A steel frame is designed which is expandable and reducible at any time. In order to reduce the assembly and disassembly time of the frame a new type of beam-to-column connection is proposed, a so-called plug & play connection.The design codes cannot be used for the estimation of the structural performance of this connection. Therefor the following objective is defined:What is the structural performance of the plug & play connection and how can the connection be reusable?In the state of art the benefits and problems plug & play connections offer over traditional steel connections is given. A case study of a steel frame, which consists of stacked units with fixed dimensions, is described. For this case study a global analysis is performed to investigate the possible internal forces on the plug & play connection.With the results obtained from the state of art and the global analysis an initial design is made. This initial design assumes a perfect fitted connection.Both the stiffness of a column major and minor axis joint is investigated for a hogging, sagging and out-of-plane bending moment. For all cases the joint is classified as semi-rigid. The inclined parts of both socket and plug will yield for all cases and the highest plastic strain will occur in the inclined parts of the connection. The thin base plate of the socket causes that the socket shows a bending deformation for all displacement cases, this bending deformation makes that the plug will be easier to pull the plug out of the socket, which reduces the stiffness. So an optimized design is checked for the minor axis case. For this optimized design the base plate thickness of the socket is increased in order to prevent the bending deformation of the socket. This optimized design also includes tolerances. The optimized design has removed the bending deformation of the socket. For a downwards displacement slip will occur, as a consequence of the tolerances, before contact between plug and socket is initiated. No slip will occur for an upwards or out-of-plane displacement as the bolt will be immediately in tension. So for the downwards case the initial stiffness is depending on the contact between plug and socket, while for the upwards and out-of-planed is placement the initial stiffness is provided by only the bolts. For all cases the stiffness is increased compared to the initial design.The final step is to evaluate the re-usability of the connection. The plastic de-formation has to be limited in order to be able to reuse the connection. For the upwards and out-of-plane case, in the optimized design, no plastic strainoccurs in the inclined parts of the connection when the moment is below the elastic moment resistance. This is because the elastic moment resistance is only provided by the bolts. For the downwards case there is plastic deformation in the inclined parts. However, increasing the thickness of the plug has reduced the maximum plastic strain compared to the initial design. So when the moments on the connection are below the elastic moment resistance the connection should be reusable. A visual inspection should prove whether the plug still fits in the socket.A real test should prove whether the plug & play connection reduces the assembly and disassembly time. If this is the case, then the moments on the joint should below the elastic moment resistance, so the connection could be reused. The joints will not be classified as rigid, so their semi-rigid behaviour should be taken into account in the global analysis.