Free form grid structures

Within defined geometric parameters, the local bending behaviour of the unstiffened column flange of a semicontinuous, extended end plate, beam to column connection, primarily governs the elasto-plastic, moment-rotation characteristics of the joint. The flange’s movement and hence moment-rotation behaviour may be determined from an empirically derived quad-linear relationship, with determinable rotational stiffnesses at each linear load stage dependent on column flange thickness and connecting beam depth. An analytical method for the design of steel frames is presented that allows for semi-continuous, extended end plate joints calculable rotational stiffnesses, to be included in the procedure. A steel frame and its elasto-plastic connections may be accurately modelled to achieve almost full joint rigidity, acceptable sway movements and a global elastic stress solution at service load levels. Increased loading up to factored load values produces more flexible and ductile joint behaviour, which is taken into consideration during the analysis, as is the formation of plastic hinges within the frame members and ultimately, where achievable, instability and the development of a collapse mechanism.

John Graham, PhD, BSc, CEng, FIStructE
Scape System Build Ltd, Nottingham