This paper is concerned with the strength and behaviour of partially connected composite plate girders. Eight simply supported composite plate girders were tested to failure under a concentrated load applied at the mid-span. The main variables considered in this study are the longitudinal spacing of stud connector, diameter of stud shank, number of studs along the upper flange and concrete strength. Test results have shown considerable variations in ultimate strength, behaviour and failure characteristic in all specimens due to effects of partial interaction. An analytical method to determine the ultimate strength of partially connected composite plate girders is outlined. Three-dimensional non-linear finite element analyses are also carried out on the girders using the general purpose computer code, LUSAS. Results obtained through the analytical method are compared with the corresponding finite element and experimental ones in respect of ultimate load, load–deflection response and deformation behaviour. Reasonably close agreement between the results establishes the accuracy of the analytical method and finite element simulation.