Construction of a New Production Hall of Volkswagen AG Bratislava Using Prefab Elements

Case Study

Reinforced steel prefab girders and purlins
3D model of prefab construction in the third construction stage
Advanced stage of the load-bearing structure of hall 2A

In April 2009, the Volkswagen AG Group decided to enlarge its production facilities in Bratislava in Slovakia. The first cars of a new model series are to roll off the production lines in the year 2011 already for delivery to customers all over the world. This 308 million euro invest-ment aims to step up annual production capacity to 400,000 vehicles and create 1,500 new jobs.

One of the extension measures was an extension to production hall 2A, which houses the paint shop. The project planning and control were managed by the client in a specially set up department within the Volkswagen AG Project Planning Department, i.e. in line with already implemented corporate standards and directives. All tasks from tendering and contract awarding to actual construction and final acceptance were performed bilingually, i.e. in German and Slovakian. The tender documents and project documentation for building permission of hall 2A were prepared by the Slovakian lead planner and project designer Coproject a.s. in August 2009. All the work specifications were compiled in two languages with the support of RIB project and cost management software.

Production hall 2A is a four-storey building with main ground plan dimensions of 251.0 m x 60.0 m, a square span width module of 12.0 m x 12.0 m, a construction height of approx. 24.0 m and a foundation depth of –2.2 m. Fig. 1 is a 3D model of the hall.

Frame Structure in In-situ Concrete in the First Planning Stage

The engineering company BF-Partners s.r.o., Bratislava, Slovakia designed the load-bearing structure of the hall as a skeleton frame structure in cast-in-place concrete with facade blocks in a 6.0 m grid. This meant that all the construction work could be contracted via a public tender that was fully accessible to the general public. The ceiling structure was made of ribbed beams and slabs hinged to continuous columns. The load-bearing roof construction was designed as a steel frame of girders and steel purlins complemented by trapezoidal sheet metal and other traditional roof finishing elements.

For reasons of fire safety and also to limit mutual interaction, ensure robustness, and last but not least, due to construction process reasons, the production hall was divided into three independent construction stages with appropriate doubling of the columns at the transition axes. The engineers planned single foundations for the columns, combined with local sub-surface improvements if necessary or exchange of soil at any soil fracture points and faults.

Basic conditions for the construction work

The tight schedule assumed that project planning, building permission, tendering and the foundation work would be done during summer and autumn of 2009 and then specified that the construction work was to be executed swiftly in the winter months and the spring of 2010.  In parallel to the actual construction work, there were other project requirements to be met, such as execution planning including completion of the detailed working plans and other ex-tensive specifications of the client. The most important of these was that the construction work was not to interrupt the factory’s production flow and had to comply with high standards of safety. 

As general contractor, the Czech company HSF System a.s. was awarded the contract to build the production hall. For reasons of time – the construction work had to adhere to the strict terms of the contract and to the schedule – the decision was made to prefabricate the entire load-bearing structure. The general contractor chose the Slovakian prefab element producer Prefa Sůčany a.s. for this task. The execution planning for it was done by the engineering company DeBondt s.r.o., Trencin from Slovakia. The entire planning process was considerably influenced by the fact that the prefab element producer had to carry out a complete reengineering to switch from the originally planned frame structure to an assembled prefab structure as force account work as part of its overall service. With the new planning variant, all the prefab parts were transported by road and assembled on site using heavy truck cranes.

Finished prefab construction

The DeBondt engineering company began with the execution planning and the required reengineering of the entire construction in December 2009. This planning work thus ran pa-rallel with the construction work, which had already started, and took from January 2010 to acceptance in June 2010. The engineers, who had designed the original frame structure in in-situ concrete, were also contracted by the client to do the official inspection of the structural analysis, although this is not a compulsory requirement of Slovakian standards. The foundation work and the erection of the column foundations on large piles and the foundation slab of level ±0.00 m were carried out by other suppliers of the general contractor.

The basic dimensions of the building and its division into three construction sections remained as originally planned. The originally planned steel frame for the roof was replaced by precast members of prestressed and reinforced concrete in the revised plan. The intermediate floors were built as a composite construction of cast-in-place concrete and filigree slabs, supported on a grillage of prefab beams. Fig. 2 is a 3D model of the prefab construction in the third construction stage. Fig. 3 illustrates the actual assembly.

Vertical bearing members

The main vertical bearing members are prefab columns with a total height of 24.0 m and a rectangular cross-section of 1000/800 mm or 800/800 mm. The columns are fixed in cast-in-place concrete sleeves, with the exception of the connecting axis to the existing hall 2. Here, the columns are supported with a connecting anchor of the type PFEIFER PSF 30.

The greatest challenge of the project was the static analysis and economical dimensioning of the columns, because the only elevator shaft (6 m x 4 m) had no functional suitability as a bracing core. The columns therefore had to ensure horizontal stability of the building as well. At each deck level, therefore, peripheral bracing was implemented of continuous prefab beams with a rectangular or inverted L-shaped cross section. The engineers found the optimal static solution with the help of the BEST program from the RIB company, using the second-order theory and applying the necessary imperfections and via effective stiffnesses of a variably reinforced cross section with possible crack formation on the tension side. In this way they obtained an economical dimensioning while ensuring adequate buckling stability of all the columns.

The engineers were able to detect shoring loads at the columns from the peripheral bracing, ceiling beams and girders with RIB RTool software. As a result, short cantilevers were used with elastomer supports and high-strength in-situ concrete mortar types.

Horizontal bearing members

The supporting structure of the trapezoidal sheet metal roof is a system of prestressed prefab girders 24.0 m long and 1.4 m and 1.5 m high, complemented by reinforced steel prefab girders 12.0 m long and 1.2 m and 1.05 m high, and 12.0 m long purlins with a wedge-shaped cross section 650 mm and 700 mm high.

In view of the limited total construction height and the fire safety regulations, the prestressed, 24.0 m long prefab girders proved to be the most economical solution. The complex static design of the prestressed girders including influences such as the transport system, technological recesses in the transverse direction and nonlinear tilting stability were carried out with RIB RTfermo software.

The load-bearing construction of the intermediate floors in the equipment area is composed of a 12.0 m x 12.0 m grillage of main girders 1,500 mm high and notched, 950 mm high joists and ribbed beams of 3 m each. The floor itself is made of a composite construction of 60 mm thick filigree slabs and 140 mm in-situ concrete. The concretion was performed in large sections, the largest job being 36.0 m x 36.0 m. A one-metre wide shrinkage strip was left along the supports of the ribbed beams on the joists, which created two construction joints. Here, the top layer of reinforcement was laid so as not to be subject to stress from both shrinkage sections simultaneously. Finally, the two shrinkage strips were cast in place.

Great care was taken throughout the project to ensure precise execution of joints and details. One important point was the formation and composite action of the peripheral braces. To-gether with the ceiling discs, these act as continuous beams. With static analysis and dimensioning of the main girders and joints in the RTbalken program of RIB, the engi-neers were able to adhere to the deflection values specified for the floors that were extremely limited by the installed technology. At the same time, they took account of the torsion load at the peripheral bracing when dimensioning the system.

Materials used

The prefab parts were made of the following materials:

  • Concrete
    • Columns    C40/50, C50/60
    • Prestressed girders    C55/67
    • Reinforced concrete girders    C50/60
    • Purlins    C50/60
    • Peripheral bracing    C35/45
    • Joists and ribs    C50/60
    • Main floor girders    C30/37
  • Steel
    • Structural steel B500B (10505 R)
    • Stressing strands D15,5 MM, ST1660/1860

Completion and evaluation of the construction project

Despite the great pressure imposed by the tight schedule and the necessary changes in plan, the prefab element producer Prefa Sucany and the engineering company DeBondt successfully met all the limiting contractual and climatic specifications for the whole building. In spite of the harsh winter of 2009/2010, the construction work was executed to schedule and in the high standard of quality that had been agreed. There was considerable press coverage of the successful construction of the building near the Slovakian capital Bratislava. The decision to use prefab parts for most of the building proved to be the right one. Without the chosen prefab construction method and the cost-effective, reliable static design and dimensioning, the contractor would hardly have been able to keep to the strict budget in view of the high floor loads caused by the technical equipment and the problems of building in the winter months.

It was also brave of the DeBondt engineers to contractually guarantee the prefab element producer the quantities of steel and concrete they had both calculated for the quotation. Their financial participation in possible savings acted as an additional incentive to improve the engineers’ solution even further. They were able to save about 350 t, i.e. nearly 20% of the steel estimated in the preliminary planning due to their expertise and experience, not to forget the use of powerful software systems of the RIB company.

Industries>Architecture, Engineering & Construction>Architects and Engineers>DeBondt

Social Bookmark: