Pull out Strength Evaluation of Steel Bars Bonded-in to 45° in Round Timbers of Corymbia citriodora Treated with CCA

Abstract

With the possibility of developing simple connections, of easy execution, strong and durable, the bonded-in steel bars with structural resins have started being applied to different situations, such as shear connectors in mixed wood-concrete structures. These connectors, when steel bars are inclined in relation to the grain, may work under axial forces transmitting more stiffness and strength to the connection. In this research, the pull out strength of bonded-in steel bars was evaluated, bent 45° in relation to wood grain, using epoxy resin Sikadur-32 Fluid. In random sample of round pieces of Eucalyptus citriodora (Corymbia citriodora), CCA treated, with six replications in each observation, and considering the variability of the parameters: natural wood mechanical properties; apparent density; bar diameters; adherence surface and the moisture content. Steel bars used were highly resistant ones (CA-50), with threaded surface solicited by axial force, under monotonic loadings, with two consecutive load cycles. From the analysis of variance (ANOVA), the increase in the moisture content promoted reductions in the values of the compressive strength. The estimate of the pullout strength by the multivariable regression model, the moisture content was considered not significant, increases in the area of anchoring strengths implied significant increases in anchorage strength values, and the interaction between the factors (anchoring area and moisture content) promoted reductions in the anchor strength values of the steel bars.

Properties of Eucalyptus umbra Wood for Timber Structures

“…Among species that can be used in civil construction, the most important are those belonging to genus Eucalyptus and Corymbia [14,15]. Because of their rapid growth, eucalypt species have emerged among the major alternatives for lumber production in Brazil for the coming years [16].…”

Characteristics Value Estimate of Steel Bar Anchor Strength by Mean Response Confidence Interval

“…This connection type has received attention and recognition by presenting excellent performance when well designed and executed, due to its aesthetic appearance and low cost. Its main advantages are: glued-bar connections allow higher strain transfer levels than conventional connections; they resist great bending moments; the holes used do not weaken the structural parts as with the bolted connections; the structural parts become more aesthetic avoiding apparent connectors like toothed plates or screws; are easily protected against fire; are potentially cheaper than the "finger-joint" system since they do not require special machines to do; presents less material and lower production cost when compared to bolted connections [2]. [3] report that there are still no general technical standards governing the glued steel bars use in wood structures, although they have been used for more than 20 years in some Scandinavian countries and Germany, however, the performance requirements and project regulations differ between them.…”

“…The structural synthetic resins most commonly used in wood structures are classified into three groups: phenol resorcinol formaldehyde (PRF), polyurethanes (PUR) and epoxies (EP), hat have been undergoing continuous development, presenting better properties and fewer defects over time. Many information and results obtained a few years ago no longer apply to new existing resins [2]. The results obtained by [5], which tested several adhesives in the development of structures reinforcement systems of glued laminated timber, show some resins properties available at the time, such as: the PRF does not present good penetrability (ability to fill faults), presents considerable retraction properties and requires hot cure; the EP has high strength, good penetrability and no retraction, and is relatively expensive.…”

“…With the development, this adhesive became the most suitable for anchoring steel bars in structural wood pieces. A significant change appears when the EP is no longer considered as a resin set, with uniform behaviors, denominated only as epoxy, but it happens to compare different brands and manufacturers [2,5].…”

“…The anchorage adhesion, initially, is formed by chemical and mechanical adhesion combination. From a solicitation level, chemical adhesion breaks, remaining only mechanical adhesion [2]. [9] concluded that bars with deformed surfaces had lower anchoring strengths, resulting in more cracking ruptures than bars with threaded surfaces.…”