Vibration Behavior Of Precast Concrete Sandwich Slab With Innovative Discrete Connections

China is a major construction country,and the construction industry consumes a large amount of resources and energy,causing serious environmental pollution.Therefore,the development of green buildings is of great significance.Precast floor coverings have been increasingly widely used due to the advantages of efficient construction,energy conservation,and environmental protection,in line with China’s "dual carbon" emission reduction goals and the development needs of new building industrialization.Discretely Connected Precast RC Sandwich Floor(DCPCF)is composed of precast sandwich slabs,slab joints and discrete connectors.It has the advantages of light weight,high construction efficiency,energy saving and sound insulation.The mechanical mechanism and vibration performance of DCPCF are changed due to the innovative slab joint connection between the precast sandwich slabs.However,there is a lack of relevant research,and the vertical vibration transfer performance in orthogonal slab laying direction(OSLD)is still unclear.Therefore,it is of great theoretical significance and application value to study the vertical vibration transfer performance in OSLD of DCPCF.In order to study the vertical vibration transfer performance in OSLD of DCPCF,the vertical vibration transfer performance in OSLD test and finite element analysis of 7 DCPCF specimens and 2 CISS specimens were carried out,and the theoretical prediction method of DCPCF natural frequency and human-induced vibration peak acceleration was deduced.This paper has carried out the following work and research:(1)Based on the hammer pulse method,the dynamic characteristics of each specimen were tested,and the effects of the number of slab joints,the number of connectors,the distance of slab joints to the mid-span and the mass ratio on the dynamic characteristics parameters(vibration mode,fundamental frequency,and damping ratio)of DCPCF specimens were analyzed.The test results indicated that DCPCF specimens had similar dynamic characteristics to CISS specimens,with the first three vibration modes basically consistent.Only the third vibration modes of DCPCF specimens were smoother than CISS specimens.The fundamental frequency of the DCPCF specimens meet the vibration serviceability requirements,and its fundamental frequency was slightly smaller than that of the CISS specimens,and its fundamental frequency increased with the decrease in the number of slab joints,the increase in the number of connectors,the decrease in the mass ratio and the distance of slab joints to the mid-span.When the slab joint was located in the mid-span,the fundamental frequency decreased significantly.The damping ratio of DCPCF specimens was slightly larger than that of CISS specimens,and both meet the requirements of the norm for damping ratio of floor.(2)The vibration responses of DCPCF under various human-induced loads were studied by applying bouncing,jumping,and walking loads to each specimen.The test results indicated that DCPCF specimens had the similar vibration transmission performance to CISS specimens,and discretely connectors could effectively transfer the vertical vibration of DCPCF in OSLD.Under the same load,the peak acceleration of the DCPCF specimen was greater than that of the CISS specimens,and its vibration response was positively correlated with the number of slab joints,while negatively correlated with the number of connectors and the distance of slab joints to the mid-span.The vibration response of the floor was positively correlated with the load frequency,and at the same frequency,the peak acceleration when bouncing was smaller than when jumping.Under multi-person loads,the farther the load distribution was from the midspan,the smaller the vibration response of each specimen.The peak acceleration of the DCPCF specimens and the CISS specimens under the condition of simple supported at both ends and the current size did not meet the vibration serviceability requirements.(3)The finite element analysis of the vertical vibration transfer performance in OSLD of DCPCF was carried out.The dynamic characteristics and human-induced vibration responses of each specimen were simulated using modal analysis and transient dynamic analysis methods.The accuracy of the modeling method was verified by experimental results.Further,the parametric analysis of the vertical vibration of DCPCF was carried out,and the concrete performance at the joint,the thickness of the GB,the specification of the anchor bar and the boundary constraint conditions were observed to study their influence on the fundamental frequency of DCPCF.The results indicated that using UHPC at the slab joints could improve the fundamental frequency of DCPCF,and the improvement effect became more obvious as the number of slab joints increased,the number of connectors decreased,and the closer the slab joints was to the mid-span.Increasing the thickness of the GB and the diameter of long anchor bar and enhancing boundary constraints could greatly improve the fundamental frequency of DCPCF.In the engineering design and application of DCPCF,it was suggested that the vibration performance of DCPCF could be improved by applying high performance concrete material at the slab joint or increasing the thickness of the GB and the diameter of the long anchor bar.(4)Based on the conjugate beam principle,the calculation method of transverse stiffness of DCPCF was optimized,and on this basis,the theoretical prediction method of natural frequency and peak acceleration of human-induced vibration of DCPCF was deduced by combining dynamic theory.By comparing the calculated results with the experimental results,it was found that the error between the calculated and measured values of the fundamental frequency of each specimen was within 7 %,and the error between the calculated and measured values of the peak acceleration was within 8 %.It shown that the optimized DCPCF transverse stiffness calculation method could better solve the stiffness calculation problem of DCPCF in dynamic analysis.The theoretical prediction method of DCPCF natural frequency and human-induced vibration peak acceleration derived in this paper had good accuracy.The above research results can provide a reference for the engineering design and application of precast RC sandwich floors.