Compressive behavior of medium strength circular glue laminated timber columns jacketed with FRP sheets

Glue laminated timber (glulam) is an aesthetical, natural, energy saving and sustainable construction material that is a renewable, easily applicable and lightweight alternative in low and medium rise buildings, unlike steel and other reinforced concrete structural elements. In high-rise buildings, however, high strength and ductile columns and long-span beams are required. To meet these requirements, mechanical properties of timber are enhanced by minimizing the effects of initial defects, knots and discontinuities in the wood and protecting against deterioration caused by moisture and weathering that result in splitting, cracks, insect damage and fungal decay. Use of fiber reinforced polymer (FRP) sheets is also among potential promising approaches to improve mechanical performance of timber members. This paper presents compression test results of medium strength circular glulam columns externally jacketed with carbon fiber reinforced polymer (CFRP) sheets to enhance the structural behaviour of timber columns. In the experimental program, 6 reference and 6 externally jacketed circular glulam columns were prepared with three different diameters and tested under uniaxial compression loading. The aim of this research is to investigate the failure modes and to obtain stress-strain relationships of these columns before and after jacketing with CFRP sheets. The external jacketing of glulam columns with CFRP sheets has resulted in significant improvement in deformability. However, in contrast, the confinement effect was not that significant for some strengthened specimens due to the presence of knots at the outer surface. In addition, generally, there was a slight gain in compression strength due to external jacketing as well.