Currently, there is no “timber moment frame structural system,” as the basic glulam beam‐to‐column connections (usually represented by the bolted connections with slotted‐in steel plates) offer ...limited rotational stiffness such that they are usually treated as pin connections. This paper proposes an innovative type of moment‐resisting glulam beam‐to‐column connection reinforced by long steel rods with screwheads (LSRSs) and long self‐tapping screws (STSs). The motivation is to provide a stiff yet resilient beam‐to‐column connection that could possibly be used for the mid‐rise timber moment frame structural system without the need of shear walls or braces. Six specimens with different diameters of LSRSs were designed and experimentally tested to explore their rotational stiffness, moment‐resisting capacities, hysteretic moment‐rotation responses, and the associated failure modes. Results indicated that the proposed connection could provide not only a satisfying moment resistance, but also the energy dissipation and fast repairability that is related with structural seismic resilience. The design procedures and recommendations for the proposed connection were also provided based on the tested results. The presented experimental study serves as a handy reference for future designs and applications of the proposed connection in practical engineering projects.
•Description of advantages of self-tapping screws as reinforcing elements.•Description of state-of-the-art in application and design approaches.•Extensive background information for all approaches ...described.•Results of German background literature summarized in English.
In timber engineering, self-tapping screws, optimized primarily for axial loading, represent the state-of-the-art in fastener and reinforcement technology. Their economic advantages and comparatively easy handling make them one of the first choices for application in both domains. This paper focuses on self-tapping screws and threaded rods applied as reinforcement, illustrating the state-of-the-art in application and design approaches in Europe, in conjunction with numerous references for background information. With regard to medium to large span timber structures which are predominately erected by using linear timber members, from e.g. glued laminated timber, the focus of this paper is on their reinforcement against stresses perpendicular to grain as well as shear. However, latest findings with respect to cross laminated timber are included as well.
•Fifty-nine cross-laminated timber orthogonal joints with screws were tested.•Joints with mixed angle screws achieved high ductility and energy dissipation.•Overstrength and ductility of screwed ...joints were determined.•Available strength models for screwed joints were adequate to predict capacity.
Cross-laminated timber (CLT) is increasingly being used in lateral load resisting systems of multi-storey buildings. Conventional in-plane CLT shear walls can be transformed into CLT core-wall structures with enhanced lateral strength and stiffness when the individual walls are connected orthogonally. In this paper, experimental studies are presented on orthogonal CLT joints with self-tapping screws (STS) installed with mixed angles, i.e. different installation angles between the STS axis and the plane of the CLT surface. A total of 59 orthogonal joint specimens were tested in 9 different configurations to derive the relevant joint performance parameters from monotonic and cyclic tests. The joint specimens used five-layer and seven-layer CLT panels connected by ∅8 mm or ∅12 mm STS. Different ratios of STS installed inclined and STS installed at 90° to the CLT surface were investigated to determine an optimum ratio of STS for enhanced joint performance. It was found that a ratio of one 90° STS for every two inclined STS ensured significant increase in ductility and displacement capacity of approximately three times when compared to specimens with only inclined STS. A minimum moderate ductility was achieved in all test series where the primary failure mode was STS withdrawal. It was found that 90° STS contributed to both strength and stiffness in joints that also contained inclined STS. The average experimental overstrength was 1.7 for most joint configurations. Existing analytical models were adequate in estimating strength but inadequate to estimate stiffness.
In this paper, a Finite-Element (FE) numerical investigation on timber-to-timber joints and composite beams with inclined self-tapping screws (STSs) is presented. Based on past experimental data and ...numerical literature efforts, full 3D solid FE models of selected geometrical and mechanical configurations of technical interest are implemented in ABAQUS software package and analysed under static loading conditions. The typical push-out samples include GL24h timber members with several types (WT-T-8.2, 190 mm and 220 mm their length), layouts (2 + 2, 4 + 4, 2 + 2 X-shaped) and inclination of screws (up to ±45°). For the full-scale beam samples in bending (8 m their span), composite systems consisting of GL24h timber beam, wooden plank, spruce floorboards and STSs are investigated. There, the STS joints take the form of two-rows or X-shaped connections, respectively (45° or 90° their inclination), including four screw types and different spacing. In both the push-out and full-scale cases, simple modelling approaches are taken from the ABAQUS library and adapted to the timber-to-timber structural system under investigation, so as to explore their structural performance in the elastic and post-damage phases, up to failure. A key role in the typical FE models is assigned to input material properties and mechanical contacts, including damage constitutive laws so as to reproduce possible local failure phenomena in the timber or steel components, as well as cohesive damage interactions for the joints. The presented FE models are calibrated in accordance with past research studies, and validated – for the examined structural typology – against experimental results available in literature. Comparative calculations are hence presented, based on the collected numerical, experimental and analytical estimations for the selected samples. As shown, the examined modelling approach can reasonably capture the expected performance of timber-to-timber joints and composite systems.
•Thirty high-capacity mixed angle screw hold-down connections were tested.•Mixed angle screws can provide a strong, stiff, and ductile hold-down connection.•Current design methods provide a ...conservative prediction for strength.
This paper experimentally examines structural performance of novel cross laminated timber (CLT) hold-down connections consisting of customised steel brackets and self-tapping screws installed with mixed angles relative to loading. The installation of screws at mixed angles combines the high strength and stiffness of inclined screws with the high ductility of 90° screws creating a strong, stiff, and ductile connection. A total of 30 high capacity connection specimens comprising two timber species and five connection configurations are tested under monotonic and cyclic loading. The ratios between inclined screws and 90° screws are investigated in order to optimise the connection seismic performance. Connections consisting of 12× Ø12 mm inclined screws and 12 to 24× Ø12mm / 10 mm 90° screws were found to demonstrate high ultimate strength (470–593 kN), high initial stiffness (212–269 kN/mm) and high ductility (µ=10–20) under cyclic loading. Current strength calculation methods for the connection design are compared to the experimental results and are shown to provide conservative design predictions.
•A novel cold-formed thin-walled steel beam-column joint entirely using self-tapping screws.•Influence of different connection modes on static load carrying effect.•Seismic behavior of H-section ...beam-square steel column joints connected by self-tapping screws.•The calculation method for yielding moment strength based on the improved component method.
This paper proposes a novel thin-walled steel beam-column joint entirely using self-tapping screws. Compared to bolted and welded connections, its advantages of easy construction, low precision requirements, and fast construction are suitable for low-rise steel structures. Four full-scale H-section beam-square steel column joints connected by self-tapping screws were tested and the force transfer mechanism was investigated. Three of the specimens were loaded monotonically at the beam ends. The effects of the L-shaped connecting plate thickness and the arrangement of stiffening ribs on the bending performance of the joints are analyzed. Monotonic loading tests have demonstrated that the increased thickness and the arrangement of stiffening ribs enhance the common forces in the clusters of self-tapping screws, thereby increasing the bending stiffness of the joints. One of the specimens was tested with cyclic loads. The cyclic loading test revealed that the hysteretic curve of the self-tapping screws connection is relatively full, with high energy dissipation capacity and low degradation of strength and stiffness. Finally, the improved component method proposed the calculation method of bending resistance of self-tapping connection joints. The calculation accuracy is within 10 %, which can be used as a reference for the design of bending resistance.
A specialized system for accurate self-tapping medical bone screw testing is developed, fully meeting the requirements of ASTM F543-A4 (YY/T 1505-2016). The onset of self-tap is identified ...automatically according to a change in the slope of the torque curve. Precise load control is applied to determine the self-tapping force accurately. A simple mechanical platform is embedded to ensure the automatic axial alignment of a tested screw with the pilot hole in a test block. In addition, comparative experiments are conducted on different self-tapping screws to verify the system's effectiveness. By the automatic identification and alignment method, both torque curves and axial force curves for each screw exhibit significant consistency. The self-tapping time point derived from the torque curve agrees well with the turning point of the axial displacement curve. The determined self-tapping forces' mean values and standard deviations are both small, which are proved to be effective and accurate in the insertion tests. This work contributes to improving the standard test method for accurate determination of the self-tapping performance of medical bone screws.
To advance sustainable development in green construction and broaden the utilization of fast-growing timber as an eco-friendly building material, this paper proposes a novel cold-formed thin-walled ...steel and fast-growing timber composite column. Axial-compression performance tests were conducted using 11 groups of column specimens. The influences of the slenderness ratio, different connection methods (screw, adhesive, and adhesive-screw hybrid), and hollow ratio on the columns were investigated. The tests revealed that the predominant failure modes of the developed composite columns were vertical splitting, compression crushing, adhesive failure, and overall instability. Wood defects are a crucial factor in initiating failures and determining damage patterns. Compared with bare timber columns, composite columns' average ultimate compressive stress is increased by 18–24 %, and the average stiffness is increased by 30–47 %, despite the presence of knots and imperfections. The load-carrying capacity exhibited noticeable differences under different connection methods for 2700 mm columns, with hybrid connections demonstrating lower lateral deflection and more stable compression strength. Furthermore, we present an analytical model for the load-carrying capacity of the composite columns. The difference between the calculated and experimental results was within 10 %, providing a basis for engineering applications. The results indicate that composite columns exhibit favorable axial-compression performance. In addition, the proposed product could provide an appropriate market for fast-growing timber.
•Sliding achievable by yielding of base shear connections can act as an energy dissipation mechanism.•Two types of connections were tested: one to yield in fasteners and the other one within a ...perforated zone.•The strength, stiffness, ductility, and failure mechanisms were determined.•Perforated connections provided 3 to 5 times greater ductility than the ones yielded in fasteners.•Perforated base shear connections could be used to achieve moderately ductile connections.
When cross-laminated timber (CLT) shear wall is designed for seismic loads, the Canadian timber design standard recognizes rocking as the sole energy dissipation kinematic mechanism to meet the capacity design requirement. The sliding mechanism, achievable by yielding of the base shear connections of CLT shear walls, is currently excluded. The focus of this research was on the yielding mechanism of base shear connections for mass timber shear walls as potential source for dissipating energy during major seismic events through sliding. Two types of base shear connections were evaluated: one was designed to exhibit ductile behavior through fastener yielding and the other was designed to yield within a perforated zone of steel bracket that was connected to the timber member with over-designed fasteners (i.e., capacity protected). In both cases, self-tapping screws (STS) were used as fasteners. Monotonic and cyclic tests were performed. The strength, stiffness, ductility, over-strength, and failure mechanisms were determined to investigate the use of these connections as reliable energy dissipating mechanisms. It was found that perforated steel plates provide a reliable yield mechanism with predictable yield and ultimate strength and displacement, and that damage in timber elements can be avoided when the fuses are combined with capacity-protected dowel-type fasteners. Both types of base shear connections under consideration behave in a ductile manner with some limitations under cyclic loading. While the perforated plate detail has the potential to qualify as moderately ductile connection, the other connection with fastener yielding mechanism may only exhibit limited ductility. An analytical model for predicting the yield and ultimate strengths, and ultimate deformation of the perforated plate was developed.
