WAYS TO REDUCE THE COST OF FIRE PROTECTION

Spatial and layout solutions

Optimization of costs for fire protective treatment of building structures is possible at any stage of construction, but fire safety measures that would also provide for fire protection of load-bearing building structures should be developed as early as at the stage of development of feasibility study for new construction or reconstruction of buildings for more economically feasible and correct performance of fire protection works. At this stage, the construction customer can obtain information on the preliminary cost of fire protection measures, depending on the expected three-dimensional characteristics of the facility and its appropriate degree of fire resistance. A reference design with calculations of basic engineering solutions, including fire protection works, their estimated cost, justification of the efficiency of investment is more informative in this regard.

When a reference design is developed, there is a possibility to optimize the cost of fire protection measures by considering a number of preliminary designs with variations in the number of floors of the building, floor area, installation of fire barriers, building materials used, etc.

Optimal design of steel structures

Optimization of fire protection costs for steel structures directly depends on the designed technical solutions of the design engineer. If in accordance with applicable construction codes the structure is subject to further fire protection, the calculation should consider possible options for its fire protection, as well as the cost of these measures in the future — to consider changing the cross section of the structure, its profile, geometry, etc.

Section factor of the elements of steel structures subject to fire protection treatment is also one of the key values determining the cost of fire protection, and hence its cost. Even its slight change can change the amount of fire protective material required to ensure the rated fire resistance parameters of steel structures. As suggested by the analysis of the data in the Certificate of Conformity for fire protective paint, reduction of the value of the profile section factor by only 30 m-1 (from 200 m-1 to 170 m-1) can reduce the cost of fire protective material by 11%.

Correct determination of the section factors of the elements of steel structures subject to fire protection, taking into account their size and geometry of heating, is one of the approaches to optimize the cost of fire protective material and the costs for its application.

Choice of fire protective material

When selecting a material for fire protection of a building structure, it is not enough just to estimate the cost of the material. At a minimum, it is necessary to analyze its costs to achieve the required limit of fire resistance of the structure, the cost of its application, as well as the service life of the obtained fire protective covering. If the cost of fire protective material X is less than the cost of fire protective material Y by 20%, but the thickness, and thus the cost of achieving the required fire resistance class of the structure with material X is more than 30%, the total cost of its application will be much higher not only because of the higher consumption but also due to labor costs for its application. The same is true for the analysis of the fire protection cost in respect of its service life, annual maintenance and possible restoration. Some fire protective plasters have a service life equal to the service life of the structure on which they are applied, which makes them more economically attractive than fire protective intumescent paints, and if we take into account their lower performance, the cost/time of fire resistance/service life, this type of fire protection is the most justified for fire resistance classes of steel structures above R60.

The certificate of conformity is the main document based on which the fire protective material is selected, which best meets the requirements for fire protective treatment of the construction facility.

In addition to all other mandatory components of the Certificate of Conformity, the Customer receives the information required for commercial assessment of the use of particular means to compare analogues in order to optimize the material costs of fire protection and eliminate risks associated with the legality of the use of fire protection materials.

Sample certificate of conformity

Annexes are an integral part of the certificate of conformity, they contain information about the minimum thicknesses of fire protective covering (mm) required to ensure a certain fire resistance class (R, min) of metal structures with different profile section factor (Am/V, m-1) at different critical temperatures

Sample annex to the certificate of conformity

In order to determine the thickness of the fire protective covering to ensure fire resistance class R45 of a steel beam with a profile section factor of 190 m-1 (corresponding to the rated thickness of 5.26 mm — the value in the first column), it is necessary to draw a perpendicular from the Section Factor column at point m-1 and a perpendicular from the Design Temperature line from the point of 500 °C (if it is the critical temperature for this type of structure). The point of intersection of these perpendiculars is "1.05 mm" and is the thickness of the fire protective covering we were looking for.

With other particular values of critical temperatures for this element of the steel structure, it is necessary to use the closest lower temperature value from the given range of design temperatures. For example, if the critical temperature is 595 ° C, we should use data from the column corresponding to 550 °C.

Optimal selection of fire protection means on the basis of a comprehensive analysis of all parameters (a type of the fire protection means, its cost, consumption, application cost and service life, etc.) is a key factor in reducing the fire protection cost at the construction project.

Determination of the critical temperature of steel structures

Critical temperature (θа,cr) is the temperature at which failure of an element of the steel structure is expected subject to uniform temperature distribution over the cross-sectional area for a given level of load (loss of load-bearing capacity).

A temperature of about 500 °C was used in Ukraine for a long time as the main critical (design) temperature of steel structures with fire protective coatings and cladding.

However, the adoption of the standards DSTU-N B EN 1993-1-2: 2010 and DSTU-N B V.2.6-211: 2016 allows to apply a differential approach to determining the critical temperature of steel elements and calculating the fire resistance of steel structures in accordance with Eurocode 3. The use of calculation methods allows to determine the critical temperature of steel elements of a particular building, taking into account the temperature and time dependence of the corresponding design scenario of the fire.

As a rule, the calculated critical temperatures of steel structures exceed the values of the generally accepted critical temperature (500 ° C), which in turn results in a significant reduction in the fire protection costs.

As an example of the economy of fire protective material, we can consider the data from the Certificate of Conformity of intumescent paint, which is widely used in Ukraine. If you design fire protection of a steel beam with a section factor Am/V = 200 m-1 in accordance with the provisions of DSTU B V.1.1-4-98 * (θa, cr = 500 °C), it is necessary to apply a coating layer with a thickness of 0.90 mm. When you design fire protection of the same beam, but using the value calculated in accordance with DSTU-N B V.2.6-211:2016, θa, cr = 650 ° C, the thickness of the coating layer is only 0.46 mm, which reduces the consumption of fire protection coating, and thus its cost, almost by half.

Annex to the Certificate of Conformity

Specialists of the UCSB Engineering Center calculated the critical temperatures of typical metal structures — beams with hinged and rigid mounting on supports, which are subject to evenly distributed load, as well as compressed and compressed-bent columns, taken from previously completed designs of buildings with steel frames.

The calculation showed that most of the considered steel structures have a critical temperature of 550 °C and higher, which automatically reduces the consumption of fire protective materials.

Structure types	Assortment	Steel grade	Length, m	Fastening type	Number of sections braced from the plane	Load	Differentiated calculation of the critical temperature of the steel element		Fixed value of the critical temperature of the steel element		Economy of fire protective material,%
							Estimated critical temperature, °C	Thickness of the fire protective covering*, mm	Fixed value of critical temperature	Thickness of the fire protective covering*, mm
Beam	I-beam No.45 according to GOST 8239-89	С245	6	hinged	2	Evenly distributed   g = 1.02  t/m, q = 2.4 t/m	562	0.75	500	0.96	22
Beam	Welded I-beam 900×10 380×25	С345	12	hinged	6	Evenly distributed g = 3.32  t/m, q = 7.2 t/m	622	0.38	500	0.66	42
Beam	Welded I-beam 940×10 420×30	С345	12	hinged	2	Evenly distributed g = 1.39  t/m, q = 2.9 t/m	611	0.38	500	0.66	42
Beam	Welded I-beam 726×8 350×12	С255	24	rigid	4	Evenly distributed g = 0.56  t/m, q = 1.35 t/m	507	0.92	500	0.92	0
Column	Welded I-beam 440×16 420×30	С345	8	rigid in a support	not braced	Ng = 126.17 t Nq = 206.98 t	668	0.24	500	0.6	60
Column	Welded I-beam 460×8 350×20	С345	6.75	frame members	not braced	Ng = 7.48 t Nq = 16.02 t Мg = 15.8 tm Мq = 32.2 tm	677	0.43	500	0.96	55
Beam	Welded I-beam 426×8 160×12	С245	6	hinged	not braced	Evenly distributed g = 1.26  t/m, q = 3.6 t/m	481	1.16	500	0.92	-26
Beam	Welded I-beam 1000×10 380×25	С345	12	hinged	6	Evenly distributed g = 3.78  t/m, q = 10.8 t/m	474	0.85	500	0.66	-29
Beam	Welded I-beam 1090×12 400×30	С345	12	hinged	2	Evenly distributed g = 1.41  t/m, q = 3.6 t/m	602	0.34	500	0.6	43
Beam	Welded I-beam  380×6 200×10	С245	12	hinged	6	Evenly distributed g = 0.37  t/m, q = 0.5 t/m	590	0.89	500	1.13	21
Column	Welded I-beam 500×16 400×25	С345	8	rigid in a support	not braced	N = 362.16 t M  = 8.72 tm	619	0.38	500	0.66	42
Column	Welded I-beam 376×10 280×12	С255	6	frame members	not braced	N = 23.3 t M  = 14.8 tm	592	0.75	500	0.96	22
Beam	Welded I-beam 500×8 360×20	С255	9	hinged	not braced	Evenly distributed g = 3  t/m, q = 5 t/m	485	1.1	500	0.87	-26
Beam strengthened with strengthening ribs	Welded I-beam  800×6 320×20	С255	6	hinged	3	Evenly distributed Fg = 20  t, Fq = 50 t	511	0.96	500	0.96	0
Beam	Welded I-beam 500×8 320×20	С255	8	hinged	4	Evenly distributed Fg = 15  t, Fq = 20 t	584	0.68	500	0.87	22
Column	Welded I-beam 300×10 300×20	С255	3	rigid in a support	not braced	Ng = 5 t Nq = 15 t Мg = 3 tm Мq = 9 tm	552	0.72	500	0.92	22
Column	Welded I-beam 300×6 300×16	С255	6	rigid in a support	not braced	Ng = 50 t Nq = 100 t	452	1.51	500	1.21	-25

*) Fire protection material Ammokote MS-90 for fire resistance class R45.

It should be noted that the Ukrainian Center for Steel Construction initiated the development of modules for calculating critical temperatures in the Crystal (SCAD Office) and STK-CAD (Lira) software packages, which already have functions for determining and visualizing the critical temperature of steel structures in accordance with DSTU-N B V.2.6-211: 2016 and DSTU-N B EN 1993-1-2, which in turn makes it possible to determine the load-bearing capacity of the structure subject to changes in the steel properties at high temperatures.

The use of design values of the critical temperature of steel elements in designing fire protective treatment can significantly reduce the cost of the fire protective material, and thus the costs for application works.