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The development of the basis for the displacement-based seismic design of unreinforced masonry (URM) structures is the ultimate objective of the present research project, which should be seen as the first step in an initiative to investigate the limits of the displacement capacity of contemporary URM walls. After a thorough survey and assessment of previous experimental and theoretical studies on the area of displacement capacity of URM walls, an experimental programme consisting of 10 static-cyclic shear tests on full-scale unreinforced clay and calcium-silicate masonry walls was carried out. The experimental programme aimed primarily at studying the effects of unit type, pre-compression level, aspect ratio, boundary conditions and size on the displacement capacity of contemporary URM walls. All the specimens (regardless of their failure mode) exhibited limited displacement capacity. The drift ratio capacity of the specimens that failed in shear was particularly small so that the mean value of the drift ratio capacity was 0.27% with a COV of 12%. However, the specimens that failed in flexure and in sliding-flexure combination exhibited larger drift ratio capacity, i.e. 0.32% and 0.62%, respectively. The test results showed that the drift ratio capacity decreases as the pre-compression level increases or as the aspect ratio decreases. Furthermore, they indicated a possible reduction in the drift ratio capacity in the case of an increase in the height (size effect). A direct relation was also found between the drift ratio capacity and the shear span, which is controlled by the boundary conditions. In addition, the calcium-silicate specimens showed slightly higher drift ratio capacity than the clay specimens. A comparison between the displacement capacity values obtained from the tests with those estimated according to current codes and guidelines showed that current codes of practice overestimate the displacement capacity of contemporary URM walls, so they could result in an unsafe design. Finally, based on the obtained test results, an empirical relationship for the force-displacement response of contemporary URM walls was proposed. In the theoretical part of the project, after a critical state-of-the-art review, a new mechanics-based model for the force-displacement response of URM walls failing in flexure was developed. The developed model gives a new insight into the seismic in-plane response of flexure-dominated URM walls. It combines the flexural and shear deformations with a rigid body rotation (a rocking type motion) resulted from the poor tensile strength of unreinforced masonry. A novel approach was developed to relate the rocking response to the strain state within the wall. The rocking response of URM walls has been widely disregarded so far; however, the developed model shows that its contribution to the seismic in-plane response of URM walls with flexural failure mode is substantial.

This paper is focused on the simulation of the fixed-ends boundary conditions in shear testing of unreinforced masonry walls. Two different approaches to simulate the fixed-ends boundary conditions, i.e. the static and kinematic approaches, are introduced, and their validity is discussed with the help of our own recent experimental data. It is shown that the static approach can result in unrealistic boundary conditions, and it is not a proper way to simulate the fixed-ends boundary conditions.

Within a research project on the deformation capacity of in-plane loaded unreinforced masonry structures, 10 tests were performed on full-scale large walls subjected to in-plane static-cyclic loading. During testing, the measurements included all applied forces together with an overall and a local picture of the deformation state of the specimens. To achieve this, in addition to the traditional hard-wired instruments, i.e., LVDTs and potentiometers, an in-house developed 2D digital image correlation (DIC) measurement system was applied. DIC is a cutting-edge, non-contact, optical measurement technique that provides the complete deformation field by comparing the digital images of the test object's surface before and after the deformation. This paper reports on the applied measurement procedure, discusses important DIC issues and the applicability of DIC for deformation field measurements when testing large masonry walls at full scale. The obtained results proved that in-house developed DIC system based on conventional DSLR cameras can be considered as an effective system to measure the complete deformation field with high level of accuracy and spatial resolution even in the case of large specimens and complicated deformation fields.

A research project on the deformation capacity of unreinforced masonry structures is underway at the Institute of Structural Engineering of ETH Zurich. The development of the basic building blocks for the displacement-based design of unreinforced masonry structures is the objective of the present research project, which should be seen as a first step in an initiative to investigate the limits of the deformation capacity of unreinforced masonry walls. This paper presents a summary review of previous experimental and analytical studies on the deformation capacity of unreinforced masonry walls subjected to in-plane loading. This review is the first phase of the aforementioned research program. A summary of 71 shear tests on unreinforced masonry walls is presented in the form of a database, along with the statistical analysis and discussion of the tests results. Furthermore, three different computational approaches for structural masonry, i.e. micro-modelling, macro-modelling and macro-element discretization, are discussed, and a review of macro-elements for the in-plane response of unreinforced masonry walls is presented. The reviewed models are discussed and a set of conclusions is given. Special attention is devoted to the deformation capacity parameter throughout the paper. Finally, the paper shows the limitations of our current state of knowledge of the deformation capacity of structural masonry. ISSN:2008-3556 ISSN:2008-6695