it's expensive, Mr. Jack said it can be done with half of this
Even though projects and approvals cost, on average, only 5% of the construction work, the popular imagination still carries the idea that hiring a specialized professional - i.e. an engineer or architect - makes the work more expensive. This idea goes back to the colonial past, when specialized labor was expensive, and most of the professionals in the AEC (Architecture, Engineering & Construction) field were connected to the empire. It is also linked to the idea of Popstar Architects, where a simple 100 m2 house can cost a million simply because of the designer's signature.
But the truth is that this thinking is far removed from the current reality of the construction market. When it comes to explaining why it is worth hiring an engineer, many professional colleagues prefer to focus their speeches on the importance of engineering, on the safety and stability of structures, or on the rationalization of the use of materials. I consider both arguments valid, but far from the reality of the client, who, faced with a large portfolio of "well-known masons", believe that the stability of 10 houses ensures that of 11 houses. I prefer to shed light on something more important, also related to the safety issue but less widespread: the Limit State Method.
This text will not deal with the technical aspect of limit states, don't worry, my mission here is just to explain to laymen how engineering projects are made. But here is a short introduction: from the beginning of the 90's, Brazilian designers began to adopt the Limit State Method, following a global trend, starting to teach this method in Engineering schools and gradually updating structural standards to work under such methods. It is a semi-probabilistic method, which came into force to replace a deterministic method. Don't worry, you don't need to know what semi-probabilistic and deterministic means, we don't need to discuss this.
What you need to know is that every structure, no matter how safe and well built, deforms, and this is a natural process that qualified professionals consider when sizing any structure. The consideration is done by taking two assumptions: the Serviceability Limit State and the Ultimate Limit State. The first state refers to how much the structure should support until its deformation represents discomfort for the user's use. An example of this is the wooden structures of roofs, which tend to form a "belly" over time. Yes my friends, that is calculated.
The second state is the "ultimate limit state", equally important in the design aspect, but infinitely more relevant when it comes to user safety. This is the state of ruin, i.e.: when the deformations in the structure lead it to collapse, causing serious risks to the physical integrity of users. Unlike the Serviceability Limit State, the Ultimate Limit State is the state in which no building, acting under its dimensioned criteria, should reach. And what does this mean? It means that the engineer calculates all the probable hypotheses of failure of a structure, and sizes it to support the forces it will be subject to. And more than that, the structure is designed to warn the user that it is reaching its limits.
You didn't read wrong, the structure warns you that it is no longer able to bear the load, not only giving you the chance to do some repair work, but also to ensure your safety in extreme cases, by allowing you to evacuate the site. In a more simplified way: in case of collapse the house will not collapse without warning you, with a thud, with apparent cracks, with warping doors and windows, with "embarrassed" or visibly bent structural elements, with water puddling in places that did not puddle before, and with several other warning signs.
"But then you just have to make a structure a little more robust that can handle all that.
Unfortunately it is not that simple. When designing a structure, the engineer works with deformation domains - for conventional concrete structures, there are similarities with steel and wood structures. The domains will tell the engineer how the structure will behave as the cross section increases, or the steel rate (amount of steel) increases. There are specific domains to which the designer must pay attention when designing a structure; these domains will indicate, for example, if the element rupture will occur abruptly, or if it will be after high deformation. For example, the excessive use of reinforcement (steel) can make the structure over-reinforced, not allowing the steel to flow. In other words, the concrete will break before the steel does. The rupture format is abrupt and uneconomical, because you have spent more steel for a less safe structure.
"oh, so just increase the section"”
Unfortunately you will fall back into the same mistake, but this time under-utilizing the concrete, and still having a sharp break.
"Ah but you think Mr. Jack doesn't know that?"
No, "Mr. Jack" doesn't know because not even the engineer who will design the construction knows, for the simple fact that each case is a case, and there are several variables that influence the design. Weather conditions, terrain, number of columns and beams, arrangement of structural elements, type of steel chosen, number of bars used, aggressiveness of the environment, number of stirrups used, type of concrete used, types of activities that will be performed by the structure, overloads of the structure, and many other aspects that are taken into account when dimensioning. You can't know off the top of your head, only by calculating.
The great truth is that Engineering is about solving problems by looking for the best solution, which always includes three basic pillars: functionality, economy, and safety. Only a professional trained in the strong academic concepts of AEC can design a structure guaranteeing these principles.
In Part II I will mention in topics the reasons to hire an engineer.
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