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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.

Research papers, University of Canterbury Library

A major lesson from the 2011 Christchurch earthquake was the apparent lack of ductility of some lightly reinforced concrete (RC) wall structures. In particular, the structural behaviour of the critical wall in the Gallery Apartments building demonstrated that the inelastic deformation capacity of a structure, as well as potentially brittle failure of the reinforcement, is dependent on the level of bond deterioration between reinforcement and surrounding concrete that occurs under seismic loading. This paper presents the findings of an experimental study on bond behaviour between deformed reinforcing bars and the surrounding concrete. Bond strength and relative bond slip was evaluated using 75 pull-out tests under monotonic and cyclic loading. Variations of the experiments include the loading rate, loading history, concrete strength (25 to 70 MPa), concrete age, cover thickness, bar diameter (16 and 20 mm), embedded length, and the position of the embedded bond region within the specimen (deep within or close to free surface). Select test results are presented with inferred implications for RC structures.

Videos, UC QuakeStudies

A video about businesses in the Christchurch central city Red Zone. The Red Zone has now been renamed the Rebuild Zone. The video shows businesses which have remained untouched since the 22 February 2011 earthquake, including the Camelot Hotel and the i-SITE visitor centre in Cathedral Square, Subway on High Street, Jeans West on High Street, Time Zone on Colombo Street, Comics Compulsion on Manchester Street, Mortgage Solutions mortgage brokers on the corner of Hereford and Manchester Streets, Pocha Bar and Restaurant off Lichfield Street, and a fabric store on Lichfield Street.

Videos, UC QuakeStudies

A video of the opening night of the Heathcote Valley Inn. The inn has been rebuilt, after the 133-year-old original inn was damaged in the 4 September 2010 earthquake. Mayor Bob Parker officially opens the new building.

Images, UC QuakeStudies

A digitally manipulated image of a sign reading "A bit of dirt never hurt". The photographer comments, "This was a sign put up on a section of land in the Port of Lyttelton where an earthquake damaged building had been removed. The cliff at the back had collapsed down probably during the demolition process".

Videos, UC QuakeStudies

A video of the demolition of The Valley Inn in Heathcote. The Valley Inn is a 133-year-old pub which was severely damaged by the 4 September 2010 earthquake. The video includes an interview with Dean Calvert, the owner of the inn, and Jim Barr, a patron at the inn.

Audio, Radio New Zealand

Johnny Moore is the owner of the Goodbye Blue Monday bar in Christchurch, which has been closed since the 22 February earthquake. He talks to Kim about the turbulent times since then and his career in the hospitality industry.