Engineering Misconceptions, Part 4 - To what extent can I not design to code? Will it still be safe against earthquakes and typhoons?

The above subject is a three-part question.

A. To what extent can your building be not designed to code?

1. To no extent! You can't not-design to code. The code is the minimum requirement by law! You can choose to not design to code only if it has been superseded.

2. But codes usually have an "escape clause" that says you can choose to not follow the code provisions if a rational analysis can justify such. In that sense, if you have a relevant "rational" justification on hand and you use it to "escape" some code typical requirements, you are in effect still following the code.

Given #2 above, some designers and owners use such "escape clauses" to justify some cost savings in the building design.

The question is, is the basis of the designer really rational, and thus, has the design been built to code? Take a look at this example case.

The code (the law) states that:

a. an earthquake faultline that is of a type (Type A) which generates the strongest earthquakes compared to another type found in the country (Type B), is just 500 meters from a certain building location which should be designed considering such a type of faultline.

b. buildings less than 5 kilometers of a faultline are all assumed to have similar effects as if they were 5 kilometers from the faultline.

Now the design has assumed:

a. the faultline is Type B based on a "rational" research work that credibly suggests it is really Type B (not Type A)

b. the building is equivalently 5 kilometers from the faultline (but not
exactly 5 kilometers)

The designer did not follow code requirement (a) based on a "rational" justification, but followed code requirement (b). We can say the designer (and the owner) were able to reduce the building cost by around 25%, which is very significant. The designer is actually very, very popular and he is known for such cost savings he is able to give
building owners.

Is there something wrong here?

YES. The code requirements (a) and (b) go together. They are not an "OR"; they are an "AND." But, to achieve the objective of cost reduction for whatever other purpose it serves him or his client, the designer basically hand-picked which code requirements to follow and not follow, and threw in some "rational justifications."

What the designer probably did not know, or he knew but did not tell his client are things that are not explicitly stated in the code: first, the code is a slight modification of an international code basis. Second, that international code basis actually states that buildings which are between 2 and 5 kilometers from the faultline are considered to have stronger earthquake ground shaking than buildings exactly 5 kilometers from the faultline.

And second, buildings less than 2 kilometers from the faultline shall be considered to have effects similar to as if they were 2 (not 5) kilometers from the faultline.

The reason why the local code has such requirements (a) and (b), and this may have been discussed already when this code came out because this certainly could cause such confusions, is that at the time of development, the local code developers could not yet ascertain if the said faultline is Type A or B so instead they selected Type A (requirement (a)) which would yield more stringent designs, but balanced it with requirement (b) which is different from its basis code.

Maybe there is something wrong in that logic by the code developers, but it made its way to the code (the law) - and surely it has gone through peer reviews within the engineering and earthquake/seismology community. The thing is, it is already the law. (Sure, some people tend to bend the law... Does that mean it is justified?)

Now the thing is, there are the requirements (a) and (b) that go together. And, that very popular designer (probably not knowing this fact), did not follow (a) but followed (b).

In short, he did not follow the code requirements. He did not understand the code requirements; but as they say, ignorance is no excuse for the law.

In effect, that very popular designer has a 25% cheaper design, but possibly 25% weaker than required by the code against earthquakes!

B. Will it be safe against earthquakes?

1. If a designer has designed to code, we cannot really say! But most likely, yes, although still possibly no. Compared to not designing to code, it is definitely safer against earthquakes, but not absolutely safe. Why? Think about it.

2. If a designer has not designed to code, most likely, no! But there is a chance it is still safe. Depends on the conditions. Codes usually require simplified procedures to be followed. If more detailed analyses are used it could be shown that designing to code is not necessary for some cases. However, there is usually some other form of code followed to conduct such "more detailed analysis."

C. Will it be safe against typhoons?

1. If a designer has designed to code, we cannot really say! But most likely, yes, although still possibly no. Compared to not designing to code, it is definitely safer against typhoons, but not absolutely safe.

2. If a designer has not designed to code, most likely, no! But there is a chance it is still safe. Depends on the conditions. Codes usually require simplified procedures to be followed. If more detailed analyses are used it could be shown that designing to code is not necessary for some cases. However, there is usually some other form of code followed to conduct such "more detailed analysis."

Another question is what code has the structure been designed to? Older codes usually are more inadequate.

Another thing about typhoons is that aside from the wind forces and the rain loads, you have to deal with wind-borne debris (i.e. a problem if your structure is resistant to winds but neighbouring structures aren't), flooding, landslides, etc. (similar with earthquakes). Has the building design considered those other things that typhoons bring about?