the fracof composite slab test - university of...

The FRACOF Composite Slab Test

Anthony Abu & Ian Burgess

Experiment, Predictions & Results

15th April 2008 © The University of Sheffield - Structural Fire Engineering Group

Introduction

Fire Resistance Assessment of partially protected

COmposite Floors - FRACOF

To increase the use of Steel in multi-storey construction

from 18% to about 65% in continental Europe

Difference – mainly due to adopted Fire Safety approach


Introduction

Introduction to Eurocodes

Objectives of the Test

1. Investigate the performance of slab panels in SCI P-288

2. Observe the impact of different construction details on slab

panel capacity

Education of people in the construction industry

• FRACOF Test

Use of optimised structural systems


Test Setup

6.66m8.735m

Primary Beams – S355 IPE 400

Secondary Beams – S235 IPE 300

Columns – S235 HEB 260

Protection Material – Cerablanket

Density = 128kg/m3

Specific Heat Capacity = 1130J/kgK

Thermal Conductivity = 0.06 – 0.27 W/mK


Test Setup

58mm155mm

COFRAPLUS 60

C30/37

Φ7mm – 150 c/c – S500

50mm cover (top)

Reinforcement welded to S235 HEB 200

flanges to ensure continuity


Shear Studs

• Φ = 19mm Primary beams – studs spaced at 100mm centres

• h = 125mm Secondary beams – studs spaced at 207mm centres

• fy = 350N/mm2

• fu = 450N/mm2

Test Setup


Furnace

ISO 834

curve

Applied Loading

= 3.87kN/m2

Test Setup

Assumed Dead

Load = 3.254kN/m2


Vulcan Prediction – Before Test

IPE400 sections


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Time (min)

Central Displacement (mm)

VulcanLite – Concrete Topping

Vulcan - Effective

Stiffness

Vulcan Prediction – Before Test


The Experiment - Observations

Edge continuity Condition not achieved on

one side


Debonding of Concrete from

the steel deck



Buckling of exposed

reinforcement



Central Crack across short

span at about 105mins



Large crack in the centre of the slab panel due to failure of the

welded joint between lapped reinforcements along that line.



Test Conclusions

1. Even with the fracture of reinforcement the test showed that the slab

panel could sustain more than 2 hours of exposure to the standard

fire

2. The integrity and insulation criteria of the slab were lost after 105

minutes, when the crack occurred due to the loss of the bond

between the lapped reinforcement

3. Provided the continuity of reinforcement is guaranteed, reinforced

slab panels will survive their specified duration once state of the art

construction details are used.



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Time (min)


VulcanLite – Concrete Topping

Vulcan - Effective

Stiffness

Test Result

Vulcan Prediction


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Time (min)

Tem

perature (oC)

Protected secondary beam Temperature

Test

Temperatures

Secondary beam

Temperature


Revised Prediction

Before Test

Slab thickness = 160mm

fcu = 40N/mm2

2 welded beams for continuity

Imposed load = 3.75kN/m2

Protection material

Thermal conductivity = 0.2W/mK

Thickness = 50mm

Revised Prediction

Slab thickness = 155mm

fcu = 37N/mm2

1 welded beam for continuity

Imposed load = 3.87kN/m2

Protection material

Thermal conductivity = 0.06W/mK

Thickness = 50mm


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Time (min)

Tem

perature (oC)

Protected secondary beam Temperature

Test

Temperatures

IPE 300

Initial Uniform Secondary

beam Temperature

Revised Beam

Temperature


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Revised Prediction

Time (min)


Test Result

TSLAB Limit

Bailey-BRE

Deflection

Revised Prediction with lower

edge beam temperature


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Time (min)

Tem

perature (oC)

Non-uniform beam temperatures

IPE 300

Test

Temperatures

Vulcan Bottom flange, web and

top flange temperatures for the

protected secondary beams


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Time (min)


Non-uniform beam temperature

Test Result

Uniform protected beam

temperatures

Non-uniform protected

beam temperatures


Mesh Temperature & Slab Thickness

Full depth

Vulcan Effective

stiffness approach

Average depth

Closest comparison

with TSLAB

Temperatures

Thin Continuous concrete depth

Most conservative approach

Increasing Reinforcement Temperature and

decreasing slab thickness


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Time (min)

Tem

perature (oC)


Reinforcement

Temperature range -

Test

Effective

Stiffness

Thin Concrete

ToppingAverage Depth


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Time (min)


Effective Stiffness

Thin Concrete

Topping Average Depth



Physical

Representation

50mm57mm14mm

Vulcan

Representation

57mm0.514mm



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Time (min)

Tem

perature (oC)


Reinforcement at

average depth of 57mm

Reinforcement at average

depth of 63.743mm


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Time (min)




depth of 63.743mm


depth of 57mm


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Conservative Estimate

VulcanLite estimate with uniform protected

beam temperatures, thermal conductivity

0.06W/mK and a thin concrete slab

TSLAB Limit

Bailey-BRE

Deflection


Conclusions

Vulcan and VulcanLite give good predictions of slab panel behaviour

Vulcan predictions and Test results differ by the observed integrity failure

of the test

Need to incorporate a plausible localised concrete failure criterion in

finite elements

Care must be taken in the selection of assumptions for finite element

analyses


Thank You!

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