Abstract:
Present advancements in concrete technology have resulted in an increased strength of concrete supplemented by light weight characteristics. At the same time they have also become prone to walking induced vibration and associated discomfort to occupants. The existing ACI serviceability limit often falls short on deciding the minimum thickness of slabs to circumvent walking induced vibration discomfort, necessitating a greater slab thickness. In the present study a finite element approach has been used to study the dynamic response of RC slab system under single person and multiple person walking excitation. This study has been conducted on symmetric slab system. A linear time history approach has been used to investigate the behavior of solid reinforced concrete slab systems with column line beams. A finite element analyses model of an intermediate floor of a multi-story building with 3 3 slab panels has been developed. The adopted methodology has also been validated against the results obtained from past experiments.
The slab system was subjected to single person and multiple person walking excitation. The response was studied in terms of the acceleration response of the central node of the central span and the frequency data obtained by converting the acceleration response to frequency domain using Fast Fourier Transformation. The responses have been compared for different thickness against the ACI serviceability limit, as well as limits suggested in other design guides. For single person walking excitation, the responses have been observed for different values of span length, slab thickness, aspect ratio and the walking direction. It was observed that the walking direction did not have any influence in the response of the slab. The response however showed variation with the change in other parameters. It appeared that, the ACI serviceability limit might be insufficient in deciding the minimum slab thickness for slab panels with larger slab spans and aspect ratio. For multiple person synchronized walking excitation on square panels, the acceleration response showed variation with the change in studied slab length and slab thickness. The minimum slab thickness required for the response to come below the allowable acceleration limit was greater than the ACI serviceability limit for all the spans studied. However, such a loading condition is less common, unless people are engaged in rhythmic activities. Thus, a study on non-synchronized walking excitation has been conducted. For such a walking excitation, the required minimum slab thickness was also greater than the ACI serviceability limit for the spans studied when compared against the allowable acceleration limit suggested in CRSI design guide.
Based on the observations from the study, guidelineson selecting slab thickness are proposed for single person and multiple person walking. For single person walking, response was obtained for slab panels with varying aspect ratio. The response for multi-person walking excitation was obtained for square slab panels only. It is expected that the suggested guideline will help engineers in selecting the minimum slab thickness based on the span length of the slab system that will circumvent walking induced vibration discomfort.
