Advanced Materials Research Vol. 778

Abstract: This paper endeavors to identify the structural characteristics that render traditional timber buildings in Istanbul earthquake-resistant even ifthey are in a deteriorated state. A traditional timber building of approximately 110 years old located in the Historical Peninsula was selected as a subject for the finite elements model. According to the structural material analysis and the condition of the elements of the load-bearing system, three modelling criteria were chosen to classify the strength capacity of the building. These are: an undamaged (new) building, a 110 year-old building with material defects, and a building with structural decay and broken node points. Seismic data from the 1999 Adapazarı and Düzce earthquakes were used for the modelling. The relative floor displacements of the systems were investigated and theresults were evaluated by comparing the cross-sectional load-bearing capacities

Abstract: The current paper deals with the analysis of the results yielded by a series of tests performed to evaluate the seismic behaviour of a model log construction. The study was based on an experimental investigation performed to improve the existing knowledge on log houses subject to seismic events. The main part of the experimental work is based on a full scale shaking table test, conducted on a two-storey log house designed by the Portuguese company Rusticasa® in compliance with design rules for timber buildings. The test was performed by the University of Minho within the framework of the SERIES Project Multi-storey timber buildings and was coordinated by the University of Trento, at LNEC, Lisbon, Portugal. The geometry of the specimen, the design of the test, the setup and the instrumentation layout are first presented in this paper. The test procedure was conducted in stages with maximum accelerations (bi-directional) of 0.07g, 0.28g and 0.5g. During this incremental test procedure, whenever damage occurred, identification tests were performed to assess any variation in the fundamental period of the house. The experimental results of each test have been analyzed and the resultant values of inter-storey drift, wall slippage and uplift measurements, shear deformations and hold-down forces measured are presented. Most importantly, the dynamic properties (fundamental period and mode shapes) of the system have been determined.

Abstract: This paper aims at applying a direct displacement-based method to assess the seismic vulnerability of existing multi-storey wooden buildings. This procedure is consistent with Priestley’s direct methodology firstly developed for reinforced concrete structures. The distinctive characteristic of the proposed method is that the system response is quantified through the use of displacements instead of equivalent elastic strengths, according to the traditional force-based approaches. Consequently, in comparison to common force-based procedures, this method cannot only be considered as a rational alternative but also as a new seismic philosophy to design or assess structures. A representative timber construction system commonly used in Italy was selected as case study. The construction system illustrated in this work was analysed in detail, with special attention given to the mechanical connections typically used. The typical failure mechanisms and the energy dissipation capacity of the structure or of its members were identified on the basis of the mechanical properties of structural parts and connections, as well as of their geometry. In the proposed direct displacement-based assessment approach, the seismic intensity that would cause the limit state to be exceeded can be calculated by means of simple formulas. Therefore, the capacity to demand ratio can be simply derived. The procedure could be used to gauge the likelihood of losses, by combining it with simple loss models to account for probabilistic aspects.

Abstract: Mechanical and dynamic in-plane properties of timber diaphragms are known to be key parameters when determining both the local and global seismic response of unreinforced masonry (URM) buildings. However, few data pertaining to experimental campaigns on this issue are available in the literature, especially regarding existing floors. In this work, the outcomes of a field testing campaign on full-scale old timber diaphragms are presented. Two specimens, whose size was 5.6 x 9.6 m² and 4.7 x 9.6 m² were obtained from a 17 x 9.6 m² floor and were subjected to a series of both cyclic and snap back tests in the direction orthogonal to the joists. Since the original anchoring system was deficient, new epoxy-grouted anchors were installed before starting the testing procedure. So as to reproduce the inertial load distribution, an ad hoc loading system was developed by means of wire ropes and steel pulleys. After testing the diaphragms in the as-built condition, the effect of different refurbishment techniques was also investigated. From the results, it seems that even simple and cost-effective solutions such as the re-nailing of the flooring are sufficient to achieve a significant increase in the equivalent shear stiffness.

Abstract: The dynamic stability of a timber shell roof structure of the Palasport located in Bologna, has been investigated by means of reduced 1/30 scale model tested on seismic shaking table at Dynamic Testing Laboratory of IZIIS, Skopje, Macedonia. The model was physically modeled according to similitude lows and Buckingham's theorem as an artificial mass simulation model, using the same material as for the prototype structure. The supporting structure of the model was constructed by 26 micro-concrete foundations, 52 micro-concrete columns and 52 steel braces. The roof structure made of wooden lamellar beams forming triangles. The roof consists of a central cylindrical part and 2 lateral spherical parts. The connection between the beams was made by steel rings. The total number of the wooden beams was 550 forming 203 internal and external joints. The model was tested in vertical and horizontal direction considering various loading conditions: symmetrical and non-symmetrical. After definition of dynamic characteristics of the model, it was subjected to seismic excitation of Ancona, as well as Montenegro earthquakes. It was found out that the cylindrical part is more flexible than the spherical one. The largest amplitudes during the tests were obtained in vertical direction. The highest stress concentration was at the cylindrical central arches. The asymmetric load produced more unfavorable behavior than the symmetric one.

Abstract: Starting from XIV century, a very interesting construction technique was developed in Northern Italy for heavy-loaded or long-span beams: these special timber beams are composed by an assemblage of multiple parts that behave practically as they were made by a single piece, thanks to a clever system of indentations, obtaining in this way the overall dimensions of slender thin-walled and high-section that could not be fit by cutting a single log. The first witness of this system can be found in L.B. Alberti treatise and some detailed drawings in Leonardo da Vinci's codes, but some examples of these beams can still be found in exercise, like those we discovered in an ancient palace in Verona, dating from XIV century. The study of the mechanical behavior of these beams is presented, taking into account the orthotropic properties of the wood, as well as some comparison with other beams found in Ferrara, together with the discussion of some proposal for their reinforcement in order to assure a safe reuse of the historic building. A sort of pre-stress can be depicted in Leonardo's drawings, in order to assure the connection of different pieces and the efficiency of the framework.

Abstract: Historic timber structures forming vaulted roofs of public and ecclesiastical buildings are present worldwide. The structural response of these constructions is usually governed by the structural performance of the joints, the interaction between the timber structure and the masonry parts, and the current condition of both joints and timber members. At present, numerical approaches, such as finite element method-based approaches are well-established tools for investigating the global response of complex historic structures. Using a FE-based software package, the authors developed a numerical model of a portion of an existing historic vaulted timber structure, which is part of the roof of the Cathedral of Ica in Peru, considering the in-plane semi-rigid response of the planked arches in the elastic range. For this purpose, the rotational and shear stiffness of the joints and the properties of the materials, which are assumed in good conditions, are calibrated by comparing the numerical outputs with experimental results available in literature. The aim of the work presented here is to compare the response of the same vault assuming either continuous (planks continuously connected) or discontinuous arches (modelling of the semi-rigid response of the joints which connect the planks together).

Abstract: Peru is one of the most seismically active countries in the world, this fact highlighted by several destructive earthquakes in recent years. The centre of Lima has a large number of historic structures with a ground floor in adobe, and their upper storeys in quincha, a traditional technique consisting of a timber frame with an infill of canes and mud. Despite the existence of a large number of buildings containing this technique, very little is known about its seismic performance. In order to investigate this, a series of experimental tests on quincha frames, with and without the infill, have been carried out previously, with the aim of quantifying the lateral behaviour and identifying vulnerable areas. The present paper details work carried out to develop a finite element model of the test frames without infill. This model of the timber frame will enable an accurate representation of the frame behaviour to be developed before adding the infill of canes and mud to the model. As the behaviour of the infill material and its connection to the frame is difficult to determine, characterising the timber frame with a high degree of accuracy ensures that the contribution of the infill can be globally quantified from the overall experimental results. The beams and posts are connected by cylindrical mortice and tenon joints, with a diagonal bracing member providing some lateral restraint. The connections have been modelled semi-rigid springs, with the stiffness calculated using variations of the component method. This was found to give very similar results to those obtained experimentally.

Abstract: This paper gives the results of an experiment on timber elements reinforced in the tension zone through the application of strips of natural flax, hemp, bamboo and basalt fibers, creating different arrangements and using different quantities. The testing consisted of several stages that concerned wood rafters and beams of low and good quality. The wooden elements were subjected to bending tests that made it possible to measure the increase in capacity and stiffness resulting from the composite reinforcement.

Abstract: A research study was undertaken to investigate the mechanical performance of glulam beams reinforced by CFRP or bamboo. Local reinforcement is proposed in order to improve the flexural strength of glulam beams. The glulam beam is strengthened in tension and along its sides with the carbon fiber-reinforced polymer CFRP or bamboo. A series of CFRP reinforced glulam beams and bamboo reinforced glulam beams were tested to determine their load-deformation characteristics. Experimental work for evaluating the reinforcing technique is reported here. According to experiment results, the CFRP and bamboo reinforcements led to a higher glulam beam performance. The results show a considerably improved stiffness of the reinforced over the non-reinforced specimens. By using CFRP and bamboo reinforcements several improvements in strength may be obtained.