Wood Screws Research Articles

Flexural performance of innovative thin-walled steel–timber composite floor slabs

A floor slab carries and distributes the floor load in a structure and is an important component that affects overall structural performance. Therefore, it is important to investigate the mechanical properties of such materials. In this study, flexural performance tests under static load are conducted for an innovative thin-walled steel–timber composite floor slab, and the failure mode, bearing capacity, stiffness, deflection, and strain development are investigated. The results show that the floor slab can be quickly assembled using self-tapping and wood screws and exhibits good flexural performance. Using ABAQUS finite-element software, the effects of the oriented-strand board (OSB) thickness, thin-walled–steel-plate height, steel strength, and boundary conditions on the flexural performance of composite floor slabs are investigated. Furthermore, based on the EN1995–1-1 code and equal-section conversion principle, the simplified beam-unit model is established for the theoretical calculation of the composite floor slab. The effective bending stiffness is calculated by considering the influence of the slip modulus of the connector, and the stress distribution law of the section is analysed. The results provide a reliable design basis and reference for the application of thin-walled steel–timber composite floor slabs in engineering practice.

The Effect of Hardwood Veneer Densification on Plywood Density, Surface Hardness, and Screw Withdrawal Capacity

Increasing environmental awareness and the carbon-storing capability of wood have amplified its relevance as a building material. The demand for high-quality wood species necessitates exploring alternative, underutilized wood sources due to limited forest areas and premium wood volume. Consequently, the veneer-based industry is considering lower-value hardwood species like grey alder (Alnus Incania), black alder (Alnus glutinosa), and aspen (Populus tremula) as substitutes for high-quality birch (Betula pendula). Initially less appealing due to their lower density and mechanical properties, these species show promise through densification, which enhances their density, strength, and hardness. This study aims to enhance plywood screw withdrawal capacity and surface hardness by densifying low-density wood species and using them in plywood face-veneer layers, or in all layers. The relationship between the wood density, surface hardness, and screw withdrawal capacity of plywood made of low-value species like aspen and black alder is examined. Experimental work with a pilot-scale veneer and plywood production line demonstrates improved surface hardness (65% and 93% for aspen and black alder, respectively) and screw withdrawal capacity (16% and 35% for aspen and black alder, respectively) in densified face veneer plywood. This research highlights the potential of densified low-value wood species to meet construction requirements, expanding their practical applications.

Experimental and analytical evaluation of semi-rigid timber connection with screwed-in threaded rods and steel coupling part

A major challenge for mid and high-rise timber buildings is fulfilling serviceability requirements. Moment-resisting timber frames with semi-rigid moment-resisting connections as the primary lateral load-resisting system can be an alternative to buildings with wind bracing or shear walls, allowing for more free space, enhanced building performance, and architectural flexibility. Moreover, introducing semi-rigid timber connections can improve the performance of floors against human-induced vibrations and potentially decrease the material used. The performance of moment-resisting frames depends mainly on the properties of their beam-to-column connections. The paper presents an experimental investigation of semi-rigid moment-resisting connections with long screwed-in threaded rods and a steel coupling part. Long threaded rods (i.e., screwed-in threaded rods with wood screw threads) feature high axial stiffness and resistance and allow for immediate load transfer without initial slip. Due to these properties, threaded rods are preferred over conventional dowel-type fasteners such as bolts and dowels. Five full-scale moment-resisting timber connections were tested under cyclic and monotonic loading to investigate moment resistance, rotational stiffness, and energy dissipation. The stiffness obtained by cyclic and monotonic tests was compared with numerical and analytical methods. The beam-to-column moment-resisting connections demonstrated a high moment resistance of 92.2 kNm and rotational stiffness of 8049 kNm/rad without initial slip. The experimental results and analytical calculations of rotational stiffness differed only by 5 %, whereas the finite element model exhibited a discrepancy of approximately 35 %. The equivalent viscous damping was determined based on cyclic load tests at service load levels and was found to be in the range of 5.5 %–10.0 %. Finally, a parametric study is presented to discuss the effect of semi-rigid connections on the performance of the timber floors and material savings. The increase in rotational stiffness of the beam-to-column connections could lead to up to 13 % material savings.

Experimental Study to Determine the Development of Axial Stiffness of Wood Screws with Increasing Load Cycles

123 withdrawal tests were conducted to investigate the change in axial stiffness of fully threaded screws under axial loading and up to four loading cycles. The screws were initially loaded in two cycles within the elastic range, followed by two cycles up to 90% of the characteristic load-carrying capacity. Several parameters relevant to construction practice were varied. The angle between the screw axis and the grain ranged from 30° to 90°, the timber material was varied between glued laminated timber (glulam) and laminated veneer lumber (LVL) made of beech, and the screw diameter ranged from 8 mm to 12 mm. The test results indicate that axial stiffness increases upon reloading compared to the initial loading. On average, axial stiffness increases by 11% between the first and second loading and remains at this level during unloading and further load cycles. However, if the load exceeds the linear–elastic range, the axial stiffness is reduced due to plastic deformation. A comparison with tests on the composite axial stiffness of fully threaded screws in glulam shows that even with a different test setup and testing objective, there is a slight increase in axial stiffness from the first to the second load cycle in the range of 4 to 8%.

Monotonic testing of single shear-plane CLT-to-CLT joint with hardwood dowels

Reducing embodied carbon emissions in buildings and striving for carbon neutrality through sustainable design has become a primary goal in the construction industry. The industry is expanding its use of wood-engineered products, such as cross-laminated timber (CLT) to achieve those sustainability goals. Furthermore, replacing steel fasteners with lower embodied carbon alternatives is gaining increased attention in timber engineering. This paper aims to quantify the mechanical behavior of single shear-plane CLT-to-CLT joints using hardwood dowels. The study includes 154 single shear-plane experimental tests with four different CLT species, two hardwood dowel species, and two dowel diameters. The test specimens were subjected to cyclic and monotonic loading until failure, and mechanical properties such as yielding and ultimate strength, serviceability and yielding stiffness, and ductility were quantified. The hardwood dowel CLT-to-CLT joints demonstrated high strength with up to 10.3 kN (2.3 kips) capacity per dowel and lateral stiffness of up to 5.2 kN/mm (30.8 k/in) per dowel. This strength and stiffness are roughly equivalent to or exceed values for mass timber wood screws, making hardwood dowels a good alternative. In addition, the observed mean ductility of joints ranged from 2.4 to 4.5. Finally, analytical equations for the joints' yielding strength, lateral serviceability stiffness, and yielding stiffness were derived with non-linear regression analysis and validated using the experimental test results.

The influence of feed rate during pilot hole drilling on screw withdrawal resistance in particleboard

Screw withdrawal resistance (SWR) is a metric that assesses the strength of furniture joints made with wood screws. The SWR value is influenced by several factors, such as the size of the screw, the depth to which it is embedded, the diameter of the pilot hole, and the material properties of the furniture components that are being joined together. These factors have been widely studied in the scientific literature. The objective of the research was to investigate the previously unexplored factor of a feed rate during pilot hole drilling and its influence on SWR. This study used three particleboards composed of raw pine material and urea–formaldehyde resins; the boards varied in average density (633, 637, and 714 kg/m3). Blind pilot holes with a diameter of 5 mm and depth of 25 mm were drilled in these boards using three significantly different feed rates (0.033, 0.33, and 3.33 mm/rev.). Subsequently, a confirmat-type furniture screw (7 mm major diameter, 4 mm minor diameter, 3 mm pitch) was screwed into these pilot holes. The ultimate SWR was measured with a universal testing machine. The results showed that the highest feed rate significantly decreases the SWR for all particleboards tested. This phenomenon can be attributed to the fact that a higher feed rate leads to a decreased precision in the internal surface of the pilot hole, consequently diminishing the screw’s anchoring capacity within the hole. The high feed rate, used to increase production efficiency, may significantly reduce furniture durability and usability.

嵌合形状加工木材を用いた非接着接合による柱間木ねじ積層パネルの可能性と課題

It is assumed that there is still the possibility of the development of non-glued Massiv Holz construction method which could be considered to improve the yielding percentage of products, mass production at factories and high workability at fields. Including the field of view of the wide spread of Massiv Holz construction method, the authors developed the non-glued laminated panels with wooden screws between columns using fitting-shaped worked timber that is able to combine with conventional post and beam structure method. This research reports the possibility and the issues of the non-glued laminated panels through comparison with other construction methods.

Experimental investigation of the lumber-plybamboo-lumber screwed connections used in midply shear walls

Common midply shear walls constructed with wood-based mid-sheathing panels and nails usually exhibit substantial sheathing edge-tear and nail withdrawal failures, which will significantly limit the midply shear wall performance. This paper introduces an approach to prevent these connection failures, namely employing plybamboo panel and wood screw as middle sheathing and fastener, respectively. A preliminary experimental study on six groups of lumber-plybamboo-lumber screwed (LPLS) connections extracted from such improved midply shear walls were conducted, taking account of variables in terms of sheathing thickness and loading direction to the framing grain. Another three groups with Oriented strand board (OSB) mid-sheathings were tested for comparison. Test results show that the combined use of plybamboo panel and wood screw in the LPLS connections can effectively reduce the sheathing edge-tear and fastener withdrawal failures, and results in an over 70% increase in ultimate strength in comparison to the double-shear nailed connections with wood-based sheathing. However, the LPLS connections showed no advantage in elastic stiffness and ductility compared to the double-shear nailed connections with wood-based sheathing. The ultimate strength and ultimate displacement of the LPLS connections subjected to cyclic loading are 1.0–25.8% and 39.1–58.2% less than those of monotonically loaded connections, respectively, due to premature screw fatigue. The European Yield Model can reasonably predict the failure mode of the LPLS connections, but will underestimate the ultimate strength by 12–44%, probably due to underestimating the plybamboo embedment strength and ignoring the friction between plybamboo sheathing and SPF lumbers. The combined use of plybamboo panel and wood screw has great potential of being used in wood construction.

Experimental and numerical evaluation on the behavior of single-shear timber connections using lag screw

In current design procedures, the capacities of single-shear timber connections with lag screws are determined based on their governing failure modes, which are assumed to occur independently. In this study, the capacity and failure modes of single-shear timber connections with lag screws are evaluated experimentally and numerically. Six specimens of Red Meranti wood and lag screws with different penetration lengths are tested to obtain their lateral load capacities and failure modes. Nonlinear 3D finite element analyses using Abaqus are conducted to simulate the test condition. The experimental and numerical results are evaluated in terms of connection failure modes and capacities. Moreover, the result will be compared with NDS 2018 predictions. The study results show that the connection capacities between experimental tests and numerical analysis are similar if the minimum penetration requirement of NDS 2018 is satisfied. It can also be seen that the dominant failure modes, both from experimental and numerical results, match with those predicted using NDS 2018, although they are slightly combined with the other failure modes.

Withdrawal Performance of Nails and Screws in Cross-Laminated Timber (CLT) Made of Poplar (Populus alba) and Fir (Abies alba).

Cross-laminated timber (CLT) can be used as an element in various parts of timber structures, such as bridges. Fast-growing hardwood species, like poplar, are useful in regions where there is a lack of wood resources. In this study, the withdrawal resistance of nine types of conventional fasteners (stainless-steel nails, concrete nails and screws, drywall screws, three types of partially and fully threaded wood screws, and two types of lag screws), with three loading directions (parallel to the grain, perpendicular to the surface, and tangential), and two layer arrangements (0-90-0° and 0-45-0°) in 3-ply CLTs made of poplar as a fast-growing species and fir as a common species in manufacturing of CLT was investigated. Lag screws (10 mm) displayed the highest withdrawal resistance (145.77 N), whereas steel nails had the lowest (13.13 N), according to the main effect analysis. Furthermore, fasteners loaded perpendicular to the grain (perpendicular to the surface and tangential) had higher withdrawal resistance than those loaded parallel to the grain (edge). In terms of the layer arrangement, fasteners in CLTs manufactured from poplar wood (0-45-0°) had the greatest withdrawal resistance, followed by CLTs manufactured from poplar wood in the (0-90-0°) arrangement, and finally, those made from fir wood in the (0-90-0°) arrangement. The fastener type had the most significant impact on the withdrawal resistance, so changing the fastener type from nails to screws increased it by about 5–11 times, which is consistent with other studies. The results showed that poplar, a fast-growth species, is a proper wood for manufacturing CLTs in terms of fastener withdrawal performance.

Withdrawal strength of hexagon head wood screws in laminated veneer lumber

Withdrawal strength of hexagon head wood screws in laminated veneer lumber

Influence of thread parameters on the withdrawal capacity of wood screws to optimize the thread geometry

For wood screw connections, the withdrawal capacity is essential and is therefore an optimization target for wood screws. The withdrawal capacity is based on the composite action between the screw thread and the wood. Optimizing thread geometry requires knowledge of how thread parameters influence the withdrawal capacity. Up to now, this knowledge is largely unknown. Therefore, the objective is to determine the influence of thread height (1 mm; 1.48 mm), flank distance (3.04 mm; 6.08 mm), lead angle (6.8°; 13.6°), and thread angle (30°; 55°) on the withdrawal capacity. The influences are investigated for a tangential screw-in direction in spruce. For this, flat ribbed bars, so-called threaded test objects, are used. The effect on the withdrawal capacity is measured using an experimental setup based on test standard EN 1382 in two different planes of the flat thread to the wood fiber. 242 tests in RT plane and 286 in TL plane were analyzed with multifactorial analyses of variance. The thread height, flank distance, and thread angle show significant effects in both planes. A larger thread height, a smaller thread pitch, and a more acute thread angle increase the withdrawal capacity. Only in RT plane, a larger lead angle shows higher withdrawal capacity. The determined effects can be used to design the thread geometry of wood screws with higher withdrawal capacities. The accuracy of calculation models for the withdrawal capacity of wood screw connections can also be improved based on the findings. With the results, confirmation could be found for known models based on the theory of compression cones explaining the influences of the flank distance and thread angle.

Moment-resisting beam-to-column timber connections with inclined threaded rods: Structural concept and analysis by use of the component method

The use of moment-resisting frames with semi-rigid connections as a lateral load-carrying system in timber buildings can reduce the need for bracing with diagonal members or walls and allow for more open and flexible architecture. The overall performance of moment-resisting frames depends largely on the properties of their connections. Screwed-in threaded rods with wood screw thread feature high axial stiffness and capacity and they may be used as fasteners in beam-to-column, moment-resisting timber connections. In the present paper, a structural concept for a beam–to-column, moment-resisting timber connection based on threaded rods is presented and explained. Analytical expressions for the estimation of the rotational stiffness and the forces in the rods were derived based on a component-method approach. The analytical predictions for stiffness were compared to experimental results from full scale tests and the agreement was good.

Mechanical Behaviour of Aluminium-Timber Composite Connections with Screws and Toothed Plates.

This paper presents an investigation of the load-slip behaviour of aluminium-timber composite connections. Toothed plates with bolts are often used for connecting timber structural members with steel structural members. In this paper, toothed plates (C2-50/M10G, C2-50/M12G or C11-50/M12) have been used as reinforcement in aluminium-timber screwed connections for the first time. The push-out test specimens consisted of laminated veneer lumber slabs, aluminium alloy beams, and hexagon head wood screws (10 mm × 80 mm and 12 mm × 80 mm). Of the specimens, 12 additionally had toothed plates as reinforcement, while 8 had no reinforcement. The load carrying-capacity, the mode of failure and the load-slip response of the strengthened and non-strengthened screwed connections were investigated. The use of toothed plate connectors was found to be effective in increasing the strength of aluminium-timber composite connections and ineffective in improving their stiffness. The examined stiffness and strength of the connections can be used in the design and numerical modelling of aluminium-timber composite beams with reinforced screwed connections.

Polymer Composite Fabrication Reinforced with Bamboo Fiber for Particle Board Product Raw Material Application.

Bamboo particles as reinforcement in composite materials are prospective to be applied to particleboard products in the industry. This study aimed to synthesize bamboo particle reinforced polymer composites as a substitute for particleboard products, which still use wood as a raw material. The parameters of the composite synthesis process were varied with powder sizes of 50, 100, and 250 mesh, each mesh with volume fractions of 10, 20, and 30%, matrix types of polyester and polypropylene, Tali Bamboo, and Haur Hejo Bamboo as reinforcements. Characterization included tensile strength, flexural strength, and morphology. Particleboard products were tested based on JIS A 5908-2003, including density testing, moisture content, thickness expansion after immersion in water, flexural strength in dry and wet conditions, bending Young’s modulus, and wood screw holding power. The results showed that the maximum flexural and tensile strength values of 91.03 MPa and 30.85 MPa, respectively, were found in polymer composites reinforced with Tali bamboo with the particle size of 250 mesh and volume fraction 30%. Particleboard made of polypropylene and polyester reinforced Tali Bamboo with a particle size of 250 mesh and a volume fraction of 30% composites meets the JIS A 5908-2003 standard.

Mechanical properties of laterally loaded threaded rods embedded in softwood

At present, the mechanical properties of laterally loaded threaded fasteners with large diameters embedded in timber elements remain unknown. An experimental study of laterally loaded threaded rods with wood screw threads embedded perpendicular to grain in softwood elements (spruce and pine glulam and spruce LVL) is presented in this paper. Embedment tests with the load acting parallel and perpendicular to grain were carried out and the embedment strength and stiffness were quantified. For some test series, the experimental embedment strengths were lower compared to the predictions according to Eurocode 5 in terms of both mean and characteristic values. This finding indicates that the predictions by Eurocode 5 are not always conservative. To investigate the effect of the thread, additional series of embedment tests were carried out with smooth dowels featuring a diameter approximately equal to the core diameter of the threaded rods. Finally, the yielding moment of threaded rods was quantified based on a series of three-point bending tests of threaded rods. The experimentally determined yielding moment was significantly higher than the prediction of Eurocode 5.

Laterally loaded performance of single dowel-type fastener used for steel plate-to-timber connections

Bolts, nails and screws are the most commonly used connectors in steel-to-timber composite (STC) system. Glued-in rod (GIR) as one kind of connectors for timber structures, is also supposed to be used as the connections in STC system. This paper reports an experimental campaign on steel plate-to-timber connections with single GIR and wood screw fastener aiming to investigate the shear performance of the connections. The experimental results indicated that under lateral load, the fasteners exhibited “one hinge” or “two hinges” deformation modes typically, which are greatly associated with the fastener anchorage length. The load-relative displacement curves were generally characterized by a linearly increasing response followed a yield plateau and a secondary non-linearly increasing response indicating the so-called rope effect of the fasteners. The fastener anchorage length showed significant influence on the load capacity of the screwed steel plate-to-timber connections while did not affect the load capacity of the steel plate-to-timber connections with GIR fasteners. The initial stiffness and ductility of the steel plate-to-timber connections were obviously influenced by the fastener anchorage length. A finite element (FE) model was developed to simulate the joint behaviour and the simulation results are in good agreement with test results. Finally, the load-carrying capacity of the steel plate-to-timber connections with screw and GIR fasteners was predicted by the calculation model reported in Eurocode 5 and a new proposed calculation model, respectively.

Effect of freezing and heating on the screw withdrawal capacity of Norway spruce and European larch wood

Wood and wooden joints are exposed to fluctuating environmental condition during its use. Temperature is one of the most important environmental factors besides humidity that affects the behavior of wood and wooden joints in use. Though, seasoned wood is considered as a good thermal insulator, nevertheless, the performance of metal screws may get affected by the fluctuating temperature. This article deals with the effect of alternating lower (freezing) and higher (heating) temperatures on the screw holding capacity of Norway spruce (Picea abies (L.) H. Karst.) and European larch (Larix decidua Mill.) wood. Two thermal loading regimes, (freezing followed by heating) were carried out at temperatures −15 °C/70 °C and −25 °C/70 °C. Three types of wood screws such as partial double thread construction screw (A), full shank single thread universal screw (B) and two intertwined threaded construction screw (C) were used for the experiment. Withdrawal capacity was determined on radial and tangential surfaces. Freezing did not cause any significant change in the density and moisture content of wood. Although anatomical directions caused variations in the withdrawal parameter in both of the species, these variations were not statistically significant. Larch wood exhibited significantly higher (64–80%) screw withdrawal parameter as compared to spruce wood and the reason being the higher wood density of larch. Reference wood (without thermal loading) with universal (B) type screws exhibited the highest withdrawal parameters (23.7 N/mm2) followed by construction (C) types (22.6 N/mm2) and construction (A) types (19.7 N/mm2) when data for both the species are pooled together. The trend was similar for thermally loaded wood also. The average screw withdrawal parameter values of universal (B) and construction (C) type screws were comparable, while these values were significantly higher as compared to the value exhibited by construction (A). Thermal loading did not cause any detrimental effect on the screw withdrawal parameter; rather, it marginally improved the screw withdrawal parameters.

TEST OF A NET DOME FRAGMENT

A geodesic or net dome, also known as a Fuller’s dome, is a spherical structure. Geodesic domes are well receptive to asymmetric loads, especially snow and wind, have high aerodynamics, increased rigidity and stability. It should be noted that the larger the diameter of the sphere, the greater its bearing capacity, and the strength of such dome slightly depends on the building materials used. With significant advantages, the design and construction of wooden net domes has not become widespread. The fact is that net domes are spatial structures with a large number of elements, which accordingly entails a large number of nodes. The elements of the dome are connected with dowels, wet film gauge, bolts, wood screws, staples, screws, nails. Adhesive connections on washers are used, also steel clamps, straps, overlays are applied. However, they all have disadvantages, the scope of each connector is different, and their cost is often comparable to the cost of the dome elements. We offer a universal connector for connecting dome parts at any angle. As a result of introduction of such technical decision of knot, we receive essential simplification of a design, reduction of quantity of components, at the same time with increase of its manufacturability. To study the operation of the joint of wooden glue-board elements of the dome with the use of a universal connector, its experimental studies were carried out. The purpose of the study: to study the actual operation of the connection of wooden parts of the dome with a universal connector in the form of rotating fasteners that rotate freely on the draw bolt, to assess its strength and deformability, to assess the possibility of using such a connection in the design of spatial structures. To solve the tasks, a full-scale fragment of the dome was tested, which includes characteristic nodes with rigid adjacency of elements to each other.

Mechanics of Screw Joints Solved as Beams Placed in a Tangential Elastic Foundation

This article deals with a new original analytical solution of deformation, force and stress states in wood screw joints up to the limit values of pulling out/breaking the screw. The screws are under tension. The wood-to-screw interaction is effectively simplified by introducing several physical model variants using a tangential elastic non-linear foundation. The experimental verification of the proposed models using pull-out tests (i.e., pulling out screws from dry spruce wood in laboratory conditions) confirms the correctness of the proposed models of the elastic linear/non-linear foundation. The validity of the model is also analytically and experimentally verified in the biomechanical model of pulling out screws from the femur of a bovine/human cadaver, which confirms and expands the validity of newly designed screw joint models outside the timber structure area.