Full scale testing of timber-concrete composite floors in an overhanging configuration
Estévez-Cimadevila, J.; Suárez Riestra, F.; Martín-Gutiérrez, E.; Otero-Chans, D.
Engineering Structures
Volume 291, Article ID 116460. 12 pages
doi: 10.1016/j.engstruct.2023.116460
June 2023 | ISSN 0141-0296
Abstract
The behavior of timber-concrete composite floors in an overhanging configuration has been analysed. The floor consisted of a prefabricated T-shape piece formed by a glulam flange glued to a plywood rib and connected to an upper concrete slab poured in situ. The connection between both materials is achieved by penetrating the concrete into the holes made in the rib. Three-point bending tests were performed with a total of 8 specimens with depth of 25, 30 and 35 cm and overhanging length of 1.50, 1.80 and 2.10 m, respectively. That means a length-to-depth ratio equal to 6 in all cases. The experimental results showed that the lowest ultimate load value obtained was 8.03 and 5.55 times higher than the estimated service load for a building with residential use (5 kN/m2) and public use (9 kN/m2), respectively. Two types of failure were observed after a marked cracking process in the concrete as the ultimate load value was approached: tensile failure affecting the plywood rib and shear failure at the glulam flange-plywood rib connection. The maximum deflection for the total load was between 1/358 and 1/523 of the overhanging span for the estimated loads for a residential use building (5 kN/m2), and between 1/266 and 1/390 for public use buildings (9 kN/m2). Regarding to vibrations, floors in an overhanging configuration with a length-to-depth ratio equal to 6 and a simply supported portion equal to four times the length of the overhanging portion, with total loads up to 9.0 kN/m2, both in multi-storey buildings for residential and office use, present a high comfort level. Consequently, the proposed timber-concrete composite (TCC) overhanging floor solution has demonstrated high stiffness and strength that make it a suitable alternative for the construction of high-performance lightweight floors in multi-storey buildings.

Flexural behaviour of a new timber-concrete composite structural flooring system. Full scale testing
Martín-Gutiérrez, E.; Estévez-Cimadevila, J.; Suárez Riestra, F.; Otero-Chans, D.
Journal of Building Engineering
Volume 64, Article ID 105606. 19 pages
doi: 10.1016/j.jobe.2022.105606
April 2023 | ISSN 2352-7102
Abstract
Timber-concrete composite systems are a high-performance alternative for building floors, of great interest in the current context of environmental concerns. Looking for a more eco-friendly solution, the paper presents a new flooring system with a wood-concrete connection that does not require adhesives or special metal elements. Four-point bending tests were performed on TCC flooring samples with a span of 6.0, 7.2 and 8.4 m. Its cross section was a prefabricated piece in the shape of an inverted T made up of a lower glulam flange, glued together with a central plywood rib with aligned holes in its upper part that go through the entire thickness of the plywood. The set was completed with a top layer of poured-in-place concrete. The connection between both materials is achieved by penetrating the concrete into the rib holes. Additionally, corrugated steel bars were placed through said holes to achieve ductile behaviour. In all cases, a slenderness ratio of L/24 was used. The experimental results showed that the lowest value of ultimate load obtained was 4.3 times higher than the total service load estimated for a building for public use (9 kN/m2). The maximum deflection of the total load was between L/573 and L/709 for the loads corresponding to a building for public use (9 kN/m2) and between L/1069 and L/1340 for the case of residential type building (5 kN/m2). An analysis of the effects of vibrations in the service limit state in relation to user comfort has been included. The results indicate that the system satisfies the requirements for the intended uses.
Consequently, the proposed solution shows its effectiveness both in terms of strength and stiffness for the construction of light floors, being easy to build and having high performance.

Timber-Timber-Composite (TTC) beam long-term behaviour. Full scale experimental campaign and simplified analytical model
Suárez Riestra, F.; Estévez-Cimadevila, J.; Martín-Gutiérrez, E.; Otero-Chans, D.
Construction and Building Materials
Volume 326, Article ID 129649. 14 pages
doi: 10.1016/j.conbuildmat.2022.129649
December 2022 | ISSN 0950-0618
Abstract
The variability of the physical and mechanical properties of wood requires that the analysis of its long-term behavior take into account all the factors capable of modifying these properties. The environmental conditions of humidity and temperature are factors that alter these properties, conditioning long-term behavior, a situation that is especially decisive in the case of structural elements in bending. The design standards establish simple corrective factors based on the type of environmental exposure that allow creep deformation to be estimated in a final stage from an initial instantaneous deformation value. A new analytical model is proposed that allows estimating the behavior at any stage from the knowledge of the environmental conditions to which the structural element has been subjected. The model is applied to different elements in various environments, from camera control situations to outdoor situations of 3-year seasonal cycles. In all cases, the precision of the model and the simplicity of its use are verified due to the basic factors on which it is based.

Perforated board shear connector for timber-concrete-composites
Otero-Chans, D.; Estévez-Cimadevila, J.; Suárez Riestra, F.; Martín-Gutiérrez, E.
Wood Material Science & Engineering
Volume 17. 14 pages
doi: 10.1080/17480272.2022.2089594
June 2022 | ISSN 1748-0272
Abstract
Timber-concrete-composite systems offer major structural advantages, as well as additional benefits in terms of sustainability in comparison with only-timber or only-concrete solutions in building work. This paper describes the behaviour of shear connections for a new and simple construction system. It is based on the transmission of shear forces between the two layers of the system through perforations in the wooden boards, without the necessary collaboration for additional connecting elements (fasteners, adhesive or notches). Tests were performed to analyse how the behaviour of the shear connectors was affected by the arrangement of the boards (single or separated), the type and distribution of the perforations and the use of slab reinforcement. The experimental results indicate that this solution has high strength values, with very high service stiffness and ductile failure when at ultimate state, which enables a high level of composite action for connection design. The stiffness coefficient varies from 283.5 to 887.7 kN/mm per meter. The test pieces with separated boards and reinforcement bars showed the best results, regardless of the size and arrangement of the holes in the boards.

Timber-concrete composite structural flooring system
Estévez-Cimadevila, J.; Martín-Gutiérrez, E.; Otero-Chans, D.; Vázquez Rodríguez, J.A.
Journal of Building Engineering
Volume 49. Article ID 104278, 16 pages
doi: 10.1016/j.jobe.2022.104078
January 2022 | ISSN 2352-7102
Abstract
An integrated solution is presented for the execution of building structures using timber-concrete composite (TCC) sections that make efficient use of the mechanical properties of both materials. The system integrates flooring and shaped prefabricated beams composed of a lower flange of glued laminated timber (GLT) glued to one or more plywood or laminated veneer lumber (LVL) ribs and linked to an upper concrete slab poured in situ. The parts may be prefabricated in T shape (only one rib), in p shape (two ribs), or with multiple ribs to create wider pieces, thereby reducing installation operations. The basis of the system is the timber-concrete shear connection in the form of holes through the ribs, which are filled by the in situ-poured concrete. The connection is complemented with the arrangement of reinforcement bars through the holes. Three test campaigns were undertaken. Shear tests of the timber-concrete connection in 12 test pieces. Shear test along the wood-wood glue line (72 planes tested) and wood -plywood (24 planes tested). Delamination test of the glued planes (24 wood-wood planes and 8 wood-plywood planes). The results indicate a high strength joint, with ductile failure and high composite effect. Likewise, the shear test results along the glue line and the delamination tests show section integrity under demanding hygrothermal conditions. Preliminary sizing curves were developed considering the Gamma Method to evaluate the performance of the system. The results show the possibilities of the system, as pouring the upper slab concrete in situ makes it possible to create continuous semi-rigid joints between the elements. This gives rise to slender flooring structures, light and with high stiffness plane against horizontal forces.

Discontinuous Π-form steel shear connectors in timber-concrete composites. An experimental approach
Martín-Gutiérrez, E.; Estévez-Cimadevila, J.; Otero-Chans, D.; Suárez-Riestra, F.
Engineering Structures
Volume 216. Article ID 110719, 11 pages
doi: 10.1016/j.engstruct.2020.110719
April 2020 | ISSN 0141-0296
Abstract
Experimental results corresponding to a new connection system for timber-concrete-composite (TCC) systems are presented. Shear tests were carried out on T-sections consisting of a laminated spruce rib and a fibre-reinforced concrete upper slab. The connection system is made with discontinuous and perforated steel plates. As a novelty, steel bars have been welded at their ends, so that they are inserted into the timber ribs as glued-in rods. Three different configurations with two connection lengths were studied, in order to achieve an effective solution with a lower consumption of adhesive. The experimental results showed great stiffness in service state. Likewise, these solutions, compared to the plate-connections without additional bars, show strength increases between 11.2% and 19% in short connections, and between 3.0% and 19.8% in the longer ones. Additionally, the connections tested show a composite action close to 100% and remarkable ductility, solving the brittle failure usually associated with glued joints in the limit state. The experimental results also show that shorter connections are more efficient, withstanding higher average shear stresses with less scattering in both strength and stiffness values.

Testing of different non-adherent tendon solutions to reduce short-term deflection in full-scale timber-concrete-composite T-section beams
Estévez-Cimadevila, J.; Otero-Chans, D.; Martín-Gutiérrez, E.; Suárez-Riestra, F.
Journal of Building Engineering
Volume 31. Article ID 101437, 11 pages
doi: 10.1016/j.jobe.2020.101437
April 2020 | ISSN 2352-7102
Abstract
Bending tests were performed on 8 timber-concrete-composite T-section beams with a span of 9 m. The aim was to study the efficacy of the timber-concrete connection system and the influence of different tensioning systems on behaviour of the beams. Four configurations were studied: joists without a tendon, ones with a pre-tensioned tendon or with an unpretensioned tendon, and others with a self-tensioning device patented by the authors. Timber-concrete connections using perforated steel plates glued to the joists by epoxy adhesive displayed an efficiency of 98.9% in terms of theoretical full composite action. Beams with a self-tensioning device attained a minimum ultimate load equivalent to a surface load of 16.26 kN/m2, which is 4.07 times the estimated load in the quasi-permanent hypothesis and 2.17 times that from the total load hypothesis. Using the self-tensioning device in stead of tendon-free beams gave rise to a 30.3% reduction in relative deflection under the total load hypothesis.

Experimental, analytical and numerical vibration analysis of long-span timber-timber composite floors in self-tensioning and non-tensioning configurations
Suárez-Riestra, F.; Estévez-Cimadevila, J.; Martín-Gutiérrez, E.; Otero-Chans, D.
Construction and Building Materials
Volume 218. Pages 341-350
doi: 10.1016/j.conbuildmat.2019.05.084
May 2019 | ISSN 0950-0618
Abstract
An experimental campaign was carried out on the dynamic behaviour of timber-timber composite pieces under different loading conditions. This study compares the behaviour of non-tensioning and selftensioning configurations under different stages of loading. The results show that the presence of an un-bonded prestressed bar hardly alters the eigenfrequency value in comparison with non-tensioned solutions, although it significantly reduces the damping ratio. An analytical methodology is presented that makes it possible to predict dynamic behaviour in terms of eigenfrequency with great exactitude. The simplicity of factors required by the analytical technique means that this method can be used as a design tool. FEM models were developed for each test configuration, and the different load states were analysed. The results show an extremely precise match with those obtained in the test campaign, indicating that this numerical methodology is suitable for the dynamic analysis of these structural elements.

Systems that improve the behaviour of joints made using glued-in rods
Otero-Chans, D.; Estévez-Cimadevila, J.; Martín-Gutiérrez, E.; Suárez-Riestra, F.
European Journal of Wood and Wood Products
Volume 77. Pages 1079-1093
doi: 10.1007/s00107-019-01461-4
April 2019 | ISSN 0018-3768
Abstract
Joints made using glued-in rods have been the subject of many numerical and experimental studies. The joints most widely used are those known as cylindrical joints, i.e., joints made using cylindrical rods of constant cross-section that are inserted into cylindrical holes that also have a constant cross-section. Although no agreement has been reached at a European level that would allow their dimensions to be included in structural standards, there is agreement in the literature on the fact that joint strength does not increase in a linear way with length. It has also been found that there is a maximum joint length above which its withdrawal strength does not increase. After reviewing the literature on the use of glued-in rods, this paper classifies the papers that describe different alternatives to cylindrical holes that have been suggested to improve joint behaviour. These alternatives modify the shape of the rods or the holes, or use additional elements. The paper also describes the results of a broad experimental campaign, which performed a comparative analysis of different types of glued-in rods based on modifying the shape of the hole to increase joint load capacity without the need to use long anchorages. Three different forms of improvement were studied, using several different anchorage lengths and wood species. The results show alternatives that improve strength by up to 60% when compared with traditional joints and which can be used in different wood species at different slenderness values.

Uniones con barras encoladas. Estudio experimental
Otero-Chans, D.; Estévez-Cimadevila, J.; Martín-Gutiérrez, E.; Vázquez-Rodríguez, J.A.; Suárez-Riestra, F.
Boletín de Información Técnica del AITIM
Volume 318. Pages 52-59
March-April 2019 | ISSN 0044-9261

Forjados autotesados de sección compuesta: Glulam+CLT | Glulam+Hormigón
Estévez-Cimadevila, J.; Martín-Gutiérrez, E.; Otero-Chans, D.; Suárez-Riestra, F.; Vázquez-Rodríguez, J.A.
Boletín de Información Técnica del AITIM
Volume 315. Pages 18-23
September-October 2018 | ISSN 0044-9261

Perforated shear + reinforcement bar connectors in a timber-concrete composite solution. Analytical and numerical approach
Suárez-Riestra, F.; Estévez-Cimadevila, J.; Martín-Gutiérrez, E.; Otero-Chans, D.
Composites Part B
Volume 156. Pages 138-147
doi: 10.1016/j.compositesb.2018.08.074
August 2018 | ISSN 1359-8368
Abstract
This paper presents a study of a novel shear connector in a timber-concrete composite solution, focussing on the determination of an analytical expression that makes it possible to predict its behaviour and a numerical analysis that describes it accurately. The shear connector is composed of a perforated steel plate inserted into a slot within the timber rib and glued, in combination with reinforcing corrugated steel bars affixed to the top of the plate. Previous tests made it possible to establish failure mode in different T composite section plate-rebar configurations. These results determine the effectiveness of the system in terms of force-slip behaviour, with systematic failure in the timber section. A simple predictive model is proposed to determine the ultimate capacity of the joint, taking into account the mechanical properties of timber in relation with the fracture plane and the timber-adhesive interface. This model makes it possible to apply a design process that is able to predict the stiffness of the connection. FEM models were analysed for each configuration in a variable load process equal to that used in the test, according to the standard procedure. A variable friction coefficient in contact definition made it possible to achieve an accurate descriptive model in association with the test procedure.

Experimental analysis of glued-in steel plates used as shear connectors in timber-concrete-composites
Otero-Chans, D.; Estévez-Cimadevila, J.; Suárez-Riestra, F.; Martín-Gutiérrez, E.
Engineering Structures
Volume 170. Pages 1-10
doi: 10.1016/j.engstruct.2018.05.062
May 2018 | ISSN 0141-0296
Abstract
This paper describes experimental research into timber-concrete composite (TCC) connections made with discrete perforated steel plates glued in timber with epoxy adhesive. Continuous steel meshes have proven to be very strong and rigid elements in TCC structural members. This paper studies the strength and stiffness of theseconnectors when used in a discrete way, alone and in combination with reinforcing bars. Six types of connector were subjected to experimental tests, analysing two connection lengths and three configuration systems of the connector elements (in which bars are added longitudinally or transversally). The experimental results show that the connections made with discrete steel meshes are very strong and rigid, and that it is possible to design them for ductile failure. Comparison of the results for plates of different lengths indicates that failure occurs in the longest connections in the wood at lower average shear stresses. No significant behavioural differences were detected between connectors made only of plate and those that were reinforced with additional bars. The high slip moduli values indicate that it would be possible to design structural elements with a composite action close to 100% using this type of connection.

Self-tensioning long-span T-shaped spruce and oak web floors with a CLT upper flange. An experimental approach
Martín Gutiérrez, E.; Estévez Cimadevila, J.; Otero Chans, D.; Suárez Riestra, F.
Engineering Structures
Volume 168. Pages 300-307
doi: 10.1016/j.engstruct.2018.04.086
April 2018 | ISSN 0141-0296
Abstract
A device is described that makes it possible to automatically apply a post-tensioning force on deflected elements in response to applied gravitational loads. The behaviour of transverse T-section beams is analysed. They are composed of a laminated oak or spruce rib and a cross-laminated timber upper flange (CLT). Fourteen 9 m span beams were subjected to a four-point bending test until failure. Six of the beams include the self-tensioning system to comparatively verify its efficacy. A numerical analysis model was also developed to describe the behaviour of the proposed device, considering a non-linear regime and interaction between moving parts. The post-tensioned elements attained a noteworthy increase in their final load in comparison with the unreinforced beams. On the other hand, in their service situation they showed a major reduction in their average relative deflection. The conclusions indicate that there is a relevant improvement in their behaviour under deformation, even with a reduced structural width. This improvement is highly useful in long-span wooden floors, where restricted deformation is usually the predominant dimensioning criterion to prevent damage to partition walls.

Experimental Analysis of Pretensioned CLT-Glulam T-Section Beams
Estévez Cimadevila, J.; Suárez Riestra, F.; Otero Chans, D.; Martín Gutiérrez, E.
Advances in Materials Science and Engineering
Volume 2018, Article ID 1528792, 12 pages
doi: 10.1155/2018/1528792
March 2018 | ISSN 1687-8434
Abstract
The bending behavior of T-section beams composed of a glulam web and an upper cross-laminated timber flange was studied. The inluence of two fundamental factors on the bending strength and stiffness was considered: the wood species used for the webs and pretensioning with unbonded tendons. Sixteen specimens with a 9m span were tested until failure: eight of them were non-tensioned (4 Picea abies webs and 4 Quercus robur webs) and the other eight were pretensioned using threaded bars with 20mm diameter anchored in plates fixed at the ends of the specimens (4 Picea abies webs and 4 Quercus robur webs). Pretensioning with unbonded tendons showed a clear improvement in the load capacity of the specimens with Picea abies webs, while the difference was not significant for the specimens with Quercus robur webs. Considering deflection, pretensioning gave the advantage of an initial precamber but also generated slight variations in the stiffness as a result of increasing the portion of the section that was in compression. The variation in the stiffness depended on the relation between the compressive and tensile moduli of elasticity parallel to the grain, and its influence on the deflection was analyzed using a finite element method.

Joints with bars glued-in softwood laminated timber subjected to climatic cycles
Otero Chans, D.; Estévez Cimadevila, J.; Martín Gutiérrez, E.
International Journal of Adhesion and Adhesives
Volume 82. Pages 27-35
doi: 10.1016/j.ijadhadh.2017.12.010
January 2018 | ISSN 0143-7496
Abstract
The effect of climatic cycles (extreme temperatures and humidity) on the performance of joints made with threaded steel rods glued by two-component epoxy adhesive in softwood glulam timber is studied. Short-term tests have been made on three types of specimens: standard condition specimens (20 °C/65%RH), specimens subjected to extreme temperature and humidity during its storage in climatic chamber in service load situation, and specimens in similar unloaded situation. The load capacity, the failure modes and the load-deflection curves have been compared for the different types of specimens. The obtained results do not show a clear influence of the previous exposition to extreme climatic situations in the strength of the joint. On the contrary, the stiffness of the joints, especially those with longer anchorage length, has been reduced up to 35% in the specimens that were previously subjected to climatic changes, both unloaded and in load service situation. This paper presents the results of an experimental study developed on joints made with glued-in rods in glued laminated chestnut, with the rods inserted parallel to the grain. Three anchor lengths have been used. The test pieces have been submitted to pull-compression test until failure after three different previous conditionings: preservation in a normalized atmosphere, artificial accelerated weathering cycles, and climate conditioning under uniform service load. The results indicate that the aging cycles lead to drops of stiffness and pull-out strength in the joints with usual anchorage lengths in practice. Therefore, there is not a significant difference in the value of those losses due to the action of the service load during the accelerated weathering cycles.

Small depth long-span timber floor design with self-tensioned systems
Otero Chans, D.; Estévez Cimadevila, J.; Suárez Riestra, F.; Pérez Valcárcel, J.
Australian Journal of Structural Engineering
Volume 168. Pages 300-307
doi: 10.1080/13287982.2017.1363958
July 2017 | ISSN 1328-7982
Abstract
The design of long-span timber floors, which are able to bear overloaded public spaces, requires the use of beams with large depths to meet the requirements of the serviceability limit state. This article studies the use of a self-tensioning system that, in combination with a pre-stressing, allows designing wooden structural floors that are able to remain practically horizontal in service load situations with depths that are no greater than 1/30 of the span. Several situations are studied, with spans between 9 and 18 m and variable loads of 3.0 and 5.0 kN/m2. These situations obtain deflections below 1/1000 of the span under a total load set-up.

Durability of joints made with threaded steel rods glued in chestnut timber. An experimental approach
Martín Gutiérrez, E.; Estévez Cimadevila, J.; Otero Chans, M.D.
Composites Part B-Engineering
Volume 108. Pages 413-419
doi: 10.1016/j.compositesb.2016.10.010
October 2016 | ISSN 1359-8368
Abstract
This paper presents the results of an experimental study developed on joints made with glued-in rods in glued laminated chestnut, with the rods inserted parallel to the grain. Three anchor lengths have been used. The test pieces have been submitted to pull-compression test until failure after three different previous conditionings: preservation in a normalized atmosphere, artificial accelerated weathering cycles, and climate conditioning under uniform service load. The results indicate that the aging cycles lead to drops of stiffness and pull-out strength in the joints with usual anchorage lengths in practice. Therefore, there is not a significant difference in the value of those losses due to the action of the service load during the accelerated weathering cycles.

Long-span wooden structural floors with self-tensioning system: performance under asymmetrical loads
Estévez Cimadevila, J.; Otero Chans, M.D.; Martín Gutiérrez; Suárez Riestra, F.
Advanced in Materials Science and Engineering
Volume 2016, Article ID 3696025, 11 pages
doi: 10.1155/2016/3696025
July 2016 | ISSN 1687-8434
Abstract
This study analyzes the performance of wooden structural floors equipped with the self-tensioning system patented by the authors, consisting of a force multiplying mechanism connected to a self-tensioning tendon, which is activated automatically when the load is applied to the structural element. The paper describes the system’s difficulties when the structural floor is subjected to asymmetrical loads. The proposed solution consists of anchoring the tendon by an adhesive connection in the central part of the piece yielding a favorable redistribution of the bending moments and an effective performance in terms of deformations. The comparative study focuses on pi-shape cross section pieces with spans of 12m and 15m, using sections without prestressing and with initial prestressing and self-tensioning system.

Application of a new system of self-tensioning to the design of larga-span wood floors framings
Otero Chans, M.D.; Estévez Cimadevila, J.; Martín Gutiérrez; Pérez Valcárcel, J.
Journal of Structural Engineering (ASCE)
Volume 142(6): 04016012
doi: 10.1061/(ASCE)ST.1943-541X.0001486
January 2016 | ISSN 0733-9445
Abstract
This study describes a self-tensioning system in which the gravitational loads acting on a horizontal structural element are automatically converted to a posttensioning force on that component. The self-tensioning effect has a variable intensity, constantly adjusted depending on the applied service loads. The self-tensioning is eccentrically applied over the cross section, and it generates a negative moment that compensates the deformations due to the gravitational loads. The system can be utilized in beams, slabs, and structural framings of different materials and can be implemented using different mechanical and hydraulic solutions. The study describes the operation of a mechanical solution for the self-tensioning system and analyzes its behavior in large-span timber floor framings. When combined with conventional pretensioning, the self-tensioning system notably improves the strength and deformation behavior and permits a design of timber floor framings with a total height of 0.03 times the span length, achieving relative deflections below 1/1,000 of the span for the service loads of the structure.

Self-tensioning system for long-span wooden structural floors
Estévez Cimadevila, J.; Otero Chans, M.D.; Martín Gutiérrez; Suárez Riestra, F.
Construction and Building Materials
Volume 102. Pages 852-860
doi: 10.1016/j.conbuildmat.2015.11.024
November 2015 | ISSN 0950-0618
Abstract
A patented self-tensioning system for long-span wooden structural floors is described that increases the performance of the deflected sections in terms of both resistance and deformation. The system is based on a force multiplier mechanism composed by two connecting rods which are secured to a post-stressing tendon. The mechanical device is activated by the transmission of the load from the structural element to the supports, causing an elongation and stressing the tendon. This transmission comes with a slight vertical displacement of the supports. Throughout this system, the intensity of the tensioning force varies with the applied load; thus, a more favorable bending moment distribution from the load is obtained, and the relative deformations of the different sections of the piece are reduced. This article presents a comparative study of the structural behavior of p-shape cross section wooden structural floors with spans from 9 m to 18 m, comparing sections with and without pre-stress, and sections with the self-tensioning system.

Orientation of bars glued on glued laminated products: Parallel vs. perpendicular
Otero Chans, M.D.; Estévez Cimadevila, J.; Martín Gutiérrez, E.
Composites Part B-Engineering
Volume 62. Pages 97-103
doi: 10.1016/j.compositesb.2014.02.028
March 2014 | ISSN 1359-8368
Abstract
This paper presents the results of a comprehensive experimental study of joints made with threaded steel bars glued with epoxy in both parallel and perpendicular directions to the timber fibres. Two types of wooden products, namely, glulam and laminated veneer lumber (LVL), were used due to their widespread use in notable timber engineering designs. Experimental results showed that the behaviour of glued joints with bars parallel and perpendicular to the timber fibres differed, depending on the slenderness of the joint. It was also observed that specimens made with LVL had lower strength than those made with glulam, regardless of whether the anchors were parallel or perpendicular to the fibres.

Adhesive multi-bulbs: A novel anchoring system using threaded steel rods glued into wood
Estévez Cimadevila, J.; Otero Chans, M.D.; Martín Gutiérrez
Construction and Building Materials
Volume 48. Pages 131–136
doi: 10.1016/j.conbuildmat.2013.06.079
June 2013 | ISSN 0950-0618
Abstract
Joints created from threaded steel rods glued into wood using epoxy could provide an interesting advantage for the construction of wooden structures. This article presents a novel anchoring system developed to increase the load capacity of a joint. This innovation utilises multiple widenings or bulbs along the length of the bore, which are filled with epoxy adhesives. These widenings increase the resistant surface of the wood against shear stress, which translates into a significant increase in the ultimate load value. This improved load capacity allows the use of high performance steels, maintaining a ductile failure mode in the joint. This article details the dril! bit design for implementing the multi-bulbs and presents the results of experiments comparing the load values of the new system with those obtained using a straight anchor.

Experimental analysis of glued-laminated timber bars with box section used in the construction of a spatial grid
Estévez Cimadevila, J.; Otero Chans, M.D.; Martín Gutiérrez, E.; Vázquez Rodríguez, J.A.
Maderas. Ciencia y tecnología
Volume 15 - nº2. Pages 153-170
doi: 10.4067/S0718-221X2013005000013
April 2013 | ISSN 0717-3644
Abstract
The construction of a spatial grid using stackable modules of glued-laminated timber bars with box section has provided the germ for an experimental approach of the behaviour of these types of bars. The paper presents the results of experimental campaign, both prior to the construction of the structure, such as real bars subsequent trials. Both tension tests and compression tests using bars with different slenderness have been conducted. The results show the interest of the proposed solutions and the feasibility of its use in this type of structure.

Influence of geometric and mechanical parameters on stress states caused by threaded rods glued in hardwood
Martín Gutiérrez, E.; Estévez Cimadevila, J.; Otero Chans, M.D.
European Journal of Wood and Wood Products
Volume 71 - nº 2. Pages 259-266
doi: 10.1007/s00107-013-0678-3
March 2013 | ISSN 0018-3768
Abstract
In the construction and rehabilitation of wooden structures, timber connections are often made using glued rods. To guarantee that these connections provide adequate resistance, it is necessary to analyse the characteristics of the connections that affect their load capacity and ductility. To address this issue, the mixed strategy of developing a broad experimental program was adopted while simultaneously performing numerical analysis of models. In this paper, the finite element method is used to study the impact of several design parameters on stress transfer between materials. This approach has facilitated design strategies that improve the effectiveness of these connections.

Withdrawal strength of threaded steel rods glued with epoxy in wood
Otero Chans, M.D.; Estévez Cimadevila, J.; Martín Gutiérrez, E.
International Journal of Adhesion & Adhesives
Volume 44. Pages 115-121
doi: 10.1016/j.ijadhadh.2013.02.008
February 2013 | ISSN 0143-7496
Abstract
In this study, the axial strength of joints made with threaded steel rods glued in timber with epoxy is investigated. Although numerous experimental studies have investigated these joints made in glued laminated timber (glulam) from softwood, experimental data concerning tests on a whole range of hardwood species are still lacking. Thus, to evaluate the influence of timber characteristics on the behaviour of the joint, test results from different species are presented and discussed in this paper. The experimental results from samples using softwood as well as high-density hardwood glued laminated timber are compared. Diverse geometries of the joint are studied in both cases. From this experimental analysis, a formula to predict the strength of the glued-in bars is proposed. The prediction of the strength is made from two parameters that are easily quantifiable the density of the timber and the slenderness of the glued joint. This model shows a good accuracy with the test results of joints made on different species both from softwood and hardwood.

New anchoring system with adhesive bulbs for steel rod joints in wood
Estévez Cimadevila, J.; Otero Chans, M.D.; Martín Gutiérrez, E.; Vázquez Rodríguez, J.A.
Construction and Building Materials
Volume 30. Pages 583–589
doi: 10.1016/j.conbuildmat.2011.12.052
December 2011 | ISSN 0950-0618
Abstract
Joints with threaded rods glued in wood are a technique of great interest for both new projects and the restoration of old structures. Our research team has developed a comprehensive study, both theoretical and experimental, on joints for different types (sawn and laminated) and species (conifers and deciduous)of wood. This article shows the new system developed to improve anchoring efficiency. The new system involves a widening in the bore that is filled with epoxy adhesive, which creates a bulb that can increase the load capacity of the anchorage and the ductility of the joint. The types of bits designed to create the inner bulb easily are likewise detailed. The article also shows the results of the experimental work performed, comparing the load values and failure modes of this type of joint with the traditional system of straight anchoring.

Experimental analysis of adhesives bulbs as a improved anchoring system for steel bars glued in timber
Estévez Cimadevila, J.; Otero Chans, M.D.; Martín Gutiérrez, E.; Vázquez Rodríguez, J.A.
Revista Portuguesa de Engenharia de Estruturas
Serie II - nº 10. Pages 15-22
December 2011 | ISSN 0870-984X
Abstract
The paper describes the solution of a new system for the improvement of joints made with steel rods glued-in timber. The system consists of the implementation of a widening or bulb at the end of the drill hole which is filled with adhesive. The adhesive bulb reduces the stress concentration, which is located in the inner end of the anchorage and, consequently, increases the load capacity of the joint. Different types of drill bits to the implementation of the bulbs were designed and manufactured by our group. A large experimental campaign has been carried out to assess the results provided by the patented system. Specimens were made from five different timber species using both straight anchorages and with bulb. The specimens have been tested with double tensile tests until failure. The results of load capacity show the great possibilities of the system to the improvement of this type of joints.

Strength of joints with epoxy-glued threaded steel rods in tali Timber
Otero Chans, M.D.; Estévez Cimadevila, J.; Martín Gutiérrez, E.
Journal of Materials in Civil Engineering. ASCE (American Society of Civil Engineers)
Volume 23. Pages 453-458
doi: 10.1061/(ASCE)MT.1943-5533.0000191
April 2011 | Available online October 2010
ISSN 0899-1561
Abstract
This paper describes the experimental analysis of joints made with threaded steel rods epoxy-glued into high-density hardwood. Seventy specimens of 10 different types were tested until failure with a pull-pull device. The objective of the study was to evaluate the influence of the geometric and mechanical parameters of the joint on axial strength. Experimental results question the application of the existing joint design formulas to the case of high-density hardwood. Hence, experimental study on glued joints should be extended to include a greater variety of timbers of different densities.

Influence of timber density on the axial strength of joints made with glued-in steel rods: An experimental approach
Otero Chans, M.D.; Estévez Cimadevila, J.; Martín Gutiérrez, E.; Vázquez Rodríguez, J.A.
International Journal of Adhesion and Adhesives
Volume 30. Pages 380-385
doi: 10.1016/j.ijadhadh.2010.03.004
March 2010 | ISSN 0143-1496
Abstract
Joints made with glued-in steel rods have many possibilities in the design of timber structures. They can be used for new buildings or for the rehabilitation of old structural elements damaged by the attack of biotic agents or humidity.
Since the 1970s many studies have been carried out to characterize the strength of these joints when made with glued laminated timber (glulam). These studies hypothesize that the axial strength of joints made in glulam depends on some geometric parameters (anchorage length, steel rod diameter, adhesive thickness, etc.) as well as on timber density.
For several years our research group has been studying the behaviour of these joints when made in sawn timber, determining the influence of different geometric and material parameters on the axial strength of the glued-in steel rods.
This work summarizes the experimental results of joints made in pieces of sawn timber of two species having different densities and mechanical properties.
The experimental study was carried out for different geometric configurations: threaded steel rods of 10 and 12 mm diameter, epoxy adhesive of 1 mm thickness, and five anchorage lengths. The aim was to test the same specimen conditions for each timber species studied, tali and chestnut.
The experimental results show that the axial strength of the joints does not increase linearly with timber density. This results contradicts many of the traditional design proposals suggested for joints made in glulam.

Model for predicting the axial strength of joints made with glued-in rods in sawn timber
Otero Chans, M.D.; Estévez Cimadevila, J.; Martín Gutiérrez, E.
Construction and Building Materials
Volume 24. Pages 1773-1778
doi: 10.1016/j.conbuildmat.2010.02.010
March 2010 | ISSN 0950-0618
Abstract
Joints made with glued-in rods in sawn timber have been used for over 40 years in timber engineering, both for joint design in new constructions as well as in the repair of wood elements damaged by humidity or xylophage attack. One of the problems limiting the use of these types of joints is the absence of legislation regulating their sizing and design. Although Eurocode has given some proposals for estimating the load capacity of these joints, in practice, destructive testing must be performed for each specific case. Recent studies have offered design criteria and sizing restrictions, in most cases, for elements of glued laminated timber. Our research group has been studying the behaviour of these joints in sawn timber for several years. The objective of this reserach is to determine the influence that different joint materials and geometric parameters have on their axial strength. A broad experimental study was performed on joints made with threaded steel rods glued with different types of adhesives and in different hardwood species. Over 400 specimens were tested with different geometric configurations, varying anchorage length, rod diameter and adhesive thickness. This paper presents a summary of the results obtained in the experimental analysis and proposes a model for predicting joint strength in sawn timber. Similarly, a comparative study of our design proposal is presented with the most recent equations for glued laminated timber connections.

Experimental analysis of bonding in steel bars glued into chestnut and tali timber
Otero Chans, M.D.; Estévez Cimadevila, J.; Martín Gutiérrez, E.
Materiales de Construcción
Volume 60. Issue 297. Pages 111-125
doi: 10.3989/mc.2010.46708
March 2010 | ISSN 0465-2746
Abstract
This article summarizes the results of an extensive experiment designed to determine the effect of geometric and mechanical parameters on the axial strength of the bonds formed when threaded steel bars are glued into sawn hardwood timber. The studies conducted to date on glued wood joints have focused primarily on softwood glued laminated timber or glulam. In the present study, specimens made from two hardwood species with very different physical and mechanical properties were used to evaluate the effect of wood characteristics on the axil strength of such bonds. Several geometries were tested by loading a total of 190 specimens to failure.

Influence of the geometric and material characteristics on the strength of glued joints made in chestnut timber
Otero Chans, M.D.; Estévez Cimadevila, J.; Martín Gutiérrez, E.
Materials and Design
Volume 30. Issue 4. Pages 1325-1332
doi: 10.1016/j.matdes.2008.06.041
April 2009 | ISSN 0261-3069
Abstract
This paper summarizes the experimental campaign carried out on joints made with threaded steel rods glued with epoxy in sawn hardwood timber. This study deals with a very little-known field of the glued joints in timber, because previous studies focus on the analysis of joints made with glued laminated timber (glulam) obtained principally from softwood. A total of 180 specimens were tested with the aim of evaluating the incidence of several geometric and material parameters in the axial strength of the joints. The experimental results were compared with the existent design criteria. The research results question the application of the existent design proposals on joints made with hardwood, and they stress the need to delve deeply into the experimental study of glued joints made with sawn timber of high density.

Glued joints in hardwood timber
Otero Chans, M.D.; Estévez Cimadevila, J.; Martín Gutiérrez, E.
International Journal of Adhesion and Adhesives
Volume 28. Issue 8. Pages 457-463
doi: 10.1016/j.ijadhadh.2008.04.008
December 2008 | ISSN 0143-1496
Abstract
The use of glued joints offers an option with ample aesthetic and functional possibilities in the design of wood structures. This type of joint is used since years 1970 in countries of North and Central Europe, for the design and construction of glulam (glued laminated timber) structures. This had led to diverse investigations in the experimental analysis of joints made with steel bars glued-in glulam subjected to axial loads. It led to diverse formulae of empirical base for the design of the same ones. Of these empirical formulae, the proposal of Riberholt is considered to be a pioneer. Likewise, the Eurocode 5 has included in more recent years a formular for the design of these unions, though only as an Informative Annex.
From these precedents, our research equipment has developed an extensive experimental campaign directed to evaluating the adjustement of these proposals to the design of joints in elements made with hardwood saw timber. This can be of great usefulness in works of restorationi, because glued joints have an enormous potential for repairing old structures.
In this paper, diverse experimental campaigns made with threaded steel bars glued-in hardwood saw timber of high density are described.

Experimental behaviour of threaded steel rods glued into high-density hardwood
Estévez Cimadevila, J.; Vázquez Rodríguez, J.A.; Otero Chans, M.D.
International Journal of Adhesion and Adhesives
Volume 27. Issue 2. Pages 136-144
doi: 10.1016/j.ijadhadh.2006.01.006
March 2007 | ISSN 0143-1496
Abstract
This paper shows the test results for resin-glued steel rods under axial load. These stell rods are glued into timber using a two-component Hilti Hit-Re 500 resin. The timber species used in the tests was tali. Three diferent anchorage lengths were combined with two rod diameters and two resin thicknesses. The test failure values have been compared to some available theoretical formulations. The formulation in the Eurocode 5 informative appendix is one of these. The results show a significant difference between the theoretical and the test strength values of these joints. This is mainly due to the fact that the theoretical formulations are based on test on lower density softwoods. Therefore, the research demands more analytical-experimental work in order to achieve more precise theoretical models.