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Images for steel reinforcement; more images...

Images, UC QuakeStudies

A photograph of a pile of twisted steel reinforcement and other rubble at the entrance to the Smiths City car park on Dundas Street. In the background a section of the collapsed car park has not been demolished yet. Many cars are still parked on the top floor.

Images, UC QuakeStudies

A photograph of the partially-demolished Smiths City car park, taken from Dundas Street. The front section of the car park has mostly been cleared, though there is still a scattering of rubble and steel reinforcement. The back section has collapsed, but the floors are largely intact, with many cars still parked on the top floor.

Images, UC QuakeStudies

A photograph looking east down Dundas Street. Piles of twisted steel reinforcement have been placed on both sides of the street. Several earthquake-damaged cars, recovered from the Smiths City car park, have been stacked on the left. On the other side of the street is an excavator grapple and bucket. In the distance two excavators are sorting through the rubble.

Images, UC QuakeStudies

A photograph of the earthquake damage to the concrete beams in a room in the PricewaterhouseCoopers Building. Sections of the concrete have crumbled to reveal the steel reinforcement underneath. A number of the ceiling panels are missing and another is hanging loose. Some of the bars that hold the ceiling panels are also hanging loose.

Images, UC QuakeStudies

The old Railway Station clock tower on Moorhouse Avenue with plywood and steel reinforcement covering two sides, a crane hanging over top. The brickwork suffered extensive cracking during the earthquake making it in need for reinforcement. The clock has stopped at around 16:35, the time of the earthquake.

Images, UC QuakeStudies

The old Railway Station clock tower on Moorhouse Avenue with plywood and steel reinforcement covering two sides, and a crane hanging over top. The brickwork suffered extensive cracking during the earthquake making it in need of reinforcement. The clock has stopped at around 16:35, the time of the earthquake.

Images, UC QuakeStudies

The old Railway Station clock tower on Moorhouse Avenue with plywood and steel reinforcement covering two sides, and a crane hanging over top. The brickwork suffered extensive cracking during the earthquake making it in need of reinforcement. The clock has stopped at around 16:35, the time of the earthquake.

Images, UC QuakeStudies

A photograph of a flight of concrete stairs salvaged from a building and placed in a car park in the Christchurch central city. Steel reinforcement can be seen sticking out of the concrete.

Research papers, University of Canterbury Library

Capacity design and hierarchy of strength philosophies at the base of modern seismic codes allow inelastic response in case of severe earthquakes and thus, in most traditional systems, damage develops at well-defined locations of reinforced concrete (RC) structures, known as plastic hinges. The 2010 and 2011 Christchurch earthquakes have demonstrated that this philosophy worked as expected. Plastic hinges formed in beams, in coupling beams and at the base of columns and walls. Structures were damaged permanently, but did not collapse. The 2010 and 2011 Christchurch earthquakes also highlighted a critical issue: the reparability of damaged buildings. No methodologies or techniques were available to estimate the level of subsequent earthquakes that RC buildings could still sustain before collapse. No repair techniques capable of restoring the initial condition of buildings were known. Finally, the cost-effectiveness of an eventual repair intervention, when compared with a new building, was unknown. These aspects, added to nuances of New Zealand building owners’ insurance coverage, encouraged the demolition of many buildings. Moreover, there was a perceived strong demand from government and industry to develop techniques for assessing damage to steel reinforcement bars embedded in cracked structural concrete elements. The most common questions were: “Have the steel bars been damaged in correspondence to the concrete cracks?”, “How much plastic deformation have the steel bars undergone?”, and “What is the residual strain capacity of the damaged bars?” Minimally invasive techniques capable of quantifying the level and extent of plastic deformation and residual strain capacity are not yet available. Although some studies had been recently conducted, a validated method is yet to be widely accepted. In this thesis, a least-invasive method for the damage-assessment of steel reinforcement is developed. Based on the information obtained from hardness testing and a single tensile test, it is possible to estimate the mechanical properties of earthquake-damaged rebars. The reduction in the low-cycle fatigue life due to strain ageing is also quantified. The proposed damage assessment methodology is based on empirical relationships between hardness and strain and residual strain capacity. If damage is suspected from in situ measurements, visual inspection or computer analysis, a bar may be removed and more accurate hardness measurements can be obtained using the lab-based Vickers hardness methodology. The Vickers hardness profile of damaged bars is then compared with calibration curves (Vickers hardness versus strain and residual strain capacity) previously developed for similar steel reinforcement bars extracted from undamaged locations. Experimental tests demonstrated that the time- and temperature-dependent strain-ageing phenomenon causes changes in the mechanical properties of plastically deformed steels. In particular, yield strength and hardness increases, whereas ductility decreases. The changes in mechanical properties are quantified and their implications on the hardness method are highlighted. Low-cycle fatigue (LCF) failures of steel reinforcing bars have been observed in laboratory testing and post-earthquake damage inspections. Often, failure might not occur during a first seismic event. However, damage is accumulated and the remaining fatigue life is reduced. Failure might therefore occur in a subsequent seismic event. Although numerous studies exist on the LCF behaviour of steel rebars, no studies had been conducted on the strain-ageing effects on the remaining fatigue life. In this thesis, the reduction in fatigue life due to this phenomenon is determined through a number of experimental tests.

Images, UC QuakeStudies

A digitally manipulated photograph of twisted reinforcing rods amongst the rubble from the demolition of QEII. The photographer comments, "These rarely seen worms live in the pressurised earth under the foundations of buildings. They need a damp soil and be under at least 100 pounds of pressure per square inch. After the destructive force of an earthquake they swiftly rise to the surface through gaps in the rubble. Unfortunately they quickly die and then crystallise as hard as iron in the dry low pressure air".