Experimental and numerical evaluation of the axial stiffness of the web-to-flange adhesive connections in composite I-beams

In most full-composite structures nowadays, pultruded profiles are joined together to form more complex cross-sections that are not produced by the pultrusion process. These unconventional crosssections represent a critical point in terms of strength and deformability of the whole structure, especially due to the presence of adhesive. This fundamental unknown aspect recently inspired the authors of the present paper to study the mechanical behavior of a glass fiber reinforced polymer (GFRP) profile with a complex cross-section shape obtained by bonding simple pultruded plates (bonded beams) by epoxy resin. The first step was to compare the behaviors of bonded beams with those of similar pultruded ones. With this aim, in a previous paper the flexural global behavior of an I-bonded beam was investigated, highlighting its better performance with respect to the pultruded I-profile in terms of failure load and stiffness. Now the authors would like to extend the study, both experimentally and numerically, to the mechanical behavior of the adhesive web–flange connections in terms of axial stiffness. Seventeen full specimens were tested by performing pull-out tests under force control. A uniformly distributed load was applied to the lower flange in order to favor the detachment of the flange from the web of the profile by using a steel device designed and realized ad hoc. The overall result of the research is that the bonded profile shows a good mechanical behavior justifying its use in technical practice. In addition, the bonded beams represents a valid alternative to the pultruded profile especially when the latter is not available on the market. In more detail, in bonded beams, the presence of the resin (instead of resin and fibers as in pultruded beams) at the web-to-flange connection does not affect the flexural global behavior but does penalize the axial behavior of their connections, as here demonstrated.