A high proportion of New Zealand's clay brick unreinforced masonry (URM) structures have not been retrofitted to resist earthquake forces, and in particular to prevent out-of-plane failures which are the most critical deficiencies of URM buildings. Despite a number of seismic improvement techniques having been applied previously there is a significant lack of experimentally validated simple and cost-effective solutions that also consider the impact on the building tenants, aesthetics and heritage building fabric. The main objectives of the research presented herein were to develop and validate seismic securing techniques for URM solid- and cavity-walls that satisfied the above conditions. Full-scale shake-table testing of two cavity and three double-leaf solid clay brick URM walls was undertaken. The vertical timber framing that is typically considered to be a non-structural support for the inner wall lining was used as part of the retrofit solution and was fixed to the wall using mechanical screw-ties in order to form a strong-back. The intended outcomes of the research reported herein included (i) measuring via laboratory testing the improvement of seismic capacity in terms of peak ground acceleration (PGA) achieved and maximum out-of-plane displacement experienced by the URM solid- or cavity-walls due to strong-back retrofit installation; (ii) comparing the performance of different strong-back configurations; (iii) providing construction details, and providing analytical formulations for response prediction.
The study of the behaviour of masonry arches represents a complex problem, which involves different aspects that can significantly affect the load bearing capacity of such structures. In this regard, geometrical imperfections, such as the irregular shape of the arch blocks, the initial position of the first and last voussoirs (boundary conditions), the alignment between the adjoining blocks and the rounded corners of each block, play an important role. An experimental campaign was conducted on a toy arch made by eleven irregular blocks, with the aim of evaluating the effect of such irregularities. A numerical model was developed basing on lower bound (LB) and upper bound (UB) limit analysis approaches (referred to as the static and the kinematic theorem, respectively). A linear programming (LP) solving algorithm was implemented in the software MATLAB and used to solve the minimization/maximization problems. The probability distribution of each considered nonlinearity was estimated, the results of the numerical analysis were correlated with the experimental outcomes and a Montecarlo simulation was carried out to validate the hypothesised probability distributions.
Unreinforced masonry (URM) building construction is prominent in the form of load-bearing, partition, and infill walls. Significant out-of-plane (OOP) failures of URM walls often occur during moderate and severe earthquake shaking and such walls are often identified in structural engineering assessments as being amongst the most vulnerable elements to OOP demands, especially earthquakes. For undamaged, in situ wall conditions where material properties are known and boundary conditions reflect idealised conditions assumed in analytical predictive models, these predictive models are easily applied, although the accuracy of the model outputs may still not be well understood. Furthermore, when in situ conditions do not reflect idealised conditions assumed in analytical predictive models, engineers are often uncertain as to which analytical models and inputs are most appropriately applied. Hence, an analytical campaign was undertaken to provide specific examples for structural engineering practitioners assessing the OOP seismic behaviour of URM walls, and the predictive results reported herein were compared to previously reported experimental results of eighteen tests on existing URM walls performed in situ. The considered wall configurations represented a variety of geometries, boundary conditions, pre-test damage states, and material properties. The average ratio and associated coefficient of variation (CV) of predicted strengths to measured strengths were determined to be 0.84 (CV 0.56) and 0.93 (CV 0.25) for the unbounded and bounded wall conditions, respectively, and corresponding recommendations for analytical assessment were made for practicing engineers.
In the present paper, an integrated intervention system applicable to concrete-framed buildings is presented. The purpose of the intervention is to improve both the seismic and the energetic behaviour of such buildings using cross-laminated timber (CLT) panels. Two alternative intervention configurations with different levels of invasiveness are described. Considering a double-wythe masonry-infilled frame, the most invasive configuration consists in the replacement of the external masonry wythe with the CLT panel, while the least invasive configuration consists in the arrangement of the CLT panel from the outside without removing the wythes. The technical details and implementation procedures were studied, considering functionality and disturbance to occupants. An isolated one-storey-one-bay frame was used as a reference for the seismic and thermal analyses. Subsequently, the two intervention configurations were applied to a case-study building by identifying two alternative intervention strategies. The obtained results showed that the proposed integrated intervention approach can significantly reduce both the seismic vulnerability and the energy consumption of concrete buildings.
The susceptibility of unreinforced masonry (URM) walls to collapse under seismic loading has been repeatedly observed and documented across a multitude of earthquakes worldwide. The out-of-plane failure of walls is commonly the critical failure mechanism for URM structures and poses a significant risk to life. Despite various seismic improvement techniques being applied previously there is a significant lack of experimentally validated simple and cost-effective solutions that also consider the impact on the building tenants, building aesthetics, and heritage fabric of the structure. Such retrofits are needed to facilitate the preservation of the URM building stock and to ensure the safety of those who work and live in and around these structures. The retrofit technique studied herein consisted of connecting vertical timber elements (strong-backs), to the interior surface of a building’s walls using mechanical anchors. Non-structural timber framing commonly exists to support the inner wall lining of URM buildings and its use, as a part of the retrofit, results in a cost effective and low impact solution. The out-of-plane behavior of as-built and retrofitted masonry walls was investigated by conducting full scale semi-static cyclic airbag tests. The outcomes of this testing regime include (i) quantification of improvement in seismic capacity and out-of-plane displacement capacity and (ii) comparison of the performance using different strong-back configurations.
Two modeling approaches with different levels of refinement were used to numerically investigate the influence of different parameters on the response of straight sheathed timber diaphragms when subjected to in-plane loading. The investigated parameters included diaphragm aspect ratio, scale factor (i.e., diaphragm size), impact of board-to-board contact phenomena, and the effects of board-to-board shear force exchange. The aim of the work presented herein was to use numerical modeling to investigate the aspects that potentially contribute to the difference in experimental behavior reported in literature and that consequently might have influenced provisions encompassed in the most recent standards for the assessment of timber diaphragms. The modeling strategies were validated against a wide range of available experimental data on newly constructed and vintage timber floor specimens. Analysis results confirmed that the in-plane behavior of straight sheathed diaphragms is significantly influenced by parameters that are often neglected by numerical studies and assessment procedures.
