Brief overview of composite slabs and columns
Composite slabs contain reinforced concrete cast on top of profiled steel decking that functions as formwork all throughout construction and external reinforcement at the final stage.
• Comprise of profiled steel decking with an in-situ reinforced concrete topping.
• The decking (profiled steel sheeting) not only functions as permanent formwork to the concrete, but also arranges adequate shear bond with the concrete in order that when the concrete attains strength, the two materials function compositely side by side.
• Spacing should remain among 3 m and 4.5 m onto supporting beams or walls.
• When the slab is unpropped at the time of construction, the decking alone can withstand the self weight of the wet concrete and construction loads. Succeeding loads are implemented to the composite section.
• When the slab is propped, all of the loads should be countered by the composite section.
• The slabs are generally designed as simply supported members in the normal condition
Profiled steel sheeting:
• Depths vary from 45 mm to over 200 mm
• Yield strengths vary from 235 N/mm2 to minimum 460 N/mm2
• 0.8 mm and 1.5 mm thick
• The different shapes offer Interlock among steel and concrete
• Decking may also be applied to make the beams stable against lateral torsional buckling all through construction.
• Make the building stable entirely by performing as a diaphragm to transmit wind loads to the walls and columns.
• Temporary construction load generally governs the choice of decking profile.
Composite Columns: A steel-concrete composite column stands for a compression member that includes either a concrete encased hot-rolled steel section or a concrete filled tubular section of hot-rolled steel. The existence of the concrete is permitted in two ways.
• Protection from fire
• It is assumed to resist a small axial load
• Composite columns minimize the effective slenderness of the steel member that improves its resistance against axial load.
The bending stiffness of steel columns with H-or I-section is much higher in the plane of the web (‘major-axis bending’) than in a plane equivalent to the flanges (‘minor-axis bending’). The ductility performance of circular type of columns is considerably superior as compared to rectangular types. It is not necessary to arrange additional reinforcing steel for composite concrete filled tubular sections. Corrosion protection is arranged with concrete to steel sections in encased columns.
When local buckling of the steel sections may be detached, the cutback in the compression resistance of the composite column because of overall buckling should be permissible positively. The plastic compression resistance of a composite cross-section demonstrates the maximum load that can be implemented to a short composite column.