design-in-steel

The British Constructional Steelwork Association have released the following forecast regarding steel prices in 2009:

“Steel prices, along with prices for concrete and rebar, have seen dramatic increases over recent years driven by global demand, particularly from China and India. The demand has been both for steel and the raw materials for steelmaking eg iron ore and coal. However in recent months there have been reductions in global demand which has resulted in a steel prices plateauing.

Looking forward through 2009, it is likely that there could be steel price reductions in the first half of 2009. However the fundamentals of world steel supply in the medium and long term are unchanged and it is anticipated that global demand and prices will eventually rebound, the key question is exactly when and this, of course, is a little difficult to forecast.

The expectations for the price of iron ore and coal would suggest modest price reductions in 2009 (though these may a while to feed into the supply chain). Whilst energy costs in the UK remain stubbornly high, shipping and other ancillary costs will react to the market volumes, falling in the short term and potentially rising with the anticipated recovery in demand..

In summary BCSA is confident that steel prices are highly unlikely to increase in the first quarter of 2009 and modest price falls are anticipated. There may be a recovery in the second quarter but again this will be modest and offset by cheaper raw material supply. The likelihood of volatility in prices seen in 2008 is very remote.”

So what if Wembley Stadium has cracks in it. Buildings crack don’t they? How big is it? Over 1 inch wide? 40 feet long? Oh dear.

So what should we make of today’s announcement? The officials say that there’s nothing to worry about; but those who witnessed the crack opening up were scared half to death. Here’s the official statement:

“As with all large structures, the stadium has been designed with movement tolerance factored in. Reports suggesting that there is a crack in the stadium as a result of this movement are incorrect.”

In the UK, structural steel must be designed by qualified structural engineers to British Standards or Eurocodes. These codes are designed along the lines of limit state philosophy. What this means to you and me is that the structure of a building must not fail to carry out its intended function. This applies to structural strength, but also many other serviceability factors. One of these factors is deflection, or movement. A building structure may move, but not so much that people feel unsafe or uncomfortable, nor should it move so greatly that finishes (e.g. plaster) are damaged. It seems both of these “limit states” have been exceeded, and therefore the building could be unfit for use.

But the situation could be much worse than that. The structural engineers who designed this stadium would (or should) have taken movement into account. If a crack of 1.5 inches has opened up in the plaster, either the designer made a mistake, or the builder did. It could point to a small error such as the builder forgetting to put in a movement joint. It could also point to incorrect assumptions made by the structural designer, completely invalidating his design. Should this worry you? Well, that depends on whether you’re going anywhere near Wembley Stadium!