The use of steel bars in the Philippines and around the world for construction is gaining popularity not only because of its structural strength, but also because of the low cost. Today, this article is going to discuss one of the most widely used kind of steels used for construction: purlins.
The word purlin is of French origin, first used in the 15 century late middle English.
Purlins are horizontal bars of steel or wood used for structural support in buildings. It is most commonly used in roof structures. Usually, wood purlins are used in the construction of roofs, called purlin plates which are horizontal supporting pieces of wood, and principal purlins or side purlins, but steel purlins are also used in buildings with metal skeletons, and are supported by walls or pillars of a building.
Purlins are cold formed steel, which means that like most other steels, they weren’t formed with heat. They are formed by rollers and presses, rolled and stamped until they form the desired shape. They are somewhat heated for the rollers and presses to bend them, but not enough that they melt. Cold formed steel makes the steel lightweight, lighter than most steel, and more flexible and elastic. It is lighter because less steel is used to create the shape it is molded into. Hot steel needs to be poured into a mold, and that uses more steel. This makes cold steel a lot less costly. This is also how they make bodies of cars.
Hot steel is used in buildings, like I-beams which are hot rolled, and cold steel like purlins, are used in smaller buildings where purlins won’t have to support a massive amount of weight.
The first type of purlin is the RHS, or the rectangular hollow section, most commonly used in roofs where the support framework can be seen even after construction is complete. They are used in patios or decks, and the ends of the purlins are sealed off by welding caps to them, preventing moisture from getting in and corroding the metal.
The second type are Cee or C purlins. They are shaped like a boxy or squared C, and are used for support in floors or walls, and to form columns in sheds. Cee purlins can be continuous and held together securely by one cleat, or two Cee purlins can be held together by double cleats.
The third type are Zed or Z purlins. They are shaped like a letter Z, and it is because of its shape that it can be overlapped with each other, making Zed purlins possibly structurally stronger than Cee purlins. They are also used for large roofs and walls.
Wood and steel purlins are easily and readily available to you and those in construction, and they can come in different materials and shapes, depending on your budget, and of course your aesthetic and strength and structural requirements. However, steel is still much stronger, cheaper, and most definitely, more durable.