24 November 2010

much of a muchness? - Part I

So we talked about the structural framework of Railway Parade, being the defining element of the "skin", which is the only area left for us as architects to design.

....All the linearity of the structure.....in our imagination it would be such an elegant geometry!

But as soon as we started to attach materiality to the geometry, we are entering a total new ball game.

We have 2 choices of material with such structural system - steel and timber.  Traditional masonry (concrete, blockwork etc) is out of the question this time.  Here we need to check a few thing...

1. Fire rating requirement of the structure.

We want the structure to be as refined as it can be, by adding fire-rated material onto the structure it will definitely make the structure bulkier.

Our building is quite small in floor area, hence we fall under Category C Construction under the BCA (Building Code of Australia) - which means structure does not require fire-rating as long as it is 3m away from fire source (here boundary onto neighbouring property is also considered as fire source).  So we went back to the drawing board, made that an executive decision and replanned the building to avoid fire-rating the structure.

Both steel and timber require extra attention with fire-rating, it has a massive impact on costing if we have to start introducing sprinkler, window drenching, etc etc to the building.  You would imagine that timber is out of the question if we are to fire-rate the structure......very wrong here!  Because timber has a charring effect during fire, the char formed on timber surface reduces the heat reaching to the timber core, hence reduces the speed of burning out.  In many ways timber performs better than steel in fire!

IN Shigeru Ban's GC Osaka Building, timber particle board was used as fire rating material to clad the steel structure. As timber does not transmit heat through, it prolonged the performance of the encased steel structure in the case of fire. Of course extensive testing was carried out and calculation is required regarding timber charring rate and density etc..... (photo taken from "Shigeru Ban" by Matilda McQuaid, published by Phaidon)

…….. to be continued tomorrow………….

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