Fully Stressed Design of Pratt and Howe Trusses

Sukanya Saxena, K.K Pathak, National Institute of Technical Teachers' Training and Research, Bhopal

In this study, fully stressed design of steel Pratt and Howe trusses have been carried out. Total 24 cases for each truss were analyzed using STAAD.Pro software and optimal cross sectional areas of all members of both trusses calculated using fully stressed design concept. A comparison is made between Pratt and Howe Truss on basis of optimal mass, volume, maximum deflection at the centre, deflection per unit mass and frequency for 24 different load cases and percentage saving of material is worked out. It is observed that considerable saving of material can be achieved by proper selection of trusses.

Introduction

Widely light weight, cost effective and aesthetic structures are used now a days. The material cost is one of the foremost driving factors in the construction of buildings which can be minimized by reducing the weight or volume of the structural system. In addition, such reduction in the used material serves as a tool for sustainable design as step for green buildings. All of the methods used for decreasing the weight intend to reach an optimum design having a set of design variables under specific design constraints. The fully stressed design (FSD) is categorized among the intuitive optimality criteria as it is based on a simple principle. This criterion is stated as-"For the optimum design, each member of the structure that is not at its minimum gage must be fully stressed under at least one of the design load conditions".

FSD can handle problems subject to stress and minimum weigh constraints. When a structural member does not reach its allowable stress, its area is reduced in order to make it "fully stressed." A minimum gage is imposed to not lose any member and compromise the stability of the structure. Some of the prominent literature on FSD are presented below-