About DegreeTutors

DegreeTutors is a site dedicated to producing high quality educational content for civil and structural engineers, students and construction industry professionals. The aim is to continue to grow a database of both free online tutorials and articles and a library of low cost well produced online courses. DegreeTutors content is biased towards developing a fundamental understanding of engineering principles and analysis techniques. This is borne out of my observation that it’s these fundamentals that engineering students struggle with the most. Failing to fully develop and intuitive understanding of structural behaviour is akin to building your house on very unstable foundations! It leads students becoming engineers that shy away from analysing structures intuitively, instead opting to lean heavily on software based analysis. Software solutions have there place but they’re no substitute for a knowledge founded on a robust understanding of first principles.

What is DegreeTutors.com and who is it for?

So why bother to build a website for this, doesn’t all of this get covered during university? Well, yes and no. Today’s university curriculum must cover a lot more ground that would have been necessary 20 to 30 years ago. The expectation is that graduate engineers will hit the ground running and emerge from university with a diverse range of academic experience in a growing number of subjects. Degrees haven’t increased in length, so there is less time to dedicate to the understanding of structural behaviour. Competency in structural analysis takes time to develop, an 11 week semester just won’t cut it for most students. So, DegreeTutors is a resource that tries to give students the extra content that we can’t spend as much time on in the curriculum anymore. While the main intended audience is civil and structural engineering students, practising engineers or indeed other construction industry professionals may well get some benefit from a quick refresher on structural analysis.

Who’s the guy writing all the content?

I’m Dr Seán Carroll, a senior lecturer in structural engineering at the University of Exeter. I’m also the Director of Education (Engineering) within the College of Engineering, Mathematics and Physical Sciences. This site is not affiliated in any way with The University of Exeter. It’s a personal project, I’m just giving you my background for the sake of transparency.

Structural engineering and engineering education are things I’m very passionate about (hence the website). I graduated with a first in structural engineering from Dublin Institute of Technology in 2006. I have a masters degree in civil engineer and a PhD in structural dynamics (crowd-induced structural vibration). After getting my degree I worked for several years in Dublin for two companies, Arup Consulting Engineers and Tobin Consulting Engineers. After completing my PhD in 2013 I took up an assistant professor post at the University of Nottingham. This was followed by a 3 year stint as an assistant professor at the University of Warwick. Following a move to Cornwall in 2016, I joined the University of Exeter as a senior lecturer in structural engineering. I’m also a chartered engineer with Engineers Ireland (I’m Irish by the way!) and a Fellow of the Higher Education Academy.

Dr Seán Carroll | DegreeTutors.com
Gratuitous picture of me looking cool with a surf kayak in Brittany. Truth be told I actually prefer sea kayaking

What I like teaching

My area of interest in terms of lecturing is structural behaviour and design. That’s why most of the courses on DegreeTutors have an analysis flavour. University courses I’ve enjoyed teaching include:

  • Structural mechanics
  • Structural dynamics and vibration engineering
  • Finite elements analysis
  • Non-linear behaviour of structures
  • Analysis of plates ad shells
  • Design of reinforced concrete structures to Eurocode 2
  • Load paths and structural stability

Upcoming DegreeTutors courses and tutorials are likely to relate to these areas.

(au0026amp;b) Multi-storey structure stabilised by a lift/stair core. Relative deflection indicated by a heat map. (c) View showing a heap map on top of the deformed structure. (d) Plan view of the deformed structure with heat map emphasising the rotation of the structure about the core.

Research Interests

I don’t do as much academic research now as I used to. My focus has very much shifted onto engineering education. However, I maintain an interest, particularly in applications of computer vision to crowd behaviour and also in crowd flow modelling and the overlap between these areas. Some of research interests are discussed further below. I may well develop some tutorials or courses around this content at some point in the future.

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. Some of my initial work in this area revolved around building algorithms for pedestrian detection, tracking and 3D trajectory reconstruction. Despite being a departure from traditional civil engineering, I find multiple view geometry and computer vision generally to be a fascinating area.

2D Pedestrian tracking and 3D trajectory reconstruction using surveillance footage
2D Pedestrian tracking and 3D trajectory reconstruction using surveillance footage in Nottingham.

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. 

Laterally oscillating treadmill I built, capable of recording the lateral component of the footfall force. Built to simulate the sensation of walking on a wobbly footbridge.
Subject instrumented with gait analysis markers to study whole-body balance behaviour while walking on the oscillating treadmill. Using motion capture cameras to study subject response to the oscillating treadmill yielded some very interesting insights.

Crowd-induced vibration and crowd modelling

Above: Simulated crowd flow over a bridge indicating 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 stationary.

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. The overlap between crowd flow modelling and structural dynamics made for a very satisfying coding challenge and some interesting predictive capabilities. 

Some papers that came out of this research

  • 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 u0026amp; 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.