Wednesday, 27 April 2016

Damage Detection in Bridges; Why it's becoming a Necessity

Hi all,

In this post I'll be covering some general aspects of why my project (ERS10) is required. In particular I will discuss the growing necessity of damage detection in bridges and some historical development down the years. I hope you'll enjoy!

The identification of structural damage in bridges is a research topic that has generated significant attention in recent years. The primary reason for its surge in popularity is an aging road and rail infrastructure, which is subjected to traffic loading conditions that far surpass their original design criteria. This unprecedented increase in loading is accelerating structural fatigue, which in turn reduces service-life. Some fatigue assessments carried out on the most common reinforced concrete bridge types constructed in Brazil since 1950 found that shorter span bridges, in the range of 7 to 10 meters, may have their fatigue performance in danger if a 100 year design-life is required [1]. As a consequence, it was deemed that a straightforward, non-destructive assessment method of bridge deterioration is urgently required.

Currently, non-destructive assessment methods entail visual inspections, hammer tests and localised damage assessment methods. These methods, although useful and inexpensive, have numerous limitations; they are infrequent, taking up to nine years between inspections [2], dependent on the competence of inspectors and are confined to localised damage and external deterioration, while the true global bridge condition remains relatively unknown. Additionally, as bridge infrastructure continues to age and deteriorate, the frequency of inspection must increase to counteract the reduction in safety of these structures. This task is made more difficult due to its sheer enormity. Recent figures show that Europe's bridge count is circa one million, and of Europe's half a million rail bridges, 35% are over 100 years old [3]. This leads to a need to reduce uncertainty regarding bridge condition through other, more efficient means apart from traditional inspection techniques.

The concept of using measured vibrations to discern damage in structures has been employed for some time. For instance, some early research by German engineers in the 1950's used vibration intensities, attained from measured accelerations, as an empirical indicator of damage in buildings [4]The use of monitoring a bridge's natural frequency over time to detect damage in structures was originally proposed by Adams et al. [5] in the late 1970s. It was a promising development as frequency is a product of a structure's mass and stiffness, and it was thought that monitoring natural frequencies over time would show how a structure's stiffness declined. However, there are many limitations to this methodology, for instance; changes in frequency would not locate damage accurately, as cracking in different locations can cause frequency changes of equal magnitude

Apart from natural frequencies, other modal properties such as mode shapes, damping ratios and modal curvatures have been traditionally used to detect damage. For instance, cracking in a cross-section will increase internal friction and thus raise the value of the section's damping ratio, however, damping ratios are heavily influenced by vibration amplitude and measuring them from vibration data produced large standard deviations, which impair their accuracy and effectiveness as a reliable damage indicator.  

The core problem is that bridges are monitored over long periods of time and are subjected to large temperature fluctuations, harsh storms and numerous traffic scenarios. These varying conditions affect changes to a bridge's stiffness and mass in a non-linear manner, which in turn alters the bridge's modal properties. This is evident in Peeters & De Roeck's [6] assessment of the Z-24 Bridge in Switzerland, where significant variation in the bridge's natural frequency was observed when the ambient temperature dropped below freezing point (see Figure 1). The cause of this bi-linear behaviour was attributable to the newly solidified ice in the bridge deck and supports contributing to its stiffness.

Figure 1.  Z-24 Bridge - Natural Frequency v Temperature - after [6]

So, that's all I will cover for now. I hope the above few paragraphs give you an idea of the need of an efficient condition assessment methodology of bridges across Europe, and that it also portrays some of the difficulties imposed by using vibration data, in particular, modal properties.

See you again soon!


[1]  Rodrigues, F., Casas, J.R. & Almeida, P. (2013). "Fatigue-Safety assessment of RC bridges. Application to the   Brazilian highway network", Structure and Infrastructure Engineering, Vol. 9, N. 6, 2013, pp.601-616.

[2]  Federal Highway Administration. (2008) "Bridge Evaluation Quality Assurance in Europe", Technical Report Document, FHWA-PL-08-016, March.

[3]  MAINLINE. Maintenance, renewal and improvement of rail transport infrastructure to reduce economic and environmental impacts. (2013) Deliverable D1.1: "Benchmark of new technologies to extend the life of elderly rail infrastructure" European Project. 7th Framework programme. European Commission.

[4]     Koch, H.W. (1953). Determining the effects of vibration in buildings, V.D.I.Z., Vol. 25, N. 21, pp. 744-747

[7]  Adams R.D., Cawley P., Pye C.J., Stone B.J. (1978) "A vibration technique for non-destructively assessing the integrity of structures." Journal of Mechanical Engineering Science. 20: 93–100.

[6]  Peeters, B & Roeck, G.D. (2001) " One-year monitoring of the Z24-Bridge: environmental effects versus damage events ". Earthquake Engineering and Structural Dynamics, 30, 149-171.

Tuesday, 23 February 2016


Hello and welcome to my blog...

As you're probably aware, this blog is designed to keep you all up to date with my hectic social life and wild adventures! Instagram in text form, if you will. Of course I'll also try to keep everyone informed of my progress with my TRUSS ITN project too! 

So to begin with a short introduction for those who don't know me; my name is JJ Moughty, short for John James, I'm 26 and from Longford, Ireland. I'm a graduate of Civil Engineering from N.U.I. Galway and, subsequently, from Trinity College Dublin where I completed a MSc. in Structural and Geotechnical Engineering. After graduating I found employment in the offshore oil & gas industry with Wood Group Kenny (WGK) in their Galway office where I specialised in the design and analysis of deep water drilling systems for semi-submersible vessels and drillships. 

The majority of projects I competed while with WGK were fatigue analyses of subsea wellheads. This is probably due to the fact that I've always been very interested in structural dynamics and how structures behave. It's an interest I've had ever since I discovered how the one of the World's tallest skyscrapers (Taipei 101see picture below) uses an enormous steel pendulum ball, suspended from the 90th floor, to maintain equilibrium during typhoons and earthquakes.  It achieves this by swaying out of phase to the structure at its natural period of oscillation in order to counteract the external environmental forces. This interest in structural behavior is also probably why I now I find myself relocated in Barcelona as one of the 14 fortunate Early Stage Researchers (ESRs) that make up TRUSS ITN.

Taipei 101 
TRUSS, or Training in Reducing Uncertainty in Structural Safety, is an Innovation Training Network (ITN), funded through European Union's Horizon 2020 research and innovation programme. My project's title is "Assessment of bridge condition and safety based on measured vibration level", which is ESR10. It is based in Universitat Politecnica de Catalunya under the supervision of Prof. Joan Ramon Casas. The motivation behind ESR 10 is to determine the structural condition of aging bridges as they decline due to a number of degradation processes over time, such as; creep, corrosion and cyclic loading from traffic and environmental effects. Recent figures show that Europe's bridge count is circa one million, and of Europe's half a million rail bridges, 35% are over 100 years old, which justifies the considerable amount of research being conducted in the area at the moment. 

My project is also in collaboration with the Spanish Engineering company COMSA, where I'll be spending some months on secondment in their Barcelona offices. This will increase my exposure to innovative environments in both academia and industry, while also allowing me to learn first hand how projects of this nature are completed in the privet sector.  

That's all for now. I'll be back soon to fill you all in on my progress with ESR10 and life in Barcelona!

Slán go fóill!