Niobium microalloyed high strength steels are widely used in various structural applications. They improve strength and toughness simultaneously, as well as the elongation and weldability of the frame set. The Desulphurization Plant II, an industrial building located at CBMM’s Plant in Araxá, Brazil, is one example of how the use of ASTM A572 Gr. 50, equivalent to Q355 of the Chinese standard GB / T 1591-2018, took advantage of these properties. This resulted with a 22% reduction in raw material consumption, when compared to using ASTM A36, equivalent to Q235 of the Chinese standard GB / T 700-2006.

This leaflet aims to show the benefits of using ASTM A572 Gr. 50 instead of ASTM A36 and consequently Q355 instead of Q235. It shows the main calculations for a single beam, under bending and a single column, under compression, which have been considered as examples of the application and use of the high strength steel concept. The selected beam is located on one of the various operational floors of the building. The selected column is in between floors, in order to simplify the calculations, considering it is pinned by both ends, without any lateral load. The beam and the column considered within this leaflet are submitted to the same projected loads intended for the building.

 Desulphurization Plant II of CBMM’s plant in Araxá

Figure 1: Desulphurization Plant II of CBMM’s plant in Araxá. Indication of the beam and the column that have been considered for structural weight calculations according with respective mechanical strength

Load conditions and combinations

Table 1: Loads applied to the building components of Desulphurization Plant II.  All calculations consider EN1993-1-1 and correlated standards


Reduction of weight and costs of beam by using  ASTM A572 GR. 50  instead of  ASTM A36 steel

Required bending moment and shear

Beams are usually the main structural element for floor systems in industrial buildings. According to the size, these beams can be hot rolled and, for the larger dimensions, fabricated sections are used. The Desulphurization Plant II has several platform levels in order to support personnel, operational processes and equipment for the important operation of reducing sulphur content of the niobium ferroalloy. The steel ASTM A36 (fy = 250 MPa) equivalent to the Chinese Q235, was used for angles in the bracing system and ASTM A572 Gr. 50 (fy = 345 MPa) equivalent to the Chinese Q355 for all other elements, including steel beams in floor systems and columns. The beams have full lateral restraint due to the floor system so lateral torsional instability will not occur.

 beam of the Desulphurization

Figure 2: Distributed design load applied to the considered beam of the Desulphurization Plant II

The geometric characteristics and design verification of the highlighted beam, located in the floor system of the building are based on EN 1993-1-1 (Eurocode 3). It was considered best to use two different steel grades, calculating the resulting beam dimensions and weight necessary to support the loads. The final weight savings and design parameters are demonstrated in Table 2. 

When using the high strength steel, there was 26% weight reduction, corresponding to 7.3 kg/m less for this component.

Table 2: Comparison of the deflection and linear weight of a beam submitted to the same load but designed using different steel grades: ASTM A36 and ASTM A572 Gr. 50.

Reduction of weight and costs of  the column using  ASTM A572 GR. 50 instead of ASTM A36 steel

The column is pinned without any lateral movement.

Figure 3: Concentrated design load applied to the corresponding column of the Desulphurization Plant II.

For the column, when using the high strength steel, there was 17% weight reduction, corresponding to 15 kg/m less for this component.

For the column, when using the high strength steel, there was 17% weight reduction, corresponding to 15 kg/m less for this component.

Reduction of structure's costs by using high strength steel

Considering the entire structure of the CBMM Desulphurization Plant II, it represented around 362,000 kg when designed with ASTM A36, but there was a total weight reduction of 22% when using ASTM A572 Gr. 50 instead. The price of these materials fluctuate according to market conditions, but currently, due to the presence of numerous, good quality suppliers, the price can be considered almost the same, being just  a little higher for ASTM A572 Gr. 50. In this example, the use of the high strength steel resulted in costs savings directly proportional to the structure weight reduction, that represented 17% less in the building structure costs. In addition, this weight reduction also contributes to reductions in the foundations, welding consumables and transportation. Due to using less steel, there was a reduction around 140 t of CO2 emissions, representing 22% of total emissions for the steel structure. This reduction of CO2  emissions is totally in line with dematerialization, a very important concept used in construction in order to reach carbon neutrality targets.

Effect of load on  buckling length of columns

Another advantage of using high strength steels is the opportunity to adopt more functional project designs. When long span ranges and high building heights are necessary for the installation and proper operation of industrial equipment, high strength steels can be a solution, as exemplified in Figure 4. Once the height between each floor of this building was higher than 5 m, there was a clear benefit for the critical buckling load when using ASTM A572 Gr. 50 when compared to ASTM A36.

Figure 4: Ultimate load for columns made with ASTM A36 and ASTM A572 Gr. 50

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