Q. At what point does steel become part of the project rather than just bricks and mortar? We are in the early stages of looking at an extension into our back garden and wanted to know why steel is needed and how much it might add to a project.
A. When we take a look into the role steel plays in extension or even house construction we first need to look at why steel is required in the first place. I remember one of the first things I learned in first year studying Civil Engineering is that ‘concrete is great in compression but poor in tension’.
Steel, however is great in tension. What this means is that if your structure is just taking an even downward weight with no span required, then concrete is a great and cost effective way of dealing with that weight (for example your concrete block walls, concrete foundations and floor slabs. However, when you need to span from A to B (e.g. over a window or between two walls for a floor above, you need to introduce steel.
There are two principal ways to do this, you can either add steel to the concrete mix (reinforced concrete or rebar) or add steel RSJ beams to support the blockwork or timber beams spanning the required distances and take up the tension (pulling effect) that would otherwise crack your concrete or cause you timber floor joists to sag too much and your floors would ‘bounce’ (something you might often see me check in an old house on Cheap Irish Homes).
When it comes to extension design, the incorporation of the structural steel design stage really comes down to who is designing it and whether it requires planning permission. If its an engineer, he will be thinking about the steel requirement form the word go though it may only be indicative until planning permission is granted and there is a body of work to fully specify the required steel beams (work out all the forces (loads) and check through the various steel beams available and their sizes etc).
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