Analysis of steel-framed open car parks under localized fire

Analysis of steel-framed open car parks 

under localized fire 

16 September 2010, Naples 

Authors: R. Zanon ArcelorMittal R&D, 

O. Vassart Luxembourg 

L.-G. Cajot 

M. Sommavilla 

R. Zandonini University of Trento, 

F. Gadotti Italy

Open Steel – framed Car Parks in Europe 

Dorneind, Helmond (NL) 

Wölfsburg (DE) 

Erfurt (DE) 

Amershan (UK) 

Naples - 16 September 2010 

Analysis of steel-framed open car parks under localized fire 

Arnhem (NL) 

1

Architectural layout of Open Car Parks 

To allow a better functionality of the building 

it is advised to avoid columns between the 

parking lots. This increases greatly the 

dynamic capacity of the car park. 

Such a layout requires rather considerable 

spans (about 16 m), which are most suited 

for steel–framed structures. 

~16 m 

Open = natural ventilation through permanent 

openings in the facades 



2

Common structural solutions 

- Steel beam + traditional composite slab 

(shallow steel decking, slab span 2.5 ... 3.3 m) 

Parking Centre Hospedalier, GD-Luxembourg 



3




- Steel beam + innovative composite slab 

(deep steel decking, slab span 5.0 m) 

Parking Bouillon, GD-Luxembourg 



4






- Steel beam + concrete slab 

(in-situ or precast concrete units, slab span 2.5 ... 5.0 m) 

Parking Auchan Kirchberg, GD-Luxembourg 



5






- Steel beam + concrete slab 

(in-situ or precast concrete units, slab span 2.5 ... 5.0 m) 

- Integrated floor beam solutions (Slim Floor) 

(Hollowcore slabs up to 16.0 m span) 

Parking City Esch, GD-Luxembourg 



6

Fire Resistance 

requirement in 

Open Car Parks 



7

Actions 

Structural Fire design approaches 

Resistance 

Single element 

Whole structure 

Nominal fire 

Prescriptive 

approach 

Natural fire 

Performance 

based 

approach 



8

Steps of the performance–based approach 

1 - Definition of fire actions according to the combustion of vehicles 

simplified model from experimental tests 

2 - Definition of fire scenarios with flame development and propagation 

simplified model from experimental tests 

3 - Thermal Analysis with localised fire model 

analytical model based on experimental results 

4 - Mechanical Analysis of the structure 

numerical model validated by experimental results 



10

1. Test on cars to determine the RHR - curve 

In the scope of various national 

and european projects, a total of 20 

cars were burnt at CTICM 

laboratory in Maizieres-les-Metz in 

order to assess the combustion 

process of standard vehicles. 

0 min. 5 min. 16 min. 34 min. 37 min. 49 min. 

The cars were ignited with 1.5 litres of petrol in an open tray under the gear lever. All doors 

and windows were closed. A hood was built to collect smokes, combustion products and 

pollutants emitted during the fire. At the same time, the car was placed on a weighting 

platform that recorded the mass loss during the test. 



11

1. Results of the tests on single vehicles 

Experimental RHR curves 

Design RHR curves 



12

2. Full scale test in Open Car Park 

In a recent European project a real steel-framed car park was built in Vernon (France) in the scope to 

validate experimentally natural fire scenarios to be applied and to determinate the way to calculate the heat 

flux which the structure is submitted. 

8 min. 15 min. 30 min. 36 min. 

Three big full scale tests involving several cars were run. No structural damage could be observed, and the 

deflection occurred during the fire could be fully recovered after cooling. From this experience the fire 

scenarios of several cars was confirmed. A propagation time of 12 minutes between a burning car and the 

ignition of the adjacent one was found to be a reasonable conservative hypothesis for fire modeling. 



13

2. Fire propagation to many vehicles 

RHR Cars 

12 min. 

RHR of Special vehicles 



14

2. Practical design: First fire scenario 

1 vehicle burning below beam mid-span 



15

2. Practical design: Second fire scenario 

4 vehicles burning around a central column 



16

2. Practical design: Third fire scenario 

Burning wave: 7 vehicles burning along the border 



17

3. Thermal analysis 

Currently two models are available in the EN1991-1-2 Annex C to describe the effects of 

localised fire to the structure: 

Dm f 3.91m 1 

c 35 0.7 W 

m 2 K 

Heskestad model 

for fire not impacting the ceiling 

Hasemi model 

for fire impacting the ceiling 

Parameters for the thermal analysis 

In the case of open Car Parks, the 

experimental campaign has been used to 

validate the Hasemi model as design tool 

able to reproduce with sufficient safety 

margin the temperature field in the structure 

caused by burning cars. 


Fire diameter: 

Convection factor: 

Steel emissivity factor: 

Fire emissivity factor: 

Stephan-Boltzmann constant: 


D 3.91m 

c 35 W 

m 2 K 

m 0.7 

f 1 

5.6710 8 W 

m 2 K 4 

18

Y 

X 

Z 

4. Mechanical analysis – FEM model 

Restraints 

Cold part of the structure 

Columns 

Heated part of the structure 

Diamond 2009.a.5 for SAFIR 

FILE: IPE500sag 

NODES: 370 

ELEMENTS: 390 

SOLIDS PLOT 

TEMPERATURE PLOT 

TIME: 1140 sec 

437.00 

407.21 

377.41 

347.62 

317.83 

288.04 

258.24 

228.45 

198.66 

168.86 

139.07 

109.28 

79.49 

49.69 

19.90 

Beams 

Ribs 

Slab 



19

Validation of the numerical model on tests 

The comparison between experiments and 

numerical simulations has been showed the 

need to use 3D models to describe properly the 

structural behaviour under fire exposure. 

Such models are able to reproduce in reliable 

way the complex load-paths (in particular the 

membrane action) which developes under 

severe fire conditions and which allows for the 

structural stability. 



20

5.0m 

Calculation example – First fire scenario 

2 levels car park 

IPE400 S355 

IPE400 S355 

5.0m 5.0m 5.0m 

IPE400 

S355 

IPE400 

S355 

IPE400 

S355 

IPE400 

S355 

16.0m 16.0m 

HEB200 S355 

Load: 

- 2.2 kN/m 2 selfweight 

- 1.0 kN/m 2 permanent loading 

- 2.5 kN/m 2 variable loading 

Slab: 

- composite slab, total thickness 120 mm, C30/37 

- open trapezoidal steel sheeting rib height 60 mm, S280GD 

- reinforcing mesh Q257, B500C 



21

Calculation example – Third fire scenario 

1. Cold 

situation 

2. Heating 

phase 

4. Cooling phase 

3. Temperature peak 

1. Slab in 

compression 

2. Slab in tension 

In central part 

3. Slab in tension with 

compression ring 

4. Slab in compression in 

cooling phase 



22

5.0m 

Calculation example – Second fire scenario 

2 levels car park 

IPE400 S355 

IPE400 S355 

5.0m 5.0m 5.0m 

12 min 

0 min 12 min 

IPE400 

S355 

IPE400 

S355 

IPE400 

S355 

IPE400 

S355 

16.0m 16.0m 

HEB200 S355 

Load: 

- 2.2 kN/m 2 selfweight 

- 1.0 kN/m 2 permanent loading 

- 2.5 kN/m 2 variable loading 

Slab: 

- composite slab, total thickness 120 mm, C30/37 

- open trapezoidal steel sheeting rib height 60 mm, S280GD 

- reinforcing mesh Q257, B500C 



23

Calculation example – Second fire scenario 

1° phase: due to 

thermal expansion of 

the column, the slab 

displaces upwards 

1° phase 2° phase 

3° phase 

2° phase: column 

buckles and the slab 

displaces downwards 

3° phase: collapse, 

the displacement 

grows indefinitely 

Column buckling about weak axis 



24

Vertical displacement [m] 

Robustness – postcritical reserves 

0.05 

Pre-critical behaviour 

0 

0 600 1200 1800 2400 3000 3600 

-0.05 

Buckling of the 

column 

-0.1 

-0.15 

-0.2 

Z 

Diamond 2008 for SAFIR 

FILE: Structural_Without_Ok 

NODES: 4702 

BEAMS: 1236 

TRUSSES: 0 

SHELLS: 3072 

SOILS: 0 

DISPLACEMENT PLOT ( x 10) 

TIME: 1307.5 sec 

X 

Y 

5.0 E 

-0.25 

Post-critical behaviour 

-0.3 

Time of fire [s] 



25

General results for fire design 

In comparison to the design of the Car Park in cold situation, the following general 

results can be stated for common steel-concrete composite structures: 

1 – Composite Beams may be left unprotected 

(provided full shear connection in cold situation) 

2 – Steel Columns may be left unprotected if overdesigned 

(otherwise they can be protected or traditional fire-resistant solutions) 

3 – Composite Slabs need to be executed as continuous 

(design according to prescriptive rules in EC4 for the cold condition is sufficient) 

4 – Connections may be left unprotected if properly designed 

(traditional simple joint solutions with correct ductile details are suitable) 



26

Detail: expansion joint 

Expansion joint 

In large car parks expansion 

joints have to be provided in a 

distance of about 100m. 

For the fire analysis they are 

structural weak points 

because of the discontinuity of 

the slab. 

e.g. Solution: overdesign 

of the primary beam in 

correspondance of the 

expansion joint 



27

Additional costs of fire design measures [%] 

- 16.5% - 16.4% 

- 9.3% 

- 7.9% - 9.6% 

With the performance based approach is possible to demonstrate that most the fire 

protection is usually not needed in well-designed open car parks. This result leads to a 

sensible cost reduction in the building erection in the range of 10 – 20%. 



32

Thank You for Your kind attention 



33

Workshop beam finishing 

Centinatura 



35

Different solutions for exposed columns 

HEM profiles without 

any protection 


HEB profiles with 

external hollow section 


HEA profiles with 

partial concrete encasement 

36

Temperature for most exposed column (1 st scenario) 



37

Partially encased profiles 



38

Close Car Park: Commercial Centre Auchan 



39



40

Thank You for Your kind attention! 



41

Analysis of steel-framed open car parks under localized fire

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