Underground car parks | Fire resistance

Understanding and enhancing the fire resistance of steel sheet piles in underground car parks

This brochure provides assistance in the fire safety design of steel sheet piles used as permanent retaining walls in underground car parks or roadworks (tunnels, underpasses,...).

It summarises the results of the full scale laboratory tests performed by ArcelorMittal, and describes one method to verify the stability of the structure under fire loading. Furthermore, it includes an easy-to-use verification procedure allowing a simplified assessment of the fire safety of the steel sheet pile structure that can be used in a preliminary design.

Download

en English AMCRPS_UCP_Fire_Resistance_EN.pdf
Pause Play

Steel sheet piles as permanent structural elements

Steel sheet piles used as permanent structural elements in underground car parks and roadworks can have multiple roles

  • serve as a temporary retaining wall during the excavation phase;
  • provide a watertight containment for the excavation pit;
  • form the permanent outer structural wall;
  • transmit parts of the vertical loads from the floors or from the superstructure into the soil.

Thus, avoiding the need for an additional temporary retaining wall on the perimeter of the structure, the permanent sheet pile wall 

  • maximises the available floor space, a key advantage in urban areas; 
  • shortens the construction time;
  • reduces the total cost of the building.

Cost-effective steel solutions

The main benefit of using steel sheet piles as permanent structural elements for underground car parks and basements is the simplified and faster construction sequence, as well as its lower cost. 

In extreme fire load cases, additional active and/or passive fire protection measures may be required. 

Steel sheet piles can also easily be painted for aesthetical reasons after completion of the works. 

Design verifications consider serviceability and ultimate limit states during each execution phase and during the whole service life. Fire safety is only one of the several load scenarios to analyse, and may not always be the governing load case.

Specifics

Like any bearing pile, steel sheet piles can safely transmit vertical loads to the substratum through skin friction and toe resistance. 

Structural connection of the floors and superstructure is easy to execute with cast in-situ concrete corbels or capping beams. 

Using the top-down method will even allow a further reduction in construction time, since temporary anchoring or propping of the retaining wall is not necessary.

Fire resistance of steel sheet piles

In most cases, the “fire” load case does not have to be considered for temporary constructions. 

However, for permanent structures, steel sheet pile solutions are often excluded right at the design stage due to unfounded prejudices or to a lack of know-how concerning fire safety, or the particular behaviour of steel sheet piles under the effect of a fire event. 

ArcelorMittal carried out extensive fire testing and numerical simulations in collaboration with the University of Liège (Belgium), focusing on the fire resistance of steel sheet piles and the positive impact of the surrounding soil layers and groundwater. 

The university developed the software SARI to verify the fire safety of steel sheet pile walls taking into account following parameters: 

  • sheet pile section and its properties (thickness, section modulus, steel grade,...)
  • the thermal characteristics of the soils on the back of the wall;
  • fire loads;
  • optionally, additional protective measures (active and/or passive).