Research On Vertical Vibration Characteristics And Human Induced Excitation Response Of Untopped Precast RC Floors

Precast floor has the characteristics of high efficiency,high quality,and environmental protection,and are widely used in countries all over the world.Our country is also vigorously promoting precast buildings,which will be an important development direction for the construction industry.However,compared with the cast-in-situ slab,the difference in the connection between the slab joint and the beam-slab connection will have a greater impact on the mechanical performance and vibration characteristics of the precast floor.Systematic research on it is of great significance to the development of the industry.The discretely connected precast RC diaphragm(DCPCD)studied in this paper is a untopped floor with precast slabs as the basic component and precast slabs connected by pre-embedded connectors.It has the advantages of good structural performance,easy construction,energy saving and environmental protection.The force performance of DCPCD has been systematically studied,but its vibration characteristics are rarely studied.To further reveal the vibration characteristics of DCPCD,this paper carried out two types of dynamic tests: 1)Two short side-to-side simply supported one-way slabs under a variety of human-induced load excitation,including 6 DCPCD specimens and 1 cast-in-situ slab specimen.2)The vibration performance test of two-sided and four-sided simply supported two-way slabs under a variety of human load excitations,including two DCPCD specimens and one cast-in-situ slab specimen.For these two types of dynamic tests,the effects of the layout and quantity of the slab joints and the connectors on the vibration characteristics of the DCPCD were studied,and the vibration serviceability of the floor under the excitation of different human loads was analyzed.The similarities and differences with the cast-in-place slab,the theoretical calculation methods of the natural frequency of the slab and the peak acceleration of the floor under the excitation of human loads were deduced.The specific content is as follows:(1)The basic dynamic characteristics of DCPCD were experimentally studied by the hammering method,and the modal parameters such as the modal shape,natural frequency and damping ratio of DCPCD,as well as the similarities and differences with the cast-in-situ slab under the same conditions were analyzed.The results show that the first three modes of the DCPCD in the one-way slab were basically the same as the cast-in-situ slab,but in the two-way slab only the first-order mode was the same.The existence of slab joints made DCPCD have the characteristics of orthogonal two-way anisotropic plates,and have different bending stiffness along the two directions.The natural frequency of DCPCD was slightly lower than the natural frequency of cast-in-situ slab.The natural frequency was directly proportional to the number of connectors,and inversely proportional to the number of slab joints.When the slab joints were located in the middle of the span,the reduction is greater.The natural frequency of the DCPCD and the cast-in-situ slab met the comfort requirements.The damping ratio of the DCPCD was obvious greater than the damping ratio of the cast-in-situ slab.(2)A variety of rhythmic load excitations were applied to DCPCD,and the vibration response of DCPCD under different working conditions such as bounce and jumping,and the similarities and differences between the DCPCD and the cast-in-situ slab under the same conditions were studied.The results show that the vibration acceleration of the DCPCD under the same load was greater than that of the cast-in-situ slab.Under simply supported conditions,the current size of DCPCD and cast-in-situ slab didn’t meet the serviceability requirements.The vibration acceleration of the DCPCD was proportional to the number of connectors and inversely proportional to the number of slab joints.The acceleration increases when the slab joint were located in the middle of the span.With the increase of the load frequency,the peak acceleration of the floor gradually increase.The acceleration when jumping at the same frequency was greater than the acceleration when on bounce.The closer the load distribution was to the mid-span,the greater the acceleration.(3)A variety of pedestrian load excitations were applied to DCPCD,and the vibration response of DCPCD under different walking and running conditions and the similarities and differences with cast-in-situ slab under the same conditions were studied.The results show that the vibration acceleration of the DCPCD under the same load was greater than that of the cast-in-situ slab.Under simply supported conditions,the current size of the DCPCD neither the cast-in-situ slab met the serviceability requirements.With the increase in step frequency,the peak acceleration of the slab gradually increases.The most unfavorable walking route for the cast-in-situ slab was along the diagonal direction,and the most unfavorable walking route for DCPCD was along the orthogonal slab laying direction(OSLD).The closer the load distribution was to the mid-span,the greater the acceleration.(4)Based on the dynamics theory,the DCPCD was theoretically analyzed,and various factors affecting the serviceability of the DCPCD were analyzed and engineering design suggestions were made.The theoretical value was in good agreement with the experimental value.The bending stiffness ratio of OSLD and slab laying direction(SLD)to the vibration characteristics of the DCPCD was analyzed.For the consideration of serviceability and economy,it was recommended that the bending stiffness ratio of OSLD and SLD be between 0.3 and 0.75.The influence of various spans and boundary support conditions on the vibration serviceability was analyzed.When a certain span and boundary constraint conditions were reached,DCPCD can meet the serviceability requirements.