Abstract

A lot of successful research does not involve major breakthroughs, but instead relies on drawing together many separate strands to form a coherent whole. The analysis of prestressed concrete (psc) is trivial but its design can be complicated. The prestressing force in a structure is typically ten times its weight, so unlike most structural elements, the unloaded state can be a critical design condition. Things are even more complicated when the structure is statically indeterminate. Finite elements don’t help because they tell you what will happen to a structure you have already designed, but not how to select that structure in the first place. The process is not governed by a small number of equations but by a large number of inequalities. The result is that design of psc is often put into the “too difficult” box and a less suitable material is chosen.

Angus Low, who worked for Arups, and who sadly died in January this year, was one of the leading exponents of prestressed concrete bridge design. He published a paper in the ICE journal that referred to a previously unknown third constraint on the required prestressing force when designing viaducts. The method undoubtedly worked but the underlying principles weren’t clear. The talk will describe methods that allow the design of prestressed concrete to be carried out in a logical sequence, and on the way explains “Angus’ 3rd equation” as it came to be known. It allows a designer to work from the applied loads all the way through to the cross section shape, the choice of the concrete strength the selection of the required prestressing force and the final cable profiles. All the required theory is taught in the third year or earlier. It shows how the method can even be deployed in an expert system, which today would be called AI. ChatPSC anyone?

Photo credit: HS2

Zoom link: Join Zoom Meeting https://eng-cam.zoom.us/j/83729338532

Meeting ID: 837 2933 8532