Behaviour of steel-concrete-steel sandwich composite beams with lacing subjected to reversed cyclic loads

Steel-concrete-steel (SCS) sandwich composite system consists of steel plates covering both sides of the concrete core and connected by mechanical means such as shear connectors. In conventional steel-concrete-steel system, shear connectors are welded to the steel cover plates. Laced steel-concrete composite (LSCC) system is a new form of steel-concrete-steel, proposed earlier by the authors. In LSCC system, steel cover plates are connected in a novel way using lacings and cross rods and hence is devoid of welding. Proposed sandwich composite system is being evaluated systematically for its structural behaviour under various modes of loading for use in special structures under severe loading such as blast loading. Damage under cyclic loading and energy absorption are extremely important, which are highlighted in this paper. An experimental investigation on the cyclic response behaviour of two LSCC beams is carried out. Angle of lacing is the parameter that is varied between the two beams. Both the beams are found to exhibit similar behaviour on most of the aspects. The envelope of hysteretic response indicates mild softening behaviour after reaching peak value. Maximum load resisted under both sagging and hogging moment conditions is found to be nearly equal, thus making the LSCC system suitable for situations where reversal of loads are encountered. Dissipated energy is observed to be nearly the same for the load applied in the upward as well as in the downward direction. Analytical prediction on energy absorption capacity is carried out by adopting a hysteretic model with strength deterioration. Cyclic ductility factor is evaluated to be about 20 for LSCC beams, while support rotation is calculated to be about 8 degrees and 10 degrees for beams with 45 degrees and 60 degrees angles of lacing, respectively. Spalling of concrete is prevented in LSCC beams by the steel cover plates.