Experimental Study On Mechanical Performance Of Steel Fiber Reinforced Recycled Concrete Composite Two-way Slab

The prefabricated construction represents a new round of the scientific and technological revolution and the direction of the industrial transformation,which is not only a major changes in traditional construction and construction methods,but also an important measure to promote the structural reform of the supply side,and also a strong support for the new-type urbanization.It is significant to have a comprehensive and in-depth study of the laminated slab,which is an important part of the fabricated structure.Previously,research group has already studied the mechanical properties of 15 dimensional unidirectional laminated plates with different materials and structural forms.In order to improve the mechanical properties of laminated floors,enrich the laminated slab structure system and improve the theory of laminated floor theory,promote the application of green and renewable materials in the assembly building.Research group proposes a new-type of steel fiber reclaimed concrete reinforced steel truss two-way slab.In the paper,static loading tests of seven full-scale laminated two-way plates(including two precast floor)were carried out.A method for calculating stiffness,deflection,bearing capacity of two-way plates with different floor materials and structural forms is presented.On the basis of the experiment,the numerical model of the composite slab is established by ABAQUS,and the rationality of the numerical model is verified comparing with load deflection curves and failure modes of tests.Based on the extended analysis of the key parameters,the influence of the length,width and thickness of the steel truss on the mechanical properties of the laminated steel fiber reinforced concrete slabs is analyzed.The main contents of this paper are as follows:1.Four full-scale laminated two-way plate,two precast floors and one Concrete cast-in-place board were designed and manufactured.Static loading test on seven piecesof specimens were carried on.Two precast floors NPS-1、RPS-2 and two laminated plates NLS-1、RLS-2 are made of different materials: Ordinary concrete and steel fiber recycled concrete.3 of them have different structural forms,which are one-way steel truss,one-way bar truss-single concrete rib and two-way steel truss.The corresponding speciens are numbered RLS-2,RLS-3 and RLS-4.The test phenomena during loading are recorded in detail.The mechanical characteristic points,cracking,yielding and failure characteristics of each specimen are systematically analyzed.Contrastive analysis draws a conclusion: the performance of steel fiber recycled concrete is better than that of ordinary concrete which has obvious effect on reducing the crack development,improving the bearing capacity and the ductility of the speciens.Among the three different structural forms,RLS-4 have the best performance,then RLS-3 and the weakest RLS-2,which shows that the reinforcement truss plays a significant role in improving the performance of the specimen,which is better than the concrete rib.The performance of cast-in-place concrete slab is the worst,and the mechanical properties of bearing capacity,stiffness and crack width are weaker than those of steel reinforced truss composite plates.2.Based on the test results,the ABAQUS numerical model of seven pieces of specimens was established,and the correctness of the numerical model was verified by comparing the bearing capacity,stiffness,load deflection curve and concrete stress damage cloud map to the test results.Establishing an extended analysis based on the change of key parameters.The influence of the length of the steel truss and the thickness of the precast slab on the mechanical performance of the steel fiber recycled concrete composite two-way slab is compared and analyzed.The stiffness and bearing capacity of the composite floor decrease with the decrease of the length of the reinforcement truss.The stiffness and bearing capacity of the laminated floor increase with the thickness of the prefabricated floor,and the thickness of the prefabricated floor is the most significant.3.Combined with the latest research results of many scholars and formula for calculating the short term stiffness of a flexural member.By introducing stiffness correction coefficient,we can reasonably consider the influence of the adjacent strip constraint and the lattice reinforcement on the stiffness of two-way slab,then thestiffness calculation method of steel fiber recycled concrete composite two-way slab is put forward.Based on the basic assumption of yield line theory,the calculation formula of normal section flexural bearing capacity of steel fiber recycled concrete composite two-way slab is derived.By analyzing its crack resistance,a formula for calculating cracking load of composite floor is established.It is proved by the test results that the method presented in this paper is not only simple and accurate,but also provides a reference for improving the stiffness,bearing capacity of the reinforced concrete two-way slab in the current standard.