Safety Factors

One of my former roommates studied Civil Engineering. I studied Aerospace Engineering. We had frequent discussions about safety factors. Whereas aerospace engineers are forced by an aircraft’s restrictions on weight to take great care in their design’s dimensioning and typically come up with a safety factor 1.25 to 1.5 of the theoretical maximum loading, civil engineers just slap another extra layer of concrete on it. If weight isn’t such an issue, it’s better to be safe than sorry right?

Well not in China apparently! Last year the driver of a truck full of sand managed to destroy a bridge near Beijing simply by driving over it (so not against it). He didn’t do anything funny or out of the ordinary, apart from overloading his truck. Judging by the pictures, the truck driver, called Mr. Zhang in Chinese media, was the only one on the bridge at the time.

Chinese police took a full year to investigate the cause of the bridge collapse and their conclusions are as simple as they are ridiculous: Mr. Zhang is the only one to blame as he shouldn’t have overloaded his truck. He is now sentenced to pay the damages incurred, valued at a grand total of RMB 156 million. Converted to Sterling at current day rates, that’s only about £15.6 million. At an average monthly salary for a truck driver in China of about £45, Mr. Zhang will only need about 29,000 years to settle the bill.

Of course this is all bollocks and Mr. Zhang is heavily screwed by the Chinese system. Apart from the fact that he was actually working for a company that should have had controls in place to avoid such things from happening – as opposed to ordering him to take on extra sand – and is thus liable, the police conclusion is of course as flawed as can possibly be. In any case no common sense could have been consulted, let alone a qualified engineer. Why? Because clearly that bridge should’ve been able to hold a convoy of non-overloaded trucks of the same total weight, which is pretty much the same thing as far as structural loading is concerned. Moreover, any qualified civil engineer would’ve designed that bridge with a safety factor of a billion and a half, not one and a half.

The police conclusion is silly, but there are a couple of other conclusions possible. Firstly, driving a truck in China is a pretty thankless job! Secondly, with Chinese police taking a whole year to suck a load of nonsense out of their thumb and call it an investigation, you had better not get into trouble in China. And thirdly, it might take a while before the money is collected to rebuild the bridge.

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