The steel structure used in the building itself is non-combustible, but when exposed to high temperatures, its overall structure and integrity may be compromised. This is why strengthening the steel structure against fire is very important in most constructions.
Due to its high strength and ductility, structural steel is one of the most common materials used in building construction. Since reinforced concrete can resist the spread of fire and withstand higher temperatures, it is used to strengthen the skeleton.
In this article, we will talk exclusively about strengthening the steel structure. So stay with us.
How does fire affect the steel structure of a structure?
A better understanding of the unique way a steel structure maintains its integrity in the event of a fire can be very beneficial to construction managers and contractors.
Steel production temperature
The unreinforced steel structure can withstand approximately 425°C before it begins to soften.
At temperatures between 600°C and 650°C, steel loses half its strength and is at risk of breaking. Of course, it is very rare for a house fire to reach temperatures above 600°C, as you can imagine, there are very few large-scale fires that seriously threaten the structural integrity of a building’s steel structure reinforcement. Therefore, steel structure is usually strengthened against fire in industrial sheds, workshops, factories and other structures where there is a possibility of huge fire.
The effect of fire on steel structures
In the event of a fire, the properties of the steel material change and it undergoes a process called thermal expansion. During this process, it changes color depending on its temperature.
From pale yellow (220°C) to a wide range of shades of violet (260°C to 285°C), to blue (290°C to 330°C) and finally to red, yellow and luster. 1400°C.
After the fire is extinguished or ends naturally, the steel structure tries to shrink back to its original shape, but it usually suffers from cracks in its structure that threaten its integrity with the main and residual loads on it.
If the fire remains below 700 °C for less than 20 minutes, the reduction in rigidity and strength of the steel structure will only be temporary. This means that although the steel may appear distorted, it returns to its original properties after a fire and is not permanently compromised. However, structural fracture can occur if the steel is deformed.
Melting point of steel structure
The lowest point at which carbon steel without fire resistance melts is 1130°C, although 0% carbon steel will not melt until 1492°C. Regardless of the type of steel, any steel usually melts completely at a temperature of about 1550°C.
How are effective agents used to strengthen the steel structure against fire?
The fire resistance of a steel structure is calculated according to the three main criteria of bearing capacity, safety and insulation, all of which are necessary to reduce the risk of building damage due to fire.
The “fire resistance time” of a steel structure, measured in minutes, refers to how long a steel structure will survive a fire before being compromised by the following factors:
- Load bearing capacity: Whether or not the steel is able to withstand the required load without collapsing.
- Integrity: The ability of steel to prevent the passage of heat, flame and smoke
- Insulation: the ability of steel to withstand exposure to high temperatures
What are the industry regulations for fire resistance of steel structures?
Requirements for fire reinforcement of a steel structure can vary greatly depending on the purpose and height of the building.
These standards are considered based on the safety principles of building fire resistance, according to which: an office building with a height of up to 30 meters and without a fire protection system has a minimum fire resistance of 90 minutes.
A commercial building (such as a shop) with a height of up to 19 meters from ground level, and a fire resistance period of at least 60 minutes.
The new standards evaluate each building according to a unique “risk profile” based on the number of occupants, ventilation and a host of other conditions.
While the above regulations do not directly refer to fire resistance, they provide sufficient context for contractors, managers and site teams to decide on the most effective solution to protect a structure from fire.
Strengthening the steel structure against fire
Given that structural steel is a common material in construction projects, both old and new, there are several ways to increase the fire resistance of a steel structure.
These methods are divided into two categories: reactive and non-reactive based on whether their ability to protect against fire is “reactive” to high temperatures.
For example, intumescent coatings are a reactive solution to protect steel because they expand when exposed to extreme heat, while cementitious coatings protect steel beams in all conditions and are a non-reactive solution.
conclusion
In general, building materials and steel reinforcement are usually classified based on different tests. For example, if a particular method of strengthening a fire-resistant steel structure is rated for 60 minutes, that means it must help maintain the integrity of the structure for at least 60 minutes. Obviously, the higher the rating, the more time will be available to evacuate and extinguish the fire while limiting the damage. You can contact the experts on our website for advice on strengthening buildings and steel structures.