@article {bnh-6808, title = {Simplified calculation of roof accelerations in existing low-rise symmetric unreinforced masonry buildings with flexible diaphragms}, journal = {Bulletin of Earthquake Engineering}, year = {2020}, month = {03/2020}, abstract = {

A formulation is presented for simplified evaluation of the roof acceleration response for the purpose of assessing non-structural components in unreinforced masonry buildings with flexible diaphragms excluding torsional effects. The method is based on modal calculations that are further studied through nonlinear time-history analysis (NLTHA) of four case study buildings. The NLTHA results for a relatively small level of ground shaking was used to validate the overall ability of the simplified modal method to predict the diaphragm flexibility effects. The NLTHA results were also used to discuss the effects of the building inelastic response in the conservatism of the simplified modal technique. It was found that, in lieu of a comprehensive modal analysis, it is possible to calculate roof accelerations in symmetric low-rise buildings with flexible diaphragms using a simplified two-mode modal method. Based on this study, a predictive method is proposed for conservative estimation of peak roof accelerations in these buildings.

}, keywords = {acceleration response, flexible diagrams, height amplification factor, unreinforced masonry}, doi = {https://doi.org/10.1007/s10518-020-00823-1}, url = {https://link.springer.com/article/10.1007/s10518-020-00823-1$\#$citeas}, author = {Hossein Derakhshan and Yasuto Nakamura and Michael Griffith and Manicka Dhanasekar} } @article {bnh-6698, title = {Suitability of Height Amplification Factors for Seismic Assessment of Existing Unreinforced Masonry Components}, journal = {Journal of Earthquake Engineering}, year = {2020}, month = {01/2020}, pages = {1-20}, abstract = {

The suitability of {\textquoteleft}design{\textquoteright} height amplification factors (HAF) for the purpose of seismic assessment of existing non-structural unreinforced masonry (URM) components with known strength was evaluated through a numerical study. Four building typologies were included that represented pre-1940 URM construction in Australia and New Zealand. Through pushover and incremental dynamic analyses, the effects of diaphragm flexibility and nonlinear building response on floor accelerations were studied. It was found that Australia/New Zealand code procedures include significant inelastic building behaviour that reduces HAF. An interpretation was made on the applicability of the assumptions in the context of assessing non-structural URM components.

}, keywords = {flexible diaphragms, height amplification factor, non-structural components, seismic input, unreinforced masonry}, doi = {https://doi.org/10.1080/13632469.2020.1716889}, url = {tandfonline.com/doi/full/10.1080/13632469.2020.1716889}, author = {Hossein Derakhshan and Yasuto Nakamura and Michael Griffith and Jason Ingham} } @article {bnh-5433, title = {Cost-Effective Mitigation Strategy Development for Building Related Earthquake Risk Annual Report 2017-2018}, number = {464}, year = {2019}, month = {03/2019}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {
This project arose out of the on-going research efforts by the group involving\ structural engineering academics at the Universities of Adelaide, Melbourne and\ Swinburne with Geoscience Australia experts all working towards seismic risk\ reduction in Australia. Most of the research team are actively involved in the\ revision to the Australian Earthquake Loads standard (AS1170.4) as well as being\ members of the Australian Earthquake Engineering Society which is a Technical\ Society of Engineers Australia. The devastating impact of the 2010{\textendash}11\ earthquakes in the Christchurch region on the New Zealand economy and\ society has further motivated this group to contribute to this CRC{\textquoteright}s aims of risk\ reduction for all natural hazards in Australia.\ This project addresses the need for an evidence base to inform decision making\ on the mitigation of the risk posed by the most vulnerable Australian buildings\ subject to earthquakes. While the focus of this project is on buildings, many of\ the project outputs will also be relevant for other Australian infrastructure such as\ bridges, roads and ports, while at the\ same time complementing other {\textquoteleft}Natural\ Hazards{\textquoteright} CRC project proposals for severe wind and flood.
}, keywords = {cost-mitigation, earthquake}, author = {Michael Griffith and Hossein Derakhshan and Elisa Lumantarna and Hing-Ho Tsang and John Wilson and Nelson Lam and Mark Edwards and Martin Wehner} } @article {bnh-6336, title = {Seismic fragility assessment of nonstructural components in unreinforced clay brick masonry buildings}, journal = {Earthquake Engineering and Structural Dynamics}, year = {2019}, month = {12/2019}, abstract = {

The results of an investigation of the probability of earthquake damage to nonstructural unreinforced masonry (URM) components are presented. The components include parapets, chimneys, and out-of-plane loaded facades typical of low-rise pre-1940 construction in Australia and New Zealand. The study is based on a street survey of component geometry, in situ data on material strength, and simplified mechanical models. Uncertainties in capacity and demand were quantified based on, respectively, stochastic and deterministic approaches. The damage probabilities were compared with relevant guidelines and empirical damage data from three earthquakes. The study established a link between the qualitative damage states reported in existing guidelines and the quantitative URM component damage states. While some median damage state thresholds correlated well with the data from the guidelines, a larger dispersion value was found in the current study due to the large variations in component properties. Comparisons with empirical data suggest that the developed fragility data provide a realistic estimate of nonstructural component damage that occurred in similar buildings, with a reasonable level of conservatism. The outcome is useful in rapid assessment of the seismic risks due to nonstructural component collapse in URM precincts.

}, keywords = {Damage, earthquake, seismic risk, unreinforced masonry}, doi = { https://doi.org/10.1002/eqe.3238}, url = {https://onlinelibrary.wiley.com/doi/pdf/10.1002/eqe.3238}, author = {Hossein Derakhshan and Kevin Walsh and Jason Ingham and Michael Griffith and David Thambiratnam} } @conference {bnh-4783, title = {Community strategy development for reducing earthquake risk in Western Australia}, booktitle = {AFAC18}, year = {2018}, month = {09/2018}, publisher = {Bushfire and Natural Hazards CRC}, organization = {Bushfire and Natural Hazards CRC}, address = {Perth}, abstract = {

While the earthquake hazard in Australia is generally low by world standards, its severity does include higher hazard in some regions. This is the case in the Yilgarn region east of Perth as highlighted by the 1968 Meckering Earthquake and the observed seismic activity of the region in the last seventy years. Where building construction has not considered earthquake hazard the risk to communities can be significant. This is an issue for the township of York which is WA{\textquoteright}s oldest inland settlement and has a high proportion of heritage buildings that are vulnerable to earthquake. The presence of high risk buildings of this type is a challenge for local government, emergency management and other government agencies with a role in community recovery after disasters.
In the Bushfire and Natural Hazards CRC (BNHCRC) a project called Cost-effective mitigation strategy development for building related earthquake risk is developing information on cost effective strategies for retrofitting vulnerable buildings. The project scope has been augmented to examine the effectiveness of a range of strategies for addressing high risk structures. This is a collaborative study involving a partnership approach between state and local government along with academic and government researchers under the BNHCRC. The project will utilise the mitigation approaches developed by the CRC within a range of potential roll-out options to virtually retrofit the town of York. The net benefits of each will be assessed considering avoided damage, impacts on occupants, lost rental income, and disruption to business activity and households.
In this presentation the motivation for this collaborative effort will be discussed in the context of an improved understanding of natural hazard risk in WA, the increasing focus on investing in risk mitigation as opposed to response and recovery, and the shared interest of both State and Local government to promote resilience in vulnerable communities. The outcomes of a broad stakeholder workshop convened in York on the 9th August 2018 will be described in which strategies for providing incentives for risk reduction were identified. The importance of risk information in informing property owners and communities is discussed and the need to address their apprehension in addressing vulnerability with heritage listed structures. Finally, the value of broader measures of avoided community impacts beyond the direct monetary in decision making is highlighted and the linkages being made to another BNHCRC project called Economics of natural hazards that will enable intangible (non-market) values to be included in a quantitative manner.

}, author = {Stephen Gray and Paul Martin and Mark Edwards and Michael Griffith and Hossein Derakhshan} } @article {bnh-5196, title = {Final report on pushover analysis of classes of URM buildings to characterise drift ratios for different damage levels}, year = {2018}, month = {12/2018}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

It is widely considered that building structural damages during earthquakes can be calibrated against building{\textquoteright}s lateral drift. A study of this relationship assists in the development of fragility curves, which can be used as part of large-scale seismic risk evaluation. In the current study, pushover analyses were conducted on four prevalent Australia/New Zealand unreinforced masonry (URM) building typologies to study this relationship. The buildings were modelled as equivalent frames using a commercial software, and the damage progress within the building under increasing lateral drifts were recorded. Limits of displacements corresponding to different damage states were established and compared to the values found in other studies and/or recommended by ASCE guidelines. The earlier studies that were used in the comparison included two NZ-based numerical research that were aimed at reproducing damages that were occurred to 3 buildings during the recent New Zealand (Gisborne 2007 and Christchurch 2011) earthquakes. The comparisons suggest that storey drift limits recommended in ASCE guidelines can be used to conservatively estimate building damage state.

}, issn = {431}, author = {Hossein Derakhshan and Michael Griffith} } @article {bnh-5152, title = {Laboratory testing of strengthened cavity unreinforced masonry walls}, journal = {Journal of Structural Engineering}, volume = {144}, year = {2018}, month = {03/2018}, abstract = {

An experimental campaign consisting of nine pressure-controlled quasi-static airbag tests on unreinforced masonry (URM) walls and accompanying material testing was completed to investigate methods for seismic retrofit of out-of-plane loaded cavity walls. Three control walls were tested to serve as a baseline for wall strength comparisons: (1)\ a double-leaf unstrengthened cavity wall; (2)\ a cavity wall with improved cavity connections; and (3)\ a single-leaf wall strengthened using a near-surface-mounted (NSM) fiber-reinforced polymer (FRP) strip. The experimental program was concluded by six tests that were conducted on walls strengthened using a NSM FRP strip and having cavity connections in the form of either standard bent metal ties, proprietary helical anchors, or industrial foam. The tests were designed to measure the ability of the different cavity connections to maintain the cavity gap until a ductile wall failure mechanism forms by FRP debonding. Three of the walls were previously damaged by testing in either unstrengthened or FRP-strengthened conditions. These tests were intended to study FRP retrofit effectiveness of precracked walls or the relative ability of different types of cavity connections to resist forces until a global FRP debonding occurs. For each of the six cavity connection configurations, the FRP-strengthening technique was shown to significantly improve the wall strength. The minimum strength increase was 282\% compared with that of the control cavity wall. The compiled data are presented followed by general discussions on the design of seismic retrofit for cavity walls.

}, doi = {https://doi.org/10.1061/(ASCE)ST.1943-541X.0001987}, url = {https://ascelibrary.org/doi/10.1061/\%28ASCE\%29ST.1943-541X.0001987}, author = {Hossein Derakhshan and Wade Lucas and Phillip Visintin and Michael Griffith} } @article {bnh-5153, title = {Out-of-plane strength of existing two-way spanning solid and cavity unreinforced masonry walls}, journal = {Structures}, volume = {13}, year = {2018}, month = {02/2018}, pages = {88-101}, chapter = {88}, abstract = {

An in-situ unreinforced masonry (URM) wall testing programme was conducted to study the effects of as-built wall boundary conditions on its out-of-plane strength. In total, eight pressure-controlled quasi-static airbag tests were done on 4 double-leaf cavity walls and 4 single-leaf solid walls, followed by relevant material testing. The walls were located in two 1960s URM properties in Adelaide, South Australia and had in-situ boundary conditions and construction details. Several walls included door openings at one edge and/or connected to flexible ceilings at top. Other as-built details included plaster finish on some of the internal walls and on the inner leaf of some of the external cavity walls. Additionally, the cavity walls had as-built wall ties that were damaged during construction and had irregular spacing. The main contributions of this study are to highlight the effects of these in-situ details, to make a comparison between strength predictions using an energy-based, virtual work method and an equilibrium-based method, and to improve the virtual work method for evaluation of the walls that have plaster finish. The calculations indicate that the improved virtual work method can be used to obtain a safe, lower bound, estimate of the wall strength.

}, doi = {https://doi.org/10.1016/j.istruc.2017.11.002}, url = {https://www.sciencedirect.com/science/article/pii/S2352012417300747}, author = {Hossein Derakhshan and Wade Lucas and Phillip Visintin and Michael Griffith} } @article {bnh-5154, title = {Case studies of material properties of late nineteenth-century unreinforced masonry buildings in Adelaide}, journal = {Australian Journal of Civil Engineering}, volume = {15}, year = {2017}, month = {11/2017}, abstract = {

An experimental programme was developed to improve our understanding of the actual\ in situ\ strength of non-structural components in typical South Australian unreinforced masonry (URM) construction. The focus was on testing URM walls and chimneys in out-of-plane direction, and in the course of this study 132 as-built URM material specimens were collected. The specimens were tested either\ in situ\ or in laboratory. In total, four URM houses located in Darlington, a southern suburb of Adelaide, South Australia, were studied. Three of the buildings were built in the 1960s and the fourth was built in the 1980s. A comparison between the buildings material strength and the default values recommended in the Australian Masonry Standards, AS3700, suggests that the code specified default lower 5\% characteristic values were often greater than the measured characteristic strength. The collected data are presented for documentation and some comparison between this and other studies are also made.

}, doi = {https://doi.org/10.1080/14488353.2017.1401196}, url = {https://www.tandfonline.com/doi/abs/10.1080/14488353.2017.1401196}, author = {Hossein Derakhshan and Phillip Visintin and Michael Griffith} } @article {bnh-4212, title = {Cost-effective mitigation strategy for building related earthquake risk: annual project report 2016-17}, number = {348}, year = {2017}, month = {09/2017}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

The 1989 Newcastle Earthquake caused damage to 70,000 properties, with an associated total economic loss of AU$ 4 billion. Consistently, the insurance industry has estimated the economic risk posed by a moderate earthquake in any of the capital cities in Australia to be of the order of billions of dollars. A major reason for this risk is that Australia has not designed buildings for earthquake-induced forces until 1995 so that a large portion of our building stock is seismically vulnerable.

As demonstrated in Christchurch, New Zealand, in 2010-11, a magnitude 6 earthquake can have a devastating impact on a city and country (damage rebuild estimated at ~ 20\% national GDP!) even though buildings there have been designed for earthquakes for many decades.

This project includes collaborative research from 4 partner institutions to establish:

  1. The relative vulnerabilities to earthquake shaking of the most common forms of building construction in Australia;
  2. What earthquake retrofit techniques worked and what didn{\textquoteright}t as a starting point in developing a {\textquoteleft}menu{\textquoteright} of economically feasible seismic retrofit techniques that could be used in Australian cities;
  3. With industry end-user support, conduct proof of concept tests on some of the most promising seismic retrofit techniques on buildings scheduled for demolition by the SA state government;
  4. Use the new damage and economic loss models developed over the first 3 years of this project to undertake a seismic risk assessment case study of the Melbourne metro area; and
  5. Advance a series of end user focused research utilization projects in the areas of improved building regulation, community risk reduction, design profession guidance and insurance industry engagement with their policy holders. These will include an Earthquake Mitigation Case Study for the historic town of York in Western Australia and Development of a Rapid Visual Screening procedure for Australian buildings

Finally, using the new damage loss models and costings for seismically retrofitting buildings, make recommendations for the development of seismic retrofit guidelines and policy based on the strong evidence base developed.

}, issn = {348}, author = {Michael Griffith and Hossein Derakhshan and Elisa Lumantarna and Hing-Ho Tsang and Helen M. Goldsworthy and John Wilson and Nelson Lam and Mark Edwards} } @article {bnh-3804, title = {Final report: seismic retrofit tests of URM cavity walls}, number = {249}, year = {2017}, month = {07/2017}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

University of Adelaide researchers were engaged by Bushfire and Natural Hazards CRC to undertake an experimental campaign aiming to identify and develop seismic retrofit methods for out-of-plane loaded cavity walls. The research is a part of a broader project titled "Cost-effective mitigation strategy development for building related earthquake risk". This report presents the details of the tested cavity walls, trialed retrofitted schemes, obtained results, and discussion. The report concludes with recommendations on the seismic retrofit of this type of wall construction.

A review of the masonry literature suggested that retrofit methods have already been developed and widely researched for solid unreinforced masonry (URM) walls, but that the methods cannot be readily applied to cavity walls due to the cyclic nature of the seismic loads and the limited access to the cavity gap. The methods generally require access to both faces of the wall to attach fiber-reinforced-polymer (FRP) strips to masonry.

The broad retrofit concept for cavity walls was conceived to be using NSM FRP technique on the exposed surfaces of the cavity wall skins, e.g. to one face of each wall skin, but with the provision that the wall ties be verified/upgraded to maintain the cavity gap. For this purpose, 6 different alternatives of cavity structure were investigated. Two options involved the use of standard wall metal ties with different densities. Two other options included the use of proprietary helical mechanical anchors with different densities, and finally two configurations of expanding foam was used to partly or wholly fill the cavity gap. All of the FRP strips were near-surface-mounted (NSM).

It was found that with NSM FRP retrofit, the existing wall ties may be sufficient to maintain cavity gap depending on the location of the wall in Australia. For walls in regions with relatively higher seismic hazard, helical anchors can be added, and the anchor spacing can be proportional to seismic hazard but need not be less than 260 mm, i.e. every 3rd course.

}, issn = {249}, author = {Hossein Derakhshan and Wade Lucas and Phillip Visintin and Michael Griffith} } @article {bnh-5155, title = {In-situ seismic verification of non-structural components of unreinforced masonry buildings}, journal = {Australian Journal of Structural Engineering}, volume = {19}, year = {2017}, month = {11/2017}, abstract = {

An experimental campaign was developed to evaluate the response of non-structural elements of unreinforced masonry buildings for simulated earthquake loads. Eleven walls within 4 URM properties were subjected,\ in situ, to uniformly distribute static loads applied using a system of airbags. The buildings were located in Darlington, a suburb of Adelaide, South Australia. Three of them were built in the 1960s and the fourth was built in the 1980s. Accompanying material tests were done\ in situ\ and in the laboratory, enabling a comparison to be made between the old buildings material strength and the default material strengths recommended in the Australian Masonry Standards, AS3700. Tests were also conducted on 3 URM chimneys to establish their failure mechanism and strength. A highlight of this research is\ the findings that existing masonry\ chimneys are vulnerable to a {\textquoteleft}design earthquake{\textquoteright} in Australia. The results also suggest that despite masonry material strength being significantly lower than the code default values, the walls satisfied expected seismic force demands. The reasons include\ the beneficial effects of\ in situ\ wall boundary conditions on out-of-plane wall strength.

}, doi = {https://doi.org/10.1080/13287982.2017.1370963}, url = {https://www.tandfonline.com/doi/abs/10.1080/13287982.2017.1370963?journalCode=tsen20}, author = {Hossein Derakhshan and Wade Lucas and Michael Griffith} }