Carpentry joints, transmitting forces between timber members by direct contact and friction, were the key-elements of traditional timber construction. Often, such joints were reinforced with metal devices with the aim at avoiding disassembly under exceptional, but undefined and not quantified, loading conditions. Currently, interventions performed to improve carpentry joints are still largely based on empirical state-of-practice schemes, or on simplified assumptions on their behaviour, without explicit reference to seismic conditions. The elastic and post-elastic behaviour of the most widely adopted joints for monotonic and cyclic load has been the object of an extended research program. Results have permitted to define general criteria for the seismic improvement or strengthening of these connections.
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MOMENT RESISTING DOWELLED JOINTS IN TIMBER STRUCTURES: MECHANICAL BEHAVIOUR UNDER CYCLIC TESTS
This paper presents an experimental study aimed at collecting information on the response of knee connections to high amplitude fully-reversed rotational deformations, and compares the findings with seismic performance requirements in Eurocode 8. The connections investigated attached twinned outer glulam members to a single glulam member sandwiched between them using steel dowels. Attention is also directed at assessing whether the timber design provisions of Eurocode 5 can be used to estimate moment capacities and rotational stiffness of such knee connections.
MODELLING THE SEISMIC BEHAVIOUR OF LIGHT-FRAME TIMBER STRUCTURES
This paper investigates the numerical modelling of the cyclic behaviour of light-frame timber structures for non-linear seismic analyses. Two models with different detail levels are used: in the first approach, called M1, every nail connecting the frame to the sheathing is schematized through two non-linear springs, acting on two perpendicular translational degrees of freedom in the plane of the wall, to represent the slip between the two timber parts; in the second approach, called M2, the entire wall is modelled using two equivalent diagonal springs, with mechanical properties derived either from experimental testing on the wall, or from detailed analysis conducted with the M1 approach. Due to its simplicity and limited computational burden, the M2 model is particularly convenient for analyses of entire buildings. The proposed models have been implemented in Abaqus via a purposely developed external user subroutine, and in SAP2000 using the multi-linear pivot hysteretic cycle available in the software library. The models are first validated on experimental tests carried out on screws and individual walls, and subsequently used for modelling an entire light-frame building for which the results of several shaking table tests are available in literature. The experimental-numerical comparison confirms the effectiveness of the models for light frame building and the possibility of use from practicing engineers via the SAP2000 or equivalent software package.
FINITE ELEMENT ANALYSIS MODEL OF YING-XING TIMBER PAGODA BASED ON THE CONFORMATION CHARACTER AND DAMAGED CONDITION
Ying-Xian timber pagoda is the existing oldest and highest wooden pagoda in China. Because of strong earthquake action and material aging, Ying-Xian timber pagoda is severely damaged and needs to be strengthened urgently. Aiming at the characteristics of complicated structural conformation and numerous damaged types of the pagoda, this paper discussed practical expression technology of computer simulation, determined the conformation character of layers-superposition and the modeling method of the pagoda based on the construction rule of traditional Chinese timber structures, and proposed the adjustment method to sectional area or elastic modulus of members according to the damage degree and position by the recognition research on damaged condition and stiffness variation of the pagoda. The finite element model of Ying-Xian timber pagoda was constructed and the dynamic behavior was analyzed by program ANSYS. The analysis results indicate that this FEA model is effective to describe the conformation character and damaged condition of the pagoda, and can be applied to seismic behavior study and security evaluation for the strengthening project of the pagoda.
TIMBER PROVISIONAL STRUCTURES FOR POST-EARTHQUAKE EMERGENCY INTERVENTIONS
The paper contains the scientific and technical considerations that accompanied the implementation of provisional safety measures for residential and monumental structures after the 2009 Abruzzo Earthquake. Emphasis is dedicated to the use of timber shoring, as most common strengthening technique.
The paper is available in Italian only.
ANALYSIS OF FIBER-REINFORCED ELASTOMERIC ISOLATORS INCLUDING STRETCHING OF REINFORCEMENT AND COMPRESSIBILITY OF ELASTOMER
The mechanics of fiber reinforced multi-layered elastomeric isolation bearings is studied in this paper. Such bearings offer the possibility of light-weight low-cost seismic isolators that can be mass-produced and used for public buildings and housing of highly seismic areas in developing countries.
The fiber reinforcement, in contrast to the steel reinforcement in conventional isolators, assumed to be rigid both in extension and flexure, is flexible in extension, but completely without flexural rigidity. In addition the rubber layers in these bearings tend to be very thin leading to large shape factors and the need to include bulk compressibility in the elastomer. These aspects of the bearings lead to interesting mechanics problems and in this paper the influence of the stretching of the reinforcement and the compressibility of the elastomer on the mechanical response is developed and confirmed by finite element analyses. A surprising result of the analysis of the combined response of the apparently unrelated effects of stretching of the reinforcement and compressibility in the elastomer is that the mathematical structure of the theory is the same for both effects and that they can be combined in the result- ing solution in a simple way. It is shown that it is possible to produce a fiber-reinforced isolator that matches the behavior of a steel-reinforced isolator. The fiber-reinforced isolator will be significantly lighter and could lead to a much less labor intensive manufacturing process.
CONCAVE SLIDING ISOLATOR’S PERFORMANCE UNDER MULTI-DIRECTIONAL EXCITATION
Due to their large displacement capability and stable energy dissipation associated with a compact shape and new highly performing materials, the use of concave sliding isolators have been continuously increasing for application in buildings and bridges. In this paper the results of dynamic tests on full scale devices are presented. Their response was studied in a wide velocity range, for bi-directional patterns under different compressive loads. In this range of loading characteristics, which is typical of design for earthquake excitation, the behavior of these isolators appears significantly affected by the multi-directionality of the motion, and more specifically by the degradation of the coefficient of friction due to heating phenomena at the sliding surface. An analytical model, applicable to the prediction of bi-directional sliding behavior of friction-based isolators has been experimentally validated. Results of this study suggest that these phenomena should be considered in the design of structures equipped with these popular anti-seismic devices.
SEISMIC ANALYSIS OF MASONRY VOUSSOIR ARCHES ACCORDING TO THE ITALIAN BUILDING CODE
This paper is addressed to construction professionals, engineers and architects entrusted to assess the seismic vulnerability level of historical and architectural heritage buildings and to ensure their safety. Masonry building collapses caused by seismic events highlight frequent cases of loss of equilibrium, that is, the rigid overturning of structural portions. The study of collapse mechanisms can be effectively performed using the kinematic analysis methods, recently adopted by the Italian Building Code. Referring to a particular structural element (the masonry arch), a typical component of historic buildings, this paper proposes an original approach to perform seismic verification based on an algorithm devoted to this topic. Thanks to this algorithm, the a-priori choice of failure interfaces is avoided, as it is possible to individualize the kinematism and its related collapse load factor. The seismic verification which follows is performed according to the Italian Building Code.
MULTI-SITE DAMAGE LOCALIZATION IN A SUSPENSION BRIDGE VIA AFTERSHOCK MONITORING
In earthquake affected areas the speed and reliability in assessing the damage suffered by strategic structures, such as long-span bridges, is of paramount importance both for civil protection operations and for organization and coordination of immediate remedial measures for the structure safety. In this paper we present the results obtained by applying a damage identification method termed Interpolation Damage Detection Method to a numerical model of the Shimotsui-Seto bridge, a suspension bridge with a long span steel truss deck (940 m). The method allows to detect localized reductions of stiffness along the bridge deck on the base of accelerometric responses recorded on the main girder during a damaging seismic event, or during an aftershock following the onset of damage. This is possible as long as responses recorded at the same locations on the undamaged structure are available. The response of the suspension bridge, subject to seismic excitation, has been calculated in the ANSYS framework using a finite element model derived from the original design data. In order to reproduce real life conditions, the numerical results in terms of temporal responses are artificially modified by including a background noise characteristic of classes of Micro Electro-Mechanical Systems type sensors. The reliability of the Interpolation Damage Detection Method has been numerically verified by simulating the damage through a reduction of stiffness in one or more elements of the deck. Several different locations of damage have been considered in order to study the influence on damage location the results provided by this Structural Health Monitoring methodology.