In practice continuous lattice girders are mainly used to provide strength and rigidity for transient situations (such as in the case of erection) in floor plates and are incorporated
generally in the longitudinal direction (i.e. parallel to the span).
Current European standards force engineers to design (the bending ultimate limit state design) the floor slabs with lattice girders by applying EN 1992-1-1:2004 and considering the strength of different materials that constitute the composite slab (i.e. use the compressive strength of the cast-in-situ concrete). Since lattice girders used in semi-precast slabs have three-dimensional metallic structure comprising an upper chord, two lower chords and continuous diagonals which are welded to the chords, hence this results to increase the bearing capacity of the final slab.
Advantages of applied lattice girder in concrete beams can be summarized as follows:
· Higher Mechanical properties (Yield Strength, Ultimate Strength and Ultimate Elongation)
· higher resistant capacity due to the higher stiffness beyond cracking.
· low mid-span deflection.
The beams reinforced with lattice girders have three reactions against the applied load. The two reactions come from concrete and longitudinal reinforcement in bending. The third one is from the lattice girders which behave as truss elements. Truss behavior introduces higher stiffness and contributes much to the load carrying capacity.
