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The Fundamental of Design Philosophy

posted Jul 28, 2022, 6:08 AM by jeffery jim

When talking about design in construction, most engineers only recognize models based on structural analysis. In this case, graduates are usually exposed to deterministic type of design with proper design calculation and all sort of parameters which are proven to be acceptable for cases considered as ultimate limit state (ULS) as well as serviceable limit state (ULS).
2. Nevertheless, what most engineers are not exposed to is the second type of design derivation which is design assisted by test. The former was deterministic and the latter is probabilistic or heuristic by nature as stipulated and acknowledged by the Eurocode in BS EN 1990. In this particular code of practice, there is no definite way to simulate an outcome which can be deemed as structurally sound, safe and economically viable. Hence, it is the task of great engineers to determine it as so.
3. Deterministic approach with all parameters and equations is essentially the day to day basis where engineers confidently produce a design knowingly that all parameters satisfied and complied with high safety factor. It is so robust, all steps in the design is governed by specifications, guidelines, code of practices and other relevant dossiers which are endorsed by institutions locally and globally.
4. Heuristic approach using models involves probabilistic approach(es) with set of criteria of concern. Where will this approach be utilized in construction field? It is vastly used in non-conventional constructions as well as during the maintenance phase of structures and infrastructures. When heuristic approach is in use, it usually renders possibilities of favoring outcome(s). This does not mean deterministic approach or methodologies do not involve statistics. The deterministic method embedded statistics with set criteria which is statistically favoring based on normal distribution.
5. In conventional design method, equations are preset with values which involve with significant values of one-tailed or two-tailed borders. In most cases, it allows for value to cover defects as low as five percent which means the characteristic values for a safe design covered until the ninety-fifth percentile of the distribution. Elaborate coverage of partial factors is another way to waive these preset values through favoring outcome based on design brief, material safety, reliability and other factors. This are involved in value engineering and reinstatement of structures that may lapse its SLS but not ULS.
6. In non-conventional design such as dam design, use of new and unproven materials, and structural strengthening or rehabilitation; heuristic design are assisted by testing, other comprehensive prior studies, and data sets. Scale models are used to derive certain parameters and/or indicative to what finite element simulation will produce. It involves prediction, correlation-regression and correction of information. It has to be conclusive through statistical analysis which sees a limit of favorable outcome(s).
7. Engineers have new horizons to explore when it comes to design and the foundation for academia to find and close gaps through their research. There is no one or single approach that is correct in proving a design is safe, sound and economical.