1. FATIGUE BEHAVIOUR OF REINFORCED CONCRETE BEAMS WITH CORRODED STEEL REINFORCEMENT GROUP 11 Priyadarshani S.T.A. RU/E/2008/139 Priyanga Y.M.H.S RU/E/2008/140 Priyankara K.M. RU/E/2008/142 Rajakaruna R.M.O.B. RU/E/2008/143 Rananjaya J.A.W. RU/E/2008/144

2. Objective Understand the behaviour of reinforced concrete beams with corroded steel reinforcements under high-cycle fatigue loading and the residual mechanical properties of corroded steel reinforcement following fatigue failure of the beam. The research was done only for the compressive and tension steel bars (not for stirrups)

3. Materials and specimen details 3600 mm 3400 mm 2T10 275 mm 300 mm 8R @ 150 150 mm 2T20 9 beams (L0 to L8) with one control beam with uncorroded steel was created. All the beams were designed to fail in flexural mode under concentrated mid spam load by providing ample uncorroded vertical shear reinforcement to prevent shear failure

4. Materials and specimen details Six 150*150*150 mm cubes were made for each beam to determine the compressive strength of concrete which was used.

6. I :- Corrosion current (A)

7. T :- Time (s)

8. F :- Faraday’s constant (96490 C/mol)

9. Z :- Valence (Fe =2)

10. M :- Atomic mass (Fe = 56 g/mol)

11. Assumption :- The applied current is fully used in the dissolution of iron∆m =(Mit)/(ZF)

12. Materials and specimen details

13. Fatigue and static tests Hydraulic fatigue testing machine was used. Auxiliary supports at both end of the beams were used to prevent shifting of beams. Magnitude of fatigue load was controlled and measured by a load cell. Frequency of repeated load was 3.5 Hz Applied maximum and minimum fatigue loads are 33 & 7 kN. When the number of cycles reached 10,000, 50,000, 100,000, 300,000, 500,000, 1million, and 2million, a static load with a maximum value equal to the maximum fatigue load was applied. The deflection at mid span and quarter span of the beams were measured by using 3 displacement transducers. The vertical displacements at the 2 pivots of the supports were also measured. When the beam did not fail after 2million cycles, the static load was applied to failure.

14. Fatigue and static tests load cell. Beam Auxiliary supports displacement transducers

15. Test results and discussions (cracks) No cracks were observed in beam L1 & L2 One of these 2 cracks were observed in other beams, Lateral surface of the beam parallel to corroded reinforced steel Bottom surface directly under the corroded reinforced steel Crack width :- 0.1mm - 0.3mm

17. The fatigue cycles have no marked effect on the beam’s static performance except for the disappearance of elastic stage due to concrete crackingDeflection – load ratio versus fatigue cycle of control beam (L0)

19. Stiffness of tested beam was characterized by 3 stages,

20. Decreasing stiffness

21. Stable response

22. Increasing stiffness

23. L0 has the lower flexural stiffness and lower compressive strength in concrete

24. L5 has the higher flexural stiffness and compressive strength than less corroded beam and maximum compressive strength

25. Main factor that influence the mechanical properties of steel

26. Mass loss percentage

28. After the failure of beams under fatigue loading The main tensile reinforcements were carefully removed. Cleaned with a brass bristle brush to remove all adhering mortar. Cleaned with an acid solution Residual rust products were removed again by using a bristle brush. The reference weight of a steel bar per unit length was measured using noncorroded bars. The mass loss percentage of corroded steel reinforcement was obtained. Cut each steel bar in 5 parts (a,b,c,d,e) and did static material test to find out fatigue damage for each section. When the corroded steel reinforcements were removed, severe corrosion pits at the location of fracture of steel reinforcement was observed Result shows that the critical section of corroded RC beam under fatigue load is at the maximum bending moment region & at the location of most severe corrosion pits in the steel reinforcement

29. Static testing of corroded steel bars after fatigue cycles Maximum fatigue strength of L0 Ratio of mechanical properties of corroded steel to original steel after fatigue loading

30. Test results and discussions The increase of fatigue stress in steel bars did not significantly change the tensile strength of steel. But decrease the ultimate tensile strain. Yield strength of steel was reduced from 389MPa to 305Mpa due to the effect of corrosion & fatigue. Yield strength of corroded steel reinforcement decreased linearly with the mass loss percentage of decrease. Fatigue stress induces several cumulative damage in corroded steel reinforcement. The effect of steel reinforcement corrosion on structural performance should have a significant consideration during the durability design of RC structures