Carpentry Joints Research Articles

Experimental investigation on strengthening lap joints subjected to bending in glulam timber beams using CFRP sheets

Abstract Strengthening the carpentry joints is considered a big challenge for designers to maintain the joined timber elements’ load transfer and integrity. This research work investigates different techniques to strengthen the lap joints in glulam timber beams using carbon fiber-reinforced polymer (CFRP) sheets. For this purpose, 12 specimens of glulam timber beams were tested using the four-point loading method. One of the glulam timber specimens was an intact nonlapped specimen, and the others were lapped at mid-span using half-height lap joints. The lap joints were strengthened using different configurations of the CFRP sheets. The test variables were the clamping scheme, bond length, and reinforcement ratio of the CFRP sheets. The analysis of the test results indicates that the CFRP strengthening configuration could be more effective in strengthening the lapped glulam timber beams when the reinforcement ratio of the longitudinal CFRP sheets was equal to 0.303%, and the wrapping CFRP sheets continued beyond the lapped joint by a distance equal to the beam height. Such a strengthening configuration could succeed in increasing the effective stiffness and ultimate load of the lapped timber specimen to 109 and 110%, respectively, relative to those of the intact nonlapped specimen. Moreover, the results reveal that increasing the length or the reinforcement ratio of the longitudinal CFRP sheets without increasing the width of the wrapping CFRP sheets could not succeed in achieving the required improvements in the structural behavior of the lapped timber beams.

Static behaviour of the selected carpentry joints in the flexural elements

The paper presents the static behaviour of the selected carpentry joints in the bending wooden elements. Experimental research on beams with the carpentry joints created according to the geometry of the historical joints was conducted. It was confirmed that some of the longitudinal joints applied in the historical structures, with the proper strengthening elements, could transfer some bending moments, which is important in the flexural elements. The load-carrying capacity of the joined beams was determined and compared to the load-carrying capacity of the reference continuous beams, which was from 30 % to 40 %, depending on the joint geometry. Moreover, the stiffness level of the joined beams was determined and compared to the stiffness of the reference continuous beams, which was from 35 % to over 60 %, also depending on the joint geometry. The force-deflection plots for the tested beams were presented. The failure patterns for the joints were described and based on them the areas of stress concentrations in the joints were identified. The joints worked asymmetrically and their failure occurred as a result of gradual loosening and then cracking – interruption of the continuity of the wood fibres. The role of the applied fasteners, which to some extent protect against loosening of the joints, and partially transfer the applied load, was confirmed. The obtained results were compared to the results from the literature regarding similar connections. Research results can be helpful in designing and performing repair and conservation work in historic wooden structures with carpentry joints, in the event of, for example, the need to recreate a historical joint or replenish part of the substance in an existing joint.

Effects of anobiid damage on shear strength parallel to the grain in single step joints

Traditional carpentry joints can be found worldwide in many timber truss structures connecting rafter and tie beam. One failure mode of this connection result from shear in the tie beam beyond the notch either due to bad design or deterioration. In this article, the reduction in shear strength of Single Step Joints (SSJ) resulting from biological attack by anobiids was analysed. For this purpose, tests were carried out in non-degraded scots pine (Pinus sylvestris L.) specimens (reference) and compared to artificially degraded specimens with three different levels of degradation. The reduction of shear resistance was analysed in relation to the density of holes drilled during the degradation simulation, the loss of mass, and the reduction of the shear-resistant area. At lower degradation levels, no significant reduction in shear strength was observed. On the other hand, the linear regression shows a trend of resistance reduction with increasing degradation. Despite the relatively low coefficient of determination (r2 = 0.25), the parameter that best correlated with the residual strength was the reduction in the shear-resistant area.

Timber Structures and Prefabricated Concrete Composite Blocks as a Novel Development in Vertical Gardening

A modern, environmentally friendly urban lifestyle requires paying attention to landscaping and green areas. The scarcity of free land in cities and the high price of land require the combination of greenery with buildings—both vertically and horizontally. The developed green technology for construction brings together computer numerical control (CNC) processing of supporting structures and prefabricated solid planting blocks made of concrete composite. The timber structures are fixed together using traditional carpentry joints. The details, which will be manufactured in the factory using CNC processing at a controlled temperature and humidity corresponding to indoor conditions, can be easily assembled on the construction site. The high bending strength but good elasticity and connections of carpentry joints endow the structure with good properties in a non-controllable environment. By combining CNC-processed wooden structures with concrete technology as substrate composites, labor-intensive manual work in landscaping and gardening will be reduced in the future. The novel material-hardening substrate composite material uses only the residues as the raw materials.

Finite element modelling and experimental verification of timber halved and tabled scarf joints

ABSTRACT Carpentry joints are very common in existing timber structures and they may gain attention for contemporary structures, due to their high degree of reversibility. Therefore, reliable Finite Element (FE) models for carpentry joints can contribute to assessing their capacity and provide a better insight into the parameters influencing their mechanical properties. This paper presents a FE study (using Abaqus) of timber halved-and-tabled scarf joints, together with experimental results. The FE-model considers fracture due to combined shear and tension perpendicular-to-grain by using cohesive zone modelling. Experimental tests on spruce solid timber specimens were performed to validate the model. The specimens were constructed by the use of a CNC-machine. For comparative purposes, two handmade specimens were tested, resulting in a lower load capacity. The FE results showed that initial gaps have a considerable effect on capacity. For certain assumed initial gaps, the FE-model could predict the capacity, however, it underestimated the deformation.

Friction Coefficients of Chestnut (Castanea sativa Mill.) Sawn Timber for Numerical Simulation of Timber Joints

This study focuses on the friction characteristics of chestnut sawn timber (Castanea sativa Mill.) of Spanish origin. The values of both the static and dynamic friction coefficients were determined, as this knowledge is of interest for the numerical simulation of the stress transmission in joints of timber structures. Therefore, two sets of tests were carried out combining different orthotropic orientations. Firstly, timber-to-timber tests were assessed to obtain the coefficients applicable to carpentry joints; secondly, timber-to-steel friction was also evaluated to determine the coefficients needed for mechanical joints with metal plates and dowels. The results presented a conventional behavior of friction, i.e., a maximum static value before sliding and a subsequent decrease. For timber-to-timber tests, global mean values of μs = 0.47 and μk = 0.36 were found, and the results were slightly higher than those obtained between pieces with the same orthotropic orientation and sliding direction. Regarding timber-to-steel tests, the resulting friction coefficients, as well as the difference existing between the static and dynamic values were lower (μs = 0.19 and μk = 0.17) compared to the timber-to-timber sets. The use of these results in numerical studies would allow for closer simulations in which chestnut wood is involved in friction. In addition, the values provided herein could be included as new data in standards that already consider other wood species.

Numerical analyses of timber beams with stop- splayed scarf carpentry joints

The article presents numerical analyses of the stop-splayed scarf joints, supported by the results of experimental research. Technical scale beams with historical connections, made of new pine wood (Pinus sylvestris L.) were tested in bending tests. On the basis of the results of the laboratory tests, load–deflection curves, strains in the cross-sections and failure modes were determined. FEM analyses were conducted using the Hill's anisotropic yield criterion. The results of the experimental tests and numerical analyses were compared. Load capacities of the tested joints were estimated also using an analytical method. Supportive analyses were performed to estimate the effect of the changes in the position of the metal connectors on the load capacity of the connections. The problem of determining the load capacity and structural analysis of historical joints of timber elements was discussed.

The influence of inaccuracies in the production process on the load-bearing behaviour of timber step joints

Inaccuracies within timber step joints are a perennial problem of the wood construction industry. Even perfectly constructed carpentry step joints can become imperfect due to a change in moisture content. The predominant question when looking at step joints with gaps is to what extent the load-bearing behaviour is influenced by these inaccuracies. The authors look beyond this question and investigate if intentionally manufactured gaps could have a positive influence on the load-bearing behaviour and the failure mode of regular and newly designed carpentry joints.

Influence of the connector shape parameters in the structural behaviour of the adhesive- free timber floor panels

Timber-to-timber panels (TTPs) are adhesive- and steel-free structural components formed by carpentry joints of Scots pine to be used as floors. Figure 1 shows a schematic on the TTPs and a detail on the connectors. A numerical model simulating bending tests on TTPs and considering timber as an orthotropic and bi-modulus material was validated from experimental results of deflection, and rolling shear strength. Since the serviceability and ultimate limit states of the TTPs was mainly defined by the rolling shear properties of the connectors, this paper aims to study the influence of different connector shape parameters in the structural behavior of the panels. For that, values of the connector height (hc varying between 40 and 100 mm), width (b1 varying between 40 and 100 mm) and the dove-tail angle (α varying between 45º and 75º) were introduced in the numerical models to obtain both failure load and stiffness for different span TTPs. Results showed that TTP deflection and shear stresses on the connectors decreases with the increase of the height and the width of the connectors. As the width of the connector (b1) increases, the maximum shear stress decreases up to 42%. For a same connector height, the angle of the dove-tail shows low influence in the maximum shear stress; however, it plays a greater role in the deflection of the panels. For the connectors of 40 mm of height TTP deflection was barely influenced by connector width; however, for higher connectors (hc ≥ 60 mm), TTP deflection decreased up to 41% as width increases. So, new TTPs configurations varying the connector parameters showed an improvement on the deflection and on the shear stresses of the connectors.

Flexural strength characterisation of oblique radiata pine splice joints

Sawn timber is marketed in limited length, so larger construction sizes require structural joining solutions for discrete elements. Traditional carpentry joints allow wood elements to be joined in a sustainable way, as they may not require adhesives or metal implements, such as nails or plates. In this research, the mechanical behaviour during the bending of four different oblique splices, made of radiata pine, has been studied. The results obtained show that the vertical oblique rabbetted splice (ROVS) had the best bending performance, with a strength of 43% compared to the solid control specimen (C), followed by the metal splice (MC) with a strength of 34%. The other splices studied, Rabbeted Oblique Scarf Splice (ROSS), Mortised Rabbeted Oblique Splice (MROS), and Oblique Splice Diamont (OSDP) showed flexural strengths of less than 25%, compared to the control specimen (C). The failure observed in the tested joints corresponds to a characteristic flexural and shear failure, where the predominant cracks retained the same direction generated by the discontinuity of the joints and were located in the central zone of the specimen, where the flexural and shear stresses are at a maximum.

Influence of the Structure of Lattice Beams on Their Strength Properties.

This paper presents the strength properties of wooden trusses. The proposed solutions may constitute an alternative to currently produced trusses, in cases when posts and cross braces are joined with flanges using punched metal plate fasteners. Glued carpentry joints, although requiring a more complicated manufacturing process, on the one hand promote a more rational utilisation of available structural timber resources, while on the other hand they restrict the use of metal fasteners. The results of the conducted analyses show that the proposed solutions at the current stage of research are characterised by an approx. 30% lower static bending strength compared to trusses manufactured using punched metal plate fasteners. However, these solutions make it possible to produce trusses with load-bearing capacities comparable to that of structural timber of grade C24 and stiffness slightly higher than that of lattice beams manufactured using punched metal plate fasteners. The strength of wooden trusses manufactured in the laboratory ranged from nearly 20 N/mm2 to over 32 N/mm2. Thus, satisfactory primary values for further work were obtained.

Innovative Carpentry and Hybrid Joints in Contemporary Wooden Architecture

Timber frame structures have a long and rich tradition. In addition to their functional and structural value, they are important elements of the cultural landscape. At the turn of the 21st century, concern for nature, resulting from the threat of environmental degradation, contributed to a growing interest in wooden constructions. For these reasons, we have observed the erection of buildings with wooden frame structures in many countries around the world. This trend contributed to the rapid development of wooden structures, new technologies, and innovative architectural solutions. The conducted research mainly focused on the joints used in their construction, as well as their perception. From among many examples, some original and innovative solutions were selected and analyzed. Their creators are famous architects: Renzo Piano, Imre Makovecz, Jürgen Meyer, Kengo Kuma, and Shigeru Ban. The objects presented in this article are distinguished by the originality of their form and by the fact that they are clearly inspired by vernacular architecture. Crucial elements of these objects, such as wooden, steel, and hybrid connections, are analyzed in this article. Because they are intentionally exposed, they play an important aesthetic role in addition to a structural one.

Structural performance of CLT shear connections with castellations and angle brackets

The advent of digital fabrication technologies and mass timber products such as cross-laminated timber (CLT) have facilitated the use of traditional carpentry joints in modern mass timber construction. Through contact bearing, mortise and tenon castellated joints can also provide high shear strength and stiffness between timber members when compared to connections using mechanical connectors/fasteners. In this study, a total of 29 connection specimens using carpentry castellations and six connection specimens using commercial angle brackets were tested under monotonic loading to evaluate their structural performance. These specimens used five-ply (175 mm thick) and seven-ply (275 mm thick) CLT panels. It was found that the shear strength and stiffness of the castellated joints were 2.5 and 7 times greater than the specimens using the commercial angle brackets. A simplified component-based analytical model was also developed to predict the strength of the castellated joints loaded parallel and perpendicular to grain of the CLT outer layers. The simplified model was found to be adequate in estimating strength given the model limitations. Overall, the study showed that these castellated CLT joints can provide one effective connection type with high shear strength and stiffness for CLT structures.

Experimental and computational study on mechanical behaviour of carpentry corner log joints

This work concerns experimental and numerical research on carpentry joints used in historic wooden buildings in southeastern Poland and western Ukraine. These structures are mainly sacred buildings, and the types of corner log joints characteristic of this region are primarily saddle-notch and dovetail joints; thus, these two types of joints were analysed in this study.The modelling of historic timber structures is a complex issue, so the following steps are necessary to obtain accurate solutions: verification, validation and uncertainty quantification. The first and third steps were performed in a previous study, so the current research aimed to validate the numerical models and perform simulations of carpentry joints. Herein, the authors created finite element models of two types of joints and subsequently analysed the mechanical behaviour of these joints.Due to issues concerning model validation, the authors designed a testing stand for corner joints, which formed a part of a biaxial testing machine. The joints were subjected to horizontal loads (deformations), which may cause damage to the connection. Thus, special parts were designed for the stand, which made it possible to fix the joint and prevented eccentric forces that could possibly damage the machine during testing.The authors presented the differences and similarities in the behaviour of both types of joints, emphasizing the corresponding advantages and disadvantages. In addition, the authors determined which type of joint was the most susceptible to damage and what elements failed first.This paper also showed the complexity of modelling timber structures and the accuracy of the proposed numerical models for both types of joints through comparisons of the numerical and experimental results. This work primary addressed the problems in accurately reflecting material, load and boundary conditions in numerical modelling of tested carpentry corner log joints.

Experimental Investigations of Timber Beams with Stop-Splayed Scarf Carpentry Joints.

The paper presents the results of an experimental investigation of stop-splayed scarf joints, which was carried out as part of a research programme at the Wroclaw University of Science and Technology. A brief description and the characteristics of scarf and splice joints appearing in historical buildings are provided, with special reference to stop-splayed scarf joints (so-called ‘Bolt of lightning’) which were widely used, for example, in Italian renaissance architecture. Analyses and studies of scarf and splice joints in bent elements presented in the literature are reviewed, along with selected examples of analyses and research on tensile joints. It is worth noting that the authors in practically all the cited literature draw attention to the need for further research in this area. Next, the results of the authors’ own research on beams with stop-splayed scarf joints, strengthened using various methods, e.g., by means of drawbolts (metal screws), steel clamps and steel clamps with wooden pegs, which were subjected to four-point bending tests are presented. Load-deflection plots were obtained for load-bearing to bending of each beam in relation to the load-bearing of a continuous reference beam. A comparative analysis of the results obtained for each beam series is presented, along with conclusions and directions for further research.

Un artesonado poliédrico manierista en Castroverde de Campos (Zamora, España)

Este artículo analiza un caso excepcional en la carpintería de armar en España. Se trata del artesonado de cinco paños de la iglesia de Santa María del Río, en Castroverde de Campos (Zamora). Construido en el s. XVI, con una trama de artesones poligonales en su intradós, combina el diseño renacentista con la tradición técnica hispano-musulmana de estructuras de madera, y presenta aportaciones novedosas como la inusual disposición de escuadrías, la duplicidad de estructuras y las poco ortodoxas uniones carpinteras utilizadas. Además, la introducción de artesones convexos junto a los convencionales artesones cóncavos le confiere un marcado aspecto manierista y resuelve ingeniosamente el encuentro entre paños. La muy posible coincidencia de diseñador y constructor en la misma persona explicaría un proceso de construcción con módulos prefabricados, con el consiguiente ahorro de costes y riesgos laborales.

The wooden rafter framing of Żuławy arcaded houses of type III - research, state of preservation and analysis

Historic arcaded houses of the delta of the Vistula were the subject of great interest of many researchers, but their work was focused mainly on historical-architectural aspects. There are no publications which would focus on details and comprehensive analyses of construction systems for this group of historic buildings. The article is the result of field research, archival query and calculations made by the author. The paper analyses the rafter framing constructions of the preserved arcaded houses of type III. The author has prepared a list of construction elements of roofs, carpentry joints, rafter inclination angles and described the state of preservation of roof structure. The paper also includes calculations of the average volume construction material of the roof structure per square meter of roof slope plan.

Analysis of the stress state at the double-step joint in heavy timber structures

The double-step joint is among the most frequently used layouts, within carpentry joints, for transmitting higher forces that would allow a single notch. They are especially effective in heavy timber structures. Nowadays, computer-aided manufacturing is being used more often, demanding further progress in its understanding. The conventional design of these joints is conducted by using simplifying assumptions, in particular regarding the shear stress distribution. This is overcome by the use of strength reduction coefficient, which is currently under study. Numerical simulation and experimental tests were carried out with heavy timber cross-sections for rafter to tie-beam truss joint. They were manufactured in glue-laminated timber owing to the large cross-sections tested. Experimental load-strain and load-displacement diagrams were compared with numerical results. This allowed observing the great shear stress concentration produced in the failure by shear crack, which suggests the application of conservative shear strength reduction coefficients.

Effects of extreme environmental exposure conditions on the mechanical behaviour of traditional carpentry joints

Abstract Timber-framed architecture is an important heritage common of many countries. However, this is being lost due to natural decay but also climatic changes and natural hazards. To preserve it, it is important to understand the influence of such actions. Timber joints significantly affect the mechanical performances of timber-framed buildings, being the weakest element. In this paper, results are presented from cyclic pull-out test conducted on traditional timber joints subjected to wind driven rain and flood, both unreinforced and retrofitted, and a comparison is made with those obtained from sound specimens. Wetting-drying cycles mainly influence the stiffness and dissipation capacity.

Retrofitting of Imperfect Halved Dovetail Carpentry Joints for Increased Seismic Resistance

This paper presents possibilities for anti-seismic improvement of traditional timber carpentry joints. It is known that the structural response of historical roof frameworks is highly dependent on the behavior of their joints, particularly, their capacity for rotation and energy dissipation. Any strengthening, or retrofitting, approach must take into account conservation requirements, usually expressed as conditions involving minimal intervention. Several retrofitting methods were tested on replicas of historical halved joints within various national and international research projects. The joints were produced with traditional hand tools, and made using aged material taken from a demolished building. The paper presents two approaches, each utilizing different retrofitting technologies that avoid completely dismantling the joint and consequently conserve frame integrity. The energy dissipation capacity is increased by inserting mild steel nails around a wooden pin, and connecting the two parts of the halved joint. In the second case, two thin plates made of a material with a high friction coefficient are inserted into the joint and fastened to the wooden elements. This is done by removing the wooden connecting pin and slightly opening a slot for the plates between the halved parts. In addition, the paper presents an application for disc brake plates, as well as thin plates made of oak.