Nail Connections Research Articles

Experimental investigation on lateral performance of southern pine nailed connections under monotonic and cyclic loading

Connections are responsible for maintaining the integrity and safety of wood structures when subjected to lateral force induced by wind or seismic event. The aim of this study is to provide a better understanding of monotonic and cyclic response of timber-to-timber nailed connections. A total of 48 groups of double-shear nailed connections were tested to investigate the effect of different variables on the lateral resistance performance of connections. Representative parameters derived from practical nailed timber connections were considered, including nail diameter, nail type, and load-to-grain angle. It is found that the failure modes of the specimens loaded monotonically are attributed to bending yield of nails. Conversely, under cyclic loading, the majority of nail failures occur as a result of fatigue fracture, which is caused by the repetitive bending stress. A reduction in ductility ranging from 76.9 % to 92.7 % is observed in specimens subjected to cyclic loading, as compared to those under monotonic loading. Utilizing larger-diameter nails as connectors can markedly improve the load-bearing capacity, ductility, and energy-dissipation capabilities of connections subjected to cyclic loading. Helically threaded nails (HTN) have a 29.4 % higher lateral capacity than smooth shank nails (SSN), but a 29.9 % lower stiffness and 22.9 % lower ductility. Experimental load capacities were compared with existing calculation models, and Eurocode 5 was identified as the most suitable design code for predicting the lateral performance of nailed timber joints. Two analytical models were proposed to better simulate the load-slip behavior of nailed connections under monotonic and cyclic loading conditions, respectively.

Seismic performance of light wood shear wall infilled timber frame structures with openings

To study the seismic performance of wood frame structures filled with light wood shear walls, three full-size single-layer single span wooden frame structures with infill walls were designed and manufactured. The beams and columns were connected by mortise-tenon joints, and quasi-static tests were conducted on the specimens under reversed cyclic load. The failure modes and load-displacement hysteresis performance of structures with door opening infill wall, window opening infill wall, and solid infill wall were investigated. The seismic performance was analyzed using indicators such as strength, ductility, and equivalent viscous damping ratio. The failure modes of light wood frame filling walls were the tearing of sheathing panel and the failure of nail connections. The filled wall with the opening initially exhibited inclined cracks at the corner of the opening, and then they extended to the periphery. Compared with the solid filled wall, the positive and negative bearing capacity of the structure with door opening decreased, and that of the structure with window opening decreased also. Because the specimens with opening in the filled wall were more conducive to the deformation of the structure when the bearing capacity was not significantly reduced, the ductility of the specimen with door opening was the highest.

Flexural properties of wooden nail friction welding of laminated timber

The properties of single shear specimens connected by wooden nail frictional welding and twist nails were studied. The single shear properties of the specimens connected by wooden nail welding were lower than that of the twist nail specimens. The single shear capacity of the wooden nail welding specimen was determined by calculating the method of design value of the bearing capacity of the pin connection. Furthermore, the flexural properties of the wooden nail welding laminated timber were analyzed. Due to the larger diameter of the wooden nails compared with the twist nails, the wooden nail welding laminated timber in the elastic phase had higher stiffness. The elastic modulus of the wooden nail welding laminated timber exceeded the average elastic modulus of the constituent lumber pieces by 9.46%. The number of wood lumbers in wooden nail welding laminated timber had little effect on the elastic modulus of laminated timber, but the nail spacing had a certain effect. Therefore, in future research, it is recommended to use the construction method of twist nail connection to design the wooden nail welding laminated timber. In addition, the nail spacing should refer to the GB 50005 (2003) standard and the wood structure design manual.

Flexural Properties of Multiple Bamboo Beams with Connection Joints

Bamboo is a natural material widely used in buildings and bridges that has good mechanical properties. However, the longitudinal connection of bamboo culms is a major problem for the bamboo industry. In this study, sleeve-nailed bamboo specimens were produced, which contained three bamboo pieces. Two bamboo pieces with similar diameters were longitudinally joined by inserting a short bamboo culm with a smaller diameter, fixed with nails. The flexural performance of single beams and two-culm beams were studied. The load-displacement curves and fracture behavior of the specimens were investigated. The results show that the flexural bearing capacity of the single connected bamboo specimen was relatively smaller than that of an unconnected one, while the flexural bearing capacity of the two-culm beam was improved significantly. It can be seen that the lateral connection of bamboo specimens can improve the bearing capacity of the combined bamboo culms. This study provides a basis for promoting the application of sleeve-type nailed connections for bamboo.

DESIGN AND PERFORMANCE OF NAIL CONNECTION IN WOOD FRAMING SHEAR WALLS

As the preferable lateral resistance system of a wood shear wall is attributedto the good lateral performance of nail connection, this paper aims at investigating the pull-out and shear performances of framing members’ nail connection in wood shear walls under monotonic loading. It was found that the main failure mode of the pull-out behavior of nail connection was the withdrawal of threaded nails from framing members. In addition, the shear behavior of nail connection was characterized by plastic hinge of threaded nails, local tear of spruce-pine-fir(SPF)on the top of nails, and nail caps that were obliquely embedded into the surface of SPF. The average ultimate load and displacement of shear mode were 1.48 times and 5.12 times higher than those of pull-out mode, respectively.According to the research results, thecorresponding exponential numerical model was established, which provided basic data for the lateral performance research and finite element simulation analysis of wood shear walls nail connection.

Investigation of Thermal Effects on Nailed Connection of Mass Ply Panels

Abstract Mass ply panels (MPP), a relatively new mass timber product, has been utilized in several construction projects as diaphragm and wall panels. Connection for MPP is a crucial structural component that requires a better understanding. This article presents an experimental investigation into elevated temperature exposure–driven property degradation of MPP nailed connections, which is important for both the design of new structures in terms of fire resistance and the rehabilitation of structures partially damaged by fire. One control group and 32 exposure groups, which were combinations of eight elevated temperatures and four exposure durations, were investigated. The failure modes and yield strength of the nailed connection were analyzed as a function of elevated temperature and exposure time and compared with the prediction from the National Design Specification and existing literature. The results show a decrease of up to 45 percent in initial stiffness and ultimate load; meanwhile, there was no statistical evidence for the change in yield load in the majority of testing groups. Two analytical models, namely, multilinear regression and first-order kinetics model, were proposed to model the degradation of initial stiffness and ultimate strength. The kinetics model provided a better prediction and suggested that the initial stiffness and ultimate strength of the nail connection degraded over time at rates depending on the exposure temperature.

Fast modeling of lightweight glubam frame structures based on connection test information

SummaryThe main lateral load‐carrying components of lightweight glued laminated bamboo (glubam) structures are shear walls. It is essential to understand lightweight glubam shear walls' performances to assess lightweight glubam structures' overall performance. A simplified numerical model was developed to predict the nonlinear response of lightweight glubam shear walls and structures. Based on the assumption that (1) the panel‐frame connectors govern the lateral resistance of the lightweight frame shear walls due to the high in‐plane shear stiffness and strength of the sheathing panel, (2) the out‐of‐plane bulking of the sheathing panel is avoided through the frame and the connections between them, and (3) the resistance capacity of the frame is negligible, the numerical model was developed based on the connection test information. Glubam nail connection tests were conducted considering different nail types and loading directions. The corresponding simplified hysteric wall model is composed of two kinds of input parameters. First are the parameters determining the wall's envelope curve under monotonic loading conditions, which regulate the hysteresis rules. The parameters related to the envelope curve are obtained through the modeling results of the nonlinear static analysis of the shear wall, whereas those related to the hysteresis rules are estimated through the connection test information. The influences of different nails, wall sizes, and openings on the walls' behavior are evaluated based on this simplified model. Based on the numerical simulation results of shear walls, the seismic performance of a glubam house was assessed.

Innovative Gypsum–Particle Composite Used as Building Structural Panels

An innovative preparation method was invented that adds adhesive to gypsum–particle composites. The effects of varying the wood particle to gypsum ratio and melamine-urea-formaldehyde adhesive (MUF) content on mechanical properties and combustion performance were examined and discussed. Microscopic analyses revealed the mechanism of improvement in this innovative gypsum–particle composite (IGP). The ignition point of IGP was high and the heat and smoke release rate low, with the peak release time greatly delayed compared to structural wood-based composites. The mass retention of IGP was greatly increased and its charred appearance slight. The internal bonding strength (IBS), bending strength (modulus of rupture, MOR), and modulus of elasticity (MOE) of IGP with 9.0% MUF content were 3.4, 4.8, and 3.9-fold higher, compared to gypsum board, respectively. IGP with 7.6% MUF appeared to be suitable as load-bearing panels. MUF content positively affected IGP properties and a 7.6% MUF content and 3/10 wood particle to gypsum ratio were found to be optimal for IGP production. The IBS, MOR, and MOE reached 1.28, 16.10, and 6,861 MPa, such that these composites could be used as building materials. The lateral elastic stiffness and maximum load of IGP nail connections were 313.6 kN·m−1 and 1,386 N under parallel-to-grain load, respectively.

Strength of Shear Nailed Connections in Thin Steel Sheets

AbstractThis paper investigated the potential applicability of the specification equation for the shear pull-out strength of a power-actuated fastener (PAF) connection to nail connections between s...

Predicting nail withdrawal resistance and bearing strength of cross-laminated timbers from mixed species

The increasing demand for sustainable architecture has led to a growing interest in wood structures. Hence, ensuring their structural stability and strength performance is an imperative. This study investigated the nail bearing strength and withdrawal resistance of mixed cross-laminated timber (CLT) using Japanese larch and yellow poplar layers. The mixed CLT was composed of three larch laminas (major) and two yellow poplar laminas (minor). The bearing strength of the mixed CLT decreased as the ratio of the thickness of the minor lamina to nail depth increased. The nail withdrawal resistance differed in the penetration and axial directions of the laminas. In the direction perpendicular to the grain, the withdrawal resistance load of the yellow poplar lamina was measured to be 1.45-times that of the larch lamina. The withdrawal resistance of the mixed CLT with the yellow poplar layer was 17% higher than that with larch. Therefore, the length of the nail used for the mixed CLT should be selected based on the thickness of the minor lamina to achieve efficient bearing and withdrawal resistance of the nail connection.

Experimental and Numerical Study on the Flexural Performance of Assembled Steel-Wood Composite Slab

This paper presents research on a new type of fabricated steel–wood composite floor material in the style of a slab-embedded beam flange, using test methods and finite element numerical analysis to study the flexural load-bearing performance of the composite slabs. Through experimental phenomena, the failure process and mechanism of the composite floor are analyzed, and the deformation performance and ultimate bearing capacity of the composite floor material are assessed. Through numerical analysis of the finite element model, the influence of the connection mode of the floor and the composite beam, the type and number of connectors, and the width of the flange of the composite beam on the bending performance of the composite beam–slab system is studied. The research results show that the fabricated steel–wood composite floor slab has good load-bearing and deformation performance. The self-tapping screw connection of the floor slab is better than the ordinary steel nail connection, and the reasonable screw spacing is 100–150 mm. Increasing the flange width of the composite beam can significantly improve the load-bearing capacity of the steel–wood composite floor component.

Three-Dimensional Equivalent Parameterized Beam Element for Nail Connections in Wood Residential Buildings

AbstractNail connections, serving as critical nodes in the loading path of wood residential buildings, could play a crucial role in structural analysis and damage prediction when the structures are...

In-situ checking various mechanical parameters of original nail connections between crossbeams and wooden support, in the framework of an innovative method for rationally dimensioning the crossbeams of panel paintings, applied on an original artwork

A collaboration aiming to improve knowledge and procedures for conservation of Panel Paintings has been in force since several years between OPD (Opificio delle Pietre Dure, Florence) and the Research Group on Wood Technology of DAGRI (University of Florence). In such framework a research is here presented, which for the first time has led to dimensioning rationally (i.e. by means of objective criteria based on Conservation, on Engineering and on Wood Science principles) the stiffness of the crossbeams of an original Panel Painting. Crossbeams typically have a double function: a) to control the deformation of the panel painting when it undergoes climate changes and b) to stiffen the panel painting for handling purposes. If too stiff or too yielding, crossbeams might damage the wooden support or the paint layers; until today the choice of their stiffness was entrusted to the expert but subjective judgment of the Restorers alone, who therefore have been calling for a confrontation with Wood and Engineering Scientists in order to develop more objective criteria. To satisfy this request the research here mentioned has been carried out, in close collaboration between the Restorers of OPD and the Wood Scientists of DAGRI, to develop a specific protocol allowing for the rational dimensioning of the stiffness of crossbeams. This protocol is based on an engineering modular approach, and for the first time it has been applied on an original artwork, the Adorazione del bambino e committente attributed to Cesare da Sesto (1514-1520). One of the modules of such protocol is to assess the stiffness of both the crossbeams and the wooden support and, in such framework, this paper presents the non-invasive mechanical tests that were designed and implemented to check in-situ various mechanical parameters (including the axial holding capacity) of the original nail connections between the crossbeams and the wooden support. Such knowledge might in general be helpful especially during the diagnostic phase, to understand the internal forces still acting into the wood structure, and possibly their influences on the degradation of the paint layers in relation to the behaviour of the wooden support.

Experiments on laminated bamboo lumber nailed connections

Laminated bamboo lumber (LBL) nailed connection made with LBL main member and sandwiched by LBL side members is introduced, which plays an essential role in the safe and reliability of bamboo buildings. However, little research attention has been paid on to the mechanical behavior of connections. This paper reports an experimental study on the effect of parameters on reference loads (yield load and maximum load), stiffness and load-slip behavior of the connections, including nail diameter, number of lines and rows of nails. For single nail connection, nail pull-through and plastic hinges forms in LBL members. Mode cross-over from ductile response to brittle failure is observed in multi-nail connections with one or more splitting cracks develop from the nails hole edges toward the ends of the side or middle members. A decreasing ductility of connections is investigated with increasing diameter and number of nails. The capacity of effective number of nails in a row is evaluated and compared with that obtained from existing analytical formulas. Predictions from existed various theoretical modes are compared with experimentally determined capacities of nailed connection per shear plane per nail and conclude that the load carrying capacity of connections with laterally load nails can be applied to accurately estimate using European yield models (EYMs). Furthermore, the model developed by Folz is capable of predicting the load-slip relationship of LBL nailed connections. The findings of this study will provide the scientific basis and useful information for the design and finite element numerical simulation of engineered bamboo structures containing LBL nailed connections and promote the rational use of bamboo resources in the field of civil engineering.

Experimental analysis of nailed LBL-to-LBL connections loaded parallel to grain

Laminated bamboo lumber (LBL) has become increasingly popular in recent years attributed to its superior mechanical properties compared to wood. The nailed LBL-to-LBL connection comprised of LBL main member sandwiched between two LBL plates is introduced, which plays an essential role in the safe and reliability design of modern bamboo structures. A comprehensive study was conducted in order to determine effect of the parameters on load-slip behavior and failure modes of specimens loaded parallel to grain, including end distance, edge distance, row spacing, center-to-center spacing, number of lines and rows of nails. Three main failure modes were investigated in the experiments, namely bearing failure, splitting failure and row shear failure. Minimum requirements of end distance, edge distance, row spacing and center-to-center spacing in nailed connections were suggested to avoid brittle failures. Results showed that the strength of a multi-nail connection equal the strength of a single nail connection multiplied by an effective number of nails, which is smaller than the actual number of nails. Furthermore, the Foschi formula used to model wood connections can also predict the full process failure of LBL nailed connections and were in good agreement with experimental results. The provided experimental results are motivation for development of design and analytical modes of LBL structures containing nailed LBL-to-LBL connections.

Ductility and overstrength of nailed CLT hold-down connections

The structural performance of nailed hold-down connection systems used for cross-laminated timber (CLT) shear walls under monotonic and cyclic loading was experimentally evaluated. Critical connection performance parameters, including strength, stiffness, ductility, and overstrength, were derived from the testing of 68 hold-down connection specimens. The nailed CLT hold-down connections achieved moderate to high ductility when fracture failures of their metal brackets were avoided. The hold-down connection systems with 3 mm thick commercial brackets achieved ductility factors ranged from 2.7 to 4.3, while the hold-down connection systems composed of 10 mm thick steel plates and longer nails achieved larger ductility factors which ranged from 4.7 to 6.3. The overstrength factors of the hold-down systems ranged from 1.45 to 1.62 except the one composed of the 10 mm thick brackets and 100 mm long nails installed at wide spacing. It was also found that the yield strength of the nailed hold-down connections under monotonic loading was similar to that obtained by cyclic loading.

Deformation diagram and slip modulus of timber-concrete nailed connection

Problem statement . The common type of ties in hybrid timber-concrete structures are nails (bolts, screws, etc.). In the design of structure the connection work is taken into account through the composite action coefficient, which in its turn depends on the slip modulus. According to the current standards [2], the calculation is based on the assumption of linear elastic behaviour of the connection, while experimental studies have shown that the deformation diagram has a clearly expressed nonlinear character. Besides, the calculated slip modulus differs significantly from the one obtained from test results. Thus, taking into account the actual nature of the operation of the compounds makes it possible to obtain more accurate calculation methods. The purpose of the article is to develop the theoretical relationship for determining the slip modulus of the nailed connection of hybrid wood-concrete structures. Conclusion. Based on the analysis of existing data on the features of the deformation of the nailed connections of hybrid timber-concrete structures, an equation is proposed for the dependence of the slip modulus of the connection on the displacement. It was revealed that the application of linear-elastic behaviour models in the calculation of timber-concrete connections leads to overestimated values of the bearing capacity.The theoretical deformation diagrams obtained correspond to the experimental ones and more accurately reflect the beaviour of the connection under load in comparison with the current design standards. The theoretical values of the slip modulus are 30-35% less than the experimental ones, which is satisfactory taking into account the heterogeneity of the physical and mechanical properties of timber and to ensure the reserve of bearing capacity. The proposed dependence for determining the slip modulus allows taking into account its change during connection operation under load.

Structural behaviour of prefabricated stressed-skin engineered timber composite flooring systems

The primary focus of this study is understanding the behaviour and structural performance of prefabricated composite timber floor cassette systems with Oriented strand board (OSB) stressed-skins. These do not have a dedicated top flange, instead their plywood webs are integrally bonded to the OSB flooring skin through a chemical connection. Subsequently, local buckling of the stressed-skin was found to occur as the first failure mode. Specimens with 150 mm and 300 mm nail spacings were investigated for its effects on performance due to the criticality of the integrated web to floor skin connection in these systems. A total of 20 stressed-skin specimens were tested in three-point bending with recordings of the applied force, displacement, slip and failure modes. It was found that local buckling of the skin is prone to occur prior to reaching the designed SLS limit. A detailed Finite Element Analysis (FEA) which takes into consideration the full behaviour of the materials and the glue and nail connections along with failure modes has been validated and used to provide insight to potential design solutions. Key parameters investigated include the adhesive properties, the ratio of clear effective outstand width of the flange to the thickness of the stressed-skin (beff,o/t), ratio of the clear depth of the web to the thickness of the web (dp/tw), ratio of the clear span to the total depth of the composite beam (Lc/D) and finally the spacing of the nails. This has resulted in a broad level understanding of the effects of these design parameters to the behaviour of stressed-skin engineered timber flooring cassettes.

A simple and rapid approach for the numerical simulation of non-linear elements and examples of its application

In earthquake design philosophy non-linear inelastic damage is concentrated at predetermined locations in a structure, with the aim being to keep structural members critical for collapse avoidance, elastic. Non-linear elements can include the beam column joints in steel and reinforced concrete moment resisting frames, the nail connections of timber sheathing-to-framing shear walls, and the hold-down connectors of shear walls. To numerically model the seismic behaviour of these structures, it is critical to be able to quickly and simply model their respective hysteretic behaviours. It is particularly important to identify the parameters that will allow for the accurate replication of the degrading and pinching qualities of the force-displacement relationships. The authors summarise the use of a proprietary multi-linear plastic link, available in most finite element packages, in order to achieve this. A step-by-step process to model the links, from previous research, is described. This process considers the initial elastic stiffness, the force-displacement curve up to ultimate-strength, the post ultimate-strength degrading stiffness, and the reversing stiffness. The procedure can be adopted for both linear and rotational cyclic excitation. The modelled individual elements are subjected to a series of displacement-controlled time-history schedules and validated against the results from experimental tests. These elements, representing non-linear behaviour, are in turn implemented in various numerical models of shear walls. The authors apply cyclic loading to a model wall, and then for a separately designed wall apply seismic ground accelerations associated with the 2011 Canterbury earthquakes in New Zealand, and the results are presented. While the examples provided in this paper involve timber shear walls, the numerical modelling method will be equally useful for a variety of structures of different material types and configuration.

Effect of Loading Speed on the Mechanical Properties of Nail Joints

Wood shear walls are the main lateral load resisting systems in light wood frame buildings to resist the wind and seismic loads. Sheathing to lumber nail connections are regarded as the key components that control the resistance and failure modes of wood shear walls. Considerable experimental tests have been conducted on performance of nail joints or wood shear walls under both static and reversed cyclic loads. However, these tests were usually conducted under different loading speed causing specimen failure in 1 min to an hour. It is unclear how the loading speed will affect the test results of nail joints or wood shear walls. Research on these topics is limited. This paper aims to evaluate the effect of loading speed on the mechanical characteristics of nail joints. 72 specimens have been tested under various loading speeds, ranging from 0.05 mm/s to 0.5 mm/s for monotonic tests and 1.5 mm/s to 15 mm/s for reversed cyclic tests. The range of loading speed was selected based on the total estimated loading time that both monotonic and reversed cyclic tests fail within around 1 min to 10 min. Two groups of nail joints, comprising two common nail sizes and two sheathing thicknesses, were assessed under both monotonic and reversed cyclic loads. From the test results, the effect of loading speed on the mechanical properties of nail joints was determined.