1. Dr S R Satish Kumar, IIT Madras1 15 Durability and 16 Fire Resistance

2. 2 Electrolyte C Metal Connection Mechanism of corrosion as a miniature battery A Anode Drop of water Metal bar C A Cathode Mechanism of Corrosion in steel

3. 3 Simple orientation of members Methods of prevention corrosion - Simple procedures Detailing to enhance air movement between joints Simple rule: Eliminate the electrolyte Avoid simultaneous presence of water and oxygen

4. 4 Is Corrosion a real Problem? Indian designers feel that steel corrodes most in India. Is it true? Steel corrodes all over the world! But they are better managed in the western countries! Excellent protective coatings which retain their life even up to 20 years are available! Corrosion-where does it matter? Normal inland there is no problem! Exposed conditions ofcourse do need attention. Corrosion is no more a disincentive for not using steel in housing sector!

5. Dr S R Satish Kumar, IIT Madras5 SECTION 15 DURABILITY 15.1 General 15.2 Requirements for Durability –Shape, Size, Orientation of Members, Connections and Details –Exposure Condition (Table 15.1) –Corrosion protection methods –Surface protection –Protective coating requirements (Table 15.2) –Special steel

6. Dr S R Satish Kumar, IIT Madras6 TABLE 15.1 ENVIRONMENTAL EXPOSURE CONDITIONS

7. Dr S R Satish Kumar, IIT Madras7 TABLE 15.2 PROTECTION GUIDE FOR STEEL WORK APPLICATION (a) Coating System Desired Life in Different Environments (In Years)

8. Dr S R Satish Kumar, IIT Madras8 TABLE 15.2 (b) Specification for Different Coating System (i) Shop Applied Treatments

9. Dr S R Satish Kumar, IIT Madras9 TABLE 15.2 (b) Specification for Different Coating System (ii) Site Applied Treatments

10. 10 FIRE PROTECTION Positive points of steel as a construction material under fire Damage to strength of steel due to fire is reversible in most of the cases Using the principle “ if the member is straight after the fire - the steel is O.K” many of the members could be salvaged. Up to about 215 0 C steel retains its strength In the case of concrete, at 235 0 C turns pink; 590 0 C turns red and irreversible damage after 600 0 C Steel exposed to 600 0 C could be strengthened and reused.

11. 11 Typical fire loads and behaviour of steel under fire

12. 12 Typical fire loads and behaviour of steel under fire Time (Minutes) 1000 500 0 0 C 306090 Furnace temperature Unprotected steel Fire protected steel temperature

13. 13 Mechanical properties of steel at elevated temperatures 0.5 1.0 1.5 2004006008001000 Young’s modulus ratio Coeff. of thermal expansion (x 10 5 ) Yield stress ratio Temperature 0 C

14. 14 High H p / A Value Low H p / A Value The section factor concept Some typical values of H P of fire protected steel sections B Dt H p =2D+3B-2t H p =2D+B H p =2D+2BH p =2D+4B-2t Fire Engineering of steel structures

15. 15 Methods of fire protection Spray protection Board protection Intumescent coatings Concrete encasement?

16. Dr S R Satish Kumar, IIT Madras16 SECTION 16 FIRE RESISTANCE 16.1Requirements 16.2 Definitions 16.3 Fire Resistance Level 16.4 Period of Structural Adequacy (PSA) 16.5 Variation of Mechanical Properties of Steel with Temp. 16.6 Limiting Steel Temperature 16.7 Temperature Increase with Time in Protected Members

17. Dr S R Satish Kumar, IIT Madras17 Fire Protection Criteria period of structural adequacy (PSA) greater than or equal to the required fire-resistance level (FRL) in minutes attained in the standard fire test FRL shall be prescribed by other standards depending on the use of the structure and the time required to evacuate. The period of structural adequacy (PSA) shall be determined using one of the following methods: (a) By calculation –(i) By determining the limiting temperature of the steel (T l ) in accordance with 16.6 and then. –(ii) By determining the PSA as the time (in minutes) from the start of the test (t) to the time at which the limiting steel temperature is attained in accordance with 16.7 for protected members and 16.8 for unprotected members. (b) By direct application of a single test in accordance with 16.9 or (c) Calculation of the temperature of the steel member by, using a rational method of analysis confirmed by test data or by methods available in Specialist literature.

18. Dr S R Satish Kumar, IIT Madras18 16.5 Variation of Mechanical Properties of Steel with T (a)Yield stress (b)Modulus of elasticity

19. Dr S R Satish Kumar, IIT Madras19 16.6 Limiting Steel Temperature limiting steel temperature (T l ) in degree Celsius shall be calculated as T l = 905-690 r f where r f r f = ratio of the design action on the member under fire to the design capacity of the member (R d = R u /  m ) at room temperature R d, R R d, R u = design and ultimate strength of the member at room temperature  m = partial safety factor for strength The design action under fire shall consider a)The reduced bond likely under fire. b)The effects of restraint to expansion of the elements during fire.

20. Dr S R Satish Kumar, IIT Madras20 Temperature Increase with Time Protected Members 16.7.1 The time (t) at which the limiting temperature (T l ) is attained shall be determined by calculation on the basis of either a suitable series of fire tests and regression analysis in accordance with 16.7.2 or from the results of a single test in accordance with 16.7.3. Unprotected Members calculate using the following equations. a) Three-sided fire exposure condition b) Four-sided fire exposure condition where t = time from the start of the test, in minutes T = steel temperature, in degrees Celsius, 500 o C  T  750  C k sm = exposed surface area to mass ratio, 2  10 3 mm 2 /kg  k sm  35  10 3 mm 2 /kg

21. 21 Fire resistant steels Very cost effective compared to structural steel FRS are available in India Very popular and cost effective - Japanese experience