As soon as two adjacent columns had been erected, a girder was hoisted into place between them and bolted onto the connectors. The columns were erected in opposite pairs, then two more girders were connected to form a self-supporting square—this was the basic frame of each module. The shears would then be moved along and an adjoining bay constructed. When a reasonable number of bays had been completed, the columns for the upper floor were erected (longer shear-legs were used for this, but the operation was essentially the same as for the ground floor). Once the ground floor structure was complete, the final assembly of the upper floor followed rapidly.