Influence of imperfections on the load capacity and stiffness of glued-in rod connections

Glued-in rods (GiR), which consist of rods glued into structural elements of wood, or engineered wood products, share the manufacturing quality concerns associated to adhesively bonded joints in general. Because of the difficulties associated with the bonding process, it is often argued within the timber engineering community that under the specific conditions prevailing in construction sites, it is not possible to meet the high-quality requirements for bonded joints typically encountered in other industries. The present study presents experimental evidence gathered on 240 individual probes in which the effect of several different types of defects (excessive wood moisture content, wood chips not removed from the borehole, simulated air inclusions by mixing polystyrene spheres, oil contaminated rods, and corroded rod) was investigated with threaded rods glued into beech spruce glued laminated timber (GLT) and beech laminated veneer lumber (LVL) using four adhesives (including 2K-epoxies and a 2K-polyurethane). Results were analysed by means of an analysis of variance (ANOVA). The findings showed that glued-in rods represent a relatively robust class of adhesively bonded joints, as the majority of defects types could not be distinguished on statistical ground from the reference sets, with the notable exception of air voids leading to a significant decrease of joint capacity

Influence of manufacturing methods and imperfections on the load capacity of glued-in rods

Previous research indicated that glued-in rods (GiR), an adhesively bonded joint in which metallic rods are glued into wood blocks, are an efficient method to connect or reinforce structures in timber engineering, and represent a success story for adhesive bonding in civil engineering. In literature, GiR are mostly manufactured under perfect conditions, regarding both surface states and geometry, with outermost care taken to avoid any deviation thereof. However, in reality GiR are typically manufactured by staff that received little to no training, in particular with regard to the peculiarities of adhesive bonding. Thus the very high standards that apply in other industries, as for example aerospace, are hard to achieve. Additional constraints result from the relatively narrow gap in which the adhesive is injected, and the difficulty to monitor its complete and correct filling. For the manufacturing of GiR-connections several different techniques are used, which were mostly validated empirically. The influence of different manufacturing methods and potential defects on joint performance was investigated. Additionally, this paper sheds additional light on the influence of different typical defects on the load capacity of GiR with steel rods. Several defects, such as corrosion, contamination by oil, dust, wood chips, sand and moisture were considered, and performance of joints manufactured thereof compared to joints without such defects. The results of the research demonstrate that defects on GiR result in a non-negligible reduction of the load capacity, but that this effect is somewhat smaller than expected. Accordingly, GiR connections might be considered as relatively robust with regard to manufacturing