Bondline shear strength and wood failure of European and tropical hardwood glulams

Abstract

The study reports on block shear investigations with bondlines of face-glued laminations and matched solid wood specimens from hardwood glulam (GLT) beams produced industrially from eight technically and stand volume-wise important species. The European hardwoods comprised oak, beech, sweet chestnut and ash and the tropical species were teak, keruing, melangangai and light red meranti. The adhesives were phenol-resorcinol and melamine-urea. When combining all species in one sample, a rather strong linear relationship of bond and wood shear strength was observed. The ratio of bond vs. wood shear strength was for all species on the mean value level ≥ 0.9, and likewise (with one exception) for the respective strengths' 5%-quantiles. Consistent with literature, the test results showed no significant correlations between bond shear strength and density, wood shear strength and wood failure percentage of individual species, respectively. The investigations render the methodological basics of some international standards on bond quality verification as being inappropriate. New, empirically validated hardwood GLT bond requirements are proposed for discussion and implementation at the CEN and ISO levels. The strength ratio specifications reflect respective ANSI provisions, yet the reference quantity wood shear strength is now determined in an unbiased manner from matched GLT specimens. The wood failure verification proposal is based on the 10%-quantile and mean level for initial type testing and factory production control. The requirements further account for the pronounced difference observed in scatter of wood failure between European and tropical species.

Use of northern hardwoods in glued-laminated timber: a study of bondline shear strength and resistance to moisture

“…provide the best available basis for comparison. In that way, findings of the current study are not consistent with those of Aicher et al (2018). In block shear tests conducted on specimens originating from industrially manufactured hardwood glued-laminated timber beams, common ash attained higher wood and bondline shear strengths than common/sessile oak with density of 695 kg/m 3 and 752 kg/m 3 , respectively.…”

“…However, the significance of this criterion should be interpreted with caution because values from this standard do not account for variation within species. As suggested by River et al (1991) and Aicher (2018), comparing the bondline shear strength with a clear wood strength value obtained from the same sample of wood material would be more meaningful. Moreover, the shear strength should always be interpreted in conjunction with the level of wood failure.…”

“…The thick cell walls and small lumens of hardwood species often lead to a limited penetration of the adhesive, and consequently to weakened bondlines (Frihart and Hunt 2010;Selbo 1975). Results from the work of Aicher et al (2018), Konnerth et al (2016), Jiang et al (2014), Knorz (2014) and Lehmann (2018) with several European and Tropical hardwoods revealed that bond strength may greatly vary depending on the adhesive system and wood species. The low dimensional stability of hardwoods also induces important stresses on the bondlines when the moisture content fluctuates (Frihart and Hunt 2010).…”

Evaluating internal condition of hardwood logs based on AR-minimum entropy deconvolution combined with wavelet based spectral kurtosis approach

“…However, despite its superior mechanical performance, hardwood is still less used in timber structural applications (Schlotzhauer et al 2019). For example, surveys (Aicher et al 2018;Kobel et al 2014) showed that most of the glulam products are made of softwood worldwide. One of the contributing factors is the large quality variations existed in hardwood logs and the significant cost associated with processing the logs.…”

Relación entre parámetros de producción y propiedades estructurales de madera laminada encolada de Eucalyptus grandis

“…La redacción de la norma para especies de frondosas se encuentra en el Comité Europeo de Normalización a la espera de información consistente que permita establecer los requisitos de fabricación correspondientes. La generación de datos experimentales relacionados con el comportamiento de la línea de cola y la resistencia de corte para MLE fabricada a partir de la extensa variedad y heterogeneidad de especies de frondosas es una ardua tarea, que ha llevado a países no europeos como Estados Unidos y Japón, a formar grupos de especies y rangos de densidad, para definir los requisitos de fabricación para MLE de frondosas (Aicher et al 2018). Independientemente de las especies, todas estas normas establecen una serie de parámetros de fabricación dentro de los cuales se incluyen: las características del adhesivo, el diente para la fabricación del endentado de las láminas, la presión aplicada, el contenido de humedad de la madera, y las condiciones climáticas (temperatura y humedad relativa) del recinto de producción.…”