Abstract
In recent earthquakes, unreinforced masonry (URM) structures built of masonry walls containing openings such as doors and windows have been shown to have poor seismic capacity. However, although different sizes and positions of openings are known to reduce the stiffness and strength of URM walls, the relationships between the size and position of openings and seismic capacity of the walls are not clear. Therefore, a series of numerical analyses has, for the first time, explored many possible opening sizes and opening positions under simulated seismic loading to identify their impact on the in-plane behaviour of URM walls. The numerical models were built using the code “3DEC” which is based on the discrete element method (DEM). The key feature of the DEM is that it allows the development of large displacements between elements with contacts being recognized automatically during the analysis. Thus, this numerical method can capture the whole degradation progress from the initial cracking of the masonry walls right through to collapse, with the bricks being modelled as rigid blocks and the mortar as Coulomb-slip joints with zero thickness. Both load-based and displacement-based quasi-static pushover analysis procedures have been studied and the modelling methodology and the calibration of numerical models is described. The results from the analyses, the crack patterns and collapse mechanisms of the masonry walls are identified and discussed, and a key output from this work is the characterization of the relationships between the sizes and positions of openings and the in-plane performance of URM walls.
Highlights
Unreinforced masonry structures (URM) are built throughout the world, but in recent earthquakes (Basset-Salom and Guardiola-Víllora 2014; Ingham and Griffith 2010; Lourenço et al 2013; Parisi and Augenti 2013; Zhang and Jin 2008) their seismic capacity has been shown to be poor
These researchers have identified the relationships between stiffness reduction and opening sizes for masonry infill walls and have proposed equations to reflect the influence of openings on the wall stiffness
1.6 specimen displayed a lower maximum horizontal capacity compared to 3DEC when using the tensile and cohesion properties of the mortar given in the experimental data (Table 2), it is worth noting that the model is sensitive to these properties and a 50% reduction in the cohesion value used for the joints resulted in a much closer match to the peak wall capacity
Summary
Unreinforced masonry structures (URM) are built throughout the world, but in recent earthquakes (Basset-Salom and Guardiola-Víllora 2014; Ingham and Griffith 2010; Lourenço et al 2013; Parisi and Augenti 2013; Zhang and Jin 2008) their seismic capacity has been shown to be poor. The in-plane walls are critical in URM structures as they provide the stability and strength to prevent the collapse of the buildings These in-plane walls are divided into small piers and spandrels by window openings and door openings. It is important to consider the impact of openings on all of these failure mechanisms for URM walls under in-plane loading and identify the variation of lateral strength and displacement capacity of URM walls when there are openings present. In Sarhosis et al (2014, 2015), Sarhosis and Sheng (2014) and Giamundo et al (2014), low-bond strength masonry walls were built in 3DEC to study in-plane masonry behaviour These papers introduced specific methods for modelling masonry in 3DEC and compared the load–displacement curves for different factors such as tensile strength, cohesion and friction angle. Explicit relationships between the opening size and location, and the in-plane performance of the masonry walls are presented considering the potential failure patterns induced by the openings
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