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This paper describes a simplified methodology for the assessment of unreinforced masonry (URM) walls under out-of-plane two-way bending seismic action. The methodology involves a force-based check derived from the principle of virtual work. This check is proposed based on experimental observations of significant cracking resistance associated with two-way spanning URM walls, indicating methodologies considering such walls to be pre-cracked or to be non-laterally supported as overly conservative. The methodology incorporates several findings and developments from recent experimental campaigns: ranging from novel characterization tests on masonry couplets to incremental dynamic tests on full-scale buildings. Such incorporations include new formulation to calculate the torsional shear strength of a bed joint and accounting for possible changes in the boundary conditions of an OOP wall during dynamic loading. Testing standards as well as recommendations in several international guidelines for masonry structures addressing the input properties required to implement the proposed methodology are enlisted and reviewed. The methodology requires the definition of the period of vibration of the assessed URM walls, to calculate which plate theory based formulation is provided. Open research questions and potential avenues for further development of the methodology are ultimately highlighted.

Out-of-plane (OOP) mechanisms are one of the major causes of structural collapse in unreinforced masonry (URM) buildings as observed in recent as well as past seismic events. Among such failures, two-way bending mechanisms involving at least one restrained vertical edge constitute a very distinct majority. Nevertheless, very little research pertaining to such mechanisms can be found currently in literature. The paper takes a step forward in this topic through the execution and interpretation of dynamic tests on four full-scale single leaf and one full-scale cavity URM walls. Each tested full-scale specimen consisting of a OOP panel and two return walls, varying in terms of commonly encountered boundary conditions, applied overburden or the presence/absence of an opening. The specimens were subjected to sequences of incremental input motion till collapse and these results are presented in terms of deformed shapes, failure mechanisms and force-displacement hysteretic curves. State of the art analytical techniques based on the method of virtual work are applied to evaluate their reliability as simplified tools for assessing the behaviour of such wall subjected to OOP two-way bending excitation. The testing campaign resulted in all specimens exhibiting a rather brittle response, despite sustaining accelerations of 1 g without any damage.

This paper describes a shake table test on a one-storey full-scale unreinforced masonry structure, which complements an earlier testing of a two-storey structure with similar characteristics. The building specimen was meant to represent the upper floors of the end-unit of a terraced house, built with cavity walls and without any particular seismic design or detailing. In these specimens, the masonry walls were composed of two leaves: a load-bearing inner one made of calcium silicate bricks sustaining a reinforced concrete floor and an external leaf made of clay-bricks connected to the inner leaf by means of metallic ties. A pitched timber roof was supported by two triangular gable walls. Floor acceleration response histories of the previously tested two-storey specimen were used as input motions. An incremental dynamic test, with vertical and horizontal inputs, was carried out up to the explicit collapse of some bearing elements of the structure. In particular, a two-way bending out-of-plane collapse of a load-bearing wall was observed and described.

Existing unreinforced masonry (URM) buildings have often exhibited both damage and collapse in the out-of-plane (OOP) direction due to the activation of a local mechanism when subjected to earthquake excitations. The assessment of the out-of-plane response of masonry structures has been largely studied in the literature, typically assuming walls responding as rigid blocks or assemblies of rigid bodies. This paper presents a single-degree-of-freedom (SDOF) numerical model for the analysis of the dynamic OOP behaviour of URM walls or portion of walls. It takes into account both the linear and the non-linear rocking response phase of URM walls. The numerical model has been developed to capture the experimental dynamic response of both single leaf and cavity wall specimens subjected to a pure one-way bending action with both top and bottom end supports of the wall moving simultaneously. A detailed investigation into the force–displacement relationships characterising both wall typologies has been carried out in order to provide reliable parameters for the simulation of their dynamic behaviour. Particular emphasis is placed on the energy dissipation involved in such mechanisms. Different equivalent viscous damping models have been adopted and compared in order to identify the most appropriate one to capture the dependency of the damping phenomenon on the oscillation amplitude and subsequently the system frequency.

This paper provides information related to the sensor measurements obtained from an unreinforced masonry building subjected to incremental dynamic shake-table tests at the EUCENTRE facilities in Pavia, Italy. These tests provide a unique data set that captures at full scale the in-plane and out-of-plane behavior of unreinforced masonry walls, and the influence of flexible diaphragms on the dynamic global response of a complete building. The authors made this information available to assist in the development of analytical and numerical models, necessary to estimate the dynamic response and the engineering parameters for the performance-based seismic assessment of unreinforced masonry buildings. All recorded data (acceleration and displacement time histories) and the videos of the tests can be requested online on the EUCENTRE repository at the URL www.eucentre.it/nam-project referring to EUC-BUILD-2. For further interpretation of the sensor recordings, and for a detailed discussion on the seismic performance of the building specimen, the reader is referred to the article entitled “Experimental seismic performance of a full-scale unreinforced clay-masonry building with flexible timber diaphragms” (Kallioras et al., 2018) [1].

This paper presents the results of a unidirectional shake-table test performed on a full-scale, single-storey unreinforced masonry building. The specimen represented a typical detached house of the Groningen region of the Netherlands, consisting of double-wythe clay-brick unreinforced masonry walls, without any specific seismic detailing. The building prototype included large openings and a reentrant corner, causing a discontinuity in one of the perimeter walls. The floor was made of timber beams and planks, resulting in a flexible diaphragm. The roof, characterized by a very steep pitch, consisted of a series of timber trusses connected by wood purlins and boards. The two facades perpendicular to the shaking direction were designed to represent two typical gable geometries. An incremental dynamic test was conducted up to the near-collapse state of the specimen, using input ground motions compatible with induced-seismicity scenarios for the examined region. This paper summarizes the main characteristics of the specimen and the shake-table experimental results, illustrating the dynamic response of the structure, the evolution of the damage mechanisms, and the attainment of significant limit states.

A shaking table test on a two-storey full scale unreinforced masonry (URM) building was performed at the EUCENTRE laboratory within a comprehensive research programme on the seismic vulnerability of the existing Dutch URM structures. The building specimen was meant to represent the end-unit of a terraced house, built with cavity walls and without any particular seismic design or detailing. Cavity walls are usually composed of an inner loadbearing leaf and an outer leaf having aesthetic and weather-protection functions. In the tested specimen, the loadbearing masonry was composed of calcium silicate bricks, sustaining two reinforced concrete floors. A pitched timber roof was supported by two gable walls. The veneer was made of clay bricks connected to the inner masonry by means of metallic ties, as seen in common construction practice. An incremental dynamic test was carried out up to the near-collapse limit state of the specimen. The input motions were selected to be consistent with the characteristics of induced seismicity ground motions. The article describes the characteristics of the building and presents the results obtained during the material characterization and the shaking table tests, illustrating the response of the structure, the damage mechanism and its evolution during the experimental phases. All the processed data are freely available upon request (see http://www.eucentre.it/nam-project ).

Damage observations from recent seismic events have confirmed that the activation of out-of-plane local mechanisms is one of the major causes of structural collapse in unreinforced masonry buildings. Particularly vulnerable are cavity walls commonly used in residential building in regions such as Central and Northern Europe, Australia, New Zealand, China and several other countries. Usually, the inner leaf has a load-bearing function, carrying vertical loads transmitted by floors and roof while the outer leaf, having only aesthetic and insulation functions, is lightly loaded. The two leaves are typically connected by means of metallic ties. The high out-of-plane vulnerability, which may prevent the exploitation of the global capacity associated with the in-plane capacity of the structural walls, is mainly due to the high slenderness of the masonry leaves and the lack, or ineffectiveness, of ties between leaves. Often ties are too widely spaced and/or heavily degraded. Despite the complexity of the composite behaviour of such a construction typology, no dynamic tests on cavity walls are reported in current literature. For this reason, four out-of-plane shaking table tests were conducted on full-scale unreinforced masonry assemblies of three cavity wall panels with different tie distributions (inner calcium silicate brick wall and outer clay brick wall) and one single-leaf wall constructed using calcium silicate brick masonry. The experimental arrangement allowed the specimens to be tested under different input signals and loading conditions, inducing an out-of-plane one-way bending action in the walls. The research is aimed at understanding the seismic behaviour of cavity walls, their failure mechanisms and how they are affected by boundary conditions and degree of connection between the two leaves. The paper describes the main experimental results, including deformed shapes, damage patterns, force-displacement relationships, and the capacities in term of acceleration sustained by the specimens. Additionally, the energy dissipation involved in the mechanism has been investigated in terms of coefficient of restitution and damping ratio. All the processed data are freely available upon request (see http://www.eucentre.it/nam-project ).

This paper presents the results of incremental dynamic tests on full-scale unreinforced masonry (URM) walls constructed with an intentionally weakened mortar under two-way bending excitation in the out-of-plane (OOP) direction. A specimen was also subjected to simultaneous vertical and horizontal excitation. Walls were also tested in boundary conditions that have not been previously reported in the literature. Emphasis was placed on the development and interpretation of a characterisation test to estimate the torsional shear strength of bed-joints, a parameter of prime importance in the OOP two-way bending behaviour of URM walls. Analytical formulation to estimate the initial stiffness of walls based on the theory of plates is then proposed and validated. Being the first experimental campaign to address the dynamic OOP two-way bending response of full-scale URM wall panels provided the opportunity to propose simple yet mechanically rational methodologies with which both the peak force resistance as well as the displacement at which such resistance is attained can be easily estimated.