Ductile moment-resisting timber connections: a review

In the last two decades, high-rise timber buildings have been built using the glulam truss system, even with limited openings. Moment-resisting timber frames (MRTF) with semi-rigid beam-to-column connections can be an architecture-friendly way to provide a load-carrying system to vertical and horizontal loads for timber buildings. In these structures, connections of adequate ductility are crucial to ensure robustness and energy dissipation. This paper presents a review of the main types of timber beam–column moment connections with improved ductility and proposes to carry out a ductility assessment of these connections based on the most relevant ductility factors. Joints have a significant influence on the global performance of MRTF, and the application of ductile connections have improved the mechanical parameters of the timber frame. The reinforced bolted slotted-in steel plate and glued-in rods connections have similar mechanical performance, with high rotation capacity and good ultimate moment, but exhibited different failure modes under cyclic loading. The connections were classified within ductility classes. In general, the glued-in steel rods presented better results because of the high influence of steel profiles in the connection yielding. Despite the excellent mechanical behavior, the reinforced bolted slotted-in steel plate connections presented medium ductility values.This research was funded by Fundação para a Ciência e a Tecnologia (FCT) grant number BD/06301/2022

Experimental analysis of Maritime pine and Iroko single shear dowel-type connections

"Available online 21 March 2016"In this study, screwed connections were experimentally evaluated, checking the plausibility of Eurocode 5 for two selected wood species, Iroko (Milícia excelsa) and Maritime pine (Pinus pinaster). Single shear screwed connections, considering self-tapping screws, were tested and the experimental campaign aimed at evaluating various mechanisms of resistance suggested by Eurocode 5 for this typology of connection, including axial withdrawal capacity of the screw, pull through parameter for screws, and local embedment of wood. The experimental results evidenced that the analyzed connection system had similar results with either wood species. The results were consistent with the calculation through Eurocode 5.This work was supported by FCT (Portuguese Foundation for Science and Technology), within ISISE, project UID/ECI/04029/2013

Screw reinforcement on dowel-type moment-resisting connections with cracks

This study uses partially threaded self-tapping screws to enhance the mechanical properties of damaged and undamaged dowel-type timber connections. The damaged connections have a 1.5 mm wide artificial crack across the middle row of the fasteners. Test results showed that screw reinforcement can restore the rotation capacity of damaged connections. The rotational capacity of reinforced connections without cracks is 45.6% higher than unreinforced connections while the improvement on moment-resisting capacity is slight. Digital image correlation (DIC) was used to detect the movement of the connections and validated that the fasteners rotate around the centre of rotation in reinforced connections. Screw reinforcement also demonstrated the ability to control crack propagation, with the reinforced groups showed a reduction of crack length by at least 37% when compared to the unreinforced groups. A calculation method is proposed to calculate the characteristic moment-resisting capacity of damaged and undamaged screw reinforced connections. The calculated values are proven to be conservative when compared with the characteristic value based on the experimental results

Glulam connections assembled with screws in different installation angles

Self-tapping screws are the recognized state-of-the-art in fastener technology for timber structures. Combining fasteners of different stiffness, such as self-tapping screws with different installation angles, can be advantageous to simultaneously achieve high connection stiffness and ductility. In this paper, experimental investigations on a total of 65 glued-laminated timber joints assembled with a variety of installation angles including several combinations of self-tapping screws acting axially in withdrawal with self-tapping screws acting laterally are presented. The connection performance was analyzed in terms of the load-carrying capacity, the deformation capacity, the stiffness, and the ductility. The findings demonstrated that joint assemblies with self-tapping screws loaded primarily laterally exhibit low stiffness but high ductility, whereas joint assemblies with self-tapping screws loaded primarily in withdrawal are very stiff but exhibit low ductility. Combining screws in different installation angles created glued-laminated timber connections that combine high stiffness with high ductility. Existing analytical expressions were deemed suitable to estimate load-carrying capacity through simple summation of the different screws’ individual resistances

Rotational Stiffness of Timber-to-Timber Connections with Self-Tapping axially loaded Screws

Self-tapping axially loaded screws provide high load-carrying capacity and great stiffness. Due to these advantages, they were preferably applied to realise connections for tension members. While the translational stiffness of those connections can be estimated for engineering purposes sufficiently, knowledge about the rotational stiffness is still low. The investigations reported here show the influence of the inclination and the geometrical arrangement of the self-tapping screws on the rotational stiffness of connections for tension members. A test set-up was therefore developed. It enables that tensile forces and rotation are simultaneously effective and quantitatively independently of each other. The experimental results show that the inclination of the screws and the resulting compressive stress in the shear plane has a major influence on the rotational stiffness and that the stiffness of the screws themselves becomes less effective

Numerical analysis of timber-to-timber joints and composite beams with inclined self-tapping screws

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\u202fmm and 220\u202fmm their length), layouts (2\u202f+\u202f2, 4\u202f+\u202f4, 2\u202f+\u202f2 X-shaped) and inclination of screws (up to \ub145\ub0). For the full-scale beam samples in bending (8\u202fm 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\ub0 or 90\ub0 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 \u2013 for the examined structural typology \u2013 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

Cross laminated timber shear wall connections for seismic applications

Master of ScienceDepartment of Architectural Engineering and Construction ScienceBill ZhangThis report gives a state-of-the-art summary of current cross-laminated timber (CLT) shear wall systems and connections for seismic applications. CLT panels are gaining popularity as a building material because of their biaxial strength and light weight. CLT panels can be used in building construction not only as floors, but also as shear walls. However, the behavior of CLT shear wall systems under seismic load has yet to be defined. CLT panels are nearly rigid under in-plane loading. While this can be beneficial, structural system qualities that are valuable in seismic loading such as ductility and energy dissipation are difficult to achieve by the panels themselves. Therefore, for the lateral force resisting system to perform as needed, ductility and energy dissipation must come from the connection systems. There is a distinction between a connection and a connection system. The performance of CLT shear walls depends on the behavior of many different connections. CLT shear walls can be categorized into conventional shear walls, and rocking walls. Conventional shear walls follow many of the practices established in light-frame wood shear walls with the use of hold-downs and brackets. Conventional shear walls typically have a base connection with (multi-panel walls) or without (single-panel walls) vertical joint(s). Selection of these two connections can have a noticeable effect on the shear wall behavior. Rocking shear walls allow panel rotation in order to redirect forces into structural fuses in the connection system. The structural fuses vary on the type of rocking wall. These include U-shaped flexural plates (UFPs), energy dissipators, slip-friction connections, and interpanel shear connections. Most of the systems covered in this report displayed favorable seismic performance. Case studies of full-scale buildings that were tested under seismic ground motions are presented. Studies indicated that CLT connections and shear walls have the capability to perform well under seismic loading

Using self-tapping screw to reinforce dowel-type connection in a timber portal frame

In this study, partially threaded self-tapping screws have been used as reinforcement on timber portal frames to enhance mechanical performance of dowel-type connections. Experimental tests on unreinforced and reinforced portal frames showed that reinforced frames achieved a 31% and 51% increase in moment-resisting capacity and ultimate rotation, respectively. The test on the reinforced frames was stopped when the stroke on the hydraulic jacks had been reached, while 20% of load drop was not observed. The test results demonstrated the performance of partially threaded self-tapping screws which reduces the drive-in torque when compared to fully threaded self-tapping screws. A theoretical prediction on the characteristic moment-resisting capacity of screw reinforced portal frames is proposed