Effect of Variation in Geometrical Parameters on the Roof Trusses

Abstract

The purpose of this project is to study the Effect of variation in geometrical parameters on the roof trusses in the design of plane truss by using angle section. The need of this study arises where sometimes it is difficult or taking much time to choose effective and economical truss geometry during the design period. In investigating the effectiveness of various truss geometry, a total of nine-truss geometry with simply pinned supports are chosen. The design loads are distributed to the joints so that there is no moment to be resisted by the members. A total of five span trusses with nine-truss geometry were analyzed and designed. Optimal trusses from each span of trusses are to be compared to determine whether the effective geometry is the same for different spans and heights. This study shows that there is no certainty in determining the most effective geometry neither with same span, height nor height over span ratio. The most effective truss geometry is actually specific for every truss span and height. For same span the among all the nine truss, Warren truss geometry seems to be the most optimum truss configuration with about 10% savings in weight when compared to its closest contenders Pratt truss or Howe truss. However, close results might be obtained where it does help to provide a good guideline in choosing a truss that does not waste much material. It has been observed from the results that warren truss is the most effective truss system in carrying the design loads. This feature has been attributed to the alignment of the compression chords and tension chords in a symmetric manner, which allows the truss to distribute the load in most effective way. Also it is noted that more the angle made by the compression and tension chords more effectively the load is distributed. Finally an optimality curve has been derived for understanding the relation between the span of the truss, optimum depth and least self-weight for the warren truss configuration. It is also observed that the optimum depth of any truss increases linearly with respect to its span.