1,721,029 research outputs found
Experimental and numerical analysis of in-plane compressed unprotected log-haus timber walls in fire conditions
No full textThe paper presents an experimental and Finite Element (FE) numerical analysis of the behavior of unprotected log-haus timber walls in fire conditions under in-plane compressive loads. The aim is to assess their overall structural performance and to provide possible design suggestions. In doing so, the main results derived from a full-scale experimental test of a log-haus specimen subjected to the standard fire curve and loaded in-plane in compression are first described. FE numerical simulations are then carried out, to further assess the test results and to perform - based on the rather close correlation between test and FE results - a parametric study on the examined structural system. The effects of several influencing parameters are then investigated, including the presence of an initial geometrical out-of-plane global curvature, the possible exposure to fire of orthogonal logs and carpentry joints acting as lateral outriggers for the main log-haus wall, and the compressive loading ratio acting in combination with the fire loading. The most significant effects of such influencing parameters are highlighted in terms of overall buckling resistance and failure mechanisms for the examined walls in fire conditions, providing evidence for the reduction of their actual load carrying capacity. In conclusion, aiming to derive useful design suggestions, a possible extension to log-haus systems of the “Reduced Cross-Section Method” (RCSM) currently in use for the verification of fire exposed timber members is proposed
Numerical investigation of the in-plane seismic performance of timber log-haus walls with reinforced dovetails.
No full textNumerical analysis of timber log-haus walls with steel dovetail reinforcements under in-plane seismic loads.
No full textCorrelation approach for the Push-Out and full-size bending short-term performances of timber-to-timber slabs with Self-Tapping Screws
No full textSelf-Tapping Screws (STSs) are commonly used to realize many geometrical configurations for connections that are characterized by enhanced stiffness and load-carrying capacity. The analysis of STS joints and composite systems, however, usually requires designers to account for several aspects in their actual load transfer mechanisms, and most of them require refined calculation tools. In this paper, an extended Finite Element (FE) investigation is proposed for timber-to-timber slabs with STS joints, based on full 3D brick models inclusive of Cohesive Zone Modelling (CZM) techniques and damage constitutive laws for the materials in use. The final goal of the study takes advantage of the global and local performance assessment of a selection of STS joints, with careful consideration for their response under a conventional Push-Out (PO) test setup or a full-size bending configuration. As shown, major FE outcomes are discussed to elaborate a design procedure that can be developed on the base of correlation coefficients for maximum force and stiffness calculations in a given slab and loading condition. Major effects due to variable loading configurations are in fact explored at the screw level. Further, geometrically simplified spring-based FE models, that hardly capture the complex behaviour of the examined systems but are largely used in design practice, are presented in comparison to refined FE approaches and literature efforts. As shown, the variation of maximum force and stiffness parameters for STSs is emphasized in the paper for a selection of configurations, and fitting curves are proposed to estimate the STS performance along a given full-size slab, thus suggesting the feasibility and possible generalization of the procedure
Dynamic testing and parameter identification of a base-isolated bridge
No full textIn this paper the results of a campaign of harmonically forced
vibration tests conducted on a two-span post-tensioned reinforced
concrete bridge with deck supported on six elastomeric isolators
are presented and discussed. The bridge is built in an area of the
Friuli Venezia Giulia Region (Northern Italy) having high level of
seismic activity. Dynamic measurements are used to update a
preliminary finite element model of the bridge. The accurate
estimate of the shearing stiffness of the isolators constitutes an
important issue of the updating process, both for the evaluation
of the dynamic response in service or under seismic actions, and
for the evaluation of possible changes in the structural behavior
as a result of degradation of the elastomeric bearings. An
identification procedure based on experimental data and analytical
models of increasing complexity is proposed to estimate the
stiffness of the isolation devices and, ultimately, to determine
an accurate numerical model of the bridge
Numerical and analytical assessment of the buckling behaviour of <i>Blockhaus</i> log-walls under in-plane compression
No full textBlockhaus structural systems are commonly obtained by assembling multiple timber logs, by stacking them horizontally on the top of one another. Although based on simple mechanisms of ancient origins, the structural behaviour of Blockhaus systems under well-defined loading and boundary conditions is complex to predict.
The paper focuses on the assessment of the typical buckling behaviour and resistance of vertically compressed
timber log-walls. The effects of various mechanical and geometrical variables such as possible load eccentricities and initial curvatures, openings (e.g. doors or windows), fully flexible or in-plane rigid inter-storey floors are investigated by means of detailed finite-element (FE) numerical models. These FE models were first validated on test results of past buckling experiments performed on scaled log-wall specimens, as well as on recent buckling experiments carried out on full-scale timber log-walls, demonstrating the capability to appropriately describe the effective interaction between timber logs and to correctly
predict the expected buckling failure mechanisms and ultimate resistance for the log-walls that were investigated. Comparisons with analytical solutions partly derived from classical theory of plate buckling and column buckling are also presented and critically discussed, in order to assess the applicability of these existing formulations – although specific for fully monolithic and isotropic plates and columns – to Blockhaus structural systems. A closed-form solution is finally proposed as a simplified design buckling method for timber log-walls under in-plane compression.</br
Influence of structural irregularity on the q-behaviour factor of light-frame timber buildings by means of incremental dynamic analysis
Full text linkThis paper investigates the role of sheathing-to-framing connection ductility in the evaluation of the structural q-behaviour factor for Light-Frame Timber (LFT) buildings, by means of Incremental Dynamic Analyses (IDA). This approach allows to consider nonlinear cyclic behaviour of the walls, which cannot be taken into account with the static approaches used in most of the available literature on LFT buildings. To this aim, Finite Element wall models, preliminary calibrated towards a cyclic full-scale experimental test, are built to study six case-study buildings, both regular and non-regular, with 2, 3 or 4 storeys, which were designed according to Eurocode and Capacity Design provisions. Parametric analyses are performed by varying the displacement-ductility of the panel. Finally, numerical results are discussed in terms of q-behaviour factor, and its sensitivity to structural irregularities, with respect to existing code provisions for timber buildings
Mechanical characterization of timber-to-timber composite (TTC) joints with self-tapping screws in a standard push-out setup
Full text linkSelf-tapping screws (STSs) can be efficiently used in various fastening solutions for timber constructions and are notoriously able to offer high stiffness and load-carrying capacity, compared to other timber-to-timber composite (TTC) joint typologies. The geometrical and mechanical characterization of TTC joints, however, is often hard and uncertain, due to a combination of various influencing parameters and mechanical aspects. Among others, the effects of friction phenomena between the system components and their reciprocal interaction under the imposed design loads can remarkably influence the final estimates on structural capacity, in the same way of possible variations in the boundary conditions. The use of Finite Element (FE) numerical models is well-known to represent a robust tool and a valid alternative to costly and time consuming experiments and allows one to further explore the selected load-bearing components at a more refined level. Based on previous research efforts, this paper presents an extended FE investigation based on full three-dimensional (3D) brick models and surface-based cohesive zone modelling (CZM) techniques. The attention is focused on the mechanical characterization of small-scale TTC specimens with inclined STSs having variable configurations, under a standard push-out (PO) setup. Based on experimental data and analytical models of literature, an extended parametric investigation is presented and correlation formulae are proposed for the analysis of maximum resistance and stiffness variations. The attention is then focused on the load-bearing role of the steel screws, as an active component of TTC joints, based on the analysis of sustained resultant force contributions. The sensitivity of PO numerical estimates to few key input parameters of technical interest, including boundaries, friction and basic damage parameters, is thus discussed in the paper
“Implementazione di un modello numerico avanzato in Abaqus per la previsione del comportamento non lineare ciclico nel piano di pareti lignee a sistema “Blockhaus”.”
No full textNumerical investigation on timber-to-timber joints and composite beams with inclined self-tapping screws
No full textThe paper presents a Finite-Element (FE) numerical investigation on timber-to-timber joints and composite beams with inclined self-tapping screws (STS). Based on past literature efforts, full 3D solid FE models were implemented in ABAQUS, for selected geometrical and mechanical configurations of composite joints of technical interest. A key role in the FE modelling approach is assigned to input material properties, including damage constitutive laws and mechanical contacts between all the model components, like surface-to-surface interactions and cohesive damage models, so as to reproduce possible local failure phenomena in the joint components. The presented FE models is then validated against push-out tests available in the literature for the examined structural typology. Comparative calculations are hence critically discussed, including numerical analytical estimations from existing models, design standards or literature research projects. Finally, the same modelling approach is applied to timber-timber composite beams, giving evidence of some preliminary FE-to-experimental observations. © WCTE 2018 Committee
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