The objective of this research is to develop a model to predict the distribution of loads within connections with multiple self-tapping screw fasteners and steel side plates, and use this model to predict the strength and stiffness of multiple-inclined self-tapping screw connections. These results would facilitate the design of large scale connections with long rows of self-tapping screw fasteners, such as may be used for mass timber shear wall connections or splice joints for long-span timber beams.
The objective of this research is to develop models for predicting lateral strength and stiffness of connections containing inclined self-tapping screws, by considering the contribution of the withdrawal and yield properties of the screws and embedment properties of the connecting members.
The research presented in this paper examines the performance of 3-ply and 5-ply Cross-laminated Timber (CLT) panels connected with Self-tapping Screws (STS). Different conventional joint types (surface spline with STS in shear and half-lap joints with STS in either shear or withdrawal) along with two innovative solutions were evaluated in a total of 198 quasi-static tests. The first novel assembly used STS with double inclination of fasteners in butt joints; the second was a combination of STS in withdrawal and shear in lap joints. The joint performance was evaluated in terms of capacity, stiffness, yield strength, and ductility. The results confirmed that joints with STS in shear exhibited high ductility but low stiffness, whereas joints with STS in withdrawal were found to be stiff but less ductile. Combining the shear and withdrawal action of STS led to high stiffness and high ductility.
Cross-Laminated-Timber (CLT) is increasingly gaining popularity in residential and non-residential applications in North America. To use CLT as lateral load resisting system, individual panels need to be connected. In order to provide in-plane shear connections, CLT panels may be joined with a variety of options including the use of self-tapping-screws (STS) in surface splines and half-lap joints. Alternatively, STS can be installed at an angle to the plane allowing for simple butt joints and avoiding any machining. This study investigated the performance of CLT panel assemblies connected with STS under vertical shear loading. The three aforementioned options were applied to join 3ply and 5-ply CLT panels. A total of 60 mid-scale quasi-static shear tests were performed to determine and compare the connection performance in terms of strength, stiffness, and ductility. It was shown that – depending on the screw layout – either very stiff or very ductile joint performance can be achieved.
The Chair of Structures and Structural Design of the RWTH Aachen University, in cooperation with the Institute of Building Materials Research Aachen (ibac) and SPAX® International, has developed timber connections using self-tapping screws as reinforcing and joining elements. The focus was put on rigid frame corners that achieved high load-bearing capacities for both negative and positive bending moments. Due to the high utilisation rate of the selftapping screws the long-term load-bearing behaviour was examined in natural outdoor climate of service class 2. The measured creep factors significantly exceeded the values for timber structures given in EC 5 and gave rise to more detailed examination of the creep behaviour.
Project contact is Thomas Miller at Oregon State University
Understanding how roof and floor systems (commonly called diaphragms by engineers) that are built from Pacific Northwest-sourced cross-laminated timber (CLT) panels perform in earthquake prone areas is a critical area of research. These building components are key to transferring normal and extreme event forces into walls and down to the foundation. The tests performed in this project will provide data on commonly used approaches to connecting CLT panels within a floor or roof space and the performance of associated screw fasteners. Structural engineers will directly benefit through improved modeling tools. A broader benefit may be increased confidence in the construction of taller wood buildings in communities at greater risk for earthquakes.
Monotonic and cyclic tests were carried out to determine strength and stiffness characteristics of 2.44 m (8 ft) long shear connections with 8 mm and 10 mm diameter self-tapping screws. The goal of this research is tocompare test values of cross-laminated timber (CLT) diaphragm connections in seismic force-resisting systems tothe design values calculated from formulas in the National Design Specification for Wood Construction (USA)and the Eurocode. Understanding and quantifying the behavior of these shear connections will provide structural engineers with increased confidence in designing these components, especially with regard to the seismic forceresisting systems. Ratios of the experimental yield strength (from the yield point on the load-deflection curve) to factored design strength were in the range of 2.1–6.1. In the ASCE 41-13 acceptance criteria analysis, the mfactors for the Life Safety performance level in cyclic tests ranged from 1.6 to 1.8 for surface spline connections and from 0.9 to 1.7 for cyclic half-lap connections. The half-lap connections with a unique combination of angled and vertical screws performed exceptionally well with both high, linear elastic initial stiffness and ductile, postpeak behavior.
Self-tapping screws, used as efficient reinforcements or connectors for timber and glulam structures, tend to “stray” from the designated axis when long and slender screws are applied. To provide a highly precise installation, the predrilling of guideholes using laser radiation has been examined. While laser cutting is already common in machining thin wood-based panels (plywood, chipboard, etc.), laser drilling has not yet been applied for higher drill depths. Based on preliminary tests, pulsed fibre laser radiation was used to drill through glulam species in different angles to the wood fibre direction to examine the geometry and thermal modification of the boreholes. Thereafter self-tapping screws were installed in the laser-drilled guideholes and their pull-out resistance was determined in comparison to screws installed in mechanically drilled holes and screws installed without predrilling. The results of the tests show the high potential for further development of this innovative wood processing method in timber construction.