During a recent marine bollard assessment at a working port, our team was carrying out testing to understand the condition and capability of a series of critical mooring assets.
The objective was straightforward: assess the bollards themselves and provide confidence in their continued operation.
However, during the assessment, we identified movement within the wider jetty structure that was beyond what would be expected from a fixed marine asset under operational loading conditions.
The bollard was fine.
The jetty was moving.
This was not a floating pontoon designed to respond to changing water levels. This was a fixed structure, anchored to the seabed and intended to transfer operational forces safely through its foundations.
The concern was not the bollard.
The concern was the supporting infrastructure.
A 100-tonne bollard is only part of the story
It was a useful reminder of a principle we see across engineering disciplines: the component you can see is not always the component carrying the greatest risk.
A bollard may have an impressive load rating, but that rating only forms part of a larger picture.
A 100-tonne, structurally sound bollard cannot compensate for movement within the wider structure supporting it.
The strength of one component cannot compensate for weakness elsewhere in the system.
For example, a perfectly maintained bollard cannot overcome:
- deterioration within the supporting concrete
- compromised anchorage systems
- movement within the jetty structure
- foundation issues
- changes in how loads transfer through the infrastructure
This is why a thorough jetty inspection must look beyond the component that is easiest to see.
Understanding movement: when is it normal and when is it a concern?
One of the most important principles in engineering is understanding that movement itself is not always a problem.
In fact, many of the structures and systems we rely on every day are designed specifically to accommodate movement.
A suspension bridge, for example, must respond to changing weather conditions, temperature variations and dynamic forces. Flexibility is part of its design.
However, movement outside the expected behaviour of a structure can indicate a much more serious issue.
A famous example of this is the Tacoma Narrows Bridge in Washington State, which became known as “Galloping Gertie” after its dramatic movement in windy conditions.
When the bridge opened in 1940, observers noticed that the deck moved significantly in response to wind. On 7 November 1940, sustained winds caused the bridge deck to develop increasingly severe twisting oscillations until the structure ultimately failed.
The disaster changed how engineers approached structural design because it demonstrated that understanding a structure’s behaviour under real-world forces is just as important as understanding its strength.
In contrast, the Golden Gate Bridge was designed to accommodate movement under expected loading conditions. During periods of high wind, it can safely sway sideways by up to 27 feet (around 8 metres). The difference isn’t whether a structure moves – it’s whether it moves as its engineers intended.
The same principles apply in aviation
This understanding of movement is something I also recognise from my own experience as a former helicopter pilot.
Helicopters are complex systems that constantly manage vibration, movement and changing forces. One phenomenon pilots are trained to understand is ground resonance.
A small imbalance can become amplified rapidly, causing the oscillations to increase rather than naturally dampen.
The danger occurs when that movement becomes unstable and begins feeding back into the system, increasing the forces rather than absorbing them.
The pilot must recognise what is happening and respond immediately, either by lifting off to break the interaction with the ground or, if lift-off isn’t possible, by shutting down the engine. Acting quickly can interrupt the feedback loop before the oscillations become severe enough to damage the aircraft. If the oscillations continue to build unchecked, the helicopter can rapidly tip onto its side.
And while a helicopter and a marine jetty are completely different structures, the engineering principle remains the same:
Understanding how a system behaves under real forces is essential to understanding whether it remains safe.
Looking beyond the bollard
The bollard assessment highlighted a wider engineering principle: individual components cannot always be considered in isolation from the structures that support them.
In this case, the bollard itself was performing as expected. However, the assessment identified movement within the supporting jetty structure, prompting further consideration of the wider marine infrastructure and its ability to safely transfer operational loads.
This is why the relationship between individual assets and the structures around them is so important. A bollard, its anchorage, the supporting concrete, the jetty and the foundations beneath it all form part of one interconnected system.
Effective engineering assessment is not simply about confirming whether a single component remains serviceable. It is about understanding how the entire system behaves when real forces are applied and identifying where attention is needed to maintain safe and reliable operation.