ACB® beams are fabricated based on the exclusive use of hot rolled sections.
A double cut-out is made in the web by flamecutting. The two obtained T-sections are shifted and rewelded, leading to an increase in height.
The structural product thus obtained has an increased ratio of moment of inertia to weight. For a given section the diameter and the spacing of openings are variable resulting in an extremely adjustable beam geometry and a perfect suitability to the project requirements.
Objective: Optimisation of the height/weight ratio
Applications: roofing, gangways/footbridges, wide-span purlins
Common steel grades: S235, S275, S355
Objective: Optimisation of the load/weight ratio
Applications: floors, carparks, offshore structures
Common steel grades: S355, S460, HISTAR® 460
IPE300 – IPE750, HE240 – HE1000, HL920 – HL1100, HD260 – HD400, UB305 – UB1016, UC305 – UC356, W310 – W1100
Light, aesthetic & functional
The lightweight appearance of ACB® cellular beams, combined with their high strength, never ceases to inspire architects to new structural forms and the optimized height/weight or load/weight ratio provides effective answers to the demands of project owners.
This solution allows large uninterrupted spaces with spans of up to 18 metres and technical installations like pipes and ducts can pass through the beams circular web openings.
Related News & Articles
Your ASOS order is on its way…courtesy of ArcelorMittal6 December 2017
If you are not familiar with the brand, ASOS is the biggest online-only clothing retailer in the UK with 14.1 million active customers and a huge catalogue composed of 80,000 branded and own-brand products. ArcelorMittal provided Hacierba® liner trays and 2,000 tonnes of sections for the construction of ASOS first warehouse outside Great Britain.Project News
Extension of the Geric Supermarket in Thionville22 June 2009
The new Geric supermarket and car park structure are really innovative structures for the French market. The construction techniques used for this project are applying the last innovations in term of structural calculation and fire engineering.Article
ArcelorMittal Cellular Beams ACB®: The Intelligent Solution for Large Spans12 May 2008
In the past 15 years, the use of cellular beams in steel structures has increased considerably as they present an interesting solution for aesthetic as well as efficient steel structures.Product News
Fire Resistance of Steel Structures: Theoretical Fundamentals and Real Case Scenario of the Natural Fire Safety Concept20 July 2009
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.Article
Your ASOS order is on its way…courtesy of ArcelorMittal
If you are not familiar with the brand, ASOS is the biggest online-only clothing retailer in the UK with 14.1 million active customers and a huge catalogue composed of 80,000 branded and own-brand products. ArcelorMittal provided Hacierba® liner trays and 2,000 tonnes of sections for the construction of ASOS first warehouse outside Great Britain.
British online retail company ASOS just started the activity of its first warehouse outside Great Britain, located in Großbeeren, in the south of Berlin. It was designed by Alcaro (a specialised investor for logistics facilities) with a roof structure built with ArcelorMittal Europe – Long Products steel provided via steel fabricator Stahlbau Süssen. ArcelorMittal Construction is also a contributor to the project with the supply of Hacierba® 150/600 SRSR liner trays for the façade of the warehouse.
The construction of this logistics centre was divided into two phases. For the first phase, which took place in 2016, four halls with a total surface of 46,000 m² were built. We had to deal with strict requirements for the construction.
First, ASOS demanded a maximum clear height to be able to place very high shelves in the hall, but due to fire safety considerations, the total height of the halls was limited. This challenge resulted in the development of a roof structure with a span of 26 metres and a height of one metre maximum which would contain the whole equipment of the building (electric cables and lamps, air conditioning, heating and sprinklers).
Second, the investor required the building to be certified by DGNB (Deutsche Gesellschaft für nachhaltiges Bauen), German Sustainable Building Council. Consequently, A.C.B.® beams were the best solution as they could meet all the requirements.
For the second phase, four new halls are being built, still using A.C.B.® beams, but this time the beams were made 6 cm higher to support additional loads due to the presence of solar panels on the roof.
ArcelorMittal’s sustainable and cost-efficient solutions
ArcelorMittal Construction’s Hacierba® liner trays provide very good load bearing capacity. They are the inner shell of the façade, bearing the wind loads and providing heat insulation of the building thanks to a mineral wool lining. It is an economic, lightweight solution that is easy to assemble. Furthermore, we could provide the customer very short delivery times.
ArcelorMittal Europe – Long Products and our technical department Tecom worked closely with customer Stahlbau Süssen to develop ACB.® beams that would fulfil all the requirements. ACB® beams allow for a very efficient structure using only few resources and they are perfectly tailored to the loads of such a structure.
Moreover, the structural shapes used to produce them were made from 98% scrap material, with 70% of that being recycled steel. And they can be used after dismantling of a structure as construction elements in new projects.
In total, we supplied for the whole project 376 tonnes of sections without finishing and 1,665 tonnes of 13-metre ACB® beams which were painted in red (the corporate color of Alcaro) and with the contact faces of the head plates covered with a special friction-resistant coating.
As the construction site and the ArcelorMittal Construction’s site in Landsberg are only 145 km apart, ArcelorMittal could provide a short delivery time for the liner trays; resulting in low transport cost for the customer, as well as less Co2 emissions.
For the beams, the delivery was just-in-time by trucks. The beams were bolted together two by two on the construction site and put in place as a roof girder. Logistics was even simplified on our side since our finishing and coating workshops are both located around the premises of the Differdange mill in Luxembourg; making internal logistics by rail simple and efficient. As for the other sections we supplied, they were produced in Differdange and in Dabrowa, Poland. The customer did the finishing and painting and delivered them directly to the construction site.
The first part of the building is already in use and the second part is expected to be completed in January 2018.
ASOS Facts & Figures
- ASOS = As Seen On Screen
- Website launched in 2000
- 14.1 million active customers
- 2,000 employees – Headquarters in London
- Sells more than 80,000 branded and own-brand products
- Ships worldwide with websites targeting Germany, France, Italy, Spain, Russia, USA and Australia
- 300,000 dresses sold per week
- 85,000 men t-shirts sold per week
Text: ArcelorMittal Europe Communications
Photos: Stahlbau Süssen GmbH & ArcelorMittal
Extension of the Geric Supermarket in Thionville
The new Geric supermarket and car park structure are really innovative structures for the French market. The construction techniques used for this project are applying the last innovations in term of structural calculation and fire engineering.
The structure of the commercial area will be the first reference of Angelina™ beams calculated partially protected taking into account the membrane action of composite structures in case of fire.
The car park will be the first car park in France that will be built using unprotected ArcelorMittal Cellular Beams.
Another particularity of this project is that the ground floor will be devoted to the shopping centre and the 3 upper floors will be an open car park (first realization of this type of structure in France).
Description of the building
The owners of the commercial centre Geric decided to extend the commercial part of their building, but it was impossible for them to extend the size of their property. It means that this extension must be done taking the actual surface of their existing open air car park surface. As the number of parking places was already a problem, the new concept must not decrease the total amount of places.
It has been decided to add, on the top of the commercial extension, a multi storey open car park. So in the end, as this multi storey car park will have 3 floor levels, the final amount of parking places will be increased compared to the previous layout of the commercial centre.
The structure is composed of 4 floors with an approximate dimension of 70m x 70m.
Choice of the structural elements
The owners, the architects and the engineering office had in mind to optimise the structural system in order to achieve the most cost effective and environmentally friendly structure. Their choice was directly oriented on steel and composite construction.
For the slab between the ground floor and the car park, the architects have chosen AngelinaTM beams to have large openings in order to pass all the ventilation and piping system into the openings (Fig. 2).
For the car park levels, cellular beams were used in order to optimise the structural system but also for architectural reasons.
As the vertical part of the beam contains a lot of openings, the level of the ceiling will be perceived by the visitor as the level of the slab and not the level of the lower flange of the beam, so for the “human brain”, the beams will become transparent. It means that the sensation of freedom and safety will be highlighted.
For the durability, it was decided to galvanise the structure that will remain visible and not protected against fire.
For the slabs, the composite flooring system Cofraplus 60 was used.
Fire engineering innovation
The French procedure for the calculation of unprotected car park structure has been followed. The three usual French fire scenarios were taken into account in the calculation (Fig. 4):
- 4 cars around a central column
- 7 cars in line at the corner of the car park
- 1 car in the circulation area
The innovation is that the structural calculation has been made for cellular beams using the models developed in the recent RFCS project FICEB+. In the past, it was not possible to perform such calculation taking into account the specificities of the cellular beams.
For the commercial area, the new calculation technique taking into account the membrane action of partially composite slab in case of fire has been used for the first time on the French market. This calculation technique is based on diverse research projects and has been implemented into the user-friendly software MACS+ ( available for free download on www.arcelormittal.com/sections or in Constructalia Software section). This technique allows saving about 50% of the fire protection, applying it only where it is really necessary (Fig. 5).
This project will become a reference for unprotected open car park and shopping centre due to the global optimisation of the structural system and architecture. This new approach was only possible thanks to diverse R&D projects led by ArcelorMittal (Fire in Car Park, FRACOF, RFCS FICEB+ and RFCS MACS+).
Text: Olivier Vassart & L.G.Cajot, ArcelorMittal Long Carbon Europe
ArcelorMittal Cellular Beams ACB®: The Intelligent Solution for Large Spans
In the past 15 years, the use of cellular beams in steel structures has increased considerably as they present an interesting solution for aesthetic as well as efficient steel structures.
The use of cellular beams allows a new architectural expression.
Structures are lightened and spans increased, pulling spaces together. This flexibility goes together with the functionality of allowing technical installations (pipes and ducts) to pass through the openings.
The lightweight appearance of cellular beams, combined with their high strength, never ceases to inspire architects to new structural forms.
Progress has now been made on a number of factors that enable the use of cellular beams to be extended:
The optimisation of manufacturing methods (flame cutting, bending, etc.) now makes it possible to adapt to the requirements of project owners and guarantee rapid delivery of cellular beams.
The Eurocodes (Eurocode 3 for steel structures and Eurocode 4 for composite structures) provide answers to the calculation of strength in normal use, for fire accident situations and with regard to the use of S460 high strength steel.
The mastery of the various aspects of composite steel and concrete construction - making the bond, use of linked trays, floating plates, fire resistance, user comfort and durability - has greatly contributed to the ACB® cellular beams" solution in floors.
The development of a high-performance design and calculation tool (ACB software), available to design offices and architects, favours the use of cellular beams. The methods adopted in this software exploit the results of tests on full-size beams and of many digital simulations.
Fire Resistance of Steel Structures: Theoretical Fundamentals and Real Case Scenario of the Natural Fire Safety Concept
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.
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.
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