Temporary Works Toolkit. Part 8: Modular hydraulic propping systems for deep excavations

In the second of two articles examining temporary works failures, Director of Structural-Safety, Alastair Soane, considers why failures occur and what steps can be taken to reduce the risk of catastrophic events.

The majestic splendour of the Millau Viaduct, towering 343m above the Tarn valley in southern France, will inspire engineers for generations to come. Emulating such feats of engineering requires an understanding of buckling beyond the simple Euler formulae for pin-ended struts, as well as the services of a celebrated architect to fine-tune the proportions and sculpt the shape and details of the extraordinary pier supports. Exceptionally tall or slender columns may necessitate finite-element (FE) modelling to determine the effects of buckling. However, in many cases, an accurate assessment of the critical buckling load can be made by hand calculations incorporating spring supports or tapered/stepped stiffness columns. This paper discusses the calculation of the buckling load for the end conditions given in Eurocode 2 (EC2), Figure 5.7, including various rotational spring restraints and variable stiffness within the length of the strut.

This article discusses some of the design issues and preconceptions related to backpropping, and gives worked examples.