COMBINED CONTRIBUTION OF PU FOAM AND GYPSUM FIBRE SHEATHING ON THE BEHAVIOUR OF LIGHTWEIGHT STEEL C- PROFILE IN A COMPOSITE WALL PANEL

Abstract

The research focuses on evaluating the mechanical contribution of the PU foam and 
sheathing to the load-bearing capacity, stiffness, and failure modes of the LSF system. Two groups of specimens were tested under axial compression: (1) bare LSF structures consisting solely of cold-formed C-profiles, and (2) composite panels  consisting of the same  LSF frame,  a PU foam core injected  under  pressure,  and  external  gypsum  fibreboard  sheathing.  The  experimental  results demonstrate a substantial enhancement in structural performance due to composite action. Composite panels achieved an average load-bearing capacity of 316.7 kN, more than double that of the bare LSF structures, which averaged 133.4 kN. In addition, the composite panels exhibited significantly higher ductility, with average vertical displacements at peak load reaching 10.27 mm, compared to 5.43 mm for  the  LSF  frames.  The  initial  stiffness  of  the  composite  system  was  also  markedly  improved, reaching 45.76 kN/mm approximately 1.5 times greater than that of the LSF structure alone. The PU foam, injected in a controlled industrial process, ensures a uniform and firm bond with both the steel frame  and  the  sheathing,  enabling  effective  composite  action  and  resistance  to  local  and  global buckling.  Visual  inspection  and  load-displacement analysis  confirmed  that  while  the  bare  LSF structures failed by local and out-of-plane buckling, the composite panels maintained stability and failed primarily through localized crushing, without global loss of structural integrity. These findings underscore the structural benefits of using composite panel systems and provide a foundation for the development of design models and future standardization of this type of construction element.