Design appraisal and letter

Part 1b of the exam requires you to write a formal letter to the client explaining the impact of a design change.

The examiners make it clear in their reports that they are looking for you to identify any issues with the design and construction and propose solutions to the problem, not a letter saying that it can't be done or explaining that it will cost more and there will be programme implications. If the change makes your design non-viable then explain why and propose an alternative.

Below is a checklist you can use for part 1A.

Railway bridges are not very common in the IStructE exam, perhaps because there are so many standard designs available. Structures carrying light railway fall into a grey area, and could be designed as highway bridges with lower span to depth ratios.

This cheat sheet sets out some common types of railway bridge that are suitable for different span ranges, along with some key considerations when laying them out. Depths are given directly instead of span to depth ratios, but you will notice that the ratios are much lower than for highway bridges.

One of the most common constraints in the IStructE exam is spanning a known distance with limited construction depth (e.g. due to headroom clearance requirements underneath the structure), so the span and span to depth ratio are two of the key pieces of information you can use to identify a suitable superstructure type.