the revival of a great material
Last September, i had the chance to attend the combined IABSE – IASS conference held in London. Among others (perhaps i’ll write about them too some other time) I came across a friend and colleague who works for Expstructural expiredition Engineering. We’ve been discussing about his works in the past but that one time he had something much more interesting to share with me. He was working in a large project in Greece with Renzo Piano (http://www.snf.org/snfcc/snfMain_en.html) which i had heard all about in the past, apart for an interesting detail : they were experimenting on using Ferrocement to construct the large canopy exposed on top of the artificial hill of the Stavros Niarchos Foundation Cultural Center.
I have read quite some stuff about the material and process in the past but i was always wondering why it ceased to be used as a building material. In fact only a few examples (but certainly exiting) mainly by Pier Luigi Nervi, showcase this great material. According to him, “…Experiments with the new material demonstrated immediately its most important and fruitful properties: it could withstand great strains without formation of cracks in the cement mortar, as a result of the subdivision of reinforcement, and it eliminated forms, because the mortar could be applied directly to the mesh, which would act as a lath to retain it”. [Structures, Pier Luigi Nervi 1956].
The roof of the Turin Exhibition Hall (below) is a great example of Nervi’s work.
image courtesy of http://www.canadianarchitect.com
So, to get on with the story, my friend went on telling me that they were currently building a prototype of a piece of the canopy on site, testing it and trying to convince the client and the authorities that the material can be used for that purpose. He promised to let me know the next time that he was going to be on site so that i could join in. And so he did, and so i got the first flight in just to visit the site and have a look at the prototype. Which brings us to why i started with this blog: the excitement of structural experimentation, something that seemed to had faded away at least in our part of the world. Structural Engineering in Eastern Europe is quite straight forward and boring I would say. Designs are ruled by the code standards and there’s not much space for innovation. The major excuse for that the ground shaking underneath, literally. But let’s face it we are not the only ones dealing with earthquakes. Countries experiencing worst earthquakes than us are much more daring, take Turkey for example. However, the visit to the SNFCC site trigged some hope. Experimenting with new materials and construction methods in a country so conservative in architecture and engineering as Greece (as in Cyprus) and particular in during the recession is definitely remarkable. Also, the idea of using a prototype at a large cost to test the actual behavior of a structure is very uncommon in Greece. And the important part is that the works were conducted by a small scale local contractor, something that proves the applicability of the method in structures of less significant and perhaps cheaper projects.
image courtesy of http://www.sng.org
The canopy is a cushion-like structure that spans between a series of perimeter columns, the major span being around 100 meters. Ferrocement behaves in a composite manner, acting as the flange of the steel space truss, hidden inside the skin. It’s really hard to believe that such a lightweight structure (ferrocement skin is less than 30mm thick, reinforced by 200mm deep and slender ribs) would span that long of a distance. The mortar (cement with silica sand and some fly ash) is placed by hand on a set of woven mesh reinforcement and vibrated so that it penetrates through. That would mean that it can work without a formwork as the dense mesh layers cover for that. The end product is a lightweight smooth concrete looking structure with very little permeability due to the fine sand with great structural properties.
Ferrocement mortar laying
The final product looks quite promising, you can have a look at: http://www.expedition-engineering.com/main.php. I am looking forward to see the end result and I am sure the whole process will signify the start of a new era in experimental structural engineering.
