1,724,021 research outputs found
Finite Element numerical modelling of the fire resistance of log-house walls
No full textThis paper presents a Finite Element (FE) numerical investigation performed on timber log‐house walls with partial thermal insulation, subjected to in‐plane compression and exposed to fire on one side. A key aspect for the design of log‐house walls is represented by geometrical details, like cross‐sectional properties of logs (typically characterised by high depth‐to‐width ratios) and outriggers.
The latter ones act as mechanical restraints for the main walls and hence markedly affect their overall load‐carrying capacity. As a result, careful consideration should be given to the choice of these details, due to the possible occurrence of local structural and/or thermo‐mechanical mechanisms. This is the case of exceptional loading conditions like fire load, as the fire resistance of log‐house systems could be affected by a multitude of variables. The FE investigation herein presented follows and extends an earlier research study on an unprotected log‐house wall, where thermal insulation panels (gypsum fibreboard layers) were added to protect part of the wall. The FE method is assessed and validated against a full‐scale furnace test, including a critical discussion of comparative results
Timber-concrete composite structures in fire conditions - Finite Element numerical modelling of tensile tests
No full textThe structural behavior of Timber‐Concrete Composite (TCC) slabs, as known, is mainly governed by the load‐bearing capacity of the metal connection between timber and concrete components.
There, a key role is assigned to possible changes in stiffness and strength, especially for TCC systems exposed to fire loading. While simplified formulae are available in the literature for the calculation of strength and stiffness properties of screwed connections, most of the influencing parameters for TCC structural systems should be preferably assessed via time and cost consuming experiments in fire conditions. In this regard, the use of refined Finite Element (FE) models can provide strong support for design developments. Key input features ‐ including
thermal and mechanical material properties, as well as boundary thermo‐mechanical conditions and interactions ‐ should be however properly assessed and calibrated, including connection detailing. In this paper, an advanced FE approach inclusive of cohesive contacts and damage laws is taken into account, from recent literature applications on timber composites in cold conditions, and preliminarily extended to TCC samples in fire. FE results are assessed towards literature test results, with special care for tensile experiments, including a critical discussion of issues and potentials
Special Issue editorial: “Design of steel and composite structures: Research developments, trends and design challenges”
No full textLong-term behavior of timber-concrete composite beams. II: Numerical analysis and simplified evaluation
Get PDFhttp://dx.doi.org/10.1061/(ASCE)0733-9445(2006)132:1(23)This second part of two companion papers investigates the contribution of different rheological phenomena and thermohygrometric variations on long-term behavior of timber–concrete composite beams (TCCs) in outdoor conditions. The numerical algorithm presented and validated against two experimental tests in the first part is employed with this aim. Such a model fully considers all rheological phenomena and, therefore, leads to rigorous solutions. Effects on the beam response include the creep and mechanosorptive creep of both timber and connection, along with concrete creep and shrinkage, and may markedly increase the elastic deflection due to live load. The inelastic strains due to yearly and daily variations of environmental conditions (temperature and relative humidity) produce an important fluctuation of the deflection. A simplified method, which is suitable for practical design of TCCs under long-term loading, is at last proposed. The effects of load, concrete shrinkage, and inelastic strains due to environmental variations are evaluated one by one using approximate formulas and are then superimposed. Creep and mechanosorptive creep are taken into account by adopting modified elastic moduli. The reliability of the proposed method is checked by way of some comparisons with numerical results. The applicability for the case of TCCs in heated indoor conditions is also discussed
Can Structural Timber Foster Short Procurement Chains within Mediterranean Forests? A Research Case in Sardinia
Get PDFBackground and Purpose: The aim of this paper is to present the idea of a timber short procurement chain as a means to provide an increased value to Mediterranean forests. It is based on the evidence that timber buildings are increasingly used for a number of reasons including sustainability, the speed of erection, and excellent structural and seismic performance. However, most of the timber currently used around the Mediterranean is imported from outside this area.
Materials and Methods: The idea is to use the best part of the tree to produce timber boards, while all the remaining part of the tree including the production waste is used for energy production. Important issues to address are the generally low mechanical properties of locally-grown timber such as maritime pine in Sardinia, which would make some wood-based products such as glue-laminated timber not technically viable. Cross-laminated timber panels are a possible solution to this problem because this wood-based product is manufactured in such a way that even with low-quality timber boards it is possible to obtain a medium quality panel. The panel is made of layers of timber boards with the adjacent layers glued under pressure at a right angle. Another issue is the need to grade the local timber, for which a number of specimens must be tested to destruction in order to identify a visual or a machine-stress grading procedure. Last but not least, the panels must be tested to destruction to correlate their mechanical properties to the properties of the boards.
Results: The preliminary mechanical tests carried out on Sardinia maritime pine confirm that the material is low-grade because it is characterized by large knots and a significant grain deviation. Nevertheless, when used in the cross-laminated panels, the properties are significantly improved due to the layout of the panel which reduces the influence of defects in the boards on the mechanical properties of the panel.
Conclusions: A timber short procurement chain is a possible means to create job opportunities and reduce depopulation, which is particularly important in several regions of the Mediterranean. By adding value to the forests by means of timber production used in prefabricated components employed in low-rise timber buildings, it is also possible to improve forest management and even extend forested areas which have all positive effects on the environment, the landscape and the reduction of hydrogeological hazard
A finite element model for long-term analysis of timber-concrete composite beams
No full textThe paper presents a finite element model for studying timber-concrete composite beams under long-term loading. Both deformability of connection system and rheological behaviour of concrete, timber and connection are fully considered. The creep of component materials and the influence of moisture content on the creep of timber and connection, the so-called “mechano-sorptive” effect, are evaluated by means of accurate linear models. The solution is obtained by applying an effective step-by-step
procedure in time, which does not require storing the whole stress history in some points in order to account for the creep behaviour. Hence the proposed method is suitable for analyses of composite beams subjected to complex loading and thermo-hygrometric histories. The possibility to accurately predict the long-term response is then shown by comparing numerical and experimental results for different tests
Comparison between rocking analysis and kinematic analysis for the dynamic out-of-plane behavior of masonry walls
No full textThis paper provides a contribution to the rocking analysis of masonry walls by making a comparison with the kinematic analysis suggested by the Italian code. It is shown that the latter approach is generally overconservative and therefore potentially inappropriate for historic buildings, where rehabilitation can be expensive and can affect their cultural value. The equation of motion given by the Housner formulation, corresponding to the movement of a rigid block, is here modified to account for different boundary conditions at different heights of the wall. These boundary conditions or horizontal restraints can represent vaults, transverse walls, or retrofitting devices such as steel tie-rods. A systemic analysis of walls having different dimensions and slenderness is performed, and the results from the Italian code and rocking analysis are compared. Finally, the improvement in the response offered by retrofitting devices is discussed in terms of reduction of amplitude ratio
"Experimental behaviour of a full-scale timber-concrete composite floor with mechanical connectors"
No full textThe timber-concrete composite (TCC) beam is a construction technique that can be used for upgrading of existing timber floors without the need of demolition. This possibility has been investigated through full-scale tests on a 6-storey experimental building with light-frame timber walls and platform construction, where the existing timber floor for
domestic use was upgraded for reuse as an office building. The acoustic flooring was replaced with a 60 mm lightweight concrete slab, connected to the existing joists with inclined shear connectors (SFS screws) to form the TCC floor. The floor and environmental conditions were monitored during the
concrete pouring and hardening, and during the
application of the live load. Two different types of construction, propped and unpropped, were compared,
and an extensive experimental investigation was performed on material components (lightweight concrete,
timber, and connection system) with the aim to fully characterise the behaviour under short- and long-term
loading. The unpropped floor was then tested to failure under monotonic loading, and two different boundary conditions, namely the actual joist-to-wall joint and a perfectly pinned support, were investigated. An advanced FE model was validated on the test results and used to predict the deflection in the long-term.
The composite floor achieved the target stiffness and the design load for satisfying ultimate and serviceability limit states for office loading in the UK. The actual joist-to-wall restraint was characterized by a low degree of fixity, however it produced
early longitudinal crack formation in the proximity of
the support. The final collapse of the floor as a whole occurred progressively under increasing load after
failure for fracture in tension of an individual joist. The higher drying shrinkage of lightweight concrete raised the deflection during concrete curing and hardening
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