Structural evaluation of axial and rotational flexibility and strength of web–flange junctions of open-web pultruded composites

Abstract

In past few decades, the interest in using pultruded fiber reinforced polymeric (PFRP) composites in construction applications has grown rapidly. Several research studies were conducted and focused on the performance of PFRP beams, columns and frame structures. The results of the majority of previous studies highlighted a major problem associated with the deficiency of the off-the-shelf, unidirectional open-web pultruded profiles. In this regards, a common conclusion was drawn by many researchers; that is: the inherent structural deficiency of commercially produced unidirectional PFRP profiles, especially at the flange/web(s) junction(s) that lacks fiber continuity. The lack of fiber continuity creates a “resin-rich” zones at the junctions that were shown to be responsible for rapid degradation of both axial and rotational stiffness as well as the strength of the majority of PFRP profiles. Another related problem is the use of incorrect framing connection details, currently being used by industry.Such connection details mimic those associated with steel structures. This approach ignores both the anisotropic and the viscoelastic nature of composites as well as the aforementioned inherent junction deficiency that, in most cases, lead to a greater risk with regard to the safety, reliability and economic aspects of such structures. This paper presents a summary of an experimental study aimed at evaluating both axial and rotational stiffnesses and strengths of web–flange junctions, which may affect stiffness, buckling, post-buckling, torsional and overall strength of PFRP structures. In particular, three sizes of commercially-produced unidirectional pultruded H-profiles and two sizes of L-profiles were evaluated under both service and ultimate loads. Using full-scale experimental data, P–δ and M–θ relations and idealized expressions for each pultruded profile were developed that can be used for accurate modeling and for establishing design limit-states for PFRP structures. In addition, two special test fixtures were designed, fabricated and validated that can be adopted by ASTM/ISO standards for characterizing such critical mechanical properties that are essential for reliable design of pultruded composite structures. Conclusions and design recommendations are also presented.