There is an increasing potential for the use structural epoxy adhesives in steel fabrications, especially where thermal distortion from fusion welding causes production difficulties. Applications may include grillage panels for ships and similar construction, especially where stiffeners are welded to relatively thin plating, using fillet joints. Substituting welding with adhesive bonding requires designers to have a good knowledge of bonded beams in term of their structural behaviours under lateral loadings and in comparison to equivalent welded beams. The bending shear in bonded beams causes large strains in the adhesives bondline, which could result in increased stresses and deflection. This research aims to provide a fundamental design guide to determine levels of stresses and deflection of such beams. This developmental research programme was largely experimental work, which was supported by numerical and analytical methodologies. Large number of small-scale stiffened beam models were designed and manufactured to represent beams with plate stiffener connections; both welded (solid) and bonded. The stiffeners include various profiles, such as T, L, Z, flat beam and inverted T sections with various spans. The models were tested under monotonic loading in a simply supported boundary condition, within both elastic and plastic limits, In addition, the variation of adhesive bondline thickness was also considered to study its effect on bonded beam behaviour. The thesis presents the methodology for evaluating and comparing these models. Besides the mechanical testing; analytical methods based on beam and sandwich theory and finite element techniques were used. The research work shows that (i) Bonded beams behave quite differently to the solid/welded beams in terms of stresses and deflection. When compared to solid beams, bonded beams tend to exhibit higher bending stresses and deflections (ii) Different beam sections were compared and evaluated in the research, and it was found that a bonded T section being most suitable to resist bending. (iii) An elastic-plastic experimentation was necessary to demonstrate failure of the bonded beams under high bending loads. The bending behaviour of the bonded beam under gross deformation was analysed (iv) The effect of varying the adhesive thickness reflected through interface coefficients may be extended to full scale bonded panel analysis through suitable techniques allowing the behaviour extrapolation to the real scale.