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Excessive floor vibrations due to human activities such as heel-drop and jumping can induce annoyance to occupants and cause a serious serviceability problem. Both field tests and finite element analysis were conducted to study the vibration behavior of the composite slab with precast ribbed panels (CSPRP), a relatively new floor system compared with the cast-in-place reinforced concrete (RC) slab. In addition, both heel-drop and jumping impacts were employed to generate the acceleration response of the floor, from which two important vibration characteristics of natural frequencies and damping ratios are obtained. A comparison of the vibration behavior of CSPRPs with RC slabs indicates that the former exhibits more satisfactory perceptibility in terms of vibration. Appropriate coefficients (i.e. ${\beta }_{\text{fp}}=0.03$ and ${\beta }_{\text{rp}}=0.14$) with the root-mean-square and peak accelerations subjected to heel-drop and jumping excitations are proposed for both CSPRPs and RC slabs. Lastly, an extensive parametric study considering different boundary conditions, floor types, and floor spans was carried out using the finite element method. It is recommended to use CSPRP under 3.3m span in order to keep the fundamental frequency above 3.0Hz.

Acoustic insulation optimization of the ship decks to contain impact noise is generally obtained by adopting suitable types of viscoelastic resilient materials. For this purpose, it is necessary to be able to make a correct choice of material. This is obtained by experimentally identifying the vibro-acoustic behavior of the combined semi-reverberant room and floor system according to an ISO standard (ISO 16283-2). These tests are generally onerous as they require the availability of the floor with both trimmed and untrimmed configurations. In addition, qualified technicians are needed to correctly spread the material on the floor. Finally, after the test has ended, the material must be removed and disposed of properly. To reduce this wasted time and cost, in this paper, a new methodology is proposed that predicts the vibro-acoustic behavior of the floor and viscoelastic material assembled together starting from separate dynamic information of the two components. Once these two elements are properly experimentally identified, the proposed method foresees the vibro-acoustic response of the overall system in presence of an impact footfall excitation.

This paper studies the subway-induced vibrations on two adjacent masonry structures in Shanghai with focus on the vibration level and frequency. The results show that: (1) the vibration levels of the two masonry structures in three directions are all higher during the peak traffic hours than the off-peak hours and are higher in the daytime than at night. In addition, they are higher at the mid-span of the floor than the wall-floor junctions and staircase. (2) The parameters of the numerical model were calibrated by the measured vibration response. The slab properties, room size, and other factors can affect the vibration response distribution. (3) The vertical vibrations in the rooms with precast slab are greater than those with cast-in-situ slab. The vertical vibrations at the ash seam between the precast slabs are amplified. In addition, the room depth has a small effect on the vibration intensity. The relationship between the room depth and the vibration intensity depends on the relative width and depth of the room. (4) The width of the room has a significant effect on the vertical vibration. The floor corner and surrounding wall constraint conditions greatly affect the vibration intensity.

We survey two of the many aspects of the standard braid order, namely its set theoretical roots, and the known connections with knot theory, including results by Netsvetaev, Malyutin, and Ito, and very recent work in progress by Fromentin and Gebhardt.