Vertical Vibration Analysis Of Long-span Prestressed Secondary Beam Roof System With Different Design Parameters

The long-span prestressed secondary beam floor has the advantages of saving material and floor net height,but this kind of floor is also softer than the ordinary reinforced concrete floor,and it is more prone to appear moderate problems under the action of man-made load.To address this deficiency,The long-span prestressed secondary-beam floor in the 2 layer of construction project 3#(gymnasium)building of Core Area Primary School in Tongliang county in Chongqing was taken as the research subject,from the point of changing the arrangement of floor structure and material strength,the height of secondary beam,the thickness of floor slab,the thickness of floor slab with or without flat beam and the modulus of elasticity of concrete are variable parameters,the modal analysis of 9 floors considering the above four factors is carried out by ANSYS.Then according to the measured working conditions,the loading scheme(including single,multi-person synchronous,multi-person asynchronous loading,a total of 8 kinds of working conditions)is made,the dynamic analysis of these floors is carried out,and the calculation results are compared and analyzed.The main conclusions reached are:①The increase of secondary beam height can effectively raise the natural frequency of floor;the increase of floor thickness will decrease the frequency of floor by a small margin;whether there is a flat beam floor has a great influence on the frequency of floor;after the addition of floor,the frequency of floor will be greatly affected by the increase of floor thickness.The change of floor thickness has relatively little effect on the foundation frequency,and the change of concrete elastic modulus has a significant effect on the floor natural vibration frequency.②Through dynamic analysis,8 kinds of working conditions were obtained under two load forms of walking and jumping for the floor of 9 schemes,which can be obtained by comparison and analysis:1)The vertical vibration acceleration of the floor is much larger than that of the nonresonance when the relationship between the load frequency and the frequency component of the floor is similar to that of the similar resonance.2)When a single person and many people move synchronously,with the increase of the height of the secondary beam,the peak acceleration of the vertical vibration of the floor cover decreases obviously;With the increase of floor thickness,the peak acceleration of floor vibration decreases only slightly or even increases.Whether or not the flat beam floor is installed has a significant effect on the vibration response of the floor.After the flat beam floor is installed,the floor thickness is changed to the floor cover.The effect of vibration response is small;with the increase of the elastic modulus of the concrete,the peak acceleration of floor vibration during non-type resonance decreases.3)When many people move synchronously,the vibration response of the floor is roughly linear with the vibration response of the single player.When three people are walking synchronously,the single player reduction factor is 1.0.When the 3-20 people walk synchronously,the single player decreases the coefficient.It is advisable that when a 0.9 or 5 person is in a synchronized jump,the one-person reduction factor may be 1.0;when a 20-person person synchronously jumps,the single-person reduction factor may be taken as 0.95.4)For non-simultaneous multi-player movements,the error between the simulated and measured values is 27.80% when the 10 persons are walking synchronously at 1.8Hz,and the simulated vibration response of the floor is 4.33 times that of the single person at the 1.8Hz simulated walking;20 people are 2.0 In the case of non-synchronous hopping of Hz,the error between the simulated value and the measured value is 29.67%,and the simulated vibration response of the floor is 6.40 times that of a single 2.0Hz analog jumping.5)Single person jumping is more unfavorable than single person walking.The ratio of single person jumping vibration response to single person walking vibration response in each scheme is 2.57 to 3.62.In summary,for the large span prestressed secondary beam floor similar to the one in this paper,the natural vibration frequency of the floor can be increased obviously and the vertical acceleration response of the floor can be reduced by setting the flat beam floor.If the conditions permit,increasing the beam height can also achieve certain effects;the effect of increasing the floor thickness is not obvious.