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Both New Zealand and Taiwan are located in the Pacific ring of fire, the most active seismic zone in the world, and therefore slope failures triggered by seismic excitation are frequent and they sometimes could cost severe damage to life and property. Earthquake induced slope failure, especially rock-block sliding failure, is usually analysed using friction coefficient measured at the sliding-interface. A tilt test is a convenient test for measuring the required values under static condition, but the applicability of measured results to analyse block sliding under dynamic condition requires further investigation. In this paper, a series of static tilt test and dynamic shaking table test were performed to simulate block sliding with base excitation. The results were compared in terms of measured sliding thresholds, and the causes of the differences were discussed. Tests on synthetic sandstone showed that friction coefficients measured by tilt tests were always larger than the ones derived by shaking table tests. Furthermore, sliding thresholds increased with increasing shaking frequency, suggesting that the sliding threshold is non-constant under excitation. In addition, the sliding threshold is lower at higher contact stresses on the sliding surface, showing that the sliding threshold varies with normal stress. This study identified the limitations of the tilt test when applied to dynamic problems, and recommended that realistic sliding threshold can only be obtained using dynamic tests, such as shaking table tests.
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The author inspected 18 racking installations at various food storage facilities in Christchurch for damage from the 4th September 2010 Darfield Earthquake. The type of racking installations and damage suffered are listed with some photographs of specific damage. The damage ranged from minor to complete collapse with large product loss. Although inspection access was limited, the collapse mechanism for racking installations is assessed and suggested. The damage inspected indicated some variation in the application of design approaches and potential areas where the behaviour of rack structures may not have been fully understood during design. General conclusions are drawn from the damage inspections, and suggestions offered for the refinement and improvement of racking design approaches.
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This paper discusses the possible means of achieving risk reduction and resilience against earthquake disasters. It begins with an enquiry into the evolving nature of the resilience concept, which has at its root the notions of participatory governance and livelihood protection. It then discusses the potential for saving human lives by greater utilisation of the evidence base derived from studies of earthquake epidemiology. For example, there may be an opportunity to improve self-protective behaviour as a means of reducing casualties, especially in combination with knowledge of typical modes of the performance of buildings during earthquakes. There follows a discussion of the particular seismic vulnerability of critical infrastructure, hospitals and schools, and the means of reducing it by planning and well-calculated intervention. Seismic risk management needs to be comprehensive and often neglects some important factors. Hence, the next section discusses three of them: the plight of minorities, the protection of cultural heritage, and the management of veterinary emergencies. Following this, there is a discussion of the requirements for viable recovery from earthquake disasters. These include the need to make reconstruction, risk reduction and emergency intervention sustainable in their own right and part of general sustainability against all of the major risks that society faces. The paper concludes with some brief reflections on the process of learning lessons, as seen in the light of organisational learning theory. The use of evidence-based practice to achieve seismic disaster risk reduction has much further to go. To be accepted, it needs to be assimilated permanently into prevailing social and organisational cultures.
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Although New Zealand bridges performed well structurally during recent Canterbury earthquakes, some critical arterial routes lost their functionality. Life Safety is still our primary objective but nowadays we are moving towards new societal needs which also, at minimum, aim to limit business disruption. Building designers are already moving towards low-damage system technology for both structural and non-structural components. Bridge engineers have to inherit those enhanced concepts and technologies. In fact, in order to protect the economy and save lives, it is vital that bridges remain drivable after a natural disaster, such as an earthquake.
More importantly asset managers and networks’ owners want rapid response, design flexibility, quick construction and limited maintenance costs. This should be possible to be achieved by contractors and designers with limited budgets. In very populated urban centres or a critical network location and moderate-to-high seismicity an Accelerated Bridge Construction (ABC) technology which combines durable materials and low-damage technology, seems to be the only viable solution to minimize traffic disruption during the bridge life.
The American Association of State Highway Transportation Officials (AASHTO) started in 2002 a long-term strategic bridge plan which aims to cover all these issues. Similar research strategy was initiated in Japan, Taiwan and Europe which is slowly going towards adaptation of ABC as a standard bridge practice. The question would be what is New Zealand vision for the next twenty-thirty years?
This paper aims to overview the current international trends and challenges and gives innovative concepts which can be contextualized for New Zealand bridges.
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Seismic isolation with energy dissipation is a technology that has been used in New Zealand since 1978 for bridges and buildings. During this period it has seen limited use, tending to be applied mainly to historically significant buildings, or buildings that have special functional requirements.
Seismic isolation has the ability to significantly improve the seismic performance of existing buildings through a seismic retrofit, or to create new earthquake-resilient buildings. Both of these applications are of greater relevance throughout New Zealand following the Canterbury earthquakes. Consequently, the consideration of seismic isolation is no longer limited to those buildings at the top end of the Importance Level spectrum.
This paper examines the broad technical issues associated with isolation and energy dissipation. It discusses the benefits and costs of seismic isolation, and presents guidelines for cost estimation at the feasibility stage of projects. We will explore the cost-benefits for building owners, and discuss whether base isolation can replace earthquake insurance for the building and its contents, and business interruption insurance.
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The Canterbury earthquake sequence was particularly disruptive for building owners and businesses located within the CBD. The initial damage to buildings in the relatively moderate September 2010 earthquake was surpassed by the significantly more damaging February 2011 event, challenging the way in which engineers have traditionally considered earthquake recovery.
Internationally, re-occupation of buildings following an earthquake has been based on the need to get businesses operating from buildings that are rapidly identified as having suffered minor structural damage. However, following the February 2011 earthquake, the shift in risk profile was reflected by limiting re-occupation unless it could be shown that the building also had a minimum capacity to resist earthquakes. This challenges the balance between continuing function and safety in the traditional post-earthquake evaluation process.
The timeframe for commencement of repairs has a significant impact on the speed of recovery. The importance of well defined regulations was highlighted in the well insured Christchurch building market, where legal arguments halted repairs in many instances. There is also a clear need for a modified, streamlined building consent process for the repair of earthquake damaged buildings.
This paper looks at the various building control policies enacted during the Canterbury earthquakes, and their effectiveness in aiding the recovery of the Christchurch CBD.
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Displacement incompatibility between reinforced concrete moment frames and precast flooring systems has been shown experimentally, and in historical earthquakes, to be an area of concern. Plastic hinge formation necessitates beam damage and the resulting elongation of the beam reduces the seating length of the floor, exacerbates the floor damage and induces unanticipated force distributions in the system. In severe cases this can lead to collapse.
The slotted beam is a detail that protects the integrity of the floor diaphragm, respects the hierarchy of strengths intended by the designer and sustains less damage. The detail provides the same ductility and moment resistance as traditional details, whilst exhibiting improved structural performance. This is achieved with only a subtle change in the detailing and no increase in build cost.
This paper briefly presents the development of the slotted beam in reinforced concrete. The design and construction of a large scale reinforced concrete slotted beam superassembly is described. The experimental method used to undertake biaxial quasi-static testing is introduced. Preliminary observations from the experiment are presented. It is shown that the reinforced concrete slotted beam is a viable replacement for the traditional monolithic detail. Extremely promising structural performance and significantly reduced damage compared to monolithic reinforced concrete details is presented.
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During the Canterbury earthquake sequence, the observed level of ground motion on the soft soils of Christchurch was very strong and highly variable. Many studies are now emerging that analyse the amplification effect of these soft soils, usually by estimating a frequency-dependent amplification function relative to a rock outcrop station, or ‘reference site’. If the rock outcrop has its own amplification due to weathering or topographic effects, then the calculated amplification for the soil sites can be compromised. This study examines ten seismic stations in Canterbury to determine the best reference site for Christchurch, using the horizontal-to-vertical spectral ratio (HVSR) method for S-wave shaking. More broadly, this study uses HVSR to expand existing knowledge of the dynamic characteristics of seismic stations in the Canterbury area. Most rock stations show their own local amplification effects that reduce their individual ability to be used as reference stations. The recently installed Huntsbury station (HUNS) appears to be the best reference site for Christchurch, but this will need to be verified when more records become available. In the meantime, the D13C temporary station is currently the best reference station for site effect studies in both Christchurch and Lyttelton.
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This paper presents an experimental study on a series of reduced-scale model GRS walls with Full-Height-Rigid facings conducted on a shake-table at the University of Canterbury. Each model was 900 mm high, reinforced by five layers of stiff Microgrid reinforcement and constructed of dry dense Albany sand. The ratio of geogrid length L to wall height H, L/H, was varied from 0.6 to 0.9, while the wall inclination was generally vertical (90° to horizontal) with 70° for one test. During sinusoidal shaking, facing displacements and accelerations within the backfill were recorded. Failure for all models was predominantly by overturning, with some small sliding component generated in the final shaking step. An increase in L/H resulted in a decrease in wall displacement, while a decrease in wall inclination from the vertical resulted in similar benefits. Detailed analysis of the deformation of one of the tests is presented. During testing, global and local deformations within the backfill were investigated using two methods: the first utilised coloured horizontal and vertical sand markers placed within the backfill; the second utilised high-speed camera imaging for subsequent analysis using Geotechnical Particle Image Velocimetry (GeoPIV) software. GeoPIV enabled strains to be identified within the soil at far smaller strain levels than that rendered visible using the coloured sand markers. These complementary methods allowed the spatial and temporal progressive development of deformation within the reinforced and retained backfill to be examined.
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During the 2010 Mw7.1 Darfield earthquake, the single span Davis Road Bridge located 5 km southeast of Lincoln, New Zealand, sustained significant lateral spreading damage to the western approach. While lateral spreading resulted in up to 450 mm of approach settlement and evidence of damage to the pile foundations, the bridge superstructure sustained no significant damage. Prior to reinstating traffic, the bridge was used for full scale dynamic testing to characterise the influence of different substructure components on the lateral dynamic behaviour of the bridge superstructure.
The bridge was characterised using an eccentric mass shaker and an array of accelerometers to perform lateral forced vibration testing in both the transverse and longitudinal directions. Modal properties were extracted from these tests using multiple system identification algorithms. The experimental testing and system identification methodology are described here. Forced vibration testing was able to detect one mode in each principal direction of the bridge, with the fundamental modes for the transverse and longitudinal direction occurring at a period of 0.118 s and 0.092 s respectively. The torsional response found during the transverse direction shaking was most likely due to the effect of gap opening around the piles on the western abutment, while the longitudinal response was dominated by the approach soil.
