Geert Ravenshorst

This work presents the application of timber-based retrofitting techniques to a case-study stone masonry church featuring a wooden roof from 18^th century. From the static point of view, the original roof structure presented a number of undersized structural elements, and its members were poorly or not connected among each other and to the masonry, making the church vulnerable to seismic loads as well. Thus, the roof was retrofitted with wood-based techniques, including an overlay of plywood panels, against seismic actions. These affordable, rapid, easily realizable interventions enabled both the conservation and seismic retrofitting of the roof, providing an adequate load-carrying capacity for static loads, and an effective diaphragm action against seismic loads. The conducted numerical analyses showed that the realized interventions greatly improve the seismic behaviour of the building. Besides, when the additional energy dissipation provided by the plywood panels overlay is taken into account in the numerical model, the church would even potentially be able to fully withstand the expected seismic action of the site.

The inadequate seismic performance of existing masonry buildings is often linked to the excessively low in-plane stiffness of timber diaphragms and the poor quality of their connections to the walls. However, relevant past studies and seismic events have also shown that rigid diaphragms could be detrimental for existing buildings and do not necessarily lead to an increase in their seismic performance. Therefore, this work explores the opportunity of optimizing the retrofitting of existing timber floors by means of a dissipative strengthening option, consisting of a plywood panel overlay. On the basis of past experimental tests and previously formulated analytical and numerical models for simulating the in-plane response of these retrofitted diaphragms, in this work nonlinear incremental dynamic analyses were performed on three case–study buildings. For each structure three configurations were analyzed: an as-built one, one having floors retrofitted with concrete slabs and one having dissipative diaphragms strengthened with plywood panels. The results showed that the additional beneficial hysteretic energy dissipation of the optimized diaphragms is relevant and can largely increase the seismic performance of the analyzed buildings, while rigid floors only localize the dissipation in the walls. These outcomes can contribute to an efficient seismic retrofitting of existing masonry buildings, demonstrating once more the great potential of wood-based techniques in comparison to the use of reinforced concrete for creating rigid diaphragms.

The main parameter that influences the bending strength of timber from tropical hardwood is the slope of grain. Although, in the grading rules, a specific threshold value is given, in these hardwoods, the global slope of grain is very difficult to quantify by visual assessment. The slope of grain measured after testing gives a better indication, but still it can only poorly describe the Hankinson relations. By rewriting the Hankinson relations, the slope of grain can be determined from the bending strength test values and from the MOE test value, both in combination with the density values and constants derived by non-linear regression analysis. These two values correlate very well, and the average value is designated as the theoretical slope of grain. With the theoretical slope of grain, five test samples of the tropical wood species okan were evaluated, and slope of grain values of 0.3 were observed, where 0.1 is the limit value. Because all pieces passed the visual grading method as applied in practice, slope of grain values should be incorporated in the strength class assignment test program, when these qualities cannot be ruled out for coming on the market. The (dynamic) modulus of elasticity can be used to evaluate the occurrence of the desired range of slope of grain values in the test samples.

The material and structural performance of calcium silicate (CS) brick masonry has received relatively little attention in the past, although this material is often used for the construction of low-rise buildings in Central and Northern Europe. Upon the occurrence of induced seismicity in the north of the Netherlands, an extensive testing programme has been conducted since 2014 at Delft University of Technology. The paper presents the outcomes of eight quasi-static cyclic tests performed within this program on CS brick masonry walls under vertical and lateral in-plane loads. Different dimensions, boundary conditions and applied pre-compression loads were considered. Overall, the tests allowed to characterise the in-plane behaviour of CS brick masonry walls. The results confirmed the influence of the shear ratio (i.e. the ratio between the effective height and the length of the wall) on the wall response in terms of prevailing failure mode, initial stiffness, force and deformation capacity, energy dissipation. Besides, the experimental outcomes stressed the difficulty in estimating the effective stiffness and near collapse drift capacity. Additionally, an empirical equation is proposed to predict the peak lateral force. The equation, calibrated against the tests presented in this paper, was validated against an extended dataset of tests performed on CS masonry walls. The equation, which does not need any input of material parameters and is applicable irrespectively of the expected failure mode, can be used to estimate the force capacity of CS masonry walls when no or limited data on the material properties are available.