25/11/2023
BUILDINGS & HURRICANE'S
Our Vanuatu building laws, the building act & the Vanuatu Building Code does not outline cyclone categories, CAT 1 to CAT 5, it does NOT exist in the structural design world. A building structure can only be design for a wind velocity. What is wind velocity? Wind velocity the measure of atmospheric air molecules that travel from one point to another point per unit of time. When engineers design buildings for cyclonic resistance they don't go to a catalog that has cyclonic ratings for a certain wind CATEGORY and conclude that a building should be design for a CAT 4 or 5 cyclone, it does not work that way and it will NEVER work that way. It is not right to say lets build this house to withstand a CAT 5 cyclone. Accordingly to our Building Act & Building Code this statement is simply NOT right. Accordingly to AS/NZ 1170, Part 2 (Cyclonic design for buildings), stipulated under our Vanuatu Building Code, we cannot dictate a building structure to withstand a desired or nominated wind velocity, ONLY the building structure can do that. Only the building structure can dictate its own wind loading. I will try to explain this. External forces (Wind, Earthquake & other Live loads) that affects a building structure are influenced or shaped by 1) The buildings functions (what the building is use for, for instance a residential building has a lower rating compared to a hospital), this is called the "The importance level", Point (2), The location of structure, where its going to be permanently located (for instance, is it going to be located next to the beach, in a valley or on top of hill) a structure in a valley has a lower rating to a structure located on a hill top for very obvious reasons, point (3) The aerodynamic shape of the building structure (For instance a building that is small and has only one level has a lower rating compared to a large & tall 5 storey structure), the higher the building structre the higher the wind rating, 4) Lastly but not least, the dominant position of cyclonic wind in reference to the weakest part of the structure in relation to building roof slopes, openings, building shape & height. These are some main reasons that I wanted to point out that ONLY a building structure can dictate its own cyclonic wind rating and NOT a nominated cyclonic wind rating. I will explain more in detail with design procedures as per our Vanuatu Building Code on cyclonic wind loading on my next post.
