Search

This paper presents the results of an experimental study carried out with the following main purposes: (i) evaluate the effect of different types of delamination of straight glulam beams on their structural behavior up to failure; (ii) evaluate the effectiveness of repairing those beams after bending failure through the use of self-drilling screws and plywood sheets; (iii) evaluate the effectiveness of a preventive repair of those beams (applied before loading them to failure) through the use of self-drilling screws. The tested elements comprised (i) reference beams, without delamination; beams with delamination at the ends involving the overall cross-section width, in (ii) moderate lengths and in (iii) significant lengths; and (iv) beams with delamination along all length at the outer thirds of the cross-section width. The results of the bending tests of the unrepaired beams showed that (i) the end delamination causes a decrease in the strength and stiffness of the beams, more markedly for longer delamination length and that (ii) the longitudinal delamination, not involving the entire cross-section width, does not significantly affect the behavior of the beams. The results of the beams repaired after failure showed that the intervention technique used is adequate and that its degree of effectiveness depends on the type of delamination and on the level of damage occurred at failure. The results of the preventively repaired beams showed that the intervention method used confers significant improvements in resistance and stiffness to unrepaired beams, although it does not allow achieving the performance of healthy beams. [ABSTRACT FROM AUTHOR]

Delamination at the glue lines is a key factor to take into account when assessing glued laminated timber members in service. In order to gain a more objective and wide knowledge about the importance of delamination in relation to its type and extension, a numerical study was developed. Finite element modeling (FEM) was used to evaluate the influence of delamination – near the surface, on the vertical faces and ends – on the mechanic performance of straight glued laminated timber beams. The FEM was validated by comparing stresses and deformations obtained with the model and with the application of the beam theory, showing satisfactory results. Results show that when delamination is non-symmetric regarding the member’s cross section, it can cause the member’s lateral instability, thus increasing its stresses and deformations. Delamination is not a problem when it occurs in members or member areas with low shear stresses, particularly when it is symmetric and does not reach the whole width of the beam. The stresses corresponding to the bending or deformation limit-states get near the elastic limit only for very important delamination. Moreover, delamination depth higher than 60% of the cross section width may be regarded as a turn point beyond which the structural integrity may be at risk. [ABSTRACT FROM AUTHOR]

• Evaluation of the bonding performance of Portuguese Maritime pine. • Delamination and shear strength tests. • Performance of different adhesives for structural applications. • Influence of the amount of adhesive and clamping pressure on bonding performance. The use of timber for construction purposes in Portugal has decreased during the last century. However, recent market requests aiming at sustainable constructions led to a rediscovery of timber structures. Glued laminated timber is one of the most used timber construction products and its production using Portuguese Maritime pine (Pinus pinaster Ait.) has been studied and validated concerning its economic and mechanical performance. This paper aims to present a state of the art of the research conducted so far on the use of Maritime Pine for glulam as well as new research conveying bonding with more recent adhesives. The ongoing study comprised an extended experimental campaign on gluing Maritime pine timber grown in Portugal, for glulam production. Eight different adhesives were considered, namely based on: i) Phenol-Resorcinol-Formaldehyde (PRF), ii) Melamine-Urea-Formaldehyde (MUF), iii) Emulsion-Polymer-Isocyanate (EPI) and iv) Single Component Polyurethane (1C-PUR). The amount of adhesive used and the clamping pressure were considered as main variables. Delamination specimens were tested according to Method A of EN 14080 [1] and shear strength tests followed Annex D of the same standard. In terms of delamination it was observed an excellent performance of all PRF adhesives. MUF, EPI and 1C-PUR adhesives presented good bonding performance, however, it is important to emphasize the need to use primer (PR) in the case of 1C-PUR adhesive. The shear strength was not influenced significantly by the adhesive type but some differences were found on Wood Failure Percentage for EPI and 1C-PUR adhesives. [ABSTRACT FROM AUTHOR]

Abstract: Epoxy adhesives have been used for many years in the rehabilitation of timber structures and are currently the most appropriate adhesive type for on-site operations. However, because they exhibit excellent initial joint strength when tested in standard climate conditions, there has not been a major concern about their service durability. In order to contribute to the ongoing discussion on the reliability of these adhesives, a study was conducted to evaluate the effect of environmental service conditions on the durability of four commercial two-component structural epoxy adhesives, as well as the effect that the type of mixing, curing and post-curing conditions, as well as the presence of moisture have on the adhesives viscoelastic properties. It was found that the preparation conditions, cure schedule and moisture have a significant effect on the performance of the bulk adhesives. Moreover, it was found that under ambient conditions there is potential for under-cure or slow progression of cure for the epoxy adhesive products typically employed in these applications, which in turn can compromise the durability of a bonded joint. [Copyright &y& Elsevier]