Test Observation (autosaved).docx

Test Observation (Crack) Short Column Corrosion induced crack Crack induced by accelerated corrosion, rust staining, flaky rust close to the crack area (because nacl enter easier i.e. prone to water infiltration) - d Crack location running parallel to reinforcing bar - d Crack along T20 and propagation of crack expansion of corrosion material – d Correlation of crack width and section mass loss Stirrups corroded more severely due to less concrete cover and smaller diameter especially near at the corner of the stirrup – d Why different sides of columns have different crack severe? (side 1 most severe for most column) Corrosion level – CC7 CC11 CC17 CC21 CC19 CC23 - d Seismic induced crack mainly diagonal cracks Spalling of cover concrete (tensile stress of T20 not transferred to cover concrete thus weaker) Damage progression, crack propagation Plastic hinge region, first crack formation Spacing between transverse cracks Last cycle crack formation Crack widening What happened at max shear and axial failure (crack?) Crack angle of most severe crack Show crack pattern at peak shear strength Cracks are primarily diagonal cracks? Comparison with uncorroded specimen Failure mode for each specimen (before shear failure what happened?) + Initial stage of occurrence What happens after shear maximum/failure and axial failure (Spalling? New crack?) Changing of crack direction horizontal to diagonal

Corrosion induced Every column face were categorized i.e. side 1 – 4. Side 1 was observed to be the most severely corroded face of the column with the most cracks (Attach corrosion crack pic), thus it is chosen to be the front face of the column. Column CC3 being the column subjected to highest corrosion level with widest crack measuring 0.6mm. From visual inspection, cracks induced by accelerated corrosion runs parallel with the longitudinal reinforcement bars. Brownish red stains and flaky rust was found to be concentrated near cracks for every specimen. The above 2 observations is caused by the expansion of corrosion product found (mainly?) on the longitudinal reinforcements (Attach figure of corroded T20?) causing the concrete cover and rebar interface to lose bond strength and subsequently the cover concrete loses its tensile strength leading to crack initiation. The opening of crack makes the column more susceptible to water infiltration which explains the concentration of stains near cracks. Transverse reinforcement – Outer transverse reinforcement is the most severely corroded reinforcement with high sectional area loss. From observation, corrosion product covers the outer transverse reinforcement almost entirely and pitting corrosion is common especially near the corner section due to thinner concrete cover and smaller diameter which allow rapid “spreading” of corrosion product. Rupture of outer transverse reinforcement’s corner after cyclic loading is also a common mode of failure (Figure) as it is under high stress concentration induced during fabrication. On the other hand, inner transverse reinforcement is protected from water infiltration due to its arrangement with higher concrete cover. Only few corrosion products are observed and pitting corrosion is minimal. Longitudinal reinforcement – Corrosion products & stains are found to be larger in size due to larger surface area of the longitudinal reinforcement, with pitting corrosion tending to be more localized. Corrosion induced cracks are more concentrated on the edge compared to the center of column face on all column sides (Figure) due to combined expansion of corrosion product found on both longitudinal and transverse outer reinforcement. Seismic induced Corroded columns – Every cracks appearing on the columns were marked with different color i.e. blue and red indicating pushing and pulling of the horizontal actuator respectively. When subjected to cyclic loading, cracks initially appear at plastic hinges of the column i.e. top and bottom – most face of the column where discontinuity in elasticity occurs.