Local Buckling of the Steel Skin in Lightweight Composites Induced by Creep and Shrinkage

“Lightweight composites” are a form of steel-concrete composite construction in which a skin of thin steel sheeting is juxtaposed with a concrete core. Examples include composite profiled slabs, beams and walls. Bond between the concrete and steel is achieved by transverse shearing stresses that are induced by mechanical shear connection through embossments in the sheeting ribs. Because the sheeting is thin, it has a propensity to buckle locally between the ribs, and this mode of buckling represents a contact problem as the buckling mode must be unilateral. Under a sustained load, the concrete creeps and shrinks, and sheds compressive stresses into the steel sheeting. In the time domain, these stresses may be large enough to precipitate local buckling of the steel. This paper considers an analytical model in which a concrete core is reinforced by a permanent and integral skin of thin-walled steel shuttering that acts compositely with the concrete, and is subjected to constant sustained stress which would be typical of a composite profiled wall. It is shown theoretically that, in the time domain, the stresses induced in the sheeting by creep and shrinkage may indeed precipitate elastic local buckling of the steel.