The effect of varying fire scenarios on fire resistance ratings of reinforced concrete columns Khaled Sharawi CE 808

Summary Characteristics of Concrete Spalling Design Methods Analysis of Reinforced Concrete columns Results Conclusion Celebration

Characteristics of Concrete Non-combustible material and retains high percentage of strength at elevated temperatures. Low thermal diffusivity and conductivity. Resists heat transmission The modulus of elasticity and shear modulus decrease with the increase of temperature. Great fire endurance No additional costs for fire proofing

Characteristics of Concrete

Spalling Spalling occurs when water vapor is driven off from the cement paste during heating, with high pore pressures creating large tensile stresses greater than the tensile strength of the concrete. There are several different types of spalling including: Surface spalling, corner spalling, aggregate spalling and explosive spalling. Prevention: The addition of fine polypropylene fibers to the concrete mix. These fibers decrease the probability of spalling because the polypropylene melts during fire exposure, increasing the porosity by leaving cavities through which water vapor can escape.

Design Methods ACI Euro code Australian Method Dr. Kodur

Analysis Characteristics of the column: 300mm x 300mm Area of Steel = 400mm2 Number of rebars = 4

Analysis The square column will be tested for 1, 2, 3, and 4 face fire exposure to determine the effect of the different fire scenarios on the fire rating of the column.

4 face exposure Use symmetry 30 mm cover

4 face exposure

4 face exposure 40 mm cover

4 face exposure

3 face exposure

3 face exposure

2 face exposure

2 face exposure

1 face exposure

1 face exposure

Summary of Results Fire Scenario Cover (mm) Time to failure (s) Fire Rating (hr) 4 faced 30 4000 = 66.7 min 1 40 6750 = 112.5 min 1.5 3 faced 4500 = 75 min 2 faced 4250 = 70 min 1 faced 6250 = 104 min

Conclusion Greater concrete cover results in higher resistance rating. The temperature in the reinforcing bars is the critical failing temperature. Usually around 550C. Different fire scenarios change the fire rating of a section. 4 faced fire exposure gives the least fire rating. 1 faced fire exposure gives the highest fire rating. The shape of an element, whether square or circular, does not prevent the occurrence of spalling. The diameter of reinforcement has no influence on surface spalling. Reinforcement closest to fire side reaches failure first.

Conclusion 2 3 3 2 1 2 2 1 1= Highest Exposure 2= Medium Exposure 2 3 3 2 1 2 2 1 1= Highest Exposure 2= Medium Exposure 3= Least Exposure

Questions???

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