy method. The truss shown in figure 7 is externally indeterminate to one degree because the numbers of reactions to be determined are three, and the conditions of equilibrium reduces to two, namely.

This truss is also internally indeterminate to one degree because there is one extra member. Your email address will not be published. Skip to content Home. Statically Determinate and Indeterminate Structure. Indeterminate Structures A structure is termed as statically indeterminate, if it can not be analysed from principles of statics alone, i. A statically indeterminate structure may be classified as: Externally indeterminate, example: continuous beams and frames shown in figure-1 a and b.

Internally indeterminate, example: trusses shown in figure-1 c and d.