THREE DIMENSIONAL ANALYSIS OF POWER HOUSE SUPERSTRUCTURES

Abstract

Power House Super-Structures have hitherto been analysed by methods that require the structures to be resolved into a system of parallel and perpendicular plane frames' togetherwith resolution of vertical, transverse and longitudinal loads into the planes in which they act. The errors inherent in this approach may be significant as it completely neglects the tor-sional and flexural rigidities of the framing members and their effect on the stress distribution. This, in general,but not always., necessitates conservative designs resulting in costlier structures. The three-dimensional analysis, On the other hand, takes into account the torsional and flexural rigidity of such cross members and', thus, gives a more rational picture of stress distribution. It acquires special significance in case of power house frames where location of control rooms and other ancillary housings make the structure very complicated. Under such circum-stances of structural and loading unsymmetry, two-dimensional analysis cannot be relied upon to give a true picture of stress distribution and nodal displacements. The present dissertation describes the method of stiffness matrix for analysis of space frames and its application to the service bay frame of a hydel power station. The frame selected is relatively a simple one with a view to compare the results of two-dimensional and three-dimensional analyses. The program (x) is, however, capable of analysing complex structures with or without skew members. The dissertation also incorporates the comparative study of the results of plane and space frame ana-lyses for the above frame. This study has revealed an average reduction in design forces by 5 to 10 percent even in case of this simple frame having members of low torsional rigidities. The percentage reduction is more pronounced in case of asymmetrical loadings. The computer program has been developed for an IBM-1620 II model, with a card reader punch, an on-line printer, three disks on line and 40 K BCD memory.