Fibre reinforced polymer and timber sandwich structures for modular construction

Overview

Fibre reinforced polymers (FRP) composite materials have been widely used in the past few decades as strengthening materials to repair existing concrete, steel and timber structures as well as structural load-carrying members such as in sandwich systems. The use of glass fibre reinforced polymer (GFRP) in particular has been increasing due to its considerable advantages such as high strength-to-weight ratio, resistance to corrosion, ease of installation and cost-effectiveness compared with carbon fibre reinforced polymer (CFRP). In comparison, wood is vulnerable to biological deterioration and harsh environmental conditions over time. Although hardwood has better mechanical properties compared to softwoods in terms of strength and stiffness, Australian hardwood becomes difficult and costly due to its slow replenishment and the high clearing rates in the 19th century as well as bushfires. In Western Australia, plantation-grown softwoods have been adopted to address hardwood timber shortages and they have recently been introduced in Queensland and Victoria. However, softwoods have low natural durability and hence may require mechanical enhancement and preservative treatments.

It appears that a proper combination of GFRP and timber may take advantage of their individual merits and provide satisfactory mechanical performance and durability for the resulting FRP/timber composite structures as prefabricated elements for construction.

Key outcomes

One promising form of prefabricated structural members to use GFRP and softwood is sandwich structures which consist of two FRP face-sheets and a lightweight core. In such sandwich structures, the face layers provide improvement in the bending stiffness and strength while the core provides the majority of the shear stiffness. FRP web-flange sandwich structures have been successfully used for the application in bridge deck construction. However, without additional core materials in web-flange sandwiches shows insufficient at the web-flange junctions. Several studies showed that the addition of core materials improves the overall structural performance in terms of strength, stiffness and prevent out-of-plane buckling. Common core materials such as honeycomb, corrugated and foam have been used in aerospace engineering. However, they are considered expensive choices for civil engineering application.

Example FRP facesheets adhered to softwood cores

The research aims to investigates the use of softwood as core materials for sandwich beams which provides an appropriate solution due to its lightweight, low cost and sufficient elastic modulus. Investigating the flexural behaviour of FRP/softwood sandwich beams with varying shear span-to-depth ratio (a/d). Examine the effects of timber fibres direction which were vertical and longitudinal on the overall structural performance in bending. In addition, understanding the degree of composite action between the upper and lower facesheet panels. An important consideration for sandwich composite structures is achieving nonlinear behaviour, as one of the most challenging issues is the linear elastic and brittle behaviour of GFRP composites materials when used as load-bearing members in building structures.

Research team

  • Ahmed D. Almutairi
  • Prof Yu Bai
  • Prof Xiao-Ling Zhao

Industry collaborator on composites research

  • Mr Juri Jeske