Study On Mechanical Properties Of Composite Thick Slabs And Joints

The underground utility tunnel is a public tunnel of urban pipelines,which integrates various municipal pipelines such as water supply and drainage,gas,electric power,communications,etc.Nowadays composite prefabricated utility tunnel is one of the main construction methods.Relying on a composite prefabricated utility tunnel project,the side walls and slabs of the utility tunnel are assembled in the form of composite slabs on the construction site.Prefabricated composite structure has the characteristics of fast construction efficiency,small environmental impact and low labor cost.In this paper,the mechanical properties of the prefabricated truss composite slabs in the composite prefabricated utility tunnel are studied,which can provide a reasonable reference for the design and construction of the composite slabs.Specific contents are as follows:(1)Experimental study on the shear capacity of composite interface in composite slabs.In this paper,the influence of cross-section area and reinforcement ratio on the shear capacity of the composite interface is studied through the shear test of nine different composite slabs.During the loading process of the shear specimens,the slip of the composite interface is very small.While reaching the ultimate load,the composite surface will rub and cause brittle failure of the structure.On the basis of the test results,the design methods of the shear capacity of the composite interface in different national codes are compared and analyzed.The results show that the bond force is the main control factor of the shear resistance of the compositeinterface,and the reasonable treatment of the composite surface can meet the requirements of the code and the actual use.(2)Experimental study on shear capacity of composite concrete slabs.This paper studies the influence of slab thickness,longitudinal reinforcement ratio and nominal reinforcement ratio of truss reinforcement on the shear capacity of composite thick slab through 3-point shear tests of 12 prefabricated composite slabs and 3 monolithic slabs.At the initial stage of loading,the deformation of the composite thick slabs increases linearly with the increase of load,and the rigidity of the specimen decreases with the appearance of inclined cracks.At the final stage of failure,the shear cracks expand along the loading point and the support.Compared with the calculation results of shear capacity of reinforced concrete beams in domestic and foreign codes,American codes have better applicability in the calculation of shear capacity of composite slabs.(3)Experimental study on flexural capacity of thick composite concrete slabs.In this paper,nine prefabricated truss composite slabs are designed and compared with three monolithic pouring slabs to study the influence of the thickness ratio of prefabricated plates and the reinforcement ratio of longitudinal bars on the ultimate bending capacity of composite plates.In the loading process,the composite slabs experiences elastic stage,elastic-plastic stage and plastic stage respectively,which has the same bending resistance as the cast-in-place slab.Through the comparison of 4-point bending test results and the calculation results of the code,it is verified that the bending performance of the prefabricated composite slabs can be equivalent to that of the monolithic cast-in-place concrete slab.(4)Experimental study on the flexural capacity of the thick concrete slabs with joints.In this paper,5 WJV and 4 WJH jointed composite slabs are designed.In the whole test process,the deflection changes of the two kinds of joints are very small.With the increase of load,the linear growth,the ultimate failure is brittle failure,which is sudden.The test results show that the existence of the joint reduces the bending capacity and deformation capacity of the composite slabs.The calculation of the bending capacity of the WJH type joint should not be included in the height of the laminated plate.It is suggested that the length of the anchorage bar should be lengthened for the WJV type joint.