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Highlights • The maximum forces from calculations based on Eurocode 5 are higher than forces from experiments. • The calculation models correlate well with experiments. • The standard EN 26891 is not convenient for joints with brackets. Abstract The aim of this study is to describe the design of steel angle bracket in timber joints. The design has insufficient support in the existing standards. The load-bearing capacity of these connections can be calculated in accordance with EN 1995-1-1 Eurocode 5, Chapter 8 Connections with metallic fasteners. The main drawback is that this manual only focuses on the metallic fasteners itself. The other disadvantage is that it does not look into the question of stiffness of the joint, its deformation, which is often a problem with these connections. This issue was confirmed by experiments in this study. Eight different angle brackets have been tested in the load direction where the part of the metallic fasteners is stressed in the pull and the second part in the shear. In addition, three different angle brackets were tested in the load direction where all the metallic fasteners are stressed in shear. These experiments were compared with computational models and the calculations according to EC 5. The computational models were performed in software RFEM5. The angle brackets were modeled, nails and wood were replaced by point or flat supports. The results from computational models are comparable to experiments. However, the values given by the calculations according to EC 5 are considerably higher than the real load-bearing capacities obtained from the experiments. Therefore the use of EC 5 for this type of connections can be dangerous in practice. The differences between experiments, models and calculations indicate the difficulty of designing timber joints with three-dimensional nailing plates. [ABSTRACT FROM AUTHOR]

The employment of timber pegs in timber structure joints is a widespread technology in the field of timber frame building in the United States, where the Timber Frame Engineering Council has published a special Standard to supplement the National Design Specification for Wood Construction. The authors have been studying the possibility of supplementing the Eurocode 5 design formulas, thought for timber joints with metal connectors, with specifications needed for a reliable design when employing timber pegs. The field of application envisaged is that of restoring timber structures and results obtained until now are quite encouraging. In this step of the research, more attention has been paid to deformation process: fir and chestnut samples have been tested to determine their dowel-bearing behavior with steel and ash timber peg while double-shear plane joints made of the same wood species, and fastened with steel as well as timber pegs, have been analyzed. [ABSTRACT FROM AUTHOR]

The goal of the work was to evaluate mechanical performance of full-scale timber beams containing scarf joint with a dowel. Work focused on standard testing using modular system to obtain effective stiffness and strength of the beams with and without the joint. The work further researched a contact zone between two timber parts of the joint – at the scarf face. This was carried out using non-destructive optical technique – digital image correlation (DIC) and newly developed algorithm. The joint was made of Norway spruce, dims. 6×0.2×0.24 m and was loaded by two modes: a) 3-point bending and b) 4-point bending. During the loading, a sequence of images was acquired for further investigation of contact zone using the proposed algorithm. The joint with scarf and dowel provided enough effective stiffness, ie. 73–93% for 3-point bending test and 71% for 4-point bending with respect to MOE measured on reference solid beams. Effective strength of the joint was also relatively high and in a range of 55% and 60% with respect to reference solid beams in both 3-point and 4-point bending tests. Contact length differed for loading modes. Mean contact length in symmetrical 4-point bending was about 40%, for asymmetrical 3-point bending test, it was approx. 20% on face closer to support and 44% on a face closer to loads.

Connections are often the weakest link in timber structures so that their failure during fire exposure may result in local or total collapse of a building. The failure modes are complex and poorly understood due to wood's orthotropicity, the temperature and moisture dependency of wood's properties, and the presence of metal fasteners that complicates the stress distribution and changes the process of heat transfer into the timber element. In this study, we investigated the coupled physics of heat and mass transfer in a test specimen made from spruce, with a steel fastener inserted in a pre-drilled hole. It imitates a central slice of a timber-to-timber connection exposed to the elevated temperature of 523 K from one side. The heat induced redistribution of the hygroscopic moisture in wood was quantified and visualized by means of neutron radiography. The temperature gradient was measured inside the specimen, at different distances from the heated surface. As the temperature increased in wood, moisture was displaced downstream of the heat source, resulting in a zone with increased moisture content ahead of the drying front and beneath the steel fastener. This wet front occurred where the temperature was below the water evaporation point. It was shown that the steel fastener affected the transport of heat and moisture within the test specimen. The occurring phenomena during the transient state may play a critical role in the embedment strength of wood and therefore influence the load-carrying capacity of timber connections in fire. [ABSTRACT FROM AUTHOR]

Timber joints used in traditional Japanese constructions have no metal plates or fasteners. Because these joints resist external force by embedment to each member, they show high ductility. The ductile joints get much attention recently. Japanese 'Watari-ago' joint used in horizontal structure is one such ductile joint. The joint consists of two beams with interlocking notches, which build resistance against in-plane shear forces. In this paper, the mechanical behavior of 'Watari-ago' joints is studied experimentally and theoretically. Experimental results show that 'Watari-ago' joints can retain resistance after reaching their yield strength and that mechanical behavior varies depending upon notch shape and size. In theoretical research, a predicting model of mechanical behavior of the joint is developed by applying wooden embedment theory. The model proposed in this study also identifies the size that gives optimal mechanical performance. By numerical calculation on the basis of the model, the authors find it quantitatively that the increase of the sizes of beam width and notch depth has greatly effect on the moment resistance. [ABSTRACT FROM AUTHOR]

Experimental and numerical analysis were performed to investigate the mechanical behavior of a lapped scarf joint with inclined contact faces and wooden dowels which is a commonly used connection for repairing damaged beams in historical structures. This study aimed to define and suggest most effective parameters that influence this particular joint’s performance. Experimental testing was done on the full scale specimens. Four- and two-dowel-joints with half-beam-width laps and with 3/8-beam-width laps were tested. Experimental data analysis concluded that the width of the lap element should be kept as half of the beam width, therefore this type of joint was further analyzed using numerical approach. Finite element models were constructed for joints with four, two, and three wooden dowels. These models and theoretical criterion according to EC5 were used to select a number of dowels used for connection, joint’s length and location. It was concluded that a lapped scarf joint with 3 wooden dowels that is 1.38 m long and located at 1/5 L from support is the most efficient joint (in terms of strength, stiffness, and manufacturing) for the beam-end reparation; however, location of joint must consider both preservation of the most of the original material and the extent of damage. Numerical model can be used for designing joints with different parameters in beams with different dimensions. It was also calculated that a jointed beam provides between 65% and 75% of the original beams’ strength while the linear stiffness is not influenced significantly. [ABSTRACT FROM AUTHOR]

A new shear connection system was tested in order to be used in off-site manufactured cassette floor elements made with glulam beams and cross laminated timber (CLT) panels. This type of floor element can present advantages from weight, structural and assembly point of view in multi-storey timber construction. The shear connection proposed is made of double-sided punched metal plate fasteners, connecting CLT and glulam members to form a T-cross-section. Inclined screws are used in combination with the double-sided nail plates to secure the shear connection. Shear test results are presented and compared with a simple calculation model for estimating the mean load-carrying capacity and stiffness of the combined joint according to methods available in the literature. [ABSTRACT FROM AUTHOR]

The research deals with a 49.0mm in diameter mechanical fastener to which load perpendicular to grain is applied. The experimental research was divided in two series: the first series was carried out with locally reinforced, and the second with non-reinforced timber specimens. The local reinforcement of timber elements with textile sheets between lamellas in a layer of adhesive was made in the production process. Furthermore, research on finite element models using Abaqus/CEA software package was carried out. UMAT subroutine and cohesive contact between surfaces were used for modelling complex timber mechanical properties and cracks opening. The research results have shown that glass fiber textile placed between lamellas in adhesive layer effectively increases the resistance and splitting capacity of timber joint. Analytical approach has been proposed for predicting the splitting capacity of the reinforced joint. [ABSTRACT FROM AUTHOR]

The article discusses the main methods for steel threaded rods pasted into timber. Single – threaded steel rod carrying capacity glued onto glulam (timber cross section – 100 x 100 mm, threaded rod – M12 and M16) has been experimentally determined. Behaviour based on the experimental results of two different methods for pasting rods into timber has been summarized: the first threaded steel rod was glued into 4 mm bigger diameter hole while the second – rod chased into 2 mm smaller diameter hole. The conducted experiment used 800 mm length glulam beams; threaded steel rods were glued to both ends of specimens (equal theoretical carrying capacity). The experiment in the tension of both ends was carried out. The obtained results were compared with theoretical expressions submitted in EC 5 – 1 – 1:2005 and STR 2.05.07:2005. The main dependences of geometrical parameters and carrying capacity have been provided. The main collapse forms of specimens and manufacturing defects having influence on the final carrying capacity and behaviour of the joint have been observed. Using the first method, a failure in the pasted rod occurs suddenly when timber splits along the fibre; in the second case, a failure is plastic when timber is compressed under thread. Additional experiments must be carried out using the first technology increasing the class of the strength of the pasted rod as under the maximum length of paste, in all cases, failure in the pasted rod occurred when a steel bar cracked. Along with an increase in the diameter of the rod, the dispersion of the results of the affixed slender part is increasing. Maximum variation in the results of applying the first method is 10%, whereas the second method of attaching makes 50%. Compared to the first method of attaching, the results of theoretical bearing capacity indicate that tests have an adequate margin which is equal to or is more than 2,0. A comparison of the second method of attaching results to theoretical bearing capacity makes clear that the experimental results of the tests have too low safety factor and in some cases are less than 1.0. This is due to the fact that the counting of attaching technology in some cases must be based on local compressed timber strength. The experimental study of two different methods for attaching steel bars reveals that the first method can be used in design practice considering both documents STR 2.05.07:2005 and EC 5-1-1:2005. The second method of attaching must be developed to ensure smooth rod surface coating adhesive. Attaching the second method should also be created in the exact form corresponding to the disintegration of the calculation model. Jungties tarp įklijuoto plieninio sriegtojo strypo ir medienos elgsenos tyrimas Santrauka Straipsnyje aptariami pagrindiniai plieninių sriegtųjų strypų įklijavimo medienoje metodai. Eksperimentais nustatytos pavienių plieninių sriegtųjų strypų (M12 ir M16), įklijuotų medienoje, jungčių laikomosios galios. Apibendrinta dviejų skirtingų įklijavimo metodų (pirmasis – strypas įklijuojamas į 4 mm didesnio skersmens kiaurymę; antrasis – strypas įsriegiamas į 2 mm mažesnio nei strypas skersmens kiaurymę) elgsena remiantis eksperimentinių tyrimų rezultatais. Pagrindiniam eksperimentui naudoti klijuotosios medienos elementai (skerspjūvio matmenys – 100×100, ilgis – 800 mm), kurių galuose lygiagrečiai su medienos pluoštu buvo įklijuoti sriegtieji plieniniai strypai. Atliktas abipusis tempimo bandymas apkrovą perduodant strypams. Eksperimentinių tyrimų rezultatai lyginami su teorinės laikomosios galios skaičiavimais, atliktais pagal Lietuvos ir Europos medinių konstrukcijų projektavimo normų taisykles. Pateiktos jungties laikomosios galios ir geometrinių parametrų priklausomybės. Aptartos pagrindinės bandinių suirimo formos ir gamybos netikslumai, turėję įtakos jungties laikomajai galiai. First Published Online: 16 May 2013 Reikšminiai žodžiai: medienoje įklijuoti strypai, įtempių pasiskirstymas medienoje, medienos jungtis.

The effects of pretension in bolts on hysteretic response of timber joints exposed to a bending had been reported by the authors, but the cyclic tests were carried out at small displacement level which might not be applicable for earthquake-resistance design. In this study, similar cyclic tests but at large displacement levels were conducted. Beam to column timber joints with steel side plates were fabricated and continuously loaded until failure. At connection, the bolts were pretension in four different magnitudes: 0 kN, 5 kN, 10 kN and 15 kN. The results showed that frictional action between the steel side plates and wood member as a result of bolt pretensioning significantly increased the (frictional) hysteretic damping and the equivalent viscous damping ratio. It is obvious from the test results that the pretension force in bolts has no influence on the maximum joint resistance but decreases the joint rotational deformation. [ABSTRACT FROM AUTHOR]

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Abstract: We present a new and alternative proposition for the traditional Asian timber column-and-beam connection, using the Kusabi–Nageshi (K–N) joint system. The mechanical behaviour is complex and relies on the embedment strength of the timber, pre-stress, friction, and elastic energy storage. Using a systematic comparative analysis, the advantages of the K–N joint over more traditional joints can be made clear. The comparison of the hysteresis from cyclic loaded cross-joint tests with varied pre-stress clarifies the enhanced mechanical behaviour of the K–N joint system. [Copyright &y& Elsevier]

Abstract: The behaviour of dowel-type steel-to-timber joints loaded in tension perpendicular to grain is analyzed experimentally and numerically. Two main types of failures are observed in the experiments such as wood splitting and embedding. The experimental results are used to validate a three-dimensional (3D) non-linear finite element model. The non-linear model uses the Hill criterion to control the plastic yielding of wood material. The Hoffman failure criterion, controlling the damage evolution in wood, is used to take into account the brittle failure in shear and tension perpendicular to grain. The comparison with experimental results shows that the numerical results are in good agreement with them. The validated model is used to investigate the effect of some influential parameters on the splitting strength of the joints loaded in tension perpendicular to grain. Besides, the splitting strengths given by the numerical model are used to evaluate the accuracy of some analytical formulae available in the literature. [Copyright &y& Elsevier]

Abstract: Dieh–Dou timber structures are commonly used as a traditional temple in Taiwan, which is located in a highly seismic area. In order to understand the not well-known behaviour of these historic timber buildings under earthquake, a preliminary FE linear analysis was performed showing that the stiffness of the timber joints is important in changing the magnitude of the overall displacement of the building. Ten laboratory tests on the set joints showed that their rotational stiffness depends on the vertical load applied to the joint while the translational stiffness is not affected by the vertical load applied, but the pull-out resistance is highly dependant on the accurateness of the connection. Inserting the appropriate values of stiffness into a refined FE model for three different frames, it is shown that the resulting displacements and stresses in the elements are in line with the failures observed after the 1999 Chi–Chi earthquake, confirming that a FE modelling can be used to assess the ultimate capacity of these historic buildings. As a further refinement, the use of a step-by-step nonlinear analysis will allow taking into account the global reduction of stiffness of the building due to the horizontal elements that reach the pull-out limit and ultimately lead to an accurate evaluation procedure for each typology. [Copyright &y& Elsevier]