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This paper provides a brief discussion of observed strong ground motions from the 14 November 2016 Mw7.8 Kaikōura earthquake. Specific attention is given to examining observations in the near-source region where several ground motions exceeding 1.0g horizontal are recorded, as well as up to 2.7g in the vertical direction at one location. Ground motion response spectra in the near-source, North Canterbury, Marlborough and Wellington regions are also examined and compared with design levels. Observed spectral amplitudes are also compared with predictions from empirical and physics-based ground motion modelling.
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We provide a summary of the surface fault ruptures produced by the Mw7.8 14 November 2016 Kaikōura earthquake, including examples of damage to engineered structures, transportation networks and farming infrastructure produced by direct fault surface rupture displacement. We also provide an overview of the earthquake in the context of the earthquake source model and estimated ground motions from the current (2010) version of the National Seismic Hazard Model (NSHM) for New Zealand. A total of 21 faults ruptured along a c.180 km long zone during the earthquake, including some that were unknown prior to the event. The 2010 version of the NSHM had considered multi-fault ruptures in the Kaikōura area, but not to the degree observed in the earthquake. The number of faults involved a combination of known and unknown faults, a mix of complete and partial ruptures of the known faults, and the non-involvement of a major fault within the rupture zone (i.e. the Hope Fault) makes this rupture an unusually complex event by world standards. However, the strong ground motions of the earthquake are consistent with the high hazard of the Kaikōura area shown in maps produced from the NSHM.
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The Mw 6.4 Meinong earthquake occurred on 6 February 2016 in the southern region of Taiwan. The earthquake caused significant damage in and around Tainan city, with a number of collapsed and severely damaged buildings and 117 deaths. A five-member Learning from Earthquakes (LFE) team visited Taiwan approximately one month after the earthquake, with particular focus on learning from changes to design practice and seismic mitigation efforts following the 1999 Chi-Chi earthquake in Taiwan. Land damage was generally modest with liquefaction and slope-failures observed in a limited number of locations. Some notable instances of liquefaction-related foundation settlement and tilting occurred in areas associated with historical filling. Following the earthquake, the Taiwanese government publically released liquefaction hazard maps that will have a significant impact on public awareness and land values. The observed structural damage was characteristic of non-ductile and poorly configured buildings. The collapsed buildings all contained irregularities and soft-storeys. The majority of older mixed-use buildings performed adequately, but severe column failures were observed in several taller apartment buildings constructed in the 1990s. The performance of schools and district offices provided valuable insight into the successful implementation of seismic assessment and strengthening programmes. A comparison of existing and strengthened buildings showed that efficient retrofit solutions can reduce the risk posed by critical structural weaknesses and improve the safety and resilience of these buildings. A similar strategy could be implemented for common critical structural weaknesses in New Zealand buildings.
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On 16 April 2016, a moment magnitude (Mw) 7.0 earthquake struck the Island of Kyushu, Japan. Two major foreshocks (Mw 6.2 and Mw 6.0) contributed to devastation in Kumamoto City, Mashiki Town and in the mountainous areas of the Mount Aso volcanic caldera. This report summarises geotechnical and geological aspects of the earthquakes that were observed during a field investigation conducted by the NZSEE Team in collaboration with Japanese engineers and researchers. Many houses and other buildings, roads, riverbanks, and an earth dam, either on or adjacent to the surface fault rupture or projected fault trace, were severely damaged as a result of both the strong ground shaking and permanent ground displacement. In the Mount Aso volcanic caldera, traces of medium to large scale landslides and rock falls were frequently observed. A number of landslides impacted homes and infrastructure, and were reported to have killed at least 10 people out of the 69 confirmed deaths associated with the earthquake. In a few suburbs of Kumamoto City and in Mashiki Town, localised liquefaction took place, causing lateral spreading, differential settlements of the ground and riverbanks, sinking and tilting of buildings, foundation failures, cracks on roads, and disruption of water and sewage pipe networks. The overall effects from liquefaction related hazards appeared relatively minor compared to the damage caused by shaking, landslides and surface fault rupture. Based on the field survey, key findings are highlighted and recommendations to NZ engineering practice are made in the report.
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This report outlines the observations of an NZSEE team of practitioners and researchers who travelled to the Kumamoto Prefecture of Japan on a reconnaissance visit following the April 2016 earthquakes. The observations presented in this report are focussed on the performance of reinforced concrete (RC) buildings throughout Kumamoto Prefecture. It was found overall that modern RC buildings performed well, with patterns of damage which highlighted a philosophy of designing stiffer buildings with less of an emphasis on ductile behaviour. To explore this important difference in design practice, the Japanese Building Standard Law (BSL) is summarised and compared with standard New Zealand seismic design practices and evaluation methods.
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Prior research into low-damage wall systems has predominately focused on the walls behaviour in isolation from other building components. Although the response of these isolated walls has been shown to perform well when subjected to both cyclic and dynamic loading, uncertainty exists when considering the effect of interactions between walls and other structural and non-structural components on the seismic response and performance of entire buildings. To help address this uncertainty a computational model was developed to simulate the response of a full-scale four-storey building with post-tensioned precast concrete walls that was subjected to tri-axial earthquake demands on the E-Defence shake table. The model accurately captured the buildings measured response by incorporating the in-plane and out-of-plane non-linear behaviour of both the wall and floor elements. The model was able to simulate the deformation demands imposed on the floor due to compatibility with the post-tensioned walls, closely matching the behaviour and damage observed during the test. Dynamic loading and wall-to-floor interaction were shown to significantly increase the over-strength actions that developed when compared to the wall system considered in isolation.
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Static loading tests on two full-scale reinforced concrete buildings were conducted at Building Research Institute in 2014 and 2015 to verify the effectiveness of damage control design utilizing walls. The tested buildings were five-storeys high with two bays in the direction of loading. The 2014 specimen was a moment resisting frame consisting of beams and columns with wing walls. The 2015 specimen contained wing walls, spandrels and hanging walls attached to the columns and beams. The measured strengths were much higher than the calculated strength of the bare frame without these walls. The hysteretic curves showed ductile behaviour in the 2014 specimen until ultimate drift, while strength deterioration was observed in the 2015 specimen. From the cracking pattern and the storey drift distributions within the specimens, the first specimen formed a beam sway mechanism, and the second specimen formed a mixed mechanism with column yielding between the 1st to 3rd storeys. The residual cracks of the specimens were generally wider due to the concentration of the plastic hinge region, although the damage was evaluated as slight at 0.33% drift and as minor at 0.75% based on the residual energy capacity. Damage grades evaluated from the residual energy capacity were obviously smaller than the damage grades evaluated from the residual crack widths in accordance with the damage evaluation guidelines.
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As a result of the 2010-2011 Canterbury earthquakes, over 60% of the concrete buildings in the Christchurch Central Business District have been demolished. This experience has highlighted the need to provide guidance on the residual capacity and repairability of earthquake-damaged concrete buildings. As limited testing has been performed on repaired components, this study focuses on the performance of severely-damaged lightly-reinforced concrete walls repaired through replacement of reinforcement and concrete in the damaged region. The damage prior to repair included buckling and fracture of longitudinal reinforcement, crushing and spalling of concrete, and, for one of the two specimens, out-of-plane instability of the gross section. Prior to repairing the wall specimens, tensile testing of reinforcement with welded connections was conducted to verify acceptable performance of welds suitable for reinstating the damaged reinforcement. Repairs to the specimens consisted of removal of damaged concrete through either hydro-demolition or jack hammering, followed by cutting and removal of damaged reinforcement and reinstatement of new reinforcement and repair mortar. The two repaired wall specimens were tested using a standard protocol that was identical to that used for one of the two original wall specimens. Aside from a difference in the elastic stiffness, the load-deformation responses of the repaired specimens were similar to that of the originally-tested specimen through to the first loading cycle at 2.0% drift, beyond which strength degradation was more pronounced for the repaired specimens. The overall performance of the repaired walls relative to the original wall indicates that it is feasible to achieve acceptable performance of severely-damaged concrete walls repaired through replacement of reinforcement and concrete in the damaged region.
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In order to use a damaged building continuously after earthquake, owners and/or stakeholders need to understand residual seismic capacity of the building. In Japan, a method to evaluate residual seismic capacity for damaged buildings had been developed. In order to evaluate residual seismic capacity of damaged building, the damage level of structural elements should be evaluated properly. This paper presents the results of damage analysis based on experimental data obtained from a full-scale static loading test [1] on a five-story reinforced concrete building tested at Building Research Institute. The damage rating for the specimens evaluated by the residual seismic capacity concept [3] was ”Moderate” or ”Heavy” at 0.5% and 1% building drift angle despite the structure maintaining horizontal load carrying capacity. This implies that the applied method gives a conservative result for ductile buildings, such as relatively new moment resisting frames designed after 1981. In order to apply the method used in this paper to new buildings, the damage evaluation method for structural elements should be advanced more in the future.
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It is needed to establish a design capacity curve of beams/columns with RC standing, hanging and wing walls for utilizing such walls as structural members in RC buildings in Japan. This paper presents the results of static loading tests on RC beam-column sub-assemblages with such walls, which were conducted to evaluate their strength, ductility, stiffness and damage. The flexural yield strength of beams with the walls can be well estimated by a flexural analysis assuming the plane section remain plane. The flexural ultimate strength can be accurately estimated at the full plastic moment. The proposed method, which is a modification of a practical design method in a distance from the centre of tensile reinforcements to the extreme compression fibre, can evaluate the secant stiffness at the yield point more precisely than the practical design method.
