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Time delay error is common in fast pseudodynamic (PSD) tests due to the effect of actuator dynamics. This type of systematic error introduces energy into a system which if not monitored or controlled, can result in test instability and cause the response to grow exponentially. This leads to premature termination of a simulation and unreliable results. This paper proposes an intuitive error-compensation algorithm to correct this error by considering the systematic error as negative damping in the system. The key to this scheme is the introduction of varying viscous damping at each integration time step during the PSD test. The magnitude of the time-varying viscous damping is derived by equating the magnitude of the energy error with that dissipated by the introduced damping at every integration time step. Numerical simulations and experimental validations are presented in this paper to illustrate the effectiveness of the algorithm, to produce reliable simulation results in the presence of systematic time delay error and noisy measurements.
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Simplified procedures for evaluating liquefaction triggering potential use the nonlinear shear stress reduction factor, rd, to estimate the peak earthquake-induced cyclic shear stress within the soil strata. Previous studies have derived rd by considering the response of representative ground profiles subjected to input ground motions with a range of ground motion characteristics. In this study, site–specific rd for serviceability limit state (SLS) and ultimate limit state (ULS) design ground motions are developed using site response models of the Christchurch Central Business District (CBD). The site response models are generated for typical geologic conditions of Christchurch CBD with shear wave velocity, Vs, profiles developed from the results of multichannel analysis of surface waves (MASW) surveys conducted across Christchurch CBD. A total of 528 simulations were conducted using 1D nonlinear time domain site response analyses using a suite of input ground motions that are representative of controlling ground motion scenarios for seismic hazard of Christchurch. The results of the ground response analyses are used to determine Christchurch CBD-specific rd relationships for liquefaction triggering assessments. The proposed relationships provide a better estimate of the cyclic stress ratios induced below Christchurch CBD when subjected to design SLS and ULS ground motions as compared to typical practice using generic liquefaction assessment methodologies.
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The seismic capacity of a structure is a function of the characteristics of the system as well as of its state, which is mainly affected by previous damage and deterioration. The cumulative damage from repeated shocks (for example during a seismic sequence or due to multiple events affecting an unrepaired building stock) affects the vulnerability of masonry buildings for subsequent events. This paper proposes an analytical methodology for the derivation of state-dependent fragility curves, taking into account cumulated seismic damage, whilst neglecting possible ageing effects. The methodology is based on nonlinear dynamic analyses of an equivalent single degree of freedom system, properly calibrated to reproduce the static and dynamic behaviour of the structure. An application of the proposed methodology to an unreinforced masonry case study building is also presented. The effect of cumulated damage on the seismic response of this prototype masonry building is further studied by means of nonlinear dynamic analyses with the accelerograms recorded during a real earthquake sequence that occurred in Canterbury (New Zealand) between 2010 and 2012.
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The 2010-2011 Canterbury earthquakes and corresponding Royal Commission reports have resulted in changes to the legislative environment and led to increased public awareness in New Zealand of the earthquake performance of unreinforced masonry (URM) buildings. As a result, building regulators, owners, tenants, users and heritage stakeholders will be facing a unique challenge in the near future where assessments, improvements and demolitions of URM buildings are expected to occur at an unusually high rate. Auckland is the largest city in New Zealand and because of the relative prosperity of Auckland during the period 1880-1935 when most URM buildings were being constructed in New Zealand, the city has the largest number of URM buildings in the country. Identifying those buildings most at seismic risk in Auckland’s large and varied building stock has warranted a rapid field assessment program supplemented by strategically chosen detailed assessments. Information that can be procured through rapid field inspections includes the building geometric typologies (e.g., heights, building footprint geometry and isolated versus row configuration), elevation type (e.g., perforated frame versus solid wall), wall construction (e.g., solid versus cavity, number of leaves) and basic construction material type (e.g., clay brick versus stone). Furthermore, investigation into the architectural history, heritage status and functional usage of Auckland’s URM buildings will affect the direction of retrofit strategies and priorities. As the owner of a large and varied portfolio of URM buildings as well as the local organisation responsible for assessing building safety, Auckland Council is developing exemplar inspection, assessment, prioritisation and retrofit strategies that will target the seismic risks associated with URM buildings, in particular, so as to preserve and enhance safety and the economic and community value of these special buildings. Collaboration amongst Auckland Council, The University of Auckland and GNS Science has resulted in a state-of-the-art rapid quantitative assessment program applied to a sampling of typologically representative URM buildings in Auckland.
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A procedure is proposed to evaluate the dynamic out-of-plane stability of cracked unreinforced masonry (URM) walls located in multi-storey URM buildings. The equations of dynamic motion are derived from first principles and representative single-degree-of-freedom (SDOF) models are proposed. The models have nonlinear stiffness properties that correspond to the restoring gravitational forces. A method is suggested to transform the nonlinear problem to a corresponding linear equivalent so that conventional spectral methods can be used to calculate wall response.
The dynamic interaction between the URM building as the main structural system and the out-of-plane loaded walls as secondary elements is addressed by developing floor response spectra. Several buildings were assumed in a parametric study and subjected to code-compatible ground motion records. The absolute acceleration response at floor levels was calculated and the response spectra for that modified acceleration were subsequently obtained.
The results from the study suggest that modifications should be made to the equations proposed for the Parts response spectra in the New Zealand seismic loading standard, NZS 1170.5:2004, in order to calculate the spectral response of out-of-plane loaded URM walls. Several worked examples are presented to demonstrate application of the procedure.
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Currently there is little guidance available on an experimentally-validated detailed seismic assessment procedure for vintage flexible timber diaphragms such as are routinely encountered in New Zealand unreinforced masonry buildings. The results from recent testing of full-scale diaphragms are presented and interpreted with particular attention given to the definition of shear stiffness and shear strength values, whilst acknowledging that the recommendations derive from a small data set. References are provided to information previously published elsewhere to justify the theoretical framework adopted, and the procedure is linked to ASCE 41-13 for guidance regarding diaphragm scenarios that have not been studied by the authors. A procedure is provided to account for the effects on diaphragm response of supplementary stiffness due to masonry end walls. The performance of several diaphragms that were improved with either overlays or underlays is reported as potential proof-tested standard solutions. The assessment procedure is demonstrated by providing a mock worked example of a detailed diaphragm assessment.
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The material properties of New Zealand’s heritage clay brick unreinforced masonry (URM) buildings were investigated and are reported herein. Material data was collected from a total of 98 New Zealand clay brick URM buildings and a database was compiled that was comprised of various masonry material properties. The intention behind the reporting of information and data presented herein was to provide indicative values to the professional engineering community to aid as preliminary input when undertaking detailed building assessments for cases where in-situ testing and brick and mortar sample extraction are not feasible. The data presented is also used to support the relationships for URM material properties that have been recommended by the authors for incorporation into the next version of the NZSEE seismic assessment guidelines for URM buildings. Although researchers from Europe, USA, India and Australia have previously studied the material properties of clay brick unreinforced masonry, knowledge on New Zealand URM material properties was poor at the time the study commenced. Therefore, a research programme was undertaken that was focused on both in-situ testing and laboratory testing of samples extracted from existing New Zealand clay brick URM buildings.
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Almost all unreinforced stone masonry (URSM) buildings in New Zealand were constructed between 1860 and 1910, typically in regions where natural stone was sourced from local quarries, fields and rivers. These buildings form an important part of the country’s architectural heritage, but the performance of URSM buildings during earthquake induced shaking can differ widely due to many aspects related to the constituent construction materials and type of masonry wall cross-section morphology. Consequently, as a step towards gaining greater knowledge of the New Zealand URSM building stock and its features, an exercise was undertaken to identify and document the country-wide URSM building inventory. The compiled building inventory database includes: (i) general building information, such as address, building owner/tenant and building use; (ii) architectural configuration, such as approximate floor area, number of storeys, connection with other buildings, plan and elevation regularity; and (iii) masonry type, such as stone and mortar types, wall texture and wall cross-section morphology. From this exercise it is estimated that there is in excess of 668 URSM buildings currently in existence throughout New Zealand. A large number of these vintage URSM buildings require detailed seismic assessment and the implementation of seismic strengthening interventions in order to conserve and enhance this component of New Zealand’s cultural and national identity. The entire stock of identified buildings is reported in the appended annex (688 total), including 20 URSM buildings that were demolished following the Canterbury earthquake sequence.
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The Sliding Hinge Joint (SHJ) is an Asymmetric Friction Connection (AFC) developed to create a repeatable, efficient means of dissipating seismic response energy and reducing structural damage without yielding of the structural frame elements. Testing has demonstrated stable efficient hysteretic behaviour. However, it is necessary to fully characterise their dynamic behaviour including any less stable aspects observed in the response of these devices for selected materials. This observed behaviour may reduce device force and energy dissipation, creating an influence on the overall structure that should be fully understood and accounted for in design. This research models the hysteretic behaviour of a SHJ with a zinc anti-corrosion coating that demonstrates less than fully stable experimental dynamic behaviour in contrast to many other SHJ material choices. The model developed uses a stick-slip mechanism based on a variable friction coefficient to capture the observed dynamics with an overall Menegotto-Pinto dynamic hysteretic model. The overall results show how the model may be realistically extended to a more general model that captures observed non-linear dynamics in these and similar friction devices, and yield new insight and design tools for use with these devices.
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Segmental tunnel linings are now often used for seismic areas in many countries. Some prescriptions and guidelines specifically address the issue of seismic design. Unfortunately, the behaviour of segmental tunnel lining under seismic loads is still somewhat unclear. The influence of segment joints on tunnel lining behaviour during seismic loading has in fact not been quantitatively estimated in the literature. This paper presents a numerical study in order to investigate the performance of segmental tunnel lining under seismic excitation. Analyses have been carried out using a two-dimensional finite difference element model. The seismic signal obtained from an earthquake in Nice has been adopted as input. The numerical results show that a segmental lining can perform better than a continuous lining during an earthquake. The effect of plasticity of the soil constitutive model on the tunnel lining has also been highlighted. The results have indicated that an elastic analysis is not sufficient to determine the seismic induced response of a soil-tunnel system. Moreover, comparative results have pointed out that equivalent static solutions could result in smaller structural lining forces than those of a true dynamic analysis.
