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 paper describes experimental and numerical analyses on a completely new connection system developed for CLT (Cross Laminated Timber) constructions. The innovative solution herein proposed, named X-RAD, consists of a point-to-point mechanical connection system, fixed to the corners of the CLT panels. This connection, that is designed to be prefabricated, is made of a metal wrapping and an inner hard wood element which are fastened to the panel by means of allthreaded self-tapping screws. Such system permits to reduce significantly the number of bolts/fasteners required to assemble two or more panels together or to connect them to the foundation. This results in the enhancement of the installation process in terms of speed, quality and safety. One of the reasons that fuelled the development of the presented system, is the desire of offering a solution to those issues (e.g. to satisfy ductility and energetic dissipation requirements) commonly related to the seismic safety of timber structures. In other words there was the will of defining a system able to guarantee an adequate level of ductility and energetic dissipation.
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.
The goal of this project is to contribute to the development of design values for cross-laminated timber (CLT) diaphragms in the seismic load-resisting system for buildings. Monotonic and cyclic tests to determine strength and stiffness characteristics of 2.44 m (8 ft) long shear connections with common self-tapping screws were performed. Understanding and quantifying the behavior of these shear connections will aid in developing design provisions in the National Design Specification for Wood Construction and the International Building Code so structural engineers can use CLT more confidently in lateral force-resisting systems and extend the heights of wood buildings. Experimental strength-to-design strength ratios were in the range of 2.1 to 8.7. In the ASCE 41 acceptance criteria analysis, the m-factors 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, where screws were installed in withdrawal, shear, shear, and withdrawal, performed exceptionally well with both high, linear-elastic, initial stiffness, and ductile, post-peak behavior.
Self-tapping screws are efficient and flexible fasteners, applicable for many types of connections. Investigations on axially loaded groups of screws pointed out, that small spacing between the screws lead to block shear failure mode. So far, block and plug shear failure mode are only analysed for laterally loaded fasteners. Corresponding models cannot be simple transferred to primary axially loaded screws, because of their load insertion continuously along the effective thread featuring a thread-fibre angle perpendicular or with an angle to grain. Results gained by means of two different test configurations, with constant 90° thread-fibre angle but different configurations of group of screws and support conditions are presented. A block shear model is presented, and for mean values for stiffness and strength properties as model parameters are discussed together with values for parameters related to the force distribution over the effective thread length for the first test configuration. Agreement between model and test results was found on a conservative basis. As outlook, considerations of additional bending stresses as well as parameter optimisation are seen as prerequisites and next steps for further model improvement and practicality.
In this paper, the performance improvement of glulam post-to-beam connections reinforced by plain round rods (PRRs) and self-tapping screws (STSs) were compared. Five non-reinforced post-to-beam bolted connections, five PRR-reinforcing connections and five STS-reinforcing connections were experimentally investigated under monotonic and low frequency cyclic loading. Their stiffness, ductility, moment resistance capacity, failure modes and seismic behavior were analyzed. The findings indicated that both of these two reinforcements could mitigate wood splitting, and change the failure mode from brittle failure to ductile failure. The maximum moment and failure rotation of PRR-reinforcing connection were increased by 29% and 6% respectively, compared with those of non-reinforced connection. In addition, those of STS-reinforcing connection increased by 86% and 145% respectively. Furthermore, the comparison of PRR-reinforcing and STS-reinforcing connections indicated that the connection ductility reinforced by self-tapping screws enhanced more significantly; 106% higher than that of PRR-reinforcing connection. Moreover, under the low frequency cyclic loading, PRR-reinforcing and STS-reinforcing connections dissipated more energy (336% and 641% respectively) with a lower stiffness degeneration rate and a higher equivalent viscous damping ratio than those of non-reinforced connection. Besides, the dissipation energy and equivalent viscous damping ratio of STS-reinforcing connection were larger than those of PRR-reinforcing connection.
The present work aims to define horizontal joint dimension tolerances for newly proposed prefabricated façade systems for applications in tall cross laminated timber (CLT) buildings based on the compression perpendicular to grain characteristics of the component. This requires a thorough understanding of structural settlement under vertical loads which can vary at each floor height. An experimental program has been carried out with reference to the case of a platform frame building construction, where major perpendicular to grain compression of the floor can occur under high loads. Five-layer CLT specimens have been tested under compression via the application of a line load with steel plate as well as actual CLT wall specimens. Strengthening contribution using full threaded self-tapping wood screws has also been investigated. Results of deformation characteristics have been validated through a non-linear finite element analysis and further elaborated in order to outline implications in the design of a prefabricated façade.