1,721,343 research outputs found
Shaking table testing of as-built and retrofitted clay brick URM cavity-walls
No full textMasonry cavity-wall construction incorporates a continuous air gap that separates the inner and outer brick leaves of the wall cross-section. This wall configuration was originally developed because of improved thermal performance and in particular reduced moisture transmission across the wall, as the presence of the air-cavity serves to capture and drain moisture back to the building exterior. However, it was subsequently established that clay-brick unreinforced masonry (URM) cavity-wall buildings typ- ically exhibit poor seismic performance due to inadequate connections between the separate masonry leaves in the wall cross-section. Experimental shaking table testing of five cavity-walls was undertaken with an emphasis on developing and experimentally validating simple and efficient retrofit solutions to improve cavity-wall seismic capacity. Wall specimens closely simulated in-situ conditions for the URM cavity-wall arrangements that are most commonly encountered in New Zealand. Two different retrofit solutions were tested, namely, the addition of mechanical screw-ties with different spacings or a combi- nation of mechanical screw-ties and timber strong-backs. Specimen construction details, retrofit proce- dures, test set-up and results are presented herein. Reported results include observed crack-patterns, peak ground acceleration (PGA) corresponding to both induced initial cracking and failure, acceleration and displacement profiles at failure, and quantification of the improvement in seismic capacity from using the proposed retrofit techniques
Damage Assessment of Unreinforced Stone Masonry Buildings After the 2010–2011 Canterbury Earthquakes
No full textThe sequence of earthquakes that has affected Christchurch and Canterbury since September 2010 has caused damage to a great number of buildings of all construction types. Following post-event damage surveys performed between April 2011 and June 2011, an inventory of the stone masonry buildings in Christchurch and surrounding areas was carried out in order to assemble a database containing the characteristic features of the building stock, as a basis for studying the vulnerability factors that might have influenced the seismic performance of the stone masonry building stock during the Canterbury earthquake sequence. The damage suffered by unreinforced stone masonry buildings is reported and different types of observed failures are described using a specific survey procedure currently in use in Italy. The observed performance of seismic retrofit interventions applied to stone masonry buildings is also described, as an understanding of the seismic response of these interventions is of fundamental importance for assessing the utility of such strengthening techniques when applied to unreinforced stone masonry structures.AM - Accepted Manuscrip
Construction Details and Observed Earthquake Performance of Unreinforced Clay Brick Masonry Cavity-walls
No full textUnreinforced masonry (URM) cavity-wall construction is a form of masonry where two leaves of clay brick masonry are separated by a continuous air cavity and are interconnected using some form of tie system. A brief historical introduction is followed by details of a survey undertaken to determine the prevalence of URM cavity-wall buildings in New Zealand. Following the 2010/2011 Canterbury earthquakes it was observed that URM cavity walls generally suffered irreparable damage due to a lack of effective wall restraint and deficient cavity-tie connections, combined withweak mortar strength. It was found that the original cavity-ties were typically corroded due to moisture ingress, resulting in decreased lateral loadbearing capacity of the cavity-walls. Using photographic data pertaining to Christchurch URM buildings that were obtained during post-earthquake reconnaissance, 252 cavity-walls were identified and utilised to study typical construction details and seismic performance. The majority (72%, 182) of the observed damage to URM cavity-wall construction was a result of out-of-plane type wall failures. Three types of out-of-plane wall failure were recognised: (1) overturning response, (2) one-way bending, and (3) two-way bending. In-plane damage was less widely observed (28%) and commonly included diagonal shear cracking through mortar bed joints or bricks. The collected data was used to develop an overview of the most commonly-encountered construction details and to identify typical deficiencies in earthquake response that can be addressed via the selection and implementation of appropriate mitigation interventions
Vulnerability Assessment of Unreinforced Masonry Churches Following the 2010–2011 Canterbury Earthquake Sequence
No full textThe 2010–2011 Canterbury, New Zealand earthquake sequence caused extensive damage to unreinforced masonry churches. A sample of 80 affected buildings was analysed and their performance statistically interpreted. Structural behaviour is described in terms of mechanisms affecting the so-called macro-elements, and damage probability matrices are computed. Regression models correlating mean damage level against macroseismic intensity are also developed for all observed mechanisms, improving the initial simple-linear formulations through use of multiple-linear regressions accounting for vulnerability modifiers, whose influence is evaluated via statistical procedures. Results presented herein will support the future development of predictive tools for decision-makers, also contributing to seismic vulnerability mitigation at a territorial scale
Seismic assessment and improvement of unreinforced stone masonry buildings: Literature review and application to New Zealand
No full textFollowing the 2010/2011 Canterbury earthquakes considerable effort was applied to the task of developing industry guidance for the seismic assessment, repair and strengthening of unreinforced masonry buildings. The recently updated “Section 10” of NZSEE 2006 is one of the primary outputs from these efforts, in which a minor amount of information is introduced regarding vintage stone unreinforced masonry (URM) buildings. Further information is presented herein to extend the resources readily available to New Zealand practitioners regarding load-bearing stone URM buildings via a literature review of the traditional European approach to this topic and its applicability to the New Zealand stone URM building stock. An informative background to typical stone URM construction is presented, including population, geometric, structural and material characteristics. The European seismic vulnerability assessment procedure is then reported, explaining each step in sequence of assessment by means of preliminary inspection (photographic, geometric, structural and crack pattern surveys) and investigation techniques, concluding with details of seismic improvement interventions. The challenge in selecting the appropriate intervention for each existing URM structure is associated with reconciling the differences between heritage conservation and engineering perspectives to reinstating the original structural strength. Traditional and modern techniques are discussed herein with the goal of preserving heritage values and ensuring occupant safety. A collection of Annexes are provided that summarise the presented information in terms of on-site testing, failure mechanisms and seismic improvement
One way bending capacity prediction of unreinforced masonry walls with varying cross section configurations
No full textPost-earthquake inspections have highlighted that out-of-plane failure of unreinforced masonry (URM) walls is one of the most life threatening hazards related to earthquakes. Connections between structural elements and interlocking across the wall section play an important role in the capacity of a URM building to withstand earthquakes. Consequently, the seismic assessment of existing URM buildings requires an appropriate methodology to correctly estimate the performance of the investigated element. International standards and guidelines for seismic assessment are often based on simplified methodologies that incorporate assumptions regarding the collapse mechanism and general behaviour of the wall. Alternatively, the Discrete Element Method (DEM) is an advanced modelling technique that can accurately predict and simulate wall behaviour without any prior assumption about the failure mechanism. Different codes capacity predictions and DEM simulations were compared to the test results of a solid two-leaf wall. The DEM proved reasonably accurate and was used to simulate one-way bending of walls with a variation of unit bond patterns and wall thickness dimensions that escape code formulations. Solid rigid elements were used to represent the distinct clay brick units and an inelastic law was assigned to the contact surfaces to simulate the mortar joints. Pushover and non-linear time history analyses were conducted and the resultant capacity curves and collapse mechanisms of each analysis were compared
Post-Earthquake Reconnaissance of Unreinforced and Retrofitted Masonry Parapets
Full text linkUnrestrained unreinforced clay brick masonry (URM) parapets are freestanding wall elements found atop a large number of vintage URM buildings. Parapets are considered to be one of the most vulnerable nonstructural components that are prone to out-of-plane collapse when subjected to earthquake induced shaking. Using data collected during the earthquake reconnaissance efforts, 959 URM parapets were identify to be in existence in the Christchurch (New Zealand) area prior to 2010, with 60% (580) of them having collapsed during the 2010/2011 Canterbury earthquake sequence. Construction details and observed performance of both as-built and retrofitted parapets were documented. The reported study provides an inventory of observed parapet failure modes and a critical review of commonly encountered parapet retrofits and their respective seismic performance
Constituent material properties of New Zealand unreinforced stone masonry buildings
No full textMost of New Zealand’s stone unreinforced masonry (URM) building stock was constructed between 1860 and 1910 by early European settlers, with approximately 670 stone URM buildings remaining throughout the country. These buildings are typically classified as earthquake-prone, indicating that they require seismic strengthening in order to avoid demolition as a seismic hazard. Practitioners and industry professionals currently lack knowledge about the traditional construction techniques used for these buildings, and about suitable methods for improving their seismic performance. To address this knowledge gap, research was conducted to classify the constituent materials used in the original construction and to document the mechanical and physical characteristics of these construction materials. Extraction of structural mortar and natural stone samples was undertaken in buildings that were deemed to be representative of the New Zealand stone URM building stock, and X-Ray Powder Diffraction (XRPD) and petrographical analyses were performed on these samples respectively in order to identify mineral composition and their original source location. In addition, the compressive strength of extracted material samples was determined. A database of New Zealand natural stones that were typically used by the early European settlers in construction, including the source and compressive strength of each stone sub-type, is summarised herein. The presented data is intended to facilitate the selection of compatible materials and suitable techniques for repair and seismic retrofit of vintage stone URM buildings
Seismic Risk Assessment of New Zealand Unreinforced Masonry Churches using Statistical Procedures
No full textThe 2010–2011 Canterbury earthquake sequence provided extensive evidence of the significant seismic vulnerability of New Zealand unreinforced masonry (URM) churches. Given the high seismicity of the country, the exposure of human lives and the societal significance of ecclesiastic buildings, for both historical and religious reasons, the reduction in seismic vulnerability of this building type is of primary importance. By analyzing the seismic performance of a sample of 80 affected buildings, regression models correlating mean damage levels against ground-motion parameters were developed for observed collapse mechanisms, accounting for vulnerability modifiers whose influence was estimated via statistical procedures. Considering the homogeneity of New Zealand URM churches, the vulnerability models developed for the Canterbury region were extended to the whole country inventory, and a synthetic index was proposed to summarise damage related to several mechanisms. Territorial scale assessment of the seismic vulnerability of churches can assist emergency management efforts and facilitate the identification of priorities for more in-depth analysis of individual buildings. After proper calibration, the proposed approach can be applied to other countries with similar building heritage
Ambient vibration tests on New Zealand unreinforced masonry churches using low cost sensors
No full textChurches are an important part of New Zealand's architectural heritage, and the extensive damage observed in stone and clay brick unreinforced masonry churches after the 2010-2011 Canterbury earthquakes has highlighted the need to appropriately describe their dynamic characteristics. Dealing with historical structures, characterized by a high level of uncertainty affecting both material properties and structural schemes, and given the paramount need of non-destructive investigation techniques, ambient vibration tests can be considered an effective tool. A test campaign was conducted on two churches located in Auckland and deemed to be representative of the New Zealand church portfolio. The structures were instrumented with low-cost tri-axial standalone accelerometer sensors based on Micro Elec-tro-Mechanical Systems (MEMS) technology. Despite such instrumentation being commonly used on more flexible structures and/or under higher service loads (such as the normal traffic on bridges), this technology potentially represents an affordable solution to provide information about the fundamental period of vibration of macro-elements of churches and bell-towers. The advantages and limitations of the adopted sensing technology, when applied to historic buildings exhibiting low response to ambient excitation, are discussed in the paper, based on the analysis of data collected
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