Bonded insert joints

Bonded Insert Joint—A joint where loads from a structural element are transferred through an adhesive material and an insert to a mechanical attachment. 

P(6) For an adhesively bonded connection and a bonded insert joint designed by testing, the following partial material safety factors shall be used ... 

Bonded insert joints should be loaded primarily in axial tension or compression. 

The maximum possible axial loads applied to a bonded insert joint are, with careful design, of the same magnitude as the ultimate strength of the composite member/section. 

P(2) In sandwich structures the properties of the core surrounding the insert have a major effect on the total load-bearing potential of the bonded insert Joint. Therefore the designer shall verify that the core material is capable of carrying the loads transferred from the insert. 

The methods to reduce Joint peak stresses described in 5.3.1.3 should be applied to the bonded insert Joint design when practical. 

P(l) Those manufacturing aspects given in 5.3.5.11 applicable to bonded insert Joints shall be considered. 

P(10) In bonded-insert joints special attention shall be paid to inadequate... 

In addition to the general principles which apply to bonded joints, there are certain manufacturing aspects specific to bonded insert joints. The insert is usually of metallic material and therefore it often requires a chemical surface treatment prior to the bonding. Once the insert is ready to be bonded, it has to be verified that the whole bond area is covered by the adhesive after the insert has been installed. This problem needs to be solved by developing production methods that guarantee the quality and consistency of the bonding. 

Bonded inserts are typically used with pultruded sections or with similar types of components having closed cross-sections. The inserts may be bonded either on the outer or inner surface of the section. The sections are typically loaded in axial tension or compression or in bending, resulting in shear loadings (primarily) in the bonded joint. 

Bonded inserts are also commonly used in sandwich structures, most typically in panels. The insert is bonded into the core and to one or both skins of the sandwich. Loads are then directed to the joint through the mechanical fasteners (i.e. the insert) in their axial direction, causing out-of-plane loading of the sandwich component. Sandwich structures typically have thin skins and therefore the loads from the insert are mainly transferred to the core. If the insert is loaded in the in-plane direction of the sandwich member, the connection is categorised as an embedded insert and it should be designed as a mechanical connection. 

Alternatively, bonded steel or fibre reinforced rods can be inserted from the sides of members in the joint area, in the direction perpendicular to the grain, thus stitching the timber fibres together and avoiding splitting (Fig. 9). Whenever possible, long rods should be driven all the way across the timber member width, or shorter ones should be driven from both sides. 

The main advantage of bonded-in rods in this case is that they can be inserted also during the service life of the structure, as a preventive or even remedial measure, although complex geometry or tri-dimensional joints may hinder access for the proper positioning of rods. 

Previous studies [1,2] examined the welded dowel surface after pull-out from the substrate. In this work, the SEM study focused on the welded-joints (Eig. 6(a-d)). Figure 6(a) shows a poorly welded joint between the dowel inserted in the hole (left side) and the maple substrate (right side), whereas Fig. 6(b) presents a well-welded bond between the dowel (right side) and the maple substrate (left side). When examining in more details the micrograph for maple, one can see the absence of visible cracks at the interface between the dowel and the substrate, as... 

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