Study On Mechanical Behaviors Of Joint Of Prefabricated Reinforced Concrete Beam And Slab Containing Demolished Concrete Lumps

Prefabricated floor slab is in line with the development trend of building industrialization and has an advantage of fast construction speed.However,after transporting to construction site,it often needs to be fully supported,making the construction procedure time-consuming and laborious.In order to solve this problem,a new type of connection method of precast concrete floor slabs and prefabricated beam is proposed in this paper,which tries to reduce or even completely cancel the bottom support of the slab while meating the need of loading requirement.To provide technical support for the engineering application of this kind of connection method,based on the concept of recycling of waste concrete,the following work is carried out in this paper:1.Flexural tests including four prefabricated beam-slab assemblies and two cast-in-situ beam-slab assemblies were carried out.Effects of production method,slab thickness,and number of extruded racks on flexural behavior of beam-slab assemblies under negative bending moment were investigated.The experimental results show that:(1)the bearing capacity of prefabricated beam-slab assemblies is higher than that of cast-in-situ beam-slab assemblies;the number of extruded racks has little effect on bearing capacity of prefabricated beam-slab assemblies;(2)the increment of ultimate loads due to the increase of slab thickness for prefabricated beam-slab assemblies is smaller than that of cast-in-situ beam-slab assemblies;(3)for the most dangerous section of prefabricated beam-slab assemblies,the bearing capacity calculated by the formula in current code has a higher safety margin than that of cast-in-situ beam-slab assemblies under negative moment.2.The finite element models of prefabricated beam-slab assemblies were established in common software ABAQUS.Effects of slab thickness,diameter of tensile reinforcement bars of slabs,and contacting type between concrete surfaces on flexural behavior of beam-slab assemblies under negative bending moment were further investigated.The results show that:(1)when the ratio of reinforcement is the same,the ultimate loads of prefabricated beam-slab assemblies increase with the increase of slab thickness(which indirectly leads to the change of the size of the extruded racks and the areas of concrete contact surfaces);(2)with the same reinforcement ratio,the ultimate loads of prefabricated beam-slab assemblies increase in varying degrees with the increase of diameter of tensile reinforcement bars of slabs(which directly leads to a change in the lap length of the tensile reinforcement bars of slabs),while the maximum increment is less than 10%;(3)compared with tie constraint,the bearingcapacities of the beam-slab assemblies under negative moment are reduced when the contact between different parts is surface-to-surface contact,while the decrements are all less than10%,and most of them are less than or close to 5%.3.Horizontal shear tests including three prefabricated beam-slab assemblies and one cast-in-situ beam-slab assembly were carried out.Effects of production method,number of extruded racks,and shear keys on structural responses of beam-slab assemblies under horizontal shear loading were investigated.The experimental results show that:(1)compared with prefabricated beam-slab assemblies,significant difference of crack development process and final failure mode could be observed for the cast-in-situ beam-slab assembly,meanwhile the latter exhibits higher ductility;(2)the shear capacity of prefabricated beam-slab assemblies proposed in this paper is lower than that of cast-in-situ beam-slab assembly,while the shear capacity of the former can be improved effectively by adding shear keys and increasing the number of extruded racks;(3)for prefabricated beam-slab assemblies with shaer keys on the extruded racks,the shear resistant effect of the pin bars developed earlier than that of prefabricated beam-slab assemblies without shear keys,but later than that of cast-in-situ beam-slab assembly;the number of extruded racks has a limited influence on shear resistant effect developing moment of pin bars;(4)compared with the measured shear capacities of prefabricated beam-slab assemblies,the shear bearing capacities calculated by existing codes are obviously lower in general;and the predicted values of American code ACI318-11 is compareble to the measured values.