Essay On Footbridge

Literature Review

Introduction

Pedestrian induced lateral vibrations of footbridges have been observed for several decades. More recently, long span footbridges around the world have experienced unacceptable levels of lateral vibration, and more locally have included the Paris Solferino and London Millennium bridges in 1999 and 2000 respectively.

As a consequence, research has been carried out as to the causes of this lateral vibration, and in particular, to a phenomenon termed ‘synchronous lateral excitation’, (SLE), where, under certain pedestrian loading conditions, a sudden sharp increase in bridge vibration occurs.

In particular, the London Millennium footbridge became a high profile case and attracted a lot of publicity, and its subsequent investigation and solution was widely monitored and publicised. Extensive testing and resulting data and analysis was carried out with respect to the structure, crowd loading effects and pedestrian modelling with respect to the vibration effects of the structure providing public accessible data.

Since this event, more attention has been drawn towards other similar experiences with footbridges and has led to the subject being more widely researched. Since 2000, the number of published papers during that decade relating to this subject has increased more than eightfold over that during the previous one, Venuti and Bruno (2009). This also brings to light the possibility of potential problems for bridges that may not have yet experienced high levels of pedestrian loading.

The London Millennium Footbridge

Examining some of the issues of this footbridge will identify areas of study and investigation will be looked at in more detail later on. The bridge opened in June 2000, and experience...

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...driven laterally in a sinusoidal manner at selected frequencies and amplitudes. Tests carried out indicated force peaks at the walking frequency and its harmonics, but also indicated an additional frequency, which was named the Self Excited force. He was also able to identify that pedestrians acted as a negative force, effectively damping the structure over a range of frequencies with an incidence of a substantially high result.

More extensive test were carried out more recently by Ingolfsson[], using the same treadmill, but for more pedestrians and a greater range of frequencies and amplitudes. He summarised that pedestrians act as negative dampers for most frequencies, and add to the overall modal mass at higher frequencies but decrease it at lower frequencies. The wide variation in measurements do, however, prevent making a deterministic description of the data