DYNAMIC BEHAVIOUR OF FOOTBRIDGES SUBJECTED TO PEDESTRIAN-INDUCED VIBRATIONS

[TAFATNEB]

DYNAMIC BEHAVIOUR OF FOOTBRIDGES SUBJECTED TO PEDESTRIAN-INDUCED VIBRATIONS

Author: FJALAR HAUKSSON | Size: 2.2 MB | Format: PDF | Quality: Unspecified | Publisher: Copyright © 2005 by Structural Mechanics, LTH, Sweden. Printed by KFS I Lund AB, Lund, Sweden, November, 2005. | Year: 2005 | pages: 118

Over the last years, the trend in footbridge design has been towards greater spans
and increased flexibility and lightness. As a consequence, stiffness and mass have
decreased which has lead to smaller natural frequencies and more sensitivity to
dynamic loads. Many footbridges have natural frequencies that coincide with the
dominant frequencies of the pedestrian-induced load and therefore they have a potential
to suffer excessive vibrations under dynamic loads induced by pedestrians.
The main focus of this thesis was on the vertical and horizontal forces that
pedestrians impart to a footbridge and how these loads can be modelled to be used
in the dynamic design of footbridges. The work was divided into four subtasks. A
literature study of dynamic loads induced by pedestrians was performed. Design
criteria and load models proposed by four widely used standards were introduced
and a comparison was made. Dynamic analysis of the London Millennium Bridge
was performed using both an MDOF-model and an SDOF-model. Finally, available
solutions to vibration problems and improvements of design procedures were studied.
The standards studied in this thesis all propose similar serviceability criteria
for vertical vibrations. However, only two of them propose criteria for horizontal
vibrations. Some of these standards introduce load models for pedestrian loads
applicable for simplified structures. Load modelling for more complex structures,
on the other hand, are most often left to the designer.
Dynamic analysis of the London Millennium Bridge according to British and
International standards indicated good serviceability. An attempt to model the
horizontal load imposed by a group or a crowd of pedestrians resulted in accelerations that exceeded serviceability criteria.
The most effective way to solve vibration problems is to increase damping by installing a damping system. Several formulas have been set forth in order to calculate
the amount of damping required to solve vibration problems. However, more
data from existing lively footbridges is needed to verify these formulas.

Code:

***************************************
Content of this section is hidden, You must be registered and activate your account to see this content. See this link to read how you can remove this limitation:

http://forum.civilea.com/thread-27464.html
***************************************

This post has been made by CivilEA Post-Generator v2.2.0