Timber structures

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Earthquakes and robustness for timber structures

Earthquakes and robustness for timber structures

Satisfactory performance of timber buildings, in general, can be partially attributed to the material characteristics of wood itself, and to the lightness and high redundancy of most wood-based structural systems. The lateral redundancy plays an important role in seismic performance of timber structures. A redundant design will almost certainly offer more parallel load paths that can transmit the applied lateral loading on the building down to the foundation. The detailing of connections is very important because the more integrated and interconnected the structure is, the more load distribution possibilities there are. The building’s structural integrity is only as good as the weakest link in the load transmission path. Good performance expectations are, however, contingent on appropriate design, quality workmanship and proper maintenance.
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FIRE PROTECTION OF TIMBER STRUCTURES STRENGTHENED WITH FRP MATERIALS

FIRE PROTECTION OF TIMBER STRUCTURES STRENGTHENED WITH FRP MATERIALS

The behavior of wood in the fire conditions is sufficiently theoretically and experimentally described. The fire resistance of unprotected wood element is usually determined by standard procedures pursuant to Eurocodes (EN 1995-1-2) [3], which provide two different methods for determining the fire resistance - method of reduced timber properties in fire conditions and method of reduced (weakened) cross-section as a result of surface charring of the wood element. A tabular (rather conservative) approach is often used in practice for determining a structure's fire resistance [4] b ased on Eurocodes or tabular approach based on the national standards (eg. ČSN 73 0821 ed. 2 [5], ČSN 73 0834 [6]). In case of fire protected timber structures, in particular using external encasing, the limit temperature of layers can be considered 120 °C while the glowing temperature, according to the wood type used ranges from 200 to 300 °C (ČSN 73 0810 [7]).
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Analysis and diagnosis of timber structures in Porto historical centre

Analysis and diagnosis of timber structures in Porto historical centre

Concerning timber structures, this type of buildings presents well defined structural damages. In relation to the timber floors, two main damages can be iden- tified: shear failure at beam extremities in the stone masonry walls, due to the reduction of section from biotic attacks (insects and dry rot fungus) associated to high moisture contents; bending failure at mid-span, originated by the presence of defects, drying cracks, reduction of section due to biotic attacks, excess of load from changes of use, etc. This degradation, asso- ciated to the wood fluency, is often responsible for the excessive deformation of the floors. Besides this defor- mation, the floors can exhibit excessive vibration, normally caused by a deficient transversal bar sys- tem, insufficient beam sections or excessive spacing between beams, etc.
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In situ measured cross section geometry of old timber structures and its influence on structural safety

In situ measured cross section geometry of old timber structures and its influence on structural safety

In general, existing timber construction resorts to simple structural systems, even if complex systems such as intricate spatial trusses or old structures with multiple interventions also exist (Valle et al, 2005). In the case of typical roof truss systems, stresses can be calculated considering linear elastic analysis, based on finite element analysis or the displacement method, due to the simple nature of most timber structures and the quasi-brittle behaviour of timber in tension and unconfined shear (Smith, 1982). Although timber evidences a ductile behaviour in compression, bending failure for lower grade timber is usually brittle (JCSS, 2006) and brittle failure in flexural buckling has also been reported (Pettigrew et al., 2006). In modelling a timber structure, difficulties arise in the definition of the mechanical properties of the material since timber properties vary not only between members of the same structure but also within the same member. Complexity is increased by wood anisotropy and the influence of load duration and moisture content on the behaviour of timber. In existing timber structures, the geometry of the cross section is an important parameter for visual grading (UNI, 2004), since members with irregular cross section and large variability along their length may be found, especially for older structures (Brites, 2011), requiring time consuming in situ measurements. Finally, existing timber structures may also be deteriorated, leading to further difficulties in the assessment of the residual cross section geometry.
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Reliability analysis of a timber truss system subjected to decay

Reliability analysis of a timber truss system subjected to decay

A simplified probabilistic model for the analysis of timber structures was imple- mented, assuming as random variables the cross-section, material properties and loads. The reliability concepts were then applied to a traditional king post truss, leading to the reliability index for a situation of no decay (time = 0), as well as its evolution over time due the effect of decay (for a period of 50 years). The decay was modeled as a reduction of the cross section, being this parameter also considered as a random vari- able. It was found that the coefficient of variation for the decay rate largely influences the estimation of the reliability evolution through time. It was shown that when decay starts (after the incubation period) the probability of failure rises exponentially. Also, it was possible to calibrate the decay model parameters to the study case by consider- ing a target reliability level that seems reasonable according to the observations in real structures. For this case, decay rates of r L = 0.079 mm/year; r T = 0.237 mm/year and
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Numerical analysis of glued laminated timber beams reinforced by Vectran fibers

Numerical analysis of glued laminated timber beams reinforced by Vectran fibers

Historically, wood and wood-based products have been extensively used as engineering material for structural purposes for a long time. However, due to the constant development of new technologies, a new range of possibilities on how to design and build timber structures is available nowadays. New systems such as Medium Density Fiberboard - MDF, Oriented Strand Board - OSB, Glued Laminated Timber - Glulam and more recently Cross Laminated Timber - CLT are currently used and allow the execution of more efficient structures. The production of Glued Laminated Timber, consisting of the association of gluing and laminating wood techniques, started when high resistance adhesives had been produced, Wood Handbook (2010). The higher resistance layers are positioned at the exterior portions of the beam, whereas lower quality layers are positioned closer to the neutral axis, resulting in an increase of strength and stiffness of structural elements, Thelandersson and Larsen (2003).
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Numerical modeling of traditional timber connections

Numerical modeling of traditional timber connections

A research program aimed on investigating the monotonic and cyclic behaviors of traditional timber connections, identifying, and evaluating suitable strengthening techniques with metal devices, was developed by the University of Minho (Portugal) in collaboration with the University of Trento (Italy) and the Timber Structures Division of National Laboratory for Civil Engineering (Portugal). This thesis uses the experimental results obtained in this research to develop a numeric modeling using Finite Element Method for unstrengthened and strengthened traditional timber connections.
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Structural analysis of the timber structure of Ica Cathedral, Peru

Structural analysis of the timber structure of Ica Cathedral, Peru

In literature, engineering methods, which are typically used for the examination and repair of historic timber structures, were presented by Feio (2005). The structural behaviour and the realistic simulation of historical timber structures were discussed by Holzer & Köck (2009), while different authors studied more in detail selected configurations. As a first example, mortise and tenon joints were examined by Bulleit et al. (1999) and design considerations were presented by Schmidt & Daniels (1999). Pegged mortise and tenon joints were investigated by Miller & Schmidt (2004). Experimental and numerical investigations into the rounded dovetail connection and the skew joint can be found in Rautenstrauch et al. (2010) and Tannert et al. (2011). The load–displacement behaviour of halved joints in historical timber structures was examined by Kock & Holzer (2010). Experimental and numerical modelling were carried out for tapered tenon joints to back up the basic understanding of failure modes and strength by Koch et al. (2013). Some research on birdsmouth connections was carried out by Tomasi et al. (2007) and connections in timber roof trusses were investigated by Branco (2008) and Palma et al. (2012).
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Orientador: Professor Doutor Balint Szabó Un iversitatea Tehnică Cluj-Napoca Facultatea de Arhitectură şi Urbanism Co-orientador: Professor Doutor Carlos Chastre Rodrigues Universidade Nova de Lisboa Faculdade de Ciências e Tecnologia

Orientador: Professor Doutor Balint Szabó Un iversitatea Tehnică Cluj-Napoca Facultatea de Arhitectură şi Urbanism Co-orientador: Professor Doutor Carlos Chastre Rodrigues Universidade Nova de Lisboa Faculdade de Ciências e Tecnologia

- In third chapter, procedures to study structures of this category are approached in order to verify its reliability for future use. The Principles for the preservation of historic timber structures (1999) [35] adopted by ICOMOS, ICOMOS CHARTER – principles for analysis, conservation and structural restoration of architectural heritage (2003) [36] and the ISO 13822:2010 Bases for design of structures – Assessment of existing structures [38] are considered. The national annexes from Italy (UNI 11119 [77] and UNI 11138 [78]) and Swiss Norm 269 [52] are analyzed as well. A methodology to approach these historic roof structures based on the standards is proposed. It is presented semi and non-destructive tests that can be completed to better understand the present timber characteristics and deterioration state. Potential reparation or strengthening solutions for the structures are mentioned.
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Mat. Res.  vol.12 número4

Mat. Res. vol.12 número4

Static and cyclic fatigue tests were performed using a DARTEC M1000/RC universal testing machine at the Laboratory of Wood and Timber Structures (LAMEM), São Carlos School of Engineer- ing – EESC, USP, Brazil. To determine the fatigue test parameters, the specimens were loaded to failure, starting from static loads at 0.10 kN/s. To accommodate the specimens, the static tests were carried out in three load cycles, as recommended by the Brazilian standard 5 . Thus, the load applied in first and second cycles represented

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Computational Model for Timber Connections Exposed to High Temperatures Abderrahim Aissa

Computational Model for Timber Connections Exposed to High Temperatures Abderrahim Aissa

Fire safety has always been a major concern in the design of timber construction. Even though wood is a highly combustible material, timber members perform adequately under elevated temperature effects. The thermal response of timber connections, however, is in most cases poor and determination of their fire resistance is usually the crucial factor in evaluating the overall loadbearing capacity of wood structures exposed to fire. The analysis of timber joints under fire conditions can be challenging due to their complexity and variety. After presenting the behaviour of the W-W-W connection with ambient temperature, this chapter reviews the fire performance on this type of connection. The temperature effect is an important factor on the fire resistance of timber connections, which leads to the joint protection, or a redefined size model with non-protected material, [39].
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TECHNICAL PAPER TIMBER BEAM REPAIR BASED ON POLYMER-CEMENTITIOUS BLENDS

TECHNICAL PAPER TIMBER BEAM REPAIR BASED ON POLYMER-CEMENTITIOUS BLENDS

The reinforcement and restoration of timber beams has also been conducted by using laminated composites. A similar research has been carried out on the use of particulate composites and blends for timber repairing proposal. Based on the previous research performed by PANZERA et al. (2010), this study evaluates the physical and mechanical properties of a polymer-cementitious blend manufactured with epoxy polymer and Ordinary Portland Cement (OPC) in order to repair or to reinforce timber beams. A powder pigment was added to the mixture to attain similar aesthetic characteristics of wood beam surface. The effect of the pigment particles into the physical and mechanical properties of the manufactured material was also assessed in this study.
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Local timber firm looking forward to develop on medium term

Local timber firm looking forward to develop on medium term

It has been concluded that a side effect of a bigger production means bigger quantities of wood chips which have to be managed in a most environmentally friendly way. Therefore, the company has to optimize the wood briquettes production and selling process. It has been recommended the selling of the briquettes not only locally, but also in bigger nearby cities like Brasov, Sf.Gheorghe, Miercurea Ciuc, or Onesti because there are potential customers having fireplaces and the briquettes represent a more environmentally friendly and a far easier solution as compared to the using of fire wood. That is why there has been recommended online advertising in the social media and also newsletters about this product for bigger timber wholesale companies in the mentioned cities.
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A CONTRIBUTION TO ASSESS THE STRUCTURAL VULNERABILITY OF TRADITIONAL TIMBER PAVEMENTS

A CONTRIBUTION TO ASSESS THE STRUCTURAL VULNERABILITY OF TRADITIONAL TIMBER PAVEMENTS

3960 EVALUATION OF DAMAGE ACCUMULATION IN HIGH PRESSURE COMPOSITE VESSELS USING FIBER.. OPTIC SENSORS.[r]

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Deformations of Einstein structures

Deformations of Einstein structures

The results in this note give rise to a few basic questions on 2k-Einstein structures that we would like to briefly discuss here. At a more basic level, it would be highly desirable to find geometric conditions on a 2k-Einstein metric in order to have the operator h 7→ ˙ R (2k) g h elliptic. Since in general the first term in the right hand side

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Invited Review Tree legumes: an underexploited resource in warm-climate silvopastures

Invited Review Tree legumes: an underexploited resource in warm-climate silvopastures

Soil erosion is a problem on overgrazed pastures. Intercropping tree legumes might be an option to mitigate soil erosion. Nichols et al. (2001) established N-fixing tree legumes (Inga edulis) intercropped with native timber trees (Terminalia amazonia) on eroded tropical pasture in Costa Rica. They observed that tree legumes rapidly restored the area and there was no need to use N fertilizer. It is important to mention that tree legumes should be combined with grasses and herbaceous legumes in the understory to improve soil cover. Benefits of tree legumes would be mainly towards BNF and reestablishment of nutrient cycling process (Macedo et al., 2008), improving primary productivity of the entire system. Sun et al. (2004) recommended the use of tree hedge legume species along contours to prevent soil erosion on sloping lands in China. Guo et al. (2008), however, indicated that trees might compete with the intercropped species for water and nutrients. Agroforestry combined with grass can be used as buffers to improve water quality in a watershed. Udawatta et al. (2010) tested two agroforestry buffers, two grass buffers, and two controls (no buffers) on water quality of grazed pastures. They observed that on pasture watersheds, the agroforestry and grass buffers reduced runoff and reduced non-point source pollution compared with the control.
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Eutalye tus_ _ tec eticocois

Eutalye tus_ _ tec eticocois

and timber trees, the banana had good yields with low costs.. In the second year of experimentation, the fruit production[r]

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MicroRNA-target binding structures mimic microRNA duplex structures in humans.

MicroRNA-target binding structures mimic microRNA duplex structures in humans.

To study if the distinctive base-pairing distributions of miRNA duplexes and miRNA-target binding structures hold at individual miRNA level, we systematically compared the 17919 pairs of miRNA duplex and miRNA-target binding structure that share a common guide strand. The RNAforester software was applied on the 17919 pairs to obtain the relative similarity score between the two members in each pair. Remarkably, nearly 69% of the pairs (12006/17919) have high similarity scores above 0.7 in a range of 0–1 (Figure 4A). The score cutoff value 0.7 was noted by RNAforester authors to indicate significant structure similarity [38]. In each of the 12006 pairs with high scores, the miRNA duplex structure is similar to its miRNA-target binding structure (Figure 4D, left). A closer way to look at this phenomenon is to individually consider the top 200 guide strands from the selected 321 miRNA duplexes that have the most number of targets, thus they have received the most number of structure similarity scores. Figure 4C reveals that most of their similarity scores are above 0.7 (green color). Among all 249 guide strands of the selected 321 miRNA duplexes that have received more than one similarity scores, 78% have received more scores above 0.7 than below, and only 14% have received more scores below 0.7 than above (Figure 4D, right). This indicates that miRNA-target binding structures generally mimic the associated miRNA duplex structure sharing the same guide strand.
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Matéria (Rio J.)  vol.13 número4

Matéria (Rio J.) vol.13 número4

The synthesis method herein reported allows us to prepare metal nanoparticles with narrow size distributions. The main structures found were fcc-like for pure Pt, decahedral for pure Au, and single and multiple twinned structures for AuPt bimetallic particles. These structures influence the electrocatalytic behavior of MEA like Nafion. Therefore, the efficiency of polymer electrolyte membrane fuel cells (PEMFC) depends on the particle size, composition, and the structure of the electrocatalytic nanomaterials.

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Effects of timber harvest on phlebotomine sand flies (Diptera: Psychodidae) in a production forest: abundance of species on tree trunks and prevalence of trypanosomatids

Effects of timber harvest on phlebotomine sand flies (Diptera: Psychodidae) in a production forest: abundance of species on tree trunks and prevalence of trypanosomatids

The Amazon forest is being exploited for timber production. The harvest removes trees, used by sand flies as resting sites, and decreases the canopy, used as refuges by some hosts. The present study evaluated the impact of the timber harvest, the abundance of sand flies, and their trypanosomatid infection rates before and after selective logging. The study was accomplished in terra-firme production forest in an area of timber harvest, state of Amazonas, Brazil. Sand fly catches were carried out in three areas: one before and after the timber harvest, and two control areas, a nature preservation area and a previously exploited area. The flies were caught by aspiration on tree trunks. Samples of sand flies were dissected for parasitological examination. In the site that suffered a harvest, a larger number of individuals was caught before the selective extraction of timber, showing significant difference in relation to the number of individuals and their flagellate infection rates after the logging. The other two areas did not show differences among their sand fly populations. This fact is suggestive of a fauna sensitive to the environmental alterations associated with selective logging.
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