Q. Explain about Vierendeel girder?

Vierendeel girder design is sometimes adopted in design of footbridges. Traditionally truss design, triangular shape of truss is generally used since the shape can't be changed without altering the length of its members. By applying loads only to joints of trusses, members of truss are only subjected to a uniform tensile or compressive stress across their cross sections since their lines of action pass through a common hinged joint. 

Vierendeel girder/truss is characterized by having only vertical members between the top and bottom chords and is a statically indeterminate structure. Therefore bending, shear and axial capacity of these members contribute to resistance to external loads. The use of this girder enables footbridge to span larger distances and present an attractive outlook. Though it suffers from the disadvantage that distribution of stresses is more complicated than normal truss structures.

Fig.Vierendeel Truss.