Influence of cladding on robustness of multi-storey buildings

In this dissertation the influence of a precast concrete cladding system on structural robustness of a multi-storey steel-composite building is studied. The analysis follows the well-established framework developed at Imperial College London for the appraisal of robustness of multi-storey buildings. For this scope a simplified nonlinear model of a typical precast concrete façade-system is developed. Particular attention is given to the connection system between structural frame and panel, recognised as the driving component of the nonlinear behaviour of the façade-system. Only connections involved in the gravity load path are evaluated (bearing connections). Together with standard connection, a newly proposed system (Slotted Bearing Connection) is designed to achieve a more ductile behaviour of the panel-connection system. A parametric study involving the dimensions of panel-connection components is developed to search for an optimal configuration of the bearing connection. From the appraisal of structural robustness of the panelised frame it is found that the standard connection systems may reduce the robustness of a multi-storey frame due to a poor ductile behaviour while the newly proposed connection is able to guarantee an enhanced response to the panelised multi-storey frame thanks to a higher ductility.

Mitigation of Train-Induced waves by resonant filled-trench (RFT)

The increase of railways near the urban areas is a significant cause of discomfort for inhabitants due to train-induced vibration and noise. Vibration characteristics can vary widely according to the train type: for high-speed trains, if train speed becomes comparable to the ground wave speed, the vibration level becomes significant; for freight trains, due to their heavier weight and lower speed, the vibration amplitudes are greater and propagate at a more considerable distance from the track; for urban tramways, although the vibration amplitude is relatively low, they can have a negative structural effect on the closest buildings [51]. Therefore, to dampen the vibration level, it is possible to carry out some interventions both on the track and the transmission path. This thesis aims to propose and numerically investigate a novel method to dampen the train-induced vibrations along the transmission path. The method is called "resonant filled-trench (RFT)" and consists of a combination of expanded polystyrene (EPS) geofoam to stabilize the trench wall against the collapse and drowned cylindrical embedded inclusions inside the geofoam, which act as a resonator, reflector, and attenuator. By means of finite element simulations, we show that up to 50% higher attenuation than the open trench is achievable after overcoming the resonance frequency of the inclusion, i.e., 35Hz, which covers the frequency contents of the train-induced vibration. Moreover, depending on the filling material used for the inclusions, trench depth can be reduced up to 17% compared to the open trench showing the same screening performance as the open trench. Also, an RFT with DS inclusion installed in dense sand soil shows a high hindrance performance (i.e., IL≥6dB) when the trench depth is larger than 0.5λ_R while it is 0.6λ_R for the open trench.