Performance of masonry buildings and churches in the 22 february 2011 christchurch earthquake

As part of the „Project Masonry‟ Recovery Project funded by the New Zealand Natural Hazards Research Platform, commencing in March 2011, an international team of researchers was deployed to document and interpret the observed earthquake damage to masonry buildings and to churches as a result of the 22nd February 2011 Christchurch earthquake. The study focused on investigating commonly encountered failure patterns and collapse mechanisms. A brief summary of activities undertaken is presented, detailing the observations that were made on the performance of and the deficiencies that contributed to the damage to approximately 650 inspected unreinforced clay brick masonry (URM) buildings, to 90 unreinforced stone masonry buildings, to 342 reinforced concrete masonry (RCM) buildings, to 112 churches in the Canterbury region, and to just under 1100 residential dwellings having external masonry veneer cladding. In addition, details are provided of retrofit techniques that were implemented within relevant Christchurch URM buildings prior to the 22nd February earthquake and brief suggestions are provided regarding appropriate seismic retrofit and remediation techniques for stone masonry buildings.The authors acknowledge the financial support for Project Masonry from the New Zealand Natural Hazards Research Platform. The testing of adhesive anchors was undertaken in conjunction with the RAPID grant CMMI-1138614 from the US National Science Foundation. The investigation of the performance of residential brick veneers was financially supported by Brickworks Building Products Australia

Shake‑table testing of a stone masonry building aggregate: overview of blind prediction study

City centres of Europe are often composed of unreinforced masonry structural aggregates, whose seismic response is challenging to predict. To advance the state of the art on the seismic response of these aggregates, the Adjacent Interacting Masonry Structures (AIMS) subproject from Horizon 2020 project Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe (SERA) provides shake-table test data of a two-unit, double-leaf stone masonry aggregate subjected to two horizontal components of dynamic excitation. A blind prediction was organized with participants from academia and industry to test modelling approaches and assumptions and to learn about the extent of uncertainty in modelling for such masonry aggregates. The participants were provided with the full set of material and geometrical data, construction details and original seismic input and asked to predict prior to the test the expected seismic response in terms of damage mechanisms, base-shear forces, and roof displacements. The modelling approaches used differ significantly in the level of detail and the modelling assumptions. This paper provides an overview of the adopted modelling approaches and their subsequent predictions. It further discusses the range of assumptions made when modelling masonry walls, floors and connections, and aims at discovering how the common solutions regarding modelling masonry in general, and masonry aggregates in particular, affect the results. The results are evaluated both in terms of damage mechanisms, base shear forces, displacements and interface openings in both directions, and then compared with the experimental results. The modelling approaches featuring Discrete Element Method (DEM) led to the best predictions in terms of displacements, while a submission using rigid block limit analysis led to the best prediction in terms of damage mechanisms. Large coefficients of variation of predicted displacements and general underestimation of displacements in comparison with experimental results, except for DEM models, highlight the need for further consensus building on suitable modelling assumptions for such masonry aggregates

Using machine learning techniques to predict seismic damage in Dunedin

Unreinforced masonry (URM) structures comprise a majority of the global built heritage. The masonry heritage of New Zealand is comparatively younger to its European counterparts. In a country facing frequent earthquakes, the URM buildings are prone to extensive damage and collapse. The Canterbury earthquake sequence proved the same, causing damage to over _% buildings. The ability to assess the severity of building damage is essential for emergency response and recovery. Following the Canterbury earthquakes, the damaged buildings were categorized into various damage states using the EMS-98 scale. This article investigates machine learning techniques such as k-nearest neighbors, decision trees, and random forests, to rapidly assess earthquake-induced building damage. The damage data from the Canterbury earthquake sequence is used to obtain the forecast model, and the performance of each machine learning technique is evaluated using the remaining (test) data. On getting a high accuracy the model is then run for building database collected for Dunedin to predict expected damage during the rupture of the Akatore fault

Analytical and Numerical Prediction of the Vulnerability of Post-Earthquake Observed URM Macroblocks

Unreinforced masonry (URM) structures are known to perform poorly when subjected to earthquake-induced ground shaking. Among others, connections between structural elements and interlocking across the cross-section play an important role in the capacity of URM structures. Consequently, a large variety of collapse mechanisms is observed after earthquakes. Nevertheless, laboratory tests have shown that heritage structures are not only vulnerable but also newly built are. The high complexity of URM behaviour has made that, only recently, researchers have shown interest in it. Such challenging mechanical behaviour makes numerical simulation a highly complicated process. Different numerical modelling approaches are available to simulate the response of masonry structures, within those, the Discrete Element Method (DEM) is summarised herein. Existing research has shown significant correlation between the behaviour exhibited in experimental campaigns and DEM numerical simulations. Different challenges arise when in-plane or out-of-plane benchmarks are modelled. Based on post-earthquake observations, a parametric study regarding geometry and boundary conditions of the walls were performed. In-depth insight of the overturning mechanism behaviour and the DEM helped to understand the details of the nature of masonry, allowing the improvement of existing assessing procedures in standards and guidelines

Seismic assessment of out-of-plane loaded unreinforced masonry walls in multi-storey buildings

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

In situ out-of-plane testing of as-built and retrofitted unreinforced masonry walls

The out-of-plane behavior of as-built and retrofitted unreinforced masonry (URM) walls was investigated by conducting in situ static airbag tests in four buildings. The age of the buildings varied from 80 to 130 years, and all but one were constructed using clay brick masonry with timber floor and roof diaphragms. The fourth building was a reinforced concrete frame structure with precracked clay block partition walls in addition to partition walls that appeared undamaged. The test program was composed of testing five one-way vertically spanning solid URM walls from the group of three URM buildings and testing four two-way spanning URM partition walls from the reinforced concrete frame building. All walls were tested with their original support conditions, but three one-way spanning walls were additionally retested with modified support conditions. These additional tests allowed the effects of wall support type to be investigated, including the influence of a concrete ring beam used at the floor levels and the influence of wall-to-timber diaphragm anchorage by means of grouted steel rods. Several walls were next retrofitted by adding either near-surface mounted (NSM) carbon fiber–reinforced polymer (CFRP) strips or NSM twisted steel bars (TSBs) and were then retested. A comparison between the results of the tests on as-built walls and the tests conducted on retrofitted walls suggests that the simple retrofit techniques that were used are suitable for URM wall strengthening to ultimate limit state (ULS) design. The test results in two buildings highlighted significant inherent variability in masonry material properties and construction quality, and recommendations were made for the seismic assessment and retrofit of URM walls. An analytical trilinear elastic model especially useful when assessing the dynamic stability of cracked one-way spanning walls proved to satisfactorily predict the maximum wall strength, excluding those walls that developed arching action