Short-Term Analysis of Adhesive Types and Bonding Mistakes on Bonded-in-Rod (BiR) Connections for Timber Structures

Abstract

Bonded-in rods (BiR) represent a structural connection type that is largely used for new timber structures and rehabilitation (repair or reinforcement) of existing structural members. The technology is based on steel / Fiber Reinforced Polymer (FRP) / Glass Fiber Reinforced Polymer (GFRP) rods bonded into predrilled holes in timber elements. The mechanical advantages of BiRs include high local force capacity, improved strength, a relatively high stiffness and the possibility of ductile behaviour. They also offer aesthetic benefits, given that rods are hidden in the cross sections of wooden members. As such, BiR connections are regarded as a solution with great potential, but still uncertain design formulations. Several research projects have dealt with BiRs, but a final definition of their mechanics and a universal design procedure is still missing. This research study explores the typical fracture mechanics modes for BiR connections. A special focus is given to the evaluation of the impact of adhesive bonds under various operational conditions (i.e., moisture content of timber). A total of 84 specimens are tested in pull-out setup, and investigated with the support of digital image correlation (DIC). The reliability of empirical equations and a newly developed analytical model in support of design, based on linear elastic fracture mechanics (LEFM), is also assessed.

Special Issue on “Buildings and Structures under Extreme Loads II”

“…Depending on their actual mechanical features and capacities, as well as sensitivity to external conditions, the structural performance assessment of the building as a whole can be strongly affected. In this regard, a first set of research papers is dedicated to the experimental, numerical or hybrid analysis of special joints for constructional systems, under a variety of mechanical properties and loading conditions [2][3][4][5][6]. For timber structures, for example, it is known that both material and geometrical parameters for connections arrangement can have severe effects on mechanical performances, in the same way of moisture, loading protocol, etc.…”

“…For timber structures, for example, it is known that both material and geometrical parameters for connections arrangement can have severe effects on mechanical performances, in the same way of moisture, loading protocol, etc. Experimental studies are thus reported in [2] for Bonded-in-Rod (BIR) connections under various operational conditions for bonding adhesives, while the study in [3] presents a critical analysis of performance indicators for timber-to-timber screwed connections with various configurations. As far as connections parameters are taken into account for steel structures are considered, several calculation approaches can be notoriously taken into account in support of design [4].…”

On-Site Gluing and Weather Effects on Tall Wooden Wind Turbine Towers

“…Standardized testing methods and requirements for glued-in rods are defined in the European standard EN 17334:2021 [5]. Some experimental studies on the gluing procedures of glued-in rod joints have shown important outcomes concerning the mechanical effects of elevated moisture contents [6] and temperatures [7]. 1 Viktor Norbäck, RISE Research Institutes of Sweden, Sweden, viktor.norback@ri.se 2 Pierre Landel, RISE Research Institutes of Sweden, pierre.landel@ri.se 3 Erik Dölerud, Modvion AB, Sweden, erik@modvion.com 4 Anders Wickström, RISE Research Institutes of Sweden, Sweden, anders.wickstrom@ri.se Connections with glued-in plates provide a strong and stiff joint compared to more traditional mechanical connections for timber structures, e.g., screws and dowels.…”

Can confined mechanical metamaterials replace adhesives?

“…In fast-growing industrial sectors for infrastructure engineering, such as transportation and energy, drives for efficiency and functionality inevitably rely on a deep understanding of confined materials and adhesive joints [1,2]i.e, joining or sealing two similar or dissimilar materials is paramount to progress. Examples are found in glass fibre composite (GFRP) parts of a wind turbine rotor blades [3], trending glass bridges connected to metallic or wooden frames [4], and timber construction with in-rod mounting [5]. In many of these instances, the assumption of idealised and seamless joints are commonly far from ideal to be considered in calculations, and disregarding their intrinsic characteristic dimensions and constitutive behaviour is more often than not leading fundamental design flaws.…”