Search

This paper investigates the feasibility of employing timber pegged joints in modern seismic-resistant structures or for retrofitting existing structures. The behavior of timber pegged connections has been investigated for about twenty years, but seismic design aspects are not treated in existing standards. In the framework of the force-based design approach, this paper analyzes and defines seismic design aspects and rules for timber pegged connections that are easy-to-use in engineering practice. A large database (more than 350 test results) has been elaborated and the data processed with the purpose of (1) analyzing the effectiveness of the European Yield Model for evaluating the maximum strength of the connection, accounting for the particular embedding behavior due to the presence of timber peg; (2) assessing and defining the capacity design rules to design the dissipative regions (i.e., overstrength factor); and (3) defining the available ductility of the connection with identification of ductility class intervals. The obtained results proved that timber pegged joints have a good potential to be used in seismic-resistant structures. In fact, data processing identified a suitable value for the overstrength factor (useful to project the joint with the capacity design) similar to that used for steel-dowelled connections, and defined a likelihood range of ductility classes. Finally, it is highlighted that the European Yield Model can be a practical tool to calculate connection strength, provided that some modifications are included to consider peg behavior.

International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies, 12, 9, 12A9C: 1-8

In the field of timber engineering, adhesive bonding remains a promising, though poorly developed, joining technique that may increase the structural stiffness and capacity of timber joints and structures. Selecting ductile adhesives may further allow to conceive ductile joints, which can compensate for the missing material ductility of timber. To demonstrate the potential of this approach, adhesively bonded double-lap timber joints were manufactured using a ductile acrylic adhesive and then subjected to axial tension and compression. The load–displacement responses were captured and compared to those of the same joints composed of a brittle epoxy adhesive. The effect of the different adhesives on the joint ductility has been studied and quantified.

Large span timber trusses are usually built with glulam. One problem with large span glulam trusses is that the connections needed to transfer the load between truss members are often complex and expensive. Another issue is transportation. Building large span trusses out of structural timber instead, could be a way of simplifying the connections and at the same time increase the degree of on-site construction and thereby solving the transportation problem.In this study, a total of 18 laboratory tests were performed with the purpose of investigating the tensile strength and the load slip behavior of different connection designs for large span structural timber trusses. Six different test groups corresponding to six different connection designs were tested. The materials used include members made of C24 timber and gusset plates made of birch plywood, aluminum, and steel. Screws were used as fasteners for five test groups and adhesive was used for one group. The influence of different reinforcement techniques including reinforcement screws and added aluminum sheets was studied.The results showed a ductile failure behavior for all test groups except for the group where adhesive was used. However, a decrease of ductility was observed for groups were aluminum sheets were used on the outsides of the mid placed plywood gusset plate. A 12-17 % increase in capacity was observed due to the presence of aluminum sheets. The reinforcement screws had no significant effect on the capacity. However, the presence of reinforcement screws did lead to a reduction in scatter both regarding capacity and stiffness.

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.

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.

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.

The research deals with a 49.0 mm 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.

Timber is one of the primary building materials of today, both in Sweden and in Europe, its uses range from single-family homes to apartment buildings and large arenas. The key reasons why timber construction continues to grow is the environmental aspects combined with the economically advantageous industrialised prefabrication process. One of the most commonly used connections in timber structures is the punched metal plate fastener, which is a perfect example of an effective connection that only can be used in a prefabrication process. It can be found in almost all kinds of buildings; from a rafter connection in small to middle sized houses up to reinforcement in heavier connections in arenas and warehouses. It is well known that the connections are the most critical parts of a structure and it is therefore crucial that these are designed for all eventualities. This project is a pilot study that seeks to evaluate the existing design methods for punched metal plate fasteners subjected to fire in Eurocode and in practice. The first conclusion is that such a method hardly exists, neither in codes nor in scientific theory, despite the fact that this is and has for decades been a very common structural detail. The theoretical analysis shows that it is very unlikely that a joint made with punched metal plate fasteners can withstand a standard fire scenario for even 15 minutes and the small-scale testing confirms this. But the project also shows that it is possible to protect the punched metal plate fasteners from fire and that it is possible to achieve up to 30 minutes resistance by installing gypsum fireboards, stone wool wood covering. Validerat; 20121013 (anonymous)

The use of timber pins in connecting timber elements is a valid alternative to the employment of metallic devices, and apart from being quite spread in prefabricated timber frames, it could be an efficient solution in the field of restoring timber structures. The design rules for pinned joints are universally based on Johansen’s theory, (European Yield Model), but their application to timber pegged connections still shows some unsolved problems, linked to: 1) dowel-bearing strength; 2) bending strength of the pin; 3) shear strength of the pin; 4) the feasibility of the fourth failure Mode of EYM. Many studies analysing one or more of those aspects can be found in literature, but there isn’t yet an analytical formulation alternative to this on which the EYM is based. Authors are carrying on an extended experimental research, trying to better understand the complex mode of failure of timber joints connected by timber pegs, and consequently improving design rules. A first phase has involved double shear plane joints of glulam fir connected by ash pins, varying thickness of jointed board, pointing out the role of bending strength. In a second step the role of dowel-bearing strength has been investigated, choosing as base material three wood essences with quite different densities. Now the final step of the whole research is presented: first of all, the role of pin shear strength has been studied; then all obtained results are employed in analyzing the behaviour of double shear plane joints with varying timber essences and its transposition in using design rules.

The paper presents the development of numerical modeling for a traditional dovetail timber joint. The objective is to find the influence of its geometrical properties on the mechanical stiffness of the joint as well as to assess the main problems and limitations faced during the numerical modeling of the structure. An experiment with a replicated timber joint was used to validate the model. Material properties were ascertained and contact adjustment was made. Parametric study was performed: two angles of the joint beams were varied. Suitable ranges of the angles for each type of loading were found. Main limitations and problems present in the modeling are depicted in the discussion.

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. Article in Lithuanian. 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. Reikšminiai žodžiai: medienoje įklijuoti strypai, įtempių pasiskirstymas medienoje, medienos jungtis. First Published Online: 16 May 2013

This study is part of a larger research devoted to the analysis of the behavior of timber joints connected with timber pins, which of course is quite different from that in presence of steel bolts. As in the last case design formulas are based on the Yield European Model, which involves mechanical characteristics of the dowel as well as of the timber elements constituting the joint, the whole research aims to the identification of similar properties in the case in hand. Specifically the present study analyzes, with an experimental approach, the dowel-bearing behavior when employing a timber pin instead of a steel connecting device. The final task is the definition of a procedure to identify the value of the dowel-bearing strength of the jointed elements' timber to be inserted in design formulas, going through the understanding of the role of the timber pin behavior when confined inside the joint and its influence on the dowel-bearing behavior.

Baigiamajame magistro darbe pateiktos pagrindinės prielaidos, kurios priimamos analizuojant klijų kontaktą tarp medienos ir metalo. Aptartos plačiausiai taikomos plieninių sriegtų strypų įklijavimo medienoje technologijos. Apibendrinti plieninių sriegtų strypų įklijavimo medienoje technologijos kontrolės metodai. Išanalizuota mokslinė literatūra, susijusi su plieninių sriegtų strypų įklijavimu medienoje. Tiriamojoje dalyje surasti ir išnagrinėti Pasaulinės patentų sistemos „esp@cenet“ 11 patentų, kuriuose pateikiami montažiniai medienos elementų mazgai, sukonstruoti panaudojant plieninius įklijuojamus strypus. Pateikti pagrindiniai standžių montuojamųjų mazgų konstravimo principai. Eksperimentinėje dalyje laboratoriniais bandymais ištirta sąveika tarp medienos ir plieninio sriegto strypo, kai kontaktas tarp jų užtikrinamas klijais. Atlikti eksperimentiniai tyrimai: plieninių sriegtų strypų takumo bei stiprumo įtempių nustatymas; medienos tankio ir drėgnio nustatymas; plieninių sriegtų strypų ištraukiamojo atspario nustatymas. Aptarti pagrindiniai gamybos netikslumai, kurie turi įtakos jungties elgsenai ir laikomajai galiai. Išanalizuota pavienio plieninio strypo, įklijuoto medienoje, gniuždomojo ir tempiamojo atspario skaičiavimo metodika, pateikiama projektavimo normose STR ir Eurokode 5. Bandymų rezultatai palyginti su teorinėmis išraiškomis, pateikiamomis projektavimo normose. Remiantis eksperimentinių bandymų rezultatais ir ankstesnių autorių tyrimų... [toliau žr. visą tekstą] In this master degree thesis submitted general assumtions which are being adopted while analysis of glued joint between timber and steel. Discussed the main technologies of glueing in steel rod into timber. Summarized technolgy control methods of glueing in steel rods process. Overviewed the scientific literature which is related to the steel rods glued in timber. In research part of the work submitted 11 patents of esp@cenet patent base of rigid joints in which construction used glued in steel rods. Given the main principles of construction of rigid joints with glued in steel rods. In experimental part of the work investigated the behavior of the timber – steel joint which contact is ensured by glue. Experimental studies were done: yield and strength stress determination of threaded steel rods; determination tests of timber moisture content and density; determination of tensile carrying capacity of threaded steel rod glued in glulam. Reported production inaccuracies and its influence on joint‘s behavior and final carrying capacity. The results are compared with theoretical expressions provided by the design rules. Based on the experimental results of the test and study reports of previous authors, submitted proposals for design rules of the addition of comments. Structure: introduction, the concept of the matter, literature review, experimental studies, conclusions and suggestions, references. Thesis consist of: 100 p. text without appendixes, 64 pictures, 20 tables, 43... [to full text]