**DEFLECTIONS IN DETERMINATE TRUSSES**Trusses comprise of members connected through pin joints. Truss members can thus transmit only axial forces (tensile and compressive forces). The basic difference in the behavior of a truss and a beam is that the

**truss comprises members that can sustain only axial forces but no bending moment or shear force**which are the dominant forces in the beam.

**analysis can be extended to indeterminate trusses as well.**Computations of

**displacements in trusses**are required quite often, especially in

**bridge structures**. Displacements in trusses are required not only for the final configurations but also during various stages of erection.

**Deflections can be due to self-weight, external loading, due to changes in temperatures of the truss members or due to a combination of these effects**.

**Method of computing Deflections in Determinate Trusses:**

The most general method of computing **displacements in trusses is by the virtual work principle**. Since a unit load (virtual load or dummy load that does not exist) is applied to the structure, this method is usually known as

**dummy load method or unit load method**. The displacement at any joint in a truss for a given loading can be determined by applying a unit virtual load in the direction of the required deflection at that joint. The displacement can be computed as

**Deflections are also possible due to changes in the length of members due to fabrication errors or changes in temperature.**In such cases, applying the principle of virtual work,