Today, organic coated steel offers exceptional economic and technological advantages, explaining its extraordinary success story in construction.

The main advantage of organic coated steel is its consistent quality: paint film thickness, corrosion resistance, and durability in addition to colour matching and surface appearance being reproducible with narrow tolerances from batch to batch.

The flexibility of the coil coating process allows us to produce a range of different surface finishes such as smooth, orange peel, grained, textured, or embossed, all of which are available in a wide choice of colours (solid, metallic, pearlescent, etc.) and the required degree of gloss: anything from matt to high gloss.

The pre-painted steel range of ArcelorMittal Europe – Flat Products offers architects, designers, and investors in building a unique range able to satisfy the most stringent criteria required by the construction industry in terms of aesthetics, durability performance, and sustainability.

AESTHETICS

The richest colours available on the market with surface textures of high aesthetic appeal such as matt satin, smooth, grainy, or impression finishes can give a unique identity to each building.

DURABILITY PERFORMANCE

Our guaranteed pre-painted steel is able to withstand the most extreme conditions in terms of temperature and weathering.

It is suitable for marine environments and other corrosive environments, offering scratch-resistance and colour brilliance with a minimal amount of maintenance.

ArcelorMittal has many years of experience in delivering high-quality organic coated products. Thanks to our know-how and skills acquired, we are able to offer long-term warranties on our steels for external applications with a validity of up to 30 years.

Our steels are subjected to comprehensive tests by our expert R&D team under extreme conditions of corrosion and weathering, both in the laboratory and on external sites.

After running our internal testing, we turn to independent institutes and laboratories that conduct a wide variety of tests in order to obtain external certification by bodies such as the CSTB in France, the BBA in the United Kingdom, the DIBt in Germany, and many more. So, our products can be chosen safely.

SUSTAINABILITY

The Nature collection includes the full range of ArcelorMittal Europe – Flat Product’s organic coated steels that are in compliance with both present and future REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) regulations from the European Union.
For example, the Nature collection is already 100% free of hexavalent chromium and heavy metals.

In addition, we are assessing the environmental impacts of our organic coated product range in accordance with the European Standard EN15804, and we offer EPD (Environmental Product Declarations) certified by third parties. These EPDs are increasingly relevant for the LCA (Life Cycle Assessment) of buildings and related building scheme regulation and certification.

DIGITALISATION

The use of digital tools is growing rapidly in the construction market.

Building Information Modelling, known as BIM, enables collaborative work between all construction project stakeholders, from the design stage to the in-use stage.

Among other digitalisation initiatives, ArcelorMittal Europe – Flat Products is now providing designers, investors, and contractors a full set of BIM objects dedicated to our organic coated product range. These provide the full set of product information, 3D rendering views, and they are compatible with most popular BIM software on the market.

Detailed product information, EPDs, and BIM objects are all available right here on our information platform dedicated to construction:
https://constructalia.arcelormittal.com

Text: Constructalia

Photos: Adam Pejcha/ArcelorMittal Europe - Flat Products, Jeroen Op de Beeck

These best practice design manuals consist of a series of technical guides for engineering offices, steel fabricators, and architects that aim at facilitating the application of the Eurocodes in the design of single-storey and multi-storey steel buildings.

The presented design manuals consist of a series of technical guides facilitating the application of the Eurocodes in the design of single-storey and multi-storey steel buildings.

These design manuals are helpful for steel fabricators and engineering offices, but the presentation of the advantages and possibilities of the use of steel also applies to architects. They provide a useful source of knowledge for designers in accordance with the Eurocodes and include topics such as numerous design details, fire engineering issues, member and connection resistance calculators, etc.

The design guides 'Single-Storey Steel Buildings' and 'Multi-Storey Steel Buildings' were produced in the framework of the European project 'Facilitating the market development for sections in industrial halls and low rise buildings (SECHALO) RFS2-CT-2008-0030', which was carried out with a financial grant from the European Union's Research Fund for Coal and Steel.

The design guides were prepared under the direction of ArcelorMittal, Peiner Träger, and Corus. The technical content was prepared by CTICM and SCI, collaborating as the Steel Alliance.

In this technical article, Gian Carlo Giuliani, structural engineer at Redesco, presents the main theory on the fire resistance calculations for structures through the presentation of a case study: the steel structure of a commercial center in Cyprus.

1. Fire Safety Assessment of Structures: General Approach

A structure subjected to fire must be safe for the time necessary for the escape of the people and for the safe operation of the rescue and fire brigade; the verification is based on the fulfilment of the following conditions for the evacuation time and the safe operation of the fire brigade:

• R structural resistance
• E structure and pavement smoke tightness
• I isolation or limit of the temperature of the floor above the fire

These conditions are verified taking into account the temperature versus time evolution by means of:

-  for the R condition: a step by step analysis of the temperature in the ambient and in the structural elements, followed by the verification of the load bearing capacity resulting from the reduction of the material mechanical parameters.
- a verification of the existence of a structure capable of satisfying the E and I conditions
 
The assessing of the structure is related to the actual use of the building and to the relevant amount of possibly combustible materials; therefore the calculations are based on the temperature development induced by a real fire in a closed space, which is bound by the floor, the ceiling and the edge partitions and connected to the open air through the side openings.

The standard fires, recommended by codes for the structural design or by the national laws, show a continuous increase of temperature which, because of the correspondent reduction of the strength of the materials, limits the time of the load bearing capacity of the structure.

On the contrary, the real fires can evolve from the amount of possibly burning material and from the oxygen available in the space or drawn in through the side openings and therefore always have a decay phase.

2. Shopping Malls & Fire Safety: Special Requirements

In many cases, recent shopping malls are based on large column grid lines and are developed over two or three stories; a steel-concrete composite structure is a very efficient solution for the floors.

Because of the appealing contrast between the elegant exhibited goods and the high technical aspect of the in sight structure, the application of any passive fire protection spoils the architectural results and only sprinkler system are accepted.

Therefore the “naked” structure fire resistance has to be assessed for the real operating conditions.

In the annexe A of the Eurocode 1, the temperature evolution developed by the natural fire is defined as depending on the fuel amount and on the ventilation conditions given by the compartment geometry, the boundary thermal characteristics and the openings...

Other parameters, defined in the annex E of the Eurocode 1, are related to the danger of fire activation as per the table E1 and to the function of active fire fighting measures, as per the table E2.

3. A Case Study

The fire resistance assessment is developed for the composite steel-concrete floor of a building which is composed of main beams continuous over 8.00 m spans and of secondary ones also continuous over 16.00 m spans.

The design value of the fire load qf,d is defined as: qf,d = qf,k m δq1  δq2 δn (MJ/m2)

where m = 0.80 is the combustion factor of the material

δq1 = is a factor taking into account the fire activation risk due to the size of the compartment
δq2 = is a factor taking into account the fire activation risk due to the type of occupancy
δn = Πδni = 0.237 is a factor taking into account the different active fire fighting measures (sprinkler, detection, automatic alarm transmission, firemen). These active measures are generally imposed for life safety reason.

qf,k  (MJ/m2) is the characteristic fire load density per unit floor area

The temperature raising depends on the kind of the fire which can occur:

- the general fire which is controlled by the ventilation
- the local fire which is controlled by the fuel amount

each one of the above said conditions yields a completely different result.

The temperature evaluation was performed for two basic fire conditions:

• local fire in a department store bounded by wood shelves; this condition yields a fire development governed by the fuel and is more stringent than the following one;
• general fire in the total floor surface bounded by masonry walls with few openings; this condition occurs as a consequence of the local fire and yields a fire development governed by the ventilation.

For the examined case history, according to the site and the building features, the following parameters were used for the calculations taken from tables E1 and E2 of EC1.

δq1 = 1,60 is a factor taking into account the fire activation risk due to the size of the compartment
δq2 = 1,00 is a factor taking into account the fire activation risk due to the type of occupancy
δn1 = 0,61 automatic water extinguishing system
δn2 = 0,87 independent water supplies
δn3 = 1,00 automatic fire detection & alarm – by heat
δn4 = 0,73 automatic fire detection & alarm – by smoke
δn5 = 0,87 automatic alarm transmission to fire brigade
δn6 = 1,00 on site fire brigade
δn7 = 0,78 off site fire brigade
δn8 = 0,90 safe access routes
δn9 = 1,00 fire fighting devices
δn10 =1,00 smoke exhaust system

Because of the above said parameters the fire can be by fuel or by ventilation controlled; the growth rate of the fire was selected as fast (tlim=15 minutes) in all the calculations.

The strategy adopted for the fire resistance assessment was based on the calculation of the maximum amount of possibly burning material which can be stored in the compartment having the internal height h=4.50 m ; the goods on show are mainly composed of cellulosic clothes and tissues having a specific calorific value Hu=20.00 MJ/kg (the same parameter for the wood is 17.5) and a combustion factor m=0.80.

Two different scenarios were used for the fires controlled by the fuel amount or by the ventilation; the growing rate of the fire was selected as fast with the corresponding limit time tlim=0.25 hours.

The relevant parameters are indicated in the following table:


(*) qtd (MJ/m2)=qfdAf/At
(**) tmax=max(0.0002qtd; tlim)

In general the fire governed by the ventilation lasts for hours but with temperatures below the steel critical ones.

An interesting remark is given for the above said condition:

- the amount of air necessary for burning one kg of cellulosic material with the relevant calorific value of Hu=20MJ/kg is Aa=0,312Hu+0.65=6.89 kg/kg
- being ρ =1.225 kg/m3 the specific mass of the air, the specific air volume which is necessary for burning the material is Va=5.62 m3/kg
- given the compartment volume V=23040 m3, the total mass M of the material which can burn by using the inside air is therefore given by M=V/Va=4100 kg, which corresponds to an average distribution of M/AF=0.8 kg/m2 <f.

The evolution of the temperatures developed by the natural fire is defined by the following function as per the annex A of the Euro code 1; a decay branch of the temperature curve is taken into account because the temperature increasing of the steel is shifted in time and the maximum value appears during the ambient cooling phase.

The gas temperature versus time is therefore given by the function:

with t expressed in hours.

4. Loading condition and material mechanical properties concurrent to the fire

• the fire was considered as an exceptional loading condition.
• the fire, originated in the floors, was considered as a local hazard.
• the material resistance safety factors were reduced accordingly to the temperature (figure 6)
• the loading safety factors were reduced also gg =1.0, gq=1.0 and the design live load q was reduced by a participation factor ψq =0.7 related to the use of the area.
  
  Figure 6: Scheme of the moment redistribution for an edge bay of the continuous beam
  

5. Structural Analysis Procedure

A step by step versus time procedure for both the cases was used for calculating the temperatures of the fire and of the materials, for determining the correspondent resistance.

- set time to 0s
- increment time 5s
- calculate the temperature of the standard fire versus time
- calculate the correspondent temperature of the steel according to the mass / exposed surface ratio of the beams and of the material and fire parameters
- calculate the resistance of the steel and of the concrete correspondent to the temperature
- for the mid span and the support sections calculate the ultimate resistance according to the schemes here under:

 - perform an elastic-plastic structural analysis taking into account the action redistribution between the most exposed sections towards the ones subjected to a lower temperature according to the scheme of figure 6: at the ultimate state, the mid span moment capacity is given by Mus=M1R+M2R/2 and the maximum resisted load is qu=8Mus/L2
- verify the resistance to the vertical shear at supports and the studs subjected to the horizontal shear
- compare the structure resistance R with the action A of the supported load
- if R>A start a new iteration ; if not, the time resistance is determined, because, due to the exhaustion of its redistribution capability, a part of or the whole structure is transformed into a mechanism.

In the examined case history, because of the limited stiffness of the columns and of the sliding supports at the relevant bases, the axial forces introduced in the beams by the constrai t of the thermal strains were not crucial for the ultimate bending resistance.

6. Calculation of the Steel Temperatures

The calculation of the temperatures takes into account the geometry of the structure:

- the bottom flange of a beam is directly hit by the fire
- the web and the upper flange are in shadow from the flame radiating effect and therefore are subjected to a lower temperature
- the top of the reinforced concrete slab and the relevant reinforcement are subjected to a much lower temperature

The following relations, taken from Eurocode 4, were used for the calculation of the temperature of the structural steel.


where :

kshadow  is a correction factor for the shadow effect
ca         is the specific heat of steel (J/kgK)
ρa         is the density of steel (kg/m3)
Ai         is the exposed surface area of the part i of the steel cross-section per unit length (m2/m)
Ai/Vi    is the section factor (m-1) of the part « i » of the steel cross-section
Θa,t     is the steel temperature at time t (°C) supposed to be uniform in each part of the steel cross-section
Δt         is the time interval (sec)

The shadow effect was determined from:


With e1, b1, ew, hw, e2, b2 and cross sectional dimensions

Because of the different section sizes and of the continuity conditions (see figure 4), the verifications were effected for any single element of the structure; the results for the edge bay of a secondary beam over the 16.00 m span are illustrated in the figures 7 and 8.

Industrial floors are the most heavily stressed elements in a `whole construction´. As a rule, warehouses, production facilities and connected open spaces are heavily used and different effects are revealed. Through extensive planning and the use of corresponding ready-made steel fibre concrete, an industrial floor can become a maintenance-free and durable structural element. A technical article by Wilhelm Nell, ArcelorMittal Wire Solutions.

The demands on industrial floors have become ever larger in recent years. Operators and clients of new, modern halls with varying use expect innovative and above all durable constructions based on these findings. In Germany, approx. 30-40% of all industrial floors is made of steel fibre concrete. In particular, seamless systems, such as TAB-Floor™ by ArcelorMittal, make it possible for large spaces to have high evenness, maintenance –free use and high resilience.

Policies
In terms of its composition and its properties, factory mixed steel fibre concrete meets the requirements of DIN EN 206-1/DIN 1045-2

Design

As stated above, industrial floor components with low hazardous potential, are not subject to building regulations as a rule and can be measured with the bending tensile strength of the steel fibre concrete. As a rule, measuring takes place according to the theory of elasticity in Stage 1 (sketching stage), with the model for elastic bedded slabs.

Requirements

Because of the numerous possible uses of an industrial floor, the possible requirements are very wide-ranging.
The load is decisive for planning and design. The industrial floor will be designed by its load, depending on type, impact and size subject to subsoil.
In addition to its load capacity, requirements on usability are becoming increasingly larger.

Load capacity:
The bending tensile strength of the concrete must not be exceeded through bending stresses resulting from exterior loads. Verification of the load capacity is recorded in the design calculations.

If the industrial floor is placed on subsoil with a permanent base course and it does not have to bear any further elements or it hardens, it is therefore not an element in the context of DIN 1045-1 [2]. With regard to the other cases, an approval must be requested per individual case.
However, in relation to the usability of the ground, it makes sense according to DIN 1045-2 [3] to plan and take exposure classes into consideration.
As of 01.06.2008, steel fibres in Germany must bear the CE mark for use in concrete [4]. The general technical approvals and Ü), load deformation behaviour and cracking behaviour [15] are decisive for durability and are improved by steel fibres.

Density/impermeability

If a concrete floor slab is required, it can be used in accordance with the WU-guideline [9]. In this instance, the cracking width limit in particular is to be established. This can be achieved very economically through a mix made from reinforced concrete and steel fibre concrete.
If the concrete floor must be sufficiently tight in order to prevent ingress of water-hazardous substances into the ground water, concrete engineering will be planned and carried out in accordance with the DAfStB guideline [8] when dealing with water-hazardous substances.
Due to the addition of steel fibres in the concrete, the shape and depth of the crack as well as its spread and width are positively affected [15]. In the tests in [15], there was already a reduction in the crack widths of over 50% due to the addition of 0.38 Vol.-% (30kg/m³) steel fibres to the reinforced concrete.

Effects and stresses

The most diverse loads have an effect on concrete floors. Not only mechanical loads and wear and tear but also chemical attacks must be taken into account in this instance.

Loads

Punctiform loads

Punctiform loads are often crucial for verifying the loading capacity of an industrial floor. These can consist of mobile loads such as lorries, HGV’s and forklifts, as well as long-term effective loads, such as shelves, supports, containers etc for example.

The three loading cases, slab centre, slab edge and slab corner are to be taken into account when measuring. Loads impacting on the edge or the corner can therefore produce higher tensions by up to 100%, than same loads on the slab centre. In contrast with conventional industrial floors with dummy joints cuts, the effect of the load on the TAB-Floor™ is taken into account with the slab centre load case.

The bending tensions of point loads are generally determined according to Westergaard. The following are accepted for the three load cases:
Block loads and surface loads
Impacts from extensively distributed loads, e.g. bulk materials, are not influential for measuring as a rule.

Mechanical stress
According to DIN 1045-2 [3], exposure class XM, attack on concrete through stress of wear and tear, applies here for load-bearing or hardened industrial floors. It is also advisable to consider the minimum requirements on industrial floors which are not load-bearing or hardened if no further surface treatment takes place.

Abrasion resistance in the face of sliding and buffeting stresses of steel fibre concrete is amplified [14]. The higher the steel fibre content, the greater the abrasion resistance. In addition, the impact strength is greatly increased. Tests [16] revealed that the addition of suitable steel fibres can increase the impact strength to 20 times that of plain control concrete.

Shrinkage

Extensive elements are always heavily exposed to shrinkage. Concrete formulae for industrial floors should have a water / cement value of ≤0.55.
The shrinkage process is further aided by the wind, high temperature and low moisture and begins on the top of the upper side of the slab. The underside is protected through its positioning. Reduction through shrinkage is therefore greater on the upper side of the slab and in extreme cases can lead to so-called curling.

Frost

The substructure must be frost protected. If necessary, a capillary breaking layer to counteract increasing moisture is required.
If concrete areas are to be used, the possibility of entering de-icing salts must be additionally taken into account. In this instance, exposure class XF2 or XF4 is to be considered.

Temperature

Concrete floor areas in halls are protected against large variations in temperature. Warming-up by means of underfloor heating is harmless because it takes place very evenly and slowly.

Chemical attack

In some warehouses, productions and industrial operations, substances are present which attack the concrete. If a penetration of water-hazardous substances in the subsoil can be expected, this must be taken into account [8] (see also "tightness").

Planning

Many parameters are to be taken into account when planning for industrial floors. For the operator and the user of the industrial floor it is even more important that certain details and minimum requirements are defined.

Subsoil:
The subsoil is the basis of the whole construction. It must always be sufficiently sustainable in order for loads to be withstood. The crucial size for the design is the EV2 deformation module which is determined by a static load platform pressure test in accordance with DIN 18134 [12]. Depending on the load and the base course, the EV2 deformation module of the subsoil should be ≥40MN/m². The quality of the sealing is evident from the ratio comparison of the second load to the first load EV2/ EV1 and must be ≤2.5. Should the required values for the deformation module in the load platform not be obtained, an enhancement of the subsoil must be carried out.

Base course:
The base course is located directly underneath the concrete flooring slab, on the subsoil. It is usually manufactured from gravel or grit, can be consolidated with cement and should be at least 15cm thick. In practice, base courses are manufactured with a thickness of approx. 20-25cm. The EV2 deformation module of the base course should be ≥100MN/m².

Joints
A joint plan must be issued for conventional industrial floors with dummy joint cuts as well as for industrial floors without joints but with joint profiles. This is in accordance with the geometry of the hall, usage, equipment and assembly capacity.
Dummy joints must be incised as early as possible (if the implemented concrete is safe to walk on without causing any damage). They are approx. 3-4mm wide and have a depth of approx. 1/3 of the slab thickness. The crack existing in the remaining slab thickness is “needled” by the steel fibres and a transfer of sheer force is possible.

No dummy joints are required for jointless industrial floors without joints according to TAB-Floor™ [13]. In this instance, large, jointless fields of up to 2500 m² are implemented. The individual fields are connected to one another with joint profiles. All joint fields should have square dimensions if possible and must not exceed an aspect ratio of 1:1.5.

Surfaces
As soon as the concrete can be walked upon, the areas of the floor can be levelled out. This takes place through positioning and troweling by machine. In this instance there are very smooth and even surfaces which can be left as finished surfaces.
If an additional wearing surface is necessary, the hard substance material [11] will be evenly placed on the concrete surface and then levelled out and undergo tolerance analysis as before.

Manufacturing of steel fibre concrete
The factory mixed steel fibre concrete is manufactured in accordance with DIN EN 206-1/DIN 1045-2 [1], [3]. Furthermore, the features of the steel fibre concrete which are not regulated in [3] are emphasized in the DBV Steel Fibre Concrete pamphlet [7].
If possible, the fibres should be mixed into the concrete in the concrete transport system via an automatic dosing system with fibre separation.
The concrete retracts through the addition of the fibres. In order to adjust the consistency, a liquifier from the construction site is entered into the concrete mixer. A mixing time of at least 1 minute per m³ of concrete must be observed.

Building construction and assembly
The regulations in DIN 1045-3, sections 8.2 to 8.6 5] are applicable.
All adjoining components are to be detached, i.e. must not make contact with the concrete floor. The industrial floor is assembled &ldquo must be observed. In this instance, the usual curing times for exposure class XM are doubled. The strength and abrasion resistance of the industrial floor surface depends on the curing to a large degree.

Practice example

An industrial floor which must be used with a coil transporter with a wheel load of 220kN must be able to withstand the heaviest loads. In the following example it is evident that a concrete floor with can be manufactured with high quality, load capacity and durability if  extensive planning is carried out and concrete engineering possibilities are optimised.

In November 2005, a new industrial floor was constructed in the coil storage area of the cold rolling mill at the steelworks in Bremen. A jointless industrial floor according to TAB-Floor™ has come into effect. The jointless areas which differ in size, are constantly driven on by an automatic coil transporter (FTC Floor-Transport-Conveyor). Therefore, a wheel load of 220kN (2 x 11t per wheel) and a contact pressure of 6N/mm² were taken into account when measuring. A factory-mixed Readymix steel fibre concrete with 40kg of ArcelorMittal HE 1/50 steel wire fibre was added to the C30/37 XC4 XF1 XA1 F4 concrete.

The industrial floor was constructed with a ready to use surface, had thicknesses of between 30 and 32cm and was manufactured without a hard substance layer. The surfaces have been manufactured with a high evenness and are completely free of cracks. Up to the present time there have been no abrasions at all upon permanent use.

Summary

The demands on an industrial floor have become ever larger in recent years. Durability in particular is ever more in the foreground. In order to substantially plan and manufacture heavy duty industrial floors, the use of steel fibre concrete as a long-lasting building material is proven through practice. By planning the concrete floor as a jointless system in accordance with TAB-Floor™, even more unfavourable load cases such as slab edging and slab corners will be additionally avoided and no high-maintenance dummy joints will exist.

The planning of such as system comprises of more than a simple measurement of load capacity. ArcelorMittal offers comprehensive concepts for various system solutions which cater for all demands and impacts on an industrial floor.

The planning and implementation of the innovative building material, steel fibre concrete, guarantees a long durability for heavy duty industrial floors.

Author: Dipl.- Ing. Wilhelm Nell (VDB)
Senior Sales Manager Steel Fibres CEE
ArcelorMittal Wire Solutions Steel Fibres Profit Center