Why do structural engineers over-specify?

In the world of construction and structural engineering, the balance between safety, cost-effectiveness, and efficiency is paramount. However, there are instances when structural engineers might over-specify in their designs. This article delves into the motivations behind such decisions, shedding light on the complexities that influence the engineering process.

Under tight deadlines, engineers may default to conservative specifications to ensure safety and compliance. The pressure to deliver quickly can lead to a preference for solutions that are known to work, albeit at a higher cost or with more material than strictly necessary. This approach, while cautious, can inflate project costs and timelines.

Engineers sometimes work on projects outside their expertise. In such cases, over-specification serves as a buffer against the unknown, compensating for a lack of direct experience or specialized knowledge in a particular area of structural engineering.

Experienced engineers, having witnessed the consequences of structural failures or having been burnt by past projects, may over-specify to mitigate personal and professional risks. Their decisions are influenced by a career's worth of cautionary tales, leading to designs that prioritize safety over cost-efficiency.

Conversely, less experienced engineers may lack the confidence to optimize specifications, defaulting to over-specification as a safeguard. Their motivation is to avoid mistakes that could cause significant damage or injury, thus erring on the side of caution.

While not representative of the profession, there are instances where over-specification stems from a lack of effort to seek optimized solutions. This approach, driven by a desire to expedite the design phase, results in using more materials or simpler, albeit oversized, solutions without thoroughly exploring alternatives.

Legal and financial repercussions from structural failures can lead engineers to adopt a more-is-better approach. Professional indemnity claims can be reputation damaging and financially ruinous, prompting business owners to favour over-specification as a guard. Events such as Grenfell have also pushed insurance premiums significantly higher and a claim can lead to a company not being able to secure insurance at the next renewal.

The field of structural engineering evolves, with standards and best practices continuously updated. However, some engineers may stick to outdated standards they are familiar with, leading to over-specification based on previous norms that no longer apply. In 2010, many British Standards were withdrawn and replaced with new Eurocodes which can provide better quality designs as they are more rigorous.

The lack of access to or knowledge of cutting-edge engineering software can hinder an engineer's ability to optimize designs. High-quality software facilitates precise calculations and simulations, enabling more tailored and efficient specifications. It is expensive to provide training to the best software and therefore many practices still use Excel spreadsheets as the core software.

A lack of established systems for design review and optimization can result in over-specification. A checker of work needs to ensure the Architect’s brief has been met and ensure the structure is safe. There is less motivation to be rigorous at this stage to refine the design because it is time consuming. There can be a tendency for reviewers to err on the side of caution, leading to unnecessarily robust designs.

It is not easy to spot over-specification of structure. Significant overdesign does get flagged by experienced Architects and Contractors, but when the excess is say only 20%, it can easily be missed. 

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