Volume Six - Pre-Victorian to the Present Day - Select Aspects - Structural Analysis of the river Ely Subway by Rota Design Limited - 2015

Stress - principal stress

After assessing the deformation under load of a structure we at Rota Design Limited look also at the stress induced into the form. We often look at areas where there are stress concentrations and revise the density of the mesh in that area and then re-run the analysis until we reach convergence i.e the results no longer vary, are steady and viable.

We found that the maximum stress in tension was 4.0 MPa and the maximum compressive stress 10.0 MPa.

Buckling Analysis

Another question we have to answer when we undertake analysis on a structure such as a tank, chamber or pipeline that is buried underground would be does it buckle under load? This analysis is undertaken using the same software but we would always have a manual calculation to check that we haven't added an extra zero or so into the software inputs (so easy to to do!). The main problem with all computer programs is if you put incorrect data in you get the wrong answer out. In this case it could have implications for the safety of people walking through the subway.

The minimum requirement is that the buckling factor should be greater than unity (1); in the case of our subway it was found to be greater than 10 (non-linear buckling factor).

Conclusions and Comment

The subway has survived the years of service by being rather over-engineered. The buckling factor is excessive by modern standards and thus would be deemed a waste of materials in today's engineering design office. The maximum deformation at approx. 7 mm is minimal and the stress levels are not of great concern. So our initial studies have not revealed any results which would suggest that the subway is liable to fail in the near future.