Jp Talbot

The vibration damping of laminated plates

Abstract A method previously developed for determination of elastic and damping parameters of orthotropic plates (McIntyre, M. E. and Woodhouse, J., Acta Metall. , 1988, 36 , 1397–1416) was applied to laminated composite plates. The necessary theory is summarised, and the predictions of laminate theory compared with experimental results for three CFRP laminated plates with different constructions. It is also shown that laminate theory can be inverted, to obtain the ply properties from measurements on the laminated plate. This can sometimes afford a good way to obtain the necessary calibration data on the material properties of the plies.

Using the PiP Model for Fast Calculation of Vibration from a Railway Tunnel in a Multi-layered Half-Space

This paper presents a new method for calculating vibration from underground railways buried in a multi-layered half-space. The method assumes that the tunnel’s near-field displacements are controlled by the dynamics of the tunnel and the layer that contains the tunnel, and not by layers further away. Therefore the displacements at the tunnel-soil interface can be calculated using a model of a tunnel embedded in a full space. The Pipe-in-Pipe (PiP) model is used for this purpose, where the tunnel wall and its surrounding ground are modelled as two concentric pipes using elastic continuum theory. The PiP model is computationally efficient on account of uniformity along and around the tunnel. The far-field displacement is calculated by using another computationally efficient model that calculates Green’s functions for a multi-layered half-space using the direct stiffness method. The model is based on the exact solution of Navier’s equations for a horizontally layered half-space in the frequency-wavenumber domain.

A computationally efficient piled-foundation model for studying the effects of ground-borne vibration on buildings

Abstract Understanding the effects of ground-borne vibration on buildings is becoming increasingly important as pressure grows to construct high-quality buildings on existing urban sites, which are often close to busy roads or railways. The motivation behind the work presented here is the development of a computational model that enables engineers to evaluate the effectiveness of isolating buildings. This paper presents one component of such a model, namely a new three-dimensional model for modelling the propagation of ground-borne vibration through a piled foundation. A row of piles is considered, with the piles modelled using the solutions for an elastic bar and Euler beam, and the soil represented by an elastic half-space. The model is comprehensive in that it accounts for the longitudinal and transverse motion of the piles due to both external pile-head loads and interaction between neighbouring piles through wave propagation in the surrounding soil. Computational efficiency is achieved by assuming that the row comprises an infinite number of identical piles and using a combination of the boundary element method and periodic structure theory.

On the Performance of Base-Isolated Buildings

Base isolation is a means of reducing the transmission of vibration into buildings and was first used in the 1960s. Since then many buildings have been mounted on springs of various types in order to reduce the effects of ground-borne vibration from roads and railways. For most applications, the building rests on steel springs or laminated rubber bearings. A typical objective is a reduction in vibration transmission of at least 10 dB for frequencies above 10 Hz, but, while difficult to verify, such performance is probably rarely ever achieved. Current practice suggests that the choice of spring type has a significant effect on the efficiency of the vibration isolation, as well as having implications on the cost and implementation of the system. However, there remain unanswered a number of fundamental questions concerning the specification and design of isolation bearings for buildings. For example, what is the most appropriate stiffness of the bearings for a given application and to what extent is damping an important part of a good system? This paper reviews current methods of predicting isolation performance and introduces an alternative model which aims to model more fully the behaviour of base-isolated buildings. The benefits of a power-flow approach in assessing isolation performance are also discussed and it is argued that this enables a more appropriate measure of performance to be defined than one based on vibration amplitudes alone.

A generic model for evaluating the performance of base-isolated buildings

Ground-borne vibration has existed ever since the development of urban road and rail networks. Vibration generated by the moving traffic propagates through the ground and into buildings, resulting in unacceptable levels of internal noise and vibration. A common solution to this increasingly significant problem is the base-isolation of buildings by incorporating vibration isolation bearings between the buildings and their foundations. This technique has been employed for over forty years but the exact performance of base isolation remains uncertain. This paper describes a generic computational model; generic in that it accounts for the essential dynamic behaviour of a typical base-isolated building in order to make predictions of isolation performance. The model is a linear one, formulated in the frequency domain, and consists of a two-dimensional portal-frame model of a building coupled to a three-dimensional boundary-element model of a piled-foundation. Both components of the model achieve computational efficiency by assuming they are infinitely long and using periodic structure theory. Following an overview of the model, a virtual case study is presented to illustrate its practical application. Along with some initial observations, the case of a point-load surface excitation of the foundation is used to investigate the isolation performance of typical isolation bearings.

On the performance of base-isolated buildings: a generic model

This work was supported by the Engineering and Physical Sciences Research Council (PhD Studentship)

The effect of side-restraint bearings on the performance of base-isolated buildings

Abstract Base-isolation of buildings is a common solution to the problem of ground-borne vibration from urban road and rail networks. Conventional designs incorporate vibration isolation bearings between a building and its foundation, aligned in the vertical direction so as to isolate the building from vertical motion of its foundation. In some cases, in order to accommodate horizontal loads, additional side-restraint bearings aligned in the horizontal direction are required. This paper describes a theoretical investigation into the effect of side-restraint bearings on the performance of base-isolated buildings. Three generic models, based on a modern concrete-framed building, are used to demonstrate that a buildings flexibility, the nature of the vibration input and the presence of a flexible foundation are all important in determining isolation performance. It is also illustrated how the concept of isolation frequency, commonly used to indirectly specify the stiffness of base bearings, may not be generally extended to side-restraint bearings. The models indicate that, for maximum performance, the stiffness of any side-restraint bearings should be minimized.

Isolation of Buildings from Rail-Tunnel Vibration: A Review:

Many buildings close to railway tunnels are built on steel springs or rubber bearings to isolate them from the ground-borne vibration. This base isolation of buildings has been employed since the 1960s and is becoming increasingly common as pressure grows to construct high-quality buildings on existing urban sites. This paper reviews the practice and theory behind base isolation, and discusses some recent developments in modelling base-isolated buildings with a view to predicting isolation performance.

Lift-over crossings as a solution to tram-generated ground-borne vibration and re-radiated noise

The operation of trams close to sensitive buildings can lead to concerns over ground-borne vibration and re-radiated noise. Vibration generated at the wheel/rail interface propagates through the track structure, through the ground and into buildings, where it may cause disturbance as perceptible vibration and/or re-radiated noise. This paper presents work undertaken to solve a re-radiated noise problem within the auditorium of the Royal Concert Hall, Nottingham, UK. The hall is situated alongside a crossover between two tracks of Nottingham’s Express Transit tramway. Initial measurements established the dominance of re-radiated noise over airborne noise. Simultaneous noise and vibration measurements were then used to establish the relative significance of the impulsive vibration generated at the various rail discontinuities of the crossover, compared with the essentially continuous vibration due to wheel/rail roughness. The results led to the selection of a new ‘lift-over’ crossing, together with an improved design of switch, as the basis for solving the problem. The paper includes descriptions of the experimental methods, together with a summary of the results. The new crossover design is described and the results of the commissioning measurements are presented as a final demonstration of the new lift-over crossing’s performance.

The dynamic interaction effects of railway tunnels: Crossrail and the Grand Central Recording Studios

In cities around the world, underground railways offer an environmentally friendly solution to society’s increasing demand for mass transport. However, they are often constructed close to sensitive buildings, where the resulting ground-borne noise and vibration can cause disturbance to both the occupants and the equipment. Such a scenario occurred in central London, where the new twin tunnels of Crossrail were bored beneath the Grand Central Recording Studios, causing an immediate concern. As a result, vibration in the studios’ building was monitored throughout the Crossrail construction period. Since Crossrail is yet to operate, the resulting data provide a unique opportunity to investigate the effect of new tunnels, acting as passive buried structures, on the existing vibration environment. This paper presents the results of such an investigation, together with complementary results from a theoretical four-tunnel boundary-element model. The data analysis, presented in the first half of the paper, indicates that the construction of the second Crossrail tunnel has led to an overall reduction in the noise and vibration levels beneath the studios, due to the operation of the nearby Central line trains of London Underground. This is predominantly due to a reduction of approximately 6 dB in the 63 Hz band-limited levels but accompanied by a slight increase, of approximately 2 dB, in the 125 Hz band. Further analysis indicates that any seasonal variations in vibration levels over the measurement period are negligible, adding weight to the conclusion that the observed changes are a causal effect of the tunnel. The second half of the paper presents results from the model, which aims to simulate the dynamic interaction between the Central line tunnels and those of Crossrail. With nominal parameter values, the results demonstrate qualitative similarities with the measurement findings, thereby adding to the growing body of evidence that dynamic interaction between neighbouring tunnels can be significant.