•The thicker the CLT panel is, the lower its bending and rolling shear strength.•Rolling shear strength values for Sitka spruce of 1.0–2.0N/mm2.•‘Global’ deformation results closely match theoretical ...stiffness.•Cross-lamination provides no strengthening effect for in-plane bending behaviour.
An investigation was carried out on CLT panels made from Sitka spruce in order to establish the effect of the thickness of CLT panels on the bending stiffness and strength and the rolling shear. Bending and shear tests on 3-layer and 5-layer panels were performed with loading in the out-of-plane and in-plane directions. ‘Global’ stiffness measurements were found to correlate well with theoretical values. Based on the results, there was a general tendency that both the bending strength and rolling shear decreased with panel thickness. Mean values for rolling shear ranged from 1.0N/mm2 to 2.0N/mm2.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Review of typical materials, cross sections and forms of timber beams.•Description of general failure modes and their possible causes.•State of the art of established retrofitting and reinforcement ...techniques.•Discussion of case studies for reinforcement techniques.
Highly loaded and large span timber beams are often used for halls, public buildings or bridges. Reinforcement of beams may be required to extend the life of the structure, due to deterioration or damage to the material/product or change of use. The paper summarises methods to repair or enhance the structural performance of timber beams. The main materials/products cross sections and geometries used for timber beam are presented. Furthermore, their general failure modes are described and typical retrofitting and reinforcement techniques are given. The techniques include wood to wood replacements, use of mechanical fasteners and additional strengthening materials/products.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•The failure behaviour of wall-floor connections in C16 CLT has been examined.•Connection strength increases with increasing fastener length.•Connection ductility generally decreased with increasing ...fastener length.•EC5 analytical connection stiffness is non-conservative for C16 CLT.•Recommendations for overstrength and strength degradation factors are presented.
An investigation was carried out to examine the influence of the fastener length on the elastic and ductile failure behaviour of typical steel-to-timber bracket connections in Cross Laminated Timber (CLT) manufactured from C16 spruce. The behaviour of single screw-type fasteners within CLT of length 25 mm, 50 mm and 75 mm are examined under tension and shear loading. Multiple screw-type fasteners have been utilised to examine monotonic and cyclic behaviour of steel bracket-fastened CLT connections under shear and tension loading. Characteristic values of the experimental results are compared to analytical models from current timber design codes and the literature. The length of fastener has been shown to influence the failure strength and ductility of the connection. The overstrength factors and strength degradation factors have been shown to be similar, regardless of fastener length, and conservative values are recommended.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Key message
Thinning affects negatively the quality of sawn timber of Douglas fir, Norway spruce, and Sitka spruce. The effect was confirmed in structural-sized boards and small clear samples, and on ...standing trees using longitudinal velocity. The loss of quality across the three species due to thinning rarely exceeds 20% and is in most cases smaller than 5%.
Context
The relationship between silvicultural management and the quality of timber produced is not entirely elucidated.
Aims
The effects of thinning on structural grade-determining properties of wood (elastic modulus, bending strength and density) were studied on Douglas fir (
Pseudotsuga menziesii
(Mirb.) Franco), Norway spruce (
Picea abies
(L.) H. Karst), and Sitka spruce (
Picea sitchensis
(Bong.) Carr)).
Methods
Acoustic velocity was measured in a total of 487 trees and their crown social status was recorded. Sixty trees were selected and cut into structural-sized boards (
N
= 1343). The amount of knots in each board was quantified using the grading machine GoldenEye702. All boards were destructively tested in four-point bending, after which a small clear specimen was cut from each board and again tested in bending (
N
= 1303). Specific stiffness and specific strength were used to estimate the size of the effect accounting for differing influence of thinning across the before-mentioned properties.
Results
Thinning reduces all three properties with the likelihood and magnitude of the effect varying between species. The loss of quality due to thinning rarely exceeds 20% and is in most cases smaller than 5%. The effect of thinning and its size were also confirmed on the full sample of trees by using longitudinal velocity.
Conclusion
The results give a clearer idea of what the trade-offs are between timber quality and silvicultural management.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•A method to assess thermal bridging heat loss using the outdoor ITT is developed.•The ITT approach is compared with hot box measurements and numerical predictions.•The wind velocity impact on ...thermal bridging is quantified.•Adjusting procedure for the Ψ-value measured at different wind velocities is developed.•This procedure allows measured and standard Ψ-value comparison.
Improving the thermal performance of the existing building stock is essential to significantly reduce the overall energy consumption in the building sector. A key objective is the retrofitting of the existing building envelope. A necessary first step in the building envelope optimization process is the assessment of its actual thermal performance. This assessment should be repeated after retrofitting to clearly define the improvements that were made and the heat loss reduction that was achieved. In this study, an efficient, non-destructive, in-situ measurement method, based on an outdoor infrared thermographic survey, is developed to determine the thermal bridging performance. As wind velocity significantly influences the heat losses through the building envelope, this study includes quantification of the wind velocity impact on the Ψ-value. This was assessed by undertaking ITT of the same thermal bridge at various wind velocities, in a controlled environment, in a hot box device. The results showed that the Ψ-value is highly dependent on wind velocity so that measurement of the Ψ-value taken at different wind conditions cannot be directly compared. An adjustment procedure is proposed that can be used to convert the Ψ-value measured at any wind velocity to a standard value corresponding to a velocity of 4m/s. From a practical point of view, this adjustment procedure makes the methodology widely applicable.
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6.
FRP reinforcement of timber structures Schober, Kay-Uwe; Harte, Annette M.; Kliger, Robert ...
Construction & building materials,
10/2015, Volume:
97
Journal Article
Peer reviewed
Open access
•Two-part, cold-cure epoxy adhesives are most suitable for on-site bonding.•Careful surface preparation is essential.•Design approaches for flexural and shear strengthening of timber beams are ...presented.•Practical guidelines for on-site bonding are given.•Approaches to bondline delamination modeling is described.
Timber engineering has advanced over recent decades to offer an alternative to traditional materials and methods. The bonding of fibre reinforced plastics (FRP) with adhesives to timber structures for repair and strengthening has many advantages. However, the lack of established design rules has strongly restrained the use of FRP strengthening in many situations, where these could be a preferable option to most traditional techniques. A significant body of research has been carried out in recent years on the performance of FRP reinforced timber and engineered wood products. This paper gives a State of the Art summary of material formulations, application areas, design approaches and quality control issues for practical engineers to introduce on-site bonding of FRP to timber as a new way in design for structural repair and rehabilitation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Quantitative ITT methodology to obtain the thermal bridge heat flow rate in buildings presented.•Methodology suitable for determining Ψ-values of any existing building envelope.•Excellent agreement ...found while testing the methodology in the hot box device.•Relative deviation in Ψ-values from ITT and from hot box measurements varied from −5% to −36%.
A key aspect in assessing the thermal standard of building envelopes is the quantification of the heat loss though thermal bridging, which can be expressed in terms of the linear thermal transmittance Ψ. Values of Ψ may be obtained from tabulated values for standard building details, from numerical modelling or from measurement. Where the internal structure of the building envelope is unknown, which is very often the case, measurement is the only option. This study shows how the infrared thermography technique (ITT) can be used as a non-invasive and easy-to-use method to provide quantitative measures of the actual thermal bridging performance. The novelty of this approach includes evaluation of the actual heat flow rate caused by thermal bridge qTB and Ψ-value by means of the ITT solely, without any supporting methods. Another important aspect of the methodology is that it accounts for the correlation between the surface temperature and the convective and radiative heat transfer coefficients. Values for these coefficients are assessed for the whole range of the surface temperatures recorded on the thermogram resulting in improve accuracy. The qTB and Ψ-value calculated using the presented methodology fully mirrors the real thermal performance of the thermal bridge. The methodology has been tested under laboratory conditions in a steady state in a hot box with excellent agreement.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Using infrared thermography, multiple thermal bridging heat loss can be easily estimated.•Installed window heat loss assessed by infrared thermography.•Results validated with hot box ...measurements.•Thermographic analysis results in good agreement with FE heat transfer and CFD simulations.
A major contribution to the global trend in reducing energy consumption can be made by improving the thermal performance of buildings. Minimization of heat loss via the building envelope is key to maximizing building energy efficiency. The building envelope contains different types of thermal bridging that must be accounted for while assessing the overall building envelope thermal performance. Multiple thermal bridges commonly occur and the distance between them determines the degree to which they interact thermally. To avoid overestimation of the linear thermal transmittance, it is important to account for interaction effects. Complex multiple thermal bridging occurs in window systems. The thermal performance of windows depends not only on the window performance itself but also on its installation into the wall. This study demonstrates an application of the quantitative infrared thermography technique to evaluate the heat lost via multiple thermal bridging. It is shown that using this methodology, the heat loss via multiple thermal bridges can be easily estimated in an existing building envelope, without any knowledge of its internal structure or material properties. For windows, it is demonstrated that jointly assessing the additional heat loss through the window and due to the installation of the window into the wall is a practical way to determine the actual heat loss caused by the presence of a window. A window thermal transmittance or M-value is introduced to quantify the total additional heat loss through the building element due to the presence of the window. The methodology was validated against experimental measurements taken on different specimens in a hot box device. Results from the thermographic analysis also co-related well with results from finite element heat transfer and computational fluid dynamics simulations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Compressed wood (CW) connectors have been used in timber moment connections.•Moment-rotation behaviour of CW fastened beam-beam connections has been evaluated.•Effect of connection parameters on ...capacity and stiffness has been examined.•Design procedures for timber-CW connections are presented.•Capacity of timber-CW connections can be conservatively predicted using EC 5 rules.
The widespread use of energy-intensive metallic connectors and synthetic adhesives in modern timber construction has negative implications for the end-of-life disposal or re-use of the structural timber components. Therefore, it is favourable to substitute metallic connectors and synthetic adhesives with bio-based alternatives such as wood-based connectors. Recent studies have shown that densified or compressed wood (CW) with superior mechanical properties could be suitable for the manufacture of wood-based connectors in the form of CW dowels and CW plates. This study experimentally examines the moment-rotation behaviour of semi-rigid type timber-CW beam-beam connections under pure bending. The study also assesses the suitability of current design rules to predict the moment capacity of timber-CW connections. The comparative study has shown that the moment capacity of the timber-CW connection can be conservatively predicted from the characteristic load-carrying capacity of the connections calculated using the EC 5 strength equations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A significant reduction in total creep deflection is observed in FRP reinforced beams.•Reduction in total creep strain observed on the tension face due to FRP reinforcement.•Reduced creep deflection ...cannot be attributed to reduced mechano-sorptive creep behaviour.•The restrained hygro-mechanical behaviour results in reduced creep deflection.
The use of Fibre Reinforced Polymer (FRP) reinforcement has been shown to improve the short-term flexural behaviour of timber elements. This is particularly important when reinforced elements are subjected to a variable climate condition, which is known to accelerate long-term or creep behaviour. In this paper, both unreinforced and Basalt FRP reinforced beams are subjected to creep tests at a common maximum compressive stress of 8 MPa over a 75-week period. Results demonstrated a significant reduction in total creep deflection due to the FRP reinforcement. Using matched groups, experimentally measured total strain behaviour is decomposed into the elastic, viscoelastic, mechano-sorptive and swelling/shrinkage strain components. Analysis has shown that the mechano-sorptive component is similar in unreinforced and reinforced beams. The reduction in creep behaviour of the reinforced members was primarily due to the restrained swelling/shrinkage response of the reinforced beams and was independent of the mechano-sorptive effect. This finding demonstrates the positive influence of FRP reinforcement on the long-term behaviour of timber elements and indicates a potential to describe the long-term deflection performance of FRP reinforced elements from short-term swelling/shrinkage tests.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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