Underground car parks | Fire resistance

Steel sheet piles as permanent structural elements

Steel sheet piles used as permanent structural elements in underground car parks and roadworks have a multiple role. They can:

• serve as a retaining wall during the excavation phase to support the horizontal pressure;
• provide watertight containment for the excavation pit;
• form the permanent outer structural wall;
• carry parts of the vertical loads from the floors or even from the superstructure.

Thus, avoiding the need for a temporary retaining wall outside, the permanent sheet pile wall: 

• maximises the available space, an important issue especially in urban areas; 
• shortens the construction time;
• reduces the total cost of the building.

Economical steel solutions

The main benefit of using steel sheet piles as permanent structural elements for underground car parks and basements is the simplification of the construction sequence and the resulting substantial savings of cost and time. 

Economical steel solutions without any protective measures can even be defined for structures subject to fire resistance requirements. 

Steel sheet piles can easily be painted after completion of the works. 

Verifications are usually confined mainly to the design at serviceability or ultimate limit states considering the temporary execution steps as well as the final situation, and focus on the most economical solution.

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 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 from the design stage due to unfounded prejudices or to a lack of know-how concerning fire safety in general or the particular behaviour of steel sheet piles under the effect of a possible fire event. 

Arcelor has carried out extensive fire testing and numerical simulations focusing on the fire resistance of steel sheet piles and the effects of the surrounding soil. 

Using the knowledge gained, the fire safety of steel sheet pile walls can be verified taking the following parameters into account: 

• the thermal characteristics of the different soils;
• different fire loads;
• different protective measures.