In the past decades, gas productions in the province of Groningen in The Netherlands have caused a significant amount of shallow human-induced earthquakes. Its building stock has shown to be highly vulnerable to these unexpected events. Among various building typologies, damage has been reported for approximately 12.9% of the churches in Groningen. From the perspective of conservation and prevention of loss of our historical and cultural heritage, the assessment of churches is of importance. As a majority of historical structures have undergone restoration works, that can be favourable for their seismic performance, it is worth noticing that for historical structures strengthening may not be necessary. Consequently, the question arises whether structural modifications during the lifespan of historical unreinforced masonry churches, positively influences their seismic performance. This thesis researches the seismic performance of the historical unreinforced masonry Dutch church Zandeweer, prior and post structural modifications, in the earthquake prone area Groningen. The church, built by the Moncks of Abdij van Aduard in the year 1230, underwent major renovation works in 1931. Its structure is composed of masonry walls, masonry ribbed cross vaults and a timber roof with timber cladding. During the restoration works in 1931 steel columns were integrated in the piers of one of the façade in the longitudinal direction, window openings in the curved façade were closed and concrete beams were added on top of the main walls. Its seismic performance was investigating in the positive longitudinal direction by studying its global nonlinear response and structural elemental behaviour and by indicating uncertainties and damage. A Nonlinear Pushover Analysis (NLPO) and the Simplified Lateral Mechanism Analysis method (SLaMA) were employed to capture the influence on the seismic performance of the church models. Although, the acquired results for the church models showed to a certain extend an insight in the influence of the structural modifications, an insight in the ductility behaviour of the structure was not acquired. Additionally, from the eigenvalue it was concluded that adopted single-mode analysis methods (SLaMA and NLPO) were not suitable, as the structural response of the church is governed by multi-modes. Moreover, with the highly unpredictable behaviour of the vaults in the structure the presented results were greatly influence by physical and numerical instabilities. For future studies is recommended to dedicate a detailed study to the numerical modelling and analysis of masonry ribbed cross vault structures. Furthermore, to conduct a detailed study on the church walls, for which subsequently various analysis methods can be employed and the influence of orthotropy of walls on the global response can be studied. Lastly, the analysis method can be changed by using methods that consider multi-modes simultaneously and that are known for less numerical instability problems than static analysis methods.

This thesis describes the creation of the Equivalent Shear Masonry Model (ESMM). This is an orthotropic material model for low bond strength masonry that uses a smeared cracking approach. It was developed as an improvement of the Engineering Masonry Model (EMM) and adopts that model’s constitutive relations for the behaviour normal to the bed joints and for the compressive behaviour normal to the head joints. However, the shear failure criterion and the tensile head joint failure options are replaced by a new failure criterion for diagonal staircase cracks that is based on the observation that these cracks often open up horizontally. This failure criterion, the equivalent shear failure criterion, is derived from horizontal force equilibrium and evaluates both the shear stress and the tensile stress normal to the head joints. The combined constitutive relation is based on the Coulomb friction shear behaviour of the bed joints, that consists of linear loading, linear softening and a residual stress plateau. The softening is dictated by both the total shear strain and the total horizontal strain. This thesis first describes the development of this theory and its implementation into a user supplied subroutine for Diana FEA. This code was then verified for a single integration point and compared to the EMM’s Diagonal stair-case cracks option for a selection of load paths, among which combinations of shear and horizontal extension. This verification showed that the ESMM is more stable and provides more probable stress-strain diagrams. Subsequently, the model was validated against a micromodelled masonry unit cell for the same selection of load paths. This validation showed that the ESMM’s stress-strain diagrams are realistic, save some details that could be improved. Finally, the model was validated at a structural level with a macromodelled prediction of shear wall experiments. This validation showed that the ESMM is able to model post-peak behaviour, with both softening and a residual force plateau. The model featured inelastic deformation, hysteresis and even peak force reduction. Compared to the EMM’s Diagonal stair-case cracks option, it had less convergence issues and more realistic crack localisation. Some adjustments to details of the theory and the code are suggested. Also, further validations are required, for more load cases and other applications. Altogether, the Equivalent Shear Masonry Model shows promising characteristics and it is recommended that it is further improved and developed into a convenient, practical material model for low bond strength masonry.