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Research papers, University of Canterbury Library

The recent earthquakes in Christchurch have made it clear that issues exist with current RC frame design in New Zealand. In particular, beam elongation in RC frame buildings was widespread and resulted in numerous buildings being rendered irreparable. Design solutions to overcome this problem are clearly needed, and the slotted beam is one such solution. This system has a distinct advantage over other damage avoidance design systems in that it can be constructed using current industry techniques and conventional reinforcing steel. As the name suggests, the slotted beam incorporates a vertical slot along part of the beam depth at the beam-column interface. Geometric beam elongation is accommodated via opening and closing of these slots during seismically induced rotations, while the top concrete hinge is heavily reinforced to prevent material inelastic elongation. Past research on slotted beams has shown that the bond demand on the bottom longitudinal reinforcement is increased compared with equivalent monolithic systems. Satisfying this increased bond demand through conventional means may yield impractical and economically less viable column dimensions. The same research also indicated that the joint shear mechanism was different to that observed within monolithic joints and that additional horizontal reinforcement was required as a result. Through a combination of theoretical investigation, forensic analysis, and database study, this research addresses the above issues and develops design guidelines. The use of supplementary vertical joint stirrups was investigated as a means of improving bond performance without the need for non-standard reinforcing steel or other hardware. These design guidelines were then validated experimentally with the testing of two 80% scale beam-column sub-assemblies. The revised provisions for bond within the bottom longitudinal reinforcement were found to be adequate while the top longitudinal reinforcement remained nominally elastic throughout both tests. An alternate mechanism was found to govern joint shear behaviour, removing the need for additional horizontal joint reinforcement. Current NZS3101:2006 joint shear reinforcement provisions were found to be more than adequate given the typically larger column depths required rendering the strut mechanism more effective. The test results were then used to further refine design recommendations for practicing engineers. Finally, conclusions and future research requirements were outlined.

Research papers, University of Canterbury Library

Describes an extensive experimental program at the University of Canterbury, for the development of new structural systems and connections for multi-storey laminated veneer lumber (LVL) timber buildings in earthquake-prone areas. The proposed innovative ductile timber connections are conceptually similar to recent seismic solutions successfully developed for precast concrete multi- storey buildings. The paper gives an overview of the research program, and the results of quasi-static cyclic tests on frame subassemblies, including exterior beam-column joints and cantilever columns, as well as pseudo-dynamic tests on cantilever columns. The experimental results showed significant dissipation of hysteretic energy, good self-centering capacity and no appreciable damage of the structural elements, confirming the expected enhanced performance of the proposed structural systems.

Images, UC QuakeStudies

A digitally manipulated image of the Bandsmen's Memorial in Hagley Park. The photographer comments, "This memorial in Hagley Park in Christchurch can no longer be used due to large cracks at the base of most columns. This was mostly caused by the earthquake in February 2011, but later earthquakes have made the memorial even more dangerous".

Images, UC QuakeStudies

A photograph of the earthquake damage to a building on Hereford Street. A column on the right side of the building has snapped and the side wall has pulled away from the building. USAR codes have been spray-painted on one of the windows on the bottom storey. In the foreground there is a police car.

Images, UC QuakeStudies

Damage to the front of the Cathedral of the Blessed Sacrament. Large cracks are visible in the stonework, and one side is supported by shipping containers and hay bales. The photographer comments, "The Cathedral of the Blessed Sacrament has a lot of cracking on the exterior and one column appears to be leaning to the right. To my non-expert eye it does look like the front could easily give way. Notice the broken supporting beam".

Images, eqnz.chch.2010

Pigeons sit on the remains of one of the tallest buildings in Christchurch that was 95% demolished two or three years ago. The basement (now filled with water) and the columns remain. Demolished due to damage from the Christchurch 2011 earthquake.

Images, Alexander Turnbull Library

Text reads 'Collateral damage'. A couple stand looking at a broken column surrounded by fallen masonry; text on the column reads 'Curbs on govt spending'. The man says 'It's a shame. It was due to be unveiled in a few weeks'. Context - the Christchurch earthquake of 22 February 2011; curbs on government spending can be seen as 'collateral damage'. In December 2010 Finance Minister Bill English pledged to keep a cap on spending to rein in a widening deficit as slower consumer demand hinders the economic recovery and hurts tax receipts. The earthquake will make economic recovery even more difficult. Quantity: 1 digital cartoon(s).

Research papers, University of Canterbury Library

Beam-column joints are addressed in the context of current design procedures and performance criteria for reinforced concrete ductile frames subjected to large earthquake motions. Attention is drawn to the significant differences between the pertinent requirements of concrete design codes of New Zealand and the United States for such joints. The difference between codes stimulated researchers and structural engineers of the United States, New Zealand, Japan and China to undertake an international collaborative research project. The major investigators of the project selected issues and set guidelines for co-ordinated testing of joint specimens designed according to the codes of the countries. The tests conducted at the University of Canterbury, New Zealand, are reported. Three full-scale beam-column-slab joint assemblies were designed according to existing code requirements of NZS 3101:1982, representing an interior joint of a one-way frame, an interior joint of a two-way frame, and an exterior joint of a two-way frame. Quasistatic cyclic loading simulating severe earthquake actions was applied. The overall performance of each test assembly was found to be satisfactory in terms of stiffness, strength and ductility. The joint and column remained essentially undamaged while plastic hinges formed in the beams. The weak beam-strong column behaviour sought in the design, desirable in tall ductile frames designed for earthquake resistance, was therefore achieved. Using the laws of statics and test observations, the action and flow of forces from the slabs, beams and column to the joint cores are explored. The effects of bond performance and the seismic shear resistance of the joints, based on some postulated mechanisms, are examined. Implications of the test results on code specifications are discussed and design recomendations are made.

Images, UC QuakeStudies

Damage to the Royal Hotel on the corner of Norwich Quay and Canterbury Street in Lyttelton. The columns next to the windows have cracked, indicating that there is major structural damage to the building. Wire fencing and cones have been used to create a cordon around the building.

Images, UC QuakeStudies

A photograph of the earthquake damage to Avonmore House on Hereford Street. Sections of the walls have crumbled, spilling bricks and masonry onto the footpath and street below. Many of the windows have warped, breaking the glass. USAR codes have been spray-painted on one of the columns.

Images, UC QuakeStudies

A photograph of emergency management personnel standing outside the Canterbury Trade Union Centre on Armagh Street. Emergency tape has been draped around the outside of the building and USAR codes have been spray-painted on a column near the entrance. Behind the building are several other earthquake-damaged buildings.

Images, UC QuakeStudies

Buckled columns on a house in Wainoni. The photographer comments, "A Sunday afternoon ride to New Brighton, then back via Aranui, Wainoni, Dallington, and Richmond. Not a cheerful experience. 'We've decided you're a repair, not a rebuild after all'. Actually, I think these houses might be red zoned".

Images, UC QuakeStudies

A photograph of bricks and other rubble on the footpath outside a building on Lichfield Street. USAR codes have been spray-painted on one of the windows and the front door. A red sticker has been stuck to a column on the right, indicating that the building is unsafe to enter.

Research papers, University of Canterbury Library

Between 2010 and 2011, Canterbury experienced a series of four large earthquake events with associated aftershocks which caused widespread damage to residential and commercial infrastructure. Fine grained and uncompacted alluvial soils, typical to the Canterbury outwash plains, were exposed to high peak ground acceleration (PGA) during these events. This rapid increase in PGA induced cyclic strain softening and liquefaction in the saturated, near surface alluvial soils. Extensive research into understanding the response of soils in Canterbury to dynamic loading has since occurred. The Earthquake Commission (EQC), the Ministry of Business and Employment (MBIE), and the Christchurch City Council (CCC) have quantified the potential hazards associated with future seismic events. Theses bodies have tested numerous ground improvement design methods, and subsequently are at the forefront of the Canterbury recovery and rebuild process. Deep Soil Mixing (DSM) has been proven as a viable ground improvement foundation method used to enhance in situ soils by increasing stiffness and positively altering in situ soil characteristics. However, current industry practice for confirming the effectiveness of the DSM method involves specific laboratory and absolute soil test methods associated with the mixed column element itself. Currently, the response of the soil around the columns to DSM installation is poorly understood. This research aims to understand and quantify the effects of DSM columns on near surface alluvial soils between the DSM columns though the implementation of standardised empirical soil test methods. These soil strength properties and ground improvement changes have been investigated using shear wave velocity (Vs), soil behaviour and density response methods. The results of the three different empirical tests indicated a consistent improvement within the ground around the DSM columns in sandier soils. By contrast, cohesive silty soils portrayed less of a consistent response to DSM, although still recorded increases. Generally, within the tests completed 50 mm from the column edge, the soil response indicated a deterioration to DSM. This is likely to be a result of the destruction of the soil fabric as the stress and strain of DSM is applied to the un‐mixed in situ soils. The results suggest that during the installation of DSM columns, a positive ground effect occurs in a similar way to other methods of ground improvement. However, further research, including additional testing following this empirical method, laboratory testing and finite 2D and 3D modelling, would be useful to quantify, in detail, how in situ soils respond and how practitioners should consider these test results in their designs. This thesis begins to evaluate how alluvial soils tend to respond to DSM. Conducting more testing on the research site, on other sites in Christchurch, and around the world, would provide a more complete data set to confirm the results of this research and enable further evaluation. Completing this additional research could help geotechnical DSM practitioners to use standardised empirical test methods to measure and confirm ground improvement rather than using existing test methods in future DSM projects. Further, demonstrating the effectiveness of empirical test methods in a DSM context is likely to enable more cost effective and efficient testing of DSM columns in future geotechnical projects.

Images, eqnz.chch.2010

Cracks have ripped through external columns of this 7 storey building (corner of Hereford Street / Manchester Street), and efforts are being made to shore up and strengthen it to save it from demolition after it suffered structural damage in the magnitude 7.1 earthquake that struck Christchurch on Saturday 4 September 2010.

Images, eqnz.chch.2010

Cracks have ripped through external columns of this 7 storey building (corner of Hereford Street / Manchester Street), and efforts are being made to shore up and strengthen it to save it from demolition after it suffered structural damage in the magnitude 7.1 earthquake that struck Christchurch on Saturday 4 September 2010.

Images, eqnz.chch.2010

Cracks have ripped through external columns of this 7 storey building (corner of Hereford Street / Manchester Street), and efforts are being made to shore up and strengthen it to save it from demolition after it suffered structural damage in the magnitude 7.1 earthquake that struck Christchurch on Saturday 4 September 2010.

Images, UC QuakeStudies

A photograph of the earthquake damage to the Kenton Chambers Building on Hereford Street. Large cracks have formed in the columns between the building's windows. A section on the bottom storey has collapsed and the bricks have spilled onto the footpath in front. Steel fences have been placed across the street as a cordon.

Videos, UC QuakeStudies

A video about engineers recovering the internal copper dome of the Cathedral of the Blessed Sacrament by lifting it out in one piece. The dome was undamaged after the 22 February 2011 earthquakes, but lost most of its supporting columns. Engineers have decided to remove the dome to ensure it will not be damaged during further aftershocks.