ArcelorMittal Office Building Luxembourg: A steel frame and prefabricated solutions

Detailed information

Location

Esch-sur-Alzette, the second largest town in Luxemburg, is situated in the south of the country, at the heart of the iron and steel region. It has good access to the capital and can be easily reached by public transport. Today, the 'Capital of steel' has been redeveloped on a former industrial site a new city centre that includes a campus of the University of Luxemburg. Since the last century, Esch has been dominated by the iron and steel industry. The site of ArcelorMittal Office Building, part of the former gardens of a palace, lies immediately next to the ArcelorMittal research centre on the outskirts of the town.

Building

In the context of an international competition in 1990, the entry submitted by Gottfried Böhm’s office in Cologne was awarded a 'special purchase' to the same value as the first price. The office was subsequently commissioned to revise its design. The building consists of two eight-storey wings, each of which contains 24 standard office units (modules) per floor, with open common areas in the centre. Electronic data processing equipment, service installations, central control systems, storage and archive rooms, and a deliveries point are housed in the basement. Further mechanical services equipment is installed on the roof of the building.

The two wings of 40 x 18 m each are laid out at an angle of 1400 to each other. The common areas in the middle of these wings are divided up by 60 m2 covered courtyard wells extending the full height of the building. Incorporated into these open wells are 30 m high wind-bracing elements.

Lifts, fire-escape staircases, and toilettes are situated at the outer end of each of these wings. Conference rooms, break room kitchens, and a third staircase in a round tower also fulfil a linking function at the pivot between the two wing galleries leading from the entrances at the ends of the wings, extending round the research centre in front of the building and linking up with the old tower, which is the only surviving part of the former palace. The tower now forms the new main entrance to the complex. The building has a volume of roughly 50 000 m3 (61 000 m3 including the galleries and tower).

Time schedule

March 1991: Beginning of the construction
March 1992: Erection of the steelwork
August 1993: Building was finished

Volume: 61 000 m3
Surface: 15 000 m2
Dimensions: 2 x 40 m x 18 m
Storey height: 3 m
Grid: 6 m x 7.2 m
Storey: R +7

Fire safety

The striking feature of the fire protection in this building is an ingenious system of active and passive measures:

- short routes to the staircases
- structural separation of staircases from the main load-bearing skeleton frame
- optimal ventilation by means of automatically opening smoke exhaust system of 2 x 2.4 m2/wing in the roof
- a sprinkler system (water reservoir of 25 000 and 2 x 7650 litres) that reacts to thermal defectors

The Natural Fire Safety Concept, as included in the Eurocodes, has been used in order to verify the global stability of the structure under fire, without adding any supplemental passive measures. The principle characteristics activated for the design are the following:

- the overall behaviour of the structure under a natural fire according to Eurocodes 1, 3, and 4
- reduction of the fire loads according to the passive and active measures used for human safety
- the additional framing effect of reinforced beam/column connections in the direction of the transversal wind bracing
- thermal insulation of the columns in the facade
- shear reinforcement bars at the support of prefabricated slab elements

All of these measures made it possible to leave the steel structure visible and unprotected:

Natural Fire Safety Concept
Passive fire protection and realistic fire design
Realistic load combinations (according to EC1, EC3, EC4)
Global stability of the structure

Active fire protection
Automatic fire alarm
Smoke
Heat
Acoustic fire alarm
Safe escape route
Firemen
Safe access (routes, hydrants)
Automatic closing of fire doors
Compartments
Sprinkler
Automatic smoke evacuation
Fire load
Local natural fire
Safety of the structure

Technical data

Thermal insulation of facade elements of 1.7 W/m2K.

Technical equipment:

Heating (hot water + convectors + ventilation): two natural gas boilers of 1163 kW
Cooling (ventilation + ceiling convectors): cooling power 2 x 630 kW (revamped in 2009 with 3 x 300 kW)
Ventilation: via two towers situated at the roof level for the office, independent devices for others technical rooms
Natural gas consumption: 220* kWh/m2 year (1 m3=10,12 kWh)
Electrical consumption for cooling and ventilation: 63* kWh/m2 year

* Mean value for 2006, 2007 and 2008

Frame

The building has a steel frame based on a 6 m x 7.2 m grid, with seven rows of four columns in each wing. The bearing structure is supported by steel pile foundations. The columns are connected to integrated floor beams (IFB) — a system developed by ArcelorMittal.

Horizontal loads are transmitted by the floor slabs to one longitudinal and four transverse wind bracing trusses. In the plane of these trusses the beam/column connections are rigid or semi-rigid.

Prefabrication and erection

A deciding factor in achieving a short assembly period, and thus reducing the overall construction time, is the extent and precision to which the elements can be prefabricated. A prerequisite for this is, in turn, a precise process of planning at ail stages. If these two conditions - detailed planning and a high degree of prefabrication - can be met without difficulty, steel structures represent an unrivalled form of building. As a rough measure for a short construction period, it should be possible to erect a floor area of 2000 m2 a week with a single crane.

Advantages of prefabrication

• Shortened construction time
• Construction time of the steel structure: 8 months
• Construction time of a conventional structure: 12 months
• Time advantage for the steel structure: 4 months
• Early rent income through shorter construction time = 800 €/unit x 384 units x 4 months = 1 228 800 €

       (fabrication cost + erection of steel structure = 1 473 750 €)

IFB (lntegrated Floor Beams)

The IFB flat slab floor system permits an uninterrupted floor area without down stand beams. The floor beams are built up sections consisting of a ½ IPE A 500 in HISTAR® 460 steel grade and a 10 mm thick bottom flange. They have an asymmetric cross-section with a wider lower flange.

Prefabricated prestressed concrete hollow core slabs are laid between the girders. The gap between these and the beams is filled with insitu concrete. This flat slab floor, using easy-to-assemble prefabricated elements, has a monolithic load-bearing behaviour. Its construction height is kept to a minimum of 30 cm, and a maximum of flexibility is given to the fixing of service pipes and ducts.

Combined office system

This is one of the first large-scale applications of a combined office design system in Europe. The underlying principle is that small single or double office spaces on the outer faces of the building are combined with a large common area in the middle, which is used for meetings, communication, storage, and equipment. The advantage of this system is that quieter, individual working areas can be linked with areas for open communication with a minimum of disturbance between employees.

Internal finishing

The standard office spaces are separated by metal stud partitions with clerestory strips of glazing. Tracks for fixing shelving are integrated into the partitions. The interior walls to the open office areas are fully glazed. The grid is based on a module of 2.4 m. Floors are covered with a rubber finishing. Perforated steel sheet acoustic panels are suspended beneath the red-coloured precast concrete slabs. The ceiling fixed cooling convectors, the hot water central heating, and the lighting can ail be individually regulated by users.

Standard office module

Dimensions: 2.4 m x 4.2 m = 10.08 m2
Module by floor: 2 x 24
Total: 384 modules

Acoustical insulation

Slab > 17 dB
Internal metal partitions
Office to office - 38 dB
Office to common area - 35 dB

The cladding to the building consists of lightweight metal and glass with integrated daylight-deflecting solar shading strips. The top-flung flaps used for ventilation are glazed with solar reflecting glass. The apron walls are clad with enamelled glass. The corrugated stainless steel facades of the staircase and WC towers are purpose made.