| Composite slab floor systems consisting of structural concrete and cold-formed profiled steel sheeting are widely used in steel framed buildings due largely to the reduction of self-weight and simplification of the construction process.The composite action between concrete and steel sheeting interface is crucial to the failure mode and deformability,which is strongly dependent on the type of basic materials used in construction including geometry of the steel sheeting,category of the concrete,length of the span as well as the end-anchored condition.The longitudinal shear bond failure is reported to be the most common failure mode in composite slabs;significant end slips are reported to occur between concrete and profiled steel sheeting interfaces well ahead of reaching its ultimate bending capacity.Therefore,research on the longitudinal shear resistance of composite slab becomes an important part of this field.The theoretical basis of longitudinal shear resistance was summarised and extended as the first part of this study.In addition to m-k method and Partial Shear Connection method(PSC)method,which are typically used for composite slabs with normal weight concrete,three other techniques such as shear-bond slenderness method,force equilibrium method and PSC composite beam method were developed and compared.Optimizations on basic material components were proposed to further reduce the structural self-weight.This paper presents full-scale experiments conducted on a new type of composite slab produced from expanded shale lightweight aggregate concrete and closed-type profiled steel sheeting.A total of 11 simply supported specimens were tested to investigate the structural behaviour of this new type of composite slab with special emphasis on their failure modes and longitudinal shear resistances.Shear bond failure was reported to be the most common failure type along with significant end slips were observed in long-span slabs.All tested slabs exhibited excellent behaviour of composite actions.The ultimate carrying capacity and the shear bond stress predicted using m-k method,slenderness method,PSC method and force equilibrium method showed very good agreement with test results;PSC composite beam method may underestimate the longitudinal shear bond strength,but still can be used as an optional method.Optimizations on structural compositions were proposed for the purpose of improving the cracking resistance and the overall performance of composite slabs.High-molecular polymer fibres as long as a new laminated pouring technique were introduced.Rational modifications on theories of longitudinal shear resistance were then proposed to include the effects of concrete in tensile zone due to the reinforcement of fibres.Based on the purpose of improving the anti-cracking resistance,a new type of composite slab using the laminated pouring technique produced consisting lightweight aggregate concrete,polypropylene fibre lightweight aggregate concrete and closed-type steel sheeting profile were tested.Results from a total of 10 simply supported specimens indicated the enhancement of anticracking resistance as a result of polypropylene fibres in tensile zone,whilst the reinforcements on ultimate load carrying capacities were ignorable.Shear bond failure dominated the failure mode,and traditional theories yielded reasonable results on predicting the longitudinal shear resistance of this new type of composite slab,especially using PSC method and force equilibrium method.Based on the purpose of improving the ultimate carrying capacity,this paper further presents a series of full-scale tests conducted on a new type of laminated composite slabs produced using both lightweight aggregate concrete and Rimix fibre reinforced lightweight aggregate concrete along with closed-type steel sheeting profile.A total of 12 simply supported specimens were tested to investigate the structural behaviour of this new type of composite slab with special emphasis on the lamination thickness,failure modes and load carrying capacity.Test results were used to obtain an effective range for the laminated pouring technique.It was observed that plane cross-sections remain plane in slabs and the longitudinal shear resistance dominated the failure mode regardless of lamination thicknesses.Proposed linear regression methods and PSC based methods using modified theories yielded reasonable results on predicting the longitudinal shear resistance of this new type of composite slab.Further rational modifications and relevant formulas for the specified configurations including the effects of tensile reinforcement have been proposed.Results predicted using the proposed analytical techniques were compared those obtained experimentally,and the comparison showed good agreement. |
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