The application of timber-based strengthening solutions to existing wooden and masonry structures, combines several benefits, such as reversibility, compatibility, lightness, sustainability, affordability, and effectiveness. With reference to existing timber floors, an efficient method to enhance their seismic response is the fastening of an overlay of plywood panels to the existing sheathing, an intervention that greatly improves in-plane strength, stiffness, and energy dissipation. In order to promote the use of this retrofitting solution in practice, this work presents a set of calculation tools supporting the design and advanced numerical modelling of timber diaphragms strengthened with plywood panels. The suite of tools allows to first estimate the full nonlinear, cyclic in-plane response of the strengthened diaphragms starting from the geometrical and material properties of the existing sheathing and the plywood overlay, as well as the mechanical characteristics of the fasteners. As second step, such estimated in-plane response can be transformed into a constitutive law for performing nonlinear numerical simulations, by means of a user-supplied subroutine developed for finite element software DIANA FEA. The presented calculation examples and the performed validation against reference studies from literature, show that the developed tools can provide an accurate estimate of the in-plane response of the diaphragms, and enable an efficient numerical simulation of their seismic behaviour. The implemented tools can be used to both obtain preliminary indication for plywood-based seismic retrofitting design, and to calibrate the interventions on existing diaphragms based on the specific characteristics and needs of a building, relying on the adaptability and versatility of this strengthening method.

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This case study explores the utilization of distributed fiber optic sensors (DFOS) in wooden foundation piles, for assessing and monitoring the stress distribution along their length. Three spruce and three pine foundation piles instrumented with DFOS were driven into the soil in a testing field in Amsterdam and axially loaded in compression. Since DFOS provided strain information, calculating the stress distribution in the piles required knowledge of their stiffness properties, which inherently vary from the head to the tip. Consequently, the piles were extracted and their overall wet dynamic elastic modulus (E_c,0,dyn,wet) was determined through frequency response measurements. Subsequently, the piles were segmented, transported to the TU Delft Laboratory and subjected to mechanical testing. For each segment, the mechanical properties were determined and their variability along the pile was studied, in particular for the static modulus of elasticity (E_c,0,stat,wet). This enabled a comprehensive assessment of the actual in-situ stress distribution (Δσ_actual,stat and Δσ_actual,dyn) along the length of the piles, calculated with DFOS strains and the pile stiffness (E_c,0,stat,wet and E_c,0,stat,dyn). Given the novelty of the DFOS application to timber piles, a validation of the accuracy was conducted on 3 pile segments equipped with DFOS. These segments underwent laboratory compression testing, allowing for a direct comparison between DFOS strain readings and strains measured with linear potentiometers attached to the pile segments. The results revealed good accuracy of DFOS in controlled lab conditions, with a maximum stress deviation of 0.65 MPa. Since the testing field featured a 6-meter-deep predrilled layer, where negligible shaft friction was mobilized, the no-friction stress (Δσ_no-friction) approximately aligned with Δσ_actual,stat on the piles. At pile tips, the maximum applied 300–350 kN compressive load (i.e. Δσ_no-friction = 20–26 MPa), resulted in Δσ_actual,stat = 4–7 MPa, highlighting shaft friction effect. The calculated Δσ_actual,dyn with a single E_c,0,stat,dyn for the whole pile, led to 3 MPa stress overestimation at pile tip. Although this calculation is conservative, the detailed knowledge of the variation of stiffness properties along the pile would result in a more efficient structural use.

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The majority of the bridges in the historic city centre of Amsterdam are supported by wooden foundation piles. Most of these were constructed 100–300 years ago, currently raising concerns about potential safety issues. The wooden piles under the bridges remain entirely under the water table, potentially subjected to bacterial decay in anaerobic conditions. Bacterial degradation proceeds at a slow rate, allowing the piles to perform their function for many years, although causing a reduction of their load-carrying capacity over time. To this end, a large experimental campaign was conducted to characterize the material and mechanical properties in relation to biological decay of 60 spruce and fir piles, dated back to 1727, 1886 and 1922, retrieved from two bridges in Amsterdam. Large-scale compression tests were carried out on 201 pile-segments extracted from head, middle-part and tip of the piles to determine their remaining short-term compressive strength. Micro-drilling measurements were conducted on each pile and analysed with a TU-Delft-developed algorithm, aimed at determining the soft shell – the width of the decayed outer layer of the piles’ cross section. Micro-drilling allowed to accurately assess the remaining sound cross section of the pile, which resulted to be well correlated to its mechanical properties. The extent of decay throughout the cross-section of the piles was assessed within sapwood and heartwood through experimental models from literature and validated with Computed Tomography (CT) scanning. This allowed to identify that bacterial decay was only present in the non-durable sapwood, even in very degraded piles. Moreover, the soft shell resulted to be rather uniform along the piles’ length. The analysis of decay, supported by micro-drilling and CT scans, allowed to develop experimental equations to predict the remaining short-term compressive strength along the pile length. The micro-drilling technique is now used on a large scale in Amsterdam, supporting the assessment of the remaining load carrying-capacity of wooden foundation piles in the city, aiding in the planning of conservation, maintenance and preservation strategies.@en

In the historic city centre of Amsterdam (NL), the predominant foundation system is comprised of wooden piles. Due to their placement below the water table, these foundations are susceptible to bacterial decay. This study aims to investigate and compare various methods for characterizing decay patterns within the cross sections of piles retrieved from two bridges in Amsterdam. The examined piles span different construction years: three originate from 1727, four from 1886, and two from 1922. Following extraction, the piles were transported to TU Delft Stevin II Laboratory, where they underwent further subdivision into three segments, each representing the head, middle, and tip, resulting in a total of 27 segments. The effects of bacterial decay were characterised by performing micro-drilling measurements, small-scale material and compressive tests on prismatic samples extracted from the segments' cross sections, computed tomography scans, and light microscopy observations. Microscopic examination revealed severe degradation in all segments dating back to 1727, extending 20–50 mm from their surface. This outcome was also confirmed by the other adopted methods: the corresponding prisms had large moisture contents and poor mechanical properties, while low basic densities and drilling amplitudes were obtained from CT scans and micro-drilling measurements, respectively. On the contrary, the internal sections of the 1727 segments exhibited no evidence of decay and demonstrated properties consistent with those observed in sound segments from 1886 and 1922. Finally, the observed gradients of density, strength, and stiffness were well correlated with micro-drilling measurements, which can therefore be reliably used as on-site assessment method to reconstruct the properties of the piles.

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The majority of bridges and quay walls in the inner city of Amsterdam rely on wooden foundation piles. Most of these were constructed 100–300 years ago, implying several challenges for the assessment of the current residual load-carrying capacity and their reliability. In Amsterdam, the wooden piles supporting bridges and quay walls remain entirely under the water table, which means that only bacterial decay can occur. Bacterial degradation proceeds at a slow rate, allowing the piles to perform their function for many years, although causing a reduction of the load-carrying capacity over time. To this end, the municipality of Amsterdam started a large project where non-destructive micro-drilling measurements were employed, with the goal of capturing the in-situ level of decay and the remaining strength of wooden foundation piles. The applicability of micro-drilling was studied on 60 wooden piles with various decay levels, driven between 1727 and 1922, and retrieved from two bridges in Amsterdam. An algorithm was developed for analysing the micro-drilling signals, aimed at determining the decayed outer layer of the pile (soft shell). The micro-drilling approach was validated with the results of mechanical testing on the piles. This study contributes to reliably assessing the decay and remaining load carrying-capacity of wooden foundation piles utilizing in-situ micro-drilling measurements.@en

The majority of bridges and quay walls in the centre of Amsterdam are supported by 100–300 years-old wooden foundation piles subjected to bacterial decay. Bacterial degradation proceeds at a slow rate, allowing the piles to perform their function for many years, although causing a reduction of their load-carrying capacity over time. In this study, micro-drilling measurements were employed to capture the amount of decay and remaining short-term compressive strength of the historic wooden piles. The applicability of micro-drilling was studied on 60 wooden piles with various decay levels, retrieved after 100–295 years of service life. An algorithm was developed for analysing the micro-drilling signals, aimed at determining the decayed outer layer of the piles’ cross section, and validated with the results of mechanical testing on the piles. The micro-drilling technique is now used on a large scale in Amsterdam, supporting the assessment of the wooden foundation piles in the city.

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Wood-based retrofitting techniques for seismic upgrading and architectural conservation of existing buildings have found increasing application in the last decades. With reference to the in-plane seismic strengthening of existing timber floors, a particularly efficient solution consists of an overlay of plywood panels fastened to the sheathing. This technique allows a great improvement in strength, stiffness, and energy dissipation of the floors. Yet, when adopting this strengthening solution for existing floors in highly seismic regions, the target design loads could require large values of in-plane strength and stiffness for the retrofitted diaphragms, and this could cause their beneficial, dissipative potential to be reduced. Thus, in this work, a strengthening solution is presented, able to retrieve high strength and at the same time activate large energy dissipation in the floors. The proposed technique consists of the creation of two independent shear planes by means of two different superimposed overlays of plywood panels. Previously developed analytical and numerical models describing the in-plane response of floors retrofitted with a single plywood overlay were adapted for the present case with two overlays, validating the results against an experimental test conducted on a sample representing a floor portion. Very good agreement was obtained between experimental and analytical as well as numerical results, thus the proposed approaches enable an efficient design process and an accurate simulation of the proposed retrofitting technique.@en

In the historic city centre of Amsterdam (NL), the most widespread foundation system consists of wooden piles. With the aim of modelling and predicting remaining service life of these foundations and the piles in particular, one of the possible methods for collecting data and monitoring their condition consists of micro-drilling (MD) measurements. This work evaluates the reliability of MD measurements in identifying decayed portions and specific features of wooden foundation piles, considering different moisture content (MC) values. To this end, 24 segments were selected, sawn from wooden piles extracted from site, and having time in service (TS) of 2 to 294 years (with reference to 2021, the year of extraction). 240 MD measurements were conducted at varying MC values of 7% to 212%. The obtained MD profiles showed for all TS a slight decrease in drilling resistance when increasing MC. However, from the MD signals it is possible to reliably detect the areas affected by biodegradation phenomena (e.g. bacterial decay) along the drilling depth, regardless the MC of the segment or its gradient along the drilling depth. The present study contributes to research aiming at utilizing (in-situ) MD techniques for reliably assessing and quantifying decay and to be used in remaining service life planning of wooden foundation piles.

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This work investigated the influence of knots on the compression strength of wooden foundation piles. The study involved 110 pile segments sawn from 18 spruce and 9 pine piles with a mean diameter of approximately 200 mm, and moisture contents above fiber saturation. The mechanical properties were determined performing both full-scale compression tests on pile segments, and small-scale experiments on discs sawn from selected segments, considering samples with and without knots. A knot ratio (KR) was defined analysing the knots layout of each wooden pile, and evaluating how the compressive strength was influenced by size, number and layout of knots. As final step, a prediction model was implemented based on the dry density and KR of wooden piles, to estimate the influence of knots on their compressive strength.

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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.

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The region of Groningen (NL) has experienced increasing human-induced seismicity caused by gas extraction in the last decades. The local building stock, not designed for seismic loads, consists for more than 50% of unreinforced masonry buildings with timber diaphragms. In this context, a detailed seismic characterization of timber and masonry structural components has taken place, and a retrofitting technique for timber floors activating their energy dissipation has been developed. Besides, specific analytical and numerical modeling strategies for as-built and retrofitted timber floors have been formulated. This work presents a design approach for creating strengthened dissipative timber diaphragms, and maximizing the seismic capacity of existing masonry buildings through this retrofitting method. The results from the performed numerical analyses prove that the proposed design approach for timber floors can increase the energy dissipation capacity of masonry buildings, while improving the box behavior at both damage and near-collapse limit state.

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Existing masonry buildings are very frequently part of the architectural context for several countries all over the world. These constructions often feature masonry walls as vertical structural elements, and timber floors and roofs as horizontal components. The often poor characteristics of masonry, along with the in-plane flexibility of the floors and their frequently weak connections to the walls, make such buildings very vulnerable against seismic actions, as proved by the destructive consequences of several earthquakes in the last decades. The improvement of seismic capacity of existing masonry buildings is still an open research topic, with several retrofitting techniques for masonry walls and timber floors being proposed and tested. An acknowledged way of increasing the structural performance of a masonry building under an earthquake consists of the development of the so-called box behaviour, enabling the construction to react as a whole to the ground motion. To pursue the box behaviour, the main adopted retrofitting methods are linked to in-plane stiffening of the timber floors, and seismic strengthening of the connections. In this context, several (nonlinear) analysis method for masonry buildings (e.g. the pushover analysis) assume that rigid floors are present, and out-of-plane failure mechanisms of masonry are prevented. Therefore, also in the context of numerical modelling, the in-plane response of the diaphragms is generally not taken into account in detail, since they are only considered as linear elastic orthotropic membranes or stiff elements. However, past seismic events demonstrated that an excessive stiffening of the diaphragms can also be detrimental. This triggered the study of several lighter, moderately stiff strengthening methods for timber floors, referred to various architectural frameworks. Since existing floors proved to be excessively flexible, but also too stiff diaphragms could not be recommendable, the overarching research question of this dissertation arises: “How is it possible to predict the global seismic behaviour of existing and retrofitted masonry buildings, and to optimize it by quantifying the influence of strengthening interventions on timber floors and timber-masonry connections?” The research question is answered starting from the specific situation of the Groningen area, in the northern part of the Netherlands, where human-induced earthquakes caused by gas extraction take place. The local building stock is composed for more than 50% of low-rise masonry constructions with timber floors and roofs, none of which was designed or realized with seismic events in mind, since earthquakes were absent until recently. Up to now, these events have not caused extensive structural damage, because their intensity was from low to moderate, but according to probabilistic studies, more intense earthquakes might also occur. For this reason, a seismic characterization of local timber and masonry structural components was firstly necessary: this dissertation focused in particular on the testing and modelling of as-built and retrofitted timber diaphragms and timber-masonry connections. As a first step, because it was not possible to test a large number of whole structural components on site, a replication method based on material properties was defined. This ensured that the specimens constructed in laboratory could be representative for the actual structural components in practice. With regard to timber diaphragms, in-plane quasi-static reversed-cyclic tests were performed on five as-built samples, which showed an approximately linear, and very flexible response. For these diaphragms, a retrofitting technique enhancing not only strength and stiffness, but also energy dissipation of the diaphragms, was designed. This dissipative contribution of the floors can be relevant, because it can potentially (greatly) dampen the seismic shear forces on masonry walls, and this characteristic can be even more important for the Groningen area, where low-quality masonry and very slender piers are often present. The strengthening technique for the floors consisted of an overlay of plywood panels screwed along their perimeter to the existing sheathing: the retrofitted diaphragms exhibited a great enhancement in seismic properties, with relevant increase in strength, stiffness, and energy dissipation. The great potential of the developed retrofitting technique could not be limited to an experimental characterization: an analytical model was also necessary to enable the design of the strengthening for other contexts or floor configurations. Hence, starting from the analytical formulation of the load-slip behaviour of the single screws connecting planks and plywood panels, the global in-plane response of the floors was derived, including their characteristic pinching behaviour. This analytical model had also another important function, because it was the basis for an advanced numerical implementation of the seismic response of timber diaphragms in finite element software. This enabled to account in detail for the (dissipative) in-plane behaviour of the diaphragms, so that the seismic response of existing masonry buildings could be optimized with a well-designed retrofitting of the floors. Yet, this energy dissipation can only be activated by means of the in-plane deflection of the diaphragms: to avoid out-of-plane collapses of masonry walls, this deflection has not to be excessive, but at the same time also effectively strengthened timber-masonry connections are needed. Therefore, an experimental characterization of two as-built and five strengthened timber-masonry connections was conducted. The joints were tested under monotonic, cyclic, and also high-frequency dynamic loading, by subjecting them to an induced Groningen seismic signal. Seven replicates per joint type were built and tested, and analytical models for evaluating strength and stiffness of the joints were derived, useful for design purposes or as input for numerical models. Finally, in order to study the possible optimization of seismic capacity of existing masonry buildings, it is also necessary to define proper criteria for an optimal retrofitting. The current seismic design framework is extensively based on peak ground acceleration, which cannot, however, take into account factors such as load duration and quantification of structural damage. These parameters can play a crucial role for the Groningen region, because of the transient nature of the local earthquakes, featuring short, high-frequency and sudden signals, if compared to the longer and more damaging tectonic earthquakes. Therefore, an energy-based approach was adopted, which allows to predict and quantify the hysteretic energy provided by a building as a function of its period and the load duration of the earthquake. This approach opened up the opportunity to quantify structural damage in terms of number of cycles on the system: the role of timber diaphragms becomes, then, even more relevant, because with an optimized retrofitting the floors are only moderately stiff, thus the period of a building would be higher than that of the same structure featuring stiff diaphragms. Furthermore, the possibility to include load duration enables a characterization of the seismic capacity independent of the context or the earthquake type. Thus, to prove the beneficial, dissipative effect of the optimized retrofitting of floors, as well as the effectiveness of the adopted modelling strategies, numerical time-history analyses were performed on three case-study buildings. The first two were typical Dutch constructions, subjected to induced earthquakes, while the third was a country house from the Italian context, to which tectonic earthquakes were imparted. This additional building was included because it enabled to demonstrate that the developed retrofitting and modelling principles, along with the energy-based characterization of seismic capacity, can be generalized to other context besides the reference Dutch one. The results from the analyses show that excessively flexible floors cause, as expected, out-of-plane collapses in masonry walls, while excessively stiff floors limit the energy dissipation to masonry piers only, thus reducing the seismic capacity of the building. On the contrary, an optimized retrofitting is able to retrieve the global base shear of the building, and at the same time its maximum displacement capacity within masonry drift limits. The optimal strengthening also corresponds to the maximum hysteretic energy that can be provided by the structure. Furthermore, the period of the building is also increased compared to stiff floor configurations, meaning that the structure is subjected to a lower number of cycles, besides benefitting from the additional damping effect activated by dissipative diaphragms. This dissipative contribution can be brought into play provided that an effective strengthening of timber-masonry joints is realized. The beneficial, dissipative effect of well-retrofitted, optimized timber floors was quantified in terms of an equivalent hysteretic damping ratio of 15% (additional to the dissipation already provided by masonry walls), and of an increased behaviour factor (q) range for masonry structures: from the usual values of q = 1.5 ÷ 2.5 to q = 2.5 ÷ 3.5 in presence of dissipative diaphragms. This research study can contribute to a more efficient seismic retrofitting of existing buildings, enabling preservation of the architectural heritage and more dissipative, earthquake-safe masonry structures.@en

In the province of Groningen (NL), where human-induced earthquakes take place due to gas extraction, a large part of the building stock is composed of brick masonry walls and timber diaphragms. In this framework, timber-masonry connections play a crucial role in the global seismic response of the buildings, but their properties and structural behaviour have not been investigated yet for the Dutch context. This work describes the experimental campaign conducted at Delft University of Technology to characterize as-built and strengthened timber-masonry connections. The joints were tested under either quasi-static monotonic, cyclic or dynamic loading, to analyse the effect of an induced earthquake signal on the connections’ response in terms of strength, stiffness and damage evolution. The obtained test results provided more insight into the capacity and properties of existing connections, and useful knowledge on the effectiveness of the tested retrofitting methods.

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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.@en

Historical or existing buildings are often composed of brick or stone masonry walls, and timber floors and roofs. When these buildings are subjected to earthquakes, the interaction among such structural components is essential to avoid collapse or excessive damage to the constructions. In this framework, a crucial role is played by the connections between horizontal and vertical structural elements: this is especially true when considering existing buildings not designed or realized taking into account seismic actions, because no measures against these events are present. An example of such a situation is noticeable in the province of Groningen, in the northern part of the Netherlands, where human-induced earthquakes take place due to gas extraction. Given the absence of seismic events until recently, a characterization of the existing buildings is necessary, and strengthening measures have to be analysed, in order to make them earthquake-safe. This work describes the experimental campaign conducted at Delft University of Technology to assess the seismic behaviour of as-built and strengthened timber-masonry connections. Results show that existing joints are not suitable to withstand earthquakes, while the proposed strengthened configurations can increase not only strength and stiffness, but also energy dissipation of the connections.@en

In the field of seismic retrofitting, a common intervention to improve box-like behaviour in an existing building is the strengthening and stiffening of existing timber floors and roofs. However, these retrofitting methods should be carefully applied, because they change the static scheme and the buildings' response to earthquakes. Strengthening solutions with high reversibility and light weight have therefore to be preferred, and in this context the overlay of plywood panels on existing floors can improve their characteristics in terms of strength and stiffness, but also enhance their energy dissipation, already at a very limited deflection. This strengthening technique was adopted and tested within an experimental campaign aimed at assessing the seismic response of timber diaphragms with typical characteristics from the Groningen area, located in the northern part of the Netherlands. In that region, human-induced earthquakes take place due to gas extraction and the existing buildings are not suitable to safely withstand these seismic events. This paper presents a summary of the results of the experimental campaign on as-built and retrofitted timber diaphragms, and evaluates the beneficial damping properties of floors strengthened with plywood panels, connected only to the underlying planks and not directly to the joists. The results are compared with the data available in literature and provide new reference values for the coming version of the Dutch seismic standard.

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In the region of Groningen (NL), human-induced earthquakes initiated by gas extraction are causing structural damage. In that area, the building stock is mainly composed of unrein- forced masonry (URM) buildings with light and flexible timber floors and roofs. Thus, an ex- perimental campaign was arranged for assessing the in-plane response of these diaphragms, and a retrofitting method was developed, consisting of an overlay of plywood panels screwed to the existing sheathing around their perimeter. This light, reversible stiffening measure showed a great increase in the in-plane strength, stiffness, and energy dissipation of the floors. Subsequently, an analytical model was developed, showing very good agreement with experimental results, and enabling the design of retrofitting interventions with this technique. Starting from the formulated model, a user-supplied subroutine was implemented in the finite element software DIANA FEA, allowing to represent the in-plane response of the diaphragms, including their energy dissipation. Finally, the impact of this retrofitting intervention on a case study of an existing building was evaluated by means of nonlinear time-history analyses. The results of numerical analyses show that the user-supplied subroutine accurately describes the in-plane behaviour of the retrofitted timber floors. Besides, the proposed retrofitting tech- nique greatly increases the global seismic performance of the building, compared with both its as-built configuration and to stiffer and less reversible strengthening measures.@en

In-plane behavior of timber diaphragms is usually characterized by means of an equivalent shear stiffness. However, this value depends on how the stiffness of the floors is evaluated from the experimental tests. Although an increasing number of research studies have provided a deeper insight into the seismic characterization of as-built and retrofitted timber diaphragms, the use of different standards or assumptions have led to inhomogeneous and not comparable results. With a focus on light, reversible, wood-based strengthening techniques applied to existing diaphragms, this study proposes a uniform and simple method based on the calculation of the secant stiffness of the floors at reference drifts. By means of this procedure, relevant research studies from the literature were compared, and homogeneous, indicative values of equivalent shear stiffness were proposed for each considered strengthening technique. These results can contribute to a more aware and reliable use, design, and linear modeling of wood-based retrofitting solutions for existing timber diaphragms.@en

In this work, the relationship for a socket-type connection in wooden foundation piles is investigated, and a trilinear moment-rotation diagram was determined by means of experiment. Numerical and analytical models confirmed that the material properties for compression perpendicular to the grain are governing for the connections’ strength and stiffness properties. This was similar to the response found in the experiment, where ductile behaviour was observed, which can be explained from the plasticization after the compression strength perpendicular was reached. Although because of the specific configuration (confined in a circular tube) the found strength perpendicular to the grain cannot be assigned to other configurations, a good estimation of the stiffness of the connection can be made with FEM models, assuming an MOE90 of 70 N/mm2 for a fully saturated pile. With a conservative assumption for the strength perpendicular to the grain the influence of the connection in a pile-soil model can be investigated also for other configurations than the tested one. A procedure to study the influence of tangential (usually horizontal) soil displacements on timber piles with concrete extensions piles on top is proposed. The outcome of a specific situation from practice with high horizontal loads showed that the bending capacity of the timber pile will in most cases be governing and not the investigated socket connection.@en

Timber diaphragms in existing buildings are often too flexible in their plane, and can thus potentially cause out-of-plane collapses of walls during earthquakes. A very efficient retrofitting method to increase their in-plane stiffness and energy dissipation is the overlay of plywood panels. However, the usual characterization of the floors by means of a general equivalent shear stiffness cannot account for their nonlinearity and dissipative properties. Therefore, in this work, an analytical model is formulated to describe the in-plane response of timber diaphragms strengthened with plywood panels screwed along their perimeter to the existing sheathing. The proposed formulation starts from the definition of the load-slip equation for a single screw connecting a plank and a plywood panel. The whole floor’s response is then derived, with the prediction of both backbone curve and pinching cycles. From the comparison between the response of tested full-scale diaphragms and the analytically calculated one, it can be concluded that the proposed model accurately predicts the in-plane behaviour and dissipative properties of timber floors retrofitted with plywood panels.@en