Study of steel - Glass Fibre-Reinforced Polymer (GFRP) bonded joints for the design of anchorage systems for flat bottom GFRP tanks subjected to seismic actions

In recent years, structural adhesive bonding has gained more interest in industrial and civil engineering. The wide use of combinations of different materials, e.g. steel and Glass-Fibre Reinforced Polymer (GFRP) adhesively bonded joints, is often the only alternative structural technique to welded or bolted joints. The structures of industrial storage tanks involved in situations that require high strength and stability to aggressive fluids make wide use of GFRP. The layout of plants usually needs slender, cylindrical and flat bottom tanks. These tanks need to be anchored at their base to withstand seismic loads. An anchorage system requires to transfer anchor bolts' vertical reactions to the tank wall through a steel hold-down lug joined to the GFRP tank shell. To date, standard codes provide solutions not involving adhesive bonding. In this research work, we propose a novel technique that uses the adhesive bonding combined with the classic overlay method to join the steel hold-down lug to the GFRP tank wall. Preliminary, for applying the new procedure to a selected case study, we provide an introduction to the composite material mechanics, then we describe the experimental campaign we performed on two selected adhesives through tensile, compression and shear bulk testing. Besides, we present the adopted procedure to assemble a double shear lap splice steel-GFRP joints and our modelling strategy regarding the finite element analysis of steel-GFRP joint. After calculated the tensile force to a single anchor bolt for a selected case study, taking into account the hydrodynamic actions induced by the earthquake to the tank, we perform a finite element analysis on a tank wall portion containing an anchorage. The results demonstrate the positive effects of the adhesive applied between the hold-down lug facing the tank shell's surface and the tank wall, in reducing the stresses on the joint's composite part.