Computer aided design and comparison of alternative building frames

A computer method for the tentative structural design of beam-column-framed buildings has been developed. It includes interactive modelling, quantity surveying and cost evaluation. It can also be utilised in optimisation as well as in preparing data for the CAD-program used for the final design. The cost evaluation is based on unit costs and the bills of quantities produced in the quantity surveying phase. In the dimensioning, use is made of the computer model of the buildings. Since the exact dimensions of the structures are not knows before the dimensioning, and as many changes are likely to occur in the tentative design, the modelling method has been especially developed to enable these changes. In the modelling, an object oriented approach has been adopted. The objects are structural units, such as beams, columns, slabs, walls and so on. Vertical and horizontal planes, called reference planes, are also introduced. These planes fix the geometry of the building. The objects are coupled to the reference planes directly or indirectly. For example, the ends of a column are coupled to horizontal reference planes, and the length of the column is determined by the co-ordinates of the horizontal planes. Thus, the length of the column is changed by changing the co-ordinates of the horizontal reference planes. Since the beams are connected to the horizontal planes and the slabs to the beams, they will move accordingly. As a result, the whole building will be vertically deformed. Virtually in the same way, the building can be deformed horizontally by changing the co-ordinates of the vertical reference planes. The topological information, i.e. information of the connections between the structural units, forms a central feature of the modelling method. It is necessary for the automation of dimensioning. Still more important is, however, that topological data can efficiently be used while creating the model. For example, a model of a rectangular hall can be generated by giving the data of one slab field, two long beams, four columns and four walls connecting the columns. The rest of the beams, columns and so on can be created just by adding vertical reference planes. A computer program has been written in FORTRAN to test this modelling method. The tests have shown that it is essentially faster to make a model of an industrial hall with this program than with programs based on conventional methods of geometric modelling.