The Town lattice truss : an appropriate bridge technology for developing countries

Abstract

The Town lattice truss is proposed as an appropriate technology for the Tshumbe Diocese of the Democratic Republic of Congo. This proposal is made based on an understanding of rural transport and appropriate technology and an in-depth analysis of the details of the Town lattice truss. The nature and importance of rural transport and accessibility are presented, and bridges are identified as a key component in rural transport development. The concept of appropriate technology is presented along with a framework consisting of required and desired characteristics of any appropriate technology, including bridges. Structural materials are compared for use in bridges in rural areas of developing countries and timber is selected as the appropriate choice for the Tshumbe Diocese. Three existing timber bridges systems for developing countries are analyzed and compared, and the Town lattice truss is proposed as an alternative to all three. The Town lattice truss is presented and described in detail with reference to a study of forty existing bridges in the northeastern United States that was conducted as a part of this work. Appropriate characteristics of the truss are identified and used to compare the truss with other timber bridge systems. The wooden pegged connections and chord structure are identified as unique components of the Town lattice truss and are the subjects of further analysis. Equations are developed for strength prediction and stiffness estimation for the wooden pegged connections.

(cont.) The chord structure is analyzed for strength and stiffness, which are determined to be combinations of underlying component properties based on the chord termination pattern that is used. A comprehensive set of possible chord termination patterns is developed and the best patterns are proposed for use in design. Finally, truss moment capacity is determined as a function of chord strength and stiffness properties and a simple methodology is proposed for the design of new Town lattice truss bridges.