|
The phone rang.
“Ello”
“Who's that?”
“It's me.”
“Me? Who's me”
“It's me, Eric”
“Eric? Eric who?”
“It's me Eric, your husband.”
“Oh that Eric. Where've you been, your tea's been on the table for three years, it's gone cold.”
“Sorry love, I'm in the shed. I've been a bit busy.”
“Messing about with another of your silly ideas I suppose.”
“No love I've discovered this wonderful invention.”
“What now? Not another electric nasal deposit remover, I've only just had the stitches out from your last wonderful idea.”
“No love. It works like this. You take grey rock. You crush it up into a powder.”
“You crush grey rock up into a powder?”
“Yes love, then you burn it.”
“Burn it? What, sort of cook it?”
“Yes, you burn it. Then you mix it with water.”
“Water.”
“Yes, water so you end up with a sort of grey mud.”
“Grey mud. Then what? Don't tell me, you pour it into a cake tin.”
“That's right love, you put it in cake tin and let it set. How did you know?”
“So that's where all my cake tins went you useless piece of genetic landfill!”
“I'm sorry love, it was for a good cause.”
“A good cause! We'll be spitting out gravel everytime we eat fruit cake for the next six months. So what do you get at the end of all this?”
“Grey rock.”
“Grey rock? Great, that's really earth shattering. You take grey rock, you crush it, burn it, mix it with water, let it set and you have grey rock. I am totally underwhelmed. You know Eric Heckmondwhyke your are a mental aberration, just like your father, I put it down to bad semen.”
“Cement, now that's a good name.”
Cement, of course, mixed with sand and gravel becomes concrete which, as we all know, has literally changed the face of our planet particularly when someone started using it with steel........
Reinforced concrete is pretty clever stuff. It was invented by a bloke from Newcastle Upon Tyne in the 1850's. It allows us to do all sorts of things in a constructional sort of way that without it we couldn't.
Concrete on it's own is hard and brittle, you can't crush or bend it but it does have a tendency to crack. It has very high compressive strength but low shear strength. It doesn't cope very well when you try to stretch it. It is very stable it does no rot or rust.
Steel on the other hand has high shear and tensile strength, Unfortunately in thin sections it bends relatively easily and it rusts.
The combination of steel and concrete however gives us a material that is far stronger and more useful than the sum of the individual components. By embedding steel rods into concrete the concrete and steel support each other. The concrete prevents the rods of steel from bending while the steel stops the concrete from cracking or shearing off. More than this the steel holds the concrete in its strongest compressed state while the concrete stops the steel from rusting.
This very useful material has revolutionised building and, incidentally, the creation of mindboggling statues we see at roundabouts and road junction.
Unfortunately there are two fundamental drawbacks in the use of reinforced concrete. Firstly the combination of steel and concrete must be properly designed by structural engineers if it is to be used for the important structural members in a building or a bridge. Secondly construction has to be carried out to certain standards if it is to be expected to perform correctly.
Unfortunately in a country where construction standards are neither known nor understood by the majority of people working in the building industry building a house can be a bit of a hit and miss affair. The problem is not assisted by the “poverty avoidance gene” (known as the PAG) which thrives in the rather accommodating genetic material of the average building entrepreneur. This is, of course, the gene that encourages its owner to save a bit of money on cement and steel with little understanding of the consequences.
It was a particularly virulent PAG that resulted in the people of the Yogya area building their houses with cement using ten parts of sand to one of cement when it should have been two parts of sand to one of the magic grey powder. “Steel in columns? Oh we don't need to bother with that.” We know the rest, 400,000 houses fell down, many on people's heads!
Anyone building any sort of serious structure needs to keep a watchful eye on the process and get some independent advice if in doubt.
Design
The structure of most buildings consists of vertical columns and horizontal beams that form a boxlike framework for the building. This framework provides the fundamental strength of the building. Walls, roofs, floors, etc. are all supported on this structure.
It is important to get this right. The structure should be designed by a civil engineer who will consider the shape and size of the building and very importantly the ground that it is on. Rock is generally a good solid foundation but if the land is unstable then the structure must be designed to withstand movement.
Here in Bali it is only a matter of time before there is a sizeable earthquake. Solid rock will transfer sharp jolts to a building while the people of Bantul near Yogyakarta told me of seeing 50cm high waves coming across the soft pliable ground of paddy fields.
The engineer must design accordingly and the structural drawings should clearly indicate the dimensions of the concrete sections and the size and spacing of the steel reinforcing bars. The drawings should be signed by the engineer.
Construction
The steel used in the actual construction should match the drawing specifications. There are few tricks to watch for here, steel is expensive in Indonesia and the PAG
really works hard at reducing the amount of steel used. Remember that once the concrete is in place you can't see the steel, you don't know what is in there. The builders contribution to his pension fund does not become obvious until you are wearing your house like an overcoat.
Reading the drawings, checking the structure and seeing through the games played by dodgy builders you are far better to leave to engineers, get a good one and make sure he performs. I recently came across a project where the clients had engaged a structural engineer they trusted, he has a good reputation and they left him to it. Unfortunately he obviously was not present when a bunch of cowboys cast the concrete around steel rods that were less than half the diameter specified.
To protect against dodgy practice it is standard convention in Britain and Australia that the engineer is present when the concrete is being poured to make sure the steel is properly installed. I don't know about America but let us hope their building standards are better than their mortgage lending processes.
Remember that the concrete must provide protection to the steel by insulating it from the atmosphere to stop it rusting. To do this the steel should have a covering of 50mms of dense concrete to prevent oxygen penetration this means that the steel reinforcing must be correctly placed to ensure sufficient cover.
Finally the concrete must be cast all in one piece to make sure there are no cracks or weaknesses in the structure. Joints between different batches of concrete can allow oxygen to enter and corrode the steel and can also provide lines of weakness where the structure can crack.
Well designed and built reinforced concrete is important for building structures and is in fact the most important component of any building. Most other things can be fixed fairly easily but structural weakness can be a serious matter. and render a building dangerous. Don't take risks and if you are in doubt get some independent advice.
Reinforced concrete is particularly important for swimming pools but we'll look at that another day.
In the meantime I must go, my tea's gone cold. I think I'll be sleeping in the doghouse.
Phil Wilson
|
