Fluid / structure interactions during flooded scouring at FlexiArch Bridges

The context of the research

Bridge failure may result in loss of lives, economic loss and increased traffic congestion. In a process called scouring, the bed and banks of the river get eroded by the river flow, deepening the river in the vicinity of the bridge. Bridges are designed with allowance for scour but scouring becomes severe during extreme floods and could undermine the bridge foundation causing the bridge to collapse. In fact, scour is the major cause of failure of bridges. There have been more than 100 scour related bridge failures with 15 casualties in the UK rail network since 1843. The historic data translate to, on average, £ 1 million per year in economic loss due to bridge failure. The risk of scour could be severe in the future as changes in climate are expected to result in increased occurrence of heavy rains in many areas of the world which will result in higher flows in rivers.
While standard flow scour at bridge piers is a well-researched area, the increased scour that occur when the water level in a river exceeds the bridge deck ("pressurised flow") is less well studied. This "pressurised scour" could be a serious threat in the future due to increased flows during extreme floods. Moreover, bed scour and its direct consequential effects on the behaviour of the bridge is an area that is not yet fully understood as earlier research tended to separate scour and structural behaviour of bridges, and it is this consequential nature of the interaction between scour and structural response that instigates failure of a bridge. Better understanding about the scour process and bridge's response to it would aid in making the current and future bridge stock more resilient.


Aims and Objectives

Bridges are a vital component of society's infrastructure. Nearly half of the bridges in UK's road and rail network are masonry arch bridges. A modern masonry arch bridge system called the 'FlexiArch' has been developed at Queen's University Belfast and has been implemented in the UK and Ireland. The system is similar in geometry to traditional masonry arch bridges but does not involve any mortar and requires much less labour and can be rapidly constructed on a site.
The aim of this PhD research is to understand the interaction between bed scour and structural response of FlexiArch bridges. To that extent, the causes of scour, the influence of pressurised flow on FlexiArch bridge systems and the structural response to scour will be investigated using both numerical modelling and laboratory investigations.


Research Methodology

A scaled model of a FlexiArch bridge will be built for the experimental analysis of the scour phenomenon as well as for its evaluation of the amount and shape of the settlement due to scour by means of hydraulic tests. The amount of scour will be measured, and the structural response of the bridge will be monitored and coupled with a detailed nonlinear finite element simulation for a better interpretation of experimental results to better understand the dynamic behaviour of the FlexiArch bridge system.


Alignment to EPSRC's strategies and research areas

This PhD project is expected to yield better understanding of bed scour under pressurised flows. Another novelty of the project would be the study of the structural response of FlexiArch bridge system under scour where the lack of mortar in the bridge could give different behavior to traditional arch bridges. Therefore, this study is aligned with EPSRC research areas in the theme of Engineering, particularly, Coastal and Waterway Engineering, Structural Engineering and Infrastructure and Urban Systems as the research output may be used to safeguard the current bridge stock and help design future arch bridges which are more resilient to scour due to increased flood risk.