The use of light steel structures in the world of construction has now grown rapidly. As the name implies, the mild steel structure is composed of profile steel bars that are relatively lighter than steel bars in general. This profile steel has a relatively thin thickness.
In general, the raw material for mild steel is G550 steel. G550 steel is a high strength steel with a high tensile strength standard of 550 Mpa (5500 kg / cm2). This strength is the basic element for the tensile strength of mild steel today. With a minimum strength of G550, the mild steel has a minimum yield strength of 550 Mpa. It was proven in laboratory tests that it should not break when it is pulled with a force of 500 Mpa. In addition, the steel also has a shear modulus of 80,000 MPa and a modulus of elasticity of 200,000 Mpa.
Mild steel is made from steel sheets or thin steel plates which are cut into pieces and made of pure steel and then formed by roll-forming machines. The process is carried out in cold conditions, so it is often known as cold-formed or cold-rolled steel. The rolling process compresses and stretches the steel, applying force or stress occurs in the process. This is why mild steel has high strength, while steel that is usually formed when it is still hot is called hot-rolled steel.
In Dewobroto et al. (2006) it is reported that the use of cold-formed steel in America for building structures has been developing since five decades ago with the support of AISI (American Iron and Steel Institute). Since then cold rolled steel has been widely used for building structures, both secondary structures, for example as a wall / partition frame or primary structure, for example a roof truss and a building's main frame (frame), Figure 1. The use of light steel as a building material such as frames roof, ceiling frame, wall frame and floor frame. This type of steel has also been widely used for simple buildings and tall buildings as a substitute for wood which is increasingly expensive, rare and easily eaten by termites.
In practice, there are several considerations for the advantages of choosing a lightweight steel structure, including:
The advantages of using mild steel are supported by professionalism and implementation in the field handled by specialist companies, so this lightweight steel structure is an alternative that needs to be considered in material selection.
Due to the fast construction period, this mild steel is also widely used for the reconstruction of houses in areas experiencing natural disasters. During the reconstruction period, it was generally demanded to build a large number of houses and finish quickly, so that the victims were not too long in the evacuation (Triwiyono, 2006).
Lightweight steel roof truss is a roof frame (truss + battens) made of G550 high-strength steel which is light, thin and coated with an anti-rust coating, but has a function equivalent to conventional steel.
In recent years, the use of mild steel materials has become increasingly widespread. Starting from housing, offices to hospitals and other public places using mild steel applications, especially for roof trusses. The use of floor frames is still not widely known in Indonesia.
In big cities such as Jakarta and its surroundings, lightweight steel roof trusses are increasingly becoming a substitute for wooden roof trusses. The supplier is also increasing. Unfortunately, not all offer lightweight steel roof trusses with clear raw material standards and application systems. Some are simply marketing mild steel profiles which are then assembled with bolts to form a roof frame. As a result, more and more often heard of the lightweight steel roof frame collapsing after it was installed. What is concerning, until now, has not seen any serious efforts by the government to make standardization or special regulations regarding cold rolled steel structures.
According to Davy Sukamta, Chair of the Indonesian Construction Experts Association (HAKI), the market for lightweight steel roof truss products was absorbed too quickly, causing a price war that ignored the safety of the application. On the other hand, consumer education is lacking. Mild steel has a very different material and application system than wood. Because it is important to be more careful about using lightweight steel as a roof truss.
Unlike flexible wood, mild steel is very rigid. If the wooden frame after being installed can still be added with other loads, the lightweight steel roof truss each new load added must be accompanied by new reinforcement too. Otherwise the frame structure may collapse or at least warp. Therefore, the application of lightweight steel roof trusses requires careful calculations, from material selection, profile shape, to installation.