Fracture mechanics based joint capacity prediction of glued-in rods with beech laminated veneer lumber

International audienceGlued-in rods (GiR) represent a very successful type of adhesively bonded joints in timber engineering. Despite their apparent geometrical simplicity, their dimensioning still challenges practitioners. A major source of mechanical complexity resides in the orthotropic nature of the wood, or engineered wood products, as laminated veneer lumber (LVL). This paper presents a relatively simple design approach based upon fracture mechanics (FM) and associated double-cantilever beam (DCB) tests that complemented tensile tests for material characterisation. In comparison with the state-of-the-art related to FM in timber engineering, the paper presents a practitioner oriented approach of a yet complex set of GiR geometries involving beech LVL (M16-8.8 threaded rods embedded in cross sections of 120 × 120 mm2 and embedment lengths of 96mm, 128mm and 160mm). The developed numerical model resulted in a good description of the load-displacement of a series of full scale, including very good estimates of their load capacities. Additionally, it allowed for significant insights regarding the complicated relationship between geometry, orthotropy, strength of the component and failure of the GiR, as for examples the complex fracture process, and the importance of transverse tensile stresses, which play a preponderant role, equal in importance to shear stresses

Rods glued in engineered hardwood products

Glued-in rods (GiR) represent an adhesively bonded structural connection widely used in timber engineering. Up to now, common practice largely focused on softwood. Most structural adhesives have been, accordingly, specifically formulated to perform on softwood, in particular spruce. The paper presents an overview over extensive research carried out with 9 adhesives, 3 engineered wood products (EWP), and 4 types of rods. Investigations started at component level, by fully characterising all adhesives, EWP, and rods. They were then extended to characterise the behaviour of interfaces, providing by this a methodology for selecting adhesives. Investigations at full scale followed, involving 5 different adhesives, 3 EWP, and 4 rod types; a total of 180 individual specimens were tested. Combining the material characterisation with finite element analysis (FEA), and reformulating strength in probabilistic terms, then allowed performing predictions of joint capacities for all 60 experimentally investigated GiR configurations. The comparison between predicted and experimental values showed a good agreement with relative difference amounting to-3% for beech glued-laminated timber (GLT), -2% for oak GLT, and +1%, respectively

Induction curing made easy - Using curie particles

Commonly used adhesives for glued-in rods in timber engineering, cold curing two-component (2K) epoxies or polyurethanes, only harden relatively slowly (usually in hours to days), which is magnitudes of times longer than mechanical fastening. Additional constraints arise from the fact that they usually necessitate some minimum temperature so that polymerisation can take place. Induction heating was investigated in the light of two timber engineering applications, glued-in glass fibre reinforced rods in timber, and timber-glass structures

Synthesis and styrene copolymerization of novel alkoxy ring-substituted isobutyl phenylcyanoacrylates

Novel alkoxy ring-substituted isobutyl phenylcyanoacrylates, RPhCH=C(CN)CO2CH2CH(CH3)2 (where R is 2-methoxy, 3-methoxy, 4-methoxy, 2-ethoxy, 3-ethoxy, 4-ethoxy, 4-propoxy, 4-butoxy, 4-hexyloxy) were prepared and copolymerized with styrene. The acrylates were synthesized by the piperidine catalyzed Knoevenagel condensation of ring-substituted benzaldehydes and isobutyl cyanoacetate and characterized by CHN elemental analysis, IR, 1H- and 13C-NMR. All the acrylates were copolymerized with styrene in solution with radical initiation (ABCN) at 70C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, 1H and 13C-NMR. Thermal properties of the copolymers are characterized by DSC and TGA. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 200-500ºC range with residue (1.8-3.3% wt.), which then decomposed in the 500-800ºC range