Luke J. Prendergast

Determining the presence of scour around bridge foundations using vehicle-induced vibrations

Bridge scour is the number one cause of failure in bridges located over waterways. Scour leads to rapid losses in foundation stiffness and can cause sudden collapse. Previous research on bridge health monitoring has used changes in natural frequency to identify damage in bridge beams. The possibility of using a similar approach to identifying scour is investigated in this paper. To assess if this approach is feasible, it is necessary to establish how scour affects the natural frequency of a bridge, and if it is possible to measure changes in frequency using the bridge dynamic response to a passing vehicle. To address these questions, a novel vehicle–bridge–soil interaction (VBSI) model was developed. By carrying out a modal study in this model, it is shown that for a wide range of possible soil states, there is a clear reduction in the natural frequency of the first mode of the bridge with scour. Moreover, it is shown that the response signals on the bridge from vehicular loading are sufficient to allow these changes in frequency to be detected.

Development of a Vehicle-Bridge-Soil Dynamic Interaction Model for Scour Damage Modelling

Damage detection in bridges using vibration-based methods is an area of growing research interest. Improved assessment methodologies combined with state-of-the-art sensor technology are rapidly making these approaches applicable for real-world structures. Applying these techniques to the detection and monitoring of scour around bridge foundations has remained challenging; however this area has gained attraction in recent years. Several authors have investigated a range of methods but there is still significant work required to achieve a rounded and widely applicable methodology to detect and monitor scour. This paper presents a novel Vehicle-Bridge-Soil Dynamic Interaction (VBSDI) model which can be used to simulate the effect of scour on an integral bridge. The model outputs dynamic signals which can be analysed to determine modal parameters and the variation of these parameters with respect to scour can be examined. The key novelty of this model is that it is the first numerical model for simulating scour that combines a realistic vehicle loading model with a robust foundation soil response model. This paper provides a description of the model development and explains the mathematical theory underlying the model. Finally a case study application of the model using typical bridge, soil, and vehicle properties is provided.

Structural Health Monitoring for Performance Assessment of Bridges under Flooding and Seismic Actions

Abstract Bridges can be subjected to damaging environmental actions due to flooding and seismic hazards. Flood actions that result in scour are a leading cause of bridge failure, while seismic actions that induce lateral forces may lead to high ductility demand that exceeds pier capacity. When combined, seismic actions and scour can lead to effects that depend on the governing scour condition affecting a bridge. Loss of stiffness under scour can reduce the ductility capacity of a bridge but can also lead to an increase in flexibility that may reduce seismic inertial forces. Conversely, increased flexibility can lead to deck collapse due to support loss, so there exists some uncertainty about the combined effect of both phenomena. A necessary step towards the performance assessment of bridges under flooding and seismic actions is to calibrate numerical models that can reproduce structural responses under different actions. A further step is verifying the achievement of performance goals defined by codes. Structural health monitoring (SHM) techniques allow the computation of performance parameters that are useful for calibrating numerical models and performing direct checks of performance goal compliance. In this paper, various strategies employed to monitor bridge health against scour and seismic actions are discussed, with a particular focus on vibration-based damage identification methods.

Numerical Modelling of a Monopile for Estimating the Natural Frequency of an Offshore Wind Turbine

Monopiles are the most common foundation system for supporting Offshore Wind Turbines (OWT’s), accounting for more than 80% of all OWT substructures installed in Europe to date [1]. Significant reductions in the cost of developing OWTs have been realized over the past few years, to the point where offshore wind can now be developed subsidy free in favorable locations. Optimizing the engineering design of these structures has played a key role in ensuring these cost reductions are possible. The largest uncertainty with respect to modelling the dynamic response of an OWT often relates to the geotechnical design. This paper examines the influence of soil-structure interaction on the dynamic response of an OWT structure. The below ground pile-soil behavior was modelled using (i) a conventional DNV (De Norske Veritas) ‘p-y’ approach and (ii) an advanced in-situ calibrated 3D FE geotechnical design approach. The results for the soil-structure interaction were inputted into a separate dynamic wind turbine model and the dynamic response using the two separate SSI approaches were compared.

Structural Health Monitoring and Design Code compliance for performance assessment of bridges under scour and seismic hazards

When dealing with asset management of infrastructural systems, maintenance planning of bridges and other critical structures has to be thought against natural deterioration due to environmental conditions, but also taking into account potential criticalities induced by the occurrence of seismic and flood hazards. The aim of this work is to focus on potential damage scenarios, assessment methods for common bridge structures potentially subject to earthquake loading and scouring phenomena due to flooding hazards.