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Dr Seán P Carroll

Teaching Interests and Experience

My teaching experience covers a wide spectrum within the structural and civil engineering disciplines. Modules I have delivered include:

- Structural Mechanics and Vibration

- Nonlinear Analysis of Structures

- Finite Element Analysis in Structural Engineering

- Analysis of Plate and Shell Structures

I currently teach third year Concrete Structures which focusses on the analysis and design of concrete building structures to Eurocode 2. I’m particularly interested in helping engineering students improve their understanding of fundamental structural behaviour. I’m also interested in the topic of structural scheme design wherein the aim is to help students realise structural designs that are efficient, stable and practical to construct.

Concrete Structures resources page
Video lecture resources

Research Interests

Research interests include occupant-induced structural vibration, human-structure interaction and crowd flow behaviour. A central theme of my research is the use of agent-based crowd modelling to better inform design stage predictive modelling. I have carried out extensive lab-based and numerical studies in these areas. A developing research interest seeks to better utilise the growing urban surveillance infrastructure to capture real-time crowd behaviour for the purpose of assessing the interaction between crowds and the space/structures they occupy.

Crowd Flow Behaviour and Pedestrian Tracking

Sporting events, protests and religious gatherings can draw crowds that range in size from thousands to millions. Such mass gatherings require careful management and often take place spontaneously or with little prior warning. As a result, crowd behaviour is often difficult to predict, making its safe management in the face of evolving circumstances exceptionally challenging. Unforeseen events can lead to development of dangerously high crowd densities that ultimately result in injury or death. The ability to predict and monitor the behaviour of the crowd is an important tool in the management of mass gatherings.
Scene recon_wm  
Top left: Still image taken from left surveillance camera showing 2D image coordinates of 3 tracked pedestrians (note also the 4 green scene orientation triangles). Top right: Still image taken from right side surveillance camera showing the corresponding image coordinates for tracked pedestrians. Bottom left: Stereo reconstruction of pedestrian trajectories projected in 2D (note green scene orientation points and reconstructed camera positions/orientations. Bottom right: 3D scene reconstruction.  

Human-Structure Interaction

If the structure on which a pedestrian walks is excited laterally to a level perceived by the pedestrian, a complex interaction may develop between the walking pedestrian and flexible structure. The perceived motion may induce alterations in the pedestrian’s gait with a knock-on influence on the footfall forces imposed on the structure. This can in turn generate larger amplitude structural oscillations. A feedback loop is thereby established between structural response and pedestrian balance behaviour. This can be considered a coupling between two dynamic systems, one of which is controlled by the human brain. This interaction mechanism is referred to as human-structure interaction.Rig testing

Laterally oscillating rig

Above: Laterally oscillating treadmill capable of recording the lateral component of the footfall force. Built to simulate the effect of walking on a wobbly footbridge.
Left: Subject instrumented with gait analysis markers to study whole-body balance behaviour while walking on the oscillating treadmill.


Crowd-induced vibration and crowd modelling

A walking pedestrian is a deceptively complex source of dynamic excitation. The problem becomes considerably more challenging when expanded to consider the dynamic influence of a pedestrian crowd. Not only must the interaction between each pedestrian and the structure be considered, but also the interactions between individual pedestrians. Pedestrians moving within a crowd are subject to many physical and psychological influences. Social norms tend to force pedestrians to maintain certain distances between each other, respecting so-called ‘personal space’. Individual pedestrians will also have varying levels of motivation to reach their destination. Each pedestrian must navigate through the environment, avoiding obstacles and other pedestrians as efficiently as possible. These factors all influence the behaviour of each individual within the crowd.

When the influence of these factors is considered for each pedestrian in parallel, the overall behaviour of the crowd emerges. Emerging crowd behaviour is characterised by a spatially and temporally varying distribution of crowd density and walking velocities. One of the most influential parameters when modelling a pedestrian-induced dynamic load is frequency. This is directly related to walking velocity which is itself a function of the local crowd density. Thus the distribution of pedestrians influences the walking speeds and therefore forcing frequencies experienced by the structure.

Crowd flow

Above: Simulated crowd flow over a bridge indicateing evolving states of human-structure interaction and how they influence crowd flow behaviour. (a) t = 120s, (b) t = 140s, (c) t = 170s, (d) t = 240s, (e) t = 300s. Green pedestrians are unaffected by bridge motion, yellow pedestrians are interaction with bridge motion and red pedestrians are

Pedestrian-to-Pedestrian Interaction...Synchronisation?

Do pedestrians 'fall into step' with each other? If so, is this triggered at a particular crowd density? It seems reasonable to suggest that as pedestrians are packed closer together they might step-synchronise. But what are the drivers, are they physical or psychological? Should a bridge designer be wary of certain triggering traffic conditions? Plenty of questions still to answer!

Right: Crowd of 'human fireflies' - simulated bi-directional traffic flow with pacing frequencies indicated by colour. Under what conditions might the crowd start 'pulsing' or steping in time?

Selected Publications

    - Carroll,S.P., Owen,J.S., Hussein,M.F.M. (2014) Experimental identification of the lateral human-structure interaction mechanism and assessment of the inverted-pendulum biomechanical model. The Journal of Sound and Vibration, vol 333 p. 5865-84
      - Carroll, S.P., Owen, J.S., Hussein, M.F.M. (2013) Reproduction of lateral ground reaction forces from visual marker data and analysis of balance response while walking on a laterally oscillating deck. Engineering Structures, vol 49 p. 1034-47
        - Carroll, S.P., Owen, J.S., Hussein, M.F.M. (2013) A coupled biomechanical/discrete element crowd model of crowd-bridge dynamic interaction & application to the Clifton Suspension Bridge. Engineering Structures, vol 49 p. 58-75

          - Carroll, S.P., Owen, J.S., Hussein, M.F.M. (2012) Modelling crowd-bridge dynamic interaction with a discretely defined crowd. The Journal of Sound and Vibration, vol 331 p. 2685-709.



          S dot P dot Carroll at warwick dot ac dot uk

          School of Engineering
          University of Warwick
          CV4 7AL, UK

          Phone: +44 (0)24 7652 4726
          Fax: +44 (0)24 76 418922