Efficient Design of Spanning Trusses Guided by Design Diagrams

Spanning structural trusses are very common items designed by engineers. Whether these are floor/roof trusses or foot bridge trusses, long or short they all have similar design approach. Engineers often are forced to use intuition or rules-of-thumb to arrive with an efficient truss type (Warren, Pratt, or other) or efficient depth to span ratio for a given load/span condition. After selecting and sizing an initially selected truss often little to no attempt is made to study other out of the box solutions to reduce structural quantities. If this is a typical floor truss in a multistory building a small saving in one truss can quickly multiply into a significant number worth an extra effort. In this paper, a method is presented that minimizes the effort of selecting the right solution. It appears that simple design aiding diagrams can be created and used in general situations. These diagrams can be easily used to estimate structural quantities before the truss is even designed. Also, if: load, span, and deflection criteria are known, an optimal depth and type of truss can be quickly established. In the process to generate these design charts it is important to consider stiffness requirements together with strength criteria to obtain most efficient design. Such diagrams can also be used to estimate a penalty on structural quantities when a design is forced away from the optimal. This paper provides a few sample truss design diagrams generated based on the theoretical derivations presented in this paper.