Glulam connections assembled with screws in different installation angles

David Hanna,Thomas Tannert

doi:10.4067/s0718-221x2021000100454

David Hanna, Thomas Tannert

Open Access

https://doi.org/10.4067/s0718-221x2021000100454

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Abstract

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 screwsâ individual resistances.

Highlights

With better awareness of its environmental impact, the building industry is increasing the use of more sustainable materials
The lower bound for stiffness and load-carrying capacity, yet exhibiting the largest deformation capacity, was exhibited by series S1 which used screws installed at 90°, acting primarily laterally
The upper bound for stiffness and load-carrying capacity, yet with low ductility was obtained for series S5 which used long screws installed at 45°, acting primarily in withdrawal

Summary

Introduction

With better awareness of its environmental impact, the building industry is increasing the use of more sustainable materials. A favorable strength to weight ratio, a small carbon footprint, and the ease of assembly are drivers for the increased use of engineered wood products (EWPs) in structural applications (Green and Karsh 2012). More recent innovations in mass timber products, e.g. Cross-laminated Timber (CLT) (Brandner et al 2016), novel ductile connections (Loo et al 2015, Zhang et al 2018), increased pre-fabrication (Connolly et al 2018), hybrid design approaches that combine wood with steel or concrete (Yeoh et al 2011, Dias et al 2016, Tesfamariam et al 2014, Zhang et al 2015), and changes in legislation (NRC 2012, Veilleux et al 2019) further extended the range of application of timber products in buildings. The design and construction of mass-timber structures is not anymore the domain for early adopters, but is becoming part of regular engineering practice (Tannert et al 2018)

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