STATIC AND DYNAMIC ANALYSIS OF GRID BEAMS

DEFINITION: Interconnected grid systems are being commonly used or supporting building floors bridge decks and overhead water tanks slabs .A grid is a planar structural system composed of continuous members that either intersect or cross each other. Grids are used to cover large column free areas and have been constructed in number of areas in India n abroad. Is subjected to loads applied normally to its plane, the structure is referred as Grid . It is composed of continuous member that either intersect or cross each other .Grids in addition to their aesthetically pleasing appearance, provide a number of advantages over the other types of roofing systems.

ADVANTAGES OF GRID BEAMS

·         Grids are very efficient in transferring concentrated loads and in having the entire structure participate in the load carrying action .

·         Reduces the depth to span ratio of rectangular grids .

·         Reduction in depth ,towers ,structural and other cost by reducing the height of the building

LOAD DISTRIBUTION IN GRID BEAMS A load set on a cable or a beam is channelled to the support along the cable line or the beam axis, an arch ,a frame, and continuous beam produce the same type of “one –directional load dispersal”. These structures are labelled “one – dimensional resisting structures” because they can be described by a straight or curved line , along which the stresses channel the loads.  

If they are used to cover a rectangular area ,the system becomes impractical and insufficient. Grid beams structure are two way load dispersal system. When two identical ,simply supported beams at right angles to each other are placed one on the top of other and a concentrated load is applied at their intersection ,the load is transferred to the supports at the ends o both beams and dispersed in two way direction .Being identical they have same deflection and carry half the load .Thus each support reactions equal to one –fourth of load . In a planar frame structure ,joint displacement are considered as translation in X and Y direction and rotation about Z-axis .However when plane frame is normally loaded ,the displacement of joint are a translation in the Z direction and rotation X and Y axis .In grid connection ,the connection between the members are assumed to be rigid .When beams connected at mid span .It moves downward but remains vertical because of symmetry but when connection is not at mid span the beam rotates and deflects .The continuity introduced by rigid connection transforms the bending rotation of one section into a twisting rotation of other .A grid frame is considered as a special case of a rigid space frame in which the joint rotations may take place about all the three axes and joint displacements may have components along all the three axes.