Simulation Of Jumping Loads And Human-Induced Vibration Analyse For Large-Span Floors Under Jumping Loads

Due to large-span floor and high strength material used in public buildings such as gymnasium,stadium grandstand and railway station,the fundamental frequency of the structure system is getting lower,and the stiffness of the floor is decreasing.Now the floor vibration due to rhythmic activities appears regularly.Thus carrying out the structure vibration response analysis under the rhythmic load will be very important theoretically significant and practical.Based on the research at home and abroad,the coherency factor of rhythmic crowd jumping was used to measure the difference and simulation of crowd jumping load was studied.The human-structure interaction effect on human-induced excitation is studied.Human-induced vibration serviceability problems of the first mast cable-stayed footbridge in Nanjing are studied using a combination of finite-element simulations and field experiments.The main concerns and corresponding conclusions are as follows:1.Experiments on crowd jumping load are conducted.The four groups of fixed frequency jumping tests and one group of free jumping test were carried out on the test subjects and acquired 31235 data.The data is analyzed based on statistical distributions and variation ranges of parameters and relationships between them.The time lag between the metronome's time and the test subject's landing time was used as the coherency factor of rhythmic crowd jumping.The statistical analysis of experimental data shows that probability distribution characteristics of coherency factor can be described as a Weibull distribution.The parameters of the probability density function were determined by experimental results.Simulation of crowd jumping load was carried out by combining the coherency factor model with the single random jumping load model.2.SDOF modal parameter identification test of the human body in the standing jump condition is carried out.A one-man jumping test was performed on the low frequency test floor with 15 people jumping on defferent step frequencies.Based on the single-degree-of-freedom Mass-Spring-Damper(MSD)model of human body in the jump condition,the model of the two-degree-of-freedom human-structure coupling system is established.Natrual frequency and damping ratio of test floor is obtained by modal test before and after one person jumping on it,then generate them into the equation to get fundamental frequency and damping ratio of the human MSD model in jump condition.The results show that: when the pacing frequency is 1.5Hz,the human MSD model frequency is about 4.209 Hz,and the damping ratio is 24.47%;when the pacing frequency is 2.0Hz,the human MSD model frequency is about 4.256 Hz,and the damping ratio is 22.78%;when the pacing frequency is 2.67 Hz,the human MSD model frequency is about 4.310 Hz,and the damping ratio is 20.41%.3.The influence of structure vibration on HSI effect is analyzed.The parameter identification results of human MSD model in jump condition under different excitation frequencies are obtained by experiment.It is found that the human frequency decreases with the increasing of the structure vibration level,while the human damping ratio increases gradually with the increasing of the structure vibration level.4.Human-induced vibration serviceability problems of the first mast cable-stayed footbridge in Nanjing are studied using a combination of finite-element simulations and field experiments.A finite element model of full bridge is established by SAP2000 software for modal analysis,while ambient vibration tests are conducted to validate the modal properties.The first vertical frequency of the footbridge is less than 3Hz within the sensitive frequency range of human activities.Thus the vibration responses need to be calculated while the tuned mass dampers(TMD)are installed to control the vertical vibration.Then the dynamic responses of the bridge before and after the installation of TMD are determined experimentally under one people,two people and three people jumping crowd excitations,and the actual damping effect is evaluated.Meanwhile,consider the human-structure interaction effects,the jumping crowd load models obtained in this paper are applied to the finite element model of the bridge.By comparing the calculated results with the measured results,it is found that the jumping load model is reasonable for calculating the structural response.