Civil Engineering Archives - Hawkins Forensic Investigation

A Structure is Only as Strong as its Weakest Link

Matthew Carrington — Mon, 09 Mar 2026 15:41:10 +0000

Construction projects of all kinds, over a wide range of scale, require structural engineering design input to direct the way they are built. The structural engineering design is almost always implemented in conjunction with architectural design, other specialisms, and the knowledge and skills of the contractor and specialist sub-contractors.

Civil and structural engineering design is a complex field where many engineers are highly qualified, with professional accreditations from engineering institutions after several years of industry experience, following a university degree. However, there is no safeguard against less qualified or less experienced people also trading as civil or structural engineers.

This article discusses the typical aspects of structural engineering design that are required in most construction projects. It includes case studies investigated by Hawkins, where the action of the structural engineering designer could be at fault.

“The strength of a structure depends on the strength of its elements and the way they are joined together.” – Gustave Eiffel

Weak Links

Some building faults might be related to issues with the structural engineering design, or omissions in it. Others may be due to the actions of other parties in the design or construction team, or faulty materials. The design process for each project must consider all the potential modes of failure of the structure. Any one thing could be missed in the design process and cause an issue with the performance of a building. Sometimes, a combination of circumstances needs to coincide to cause a failure. Almost every construction project is a prototype due to the varying combinations of building shape, location and formation of the team performing the work. The following sections describe five links in the structural engineering design chain.

1. Design Issues

It is possible for a structural engineer to completely design the strength and stiffness of the individual elements for the structure but miss a wider issue that can lead to damage or failure.

For example:

The lateral sway stability of part of a building can be reduced by replacing the vertical support from a solid masonry wall with a steel beam;
Loads on a gravity retaining wall at a change of level of external ground that were not allowed for in the design can occur if drainage is not detailed (Figure 2);
Overall structural capacity can be exceeded if a whole category of loading is omitted, such as wind or snow load.

2. Site Issues

There are cases where the design might have considered the typical scenario for the type of structure they designed, but there was something different on site that they did not allow for.

For instance:

If a designer assumed that a wall was a cavity brick/block wall, when it was in fact a solid stone wall, then the wall would be heavier than assumed. A beam installed to create an opening and support the wall could then be overloaded;
A wall that was retaining higher ground could collapse if the rest of the building that was providing lateral support to the wall was removed without considering the interaction (Figure 3);
The effect of a row of small trees on building foundations movement can be greater than the individual trees;
Different ground conditions can have more or less aggressive reactions to the concrete they are in contact with. The wrong mix of concrete might look suitable initially, but in aggressive ground conditions, it can degrade over time.

3. Calculations

Sometimes, the structural designer can miscalculate their designs.

Examples might include:

An assumed length of a beam was not updated in the design calculation when the length of the opening was longer than first planned;
In a structural assessment, the engineer might have used the material properties for normal density concrete when the element was lightweight or aerated concrete, which can only provide lower strengths;
In computer aided design, using finite-element modelling or calculation sheets prepared by a software company, the wrong input for the situation being built can lead to an understrength member. This might arise from one wrong tick in a box within the software options.

4. Stages of Design

There have been cases where the structural engineer provided sufficient design information for a preliminary stage of the design, such as submission to building control, to gain approval for the project to proceed. Then, the client or contractor did not go back to the engineer to ask for detailed design and construction details, or did not correctly apply the submitted preliminary design.

These cases have included:

Where relative positioning between structural members and their supports was critical to the building performance, but the individual member capacity design was sufficient to pass the building control plans check;
Where the order of construction would be critical to the capacity of the structural members. During construction, an unrestrained steel beam would have considerably less capacity to carry vertical loads until it was restrained by the floors to both sides (Figure 4);
Often, changes that appear to make the building simpler to construct can introduce complications to the way they would perform. The changes would need further structural design and could cause a problem if the designer had not been notified.

5. Missing Design

We have investigated cases where an item was overlooked as needing civil or structural engineering design. This can occur at interfaces between specialist contractors’ responsibilities:

i. Roof vents (Figure 5);
ii. Cladding boards (Figure 6).

These will likely perform satisfactorily in normal conditions but might not be sufficient for high winds or rain. This would likely present in the failure of several of the same items. Identifying the fault early might allow the rest of the items to be remediated.

Failures can exhibit a range of states of distress and at different times in the life cycle of a building.

The questions which must be considered when investigating the root cause of the failure will vary with the scenario, including:

Was the designer provided all the necessary and correct information?
Should the designer have found out the correct information by looking into the situation more than relying on drawing or reports they were provided?
Was there information that the designer needed to show in more detail to a competent contractor?
Was there a coordination responsibility to make sure the correct information was provided?
Should a competent contractor have given feedback to the designer that the situation was not as allowed for in the design?
Did the client appointment limit how much the designer could do in any of these aspects?

In some cases, we have been able to advise that urgent action needed to be taken to avoid further damage occurring. This can save people spending time in a position of danger looking for material damage or conducting intrusive investigations that might tip the situation further towards collapse.

“The best design is the simplest one that works”. – Albert Einstein

Conclusions

Sufficient structural engineering design relies on considering all the relevant design issues and all the particular conditions on the site. The structural engineer must complete the design calculations correctly and present the construction information clearly to the contractor. Greater levels of detail are required for the construction issue of the structural drawings than for the building control submission. That is a situation where misunderstandings can arise. Also, there are proprietary and peripheral items related to construction that might not be part of the scope of a structural engineering appointment but would have benefitted from a review by a structural engineer.

How can Hawkins Help?

Hawkins’ Built Environment team can review when something has gone wrong and assess the relevant specialism or party that might have contributed to the issue. Professional experience is important in engineering, including experience of investigation.

About the Author

Jolyon Antill is a Chartered Civil Engineer based in our Reigate office. Graduating with a first-class Master’s Degree in Civil and Structural Engineering, Jolyon has 27 years of design consultancy experience.

His range of industrial and commercial project design work includes new builds, renovations, and structural surveys, both in the UK and overseas. Jolyon also has extensive experience in regional civil and structural engineering consultancies working on educational, residential, leisure and commercial projects. If you have a civil or structural issue and need Jolyon or one of the team to investigate, please contact us.

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Bye Bye Bamboo: Why Hong Kong is Phasing Out Traditional Scaffolding

Matthew Carrington — Mon, 24 Nov 2025 10:56:48 +0000

Bamboo scaffolding, alongside neon signs and red taxis, has long been a defining feature of Hong Kong’s urban landscape. But like many cultural icons, it is now facing a quiet retreat. In a move driven by safety concerns, The Government of Hong Kong is beginning to phase out bamboo scaffolding in public construction projects, marking a significant shift in the city’s construction practices.

A Policy Pivot Toward Metal

On the 17 March 2025, the Development Bureau of Hong Kong issued a circular memo titled “Adopting of Metal Scaffolds in Public Works”. This document outlines a new requirement that from 21 March 2025, all public works tenders must specify the use of metal scaffolding. Bamboo may only be used in exceptional cases, and only with detailed justification.

The Bureau cited bamboo’s “intrinsic weaknesses,” including inconsistent mechanical properties, susceptibility to deterioration, and high combustibility, as key reasons for the change. Additionally, the Bureau is cognisant of the wide adoption of metal scaffolding in Mainland China and other advanced economies.

The Case for Bamboo

Despite its drawbacks, Hong Kong has historically favoured bamboo scaffolding for several compelling reasons. It is:

These advantages have contributed to bamboo scaffolding becoming a staple of the city’s construction industry for decades. However, safety concerns have persisted.

Putlogs: A Common Source of Failure

A 2004 study by Tsinghua University titled “Comparative Study of Safety and Application of Bamboo and Metal Scaffolding in Hong Kong”^[1]found that the most significant hazard in both systems was the failure or absence of putlogs – horizontal members that tie scaffolding to the building structure. An excerpt from the paper showing the hazards associated with both types of scaffolding can be seen below.

Interestingly, Hong Kong’s safety codes impose stricter requirements on bamboo scaffolding putlogs than on metal ones. Bamboo scaffolds (under 100m in height from ground) must have putlog ties spaced no more than 3 meters horizontally and 6.3 meters vertically (equivalent to one per 18.9m²), with each tie capable of withstanding 7kN^[2]. In contrast, metal scaffolds require only one tie per 25m², with a lower strength threshold of 6.25kN^[3].

This raises a critical question: if bamboo scaffolding is held to higher standards with regards to putlogs, why is it perceived as less safe?

The Real Risk: Lack of Oversight

A recent scaffolding collapse involving 20 workers revealed the true issue: inadequate professional oversight. Investigators found that the metal ties used for the bamboo putlogs were as thin as 1.06mm – far below the required 6.00mm^[4]. The collapse was not due to the use of bamboo itself, but to unauthorised modifications and a lack of professional design and supervision. A government safety officer emphasised the need for scaffolding to be professionally designed and approved. The Chairman of the Construction Industry Council echoed this, calling for better coordination among engineers, supervisors, and qualified personnel to prevent such failures^[4].

Looking Ahead: A Role for Expertise

While the shift to metal scaffolding may reduce some material-related risks, it does not reduce the need for professional oversight. Whether bamboo or metal, scaffolding systems must be properly designed, installed, and maintained.

The phasing out of bamboo scaffolding in public works marks the end of an era in Hong Kong’s construction history. Although the decision is rooted in legitimate material safety concerns, it also reflects a broader shift toward modernisation and regulatory rigour. As this transition unfolds, it is essential to recognise that safety is not solely a matter of materials and regulations – it is also a matter of professional expertise.

How can Hawkins Help?

At Hawkins, our chartered civil and structural engineers bring deep industry experience in design consultancy, site supervision, and forensic investigation. We offer guidance to the construction industry, helping define and develop working procedures and practices that reduce the risk of incidents and lead to safer outcomes. Our Hong Kong team has investigated a wide range of incidents, including, crane and material hoist collapses, concrete spalling, slope failures, and structural damage from vehicle collisions. Our goal is to provide clarity, accountability, and actionable insights that help prevent future incidences.

About the Author

Patrick is a Chartered Structural Engineer based in our Hong Kong office. He has many years of experience in the construction industry and has worked for both contractors and consultants on temporary and permanent structural works. He has designed temporary supporting structures for both metal and bamboo scaffolds. As a resident site engineer, he has also monitored scaffold construction safety and ensured that temporary working platforms are adequate to support all intended loads.

Patrick joined Hawkins as an associate in 2024 to expand the forensic structural engineering capabilities of Hawkins in the Greater China and Asia region.

If you would like to discuss any incident—whether related to the built environment or any of the many other scientific and engineering disciplines Hawkins supports its clients with worldwide, please get in touch.

References:

[1] Fang, DP, Wu, SH, Wong, KW & Shen, Q 2004, A comparative study on safety use of bamboo and metal scaffolding in Hong Kong. in Construction safety management systems. Spon Press, pp. 373-386.

[2] Hong Kong Labour Department 2024, Code of Practice for Bamboo Scaffolding Safety, Fifth Edition.

[3] Hong Kong Labour Department 2013, Code of Practice for Metal Scaffolding Safety, Second Edition.

[4] Hong Kong Construction Industry Council 13 February 2025, Life First Walk the Talk Webinar – Bamboo Scaffolding Safety and Code of Practice.

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Collisions with Cobots

Chloe Duggan — Fri, 10 Nov 2023 13:20:57 +0000

What is a Cobot?

The 1980’s saw the rapid deployment of industrial robots for mass-production in a drive to reduce costs and improve quality. Industrial robots were typically seen in production lines, sparsely populated with technicians; or robots in cages, both designed to prevent a collision between humans and machines. Whilst the argument for utilising robots in terms of ‘a labourer that never sleeps’ and ‘improvement in quality through consistent output’ is well established, they also lack the dexterity and adaptability of a human worker. The last decade has seen a surge in demand for cobots (collaborative robots), that is, robots that have been designed to work alongside human workers, to combine the skillset of robots and humans whilst maintaining the safety of the human worker.

In 2023, the estimated annual sales of cobots globally was in the order of USD 1 bn, and some market research companies predict a rapid growth of up to USD 11.4 bn by 2030. A multi-billion dollar market, growing at between 15% to 32% annually led Allianz Global & Corporate Speciality insurers to identify the growth of cobots as an important trend in their industry in the next 15 years (reported in Sept 2019).

Cobot Variations and How They Work

There are significant differences in cobots, compared to the familiar industrial robots, which are intended to mitigate the risk to human safety during close interaction.

In the late 2000’s, Kuka Robotics and Universal Robots, world leaders in the design and manufacture of industrial robots, released the first generally available production cobot models. Kuka Robotics released the LBR 3 and shortly afterwards Universal Robotics released the UR5, both of which were cobot versions of the familiar articulated arm robot (arm sections referred to as links, joined together with rotational elbow or wrist type joints). Unlike their robot predecessors, which relied on external sensors such as light curtains and proximity switches to activate safety protocols (e.g., to stop or slow down), cobots rely on physical differences and internal sensors for safety. The articulated-arm cobots are typically lightweight in comparison to robots and are limited to small payloads (typically 3 kg in early models) in order to reduce their inertia and the energy transfer to the co-worker when a collision occurs. They commonly employ sensitive torque sensors at each joint to detect a collision with a co-worker, enabling them to respond rapidly according to their control system.

The YuMi dual arm cobot, manufactured by ABB, was released in 2015 and is probably the highest profile cobot, as far as public awareness is concerned, and is considered to be state-of-the-art in the cobot sector. It was designed to work side-by-side or opposite human co-workers on precision tasks such as electronic component assemblies. YuMi incorporates many of the safety control systems employed by the earlier articulated arm models, with the addition of cameras that view the workspace – also used to adapt to changing situations such as picking up misaligned parts. YuMi has also adopted padding on its arms and has removed all pinch-points so that its co-worker’s fingers cannot become trapped.

We can assume then, that collisions are expected to happen, and so systems must be in place to minimise the severity of the injury to the human co-worker.

Safety Systems and Industrial Standards

There are numerous ways in which workers interact with cobots. Some cobots operate independently, but in close proximity to workers; others are guided by hand to provide the operator with increased strength and stability. The safety systems employed are required to be designed to reflect the cobot’s intended use. ISO 10218-1:2011 provides a specification and guidelines for the safe design of robots (including cobots), and describes basic hazards associated with them. ISO/TS 15066 is a technical specification, and a supplement to ISO 10218, which provides guidance on risk assessment of robots in collaborative applications i.e., cobots.

From a forensic investigation perspective, when investigating a human-cobot collision, one consideration is likely to be the system response. When a cobot’s internal sensor detects a collision, the system should produce a response based on a stopping category. IEC 60204-1 (and EN 60204-1) describes three stopping categories: 0, 1 and 2 for electrical machines. Universal Robotics defines most of its cobot collision safety systems (referred to as safeguarding) as stopping category 2 (stopping with power left available to the robot i.e., slows quickly to a standstill, but remains powered) and also specifies the maximum stopping time for different responses, which can be referred to by the investigator.

Summary: What Does This Mean for Insurers and Investigators?

The rapid growth of industrial, human-robot, collaboration tasks has the potential to lead to an increasing number of personal injury cases relating to human-robot collisions Large variations in cobot solutions means that determining whether a failure is a result of a manufacturing or software design defect, or other cause, will be a challenge for both the insurer and investigator. Awareness of the developments in this sector, in particular, how the system was designed to respond to a collision between cobot and human co-worker, may be key.

About the Author

Dr Ian Jeavons is a mechanical engineer with over a decade of experience in a range of manufacturing environments. His involvement with industrial robots and cobots stems from his doctorate research whereby he used machine learning and laser tracker measurements to improve the accuracy of an industrial robot for machining purposes.

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Sprinkler Systems – are they too good?

Chloe Duggan — Fri, 04 Aug 2023 15:26:17 +0000

Automatic suppression systems are designed to react to a fire and either extinguish or control it such that extinguishment can be completed by other means. There are several different types of suppression systems, with the most familiar and widespread being water sprinkler systems.

Sprinkler systems typically consist of a water tank, pumps, valves, arrays of pipework, and sprinkler heads. Their operation is most effective during the initial stages of a fire’s development, where the fire growth is disrupted by wetting surrounding combustible materials and smothering flames through evaporation. It is for this reason that sprinklers are effective at safeguarding evacuation and protecting property. Evidence demonstrating the effectiveness of sprinkler systems is well-accepted globally and it would be difficult to find anyone arguing that they are not one of the most effective fire safety provisions available. As an example, UK research commissioned by The National Fire Chiefs Council identified that the operational reliability of sprinkler systems was 94% and they were 99% effective in controlling or extinguishing fires.[1].

In the UK, current fire safety guidance recommends that sprinklers are provided in non-residential buildings that are over 30 metres in height (roughly equating to buildings with at least nine storeys). As such, low and medium-rise non-residential buildings are often not fitted with sprinklers.

Therefore, whilst sprinkler protection is considered to be highly efficient at minimising the consequences of a fire, it might appear surprising that they are not installed in most buildings in the UK. Could the fire safety industry be doing more to encourage their installation in low and medium-rise buildings?

Based on my professional experience as a fire engineer advising on fire-safety decision-making during various stages of a building’s design and construction, there are two common reasons that discourage stakeholders from installing sprinklers within low and medium-rise non-residential buildings. These are the spatial requirements and the costs associated with such systems. In this article, I evaluate both factors and question whether current sprinkler design guidance is demanding systems that are “too good”, i.e. with a performance that could be reduced so that smaller and more cost-effective solutions could be installed in more buildings, whilst still being effective.

Spatial Requirements

A frequent concern I have heard in the design of sprinkler systems is related to the space requirements for the water tank. This is significant, as designers seek to maximise the commercial value of buildings by proportioning as much space as possible as saleable area. Furthermore, as buildings continue to increase in complexity and usability, physical space for plant equipment is at a premium.

The design of non-residential automatic sprinkler systems typically follows the recommendations found in BS EN 12845. With reference to this guidance, and assuming parameters associated with typical buildings (e.g. less than 18 metres in height and containing similar fire hazards as those which can be found in a hotel or office etc.), a pre-calculated minimum effective water volume of 55,000 litres is advised. Allowing for any inefficiencies of the tank volume, that equates to a tank with approximate dimensions of 6m x 6m x 2m, not allowing for additional surrounding space for the associated pumps and fittings, and maintenance access.

That is a significant footprint for designers to locate, particularly within buildings that might be seven storeys or less. The appetite to include such a sprinkler system is made especially more difficult when there is little regulatory pressure for such buildings to have automatic suppression at all. So, is this demand for water storage proportionate? Could it be possible to reduce tank sizes, maintain adequate sprinkler performance in a fire, and encourage more installations?

To explore this, I refer to evidence that shows that 95% of fires are suppressed with five or less[2] sprinkler heads operating; and BAFSA guidance which states that a single sprinkler head discharges up to 100 litres per minute. Combining this information results in a generous flow rate estimate of 500 litres per minute, demanded by a sprinkler system during a fire.

At this flowrate, water from a tank with an effective capacity of 55,000 litres can suppress a fire for 1 hour and 50 minutes. This is a considerable duration for a fire, before which it could be expected that both the Fire Service will have intervened and the full evacuation of a typical building to have completed.

It could be argued that a timeframe of 30 minutes might be more appropriate. This should ensure protection during the most critical stages of fire development, and beyond such point that the Fire Service are likely to have attended and begun to extinguish a suppressed fire. Such a sprinkler system duration should be sustainable from a tank with an effective capacity of 15,000 litres; which would occupy approximately 3.5m x 3m x 2m. In comparison to the pre-calculated system from BS EN 12845 this represents a 51m3 saving of vital building space.

This demonstrates that it might be possible to provide more optimal sprinkler systems that still have adequate fire safety performance, but present less of a hinderance to the usability and commerciality of a building. This could make the installation of sprinklers a more attractive proposition to building designers and developers, and increase the propensity for sprinklers to be installed in buildings that otherwise might have had no fire suppression at all.

I should acknowledge other methods, acceptable in the design guidance, which can also help to reduce the pre-calculated tank size. For instance, it is possible to hydraulically calculate the system to identify more bespoke sizing, utilise towns mains as the water source, share tanks with other buildings or install water mist suppression systems. However, in my experience these each have their own pitfalls: hydraulic calculations can still demand sizable tanks; water suppliers will not guarantee the water flows and pressures necessary for towns mains support, water mist systems are relatively new and therefore introduce approvals risks with Building Control and Insurers; and shared tanks between different operators is a novel idea with issues relating to maintenance and responsibility.

Cost

A second common concern is the up-front capital cost.

It is true that initial costs associated with equipment and installation can be considerable. However, in my experience, the flexibility in the fire safety design of buildings that incorporate sprinkler systems is often overlooked. For example, sprinklers can allow a reduction in the level of fire resistance of walls, floors, and elements of the structure. This can introduce significant cost savings (and often environmental benefits).

Equally notable is that the provision of sprinklers can greatly assist the Building Regulation approvals process; Authorities Having Jurisdiction (including the Fire Service) unsurprisingly view the inclusion of a sprinkler system favourably. A more efficient building approvals procedure can make a considerable difference to cost, as any redesign or technical justification can become expensive, especially at the latter stages of a project programme when the design is largely fixed.

It should also be noted that any advancements towards reducing sprinkler tank sizes, as discussed above, would also mean lower up-front capital costs. Not only are smaller tanks cheaper assets, but the associated pumps and pipework are also likely to be more cost-effective.

Conclusion

This article seeks to discuss the benefits of sprinkler systems and ways in which they could be introduced into more buildings; I question whether current sprinkler design guidance is demanding systems that are “too good” and, by doing so, could be inadvertently reducing the number of buildings that could benefit from effective sprinkler protection.

It might be possible that, by relaxing current design guidance somewhat, particularly in relation to tank sizing, we might be able to gain sprinkler protection within buildings that previously would not have any. Overall, this could reduce the societal risk from fire and decrease the losses sustained from such incidents.

About the Author

Since joining Hawkins’ Birmingham office in 2022, Tom has utilised his fire safety experience to conduct investigations into the fire engineering design, construction and management of a range of building types. These investigations allow Tom to advise on proportional remediation measures to ensure fire risk levels are managed; and/or identify any relevant breaches in legislation that might have contributed to fire damage.

[1][2] National Fire Chiefs Council. Efficiency and Effectiveness of Sprinkler Systems in the United Kingdom: An Analysis from Fire Service Data. May 2017

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